Effect of initial grain size on inhomogeneous plastic deformation and twinning behavior in high manganese austenitic steel with a polycrystalline microstructure

NASA Astrophysics Data System (ADS)

Ueji, R.; Tsuchida, N.; Harada, K.; Takaki, K.; Fujii, H.

2015-08-01

The grain size effect on the deformation twinning in a high manganese austenitic steel which is so-called TWIP (twining induced plastic deformation) steel was studied in order to understand how to control deformation twinning. The 31wt%Mn-3%Al-3% Si steel was cold rolled and annealed at various temperatures to obtain fully recrystallized structures with different mean grain sizes. These annealed sheets were examined by room temperature tensile tests at a strain rate of 10-4/s. The coarse grained sample (grain size: 49.6μm) showed many deformation twins and the deformation twinning was preferentially found in the grains in which the tensile axis is parallel near to [111]. On the other hand, the sample with finer grains (1.8 μm) had few grains with twinning even after the tensile deformation. The electron back scattering diffraction (EB SD) measurements clarified the relationship between the anisotropy of deformation twinning and that of inhomogeneous plastic deformation. Based on the EBSD analysis, the mechanism of the suppression of deformation twinning by grain refinement was discussed with the concept of the slip pattern competition between the slip system governed by a grain boundary and that activated by the macroscopic load.

The effect of ultrasonics on the strength properties of carbon steel processed by cold plastic deformation

NASA Technical Reports Server (NTRS)

Atanasiu, N.; Dragan, O.; Atanasiu, Z.

1974-01-01

A study was made of the influence of ultrasounds on the mechanical properties of OLT 35 carbon steel tubes cold-drawn on a plug ultrasonically activated by longitudinal waves. Experimental results indicate that: 1. The reduction in the values of the flow limit and tensile strength is proportional to the increase in acoustic energy introduced into the material subjected to deformation. 2. The diminution in influence of ultrasounds on tensile strength and flow rate that is due to an increased degree of deformation is explained by a reduction in specific density of the acoustic energy at the focus of deformation. 3. The relations calculated on the basis of the variation in the flow limit and tensile strength as a function of acoustic energy intensity was verified experimentally.

A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal–metal composites

DOE PAGES

Tian, Liang; Russell, Alan; Anderson, Iver

2014-01-03

Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts themore » strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.« less

Influence of Al on the Microstructural Evolution and Mechanical Behavior of Low-Carbon, Manganese Transformation-Induced-Plasticity Steel

NASA Astrophysics Data System (ADS)

Suh, Dong-Woo; Park, Seong-Jun; Lee, Tae-Ho; Oh, Chang-Seok; Kim, Sung-Joon

2010-02-01

Microstructural design with an Al addition is suggested for low-carbon, manganese transformation-induced-plasticity (Mn TRIP) steel for application in the continuous-annealing process. With an Al content of 1 mass pct, the competition between the recrystallization of the cold-rolled microstructure and the austenite formation cannot be avoided during intercritical annealing, and the recrystallization of the deformed matrix does not proceed effectively. The addition of 3 mass pct Al, however, allows nearly complete recrystallization of the deformed microstructure by providing a dual-phase cold-rolled structure consisting of ferrite and martensite and by suppressing excessive austenite formation at a higher annealing temperature. An optimized annealing condition results in the room-temperature stability of the intercritical austenite in Mn TRIP steel containing 3 mass pct Al, permitting persistent transformation to martensite during tensile deformation. The alloy presents an excellent strength-ductility balance combining a tensile strength of approximately 1 GPa with a total elongation over 25 pct, which is comparable to that of Mn TRIP steel subjected to batch-type annealing.

Reprint of: Effects of cold deformation, electron irradiation and extrusion on deuterium desorption behavior in Zr-1%Nb alloy

NASA Astrophysics Data System (ADS)

Morozov, O.; Mats, O.; Mats, V.; Zhurba, V.; Khaimovich, P.

2018-01-01

The present article introduces the data of analysis of ranges of ion-implanted deuterium desorption from Zr-1% Nb alloy. The samples studied underwent plastic deformation, low temperature extrusion and electron irradiation. Plastic rolling of the samples at temperature ∼300 K resulted in plastic deformation with the degree of ε = 3.9 and the formation of nanostructural state with the average grain size of d = 61 nm. The high degree of defectiveness is shown in thermodesorption spectrum as an additional area of the deuterium desorption in the temperature ranges 650-850 K. The further processing of the sample (that had undergone plastic deformation by plastic rolling) with electron irradiation resulted in the reduction of the average grain size (58 nm) and an increase in borders concentration. As a result the amount of deuterium desorpted increased in the temperature ranges 650-900 K. In case of Zr-1% Nb samples deformed by extrusion the extension of desorption area is observed towards the temperature reduction down to 420 K. The formation of the phase state of deuterium solid solution in zirconium was not observed. The structural state behavior is a control factor in the process of deuterium thermodesorption spectrum structure formation with a fixed implanted deuterium dose (hydrogen diagnostics). It appears as additional temperature ranges of deuterium desorption depending on the type, character and defect content.

Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

NASA Astrophysics Data System (ADS)

Cissé, Sarata; Laffont, Lydia; Lafont, Marie-Christine; Tanguy, Benoit; Andrieu, Eric

2013-02-01

The sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δɛp/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown.

Influence of Localized Plasticity on IASCC Sensitivity of Austenitic Stainless Steels under PWR Primary Water

NASA Astrophysics Data System (ADS)

Cissé, Sarata; Tanguy, Benoit; Laffont, Lydia; Lafont, Marie-Christine; Guerre, Catherine; Andrieu, Eric

The sensibility of precipitation-strengthened A286 austenitic stainless steel to Stress Corrosion Cracking (SCC) is studied by means of Slow Strain Rate Tests (SSRT). First, alloy cold working by Low Cycle Fatigue (LCF) is investigated. Fatigue tests under plastic strain control are performed at different strain levels (Δ ɛp/2=0.2%, 0.5% and 0.8%) in order to establish correlation between stress softening and deformation microstructure resulting from LCF tests. Deformed microstructures have been identified through TEM investigations. Three states of cyclic behaviour for precipitation-strengthened A286 have been identified: hardening, cyclic softening and finally saturation of softening. It is shown that the A286 alloy cyclic softening is due to microstructural features such as defects — free deformation bands resulting from dislocations motion along family plans <111>, that swept defects or γ' precipitates and lead to deformation localization. In order to quantify effects of plastic localized deformation on intergranular stress corrosion cracking (IGSCC) of the A286 alloy in PWR primary water, slow strain rate tests are conducted. For each cycling conditions, two specimens at a similar stress level are tested: the first containing free precipitate deformation bands, the other not significant of a localized deformation state. SSRT tests are still in progress.

Effect of the determination method of the material parameters on the accuracy of the hole expansion simulation for cold rolled steel sheet

NASA Astrophysics Data System (ADS)

Nakano, Hayato; Hakoyama, Tomoyuki; Kuwabara, Toshihiko

2017-10-01

Hole expansion forming of a cold rolled steel sheet is investigated both experimentally and analytically to clarify the effects of material models on the predictive accuracy of finite element analyses (FEA). The multiaxial plastic deformation behavior of a cold rolled steel sheet with a thickness of 1.2 mm was measured using a servo-controlled multiaxial tube expansion testing machine for the range of strain from initial yield to fracture. Tubular specimens were fabricated from the sheet sample by roller bending and laser welding. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the contours of plastic work in stress space up to a reference plastic strain of 0.24 along with the directions of plastic strain rates. The anisotropic parameters and exponent of the Yld2000-2d yield function (Barlat et al., 2003) were optimized to approximate the contours of plastic work and the directions of plastic strain rates. The hole expansion forming simulations were performed using the different model identifications based on the Yld2000-2d yield function. It is concluded that the yield function best capturing both the plastic work contours and the directions of plastic strain rates leads to the most accurate predicted FEA.

Direct observation of the residual plastic deformation caused by a single tensile overload

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bichler, C.; Pippan, R.

1999-07-01

The fatigue crack growth behavior following single tensile overloads at high stress intensity ranges in a cold-rolled austenitic steel has been studied experimentally. After tensile overloads, fatigue cracks initially accelerate, followed by significant retardation, before the growth rates return to their baseline level. The initial acceleration was attributed to an immediate reduction in near-tip closure. Scanning electron micrography and stereophotogrammetric reconstruction of the fracture surface were applied to study the residual plastic deformation caused by a single tensile overload in the mid-thickness of the specimen. The measured residual opening displacement of the crack as a function of the overload ismore » presented and compared with simple estimations. Also, free specimen surface observations of the residual plastic deformation and crack growth rate were performed. In the midsection of the specimens the striation spacing-length, i.e., the microscopic growth rates, were measured before and after the applied overload. It will be shown that the measured plasticity-induced wedges from the single overload and the observed propagation behavior support the significance of the concept of crack closure.« less

Micro-structure and properties of Cu-0.5 wt%Ag alloy fine wires with severe cold plastic deformation treatment

NASA Astrophysics Data System (ADS)

Shu-sen, Wang; Yuan-wang, Zhang; Da-wei, Yao

2018-04-01

In this work, the Cu-0.5 wt% Ag alloy was prepared and then sold solution treated at 760 °C for 4 h and aged at 400 °C for 4 h. The severe cold plastic deformation treatment with a maximum true strain of 11.48 was applied to obtain the Cu-0.5 wt%Ag fine wires with the diameter of 0.087 mm. Then the fine wires were given eight intermediate heat treatments at 300 °C–350 °C for 10–60 min. Properties of the fine wires with different annealing heat treatments were analyzed, results showed that after the annealing process of 350 °C, 20 min was applied to Cu-0.5 wt% Ag fine wires, their conductivity, tensile strength and elongation could reach 98.6%IACS, 367 MPa and 8%, respectively. This demonstrated that the Cu-0.5 wt% Ag processes high strength and high conductivity properties and was a promising conductive material.

Strain Evolution in Cold-Warm Forged Steel Components Studied by Means of EBSD Technique

PubMed Central

Bonollo, Franco; Bassan, Fabio; Berto, Filippo

2017-01-01

Electron BackScatter Diffraction (EBSD) in conjunction with Field-Emission Environmental Scanning Electron Microscopy (FEG-ESEM) has been used to evaluate the microstructural and local plastic strain evolution in different alloys (AISI 1005, AISI 304L and Duplex 2205) deformed by a single-stage cold and warm forging process. The present work is aimed to describe the different behavior of the austenite and ferrite during plastic deformation as a function of different forging temperatures. Several topological EBSD maps have been measured on the deformed and undeformed states. Then, image quality factor, distributions of the grain size and misorientation have been analyzed in detail. In the austenitic stainless steel, the γ-phase has been found to harden more easily, then α-phase and γ-phase in AISI 1005 and in duplex stainless steel, sequentially. Compared to the high fraction of continuous dynamic recrystallized austenitic zones observed in stainless steels samples forged at low temperatures, the austenitic microstructure of samples forged at higher temperatures, 600–700 °C, has been found to be mainly characterized by large and elongated grains with some colonies of fine nearly-equiaxed grains attributed to discontinuous dynamic recrystallization. PMID:29258249

Effect of hot and cold severe deformation by extrusion on the properties of lead and aluminum alloys

NASA Astrophysics Data System (ADS)

Ganiev, M. M.; Shibakov, V. G.; Pankratov, D. L.; Shibakov, R. V.

2015-07-01

The study of the effect of severe plastic deformation (SPD) by extrusion shows that the ductility of lead after several cycles of SPD increases significantly (3-4 times) as compared to as-cast samples. An aluminum alloy after this processing is hardened by a factor of 2.3-2.5, with ductility decreasing by 2.5-2.7 times, as compared to the as-delivered state.

USSR and Eastern Europe Scientific Abstracts, Engineering and Equipment, Number 34

DTIC Science & Technology

1977-09-07

indices of refraction and absorption and the optical homogeneity. Values of the indices of refraction and ab- sorption of IR glasses are presented...was found that cold plastic 20 deformation accelerates processes of breakdown of the gamma solid solution. The resistance to microplastic

Change and anisotropy of elastic modulus in sheet metals due to plastic deformation

NASA Astrophysics Data System (ADS)

Ishitsuka, Yuki; Arikawa, Shuichi; Yoneyama, Satoru

2015-03-01

In this study, the effect of the plastic deformation on the microscopic structure and the anisotropy of the elastic modulus in the cold-rolled steel sheet (SPCC) is investigated. Various uniaxial plastic strains (0%, 2.5%, 5%, 7.5%, and 10%) are applied to the annealed SPCC plates, then, the specimens for the tensile tests are cut out from them. The elastic moduli in the longitudinal direction and the transverse direction to the direction that are pre-strained are measured by the tensile tests. Cyclic tests are performed to investigate the effects of the internal friction caused by the movable dislocations in the elastic deformation. Also, the movable dislocations are quantified by the boundary tracking for TEM micrographs. In addition, the behaviors of the change of the elastic modulus in the solutionized and thermal aged aluminum alloy (A5052) are measured to investigate the effect on the movable dislocations with the amount of the depositions. As a result in SPCC, the elastic moduli of the 0° and 90° directions decrease more than 10% as 10% prestrain applied. On the other hand, the elastic modulus shows the recovery behavior after the strain aging and the annealing. The movable dislocation and the internal friction show a tendency to increase as the plastic strain increases. The marked anisotropy is not observed in the elastic modulus and the internal friction. The elastic modulus in A5052 with many and few depositions decreases similarly by the plastic deformation. From the above, the movable dislocations affect the elastic modulus strongly without depending on the deposition amount. Moreover, the elastic modulus recovers after the plastic deformation by reducing the effects of them with the strain aging and the heat treatment.

Effect of Production Process on Microstructure and Mechanical Properties of Copper Coatings of Jet Charges

NASA Astrophysics Data System (ADS)

Gleener, R. E.; Cheerova, M. N.; Shadiev, B. Sh.; Katyukhin, E. B.

2017-07-01

Special features of formation of the grain structure and mechanical properties of copper during recrystallization annealing after cold deformation with a wide range of reduction are studied. The constants of the Hall-Petch equation are determined for copper, the microstructure of which forms in the course of plastic deformation and subsequent heat treatment. The results of the study are allowed for in the process of production of claddings for jet charges.

Investigation of primary static recrystallization in a NiTiFe shape memory alloy subjected to cold canning compression using the coupling crystal plasticity finite element method with cellular automaton

NASA Astrophysics Data System (ADS)

Zhang, Yanqiu; Jiang, Shuyong; Hu, Li; Zhao, Yanan; Sun, Dong

2017-10-01

The behavior of primary static recrystallization (SRX) in a NiTiFe shape memory alloy (SMA) subjected to cold canning compression was investigated using the coupling crystal plasticity finite element method (CPFEM) with the cellular automaton (CA) method, where the distribution of the dislocation density and the deformed grain topology quantified by CPFEM were used as the input for the subsequent SRX simulation performed using the CA method. The simulation results were confirmed by the experimental ones in terms of microstructures, average grain size and recrystallization fraction, which indicates that the proposed coupling method is well able to describe the SRX behavior of the NiTiFe SMA. The results show that the dislocation density exhibits an inhomogeneous distribution in the deformed sample and the recrystallization nuclei mainly concentrate on zones where the dislocation density is relatively higher. An increase in the compressive deformation degree leads to an increase in nucleation rate and a decrease in grain boundary spaces in the compression direction, which reduces the growth spaces for the SRX nuclei and impedes their further growth. In addition, both the mechanisms of local grain refinement in the incomplete SRX and the influence of compressive deformation degree on the grain size of SRX were vividly illustrated by the corresponding physical models.

Mechanical properties of Fe -10Ni -7Mn martensitic steel subjected to severe plastic deformation via cold rolling and wire drawing

NASA Astrophysics Data System (ADS)

Ghasemi-Nanesa, H.; Nili-Ahmadabadi, M.; Shirazi, H.

2010-07-01

Fe-Ni-Mn martensitic steels are one of the major groups of ultra-high strength steels that have good mechanical properties and ductility in as annealed condition but they suffer from severe inter-granular embitterment after aging. In this paper, the effect of heavy shaped cold rolling and wire drawing on the mechanical properties of Fe-Ni-Mn steel was investigated. This process could provide a large strain deformation in this alloy. The total strain was epsilon ~7. Aging behavior and tensile properties of Fe-10Ni-7Mn were studied after aging at 753 K. The results showed that the ultimate tensile strength and ductility after cold rolling, wire drawing and aging increased up to 2540 MPa and 7.1 %, respectively, while the conventional steels show a premature fracture stress of 830 MPa with about zero ductility after aging.

Deformation and recrystallization behavior of super high-purity niobium for SRF cavity

NASA Astrophysics Data System (ADS)

Yamaguchi, Y.; Doryo, H.; Yuasa, M.; Miyamoto, H.; Yamanaka, M.

2017-05-01

Deformation and recyrstallization behavior of pure niobium was investigated in order to clarify the origin of its low hydro-formability despite of its high ductility comparable with pure iron. It was found that pure niobium exhibits lower strain hardening in cold rolling compared with pure iron. Furthermore, in post-deformation annealing, the hardness of niobium decreased monotonously with an increase of temperature, and the typical sharp drop by recrystallization was not evident. This softening behavior was contrasted with the high-purity iron. It is suggested that niobium exhibit the so-called in-situ recrystallization possibly because of low elastic modulus and low accumulative plastic strain energy in spite of high melting temperature. The low hydro-formability of pure niobium sheets or tubes is caused by its low strain hardening and its unique plastic anisotropy which is associated with this recovered residual rolled texture.

Properties of welded joints in laser welding of aeronautic aluminum-lithium alloys

NASA Astrophysics Data System (ADS)

Malikov, A. G.; Orishich, A. M.

2017-01-01

The work presents the experimental investigation of the laser welding of the aluminum-lithium alloys (system Al-Mg-Li) and aluminum alloy (system Al-Cu-Li) doped with Sc. The influence of the nano-structuring of the surface layer welded joint by the cold plastic deformation method on the strength properties of the welded joint is determined. It is founded that, regarding the deformation degree over the thickness, the varying value of the welded joint strength is different for these aluminum alloys.

Effect of oxide particles on the stabilization and final microstructure in aluminium

PubMed Central

Bachmaier, Andrea; Pippan, Reinhard

2011-01-01

Bulk aluminium samples containing alumina particles have been produced by different severe plastic deformation methods. Aluminium foils with different initial foil thicknesses were cold rolled to different amounts of strain and aluminium powders were consolidated and deformed by high pressure torsion (HPT). During processing, alumina particles from the foil or particle surface are easily incorporated and dispersed in the bulk material. The influence of these alumina particles on the developing microstructures and the mechanical properties has been studied. PMID:21976787

Effect of ultrafine grain on tensile behaviour and corrosion resistance of the duplex stainless steel.

PubMed

Jinlong, Lv; Tongxiang, Liang; Chen, Wang; Limin, Dong

2016-05-01

The ultrafine grained 2205 duplex stainless steel was obtained by cold rolling and annealing. The tensile properties were investigated at room temperature. Comparing with coarse grained stainless steel, ultrafine grained sample showed higher strength and plasticity. In addition, grain size changed deformation orientation. The strain induced α'-martensite was observed in coarse grained 2205 duplex stainless steel with large strain. However, the grain refinement inhibited the transformation of α'-martensite;nevertheless, more deformation twins improved the strength and plasticity of ultrafine grained 2205 duplex stainless steel. In addition, the grain refinement improved corrosion resistance of the 2205 duplex stainless steel in sodium chloride solution. Copyright © 2016 Elsevier B.V. All rights reserved.

Development of TRIP-Aided Lean Duplex Stainless Steel by Twin-Roll Strip Casting and Its Deformation Mechanism

NASA Astrophysics Data System (ADS)

Zhao, Yan; Zhang, Weina; Liu, Xin; Liu, Zhenyu; Wang, Guodong

2016-12-01

In the present work, twin-roll strip casting was carried out to fabricate thin strip of a Mn-N alloyed lean duplex stainless steel with the composition of Fe-19Cr-6Mn-0.4N, in which internal pore defects had been effectively avoided as compared to conventional cast ingots. The solidification structure observed by optical microscope indicated that fine Widmannstatten structure and coarse-equiaxed crystals had been formed in the surface and center, respectively, with no columnar crystal structures through the surface to center of the cast strip. By applying hot rolling and cold rolling, thin sheets with the thickness of 0.5 mm were fabricated from the cast strips, and no edge cracks were formed during the rolling processes. With an annealing treatment at 1323 K (1050 °C) for 5 minutes after cold rolling, the volume fractions of ferrite and austenite were measured to be approximately equal, and the distribution of alloying elements in the strip was further homogenized. The cold-rolled and annealed sheet exhibited an excellent combination of strength and ductility, with the ultimate tensile strength and elongation having been measured to be 1000 MPa and 65 pct, respectively. The microstructural evolution during deformation was investigated by XRD, EBSD, and TEM, indicating that ferrite and austenite had different deformation mechanisms. The deformation of ferrite phase was dominated by dislocation slipping, and the deformation of austenite phase was mainly controlled by martensitic transformation in the sequence of γ→ ɛ-martensite→ α'-martensite, leading to the improvement of strength and plasticity by the so-called transformation-induced plasticity (TRIP) effect. By contrast, lean duplex stainless steels of Fe-21Cr-6Mn-0.5N and Fe-23Cr-7Mn-0.6N fabricated by twin-roll strip casting did not show TRIP effects and exhibited lower strength and elongation as compared to Fe-19Cr-6Mn-0.4N.

Effect of upsetting deformation temperature on the formation of the fine-grained cast alloy structure of the Ni-Mn-Ga system

NASA Astrophysics Data System (ADS)

Musabirov, I. I.; Safarov, I. M.; Sharipov, I. Z.; Nagimov, M. I.; Koledov, V. V.; Khovailo, V. V.; Mulyukov, R. R.

2017-08-01

The plastic behavior during deformation by upsetting and its effect on the microstructure in the polycrystalline Ni2.19Fe0.04Mn0.77Ga alloy are studied. The temperatures of martensitic and magnetic phase transformations were determined by the method for analyzing the temperature dependence of the specific magnetization as M F = 320 K, A S = 360 K, and T C = 380 K. Using differential scanning calorimetry, it is shown that the phase transition from the ordered phase L21 to the disordered phase B2 is observed in the alloy during sample heating in the temperature range of 930-1070 K. The melting temperature is 1426 K. An analysis of the load curves constructed for sample deposition at temperatures of 773, 873, and 973 K shows that the behavior of the stress-strain curve at a temperature of 773 K is inherent to cold deformation. The behavior of the dependences for 873 and 973 K is typical of hot deformation. After deforming the alloy, its microstructure is studied using backscattered scanning electron microscopy. Plastic deformation of the alloy at study temperatures results in grain structure fragmentation in the localized deformation region. At all temperatures, a recrystallized grain structure is observed. It is found that the structure is heterogeneously recrystallized after upsetting at 973 K due to the process intensity at such a high temperature. The alloy microstructure after plastic deformation at a temperature of 873 K is most homogeneous in terms of the average grain size.

Study of thermite mixture consolidated by the cold gas dynamic spray process

NASA Astrophysics Data System (ADS)

Bacciochini, A.; Maines, G.; Poupart, C.; Akbarnejad, H.; Radulescu, M.; Jodoin, B.; Zhang, F.; Lee, J. J.

2014-05-01

The present study focused on the cold gas dynamic spray process for manufacturing porosity free, finely structured energetic materials with high reactivity and structural integrity. The experiments have focused the reaction between the aluminium and metal oxide, such as Al-CuO system. The consolidation of the materials used the cold gas dynamic spray technique, where the particles are accelerated to high speeds and consolidated via plastic deformation upon impact. Reactive composites are formed in arbitrary shapes with close to zero porosity and without any reactions during the consolidation phase. Reactivity of mixtures has been investigated through flame propagation analysis on cold sprayed samples and compacted powder mixture. Deflagration tests showed the influence of porosity on the reactivity.

Aluminium. II - A review of deformation properties of high purity aluminium and dilute aluminium alloys.

NASA Technical Reports Server (NTRS)

Reed, R. P.

1972-01-01

The elastic and plastic deformation behavior of high-purity aluminum and of dilute aluminum alloys is reviewed. Reliable property data, including elastic moduli, elastic coefficients, tensile, creep, fatigue, hardness, and impact are presented. Single crystal tensile results are discussed. Rather comprehensive reference lists, containing publications of the past 20 years, are included for each of the above categories. Defect structures and mechanisms responsible for mechanical behavior are presented. Strengthening techniques (alloys, cold work, irradiation, quenching, composites) and recovery are briefly reviewed.

Correlation of Microstructure and Texture in a Two-Phase High-Mn Twinning-Induced Plasticity Steel During Cold Rolling

NASA Astrophysics Data System (ADS)

Ashiq, Mohammad; Dhekne, Pushkar; Hamada, Atef Saad; Sahu, Puspendu; Mahato, B.; Minz, R. K.; Ghosh Chowdhury, Sandip; Pentti Karjalainen, L.

2017-10-01

The evolution of microstructure and texture of a two-phase austenite-ferrite twinning-induced plasticity steel during cold rolling was investigated and different deformation mechanisms were found to become active with increasing thickness reductions. Optical microscopy showed the formation of brass-type shear bands across several austenite grains at reductions greater than 50 pct. TEM observations reveal the presence of deformation twinning in austenite. The austenite phase initially shows the Cu-type texture, i.e., Cu {1 1 2}〈1 1 1〉, Goss {0 1 1}〈1 0 0〉 with a spread toward Brass {1 1 0}〈1 1 2〉. With continued cold rolling, the Cu {1 1 2}〈1 1 1〉 component moves toward CuT component {552}〈115〉 and the other two components increase in intensity. There is also emergence of {111} fiber after 90 pct cold rolling. The ferrite phase exhibits the evolution of ND-rotated Cube component {001}〈110〉 along with 〈110〉 fiber at lower as well as at higher rolling reductions. An exception is at 75 pct reduction, when the ferrite texture contains {111} fiber in place of 〈110〉 fiber with a weak rotated-Cube component. Phase fraction analysis by X-ray diffraction indicates a decrease in the austenite fraction up to 75 pct reduction followed by an increase at 90 pct reduction. After 90 pct cold rolling, the phase fraction is similar to that of the "as-received" state. Elongated grains of ferrite phase in finer dimensions after 90 pct cold rolling indicate softening within that phase; at similar stage, there are finer scale austenite grains mostly at the grain boundaries. The above has been suggested to be related with the adiabatic heating during cold rolling due to the high strain hardening of the austenite phase.

MD Simulation on Collision Behavior Between Nano-Scale TiO₂ Particles During Vacuum Cold Spraying.

PubMed

Yao, Hai-Long; Yang, Guan-Jun; Li, Chang-Jiu

2018-04-01

Particle collision behavior influences significantly inter-nano particle bonding formation during the nano-ceramic coating deposition by vacuum cold spraying (or aerosol deposition method). In order to illuminate the collision behavior between nano-scale ceramic particles, molecular dynamic simulation was applied to explore impact process between nano-scale TiO2 particles through controlling impact velocities. Results show that the recoil efficiency of the nano-scale TiO2 particle is decreased with the increase of the impact velocity. Nano-scale TiO2 particle exhibits localized plastic deformation during collision at low velocities, while it is intensively deformed by collision at high velocities. This intensive deformation promotes the nano-particle adhesion rather than rebounding off. A relationship between the adhesion energy and the rebound energy is established for the bonding formation of the nano-scale TiO2 particle. The adhesion energy required to the bonding formation between nano-scale ceramic particles can be produced by high velocity collision.

Features of structure formation in the low modulus quasi-single crystal from Zr-25%Nb alloy at cold rolling

NASA Astrophysics Data System (ADS)

Isaenkova, M.; Perlovich, Yu.; Fesenko, V.; Babich, Y.; Zaripova, M.; Krapivka, N.

2018-05-01

The paper presents the results of investigation of the regularities of the structure and texture formation during rolling of single crystals of Zr-25%Nb alloy differing in their initial orientations relative to the external principal directions in the rolled plate: normal (ND) and rolling directions (RD). The features of rolled single crystals with initial orientations of planes {001}, {011} or {111} parallel to the rolling plane and different crystallographic directions along RD are considered. A comparison of the peculiarities of plastic deformation in a polycrystalline alloy of the same composition is made. For the samples studied, a decrease in the lattice parameter of the β-phase has been recorded, the minimum of the parameter being observed for different degrees of deformation, varying from 20 to 50%. Observed decrease in the unit cell parameter can be connected with the precipitation of the α(α')-Zr phase from the deformed nonequilibrium β-phase of the Zr-25%Nb alloy, i.e. change in the composition of the solid solution. Distributions of the increase in the dimensions of the deformed single crystal along RD and the transverse direction (TD) with its deformation up to 30% in thickness, which indicate the anisotropy of the plasticity of single crystals during their rolling, are constructed on stereographic projection. It is shown, that the deformation of single crystals occurs practically without increasing of their dimensions in the <110> direction with a total thickness deformation of up to 30%. Direction <110> is characterized by maximum hardening (microhardness) with indentation along it, which causes low plasticity of deformed and annealed foils from Zr-25%Nb alloy at the stretching along and across RD, that is connected with the features of their crystallographic texture.

Imprinting bulk amorphous alloy at room temperature

DOE PAGES

Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; ...

2015-11-13

We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the abilitymore » of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.« less

The influence of heat treatment on properties of cold rolled alloyed steel and nickel superalloys sheets used in aircraft industry

NASA Astrophysics Data System (ADS)

Zaba, K.; Dul, I.; Puchlerska, S.

2017-02-01

Superalloys based on nickel and selected steels are widely used in the aerospace industry, because of their excellent mechanical properties, heat resistance and creep resistance. Metal sheets of these materials are plastically deformed and applied, inter alia, to critical components of aircraft engines. Due to their chemical composition these materials are hardly deformable. There are various methods to improve the formability of these materials, including plastic deformation at an elevated or high temperature, or a suitable heat treatment before forming process. The paper presents results of the metal sheets testing after heat treatment. For the research, sheets of two types of nickel superalloys type Inconel and of three types of steel were chosen. The materials were subjected to multivariate heat treatment at different temperature range and time. After this step, mechanical properties were examined according to the metal sheet rolling direction. The results were compared and the optimal type of pre-trial softening heat treatment for each of the materials was determined.

Deformation and damage mechanisms of zinc coatings on hot-dip galvanized steel sheets: Part II. Damage modes

NASA Astrophysics Data System (ADS)

Parisot, Rodolphe; Forest, Samuel; Pineau, André; Grillon, François; Demonet, Xavier; Mataigne, Jean-Michel

2004-03-01

Zinc-based coatings are widely used for protection against corrosion of steel-sheet products in the automotive industry. The objective of the present article is to investigate the damage modes at work in three different microstructures of a zinc coating on an interstitial-free steel substrate under tension, planestrain tension, and expansion loading. Plastic-deformation mechanisms are addressed in the companion article. Two main fracture mechanisms, namely, intergranular cracking and transgranular cleavage fracture, were identified in an untempered cold-rolled coating, a tempered cold-rolled coating, and a recrystallized coating. No fracture at the interface between the steel and zinc coating was observed that could lead to spalling, in the studied zinc alloy. A complex network of cleavage cracks and their interaction with deformation twinning is shown to develop in the material. An extensive quantitative analysis based on systematic image analysis provides the number and cumulative length of cleavage cracks at different strain levels for the three investigated microstructures and three loading conditions. Grain refinement by recrystallization is shown to lead to an improved cracking resistance of the coating. A model for crystallographic cleavage combining the stress component normal to the basal plane and the amount of plastic slip on the basal slip systems is proposed and identified from equibiaxial tension tests and electron backscattered diffraction (EBSD) analysis of the cracked grains. This analysis requires the computation of the nonlinear stress-strain response of each grain using a crystal-plasticity constitutive model. The model is then applied successfully to other loading conditions and is shown to account for the preferred orientations of damaged grains observed in the case of plane-strain tension.

Effect of different stages of deformation on the microstructure evolution of Ti-rich NiTi shape memory alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tadayyon, Ghazal, E-mail: Ghazal.tadayyon@gmail.co

The main objective of this work was to investigate the thermomechanical behavior and microstructural changes of a Ti-rich NiTi shape memory alloy (SMA). The microstructural and texture evolution of aged NiTi alloy at different degrees of deformation were elicited by transmission electron microscopy (TEM). An effort was made to correlate results obtained from the tensile test with results from microstructure studies. The undeformed sample reveals a self-accommodated morphology with straight and well defined twin boundaries. At different stages of deformation, diverse mechanisms were involved. These mechanisms include marstraining, detwinning accompanied by dislocation movement, and finally, severe plastic deformation, subdivision andmore » amorphization of the matrix. Under increasing strains, high density lattice defects were generated and the morphology of B19’ became disordered. - Graphical abstract: The summary of microstructure changes of the martensite twins during tensile deformation in polycrystalline NiTi SMAs. - Highlights: • Initial elastic response, dislocation avalanche and deformation bands were studied. • < 011 > Type II twin accompanied by detwinned area after 2% cold work was observed. • Visible parallel fine stacking faults showed plastic flow of the material. • At higher strains, subgrains changed to recrystallized, finely amorphous structure.« less

Asymmetrical bonding in cold spraying of dissimilar materials

NASA Astrophysics Data System (ADS)

Nikbakht, R.; Seyedein, S. H.; Kheirandish, S.; Assadi, H.; Jodoin, B.

2018-06-01

Characteristics of particle bonding, especially for dissimilar materials, remains a key question in cold spray deposition. There are limited reports in direct correlation to particle/substrate bonding and peripheral shear zones. Cold spraying experiments and numerical simulations are conducted to characterise and analyse the correlation between bonding and peripheral shear zones for asymmetric particle/substrate pairs of intermetallic-forming elements of nickel and titanium. The correlation between metallic bonding and highly strained areas is explored in view of the growth of the intermetallic phase at the particle/substrate interface during subsequent heat treatments. Characterisation of the as-sprayed samples reveal that for the Ni(particle)/Ti(substrate) pair, plastic deformation of the particle is dominating over substrate deformation. However, for the Ti(particle)/Ni(substrate) pair, it is observed that the substrate and particle deform to similar extents. Characterisation of the samples after a brief heat treatment at 700 °C indicate that intermetallic formation, and hence metallurgical bonding of the pairs is more likely to occur at the particle peripheries where the interface areas are highly strained, and rarely achieved at the particle base. Results also reveal that bonding extends from peripheries toward the central part of the interfaces with increasing the impact velocity. The kinetics of interfacial intermetallic formation at peripheral areas and its correlation to particle bonding is discussed in view of deformation-enhanced interdiffusion.

Triple shape memory polymers by 4D printing

NASA Astrophysics Data System (ADS)

Bodaghi, M.; Damanpack, A. R.; Liao, W. H.

2018-06-01

This article aims at introducing triple shape memory polymers (SMPs) by four-dimensional (4D) printing technology and shaping adaptive structures for mechanical/bio-medical devices. The main approach is based on arranging hot–cold programming of SMPs with fused decomposition modeling technology to engineer adaptive structures with triple shape memory effect (SME). Experiments are conducted to characterize elasto-plastic and hyper-elastic thermo-mechanical material properties of SMPs in low and high temperatures at large deformation regime. The feasibility of the dual and triple SMPs with self-bending features is demonstrated experimentally. It is advantageous in situations either where it is desired to perform mechanical manipulations on the 4D printed objects for specific purposes or when they experience cold programming inevitably before activation. A phenomenological 3D constitutive model is developed for quantitative understanding of dual/triple SME of SMPs fabricated by 4D printing in the large deformation range. Governing equations of equilibrium are established for adaptive structures on the basis of the nonlinear Green–Lagrange strains. They are then solved by developing a finite element approach along with an elastic-predictor plastic-corrector return map procedure accomplished by the Newton–Raphson method. The computational tool is applied to simulate dual/triple SMP structures enabled by 4D printing and explore hot–cold programming mechanisms behind material tailoring. It is shown that the 4D printed dual/triple SMPs have great potential in mechanical/bio-medical applications such as self-bending gripers/stents and self-shrinking/tightening staples.

Numerical Studies of Friction Between Metallic Surfaces and of its Dependence on Electric Currents

NASA Astrophysics Data System (ADS)

Meintanis, Evangelos; Marder, Michael

2009-03-01

We will present molecular dynamics simulations that explore the frictional mechanisms between clean metallic surfaces. We employ the HOLA molecular dynamics code to run slider-on-block experiments. Both objects are allowed to evolve freely. We recover realistic coefficients of friction and verify the importance of cold-welding and plastic deformations in dry sliding friction. We also find that plastic deformations can significantly affect both objects, despite a difference in hardness. Metallic contacts have significant technological applications in the transmission of electric currents. To explore the effects of the latter to sliding, we had to integrate an electrodynamics solver into the molecular dynamics code. The disparate time scales involved posed a challenge, but we have developed an efficient scheme for such an integration. A limited electrodynamic solver has been implemented and we are currently exploring the effects of currents in the friction and wear of metallic contacts.

Structure, Dynamic Cracking Resistance, and Crack Growth Micromechanism in Pipe Billets after Thermomechanical Treatment

NASA Astrophysics Data System (ADS)

Simonov, M. Yu.; Simonov, Yu. N.; Shaimanov, G. S.

2018-01-01

The structure, dynamic cracking resistance, and micromechanisms of crack growth in initially highly tempered pipe billets made of structural carbon steel are studied after thermomechanical treatment, including cold plastic deformation by radial forging followed by annealing, under various conditions. The strength is found to be maximum after cold radial forging followed by annealing at 300°C. Cold radial forging and annealing at 600°C are shown to cause the formation of an ultrafine-grained structure with an average grain/subgrain size of 900 nm. The structural features formed in both the axial and the transverse direction after cold radial forging have been revealed. The mechanism of crack growth after heat treatment and thermomechanical treatment has been studied. The fracture surface elements formed during dynamic-crackingresistance tests have been qualitatively analyzed.

The Work Softening by Deformation-Induced Disordering and Cold Rolling of 6.5 wt pct Si Steel Thin Sheets

NASA Astrophysics Data System (ADS)

Wang, Xianglong; Li, Haoze; Zhang, Weina; Liu, Zhenyu; Wang, Guodong; Luo, Zhonghan; Zhang, Fengquan

2016-09-01

As-cast strip of 6.5 wt pct Si steel was fabricated by twin-roll strip casting. After hot rolling at 1323 K (1050 °C), thin sheets with the thickness of 0.35 mm were produced by warm rolling at 373 K (100 °C) with rolling reductions of 15, 25, 35, 45, 55, and 65 pct. Influence of warm rolling reduction on ductility was investigated by room temperature bending test. The measurement of macro-hardness showed that "work softening" could begin when the warm rolling reduction exceeded 35 pct. The room temperature ductility of the thin sheets gradually increased with the increase of warm rolling reductions, and the plastic deformation during bending began to form when the warm rolling reduction was greater than 45 pct, the 65 pct rolled thin sheet exhibited the maximum plastic deformation of about 0.6 pct during bending at room temperature, with a few small dimples having been observed on the fracture surfaces. B2-ordered domains were formed in the 15, 25, 35, 45, and 55 pct rolled specimens, and their average size decreased with the increase of warm rolling reductions. By contrast, no B2-ordered domain could be found in the 65 pct rolled specimen. It had been observed that large-ordered domains could be split into several small parts by the slip of partial super-dislocations during warm rolling, which led to significant decrease of the order degree to cause the phenomenon of deformation-induced disordering. On the basis of these results, cold rolling schedule was developed to successfully fabricate 0.25-mm-thick sheets with good surface qualities and magnetic properties from warm rolled sheets.

Thermo-elasto-plastic simulations of femtosecond laser-induced structural modifications: Application to cavity formation in fused silica

NASA Astrophysics Data System (ADS)

Beuton, Romain; Chimier, Benoît; Breil, Jérôme; Hébert, David; Maire, Pierre-Henri; Duchateau, Guillaume

2017-11-01

The absorbed laser energy of a femtosecond laser pulse in a transparent material induces a warm dense matter region relaxation of which may lead to structural modifications in the surrounding cold matter. The modeling of the thermo-elasto-plastic material response is addressed to predict such modifications. It has been developed in a 2D plane geometry and implemented in a hydrodynamic Lagrangian code. The particular case of a tightly focused laser beam in the bulk of fused silica is considered as a first application of the proposed general model. It is shown that the warm dense matter relaxation, influenced by the elasto-plastic behavior of the surrounding cold matter, generates both strong shock and rarefaction waves. Permanent deformations appear in the surrounding solid matter if the induced stress becomes larger than the yield strength. This interaction results in the formation of a sub-micrometric cavity surrounded by an overdense area. This approach also allows one to predict regions where cracks may form. The present modeling can be used to design nanostructures induced by short laser pulses.

Cold Spray Deposition of Ni and WC-Reinforced Ni Matrix Composite Coatings

NASA Astrophysics Data System (ADS)

Alidokht, S. A.; Vo, P.; Yue, S.; Chromik, R. R.

2017-12-01

Ni-WC composites are ideal protective coatings against wear and are often fabricated using laser cladding and thermal spray processes, but the high temperatures of these processes result in decarburization, which deteriorates the performance of the coating. Cold spray has the potential to deposit Ni-WC composite coatings and retain the composition of the initial WC feedstock. However, the insignificant plastic deformation of hard WC particles makes it difficult to build up a high WC content coating by cold spray. By using three different WC powder sizes, the effect of feedstock powder size on WC retention was tested. To improve WC retention, a WC/Ni composite powder in mixture with Ni was also sprayed. Microstructural characterization, including the deformed structure of Ni splats, retention, distribution, and fragmentation of WC, was performed by scanning electron microscopy. An improvement in WC retention was achieved using finer WC particles. Significant improvement in WC particles retention was achieved using WC/Ni composite powder, with the WC content in the coating being close to that of the feedstock.

Mechanisms of Forming Intergranular Microcracks and Microscopic Surface Discontinuities in Welds

DTIC Science & Technology

1992-06-01

SCC) is defined as slow stable crack extension occurring under static loading in sea water at stress intensity values below KIc (critical stress...preheating on the cold cracking resistance is reflected mainly in a reduction of the degree of localization of microplastic strains, their...deconcentration and an increase of the basis over which microplastic yielding takes place. This increases the amount of energy used for local plastic deformation

Patterns of residual stresses due to welding

NASA Technical Reports Server (NTRS)

Botros, B. M.

1983-01-01

Residual stresses caused by welding result from the nonuniform rate of cooling and the restrained thermal contraction or non-uniform plastic deformation. From the zone of extremely high temperature at the weld, heat flows into both the adjoining cool body and the surrounding atmosphere. The weld metal solidifies under very rapid cooling. The plasticity of the hot metal allows adjustment initially, but as the structure cools the rigidity of the surrounding cold metal inhibits further contraction. The zone is compressed and the weld is put under tensile stresses of high magnitude. The danger of cracking in these structural elements is great. Change in specific volume is caused by the change in temperature.

Study of thermite mixtures consolidated by cold gas dynamic spray process

NASA Astrophysics Data System (ADS)

Bacciochini, Antoine; Maines, Geoffrey; Poupart, Christian; Radulescu, Matei; Jodoin, Bertrand; Lee, Julian

2013-06-01

The present study focused on the cold gas dynamic spray process for manufacturing finely structured energetic materials with high reactivity, vanishing porosity, as well as structural integrity and arbitrary shape. The experiments have focused the reaction between the aluminum and metal oxides, such as Al-CuO and Al-MoO3 systems. To increase the reactivity, an initial mechanical activation was achieved through interrupted ball milling. The consolidation of the materials used the supersonic cold gas spray technique, where the particles are accelerated to high speeds and consolidated via plastic deformation upon impact, forming activated nano-composites in arbitrary shapes with close to zero porosity. This technique permits to retain the feedstock powder micro-structure and prevents any reactions during the consolidation phase. Reactivity of mixtures has been investigated through flame propagation analysis on cold sprayed samples and compacted powder mixture. Deflagration tests showed the influence of porosity on the reactivity.

Microstructure and Texture Development during Cold Rolling in UNS S32205 and UNS S32760 Duplex Stainless Steels

NASA Astrophysics Data System (ADS)

Kumar, Amit; Khatirkar, Rajesh Kisni; Chalapathi, Darshan; Kumar, Gulshan; Suwas, Satyam

2017-05-01

In the present study, microstructure and texture evolution during cold rolling in UNS S32205 and UNS S32760 duplex stainless steel was investigated. Both steels were unidirectionally cold rolled up to 80 pct thickness reduction. Scanning electron microscopy and electron backscattered diffraction (EBSD) were used for microstructural characterization, while X-ray diffraction (XRD) was used for the measurement of bulk texture. Strain-induced martensite (SIM) was identified and quantified with the help of magnetic measurements (B-H curve and magnetization saturation). With the increase in plastic strain, the grains became morphologically elongated along the rolling direction with the reduction in average band thickness and band spacing. SIM increased with the increase in deformation and was found to be a function of strain and the SFE of austenite. The increase in SIM was much more pronounced in UNS S32205 steel as compared to UNS S32760 steel. After cold rolling, strong α-fiber (RD//<110>) texture was developed in ferrite, while brass texture was dominant in austenite for both steels. The strength of texture components and fibers was stronger in UNS S32760 steel. Another significant feature was the development of weak γ-fiber (ND//<111>) in UNS S32760 steel at intermediate deformation.

Evaluation of an Eulerian multi-material mixture formulation based on a single inverse deformation gradient tensor field

DOE PAGES

Ghaisas, N. S.; Subramaniam, A.; Lele, S. K.; ...

2017-12-31

We report high energy-density solids undergoing elastic-plastic deformations coupled to compressible fluids are a common occurrence in engineering applications. Examples include problems involving high-velocity impact and penetration, cavitation, and several manufacturing processes, such as cold forming. Numerical simulations of such phenomena require the ability to handle the interaction of shock waves with multi-material interfaces that can undergo large deformations and severe distortions. As opposed to Lagrangian (Benson 1992) and arbitrary Lagrangian-Eulerian (ALE) methods (Donea et al. 2004), fully Eulerian methods use grids that do not change in time. Consequently, Eulerian methods do not suffer from difficulties on account of meshmore » entanglement, and do not require periodic, expensive, remap operations.« less

Evaluation of an Eulerian multi-material mixture formulation based on a single inverse deformation gradient tensor field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghaisas, N. S.; Subramaniam, A.; Lele, S. K.

We report high energy-density solids undergoing elastic-plastic deformations coupled to compressible fluids are a common occurrence in engineering applications. Examples include problems involving high-velocity impact and penetration, cavitation, and several manufacturing processes, such as cold forming. Numerical simulations of such phenomena require the ability to handle the interaction of shock waves with multi-material interfaces that can undergo large deformations and severe distortions. As opposed to Lagrangian (Benson 1992) and arbitrary Lagrangian-Eulerian (ALE) methods (Donea et al. 2004), fully Eulerian methods use grids that do not change in time. Consequently, Eulerian methods do not suffer from difficulties on account of meshmore » entanglement, and do not require periodic, expensive, remap operations.« less

An EBSD Investigation of Ultrafine-Grain Titanium for Biomedical Applications

DTIC Science & Technology

2015-09-21

angular pressing (ECAP) using a Conform scheme followed by rod drawing. The microstructure was found to be bimodal consisting of relatively coarse...produced for medical implants. The UFG ma- terial was obtained by equal channel angular pressing (ECAP) using a Conform scheme followed by rod drawing...1–6]. The method is based on severe plastic deformation (SPD) and typically includes warm equal-channel angular pressing (ECAP) followed by ether cold

Development of Mathematic Model of Cold Welding at Drawing-up the Flange Joint of Pneumohydraulic Systems

NASA Astrophysics Data System (ADS)

Boyko, Y. S.

2002-01-01

Provision of high airtightness of joints of pipe- lines of pneumohydraulic systems (PHS) operating under high pressure, is an important task for designing and operation of launch vehicles. In the process of assembly and tests of PHS of launch vehicles, it was found that detachable flange joints do not lose their airtightness after removal of fastening elements, even in conditions of standard loads. The task of this work is in studying a phenomenon connected with initiation of the observed effect of adhesion and also stresses in the zone of contact at drawing- up the flange detachable joints with a plastic gasket. Investigations have shown that density of the joint is kept due to cold welding, as the created conditions are helpful for that process. As a result of the investigations performed, we have developed a mathematic model which is based on application of the theory of metal bonds; that theory explains the essence of the effect observed. Basic factors which provide optimum mode of cold welding, are effort which can cause microplastic deformation and form maximum contact, and also quality of processing the material of the surfaces joined. Strength of all- metal joint depends on factual area of contact. So, surface processing quality defines a configuration of microbulges which come into contact not simultaneously, and their stressed state is different, and it influences the character of dependence of the contact area on loading. Results of calculations by the mathematic model are expressed by dependencies of factual area of contact and a single diameter of the contact spot on the load applied which compresses the materials with various physical properties, and on the surface processing quality. The mathematic model allows to explain the common character of the cold welding process in detachable flange joints with the plastic gasket, to determine the nature and the character of acting forces, to define kinetics and the mechanism of formation of cold welding of detachable joints. It also helps to analyze the state of airtightness and to metal welding technology in the plastic state at drawing- up of detachable flange joints with a plastic gasket and to review cold welding as a positive phenomenon.

Computational thermo-hydro-mechanics for freezing and thawing multiphase geological media in the finite deformation range

NASA Astrophysics Data System (ADS)

Sun, W.; Na, S.

2017-12-01

A stabilized thermo-hydro-mechanical (THM) finite element model is introduced to investigate the freeze-thaw action of frozen porous media in the finite deformation range. By applying the mixture theory, frozen soil is idealized as a composite consisting of three phases, i.e., solid grain, unfrozen water and ice crystal. A generalized hardening rule at finite strain is adopted to replicate how the elasto-plastic responses and critical state evolve under the influence of phase transitions and heat transfer. The enhanced particle interlocking and ice strengthening during the freezing processes and the thawing-induced consolidation at the geometrical nonlinear regimes are both replicated in numerical examples. The numerical issues due to lack of two-fold inf-sup condition and ill-conditioning of the system of equations are addressed. Numerical examples for engineering applications at cold region are analyzed via the proposed model to predict the impacts of changing climate on infrastructure at cold regions.

Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine

PubMed Central

Kumamoto, Kathryn M.; Thom, Christopher A.; Wallis, David; Hansen, Lars N.; Armstrong, David E. J.; Warren, Jessica M.; Goldsby, David L.; Wilkinson, Angus J.

2017-01-01

The strength of olivine at low temperatures and high stresses in Earth’s lithospheric mantle exerts a critical control on many geodynamic processes, including lithospheric flexure and the formation of plate boundaries. Unfortunately, laboratory-derived values of the strength of olivine at lithospheric conditions are highly variable and significantly disagree with those inferred from geophysical observations. We demonstrate via nanoindentation that the strength of olivine depends on the length scale of deformation, with experiments on smaller volumes of material exhibiting larger yield stresses. This “size effect” resolves discrepancies among previous measurements of olivine strength using other techniques. It also corroborates the most recent flow law for olivine, which proposes a much weaker lithospheric mantle than previously estimated, thus bringing experimental measurements into closer alignment with geophysical constraints. Further implications include an increased difficulty of activating plasticity in cold, fine-grained shear zones and an impact on the evolution of fault surface roughness due to the size-dependent deformation of nanometer- to micrometer-sized asperities. PMID:28924611

Study of Cold Coiling Spring Steel on Microstructure and Cold Forming Performance

NASA Astrophysics Data System (ADS)

Jiang, Y.; Liang, Y. L.; Ming, Y.; Zhao, F.

2017-09-01

Medium-carbon cold-coiling locomotive spring steels were treated by a novel Q-P-T (quenching-partitioning-tempering) process. Scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD) were used to characterize the relevant parameters of the steel. Results show that the microstructure of tested steel treated by Q-P-T process is a complex microstructures composed of martensite, bainite and retained austenite. The volume fraction of retained austenite (wt.%) is up to 31%. After pre-deforming and tempering again at 310°C, the plasticity of samples treated by Q-P-T process is still well. Fracture images show that the Q-P-T samples are ductile fracture. It is attributed to the higher volume fraction of the retained austenite and the interactions between the multi-phases in Q-P-T processed sample.

A Study on Passive and Electrochemical Response of Pure Nickel in Borate Buffer Solutions: Effect of Cold Deformation

NASA Astrophysics Data System (ADS)

Fattah-alhosseini, Arash; Naseri, Majid; Gashti, Seyed Omid; Vafaeian, Saeed; Keshavarz, Mohsen K.

2018-06-01

In the present work, influences of the cold deformation on electrochemical and passive response of pure nickel in three solutions with adjusted pH values of 8.5, 9.0, and 9.5 at 298 ± 1 K (25 ± 1 °C) were investigated. A cold deformation process was applied by means of cold rolling. Implementation of the cold deformation process resulted in samples having a finer microstructure. Also, the cold work and grain refinement led to increased hardness. In addition, open-circuit potential and potentiodynamic polarization tests were performed and results showed that corrosion current density was reduced by applying the cold deformation. Moreover, the results of the electrochemical impedance spectroscopy and Mott-Schottky analyses indicated higher corrosion resistance of pure nickel after cold deformation. This behavior is attributed to the growth of much thicker, with less point defects, passive layer on the surface of cold-deformed samples.

Feasibility of Steel Fiber-Reinforced Rubberized Concrete in Cold Regions for High Volume Intersections

NASA Astrophysics Data System (ADS)

Abou Eid, Mahear A.

There are many challenges faced with the use of Portland Cement Concrete (PCC) in cold regions, but with the inclusion of new technologies such as steel fibers and recycled tire crumb rubber efficient construction may be possible. Research was conducted on a modified concrete material that included both steel fibers and crumb rubber. The composite material was called Steel Fiber-Reinforced Rubberized Concrete (SFRRC). The objective of this investigation was to provide evidence showing that SFRRC can reduce tire rutting compared to asphaltic pavement. In addition, the research showed that the SFRRC could withstand freeze-thaw cycles and increase service life of roadways. Several tests were performed to determine the characteristics of the material. Freeze-thaw testing was performed to determine compressive strength loss and visual deterioration of the material. Wheel tracker rut testing was performed both with the standard steel wheel and with a modified studded rubber tire to determine plastic deformation and rut resistance. An experimental test slab was cast in place on a public approach to observe the construction procedures, the effects of studded tire wear and the frost actions in cold region conditions. Based on freeze-thaw and wheel tracker test results and observations of the experimental test slab, the SFRRC material shows viability in cold regions for resisting freeze-thaw actions. The freeze-thaw testing resulted in increased compressive strength after 300 freeze-thaw cycles and very low deterioration of material compared to standard PCC. The wheel tracker testing resulted in very low plastic deformation and minor material rutting with use of the studded rubber tire. The test slab showed very minor surface wear, no freeze-thaw cracking and no rutting after one winter of use. It is recommended that further testing of the material be conducted by means of a large-scale trial section. This would provide information with respect to cost analysis and integration of the material into the Department of Transportation construction program.

Study of the Micro-Nonuniformity of the Plastic Deformation of Steel

NASA Technical Reports Server (NTRS)

Chechulin, B. B.

1957-01-01

The plastic flow during deformation of real polycrystalline metals has specific characteristics which distinguish the plastic deformation of metals from the deformation of ordinary isotropic bodies. One of these characteristics is the marked micro-nonuniformity of the plastic deformation of metals. P.O. Pashkov demonstrated the presence of a considerable micro-nonuniformity of the plastic deformation of coarse-grained steel wit medium or low carbon content. Analogous results in the case of tension of coarse-grained aluminum were obtained by W. Boas, who paid particular attention to the role of the grain boundaries in plastic flow. The nonuniformit of the plastic deformation in microvolumes was also recorded by T.N. Gudkova and others, on the alloy KhN80T. N.F. Lashko pointed out the nonuniformity of the plastic deformation for a series of pure polycrystalline metals and one-phase alloys. In his later reports, P.O. Pashkov arrives at he conclusion that the nonuniformity of the distribution of the deformation along the individual grains has a significant effect on the strength and plastic characteristics of polycrystalline metals in the process of plastic flow. However, until now there has not existed any systematic investigation of the general rules of the microscopic nonuniformit of plastic deformation even though the real polycrystalline metals are extremely simple with regard to structure. In the present report, an attempt is made to study the micrononuniformity of the flow of polycrystalline metals by the method of statistical analysis of the variation of the frequency diagrams of the nonuniformity of the grains in the process of plastic deformation.

Present Situation of the Anti-Fatigue Processing of High-Strength Steel Internal Thread Based on Cold Extrusion Technology: A Review

NASA Astrophysics Data System (ADS)

Miao, Hong; Jiang, Cheng; Liu, Sixing; Zhang, Shanwen; Zhang, Yanjun

2017-03-01

The adoption of cold-extrusion forming for internal thread net forming becomes an important component of anti-fatigue processing with the development of internal thread processing towards high performance, low cost and low energy consumption. It has vast application foreground in the field of aviation, spaceflight, high speed train and etc. The internal thread processing and anti-fatigue manufacture technology are summarized. In terms of the perspective of processing quality and fatigue serving life, the advantages and disadvantages of the processing methods from are compared. The internal thread cold-extrusion processing technology is investigated for the purpose of improving the anti-fatigue serving life of internal thread. The superiorities of the plastic deformation law and surface integrity of the metal layer in the course of cold extrusion for improving its stability and economy are summed up. The proposed research forecasts the development tendency of the internal thread anti-fatigue manufacturing technology.

Improvement of mechanical properties on metastable stainless steels by reversion heat treatments

NASA Astrophysics Data System (ADS)

Mateo, A.; Zapata, A.; Fargas, G.

2013-12-01

AISI 301LN is a metastable austenitic stainless steel that offers an excellent combination of high strength and ductility. This stainless grade is currently used in applications where severe forming operations are required, such as automotive bodies. When these metastable steels are plastically deformed at room temperature, for example by cold rolling, austenite transforms to martensite and, as a result, yield strength increases but ductility is reduced. Grain refinement is the only method that allows improving strength and ductility simultaneously. Several researchers have demonstrated that fine grain AISI 301LN can be obtained by heat treatment after cold rolling. This heat treatment is called reversion because it provokes the reversion of strain induced martensite to austenite. In the present work, sheets of AISI 301LN previously subjected to 20% of cold rolling reduction were treated and a refined grain austenitic microstructure was obtained. Mechanical properties, including fatigue limit, were determined and compared with those corresponding to the steel both before and after the cold rolling.

Tensile Properties of Under-Matched Weld Joints for 950 MPa Steel.

NASA Astrophysics Data System (ADS)

Yamamoto, Kouji; Arakawa, Toshiaki; Akazawa, Nobuki; Yamamoto, Kousei; Matsuo, Hiroki; Nakagara, Kiyoyuki; Suita, Yoshikazu

In welding of 950 MPa-class high tensile strength steel, preheating is crucial in order to avoid cold cracks, which, however, eventually increases welding deformations. One way to decrease welding deformations is lowering preheating temperature by using under-matched weld metal. Toyota and others clarify that although breaking elongation can decrease due to plastic constraint effect under certain conditions, static tensile of under-matched weld joints is comparable to that of base metal. However, there has still been no report about joint static tensile of under-matched weld joints applied to 950 MPa-class high tensile strength steel. In this study, we aim to research tensile strength and fatigue strength of under-matched weld joints applied to 950 MPa-class high tensile steel.

Research of thread rolling on difficult-to-cut material workpieces

NASA Astrophysics Data System (ADS)

Popov, A. Yu; Bugay, I. A.; Nazarov, P. V.; Evdokimova, O. P.; Popov, P. E.; Vasilyev, E. V.

2018-01-01

In medicine production Ti-6Al-4V Grade 5 alloys are used. One of the most important tasks is to increase the strength of the products and decrease in value. The possibility to roll special thread on Ti-6Al-4V Grade 5 alloy workpiece on 2-roller thread rolling machine has been studied. This is wrought alloy, treatment of which in cold condition causes difficulties due to low plasticity. To obtain Ti-6Al-4V Grade 5 alloy product with thread by rolling is rather difficult. This is due to large axial workpiece displacements resulting from large alloy resistance to cold plastic deformation. The provision of adequate kinematics requires experimental researches and the selection of modes - speed of rolling and pressure on the movable roller. The purpose of the work is to determine the optimal modes for rolling thread on titanium alloy workpiece. It has been stated that, after rolling, the product strength has increased up to 30%. As a result of the work, the unit has been made and recommendations to choose the optimal rolling process modes have been offered.

Hall coefficient measurement for residual stress assessment in precipitation hardened IN718 nickel-base superalloy

NASA Astrophysics Data System (ADS)

Velicheti, Dheeraj; Nagy, Peter B.; Hassan, Waled

2017-02-01

We investigated the feasibility of residual stress assessment based on Hall coefficient measurements in precipitation hardened IN718 nickel-base superalloy. As a first step, we studied the influence of microstructural variations on the galvanomagnetic properties of IN718 nickel-base superalloy. We found that the Hall coefficient of IN718 increases from ≈ 8.0×10-11 m3/C in its fully annealed state of 15 HRC Rockwell hardness to ≈ 9.4×10-11 m3/C in its fully hardened state of 45 HRC. We also studied the influence of cold work, i.e., plastic deformation, at room temperature and found that cold work had negligible effect on the Hall coefficient of fully annealed IN718, but significantly reduced it in hardened states of the material. For example, measurements conducted on fully hardened IN718 specimens showed that the Hall coefficient decreased more or less linearly with cold work from its peak value of ≈ 9.4×10-11 m3/C in its intact state to ≈ 9.0×10-11 m3/C in its most deformed state of 22% plastic strain. We also studied the influence of applied stress and found that elastic strain significantly increases the Hall coefficient of IN718 regardless of the state of hardening. The relative sensitivity of the Hall coefficient to elastic strain was measured as a unitless gauge factor K that is defined as the ratio of the relative change of the Hall coefficient ΔRH/RH divided by the axial strain ɛ = σ/E, where σ is the applied uniaxial stress and E is the Young's modulus of the material. We determined that the galvanomagnetic gauge factor of IN718 is κ ≈ 2.6 - 2.9 depending on the hardness level. Besides the fairly high value of the gauge factor, it is important that it is positive, which means that compressive stress in surface-treated components decreases the Hall coefficient in a similar way as plastic deformation does, therefore the unfortunate cancellation that occurs in fully hardened IN718 in the case of electric conductivity measurements will not happen in this case. Additionally, the temperature dependence of the Hall coefficient was measured at three different hardness levels and the influence of thermal exposure was studied in fully hardened IN718 up to 700 °C.

Efficient rolling texture predictions and texture-sensitive properties of α-uranium foils

DOE PAGES

Steiner, Matthew A.; Klein, Robert W.; Calhoun, Christopher A.; ...

2017-01-01

Here, finite element (FE) analysis was used to simulate the strain history of an α-uranium foil during cold-rolling, with the sheet modeled as an isotropic elastoplastic continuum. The resulting strain history was then used as input for a viscoplastic self-consistent (VPSC) polycrystal plasticity model to simulate crystallographic texture evolution. Mid-plane textures predicted via the combined FE→VPSC approach show alignment of the (010) poles along the rolling direction (RD), and the (001) poles along the normal direction (ND) with a symmetric splitting along RD. The surface texture is similar to that of the mid-plane, but with a shear-induced asymmetry that favorsmore » one of the RD split features of the (001) pole figure. Both the mid-plane and surface textures predicted by the FE→VPSC approach agree with published experimental results for cold-rolled α-uranium plates, as well as predictions made by a more computationally intensive full-field crystal plasticity based finite element model. α-uranium foils produced by cold-rolling must typically undergo a final recrystallization anneal to restore ductility prior to their final application, resulting in significant texture evolution from the cold-rolled plate deformation texture. Using the texture measured from a foil in the final recrystallized state, coefficients of the thermal expansion and elastic stiffness tensors were calculated using a thermo-elastic self-consistent model, and the anisotropic yield loci and flow curves along the RD, TD, and ND were predicted using the VPSC code.« less

Efficient rolling texture predictions and texture-sensitive properties of α-uranium foils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steiner, Matthew A.; Klein, Robert W.; Calhoun, Christopher A.

Here, finite element (FE) analysis was used to simulate the strain history of an α-uranium foil during cold-rolling, with the sheet modeled as an isotropic elastoplastic continuum. The resulting strain history was then used as input for a viscoplastic self-consistent (VPSC) polycrystal plasticity model to simulate crystallographic texture evolution. Mid-plane textures predicted via the combined FE→VPSC approach show alignment of the (010) poles along the rolling direction (RD), and the (001) poles along the normal direction (ND) with a symmetric splitting along RD. The surface texture is similar to that of the mid-plane, but with a shear-induced asymmetry that favorsmore » one of the RD split features of the (001) pole figure. Both the mid-plane and surface textures predicted by the FE→VPSC approach agree with published experimental results for cold-rolled α-uranium plates, as well as predictions made by a more computationally intensive full-field crystal plasticity based finite element model. α-uranium foils produced by cold-rolling must typically undergo a final recrystallization anneal to restore ductility prior to their final application, resulting in significant texture evolution from the cold-rolled plate deformation texture. Using the texture measured from a foil in the final recrystallized state, coefficients of the thermal expansion and elastic stiffness tensors were calculated using a thermo-elastic self-consistent model, and the anisotropic yield loci and flow curves along the RD, TD, and ND were predicted using the VPSC code.« less

Efficient rolling texture predictions and texture-sensitive thermomechanical properties of α-uranium foils

NASA Astrophysics Data System (ADS)

Steiner, Matthew A.; Klein, Robert W.; Calhoun, Christopher A.; Knezevic, Marko; Garlea, Elena; Agnew, Sean R.

2017-11-01

Finite element (FE) analysis was used to simulate the strain history of an α-uranium foil during cold straight-rolling, with the sheet modeled as an isotropic elastoplastic continuum. The resulting strain history was then used as input for a viscoplastic self-consistent (VPSC) polycrystal plasticity model to simulate crystallographic texture evolution. Mid-plane textures predicted via the combined FE→VPSC approach show alignment of the (010) poles along the rolling direction (RD), and the (001) poles along the normal direction (ND) with a symmetric splitting along RD. The surface texture is similar to that of the mid-plane, but with a shear-induced asymmetry that favors one of the RD split features of the (001) pole figure. Both the mid-plane and surface textures predicted by the FE→VPSC approach agree with published experimental results for cold straight-rolled α-uranium plates, as well as predictions made by a more computationally intensive full-field crystal plasticity based finite element model. α-uranium foils produced by cold-rolling must typically undergo a recrystallization anneal to restore ductility prior to their final application, resulting in significant texture evolution from the cold-rolled plate deformation texture. Using the texture measured from a foil in the final recrystallized state, coefficients of thermal expansion and the elastic stiffness tensors were calculated using a thermo-elastic self-consistent model, and the anisotropic yield loci and flow curves along the RD, TD, and ND were predicted using the VPSC code.

Finite Element Analysis of Plastic Deformation During Impression Creep

NASA Astrophysics Data System (ADS)

Naveena; Ganesh Kumar, J.; Mathew, M. D.

2015-04-01

Finite element (FE) analysis of plastic deformation associated with impression creep deformation of 316LN stainless steel was carried out. An axisymmetric FE model of 10 × 10 × 10 mm specimen with 1-mm-diameter rigid cylindrical flat punch was developed. FE simulation of impression creep deformation was performed by assuming elastic-plastic-power-law creep deformation behavior. Evolution of the stress with time under the punch during elastic, plastic, and creep processes was analyzed. The onset of plastic deformation was found to occur at a nominal stress about 1.12 times the yield stress of the material. The size of the developed plastic zone was predicted to be about three times the radius of the punch. The material flow behavior and the pile-up on specimen surface have been modeled.

The notion of a plastic material spin in atomistic simulations

NASA Astrophysics Data System (ADS)

Dickel, D.; Tenev, T. G.; Gullett, P.; Horstemeyer, M. F.

2016-12-01

A kinematic algorithm is proposed to extend existing constructions of strain tensors from atomistic data to decouple elastic and plastic contributions to the strain. Elastic and plastic deformation and ultimately the plastic spin, useful quantities in continuum mechanics and finite element simulations, are computed from the full, discrete deformation gradient and an algorithm for the local elastic deformation gradient. This elastic deformation gradient algorithm identifies a crystal type using bond angle analysis (Ackland and Jones 2006 Phys. Rev. B 73 054104) and further exploits the relationship between bond angles to determine the local deformation from an ideal crystal lattice. Full definitions of plastic deformation follow directly using a multiplicative decomposition of the deformation gradient. The results of molecular dynamics simulations of copper in simple shear and torsion are presented to demonstrate the ability of these new discrete measures to describe plastic material spin in atomistic simulation and to compare them with continuum theory.

Numerical assessment of residual formability in sheet metal products: towards design for sustainability

NASA Astrophysics Data System (ADS)

Falsafi, Javad; Demirci, Emrah; Silberschmidt, Vadim. V.

2016-08-01

A new computational scheme is presented to addresses cold recyclability of sheet- metal products. Cold recycling or re-manufacturing is an emerging area studied mostly empirically; in its current form, it lacks theoretical foundation especially in the area of sheet metals. In this study, a re-formability index was introduced based on post-manufacture residual formability in sheet metal products. This index accounts for possible levels of deformation along different strain paths based on Polar Effective Plastic Strain (PEPS) technique. PEPS is strain-path independent, hence provides a foundation for residual formability analysis. A user- friendly code was developed to implement this assessment in conjunction with advanced finite- element (FE) analysis. The significance of this approach is the advancement towards recycling of sheet metal products without melting them.

Two Back Stress Hardening Models in Rate Independent Rigid Plastic Deformation

NASA Astrophysics Data System (ADS)

Yun, Su-Jin

In the present work, the constitutive relations based on the combination of two back stresses are developed using the Armstrong-Frederick, Phillips and Ziegler’s type hardening rules. Various evolutions of the kinematic hardening parameter can be obtained by means of a simple combination of back stress rate using the rule of mixtures. Thus, a wide range of plastic deformation behavior can be depicted depending on the dominant back stress evolution. The ultimate back stress is also determined for the present combined kinematic hardening models. Since a kinematic hardening rule is assumed in the finite deformation regime, the stress rate is co-rotated with respect to the spin of substructure obtained by incorporating the plastic spin concept. A comparison of the various co-rotational rates is also included. Assuming rigid plasticity, the continuum body consists of the elastic deformation zone and the plastic deformation zone to form a hybrid finite element formulation. Then, the plastic deformation behavior is investigated under various loading conditions with an assumption of the J2 deformation theory. The plastic deformation localization turns out to be strongly dependent on the description of back stress evolution and its associated hardening parameters. The analysis for the shear deformation with fixed boundaries is carried out to examine the deformation localization behavior and the evolution of state variables.

Response of explosive HMX to low-velocity impact: modeling by the crystal plasticity finite element method

NASA Astrophysics Data System (ADS)

Ilnitsky, Denis; Inogamov, Nail; Zhakhovsky, Vasily

2017-12-01

Crystal plasticity finite element method (CPFEM) is a powerful tool for modeling the various deformation problems, which takes into account the different plasticity mechanisms at microscale of grain sizes and contribution of anisotropic behavior of each grain to macroscopic deformation pattern. Using this method we simulated deformation and plasticity of high explosive HMX produced by relatively low velocity impact. It was found that such plastic deformations of grains cause local heating which is sufficient to induce chemical reactions.

Advantages of formulating an evolution equation directly for elastic distortional deformation in finite deformation plasticity

NASA Astrophysics Data System (ADS)

Rubin, M. B.; Cardiff, P.

2017-11-01

Simo (Comput Methods Appl Mech Eng 66:199-219, 1988) proposed an evolution equation for elastic deformation together with a constitutive equation for inelastic deformation rate in plasticity. The numerical algorithm (Simo in Comput Methods Appl Mech Eng 68:1-31, 1988) for determining elastic distortional deformation was simple. However, the proposed inelastic deformation rate caused plastic compaction. The corrected formulation (Simo in Comput Methods Appl Mech Eng 99:61-112, 1992) preserves isochoric plasticity but the numerical integration algorithm is complicated and needs special methods for calculation of the exponential map of a tensor. Alternatively, an evolution equation for elastic distortional deformation can be proposed directly with a simplified constitutive equation for inelastic distortional deformation rate. This has the advantage that the physics of inelastic distortional deformation is separated from that of dilatation. The example of finite deformation J2 plasticity with linear isotropic hardening is used to demonstrate the simplicity of the numerical algorithm.

Multiple deformation mechanisms of Ti-22.4Nb-0.73Ta-2.0Zr-1.34O alloy

NASA Astrophysics Data System (ADS)

Yang, Y.; Li, G. P.; Cheng, G. M.; Li, Y. L.; Yang, K.

2009-02-01

Ti-22.4Nb-0.73Ta-2.0Zr-1.34O (at. %) alloy after cold compression to ˜5.2% strain was investigated. The alloy exhibited multiple plastic deformation mechanisms, including the stress-induced α″ martensitic (SIM α″) and ω phase transformations, 1/2⟨111⟩ dislocations slipping on the {112}β planes as well as {332}⟨113⟩β and {112}⟨111⟩β twinning, which have not previously been reported to coexist in a titanium alloy. It was also found that β phase with the {200} planes vertical to the compression direction was almost completely consumed away by a β →SIM α″ transformation, and a (100) texture of SIM α″ formed.

Deformation Mechanisms of Gum Metals Under Nanoindentation

NASA Astrophysics Data System (ADS)

Sankaran, Rohini Priya

Gum Metal is a set of multi-component beta-Ti alloys designed and developed by Toyota Central R&D Labs in 2003 to have a nearly zero shear modulus in the direction. After significant amounts of cold-work (>90%), these alloys were found to have yield strengths at a significant fraction of the predicted ideal strengths and exhibited very little work hardening. It has been speculated that this mechanical behavior may be realized through an ideal shear mechanism as opposed to conventional plastic deformation mechanisms, such as slip, and that such a mechanism may be realized through a defect structure termed "nanodisturbance". It is furthermore theorized that for near ideal strength to be attained, dislocations need to be pinned at sufficiently high stresses. It is the search for these defects and pinning points that motivates the present study. However, the mechanism of plastic deformation and the true origin of specific defect structures unique to gum metals is still controversial, mainly due to the complexity of the beta-Ti alloy system and the heavily distorted lattice exhibited in cold worked gum metals, rendering interpretation of images difficult. Accordingly, the first aim of this study is to clarify the starting as-received microstructures of gum metal alloys through conventional transmission electron microscopy (TEM) and aberration-corrected high resolution scanning transmission electron microscopy with high-angle annular dark field detector (HAADF-HRSTEM) imaging. To elucidate the effects of beta-stability and starting microstructure on the deformation behavior of gum metals and thus to provide adequate context for potentially novel deformation structures, we investigate three alloy conditions: gum metal that has undergone solution heat treatment (STGM), gum metal that has been heavily cold worked (CWGM), and a solution treated alloy of nominal gum metal composition, but leaner in beta-stabilizing content (ST Ref-1). In order to directly relate observed defect structures to applied loading, we perform ex-situ nanoindentation. Nanoindentation is a convenient method as the plastic deformation is localized and probes a nominally defect free volume of the material. We subsequently characterize the defect structures in these alloys with both conventional TEM and advanced techniques such as HAADF HRSTEM and nanoprobe diffraction. These advanced techniques allow for a more thorough understanding of the observed deformation features. The main findings from this investigation are as follows. As expected we observe that a non-equilibrium phase, o, is present in the leaner beta-stabilized alloy, ST Ref-1. We do not find any direct evidence of secondary phases in STGM, and we find the beta phase in CWGM, along with lath microstructure with subgrain structure consisting of dislocation cell networks. Upon nanoindentation, we find twinning accompanied by beta nucleation on the twin boundary in ST Ref-1 samples. This result is consistent with previous findings and is reasonable considering the alloy is unstable with respect to beta transformation. We find deformation nanotwinning in cold worked gum metals under nanoindentation, which is initially surprising. We argue that when viewed as a nanocrystalline material, such a deformation mechanism is consistent with previous work, and furthermore, a deformation nanotwinned structure does not preclude an ideal shear mechanism from operating in the alloy. Lastly, we observe continuous lattice rotations in STGM under nanoindentation via nanoprobe diffraction. With this technique, for the first time we can demonstrate that the lattice rotations are truly continuous at the nanoscale. We can quantify this lattice rotation, and find that even though the rotation is large, it may be mediated by a reasonable geometrically necessary dislocation density, and note that similar rotations are typically observed in other materials under nanoindentation. HRSTEM and conventional TEM data confirm the presence of dislocations in regions that have sustained large lattice rotations. Finally, we report on the nature of indirectly observed "pinning points" in STGM under nanoindentation that was reported in a previous study. We find through ADF/HAADF STEM that the "pinning points" which cause dislocation bowing in STGM under nanoindentation are actually other dislocations with the line direction normal to the TEM foil, and, in support of this finding, we also observe other in-plane dislocation-dislocation interactions that is responsible for resultant bowing. We observe no direct evidence of any secondary phases, twinning, or nanodisturbances in the STGM case, and the majority of deformation features can be explained by conventional slip mechanism. However, it remains a possibility that an ideal shear mechanism may be accompanying conventional slip in STGMs that may account for the truly continuous nature of the lattice rotations.

The deformation of gum metal under nanoindentation and sub-micron pillar compression

NASA Astrophysics Data System (ADS)

Withey, Elizabeth Ann

Reaching ideal strength has proven to be difficult in most materials. Dislocation slip, phase transformations, twinning, and fracture all tend to occur at stresses well below the ideal strength of a material. Only on very small scales has it been possible to approach ideal strength. Thus, it was of great interest when a set of beta-Ti alloys, Gum Metal, were found to have a bulk yield strength close to half of its ideal strength. However, some recent studies have questioned the reliability of this claim. Several studies have suggested Gum Metal deforms by dislocation slip. Others have suggested the possibility of transformation-induced plasticity. The present study was undertaken in order to help clarify if and how Gum Metal can reach ideal strength. Two different experiments, ex situ nanoindentation and quantitative in situ nanopillar compression in a transmission electron microscope to correlate real-time deformation behavior, were performed on a single composition of Gum Metal, Ti-23Nb-0.7Ta-2Zr-1.20 at. %, obtained from Toyota Central R&D Laboratories. Nanoindented specimens were thinned from the bottom surface until the pits of multiple indentations became electron-transparent allowing for qualitative analysis of the deformation microstructure in both fully cold-worked and solution-treated specimens. Real-time load-displacement behavior from the nanopillar compression tests was correlated with real-time video recorded during each compression to determine both the compressive strength of each pillar and the timing and strengths of different deformation behaviors observed. Combining the results from both experiments provided several important conclusions. First, Gum Metal approaches and can attain ideal strength in nanopillars regardless of processing condition. While dislocations exist in Gum Metal, they can be tightly pinned by obstacles with spacing less than ˜20 nm, which should inhibit their motion at strengths below the ideal shear strength. The plastic deformation of Gum Metal is not controlled by giant faults or by stress-induced phase transformations. Both of these phenomena, while active, are not the source of plasticity in Gum Metal.

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response

PubMed Central

Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-01-01

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process. PMID:29027925

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response.

PubMed

Hu, Li; Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-10-13

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process.

Optimization of Cold Spray Deposition of High-Density Polyethylene Powders

NASA Astrophysics Data System (ADS)

Bush, Trenton B.; Khalkhali, Zahra; Champagne, Victor; Schmidt, David P.; Rothstein, Jonathan P.

2017-10-01

When a solid, ductile particle impacts a substrate at sufficient velocity, the resulting heat, pressure and plastic deformation can produce bonding between the particle and the substrate. The use of a cool supersonic gas flow to accelerate these solid particles is known as cold spray deposition. The cold spray process has been commercialized for some metallic materials, but further research is required to unlock the exciting potential material properties possible with polymeric particles. In this work, a combined computational and experimental study was employed to study the cold spray deposition of high-density polyethylene powders over a wide range of particle temperatures and impact velocities. Cold spray deposition of polyethylene powders was demonstrated across a range broad range of substrate materials including several different polymer substrates with different moduli, glass and aluminum. A material-dependent window of successful deposition was determined for each substrate as a function of particle temperature and impact velocity. Additionally, a study of deposition efficiency revealed the optimal process parameters for high-density polyethylene powder deposition which yielded a deposition efficiency close to 10% and provided insights into the physical mechanics responsible for bonding while highlighting paths toward future process improvements.

Core Characteristics Deterioration due to Plastic Deformation

NASA Astrophysics Data System (ADS)

Kaido, Chikara; Arai, Satoshi

This paper discusses the effect of plastic deformation at core manufacturing on the characteristics of cores where non-oriented electrical steel sheets are used as core material. Exciting field and iron loss increase proportionally to plastic deformation in the case of rP<10, where rP is a ratio of plastic deformation to that at yield point. In this region, anomalous eddy currents increase because plastic deformations of crystalline grains are distributed and then the flux distribution is induced. In the case of rP>20, the deterioration tend to saturate, and the increases in magnetic field and iron loss are 1000 to 1500A/m and 2 to 4W/kg. They are related to grain size, and high grade with larger grain may have lager field increase and smaller iron loss increase. Anomalous eddy current losses scarcely increase in this region. In actual motors, the plastic deformation affects iron loss increase although exciting current increases a little.

Influence of the Substrate on the Formation of Metallic Glass Coatings by Cold Gas Spraying

NASA Astrophysics Data System (ADS)

Henao, John; Concustell, Amadeu; Dosta, Sergi; Cinca, Núria; Cano, Irene G.; Guilemany, Josep M.

2016-06-01

Cold gas spray technology has been used to build up coatings of Fe-base metallic glass onto different metallic substrates. In this work, the effect of the substrate properties on the viscoplastic response of metallic glass particles during their impact has been studied. Thick coatings with high deposition efficiencies have been built-up in conditions of homogeneous flow on substrates such as Mild Steel AISI 1040, Stainless Steel 316L, Inconel 625, Aluminum 7075-T6, and Copper (99.9%). Properties of the substrate have been identified to play an important role in the viscoplastic response of the metallic glass particles at impact. Depending on the process gas conditions, the impact morphologies show not only inhomogeneous deformation but also homogeneous plastic flow despite the high strain rates, 108 to 109 s-1, involved in the technique. Interestingly, homogenous deformation of metallic glass particles is promoted depending on the hardness and the thermal diffusivity of the substrate and it is not exclusively a function of the kinetic energy and the temperature of the particle at impact. Coating formation is discussed in terms of fundamentals of dynamics of undercooled liquids, viscoplastic flow mechanisms of metallic glasses, and substrate properties. The findings presented in this work have been used to build up a detailed scheme of the deposition mechanism of metallic glass coatings by the cold gas spraying technology.

Plastic strain is a mixture of avalanches and quasireversible deformations: Study of various sizes

NASA Astrophysics Data System (ADS)

Szabó, Péter; Ispánovity, Péter Dusán; Groma, István

2015-02-01

The size dependence of plastic flow is studied by discrete dislocation dynamical simulations of systems with various amounts of interacting dislocations while the stress is slowly increased. The regions between avalanches in the individual stress curves as functions of the plastic strain were found to be nearly linear and reversible where the plastic deformation obeys an effective equation of motion with a nearly linear force. For small plastic deformation, the mean values of the stress-strain curves obey a power law over two decades. Here and for somewhat larger plastic deformations, the mean stress-strain curves converge for larger sizes, while their variances shrink, both indicating the existence of a thermodynamical limit. The converging averages decrease with increasing size, in accordance with size effects from experiments. For large plastic deformations, where steady flow sets in, the thermodynamical limit was not realized in this model system.

Deformation partitioning provides insight into elastic, plastic, and viscous contributions to bone material behavior.

PubMed

Ferguson, V L

2009-08-01

The relative contributions of elastic, plastic, and viscous material behavior are poorly described by the separate extraction and analysis of the plane strain modulus, E('), the contact hardness, H(c) (a hybrid parameter encompassing both elastic and plastic behavior), and various viscoelastic material constants. A multiple element mechanical model enables the partitioning of a single indentation response into its fundamental elastic, plastic, and viscous deformation components. The objective of this study was to apply deformation partitioning to explore the role of hydration, tissue type, and degree of mineralization in bone and calcified cartilage. Wet, ethanol-dehydrated, and PMMA-embedded equine cortical bone samples and PMMA-embedded human femoral head tissues were analyzed for contributions of elastic, plastic and viscous deformation to the overall nanoindentation response at each site. While the alteration of hydration state had little effect on any measure of deformation, unembedded tissues demonstrated significantly greater measures of resistance to plastic deformation than PMMA-embedded tissues. The PMMA appeared to mechanically stabilize the tissues and prevent extensive permanent deformation within the bone material. Increasing mineral volume fraction correlated with positive changes in E('), H(c), and resistance to plastic deformation, H; however, the partitioned deformation components were generally unaffected by mineralization. The contribution of viscous deformation was minimal and may only play a significant role in poorly mineralized tissues. Deformation partitioning enables a detailed interpretation of the elastic, plastic, and viscous contributions to the nanomechanical behavior of mineralized tissues that is not possible when examining modulus and contact hardness alone. Varying experimental or biological factors, such as hydration or mineralization level, enables the understanding of potential mechanisms for specific mechanical behavior patterns that would otherwise be hidden within a more complex set of material property parameters.

Experiences issues with plastic parts at cold temperatures

NASA Technical Reports Server (NTRS)

Sandor, Mike; Agarwal, Shri

2005-01-01

Missions to MARS/planets/asteroids require electronic parts to operate and survive at extreme cold conditions. At extreme cold temperatures many types of cold related failures can occur. Office 514 is currently evaluating plastic parts under various cold temperature conditions and applications. Evaluations, screens, and qualifications are conducted on flight parts.

Strain Rate Dependant Material Model for Orthotropic Metals

NASA Astrophysics Data System (ADS)

Vignjevic, Rade

2016-08-01

In manufacturing processes anisotropic metals are often exposed to the loading with high strain rates in the range from 102 s-1 to 106 s-1 (e.g. stamping, cold spraying and explosive forming). These types of loading often involve generation and propagation of shock waves within the material. The material behaviour under such a complex loading needs to be accurately modelled, in order to optimise the manufacturing process and achieve appropriate properties of the manufactured component. The presented research is related to development and validation of a thermodynamically consistent physically based constitutive model for metals under high rate loading. The model is capable of modelling damage, failure and formation and propagation of shock waves in anisotropic metals. The model has two main parts: the strength part which defines the material response to shear deformation and an equation of state (EOS) which defines the material response to isotropic volumetric deformation [1]. The constitutive model was implemented into the transient nonlinear finite element code DYNA3D [2] and our in house SPH code. Limited model validation was performed by simulating a number of high velocity material characterisation and validation impact tests. The new damage model was developed in the framework of configurational continuum mechanics and irreversible thermodynamics with internal state variables. The use of the multiplicative decomposition of deformation gradient makes the model applicable to arbitrary plastic and damage deformations. To account for the physical mechanisms of failure, the concept of thermally activated damage initially proposed by Tuller and Bucher [3], Klepaczko [4] was adopted as the basis for the new damage evolution model. This makes the proposed damage/failure model compatible with the Mechanical Threshold Strength (MTS) model Follansbee and Kocks [5], 1988; Chen and Gray [6] which was used to control evolution of flow stress during plastic deformation. In addition the constitutive model is coupled with a vector shock equation of state which allows for modelling of shock wave propagation in orthotropic the material. Parameters for the new constitutive model are typically derived on the basis of the tensile tests (performed over a range of temperatures and strain rates), plate impact tests and Taylor anvil tests. The model was applied to simulate explosively driven fragmentation, blast loading and cold spraying impacts.

Contraction Twinning Dominated Tensile Deformation and Subsequent Fracture in Extruded Mg-1Mn (Wt Pct) at Ambient Temperature

NASA Astrophysics Data System (ADS)

Chakkedath, A.; Maiti, T.; Bohlen, J.; Yi, S.; Letzig, D.; Eisenlohr, P.; Boehlert, C. J.

2018-06-01

Due to their excellent strength-to-weight ratio, Mg alloys are attractive for applications where weight savings are critical. However, the limited cold formability of wrought Mg alloys severely restricts their widespread usage. In order to study the role that deformation twinning might play in limiting the elongation-to-failure ({ɛ} _{ {f}}), in-situ tensile tests along the extrusion axis of Mg-1Mn (wt pct) were performed at 323 K, 423 K, and 523 K. The alloy exhibited a strong basal texture such that most of the grains experienced compression along their < {c}> -axis during deformation. At 323 K, fracture occurred at about 10 pct strain. Although basal, prismatic, and pyramidal < {c+a}> slip activity was observed along with extension twinning, contraction twinning significantly influenced the deformation, and such twins evolved into {10{\\bar{1}}1}-{10{\\bar{1}}2} double twins. Crystal plasticity simulation showed localized shear deformation within the contraction twins and double twins due to the enhanced activity of basal slip in the reoriented twin volume. Due to this, the twin-matrix interface was identified to be a potential crack initiation site. Thus, contraction twins were considered to have led to the failure of the material at a relatively low strain, suggesting that this deformation mode is detrimental to the cold formability of Mg and its alloys. With increasing temperature, there was a significant decrease in the activity of contraction twinning as well as extension twinning, along with a decrease in the tensile strength and an increase in the {ɛ} _{ {f}} value. A combination of basal, prismatic, and pyramidal < {c+a}> slips accounted for a large percentage of the observed deformation activity at 423 K and 523 K. The lack of contraction twinning was explained by the expected decrease in the critical resolved shear stress values for pyramidal < {c+a}> slip, and the improved {ɛ} _{ {f}} values at elevated temperatures were attributed to the vanishing activity of contraction twinning.

Contraction Twinning Dominated Tensile Deformation and Subsequent Fracture in Extruded Mg-1Mn (Wt Pct) at Ambient Temperature

NASA Astrophysics Data System (ADS)

Chakkedath, A.; Maiti, T.; Bohlen, J.; Yi, S.; Letzig, D.; Eisenlohr, P.; Boehlert, C. J.

2018-03-01

Due to their excellent strength-to-weight ratio, Mg alloys are attractive for applications where weight savings are critical. However, the limited cold formability of wrought Mg alloys severely restricts their widespread usage. In order to study the role that deformation twinning might play in limiting the elongation-to-failure ({ɛ} f ), in-situ tensile tests along the extrusion axis of Mg-1Mn (wt pct) were performed at 323 K, 423 K, and 523 K. The alloy exhibited a strong basal texture such that most of the grains experienced compression along their < {c}> -axis during deformation. At 323 K, fracture occurred at about 10 pct strain. Although basal, prismatic, and pyramidal < {c+a}> slip activity was observed along with extension twinning, contraction twinning significantly influenced the deformation, and such twins evolved into {10{\\bar{1}} 1}-{10{\\bar{1}} 2} double twins. Crystal plasticity simulation showed localized shear deformation within the contraction twins and double twins due to the enhanced activity of basal slip in the reoriented twin volume. Due to this, the twin-matrix interface was identified to be a potential crack initiation site. Thus, contraction twins were considered to have led to the failure of the material at a relatively low strain, suggesting that this deformation mode is detrimental to the cold formability of Mg and its alloys. With increasing temperature, there was a significant decrease in the activity of contraction twinning as well as extension twinning, along with a decrease in the tensile strength and an increase in the {ɛ} f value. A combination of basal, prismatic, and pyramidal < {c+a}> slips accounted for a large percentage of the observed deformation activity at 423 K and 523 K. The lack of contraction twinning was explained by the expected decrease in the critical resolved shear stress values for pyramidal < {c+a}> slip, and the improved {ɛ} f values at elevated temperatures were attributed to the vanishing activity of contraction twinning.

Development of Age-Hardening Technology for Ultrafine-Grained Al-Li-Cu Alloys Fabricated by High-Pressure Torsion

NASA Astrophysics Data System (ADS)

Motoshima, Hiroaki; Hirosawa, Shoichi; Lee, Seungwon; Horita, Zenji; Matsuda, Kenji; Terada, Daisuke

The age-hardening behavior and precipitation microstructures with high dislocation density and ultrafine grains have been studied for cold-rolled and severely deformed 2091 Al-Li-Cu alloy. The age-hardenability at 463K was reduced by high-pressure torsion (HPT) due to the accelerated formation of larger 8-AlLi precipitates at grain boundaries, in place of transgranular precipitation of refined δ'-Al3Li particles that are predominantly observable in the no-deformed and 10%-rolled specimens. When aged at 373K, however, it was successfully achieved for the HPT specimen to increase the hardness up to 290HV, the highest level of hardness among conventional wrought aluminum alloys. The corresponding TEM microstructures confirmed that refined δ' particles precipitate within ultrafine grains while keeping the grain size at 206nm. This result suggests that the combined processing of severe plastic deformation with age-hardening technique enables the fabrication of novel aluminum alloys concurrently strengthened by ultrafine-grained and precipitation hardenings.

Plasticity of the dense hydrous magnesium silicate phase A at subduction zones conditions

DOE PAGES

Gouriet, K.; Hilairet, N.; Amiguet, E.; ...

2015-09-12

The plasticity of the dense hydrous magnesium silicate (DHMS) phase A, a key hydrous mineral within cold subduction zones, was investigated by two complementary approaches: high-pressure deformation experiments and computational methods. The deformation experiments were carried out at 11 GPa, 400 and 580 °C, with in situ measurements of stress, strain and lattice preferred orientations (LPO). Based on viscoplastic self-consistent modeling (VPSC) of the observed LPO, the deformation mechanisms at 580 °C are consistent with glide on the (0 0 0 1) basal and prismatic planes. At 400 °C the deformation mechanisms involve glide on prismatic, (0 0 0 1)more » basal and pyramidal planes. Both give flow stresses of 2.5–3 GPa at strain rates of 2–4 × 10-5 s-1. We use the Peierls–Nabarro–Galerkin (PNG) approach, relying on first-principles calculations of generalized stacking fault (γ-surface), and model the core structure of potential dislocations in basal and prismatic planes. The computations show multiple dissociations of the and dislocations (⟨a⟩ and ⟨b⟩ dislocations) in the basal plane, which is compatible with the ubiquity of basal slip in the experiments. The γ-surface calculations also suggest and dislocations (⟨a+c⟩ or ⟨c-b⟩ directions) in prismatic and pyramidal planes, which is also consistent with the experimental data. Phase A has a higher flow strength than olivine. When forming at depths from the dehydration of weak and highly anisotropic hydrated ultramafic rocks, phase A may not maintain the mechanical softening antigorite can provide. The seismic properties calculated for moderately deformed aggregates suggest that S-wave seismic anisotropy of phase A-bearing rocks is lower than hydrous subduction zone lithologies such as serpentinites and blueschists.« less

Estimating Tunnel Strain in the Weak and Schistose Rock Mass Influenced by Stress Anisotropy: An Evaluation Based on Three Tunnel Cases from Nepal

NASA Astrophysics Data System (ADS)

Panthi, Krishna Kanta; Shrestha, Pawan Kumar

2018-06-01

Total plastic deformation in tunnels passing through weak and schistose rock mass consists of both time-independent and time-dependent deformations. The extent of this total deformation is heavily influenced by the rock mass deformability properties and in situ stress condition prevailing in the area. If in situ stress is not isotropic, the deformation magnitude is not only different along the longitudinal alignment but also along the periphery of the tunnel wall. This manuscript first evaluates the long-term plastic deformation records of three tunnel projects from the Nepal Himalaya and identifies interlink between the time-independent and time-dependent deformations using the convergence law proposed by Sulem et al. (Int J Rock Mech Min Sci Geomech 24(3):145-154, 1987a, Int J Rock Mech Min Sci Geomech 24(3):155-164, 1987b). Secondly, the manuscript attempts to establish a correlation between plastic deformations (tunnel strain) and rock mass deformable properties, support pressure and in situ stress conditions. Finally, patterns of time-independent and time-dependent plastic deformations are also evaluated and discussed. The long-term plastic deformation records of 24 tunnel sections representing four different rock types of three different headrace tunnel cases from Nepal Himalaya are extensively used in this endeavor. The authors believe that the proposed findings will be a step further in analysis of plastic deformations in tunnels passing through weak and schistose rock mass and along the anisotropic stress conditions.

Molecular dynamics simulations of metallic friction and of its dependence on electric currents - development and first results

NASA Astrophysics Data System (ADS)

Meintanis, Evangelos Anastasios

We have extended the HOLA molecular dynamics (MD) code to run slider-on-block friction experiments for Al and Cu. Both objects are allowed to evolve freely and show marked deformation despite the hardness difference. We recover realistic coefficients of friction and verify the importance of cold-welding and plastic deformations in dry sliding friction. Our first data also show a mechanism for decoupling between load and friction at high velocities. Such a mechanism can explain an increase in the coefficient of friction of metals with velocity. The study of the effects of currents on our system required the development of a suitable electrodynamic (ED) solver, as the disparity of MD and ED time scales threatened the efficiency of our code. Our first simulations combining ED and MD are presented.

Plastic Deformation and Failure Analysis of Phase Change Random Access Memory

NASA Astrophysics Data System (ADS)

Yang; Hongxin; Shi; Luping; Lee; Koon, Hock; Zhao; Rong; Li; Jianming; Lim; Guan, Kian; Chong; Chong, Tow

2009-04-01

Although lateral phase change random access memory (PCRAM) has attracted a lot of interest due to its simpler fabrication process and lower current compared to ovonic unified memory (OUM), it faces a problem of poor lifetime. This paper studied relation between plastic deformation and the failure of PCRAM through both experiment and simulation. OUM and lateral PCRAM incorporating Ge2Sb2Te5 were fabricated and tested. The overwriting test showed that lifetime of OUM exceeded 106 while that of lateral PCRAM was only about 100. Using atomic force microscopy (AFM), it was found that the plastic deformation after 106 overwriting reached several tens of nm for lateral PCRAM while it was negligible for OUM. The thermo-mechanical simulation results confirmed the similar results on larger plastic deformation of lateral PCRAM than that of OUM during overwriting. As plastic deformation involves of atomic bonds breaking and reforming in phase change material, the plastic deformation may be one main reason for the failure of lateral PCRAM.

Residual stresses and plastic deformation in GTA-welded steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brand, P.C.; Keijser, T.H. de; Ouden, G. den

1993-03-01

Residual stresses and plastic deformation in single pass GTA welded low-carbon steel were studied by means of x-ray diffraction in combination with optical microscopy and hardness measurements. The residual stresses and the amount of plastic deformation (microstrain) were obtained from x-ray diffraction line positions and line broading. Since the plates were polished before welding, it was possible to observe in the optical microscope two types of Lueders bands. During heating curved Lueders bands and during cooling straight Lueders bands perpendicular to the weld are formed. The curved Lueders bands extend over a larger distance from the weld than the straightmore » Lueders bands. The amount of plastic deformation as obtained from the x-ray diffraction analysis is in agreement with these observations. An explanation is offered for the stresses measured in combination with plastic deformations observed. It is concluded that in the present experiments plastic deformation is the main cause of the residual stresses.« less

Analysis of factors influencing the bond strength in roll bonding processes

NASA Astrophysics Data System (ADS)

Khaledi, Kavan; Wulfinghoff, Stephan; Reese, Stefanie

2018-05-01

Cold Roll Bonding (CRB) is recognized as an industrial technique in which the metal sheets are joined together in order to produce laminate metal composites. In this technique, a metallurgical bond resulting from severe plastic deformation is formed between the rolled metallic layers. The main objective of this paper is to analyse different factors which may affect the bond formation in rolling processes. To achieve this goal, first, an interface model is employed which describes both the bonding and debonding. In this model, the bond strength evolution between the metallic layers is calculated based on the film theory of bonding. On the other hand, the debonding process is modelled by means of a bilinear cohesive zone model. In the numerical section, different scenarios are taken into account to model the roll bonding process of metal sheets. The numerical simulation includes the modelling of joining during the roll bonding process followed by debonding in a Double Cantilever Beam (DCB) peeling test. In all simulations, the metallic layers are regarded as elastoplastic materials subjected to large plastic deformations. Finally, the effects of some important factors on the bond formation are numerically investigated.

Plastic deformation behaviors of Ni- and Zr-based bulk metallic glasses subjected to nanoindentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weizhong, Liang, E-mail: wzliang1966@126.com; Zhiliang, Ning; Zhenqian, Dang

2013-12-15

Plastic deformation behaviors of Ni{sub 42}Ti{sub 20}Zr{sub 21.5}Al{sub 8}Cu{sub 5}Si{sub 3.5} and Zr{sub 51}Ti{sub 5}Ni{sub 10}Cu{sub 25}Al{sub 9} bulk metallic glasses at room temperature were studied by nanoindentation testing and atomic force microscopy under equivalent indentation experimental conditions. The different chemical composition of these two bulk metallic glasses produced variant tendencies for displacement serrated flow to occur during the loading process. The nanoindentation strain rate was calculated as a function of indentation displacement in order to verify the occurrence of displacement serrated flow at different loading rates. Atomic force microscopy revealed decreasing numbers of discrete shear bands around the indentationmore » sites as loading rates increased from 0.025 to 2.5 mNs{sup −1}. Variations in plastic deformation behaviors between Ni and Zr-based glasses materials can be explained by the different metastable microstructures and thermal stabilities of the two materials. The mechanism governing plastic deformation of these metallic glasses was analyzed in terms of an established model of the shear transformation zone. - Highlights: • Plastic deformation of Ni- and Zr-based BMG is studied under identical conditions • Zr-based BMG undergoes a greater extent of plastic deformation than Ni-based BMG • Nanoindentation strain rate is studied to clarify variation in plastic deformation • Metastable microstructure, thermal stability affect BMG plastic deformation.« less

Research and Development on Plastic Deformation and Directional Properties of Titanium

DTIC Science & Technology

1952-08-15

REORYSTALLIZATION OF ALPIIA TITANIUM Introduction It iu important to the study of any new metal or alloy that information be sought on the response to cold work...tations called a tuxture. Thie otudy of the textAurva developed in a now metal or alloy by various d.:orwations auid heat treat- mentu is an...705 44200 50 32 55,-2 44200 56 33 56i -3 44500 60 32 56" 4 44300 52 36 57-5 _ 44300 5S- _34.-.. 5_6 _Average � 55 33 ,56 Ti-i16 PH294T-I I1 30

On the elastic–plastic decomposition of crystal deformation at the atomic scale

DOE PAGES

Stukowski, Alexander; Arsenlis, A.

2012-03-02

Given two snapshots of an atomistic system, taken at different stages of the deformation process, one can compute the incremental deformation gradient field, F, as defined by continuum mechanics theory, from the displacements of atoms. However, such a kinematic analysis of the total deformation does not reveal the respective contributions of elastic and plastic deformation. We develop a practical technique to perform the multiplicative decomposition of the deformation field, F = F eF p, into elastic and plastic parts for the case of crystalline materials. The described computational analysis method can be used to quantify plastic deformation in a materialmore » due to crystal slip-based mechanisms in molecular dynamics and molecular statics simulations. The knowledge of the plastic deformation field, F p, and its variation with time can provide insight into the number, motion and localization of relevant crystal defects such as dislocations. As a result, the computed elastic field, F e, provides information about inhomogeneous lattice strains and lattice rotations induced by the presence of defects.« less

Description of plastic deformation of structural materials in triaxial loading

NASA Astrophysics Data System (ADS)

Lagzdins, A.; Zilaucs, A.

2008-03-01

A model of nonassociated plasticity is put forward for initially isotropic materials deforming with residual changes in volume under the action of triaxial normal stresses. The model is based on novel plastic loading and plastic potential functions, which define closed, convex, every where smooth surfaces in the 6D space of symmetric second-rank stress tensors. By way of example, the plastic deformation of a cylindrical concrete specimen wrapped with a CFRP tape and loaded in axial compression is described.

Comprehensive Deformation Analysis of a Newly Designed Ni-Free Duplex Stainless Steel with Enhanced Plasticity by Optimizing Austenite Stability

NASA Astrophysics Data System (ADS)

Moallemi, Mohammad; Zarei-Hanzaki, Abbas; Eskandari, Mostafa; Burrows, Andrew; Alimadadi, Hossein

2017-08-01

A new metastable Ni-free duplex stainless steel has been designed with superior plasticity by optimizing austenite stability using thermodynamic calculations of stacking fault energy and with reference to literature findings. Several characterization methods comprising optical microscopy, magnetic phase measurements, X-ray diffraction (XRD) and electron backscattered diffraction were employed to study the plastic deformation behavior and to identify the operating plasticity mechanisms. The results obtained show that the newly designed duplex alloy exhibits some extraordinary mechanical properties, including an ultimate tensile strength of 900 MPa and elongation to fracture of 94 pct due to the synergistic effects of transformation-induced plasticity and twinning-induced plasticity. The deformation mechanism of austenite is complex and includes deformation banding, strain-induced martensite formation, and deformation-induced twinning, while the ferrite phase mainly deforms by dislocation slip. Texture analysis indicates that the Copper and Rotated Brass textures in austenite (FCC phase) and {001}<110> texture in ferrite and martensite (BCC phases) are the main active components during tensile deformation. The predominance of these components is logically related to the strain-induced martensite and/or twin formation.

Room temperature creep behavior of Ti–Nb–Ta–Zr–O alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei-dong

The room temperature creep behavior and deformation mechanisms of a Ti–Nb–Ta–Zr–O alloy, which is also called “gum metal”, were investigated with the nanoindentation creep and conventional creep tests. The microstructure was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the creep stress exponent of the alloy is sensitive to cold deformation history of the alloy. The alloy which was cold swaged by 85% shows high creep resistance and the stress exponent is approximately equal to 1. Microstructural observation shows that creep process of the alloy without cold deformation is controlled by dislocationmore » mechanism. The stress-induced α' martensitic phase transformation also occurs. The EBSD results show that the grain orientation changes after the creep tests, and thus, the creep of the cold-worked alloy is dominated by the shear deformation of giant faults without direct assistance from dislocations. - Highlights: •Nanoindentation was used to investigate room temperature creep behavior of gum metal. •The creep stress exponent of gum metal is sensitive to the cold deformation history. •The creep stress exponent of cold worked gum metal is approximately equal to 1. •The creep of the cold-worked gum metal is governed by the shear deformation of giant faults.« less

Non-Contact Acousto-Thermal Signatures of Plastic Deformation in TI-6AL-4V

NASA Astrophysics Data System (ADS)

Welter, J. T.; Malott, G.; Schehl, N.; Sathish, S.; Jata, K. V.; Blodgett, M. P.

2010-02-01

Plastic deformation introduces changes in a material which include increases in: dislocations, strains, residual stress, and yield stress. However, these changes have a very small impact on the material properties such as elastic modulus, conductivity and ultrasonic wave speed. This is due to the fact that interatomic forces govern these properties, and they are not affected by plastic deformation to any large degree. This is evident from the fact that the changes in electrical resistance and ultrasonic velocity in plastically deformed and virgin samples are very small and can only be determined by highly controlled experiments. Except for X-ray diffraction, there are no direct nondestructive methods for measuring strain and the residual stress. This paper presents an application of the non-contact acousto-thermal signature (NCATS) NDE methodology to detect plastic deformation in flat dog bone Ti-6Al-4V samples. Results of the NCATS measurements on samples subjected to incremental amounts of plastic deformation are presented. The maximum temperature attained by the sample due to acoustic excitation is found to be sensitive to the amount of plastic strain. It is observed that the temperature induced by acoustic excitation increases to a peak followed by a decrease to failure. The maximum temperature peak occurs at plastic strains of 12-14%. It is observed that there is a correlation between the peak in maximum temperature rise and the strain at the experimentally determined ultimate tensile strength. A microstructural based explanation for this will be presented. The results are discussed in reference to utilizing this technique for detection and evaluation of plastic deformation.

OpenFOAM Modeling of Particle Heating and Acceleration in Cold Spraying

NASA Astrophysics Data System (ADS)

Leitz, K.-H.; O'Sullivan, M.; Plankensteiner, A.; Kestler, H.; Sigl, L. S.

2018-01-01

In cold spraying, a powder material is accelerated and heated in the gas flow of a supersonic nozzle to velocities and temperatures that are sufficient to obtain cohesion of the particles to a substrate. The deposition efficiency of the particles is significantly determined by their velocity and temperature. Particle velocity correlates with the amount of kinetic energy that is converted to plastic deformation and thermal heating. The initial particle temperature significantly influences the mechanical properties of the particle. Velocity and temperature of the particles have nonlinear dependence on the pressure and temperature of the gas at the nozzle entrance. In this contribution, a simulation model based on the reactingParcelFoam solver of OpenFOAM is presented and applied for an analysis of particle velocity and temperature in the cold spray nozzle. The model combines a compressible description of the gas flow in the nozzle with a Lagrangian particle tracking. The predictions of the simulation model are verified based on an analytical description of the gas flow, the particle acceleration and heating in the nozzle. Based on experimental data, the drag model according to Plessis and Masliyah is identified to be best suited for OpenFOAM modeling particle heating and acceleration in cold spraying.

Directional selection on cold tolerance does not constrain plastic capacity in a butterfly.

PubMed

Franke, Kristin; Dierks, Anneke; Fischer, Klaus

2012-12-05

Organisms may respond to environmental change by means of genetic adaptation, phenotypic plasticity or both, which may result in genotype-environment interactions (G x E) if genotypes differ in their phenotypic response. We here specifically target the latter source of variation (i.e. G x E) by comparing plastic responses among lines of the tropical butterfly Bicyclus anynana that had been selected for increased cold tolerance and according controls. Our main aim here was to test the hypothesis that directional selection on cold tolerance will interfere with plastic capacities. Plastic responses to temperature and feeding treatments were strong, with e.g. higher compared to lower temperatures reducing cold tolerance, longevity, pupal mass, and development time. We report a number of statistically significant genotype-environment interactions (i.e. interactions between selection regime and environmental variables), but most of these were not consistent across treatment groups. We found some evidence though for larger plastic responses to different rearing temperatures in the selection compared to the control lines, while plastic responses to different adult temperatures and feeding treatments were overall very similar across selection regimes. Our results indicate that plastic capacities are not always constrained by directional selection (on cold tolerance) and therefore genetic changes in trait means, but may operate independently.

Development of a 2-stage shear-cutting-process to reduce cut-edge-sensitivity of steels

NASA Astrophysics Data System (ADS)

Gläsner, T.; Sunderkötter, C.; Hoffmann, H.; Volk, W.; Golle, R.

2017-09-01

The edge cracking sensitivity of AHSS and UHSS is a challenging factor in the cold forming process. Expanding cut holes during flanging operations is rather common in automotive components. During these flanging operations the pierced hole is stretched so that its diameter is increased. These flanging operations stretch material that has already been subjected to large amounts of plastic deformation, therefore forming problems may occur. An innovative cutting process decreases micro cracks in the cutting surface and facilitates the subsequent cold forming process. That cutting process consists of two stages, which produces close dimensional tolerance and smooth edges. As a result the hole expanding ratio was increased by nearly 100 % when using thick high strength steels for suspension components. The paper describes the mechanisms of the trimming process at the cut edge, and the positive effect of the 2-stage shear-cutting process on the hole extension capability of multiphase steels.

Elastic Properties in Tension and Shear of High Strength Nonferrous Metals and Stainless Steel - Effect of Previous Deformation and Heat Treatment

NASA Technical Reports Server (NTRS)

Mebs, R W; Mcadam, D J

1947-01-01

A resume is given of an investigation of the influence of plastic deformation and of annealing temperature on the tensile and shear elastic properties of high strength nonferrous metals and stainless steels in the form of rods and tubes. The data were obtained from earlier technical reports and notes, and from unpublished work in this investigation. There are also included data obtained from published and unpublished work performed on an independent investigation. The rod materials, namely, nickel, monel, inconel, copper, 13:2 Cr-Ni steel, and 18:8 Cr-Ni steel, were tested in tension; 18:8 Cr-Ni steel tubes were tested in shear, and nickel, monel, aluminum-monel, and Inconel tubes were tested in both tension and shear. There are first described experiments on the relationship between hysteresis and creep, as obtained with repeated cyclic stressing of annealed stainless steel specimens over a constant load range. These tests, which preceded the measurements of elastic properties, assisted in devising the loading time schedule used in such measurements. From corrected stress-set curves are derived the five proof stresses used as indices of elastic or yield strength. From corrected stress-strain curves are derived the secant modulus and its variation with stress. The relationship between the forms of the stress-set and stress-strain curves and the values of the properties derived is discussed. Curves of variation of proof stress and modulus with prior extension, as obtained with single rod specimens, consist in wavelike basic curves with superposed oscillations due to differences of rest interval and extension spacing; the effects of these differences are studied. Oscillations of proof stress and modulus are generally opposite in manner. The use of a series of tubular specimens corresponding to different amounts of prior extension of cold reduction gave curves almost devoid of oscillation since the effects of variation of rest interval and extension spacing were removed. Comparison is also obtained between the variation of the several properties, as measured in tension and in shear. The rise of proof stress with extension is studied, and the work-hardening rates of the various metals evaluated. The ratio between the tensile and shear proof stresses for the various annealed and cold-worked tubular metals is likewise calculated. The influence of annealing or tempering temperature on the proof stresses and moduli for the cold-worked metals and for air-hardened 13:2 Cr-Ni steel is investigated. An improvement of elastic strength generally is obtained, without important loss of yield strength, by annealing at suitable temperature. The variation of the proof stress and modulus of elasticity with plastic deformation or annealing temperature is explained in terms of the relative dominance of three important factors: namely, (a) internal stress, (b) lattice-expansion or work-hardening, and (c) crystal reorientation. Effective values of Poisson's ratio were computed from tensile and shear moduli obtained on tubular specimens. The variation of Poisson's ratio with plastic deformation and annealing temperature is explained in terms of the degree of anisotropy produced by changes of (a) internal stress and (b) crystal orientation.

Elastic plastic self-consistent (EPSC) modeling of plastic deformation in fayalite olivine

DOE PAGES

Burnley, Pamela C

2015-07-01

Elastic plastic self-consistent (EPSC) simulations are used to model synchrotron X-ray diffraction observations from deformation experiments on fayalite olivine using the deformation DIA apparatus. Consistent with results from other in situ diffraction studies of monomineralic polycrystals, the results show substantial variations in stress levels among grain populations. Rather than averaging the lattice reflection stresses or choosing a single reflection to determine the macroscopic stress supported by the specimen, an EPSC simulation is used to forward model diffraction data and determine a macroscopic stress that is consistent with lattice strains of all measured diffraction lines. The EPSC simulation presented here includesmore » kink band formation among the plastic deformation mechanisms in the simulation. The inclusion of kink band formation is critical to the success of the models. This study demonstrates the importance of kink band formation as an accommodation mechanism during plastic deformation of olivine as well as the utility of using EPSC models to interpret diffraction from in situ deformation experiments.« less

Theory for plasticity of face-centered cubic metals.

PubMed

Jo, Minho; Koo, Yang Mo; Lee, Byeong-Joo; Johansson, Börje; Vitos, Levente; Kwon, Se Kyun

2014-05-06

The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control.

Theory for plasticity of face-centered cubic metals

PubMed Central

Jo, Minho; Koo, Yang Mo; Lee, Byeong-Joo; Johansson, Börje; Vitos, Levente; Kwon, Se Kyun

2014-01-01

The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control. PMID:24753563

Simulation of high-temperature superlocalization of plastic deformation in single-crystals of alloys with an L12 superstructure

NASA Astrophysics Data System (ADS)

Solov'eva, Yu. V.; Fakhrutdinova, Ya. D.; Starenchenko, V. A.

2015-01-01

The processes of the superlocalization of plastic deformation in L12 alloys have been studied numerically based on a combination of the model of the dislocation kinetics of the deformation-induced and heat-treatment-induced strengthening of an element of a deformable medium with the model of the mechanics of microplastic deformation described in terms of elastoplastic medium. It has been shown that the superlocalization of plastic deformation is determined by the presence of stress concentrators and by the nonmonotonic strengthening of the elements of the deformable medium. The multiple nonmonotonicity of the process of strengthening of the elementary volume of the medium can be responsible for the multiplicity of bands of microplastic localization of deformation.

Softening and Hardening of Alloys of the Al - Zn System Under Plastic Deformation

NASA Astrophysics Data System (ADS)

Skvortsov, A. I.; Polev, V. V.

2017-11-01

The proportion of hardening and softening under plastic deformation at room temperature in metals and alloys of the Al - Zn system has been studied as dependent on the regime of preliminary heat treatment. The influence of the strain rate on the dependence of alloy hardness on the degree of plastic deformation is estimated.

Structural defects in natural plastically deformed diamonds: Evidence from EPR spectroscopy

NASA Astrophysics Data System (ADS)

Mineeva, R. M.; Titkov, S. V.; Speransky, A. V.

2009-06-01

Structural defects formed as a result of plastic deformation in natural diamond crystals have been studied by EPR spectroscopy. The spectra of brown, pink-brown, black-brown, pink-purple, and gray plastically deformed diamonds of type Ia from deposits in Yakutia and the Urals were recorded. The results of EPR spectroscopy allowed us to identify various deformation centers in the structure of natural diamonds and to show that nitrogen centers were transformed under epigenetic mechanical loading. Abundant A centers, consisting of two isomorphic nitrogen atoms located in neighboring structural sites, were destroyed as a result of this process to form a series of N1, N4, W7, M2, and M3 nitrogen centers. Such centers are characterized by an anisotropic spatial distribution and a positive charge, related to the mechanism of their formation. In addition, N2 centers (probably, deformation-produced dislocations decorated by nitrogen) were formed in all plastically deformed diamonds and W10 and W35 centers (the models have not been finally ascertained) were formed in some of them. It has been established that diamonds with various types of deformation-induced color contain characteristic associations of these deformation centers. The diversity of associations of deformation centers indicates appreciable variations in conditions of disintegration of deep-seated rocks, transfer of diamonds to the Earth’s surface, and formation of kimberlitic deposits. Depending on the conditions of mechanical loading, the diamond crystals were plastically deformed by either dislocation gliding or mechanical twinning. Characteristic features of plastic deformation by dislocation gliding are the substantial prevalence of the N2 centers over other deformation centers and the occurrence of the high-spin W10 and W35 centers. The attributes of less frequent plastic deformation by mechanical twinning are unusual localization of the M2 centers and, in some cases, the N1 centers in microtwinned lamellae. Numerous data on models of deformation centers in natural diamonds, including the M2 and M3 centers, which were observed in the studied collection for the first time, are discussed.

Rebound mechanics of micrometre-scale, spherical particles in high-velocity impacts.

PubMed

Yildirim, Baran; Yang, Hankang; Gouldstone, Andrew; Müftü, Sinan

2017-08-01

The impact mechanics of micrometre-scale metal particles with flat metal surfaces is investigated for high-velocity impacts ranging from 50 m s -1 to more than 1 km s -1 , where impact causes predominantly plastic deformation. A material model that includes high strain rate and temperature effects on the yield stress, heat generation due to plasticity, material damage due to excessive plastic strain and heat transfer is used in the numerical analysis. The coefficient of restitution e is predicted by the classical work using elastic-plastic deformation analysis with quasi-static impact mechanics to be proportional to [Formula: see text] and [Formula: see text] for the low and moderate impact velocities that span the ranges of 0-10 and 10-100 m s -1 , respectively. In the elastic-plastic and fully plastic deformation regimes the particle rebound is attributed to the elastic spring-back that initiates at the particle-substrate interface. At higher impact velocities (0.1-1 km s -1 ) e is shown to be proportional to approximately [Formula: see text]. In this deeply plastic deformation regime various deformation modes that depend on plastic flow of the material including the time lag between the rebound instances of the top and bottom points of particle and the lateral spreading of the particle are identified. In this deformation regime, the elastic spring-back initiates subsurface, in the substrate.

Influence of Severe Plastic Deformation on the Structure and Properties of Al-Li-Cu-Mg-Zr-Sc-Zn Alloy

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2018-02-01

The structural and phase transformations in the Al-Li-Cu-Mg-Zr-Sc-Zn alloy have been studied by the electron microscopy after the aging for the maximum strength and in the nanostructured state after severe plastic deformation by high-pressure torsion. It has been shown that severe plastic deformation leads to the formation of a nanostructured state in the alloy, the nature of which is determined by the magnitude of deformation and the degree of completeness of the dynamic recrystallization. It has been established that deformation also causes a change in the phase composition of the alloy. The influence of the structural components of the severely deformed alloy on the level of mechanical properties, such as the hardness, plasticity, elastic modulus, and stiffness has been discussed.

In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

DOE PAGES

Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.; ...

2015-12-17

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

Inelastic deformation of metal matrix composites: Plasticity and damage mechanisms, part 2

NASA Technical Reports Server (NTRS)

Majumdar, B. S.; Newaz, G. M.

1992-01-01

The inelastic deformation mechanisms for the SiC (SCS-6)/Ti-15-3 system were studied at 538 C (1000 F) using a combination of mechanical measurements and detailed microstructural examinations. The objectives were to evaluate the contributions of plasticity and damage to the overall MMC response, and to compare the room temperature and elevated temperature deformation behaviors. Four different laminates were studied: (0)8, (90)8,(+ or -45)2s, and (0/90)2s, with the primary emphasis on the unidirectional (0)8, and (90)8 systems. The elevated temperature responses were similar to those at room temperature, involving a two-stage elastic-plastic type of response for the (0)8 system, and a characteristic three-stage deformation response for the (90)8 and (+ or -45)2s systems. The primary effects of elevated temperatures included: (1) reduction in the 'yield' and failure strengths; (2) plasticity through diffused slip rather than concentrated planar slip (which occurred at room temperature); and (3) time-dependent deformation. The inelastic deformation mechanism for the (0)8 MMC was dominated by plasticity at both temperatures. For the (90)8 and (+ or -45)2s MMCs, a combination of damage and plasticity contributed to the deformation at both temperatures.

Numerical investigations on the rebound phenomena and the bonding mechanisms in cold spray processes

NASA Astrophysics Data System (ADS)

Viscusi, A.

2018-05-01

Cold spray technology is a relatively new additive process allowing to create high quality metallic coatings, on both metallic and non-metallic substrates, without extensive heating of the powders sprayed. Upon impact with a target surface, conversion of kinetic energy to plastic deformation occurs, the solid particles deform and bond together. The actual bonding mechanism for cold spray particles is still not well understood, a high number of works has been carried out during the past two decades, several theories have been proposed to explain the adhesion/rebound mechanisms making the system ineffective for industrial applications. Therefore, the aim of this research activity is to better explain the complex adhesion/rebound phenomena into cold spray impact processes through numerical simulations; for this purpose, on the base of simplified hypothesis and results found in literature, an original 3D Finite Element Method (FEM) model of an aluminium particle impacting on an aluminium substrate was proposed. A cohesive behaviour algorithm was implemented in the particle-substrate contact regions aiming to simulate the bonding between the impacting particle and the substrate under specific working conditions. A rebound coefficient was also defined representing the particle residual energy. Different simulations were performed using a range of impact velocities and varying the interfacial cohesive strength. It was shown that at low impact velocities the rebound phenomenon is governed by the elastic energy stored in the system, meanwhile at high impact velocities, the rebound phenomenon is mainly due to the strain rate effects making the system mechanically stronger; therefore, a specific range of bonding velocities depending on substrate-particle contact area were found.

Semantic modeling of the structural and process entities during plastic deformation of crystals and rocks

NASA Astrophysics Data System (ADS)

Babaie, Hassan; Davarpanah, Armita

2016-04-01

We are semantically modeling the structural and dynamic process components of the plastic deformation of minerals and rocks in the Plastic Deformation Ontology (PDO). Applying the Ontology of Physics in Biology, the PDO classifies the spatial entities that participate in the diverse processes of plastic deformation into the Physical_Plastic_Deformation_Entity and Nonphysical_Plastic_Deformation_Entity classes. The Material_Physical_Plastic_Deformation_Entity class includes things such as microstructures, lattice defects, atoms, liquid, and grain boundaries, and the Immaterial_Physical_Plastic_Deformation_Entity class includes vacancies in crystals and voids along mineral grain boundaries. The objects under the many subclasses of these classes (e.g., crystal, lattice defect, layering) have spatial parts that are related to each other through taxonomic (e.g., Line_Defect isA Lattice_Defect), structural (mereological, e.g., Twin_Plane partOf Twin), spatial-topological (e.g., Vacancy adjacentTo Atom, Fluid locatedAlong Grain_Boundary), and domain specific (e.g., displaces, Fluid crystallizes Dissolved_Ion, Void existsAlong Grain_Boundary) relationships. The dynamic aspect of the plastic deformation is modeled under the dynamical Process_Entity class that subsumes classes such as Recrystallization and Pressure_Solution that define the flow of energy amongst the physical entities. The values of the dynamical state properties of the physical entities (e.g., Chemical_Potential, Temperature, Particle_Velocity) change while they take part in the deformational processes such as Diffusion and Dislocation_Glide. The process entities have temporal parts (phases) that are related to each other through temporal relations such as precedes, isSubprocessOf, and overlaps. The properties of the physical entities, defined under the Physical_Property class, change as they participate in the plastic deformational processes. The properties are categorized into dynamical, constitutive, spatial, temporal, statistical, and thermodynamical. The dynamical properties, categorized under the Dynamical_Rate_Property and Dynamical_State_Property classes, subsume different classes of properties (e.g., Fluid_Flow_Rate, Temperature, Chemical_Potential, Displacement, Electrical_Charge) based on the physical domain (e.g., fluid, heat, chemical, solid, electrical). The properties are related to the objects under the Physical_Entity class through diverse object type (e.g., physicalPropertyOf) and data type (e.g., Fluid_Pressure unit 'MPa') properties. The changes of the dynamical properties of the physical entities, described by the empirical laws (equations) modeled by experimental structural geologists, are modeled through the Physical_Property_Dependency class that subsumes the more specialized constitutive, kinetic, and thermodynamic expressions of the relationships among the dynamic properties. Annotation based on the PDO will make it possible to integrate and reuse experimental plastic deformation data, knowledge, and simulation models, and conduct semantic-based search of the source data originating from different rock testing laboratories.

Micrographic detection of plastic deformation in nickel base alloys

DOEpatents

Steeves, Arthur F.; Bibb, Albert E.

1984-01-01

A method for detecting low levels of plastic deformation in metal articles comprising electrolytically etching a flow free surface of the metal article with nital at a current density of less than about 0.1 amp/cm.sup.2 and microscopically examining the etched surface to determine the presence of alternating striations. The presence of striations indicates plastic deformation in the article.

Micrographic detection of plastic deformation in nickel-base alloys

DOEpatents

Steeves, A.F.; Bibb, A.E.

1980-09-20

A method for detecting low levels of plastic deformation in metal articles comprising electrolytically etching a flow free surface of the metal article with nital at a current density of less than about 0.1 amp/cm/sup 2/ and microscopically examining the etched surface to determine the presence of alternating striations. The presence of striations indicates plastic deformation in the article.

Thermodynamically consistent constitutive equations for nonisothermal large strain, elasto-plastic, creep behavior

NASA Technical Reports Server (NTRS)

Riff, R.; Carlson, R. L.; Simitses, G. J.

1985-01-01

The paper is concerned with the development of constitutive relations for large nonisothermal elastic-viscoplastic deformations for metals. The kinematics of elastic-plastic deformation, valid for finite strains and rotations, is presented. The resulting elastic-plastic uncoupled equations for the deformation rate combined with use of the incremental elasticity law permits a precise and purely deductive development of elastic-viscoplastic theory. It is shown that a phenomenological thermodynamic theory in which the elastic deformation and the temperature are state variables, including few internal variables, can be utilized to construct elastic-viscoplastic constitutive equations, which are appropriate for metals. The limiting case of inviscid plasticity is examined.

Size effect on the deformation mechanisms of nanocrystalline platinum thin films.

PubMed

Shu, Xinyu; Kong, Deli; Lu, Yan; Long, Haibo; Sun, Shiduo; Sha, Xuechao; Zhou, Hao; Chen, Yanhui; Mao, Shengcheng; Liu, Yinong

2017-10-16

This paper reports a study of time-resolved deformation process at the atomic scale of a nanocrystalline Pt thin film captured in situ under a transmission electron microscope. The main mechanism of plastic deformation was found to evolve from full dislocation activity-enabled plasticity in large grains (with grain size d > 10 nm), to partial dislocation plasticity in smaller grains (with grain size 10 nm < d < 6 nm), and grain boundary-mediated plasticity in the matrix with grain sizes d < 6 nm. The critical grain size for the transition from full dislocation activity to partial dislocation activity was estimated based on consideration of stacking fault energy. For grain boundary-mediated plasticity, the possible contributions to strain rate of grain creep, grain sliding and grain rotation to plastic deformation were estimated using established models. The contribution of grain creep is found to be negligible, the contribution of grain rotation is effective but limited in magnitude, and grain sliding is suggested to be the dominant deformation mechanism in nanocrystalline Pt thin films. This study provided the direct evidence of these deformation processes at the atomic scale.

Effect of the laser heat treatment on the formation of the gradient structures in alloys based on Fe - Cr - Ni system

NASA Astrophysics Data System (ADS)

Andreev, A. O.; Bykovskiy, D. P.; Osintsev, A. V.; Petrovskiy, V. N.; Ryashko, I. I.; Blinova, E. N.; Libman, M. A.; Glezer, A. M.

2017-12-01

The possibility of producing gradient materials, i.e. materials with pre-set distribution of areas having fundamentally different physical and mechanical characteristics, with the help of laser heat treatment was investigated. Using as an example austenitic-martensitic alloys of iron-chromium-nickel, subjected to cold plastic deformation led to formation of martensite, we show that using laser at the temperature higher than the temperature of reverse martensite transformation leads to the formation of areas of high-strength austenite having predetermined form inside the martensite matrix. Influence of austenite areas geometry on mechanical properties of gradient material was studied.

Phase transformations in the hematite-metal system during mechanical alloying

NASA Astrophysics Data System (ADS)

Kozlov, K. A.; Shabashov, V. A.; Litvinov, A. V.; Sagaradze, V. V.

2009-04-01

Mössbauer spectroscopy and X-ray diffraction are used to show that the phase transformations in hematite α-Fe2O3-metal ( M = Fe, Ni, Ti, Zr) powder mixtures induced by severe cold plastic deformation in ball mills occur via the formation of M-Fe-O solid solutions, redox reactions with the reduction of metallic iron, and the formation of secondary M x O y oxides and M x Fe y intermetallics. Mechanical activation in a ball mill is compared to that under high-pressure shear in Bridgman anvils. The transformations that take place in a ball mill are found to have several stages and to be accelerated.

“Ductile to brittle” transition in thermally stable antigorite gouge at mantle pressures

USGS Publications Warehouse

Proctor, Brooks; Hirth, Greg

2016-01-01

General shear experiments on antigorite-rich serpentinite show a transition from ductile (distributed) to brittle (localized) deformation with increasing temperature from 300°C to 500°C at confining pressures from 1 to 2 GPa. The coefficient of friction associated with slip along fractures decreases from 0.23 to 0.07 with an increase in temperature from 300°C to 500°C. Velocity stepping experiments exhibit a positive rate dependence, as parameterized by a-b values, that decrease modestly with increasing temperature from ~0.015 at 300°C to ~0.01 at 500°C. Fractures contain fine-grained foliated antigorite, and there is no evidence of dehydration. All samples have a moderate foliation and show microstructural evidence for both plastic and brittle deformation mechanisms. Under certain conditions the transition to brittle deformation, at high pressures and temperatures in antigorite, might generate earthquakes, which could explain the occurrence of some intermediate-depth seismicity within subduction zones in serpentinized regions that are too cold to induce dehydration.

Deformation processes within wheel-rail adhesion in contact area

NASA Astrophysics Data System (ADS)

Albagachiev, A. Yu; Keropyan, A. M.

2018-03-01

The study of working surface deformation during interaction of open-pit locomotive tires allowed defining outstanding features of phenomena occurring in the contact area of interacting surfaces. It was found that processes typical for plastic saturated contact occur in the area of wheel-rail interaction of industrial railway transport. In case of plastic deformation exposed to heavy loads typical for open-pit locomotives, upon all rough surfaces of the contour contact area being fully deformed, the frame on which they are found is exposed to plastic deformation. Plastic deformation of roughness within the contact area of interacting surfaces leads to the increase in the actual area of their contact and, therefore, increases the towing capacity of mining machines. Finally, the available data on deformation characteristics with regard to processes occurring in the contact area of wheel-rail interaction will allow making theoretical forecasts on the expected design value of friction coefficient and, therefore, the towing capacity of open-pit locomotives.

Finite element simulation of the T-shaped ECAP processing of round samples

NASA Astrophysics Data System (ADS)

Shaban Ghazani, Mehdi; Fardi-Ilkhchy, Ali; Binesh, Behzad

2018-05-01

Grain refinement is the only mechanism that increases the yield strength and toughness of the materials simultaneously. Severe plastic deformation is one of the promising methods to refine the microstructure of materials. Among different severe plastic deformation processes, the T-shaped equal channel angular pressing (T-ECAP) is a relatively new technique. In the present study, finite element analysis was conducted to evaluate the deformation behavior of metals during T-ECAP process. The study was focused mainly on flow characteristics, plastic strain distribution and its homogeneity, damage development, and pressing force which are among the most important factors governing the sound and successful processing of nanostructured materials by severe plastic deformation techniques. The results showed that plastic strain is localized in the bottom side of sample and uniform deformation cannot be possible using T-ECAP processing. Friction coefficient between sample and die channel wall has a little effect on strain distributions in mirror plane and transverse plane of deformed sample. Also, damage analysis showed that superficial cracks may be initiated from bottom side of sample and their propagation will be limited due to the compressive state of stress. It was demonstrated that the V shaped deformation zone are existed in T-ECAP process and the pressing load needed for execution of deformation process is increased with friction.

Plastic deformation and failure mechanisms in nano-scale notched metallic glass specimens under tensile loading

NASA Astrophysics Data System (ADS)

Dutta, Tanmay; Chauniyal, Ashish; Singh, I.; Narasimhan, R.; Thamburaja, P.; Ramamurty, U.

2018-02-01

In this work, numerical simulations using molecular dynamics and non-local plasticity based finite element analysis are carried out on tensile loading of nano-scale double edge notched metallic glass specimens. The effect of acuteness of notches as well as the metallic glass chemical composition or internal material length scale on the plastic deformation response of the specimens are studied. Both MD and FE simulations, in spite of the fundamental differences in their nature, indicate near-identical deformation features. Results show two distinct transitions in the notch tip deformation behavior as the acuity is increased, first from single shear band dominant plastic flow localization to ligament necking, and then to double shear banding in notches that are very sharp. Specimens with moderately blunt notches and composition showing wider shear bands or higher material length scale characterizing the interaction stress associated with flow defects display profuse plastic deformation and failure by ligament necking. These results are rationalized from the role of the interaction stress and development of the notch root plastic zones.

The thermostimulated luminescence of radiation defects in KCl, KBr and KI crystals at elastic and plastic deformation

NASA Astrophysics Data System (ADS)

Shunkeyev, K.; Myasnikova, L.; Barmina, A.; Zhanturina, N.; Sagimbaeva, Sh; Aimaganbetova, Z.; Sergeyev, D.

2017-05-01

The efficiency of radiation defects formation in alkali halide crystals (AHC) was studied by the method of absorption spectroscopy. However, it is not possible to study the deformation-stimulated processes in detail by the absorption spectrum of radiation defects due to the limited sensitivity compared with luminescent spectroscopy. In this regard, thermally stimulated luminescence (TSL) of radiation defects at elastic and plastic deformation was applied in AHC. In the absence of deformation, the dominant peaks in TSL are ≤ft( {X_3^ - } \\right)aca^0-centers. After elastic deformation, low temperature peaks of TSL corresponding to F‧-, VK- and VF-centers became dominant. After plastic deformation, the peaks of TSL corresponding to ≤ft( {X_3^ - } \\right)aca^0-centers became dominant. The elastic deformation contributes to the increase in concentration of low-temperature F‧-, VK- and VF-centers, and the plastic one contributes to that of high temperature ≤ft( {X_3^ - } \\right)aca^0-centers (peaks of TSL in KCl at 360K, in KBr at 365K, in KI at 340K), composed by divacancies created by plastic deformation. At elastic deformation, unrelaxed interstitial halogen atoms are converted into VK- and VF-centers, and due to this fact the long-range interaction is absent, the result of which are the X_3^ - -centers.

Modeling plasticity by non-continuous deformation

NASA Astrophysics Data System (ADS)

Ben-Shmuel, Yaron; Altus, Eli

2017-10-01

Plasticity and failure theories are still subjects of intense research. Engineering constitutive models on the macroscale which are based on micro characteristics are very much in need. This study is motivated by the observation that continuum assumptions in plasticity in which neighbour material elements are inseparable at all-time are physically impossible, since local detachments, slips and neighbour switching must operate, i.e. non-continuous deformation. Material microstructure is modelled herein by a set of point elements (particles) interacting with their neighbours. Each particle can detach from and/or attach with its neighbours during deformation. Simulations on two- dimensional configurations subjected to uniaxial compression cycle are conducted. Stochastic heterogeneity is controlled by a single "disorder" parameter. It was found that (a) macro response resembles typical elasto-plastic behaviour; (b) plastic energy is proportional to the number of detachments; (c) residual plastic strain is proportional to the number of attachments, and (d) volume is preserved, which is consistent with macro plastic deformation. Rigid body displacements of local groups of elements are also observed. Higher disorder decreases the macro elastic moduli and increases plastic energy. Evolution of anisotropic effects is obtained with no additional parameters.

Deformation behavior of Nb nanowires in TiNiCu shape memory alloy matrix

DOE PAGES

Jiang, Daqiang; Liu, Yinong; Yu, Cun; ...

2015-08-18

An in-situ nanowire Nb/TiNiCu composite is fabricated based on the concept of strain under-matching between a phase transforming matrix and high strength nanomaterials. The deformation behavior of the Nb nanowire was investigated by means of in-situ synchrotron X-ray diffraction when the TiNiCu matrix underwent different deformation modes. The maximum lattice strain of the Nb nanowires was about 5% when the matrix deformed via martensitic transformation or 1% when deforming plastically by dislocation slip. As a result, the Nb nanowires showed a lattice strain of 3.5% when the matrix deformed in the mixed mode of plastic deformation and martensitic transformation, whichmore » means that the occurrence of plastic deformation does not impede load transfer from the matrix to the nanowires.« less

Plastic deformation in a metallic granular chain

NASA Astrophysics Data System (ADS)

Musson, Ryan W.; Carlson, William

2016-03-01

Solitary wave response was investigated in a metallic granular chain-piston system using LS-DYNA. A power law hardening material model was used to show that localized plastic deformation is present in a metallic granular chain for an impact velocity of 0.5 m/s. This loss due to plastic deformation was quantified via impulse, and it was shown that the loss scales nearly linearly with impact velocity. Therefore, metallic grains may not be suitable for devices that require high-amplitude solitary waves. There would be too much energy lost to plastic deformation. One can assume that ceramics will behave elastically; therefore, the response of an aluminum oxide granular chain was compared to that of a steel chain.

Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. I. Dislocation microstructures in as-received state and at different plastic strains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, Fei; Daymond, Mark R., E-mail: mark.daymond@queensu.ca; Yao, Zhongwen

Thin foil dog bone samples prepared from a hot rolled Zr-2.5Nb alloy have been deformed by tensile deformation to different plastic strains. The development of slip traces during loading was observed in situ through SEM, revealing that deformation starts preferentially in certain sets of grains during the elastic-plastic transition region. TEM characterization showed that sub-grain boundaries formed during hot rolling consisted of screw 〈a〉 dislocations or screw 〈c〉 and 〈a〉 dislocations. Prismatic 〈a〉 dislocations with large screw or edge components have been identified from the sample with 0.5% plastic strain. Basal 〈a〉 and pyramidal 〈c + a〉 dislocations were found in themore » sample that had been deformed with 1.5% plastic strain, implying that these dislocations require larger stresses to be activated.« less

Elasto-plastic impact of hemispherical shell impacting on hard rigid sphere

NASA Technical Reports Server (NTRS)

Raftopoulos, D. D.; Spicer, A. L.

1976-01-01

An analysis of plastic stress waves for cylindrical metallic projectile in impact is extended to an analysis of a hemispherical shell suffereing plastic deformation during the process of impact. It is assumed that the hemispherical shell with a prescribed launch velocity impinges a fixed rigid sphere of diameter equal to the internal diameter of the shell. The dynamic biaxial state of stress present in the shell during deformation is investigated. The analysis is valuable for studying the state of stress during large plastic deformation of a hemispherical shell.

Demonstration of finite element simulations in MOOSE using crystallographic models of irradiation hardening and plastic deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patra, Anirban; Wen, Wei; Martinez Saez, Enrique

This report describes the implementation of a crystal plasticity framework (VPSC) for irradiation hardening and plastic deformation in the finite element code, MOOSE. Constitutive models for irradiation hardening and the crystal plasticity framework are described in a previous report [1]. Here we describe these models briefly and then describe an algorithm for interfacing VPSC with finite elements. Example applications of tensile deformation of a dog bone specimen and a 3D pre-irradiated bar specimen performed using MOOSE are demonstrated.

Modelling of deformation around magmatic intrusions with application to gold-related structures in the Yilgarn Craton, Western Australia

NASA Astrophysics Data System (ADS)

Zhang, Y.; Karrech, A.; Schaubs, P. M.; Regenauer-Lieb, K.; Poulet, T.; Cleverley, J. S.

2012-03-01

This study simulates rock deformation around high temperature granite intrusions and explores how gold bearing shear zones near intrusions were developed in the Yilgarn, using a new continuum damage mechanics algorithm that considers the temperature and time dependent elastic-visco-plastic constitutive behaviour of crustal materials. The results demonstrate that strain rates have the most significant effects on structural patterns for both extensional and compressional cases. Smaller strain rates promote the formation of narrow high-strain shear zones and strong strain localisation along the flank or shoulder areas of the intrusion and cold granite dome. Wider diffuse shear zones are developed under higher strain rates due to strain hardening. The cooling of the intrusion to background temperatures occurred over a much shorter time interval when compared to the duration of deformation and shear zones development. Strong strain localisation near the intrusion and shear zone development in the crust occurred under both extensional and compressional conditions. There is always clear strain localisation around the shoulders of the intrusion and the flanks of the "cold" granitic dome in early deformation stages. In the models containing a pre-existing fault, strain localisation near the intrusion became asymmetric with much stronger localisation and the development of a damage zone at the shoulder adjacent to the reactivated fault. At higher deformation stages, the models produced a range of structural patterns including graben and half graben basin (extension), "pop-up" wedge structures (compression), tilted fault blocks and switch of shear movement from reverse to normal on shear zones. The model explains in part why a number of gold deposits (e.g. Wallaby and Paddington deposits) in the Yilgarn were formed near the flank of granite-cored domes and deep "tapping" faults, and shows that the new modelling approach is capable of realistically simulating high strain localisation and shear zone development.

Dependence of stress-induced omega transition and mechanical twinning on phase stability in metastable β Ti–V alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, X.L.; Li, L.; Mei, W.

2015-09-15

Tensile properties and deformation microstructures of a series of binary β Ti–16–22V alloys have been investigated. The results show that the plastic deformation mode changes from the plate-like stress-induced ω phase transformation with a special habit plane of (− 5052){sub ω}//(3 − 3 − 2){sub β} to (332)<113> type deformation twinning with increasing the content of vanadium in the β Ti–16–22 wt.% V alloys. The plate-like stress-induced ω phase has a special orientation relationship with the β phase matrix, i.e., [110]{sub β}//[− 12 − 10]{sub ω}, (3 − 3 − 2){sub β}//(− 5052){sub ω} and (− 55 − 4){sub β}//(30more » − 31){sub ω}. The alloys plastically deformed by stress-induced ω phase transformation exhibit relatively higher yield strength than those deformed via (332)<113> type deformation twinning. It can be concluded that the stability of β phase plays a significant role in plastic deformation mode, i.e., stress-induced ω phase transformation or (332)<113> type deformation twinning, which governs the mechanical property of the β Ti–16–22 wt.% V alloys. - Highlights: • Tensile properties and deformed microstructures of β Ti–16–22V alloys were studied. • Stress-induced ω phase transformation and (332)<113> twinning occur in the alloys. • Stability of β phase plays a significant role in plastic deformation mode. • Plastic deformation mode governs the mechanical property of the alloys.« less

Thermal Microstructural Stability of AZ31 Magnesium after Severe Plastic Deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, John P.; Askari, Hesam A.; Hovanski, Yuri

2015-03-01

Both equal channel angular pressing and friction stir processing have the ability to refine the grain size of twin roll cast AZ31 magnesium and potentially improve its superplastic properties. This work used isochronal and isothermal heat treatments to investigate the microstructural stability of twin roll cast, equal channel angular pressed and friction stir processed AZ31 magnesium. For both heat treatment conditions, it was found that the twin roll casted and equal channel angular pressed materials were more stable than the friction stir processed material. Calculations of the grain growth kinetics showed that severe plastic deformation processing decreased the activation energymore » for grain boundary motion with the equal channel angular pressed material having the greatest Q value of the severely plastically deformed materials and that increasing the tool travel speed of the friction stir processed material improved microstructural stability. The Hollomon-Jaffe parameter was found to be an accurate means of identifying the annealing conditions that will result in substantial grain growth and loss of potential superplastic properties in the severely plastically deformed materials. In addition, Humphreys’s model of cellular microstructural stability accurately predicted the relative microstructural stability of the severely plastically deformed materials and with some modification, closely predicted the maximum grain size ratio achieved by the severely plastically deformed materials.« less

Direct in situ observation of metallic glass deformation by real-time nano-scale indentation

NASA Astrophysics Data System (ADS)

Gu, Lin; Xu, Limei; Zhang, Qingsheng; Pan, Deng; Chen, Na; Louzguine-Luzgin, Dmitri V.; Yao, Ke-Fu; Wang, Weihua; Ikuhara, Yuichi

2015-03-01

A common understanding of plastic deformation of metallic glasses (MGs) at room temperature is that such deformation occurs via the formation of runaway shear bands that usually lead to catastrophic failure of MGs. Here we demonstrate that inhomogeneous plastic flow at nanoscale can evolve in a well-controlled manner without further developing of shear bands. It is suggested that the sample undergoes an elasto-plastic transition in terms of quasi steady-state localized shearing. During this transition, embryonic shear localization (ESL) propagates with a very slow velocity of order of ~1 nm/s without the formation of a hot matured shear band. This finding further advances our understanding of the microscopic deformation process associated with the elasto-plastic transition and may shed light on the theoretical development of shear deformation in MGs.

Method of determining elastic and plastic mechanical properties of ceramic materials using spherical indenters

DOEpatents

Adler, Thomas A.

1996-01-01

The invention pertains a method of determining elastic and plastic mechanical properties of ceramics, intermetallics, metals, plastics and other hard, brittle materials which fracture prior to plastically deforming when loads are applied. Elastic and plastic mechanical properties of ceramic materials are determined using spherical indenters. The method is most useful for measuring and calculating the plastic and elastic deformation of hard, brittle materials with low values of elastic modulus to hardness.

Effect of cold deformation on the electrochemical behaviour of 304L stainless steel in contaminated sulfuric acid environment

NASA Astrophysics Data System (ADS)

Luo, Hong; Su, Huaizhi; Ying, Guobing; Dong, Chaofang; Li, Xiaogang

2017-12-01

The effect of cold deformation on the microstructure and electrochemical corrosion behaviour of 304L stainless steel in contaminated sulfuric acid solutions (simulated proton exchange membrane fuel cells environments) were evaluated using electron backscatter diffraction analyses, electrochemical measurements, and surface analyses. The internal microstructure,including the grain sizes, angles of the grain boundaries, low coincidence site lattice boundaries, and phase transformations, was changed due to the cold deformation. No noticeable modifications of the pitting corrosion potential were observed during the various deformations, except for a slight enhancement in the passive current density with an increase in the deformation. The CrO3 and metal Ni species in the passive film were investigated after deformation. After heavy deformation (greater than 60%), nickel oxides were detected. Moreover, the Cr/Fe and O2-/OH- ratios in the passive film were higher before deformation, and they decreased with an increase in the deformation level.

A stress-free model for residual stress assessment using thermoelastic stress analysis

NASA Astrophysics Data System (ADS)

Howell, Geoffrey; Dulieu-Barton, Janice M.; Achintha, Mithila; Robinson, Andrew F.

2015-03-01

Thermoelastic Stress Analysis (TSA) has been proposed as a method of obtaining residual stresses. The results of a preliminary study demonstrated that when Al-2024 plate containing holes that were plastically deformed by cold expansion process to 2% and 4% strain the thermoelastic response in the material around the hole was different to that obtained from a plate that had not experienced any plastic cold expansion (i.e. a reference specimen). This observation provides an opportunity for obtaining residual stresses based on TSA data. In many applications a reference specimen (i.e. residual stress free specimen) may not be available for comparison, so a synthetic, digital bitmap has been proposed as an alternative. An elastic finite element model is created using commercially available software Abaqus/Standard and the resultant stress field is extracted. The simulated stress field from the model is mapped onto a grid that matches the TSA pixel data from a physical reference specimen. This stress field is then converted to a ΔT/T field that can be compared to the full-field TSA data. When the reference experimental data is subtracted from the, bitmap dataset the resultant ΔT/T field is approximately zero. Further work proposes replacing the experimental reference data with that from specimens that have undergone cold expansion with the aim of revealing the regions affected by residual stress through a departure from zero in the resultant stress field. The paper demonstrates the first steps necessary for deriving the residual stresses from a general specimen using TSA.

Correlating elastic and plastic deformation with magnetic permeability values

NASA Astrophysics Data System (ADS)

Papadopoulou, S.

2017-12-01

This paper investigates the utilization of magnetic permeability method in determining elastic and plastic deformation state of ferromagnetic steels. The results have shown a strong degradation of the magnetic values on plastically region due to the irreversible movements of the magnetic domain walls.

Nano-deformation behavior of silicon (100) film studied by depth sensing indentation and nanoscratch technique

NASA Astrophysics Data System (ADS)

Geetha, D.; Pratyank, R.; Kiran, P.

2018-04-01

Silicon being the most important material applied in microelectronic and photovoltaic technology, repeated investigation of the mechanical properties becomes essential. The nanoscale elastic-plastic deformation characteristics of Si (100) film were analyzed using nanoindentation and nanoscratch techniques. The hardness and elastic modulus values of the film obtained from nanoindentation tests were found to be consistent with the reported values. The load-displacement curves showed discontinuities and kinks which confirms the plastic behaviour of Si. The indentation induced plastic deformations were the consequences of the phase transformations. The critical shear stress, tensile strength and plastic zone size, of the Si film when subjected to nanoindentation were determined. The nanoscratch tests were performed to understand the tribological properties of the film. The SPM images of both the nanoindentation and nanoscratch profiles were useful in revealing the plastic character in terms of the piling up of matter in the vicinity of the dents. Conclusions were drawn in quantifying the plastic deformations and phase transformations.

Plastic deformation of silicon dendritic web ribbons during the growth

NASA Technical Reports Server (NTRS)

Cheng, L. J.; Dumas, K. A.; Su, B. M.; Leipold, M. H.

1984-01-01

The distribution of slip dislocations in silicon dendritic web ribbons due to plastic deformation during the cooling phase of the growth was studied. The results show the existence of two distinguishable stress regions across the ribbon formed during the plastic deformation stage, namely, shear stress at the ribbon edges and tensile stress at the middle. In addition, slip dislocations caused by shear stress near the edges appear to originate at the twin plane.

[Plastic surgery to correct deformities of the ear].

PubMed

Naumann, A

2005-08-18

For the plastic-surgical correction of mild deformities of the ears, well-proven incisional and suturing techniques are available. Only in exceptional cases is skin grafting or the use of cartilage ersatz material required. In the plastic surgical treatment of moderate to severe ear deformities, in contrast, not only incisional and suturing techniques, but also free skin grafts and ersatz materials are needed. At the ENT Department of the Ludwig-Maximilian University in Munich, plastic reconstruction of moderate to severe deformities of the external ear using porous polyethylene implants instead of rib cartilage grafts has been practiced with success for the past two years or so. Porous polyethylene implants provide good results and may help to avoid pre- and postoperative morbidity at donor site defects.

Practical solution of plastic deformation problems in elastic-plastic range

NASA Technical Reports Server (NTRS)

Mendelson, A; Manson, S

1957-01-01

A practical method for solving plastic deformation problems in the elastic-plastic range is presented. The method is one of successive approximations and is illustrated by four examples which include a flat plate with temperature distribution across the width, a thin shell with axial temperature distribution, a solid cylinder with radial temperature distribution, and a rotating disk with radial temperature distribution.

Elastic-plastic analysis of AS4/PEEK composite laminate using a one-parameter plasticity model

NASA Technical Reports Server (NTRS)

Sun, C. T.; Yoon, K. J.

1992-01-01

A one-parameter plasticity model was shown to adequately describe the plastic deformation of AS4/PEEK (APC-2) unidirectional thermoplastic composite. This model was verified further for unidirectional and laminated composite panels with and without a hole. The elastic-plastic stress-strain relations of coupon specimens were measured and compared with those predicted by the finite element analysis using the one-parameter plasticity model. The results show that the one-parameter plasticity model is suitable for the analysis of elastic-plastic deformation of AS4/PEEK composite laminates.

Formation of the structure and properties of an Mg-Al-Zn-Mn alloy during plastic deformation by rolling

NASA Astrophysics Data System (ADS)

Bozhko, S. A.; Betsofen, S. Ya.; Kolobov, Yu. R.; Vershinina, T. N.

2015-03-01

The laws of formation of an ultrafine structure in an Mg-Al-Zn-Mn alloy (MA5 alloy) under severe plastic deformation have been studied during lengthwise section rolling at a strain e = 1.59. The deformation behavior and the physical factors of anisotropy of yield strength during compression tests in various directions with respect to axis of rolling are analyzed. The role of crystallographic texture and twinning processes in the generation of strength processes and the development of plastic deformation of the alloy is analyzed.

The effect of hydrogen embrittlement on the localized plastic deformation of aluminum alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bochkareva, Anna, E-mail: avb@ispms.tsc.ru; Lunev, Aleksey, E-mail: agl@ispms.tsc.ru; National Research Tomsk Polytechnic University, Tomsk, 634050

2015-10-27

The effect of hydrogen embrittlement on the localized plastic deformation of aluminum alloy D1 was investigated. The studies were performed for the test samples of aluminum alloy subjected to electrolytic hydrogenation. It is found that the mechanical properties and localized plastic deformation parameters of aluminum alloy are affected adversely by hydrogen embrittlement. The hydrogenated counterpart of alloy has a lower degree of ductility relative to the original alloy; however, the plastic flow behavior of material remains virtually unaffected. Using scanning electron and atomic force microscopy methods, the changes in the fracture surface were investigated. The deformation diagrams were examined formore » the deformed samples of aluminum alloy. These are found to show all the plastic flow stages: the linear, parabolic and pre-failure stages would occur for the respective values of the exponent n from the Ludwik-Holomon equation. Using digital speckle image technique, the local strain patterns were being registered for the original alloy D1 and the counterpart subjected to electrolytic hydrogenation for 100 h.« less

Investigation of coatings of austenitic steels produced by supersonic laser deposition

NASA Astrophysics Data System (ADS)

Gorunov, A. I.; Gilmutdinov, A. Kh.

2017-02-01

The structure and properties of stainless austenitic steel coatings obtained by the supersonic laser deposition are studied in the paper. Implantation of the powder particles into the substrate surface and simultaneous plastic deformation at partial melting improved the mechanical properties of the coatings - tensile strength limit was 650 MPa and adhesion strength was 105 MPa. It was shown that insufficient laser power leads to disruption of the deposition process stability and coating cracking. Surface temperature increase caused by laser heating above 1300 °C resulted in coating melting. The X-ray analysis showed that radiation intensifies the cold spray process and does not cause changes in the austenitic base structure.

Solution of elastic-plastic stress analysis problems by the p-version of the finite element method

NASA Technical Reports Server (NTRS)

Szabo, Barna A.; Actis, Ricardo L.; Holzer, Stefan M.

1993-01-01

The solution of small strain elastic-plastic stress analysis problems by the p-version of the finite element method is discussed. The formulation is based on the deformation theory of plasticity and the displacement method. Practical realization of controlling discretization errors for elastic-plastic problems is the main focus. Numerical examples which include comparisons between the deformation and incremental theories of plasticity under tight control of discretization errors are presented.

Simultaneous observations of reaction kinetics, creep behavior, and AE activities during syndeformational antigorite dehydration at high pressures

NASA Astrophysics Data System (ADS)

Kubo, T.; Iwasato, T.; Higo, Y.; Kato, T.; Kaneshima, S.; Uehara, S.; Koizumi, S.; Imamura, M.; Tange, Y.

2015-12-01

Intermediate-depth earthquakes are seismic activities in Wadati-Benioff zone at depths from 60 km to 300 km, where subducting plates deform plastically rather than brittle failure. Although it has been reported that unstable faulting occurred during antigorite dehydration even at higher pressures than ~2 GPa (e.g., Jung et al., 2009), the recent study by Chernak and Hirth (2011) revealed that the syndefromational antigorite dehydration does not produces stick-slip instabilities but stable fault slip. In the present study, we newly developed an AE monitoring system for high-pressure reaction-deformation processes combined with D-DIA and synchrotron monochromatic X-ray to observe reaction kinetics, creep behaviors, and AE activities simultaneously. We applied this technique to investigate shear instability during syndeformational antigorite dehydration. High-pressure deformation experiments were conducted up to ~8 GPa, ~1050 K, and strain rates of 3.4-9.2 x 10-5 s-1 in compression using a D-DIA type apparatus installed at BL-04B1, SPring-8. 50 keV mono X-ray were used to measure reaction kinetics and stress-strain data. To monitor shear instabilities by detecting AEs, six piezoelectric devices were positioned between first and second stage anvils of MA 6-6 type system. We used three kinds of starting materials of polycrystalline antigorite, fine-grained forsterite polycrystal, and two-phase mixtures of antigorite and San Carlos olivine (10%, 30%, and 50%atg). Clear contrasts were observed in AE activities between forsterite and antigorite samples. AE activities detected within the forsterite polycrystal suggested (semi) brittle behaviors at low pressures during the cold compression stage.
Almost no AEs were detected within the antigorite samples during any stages of cold compression, ramping, deformation, and syndeformational dehydration although localized deformation textures were observed in recovered samples. Instead, we detected some AEs outside the sample, indicating the stick slipping at the boundaries of cylindrical parts. Our results suggest that localized deformation and dehydration of antigorite do not enhance shear instability at high pressures at least in compression under drained condition.

Extraordinary plasticity of an inorganic semiconductor in darkness.

PubMed

Oshima, Yu; Nakamura, Atsutomo; Matsunaga, Katsuyuki

2018-05-18

Inorganic semiconductors generally tend to fail in a brittle manner. Here, we report that extraordinary "plasticity" can take place in an inorganic semiconductor if the deformation is carried out "in complete darkness." Room-temperature deformation tests of zinc sulfide (ZnS) were performed under varying light conditions. ZnS crystals immediately fractured when they deformed under light irradiation. In contrast, it was found that ZnS crystals can be plastically deformed up to a deformation strain of ε t = 45% in complete darkness. In addition, the optical bandgap of the deformed ZnS crystals was distinctly decreased after deformation. These results suggest that dislocations in ZnS become mobile in complete darkness and that multiplied dislocations can affect the optical bandgap over the whole crystal. Inorganic semiconductors are not necessarily intrinsically brittle. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

SHAKING TABLE TESTS ON SEISMIC DEFORMATION OF PILE SUPPORTED PIER

NASA Astrophysics Data System (ADS)

Fujita, Daiki; Kohama, Eiji; Takenobu, Masahiro; Yoshida, Makoto; Kiku, Hiroyoshi

The seismic deformation characeteristics of a pile supported pier was examined with the shake table test, especially focusing on the pier after its deformation during earthquakes. The model based on the similitude of the fully-plastic moment in piles was prepared to confirm the deformation and stress characteristic after reaching the fully-plastic moment. Moreover, assuming transportation of emergency supplies and occurrence of after shock in the post-disaster period, the pile supported pier was loaded with weight after reaching fully-plastic moment and excited with the shaking table. As the result, it is identified that the displacement of the pile supported pier is comparatively small if bending strength of piles does not decrease after reaching fully-plastic moment due to nonoccourrence of local backling or strain hardening.

Measurement of plastic and elastic deformation due to third-order torque in self-ligated orthodontic brackets.

PubMed

Major, Thomas W; Carey, Jason P; Nobes, David S; Heo, Giseon; Major, Paul W

2011-09-01

Control of root torque is often achieved by introducing a twist in a rectangular archwire. The purpose of this study was to investigate third-order torque on different types of self-ligated brackets by analyzing the bracket's elastic and plastic deformations in conjunction with the expressed torque at varying angles of twist. An orthodontic bracket was mounted to a load cell that measured forces and moments in all directions. The wire was twisted in the bracket via a stepper motor, controlled by custom software. Overhead images were taken by a camera through a microscope and processed by using optical correlation to measure deformation. At the maximum torquing angle of 63° with 0.019 × 0.025-in stainless steel wire, the total elastic and plastic deformation values were 0.063, 0.033, and 0.137 mm for Damon Q (Ormco, Orange, Calif), In-Ovation R (GAC, Bohemia, NY), and Speed (Strite Industries, Cambridge, Ontario, Canada), respectively. The total plastic deformation values were 0.015, 0.006, and 0.086 mm, respectively, measured at 0° of unloading. In-Ovation R had the least deformation due to torquing of the 3 investigated bracket types. Damon Q and Speed on average had approximately 2.5 and 14 times greater maximum plastic deformation, respectively, than did In-Ovation R. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Microstructure Evolution and Mechanical Behavior of a Hot-Rolled High-Manganese Dual-Phase Transformation-Induced Plasticity/Twinning-Induced Plasticity Steel

NASA Astrophysics Data System (ADS)

Fu, Liming; Shan, Mokun; Zhang, Daoda; Wang, Huanrong; Wang, Wei; Shan, Aidang

2017-05-01

The microstructures and deformation behavior were studied in a high-temperature annealed high-manganese dual-phase (28 vol pct δ-ferrite and 72 vol pct γ-austenite) transformation-induced plasticity/twinning-induced plasticity (TRIP/TWIP) steel. The results showed that the steel exhibits a special Lüders-like yielding phenomenon at room temperature (RT) and 348 K (75 °C), while it shows continuous yielding at 423 K, 573 K and 673 K (150 °C, 300 °C and 400 °C) deformation. A significant TRIP effect takes place during Lüders-like deformation at RT and 348 K (75 °C) temperatures. Semiquantitative analysis of the TRIP effect on the Lüders-like yield phenomenon proves that a softening effect of the strain energy consumption of strain-induced transformation is mainly responsible for this Lüders-like phenomenon. The TWIP mechanism dominates the 423 K (150 °C) deformation process, while the dislocation glide controls the plasticity at 573 K (300 °C) deformation. The delta-ferrite, as a hard phase in annealed dual-phase steel, greatly affects the mechanical stability of austenite due to the heterogeneous strain distribution between the two phases during deformation. A delta-ferrite-aided TRIP effect, i.e., martensite transformation induced by localized strain concentration of the hard delta-ferrite, is proposed to explain this kind of Lüders-like phenomenon. Moreover, the tensile curve at RT exhibits an upward curved behavior in the middle deformation stage, which is principally attributed to the deformation twinning of austenite retained after Lüders-like deformation. The combination of the TRIP effect during Lüders-like deformation and the subsequent TWIP effect greatly enhances the ductility in this annealed high-manganese dual-phase TRIP/TWIP steel.

Investigation of plastic deformation heterogeneities in duplex steel by EBSD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wronski, S., E-mail: wronski@ftj.agh.edu.pl; Tarasiuk, J., E-mail: tarasiuk@ftj.agh.edu.pl; Bacroix, B., E-mail: brigitte.bacroix@univ-paris13.fr

2012-11-15

An EBSD analysis of a duplex steel (austeno-ferritic) deformed in tension up to fracture is presented. The main purpose of the paper is to describe, qualitatively and quantitatively, the differences in the behavior of the two phases during plastic deformation. In order to do so, several topological maps are measured on the deformed state using the electron backscatter diffraction technique. Distributions of grain size, misorientation, image quality factor and texture are then analyzed in detail. - Highlights: Black-Right-Pointing-Pointer Heterogeneities in duplex steel is studied. Black-Right-Pointing-Pointer The behavior of the two phases during plastic deformation is studied. Black-Right-Pointing-Pointer IQ factor distributionmore » and misorientation characteristics are examined using EBSD.« less

Microstructure and properties of ultrafine grained structure of Cu-Zn-Si alloy fabricated by heavy cold rolling

NASA Astrophysics Data System (ADS)

Miura, H.; Kobayashi, T.; Kobayashi, M.

2014-08-01

Cu-18.2Zn-1.5Si-0.25Fe (mass%) alloy was heavily cold rolled. Ultrafine grained (UFGed) structure, containing a mixture of lamellar and mechanical twins, was easily and homogeneously formed. The average grain size was approximately 100 nm. The as-rolled sample showed quite high ultimate tensile strength (UTS) over 1 GPa. The UTS was higher than those obtained by multi directional forging. When the samples were annealed at relatively low temperatures between 553 K and 653 K, they showed slight hardening followed by large softening due to occurrence of static recrystallization (SRX). Annealing of UFGed structure at relatively low temperature of around 0.4 Tm caused extensive SRX that, in turn, induces ultrafine RXed grained structure. The grain size of the RXed sample was as fine as 200 nm. Although the annealing induced recovery of ductility while UTS gradually reduces, UTS over 1 GPa with ductility of 15 % were attained. The RXed grains mainly contained ultrafine annealing twins. Therefore, UFGed structure and superior mechanical properties could be achieved by a simple process of cold rolling, i.e., without severe plastic deformation.

Processing Conditions Affecting Grain Size and Mechanical Properties in Nanocomposites Produced via Cold Spray

NASA Astrophysics Data System (ADS)

Cavaliere, P.; Perrone, A.; Silvello, A.

2014-10-01

Cold spray is a coating technology based on aerodynamics and high-speed impact dynamics. In this process, spray particles (usually 1-50 μm in diameter) are accelerated to a high velocity (typically 300-1200 m/s) by a high-speed gas (pre-heated air, nitrogen, or helium) flow that is generated through a convergent-divergent de Laval-type nozzle. A coating is formed through the intensive plastic deformation of particles impacting on a substrate at a temperature below the melting point of the spray material. In the present paper the main processing parameters affecting the microstructural and mechanical behavior of metal-metal cold spray deposits are described. The effect of process parameters on grain refinement and mechanical properties were analyzed for composite particles of Al-Al2O3, Ni-BN, Cu-Al2O3, and Co-SiC. The properties of the formed nanocomposites were compared with those of the parent materials sprayed under the same conditions. The process conditions, leading to a strong grain refinement with an acceptable level of the deposit mechanical properties such as porosity and adhesion strength, are discussed.

Modelling of the plastic deformation and primary creep of metals coupled with DC in terms of the synthetic theory of irrecoverable deformation

NASA Astrophysics Data System (ADS)

Rusinko, Andrew; Varga, Peter

2018-04-01

The paper deals with modelling of the plastic and creep deformation of metals coupled with current. The passage of DC manifests itself in the increase in creep deformation and leads to primary creep time shortening. With plastic deformation, a short electric impulse results in the step-wise decrease of stress (stress-drop) on the stress-strain diagram. To catch these phenomena, we utilize the synthetic theory of recoverable deformation. The constitutive equation of this theory is supplemented by a term taking into account the intensity of DC. Further, we introduce DC intensity into the function governing transient creep. As a result, we predict the parameters of transient creep and calculate the stress-drop as a function of current intensity. The model results show good agreement with experimental data.

Cyclic Deformation Microstructure in Heavily Cold-Drawn Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Xie, Xingfei; Ning, Dong; Sun, Jian

2018-04-01

Cyclic deformation microstructure of the heavily cold-drawn austenitic stainless steel is significantly influenced by the spacing between mechanical twins introduced by prior cold drawing. Well-developed dislocation cells form between mechanical twins with the spacing larger than about 800 nm. Persistent slip band (PSB)-like structure with ladders takes place between mechanical twins spacing from 300 to 800 nm. Few dislocations occur between neighboring mechanical twins with spacing less than about 100 nm. Pre-existing mechanical twins and deformation bands segment austenitic grains, facilitating multi-slip and consequently suppressing PSB formation.

Cyclic Deformation Microstructure in Heavily Cold-Drawn Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Xie, Xingfei; Ning, Dong; Sun, Jian

2018-07-01

Cyclic deformation microstructure of the heavily cold-drawn austenitic stainless steel is significantly influenced by the spacing between mechanical twins introduced by prior cold drawing. Well-developed dislocation cells form between mechanical twins with the spacing larger than about 800 nm. Persistent slip band (PSB)-like structure with ladders takes place between mechanical twins spacing from 300 to 800 nm. Few dislocations occur between neighboring mechanical twins with spacing less than about 100 nm. Pre-existing mechanical twins and deformation bands segment austenitic grains, facilitating multi-slip and consequently suppressing PSB formation.

Plastic strain arrangement in copper single crystals in sliding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chumaevskii, Andrey V., E-mail: tch7av@gmail.com; Lychagin, Dmitry V., E-mail: dvl-tomsk@mail.ru; Tarasov, Sergei Yu., E-mail: tsy@ispms.tsc.ru

2014-11-14

Deformation of tribologically loaded contact zone is one of the wear mechanisms in spite of the fact that no mass loss may occur during this process. Generation of optimal crystallographic orientations of the grains in a polycrystalline materials (texturing) may cause hardening and reducing the deformation wear. To reveal the orientation dependence of an individual gain and simplify the task we use copper single crystals with the orientations of the compression axis along [111] and [110]. The plastic deformation was investigated by means of optical, scanning electron microscopy and EBSD techniques. It was established that at least four different zonesmore » were generated in the course of sliding test, such as non-deformed base metal, plastic deformation layer sliding, crystalline lattice reorientation layer and subsurface grain structure layer. The maximum plastic strain penetration depth was observed on [110]-single crystals. The minimum stability of [111]-crystals with respect to rotation deformation mode as well as activation of shear in the sliding contact plane provide for rotation deformation localization below the worn surface. The high-rate accumulation of misorientations and less strain penetration depth was observed on [111]-crystals as compared to those of [110]-oriented ones.« less

Inelastic Deformation of Metal Matrix Composites. Part 1; Plasticity and Damage Mechanisms

NASA Technical Reports Server (NTRS)

Majumdar, B. S.; Newaz, G. M.

1992-01-01

The deformation mechanisms of a Ti 15-3/SCS6 (SiC fiber) metal matrix composite (MMC) were investigated using a combination of mechanical measurements and microstructural analysis. The objectives were to evaluate the contributions of plasticity and damage to the overall inelastic response, and to confirm the mechanisms by rigorous microstructural evaluations. The results of room temperature experiments performed on 0 degree and 90 degree systems primarily are reported in this report. Results of experiments performed on other laminate systems and at high temperatures will be provided in a forthcoming report. Inelastic deformation of the 0 degree MMC (fibers parallel to load direction) was dominated by the plasticity of the matrix. In contrast, inelastic deformations of the 90 degree composite (fibers perpendicular to loading direction) occurred by both damage and plasticity. The predictions of a continuum elastic plastic model were compared with experimental data. The model was adequate for predicting the 0 degree response; however, it was inadequate for predicting the 90 degree response largely because it neglected damage. The importance of validating constitutive models using a combination of mechanical measurements and microstructural analysis is pointed out. The deformation mechanisms, and the likely sequence of events associated with the inelastic deformation of MMCs, are indicated in this paper.

Characterization of plastic deformation in a disk bend test

NASA Astrophysics Data System (ADS)

Byun, T. S.; Lee, E. H.; Hunn, J. D.; Farrell, K.; Mansur, L. K.

2001-04-01

A disk bend test technique has been developed to study deformation mechanisms as well as mechanical properties. In the disk bend test, a transmission electron microscopy (TEM) disk size specimen of 3 mm diameter ×0.25 mm thick is clamped around its rim in a circular holder and indented with a tungsten carbide ball of 1 mm diameter on its back face. AISI 316LN austenitic stainless steel and 9Cr-2WVTa ferritic/martensitic steel were selected as test materials. A model was developed to determine the average plastic strain and surface plastic strain in the disk bend test. The deformation regimes of the plastic strain versus deflection curves corresponded to those of the load versus deflection curves. The stress state of the disk bend deformation was analyzed for the two test materials and compared with those of other mechanical tests such as uniaxial tensile, compact tension, and ball indentation tests. Slip line features at the deformed surface and the corresponding TEM microstructures were examined for both tensile and disk bend specimens. Differences and similarities in deformation between the disk bend and the tensile tests are described.

Effects of Annealing Treatment Prior to Cold Rolling on Delayed Fracture Properties in Ferrite-Austenite Duplex Lightweight Steels

NASA Astrophysics Data System (ADS)

Sohn, Seok Su; Song, Hyejin; Kim, Jung Gi; Kwak, Jai-Hyun; Kim, Hyoung Seop; Lee, Sunghak

2016-02-01

Tensile properties of recently developed automotive high-strength steels containing about 10 wt pct of Mn and Al are superior to other conventional steels, but the active commercialization has been postponed because they are often subjected to cracking during formation or to the delayed fracture after formation. Here, the delayed fracture behavior of a ferrite-austenite duplex lightweight steel whose microstructure was modified by a batch annealing treatment at 1023 K (750 °C) prior to cold rolling was examined by HCl immersion tests of cup specimens, and was compared with that of an unmodified steel. After the batch annealing, band structures were almost decomposed as strong textures of {100}<011> α-fibers and {111}<112> γ-fibers were considerably dissolved, while ferrite grains were refined. The steel cup specimen having this modified microstructure was not cracked when immersed in an HCl solution for 18 days, whereas the specimen having unmodified microstructure underwent the delayed fracture within 1 day. This time delayed fracture was more critically affected by difference in deformation characteristics such as martensitic transformation and deformation inhomogeneity induced from concentration of residual stress or plastic strain, rather than the difference in initial microstructures. The present work gives a promise for automotive applications requiring excellent mechanical and delayed fracture properties as well as reduced specific weight.

Significance of the contacting and no contacting thermoelectric power measurements applied to grit blasted medical Ti6Al4V.

PubMed

Carreon, H; Barriuso, S; Lieblich, M; González-Carrasco, J L; Jimenez, J A; Caballero, F G

2013-04-01

Grit blasting is a surface plastic deformation technique aimed to increase the surface area available for bone/implant apposition, which contributes to improve fixation and mechanical stability of Ti-6Al-4V implants. Besides roughening, grit blasting also causes surface contamination with embedded grit particles and subtle subsurface microstructural changes that, although does not challenge their biocompatibility, might influence other surface dominated properties like corrosion and ion release. Additional benefits are expected due to the induced compressive residual stresses, hence enhancing fatigue strength. The net effect depends on the type of particles used for blasting, but also on the amount of the subsurface cold work associated to the severe surface plastic deformation. In this work we study the potential of the non-contacting and contacting thermoelectric power (TEP) measurements in the analysis of the global changes induced in the Ti6Al4V when blasting the alloy with Al2O3 or ZrO2 particles, which yields a coarse and a fine rough surface, respectively. To reveal the effect of residual stresses, a set of specimens were thermally treated. The study proves that the non-contacting technique is more sensitive to the presence of residual stresses, whereas the contact technique is strongly influenced by the grain size refinements, work hardening and changes in solute. Copyright © 2012 Elsevier B.V. All rights reserved.

The mechanical properties of austenite stainless steel 304 after structural deformation through cold work

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mubarok, Naila; Manaf, Azwar, E-mail: azwar@ui.ac.id; Notonegoro, Hamdan Akbar

The 304 stainless steel (SS) type is widely used in oil and gas operations due to its excellent corrosion resistance. However, the presence of the fine sand particles and H{sub 2}S gas contained in crude oil could lead the erosion and abrasion in steel. In this study, cold rolled treatments were conducted to the 304 SS in order to increase the wear resistance of the steel. The cold work has resulted in thickness reduction to 20%, 40% and 60% of the original. Various microstructural characterizations were used to analyze the effect of deformation. The hardness characterization showed that the initialmore » hardness value increased from 145 HVC to 395 HVC as the level of deformation increase. Further, the wear resistance increased with the deformation rate from 0% to 40% and subsequently decreased from 40% to 60% deformation rate. Microstructural characterization shows that the boundary change to coincide by 56 µm, 49 µm, 45 µm, and 43 µm width and the grain go to flatten and being folded like needles. The effect of deformation on the grain morphology and structure was also studied by optical metallography and X-Ray Diffraction. It is shown that the deformation by means of a cold rolled process has transformed the austenite structure into martensitic structure.« less

Influence of thermally activated processes on the deformation behavior during low temperature ECAP

NASA Astrophysics Data System (ADS)

Fritsch, S.; Scholze, M.; F-X Wagner, M.

2016-03-01

High strength aluminum alloys are generally hard to deform. Therefore, the application of conventional severe plastic deformation methods to generate ultrafine-grained microstructures and to further increase strength is considerably limited. In this study, we consider low temperature deformation in a custom-built, cooled equal channel angular pressing (ECAP) tool (internal angle 90°) as an alternative approach to severely plastically deform a 7075 aluminum alloy. To document the maximum improvement of mechanical properties, these alloys are initially deformed from a solid solution heat-treated condition. We characterize the mechanical behavior and the microstructure of the coarse grained initial material at different low temperatures, and we analyze how a tendency for the PLC effect and the strain-hardening rate affect the formability during subsequent severe plastic deformation at low temperatures. We then discuss how the deformation temperature and velocity influence the occurrence of PLC effects and the homogeneity of the deformed ECAP billets. Besides the mechanical properties and these microstructural changes, we discuss technologically relevant processing parameters (such as pressing forces) and practical limitations, as well as changes in fracture behavior of the low temperature deformed materials as a function of deformation temperature.

A defect density-based constitutive crystal plasticity framework for modeling the plastic deformation of Fe-Cr-Al cladding alloys subsequent to irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patra, Anirban; Wen, Wei; Martinez Saez, Enrique

2016-02-05

It is essential to understand the deformation behavior of these Fe-Cr-Al alloys, in order to be able to develop models for predicting their mechanical response under varied loading conditions. Interaction of dislocations with the radiation-induced defects governs the crystallographic deformation mechanisms. A crystal plasticity framework is employed to model these mechanisms in Fe-Cr-Al alloys. This work builds on a previously developed defect density-based crystal plasticity model for bcc metals and alloys, with necessary modifications made to account for the defect substructure observed in Fe-Cr-Al alloys. The model is implemented in a Visco-Plastic Self Consistent (VPSC) framework, to predict the mechanicalmore » behavior under quasi-static loading.« less

Plastic Deformation of Magnesium Alloy Subjected to Compression-First Cyclic Loading

NASA Astrophysics Data System (ADS)

Lee, Soo Yeol; Gharghouri, Michael A.; Root, John H.

In-situ neutron diffraction has been employed to study the deformation mechanisms in a precipitation-hardened and extruded Mg-8.5wt.% Al alloy subjected to compression followed by reverse tension. The starting texture is such that the basal poles of most grains are oriented normal to the extrusion axis and a small portion of grains are oriented with the basal pole parallel to the extrusion axis. Diffraction peak intensities for several grain orientations monitored in-situ during deformation show that deformation twinning plays an important role in the elastic-plastic transition and subsequent plastic deformation behavior. Significant non-linear behavior is observed during unloading after compression and appears to be due to detwinning. This effect is much stronger after compressive loading than after tensile loading.

Mapping and analysis of microplasticity in tensile-deformed double-notched silicon crystals by computer-aided X-ray rocking curve analyzer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, H.Y.; Mayo, W.E.; Weissmann, S.

A computer-aided X-ray rocking curve analyzer (CARCA) was developed to map and analyze rapidly the distribution of plastic and elastic strains in deformed single crystals. Double-notched silicon crystal, tensile deformed at 800 C, was selected as a model material. For small stresses the interaction effects of the strained plastic zones were negligible. With increased deformation interaction of microplasticity caused modifications of the characteristics of the plastic zones at the notch tips. The microplastic trajectory of the internotch zone outlined the future fracture path at an early stage of deformation. The observed decrease of micrplasticity with depth from the surface ismore » explained both from the micro and macromechanics viewpoint.« less

Calculation of recovery plasticity in multistage hot forging under isothermal conditions.

PubMed

Zhbankov, Iaroslav G; Perig, Alexander V; Aliieva, Leila I

2016-01-01

A widely used method for hot forming steels and alloys, especially heavy forging, is the process of multistage forging with pauses between stages. The well-known effect which accompanies multistage hot forging is metal plasticity recovery in comparison with monotonic deformation. A method which takes into consideration the recovery of plasticity in pauses between hot deformations of a billet under isothermal conditions is proposed. This method allows the prediction of billet forming limits as a function of deformation during the forging stage and the duration of the pause between the stages. This method takes into account the duration of pauses between deformations and the magnitude of subdivided deformations. A hot isothermal upsetting process with pauses was calculated by the proposed method. Results of the calculations have been confirmed with experimental data.

A method of increasing the depth of the plastically deformed layer in the roller burnishing process

NASA Astrophysics Data System (ADS)

Kowalik, Marek; Trzepiecinski, Tomasz

2018-05-01

The subject of this paper is an analysis of the determination of the depth of the plastically deformed layer in the process of roller burnishing a shaft using a newly developed method in which a braking moment is applied to the roller. It is possible to increase the depth of the plastically deformed layer by applying the braking moment to the roller during the burnishing process. The theoretical considerations presented are based on the Hertz-Bielayev and Huber-Mises theories and permit the calculation of the depth of plastic deformation of the top layer of the burnished shaft. The theoretical analysis has been verified experimentally and using numerical calculations based on the finite element method using the Msc.MARC program. Experimental tests were carried out on ring-shaped samples made of C45 carbon steel. The samples were burnished at different values of roller force and different values of braking moment. A significant increase was found in the depth of the plastically deformed surface layer of roller burnished shafts. Usage of the phenomenon of strain hardening of steel allows the technology presented here to increase the fatigue life of the shafts.

Microstructure and texture evolution in cold-rolled and annealed alloy MA-956

NASA Astrophysics Data System (ADS)

Hosoda, Takashi

The microstructural and texture development with thermomechanical processing, performed through a combination of cold-rolling and annealing, in MA-956 plate consisting of a layered and inhomogeneous microstructure was systematically assessed. The alloy contained in mass percent, 20 Cr, 4.8 Al, 0.4 Ti, 0.4 Y2O3, and the balance iron. The starting material was as-hot-rolled plate, 9.7 mm thick. The as-hot-rolled plate was subjected to 40%, 60%, and 80% cold-rolling reduction and subsequently annealed at 1000, 1200, or 1380. Assessment of microstructural and texture developments before and after cold-rolling and annealing was performed using light optical microscopy (LOM), Vickers hardness testing, and electron backscatter diffraction (EBSD). Locally introduced misorientations by cold-rolling in each region were evaluated by Kernel Average Misorientation (KAM) maps. The as-hot-rolled condition contained a layered and inhomogeneous microstructure consisting of thin and coarse elongated grains, and aggregated regions which consisted of fine grains and sub-grains with {100} texture parallel to the longitudinal direction. The microstructure of the 40% cold-rolled condition contained deformation bands, and the 60% and 80% cold-rolled conditions also contained highly deformed regions where the deformation bands were intricately tangled. A predominant orientation of (001) parallel to the rolling direction was developed during cold-rolling, becoming more prominent with increasing reduction. The magnitudes of KAM angles varied through the thickness depending on the initial microstructures. Recrystallization occurred in regions where high KAM angles were dense after annealing and nucleation sites were the aggregation regions, deformation bands, and highly deformed regions. The shape and size of the recrystallized grains varied depending on the nucleation sites.

Nonlinear analysis of AS4/PEEK thermoplastic composite laminate using a one parameter plasticity model

NASA Technical Reports Server (NTRS)

Sun, C. T.; Yoon, K. J.

1990-01-01

A one-parameter plasticity model was shown to adequately describe the orthotropic plastic deformation of AS4/PEEK (APC-2) unidirectional thermoplastic composite. This model was verified further for unidirectional and laminated composite panels with and without a hole. The nonlinear stress-strain relations were measured and compared with those predicted by the finite element analysis using the one-parameter elastic-plastic constitutive model. The results show that the one-parameter orthotropic plasticity model is suitable for the analysis of elastic-plastic deformation of AS4/PEEK composite laminates.

Development of mathematical models for automation of strength calculation during plastic deformation processing

NASA Astrophysics Data System (ADS)

Steposhina, S. V.; Fedonin, O. N.

2018-03-01

Dependencies that make it possible to automate the force calculation during surface plastic deformation (SPD) processing and, thus, to shorten the time for technological preparation of production have been developed.

In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation

PubMed Central

Gerbig, Y.B; Michaels, C.A.; Bradby, J.E.; Haberl, B.; Cook, R.F.

2016-01-01

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline β-tin phase within the a-Si network. PMID:26924926

Understanding the Effect of Plastic Deformation on Elastic Modulus of Metals Based on a Percolation Model with Electron Work Function

NASA Astrophysics Data System (ADS)

Li, Qingda; Hua, Guomin; Lu, Hao; Yu, Bin; Li, D. Y.

2018-05-01

The elastic modulus of materials is usually treated as a constant in engineering applications. However, plastic deformation may result in changes in the elastic modulus of metallic materials. Using brass, aluminum, and low-carbon steel as sample materials, it is demonstrated that plastic deformation decreased the elastic modulus of the materials by 10% to 20%. A percolation model incorporating the electron work function is proposed to correlate such plastic-strain-induced variations in the elastic modulus to corresponding changes in the electron work function. Efforts are made to understand the observed phenomenon on an electronic basis. The obtained experimental results are consistent with the theoretical analysis.

In situ nanoindentation study of plastic Co-deformation in Al-TiN nanocomposites

DOE PAGES

Li, N.; Wang, H.; Misra, A.; ...

2014-10-16

We performed in situ indentation in a transmission electron microscope on Al-TiN multilayers with individual layer thicknesses of 50 nm, 5 nm and 2.7 nm to explore the effect of length scales on the plastic co-deformability of a metal and a ceramic. At 50 nm, plasticity was confined to the Al layers with easy initiation of cracks in the TiN layers. At 5 nm and below, cracking in TiN was suppressed and post mortem measurements indicated a reduction in layer thickness in both layers. Our results demonstrate the profound size effect in enhancing plastic co-deformability in nanoscale metal-ceramic multilayers.

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

PubMed Central

Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

2016-01-01

NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

The use of ion beam cleaning to obtain high quality cold welds with minimal deformation

NASA Technical Reports Server (NTRS)

Sater, B. L.; Moore, T. J.

1978-01-01

A variation of cold welding is described which utilizes an ion beam to clean mating surfaces prior to joining in a vacuum environment. High quality solid state welds were produced with minimal deformation.

Deformation behavior of human dentin in liquid nitrogen: a diametral compression test.

PubMed

Zaytsev, Dmitry; Panfilov, Peter

2014-09-01

Contribution of the collagen fibers into the plasticity of human dentin is considered. Mechanical testing of dentin at low temperature allows excluding the plastic response of its organic matrix. Therefore, deformation and fracture behavior of the dentin samples under diametral compression at room temperature and liquid nitrogen temperature are compared. At 77K dentin behaves like almost brittle material: it is deformed exclusively in the elastic regime and it fails due to growth of the sole crack. On the contrary, dentin demonstrates the ductile response at 300K. There are both elastic and plastic contributions in the deformation of dentin samples. Multiple cracking and crack tip blunting precede the failure of samples. Organic phase plays an important role in fracture of dentin: plasticity of the collagen fibers could inhibit the crack growth. Copyright © 2014 Elsevier B.V. All rights reserved.

Thermally induced processes in mixtures of aluminum with organic acids after plastic deformations under high pressure

NASA Astrophysics Data System (ADS)

Zhorin, V. A.; Kiselev, M. R.; Roldugin, V. I.

2017-11-01

DSC is used to measure the thermal effects of processes in mixtures of solid organic dibasic acids with powdered aluminum, subjected to plastic deformation under pressures in the range of 0.5-4.0 GPa using an anvil-type high-pressure setup. Analysis of thermograms obtained for the samples after plastic deformation suggests a correlation between the exothermal peaks observed around the temperatures of degradation of the acids and the thermally induced chemical reactions between products of acid degradation and freshly formed surfaces of aluminum particles. The release of heat in the mixtures begins at 30-40°C. The thermal effects in the mixtures of different acids change according to the order of acid reactivity in solutions. The extreme baric dependences of enthalpies of thermal effects are associated with the rearrangement of the electron subsystem of aluminum upon plastic deformation at high pressures.

Predicting Hot Deformation of AA5182 Sheet

NASA Astrophysics Data System (ADS)

Lee, John T.; Carpenter, Alexander J.; Jodlowski, Jakub P.; Taleff, Eric M.

Aluminum 5000-series alloy sheet materials exhibit substantial ductilities at hot and warm temperatures, even when grain size is not particularly fine. The relatively high strain-rate sensitivity exhibited by these non-superplastic materials, when deforming under solute-drag creep, is a primary contributor to large tensile ductilities. This active deformation mechanism influences both plastic flow and microstructure evolution across conditions of interest for hot- and warm-forming. Data are presented from uniaxial tensile and biaxial bulge tests of AA5182 sheet material at elevated temperatures. These data are used to construct a material constitutive model for plastic flow, which is applied in finite-element-method (FEM) simulations of plastic deformation under multiaxial stress states. Simulation results are directly compared against experimental data to explore the usefulness of this constitutive model. The effects of temperature and stress state on plastic response and microstructure evolution are discussed.

Microstructural Analysis of Severe Plastic Deformed Twin Roll Cast AZ31 for the Optimization of Superplastic Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, John P.; Askari, Hesam A.; Heiden, Michael J.

2013-07-08

In recent years magnesium alloys have attracted significant attention as potential candidates to replace many of the heavier metals used in some automotive applications. However, the limited formability of magnesium and its alloys at room temperature has driven interest in the superplastic forming magnesium as an alternative shaping method. Severe plastic deformation techniques have become a well studied method of refining the grain size and modifying the microstructural characteristics of many magnesium alloys to achieve greater superplastic properties. In this study twin roll cast (TRC) AZ31 magnesium alloy was subjected to equal channel angular pressing (ECAP) and friction stir weldingmore » (FSW). The influence of these severe plastic deformation processes on the grain size, texture and grain boundary character distribution was investigated to identify the optimum severe plastic deformation process for the superplastic forming of AZ31.« less

Changes in the physical and mechanical properties of Al-Mg alloy processed by severe plastic deformation

NASA Astrophysics Data System (ADS)

Krasnoveikin, V. A.; Kozulin, A. A.; Skripnyak, V. A.; Moskvichev, E. N.; Borodulin, D. A.

2017-12-01

This paper presents the results of studies into the effect of severe plastic deformation on the microstructure, physical and mechanical properties of coarse-grained Al-Mg alloy 1560 in the as-received state with an average grain size of 50 µm. Severe plastic deformation is performed by four-pass equal channel angular pressing (ECAP), which results in the formation of an ultrafine-grained structure with an average grain size of 3 µm in the alloy. Analysis of experimental data revealed that the physical and mechanical properties change significantly after severe plastic deformation. The microhardness of the ECAPed alloy increases by 50%, tensile yield strength by 80%, and ultimate strength by 44% in comparison with these parameters in the as-received state. The constants of approximating functions have been determined for the experimental stress-strain curves of the alloy specimens in the as-received and ECAPed states.

Model of Nanostructuring Burnishing by a Spherical Indenter Taking into Consideration Plastic Deformations

NASA Astrophysics Data System (ADS)

Lyashenko, Ya. A.; Popov, V. L.

2018-01-01

A dynamic model of the nanostructuring burnishing of a surface of metallic details taking into consideration plastic deformations has been suggested. To describe the plasticity, the ideology of dimension reduction method supplemented with the plasticity criterion is used. The model considers the action of the normal burnishing force and the tangential friction force. The effect of the coefficient of friction and the periodical oscillation of the burnishing force on the burnishing kinetics are investigated.

Microstructural Characteristics and Oxidation Behavior of Low-Pressure Cold-Sprayed CoNiCrAlY Coatings

NASA Astrophysics Data System (ADS)

Zhang, Lin-wei; Lu, Lei; Wang, Lu; Ning, Xian-jin; Wang, Quan-sheng; Wang, Ri-xin

2017-10-01

CoNiCrAlY coatings were deposited by low-pressure cold spraying and subsequently heat-treated at 1050 °C for 4 h in a vacuum environment. The microstructural characteristics and oxidation behavior of CoNiCrAlY coatings were investigated. The as-sprayed coating exhibited low porosity and oxygen content. The high plastic deformation of the sprayed particles led to significant refinement of γ-matrix and dissolution of β-(Ni,Co)Al phase in the as-sprayed coating. After heat treatment, the single phase (γ) in the as-sprayed coating was converted into a γ/β microstructure, and a continuous single α-Al2O3 scale was formed on the coating surface. Vacuum heat treatment can postpone the formation of spinel oxides within 100 h. After being oxidized at 1050 °C for 400 h, the heat-treated coating exhibited better oxidation resistance than the as-sprayed coating. The reduced growth rate of the oxide scale and the suppression of the formation of spinel oxides can be attributed to the vacuum heat treatment, as well as the intrinsic microstructure of the cold-sprayed coating. Finally, the effects of the microstructural changes induced during the cold spraying process on the growth of the thermally grown oxide and the oxidation mechanisms of the CoNiCrAlY coatings were discussed.

Model for texture evolution in cold rolling of 2.4 wt.-% Si non-oriented electrical steel

NASA Astrophysics Data System (ADS)

Wei, X.; Hojda, S.; Dierdorf, J.; Lohmar, J.; Hirt, G.

2017-10-01

Iron loss and limited magnetic flux density are constraints for NGO electrical steel used in highly efficient electrical machinery cores. The most important factors that affect these properties are the final microstructure and the texture of the NGO steel. Reviewing the whole process chain, cold rolling plays an important role because the recrystallization and grain growth during the final heat treatment can be strongly affected by the stored energy and microstructure of cold rolling, and some texture characteristics can be inherited as well. Therefore, texture evolution during cold rolling of NGO steel is worth a detailed investigation. In this paper, texture evolution in cold rolling of non-oriented (NGO) electrical steel is simulated with a crystal plasticity finite element method (CPFEM) model. In previous work, a CPFEM model has been implemented for simulating the texture evolution with periodic boundary conditions and a phenomenological constitutive law. In a first step the microstructure in the core of the workpiece was investigated and mapped to a representative volume element to predict the texture evolution. In this work an improved version of the CPFEM model is described that better reflects the texture evolution in cold rolling of NGO electrical steel containing 2.4 wt.-% Si. This is achieved by applying the deformation gradient and calibrating the flow curve within the CPFEM model. Moreover, the evolution of dislocation density is calculated and visualized in this model. An in depth comparison of the numerical and experimental results reveals, that the improved CPFEM model is able to represent the important characteristics of texture evolution in the core of the workpiece during cold rolling with high precision.

Forming an age hardenable aluminum alloy with intermediate annealing

NASA Astrophysics Data System (ADS)

Wang, Kaifeng; Carsley, John E.; Stoughton, Thomas B.; Li, Jingjing; Zhang, Lianhong; He, Baiyan

2013-12-01

A method to improve formability of aluminum sheet alloys by a two-stage stamping process with intermediate annealing was developed for a non-age hardenable Al-Mg alloy where the annealing heat treatment provided recovery of cold work from the initial stamping and recrystallization of the microstructure to enhance the forming limits of the material. This method was extended to an age hardenable, Al-Mg-Si alloy, which is complicated by the competing metallurgical effects during heat treatment including recovery (softening effect) vs. precipitation (hardening effect). An annealing heat treatment process condition was discovered wherein the stored strain energy from an initial plastic deformation can be sufficiently recovered to enhance formability in a second deformation; however, there is a deleterious effect on subsequent precipitation hardening. The improvement in formability was quantified with uniaxial tensile tests as well as with the forming limit diagram. Since strain-based forming limit curves (FLC) are sensitive to pre-strain history, both stress-based FLCs and polar-effective-plastic-strain (PEPS) FLCs, which are path-independent, were used to evaluate the forming limits after preform annealing. A technique was developed to calculate the stress-based FLC in which a residual-effective-plastic-strain (REPS) was determined by overlapping the hardening curve of the pre-strained and annealed material with that of the simply-annealed- material. After converting the strain-based FLCs using the constant REPS method, it was found that the stress-based FLCs and the PEPS FLCs of the post-annealed materials were quite similar and both tools are applicable for evaluating the forming limits of Al-Mg-Si alloys for a two-step stamping process with intermediate annealing.

Investigation of features of plastic deformation and fracture of fine-crystalline V-4Ti-4Cr alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grinyaev, Konstantin V., E-mail: kvgrinyaev@inbox.ru; Tyumentsev, Alexander N., E-mail: tyuments@phys.tsu.ru; Siberian Physical-Technical Institute, Tomsk, 634050

2014-11-14

With the use of transmission electron microscopy the investigation of defect substructure was carried out in the V-4Ti-4Cr-(C, N, O) alloy with disperse strengthening (by nanoparticles of oxy-carbo-nitride phase) after deformation by active tension at temperatures of 20 and 800 °C. It has been shown that an important feature of plastic deformation is deformation localization with crystal lattice reorientation.

Low temperature dissolution creep induced B-type olivine fabric during serpentinization and deformation in mantle wedge

NASA Astrophysics Data System (ADS)

Liu, W.; Zhang, J.

2017-12-01

The B-type olivine fabric (i.e., the [010]ol axes subnormal to foliation and the [001]ol axes subparallel to the lineation) has been regarded as an important olivine fabric for interpreting global trench-parallel S-wave polarization in fore-arc regions. However, strong serpentinization and cold temperature environment in the mantle wedge should inhibit development of the B-type olivine fabric that requires high temperature to activate solid-state plastic deformation. Here we report fabrics of olivine and antigorite generated at low temperatures (300-370 oC) during serpentinization in a fossil mantle wedge of the Val Malenco area, Central Alps. Olivine in the serpentine matrix develops a pronounced B-type fabric, while antigorite in the same matrix displays a strong crystallographic orientation (CPO) with the (001) and the [010] subparallel to foliation and lineation, respectively. The following evidence leads to the conclusion that the B-type olivine fabric is resulted from dissolution creep assisted by grain boundaries sliding (GBS) and grain rotation, rather than solid-state plastic deformation: (1) serpentinization took place at low temperatures and a fluid-enriched environment, ideal for dissolution-precipitation creep; (2) the voids and zigzag boundaries along the interface between antigorite and olivine suggest a fluid dissolution reaction; (3) the primary coarse olivine develops a nearly random fabric, indicating the B-type fabrics in the fine-grained olivine can't be inherited fabrics. These results document for the first time the B-type olivine CPO formed by dissolution creep at low temperatures during serpentinization and provide a mechanism to reconcile petrofabric observations with geophysical observations of trench parallel fast S-wave seismic anisotropy in fore-arc mantle wedge regions.

B-type olivine fabric induced by low temperature dissolution creep during serpentinization and deformation in mantle wedge

NASA Astrophysics Data System (ADS)

Liu, Wenlong; Zhang, Junfeng; Barou, Fabrice

2018-01-01

The B-type olivine fabric (i.e., the [010] axes subnormal to foliation and the [001] axes subparallel to the lineation) has been regarded as an important olivine fabric for interpreting global trench-parallel S-wave polarization in fore-arc regions. However, strong serpentinization and cold temperature environment in the mantle wedge should inhibit development of the B-type olivine fabric that requires high temperature to activate solid-state plastic deformation. Here we report fabrics of olivine and antigorite generated at low temperatures (300-370 °C) during serpentinization in a fossil mantle wedge of the Val Malenco area, Central Alps. Olivine in the serpentine matrix develops a pronounced B-type fabric, while antigorite in the same matrix displays a strong crystallographic preferred orientation (CPO) with the (001) planes and the [010] axes subparallel to foliation and lineation, respectively. The following evidence leads to the conclusion that the B-type olivine fabric results from dissolution creep assisted by grain boundary sliding (GBS) and grain rotation, rather than solid-state plastic deformation: (1) serpentinization took place at low temperatures and a fluid-enriched environment, ideal for dissolution-precipitation creep; (2) the voids and zigzag boundaries along the interface between antigorite and olivine suggest a fluid dissolution reaction; (3) the primary coarse olivine develops a nearly random fabric, indicating the B-type fabrics in the fine-grained olivine may not be inherited fabrics. These results document for the first time the B-type olivine CPO formed by dissolution creep at low temperatures during serpentinization and provide a mechanism to reconcile petrofabric observations with geophysical observations of trench parallel fast S-wave seismic anisotropy in fore-arc mantle wedge regions.

A Reformulation of Nonlinear Anisotropic Elasticity for Impact Physics

DTIC Science & Technology

2014-02-01

aluminum, copper, and magnesium . 15. SUBJECT TERMS impact physics, shock compression, elasticity, plasticity 16. SECURITY CLASSIFICATION OF: 17... deformation wave propagation code accounting for dissipative inelastic mechanisms. • Accuracy of the new nonlinear elastic- plastic model(s) will be...gradient and its transpose. A new general thermomechanical theory accounting for both elastic and plastic deformations has been briefly outlined in

Stress relaxation study of fillers for directly compressed tablets

PubMed Central

Rehula, M.; Adamek, R.; Spacek, V.

2012-01-01

It is possible to assess viscoelastic properties of materials by means of the stress relaxation test. This method records the decrease in pressing power in a tablet at its constant height. The cited method was used to evaluate the time-dependent deformation for six various materials: microcrystalline cellulose, cellulose powder, hydroxypropyl methylcellulose, mannitol, lactose monohydrate, and hydrogen phosphate monohydrate. The decrease in pressing powering of a tablet during a 180 s period was described mathematically by the parameters of three exponential equations, where the whole course of the stress relaxation is divided into three individual processes (instant elastic deformation, retarded elastic deformation and permanent plastic deformation). Three values of the moduli of plasticity and elasticity were calculated for each compound. The values of elastic parameters ATi have a strong relationship with bulk density. The plastic parameters PTi represent particle tendency to form bonds. The values of plasticity in the third process PT3 ranged from 400 to 600 MPas. Mannitol had higher plasticity and lactose monohydrate on the contrary reduced plasticity. A linear relation exists between AT3 and PT3 for the third process. No similar interpretation of moduli calculated on the basis of three exponential equations has been realized yet. PMID:24850972

Deformation field heterogeneity in punch indentation

PubMed Central

Murthy, Tejas G.; Saldana, Christopher; Hudspeth, Matthew; M'Saoubi, Rachid

2014-01-01

Plastic heterogeneity in indentation is fundamental for understanding mechanics of hardness testing and impression-based deformation processing methods. The heterogeneous deformation underlying plane-strain indentation was investigated in plastic loading of copper by a flat punch. Deformation parameters were measured, in situ, by tracking the motion of asperities in high-speed optical imaging. These measurements were coupled with multi-scale analyses of strength, microstructure and crystallographic texture in the vicinity of the indentation. Self-consistency is demonstrated in description of the deformation field using the in situ mechanics-based measurements and post-mortem materials characterization. Salient features of the punch indentation process elucidated include, among others, the presence of a dead-metal zone underneath the indenter, regions of intense strain rate (e.g. slip lines) and extent of the plastic flow field. Perhaps more intriguing are the transitions between shear-type and compression-type deformation modes over the indentation region that were quantified by the high-resolution crystallographic texture measurements. The evolution of the field concomitant to the progress of indentation is discussed and primary differences between the mechanics of indentation for a rigid perfectly plastic material and a strain-hardening material are described. PMID:24910521

Static-transmission-error vibratory-excitation contributions from plastically deformed gear teeth caused by tooth bending-fatigue damage

NASA Astrophysics Data System (ADS)

Mark, W. D.; Reagor, C. P.

2007-02-01

To assess gear health and detect gear-tooth damage, the vibratory response from meshing gear-pair excitations is commonly monitored by accelerometers. In an earlier paper, strong evidence was presented suggesting that, in the case of tooth bending-fatigue damage, the principal source of detectable damage is whole-tooth plastic deformation; i.e. yielding, rather than changes in tooth stiffness caused by tooth-root cracks. Such plastic deformations are geometric deviation contributions to the "static-transmission-error" (STE) vibratory excitation caused by meshing gear pairs. The STE contributions caused by two likely occurring forms of such plastic deformations on a single tooth are derived, and displayed in the time domain as a function of involute "roll distance." Example calculations are provided for transverse contact ratios of Qt=1.4 and 1.8, for spur gears and for helical-gear axial contact ratios ranging from Qa=1.2 to Qa=3.6. Low-pass- and band-pass-filtered versions of these same STE contributions also are computed and displayed in the time domain. Several calculations, consisting of superposition of the computed STE tooth-meshing fundamental harmonic contribution and the band-pass STE contribution caused by a plastically deformed tooth, exhibit the amplitude and frequency or phase modulation character commonly observed in accelerometer-response waveforms caused by damaged teeth. General formulas are provided that enable computation of these STE vibratory-excitation contributions for any form of plastic deformation on any number of teeth for spur and helical gears with any contact ratios.

Numerical Study of the Plasticity-Induced Stabilization Effect on Martensitic Transformations in Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Junker, Philipp; Hempel, Philipp

2017-12-01

It is well known that plastic deformations in shape memory alloys stabilize the martensitic phase. Furthermore, the knowledge concerning the plastic state is crucial for a reliable sustainability analysis of construction parts. Numerical simulations serve as a tool for the realistic investigation of the complex interactions between phase transformations and plastic deformations. To account also for irreversible deformations, we expand an energy-based material model by including a non-linear isotropic hardening plasticity model. An implementation of this material model into commercial finite element programs, e.g., Abaqus, offers the opportunity to analyze entire structural components at low costs and fast computation times. Along with the theoretical derivation and expansion of the model, several simulation results for various boundary value problems are presented and interpreted for improved construction designing.

Finite element analysis of large transient elastic-plastic deformations of simple structures, with application to the engine rotor fragment containment/deflection problem

NASA Technical Reports Server (NTRS)

Wu, R. W.; Witmer, E. A.

1972-01-01

Assumed-displacement versions of the finite-element method are developed to predict large-deformation elastic-plastic transient deformations of structures. Both the conventional and a new improved finite-element variational formulation are derived. These formulations are then developed in detail for straight-beam and curved-beam elements undergoing (1) Bernoulli-Euler-Kirchhoff or (2) Timoshenko deformation behavior, in one plane. For each of these categories, several types of assumed-displacement finite elements are developed, and transient response predictions are compared with available exact solutions for small-deflection, linear-elastic transient responses. The present finite-element predictions for large-deflection elastic-plastic transient responses are evaluated via several beam and ring examples for which experimental measurements of transient strains and large transient deformations and independent finite-difference predictions are available.

Analysis and Modeling of Process of Residual Deformations Accumulation in Soils and Granular Materials

NASA Astrophysics Data System (ADS)

Aleksandrov, A. S.; Dolgih, G. V.; Kalinin, A. L.

2017-11-01

It is established that under the influence of repeated loads the process of plastic deformation in soils and discrete materials is hereditary. To perform the mathematical modeling of plastic deformation, the authors applied the integral equation by solution of which they manage to obtain the power and logarithmic dependencies connecting plastic deformation with the number of repeated loads, the parameters of the material and components of the stress tensor in the principal axes. It is shown that these dependences generalize a number of models proposed earlier in Russia and abroad. Based on the analysis of the experimental data obtained during material testing in the dynamic devices of triaxial compression at different values of the stress deviator, the coefficients in the proposed models of deformation are determined. The authors determined the application domain for logarithmic and degree dependences.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binder, I.

TiC/Ni compositions with 10, 20, and 40 percent nickel were tested for transverse rupture strengths up to 1600 deg C. Transverse bend, cantilever beam, hot deformation, and hot extrusion experiments were performed in order to study the onset of plastic deformation. These materials were plastically deformed, and their microstructures were studied to learn about the mode of deiormation, plastic flow of the nickel binder, and alignment of the carbide grains. Other refractory hardmetal compositions, both single phase and cemented, were tested in transverse rupture up to 1600 deg C and were also subjected to various forms of hot deformation. Transversemore » strength peaks, versus temperature, were found for each material in the range 800 to 1500 deg C. Reasons for this behavior are developed. Microstructures of these materials were examined in connection with the strength tests and deformation studies. (auth)« less

Effects of Mode of Deformation and Extent of Reduction on Evolution of {111}-Fiber During Cold Rolling of Ni-16Cr Alloy

NASA Astrophysics Data System (ADS)

Mehta, K. K.; Mandal, R. K.; Singh, A. K.

2018-07-01

The high ratio of relative resolved shear stress on a twin to planar slip system results in microstructural latent hardening (some kind of overshooting) by the twin system on the primary slip planes, which leads to development of the {111}-fiber in Ni-16Cr alloy. The development of {111}-fiber starts as early as around 16 pct cold reduction in Ni-16Cr alloy and persists with maximum average intensity ranging from 35 to 40 pct additional deformation, i.e., around 50 pct cold reduction in unidirectional (U) and two-step cross (T)-rolling modes. In between 50 and 68 pct reductions in U and T modes, the fiber becomes unstable and starts disappearing. However, in multistep cross (M) rolling, the {111}-fiber formation starts late, i.e., at around 50 pct reduction, and maintains its stability up to additional deformation ranging from 35 to 40 pct, i.e., around 90 pct cold reduction. Thus, the life of {111}-fiber remains stable only within the range from 35 to 40 pct intermediate deformation during cold rolling of Ni-16Cr alloy irrespective of modes of rolling. However, the start and end of fiber stabilities depend on the modes of deformation by rolling. The maximum average intensity of {111}-fiber that can be attained in Ni-16Cr alloy is around 3.6× random in any of the deformation modes.

Effects of Mode of Deformation and Extent of Reduction on Evolution of {111}-Fiber During Cold Rolling of Ni-16Cr Alloy

NASA Astrophysics Data System (ADS)

Mehta, K. K.; Mandal, R. K.; Singh, A. K.

2018-04-01

The high ratio of relative resolved shear stress on a twin to planar slip system results in microstructural latent hardening (some kind of overshooting) by the twin system on the primary slip planes, which leads to development of the {111}-fiber in Ni-16Cr alloy. The development of {111}-fiber starts as early as around 16 pct cold reduction in Ni-16Cr alloy and persists with maximum average intensity ranging from 35 to 40 pct additional deformation, i.e., around 50 pct cold reduction in unidirectional (U) and two-step cross (T)-rolling modes. In between 50 and 68 pct reductions in U and T modes, the fiber becomes unstable and starts disappearing. However, in multistep cross (M) rolling, the {111}-fiber formation starts late, i.e., at around 50 pct reduction, and maintains its stability up to additional deformation ranging from 35 to 40 pct, i.e., around 90 pct cold reduction. Thus, the life of {111}-fiber remains stable only within the range from 35 to 40 pct intermediate deformation during cold rolling of Ni-16Cr alloy irrespective of modes of rolling. However, the start and end of fiber stabilities depend on the modes of deformation by rolling. The maximum average intensity of {111}-fiber that can be attained in Ni-16Cr alloy is around 3.6× random in any of the deformation modes.

Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

PubMed Central

Kim, J. T.; Hong, S. H.; Park, H. J.; Kim, Y. S.; Suh, J. Y.; Lee, J. K.; Park, J. M.; Maity, T.; Eckert, J.; Kim, K. B.

2017-01-01

In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition. PMID:28067248

Simulating Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi

NASA Technical Reports Server (NTRS)

Manchiraju, Sivom; Gaydosh, Darrell J.; Noebe, Ronald D.; Anderson, Peter M.

2011-01-01

A microstructure-based FEM model that couples crystal plasticity, crystallographic descriptions of the B2-B19' martensitic phase transformation, and anisotropic elasticity is used to simulate thermal cycling and isothermal deformation in polycrystalline NiTi (49.9at% Ni). The model inputs include anisotropic elastic properties, polycrystalline texture, DSC data, and a subset of isothermal deformation and load-biased thermal cycling data. A key experimental trend is captured.namely, the transformation strain during thermal cycling is predicted to reach a peak with increasing bias stress, due to the onset of plasticity at larger bias stress. Plasticity induces internal stress that affects both thermal cycling and isothermal deformation responses. Affected thermal cycling features include hysteretic width, two-way shape memory effect, and evolution of texture with increasing bias stress. Affected isothermal deformation features include increased hardening during loading and retained martensite after unloading. These trends are not captured by microstructural models that lack plasticity, nor are they all captured in a robust manner by phenomenological approaches. Despite this advance in microstructural modeling, quantitative differences exist, such as underprediction of open loop strain during thermal cycling.

Effect of small perturbations on the evolution of polycrystalline structure during plastic deformation

NASA Astrophysics Data System (ADS)

Korznikova, E. A.; Baimova, Yu. A.; Kistanov, A. A.; Dmitriev, S. V.; Korznikov, A. V.

2014-09-01

The method of molecular dynamics has been used to study the influence of initial perturbations on the evolution of grain boundaries during the shear plastic deformation of a two-dimensional polycrystalline material with nanoscale grains. It has been shown that short-term thermalization-induced small perturbations result in noticeable differences in grain boundaries configurations at the deformation of 0.05 and the polycrystal completely loses its initial grain boundary structure at the deformation of 0.4.

Method for measuring residual stresses in materials by plastically deforming the material and interference pattern comparison

DOEpatents

Pechersky, Martin J.

1995-01-01

A method for measuring residual stress in a material comprising the steps of establishing a speckle pattern on the surface with a first laser then heating a portion of that pattern with an infrared laser until the surface plastically deforms. Comparing the speckle patterns before and after deformation by subtracting one pattern from the other will produce a fringe pattern that serves as a visual and quantitative indication of the degree to which the plasticized surface responded to the stress dung heating and enables calculation of the stress.

Atomic simulations of deformation mechanisms of crystalline Mg/amorphous Mg-Al nanocomposites

NASA Astrophysics Data System (ADS)

Song, H. Y.; Li, Y. L.

2015-09-01

The effects of amorphous boundary (AB) spacing on the deformation behavior of crystalline/amorphous (C/A) Mg/Mgsbnd Al nanocomposites under tensile load are investigated using molecular dynamics method. The results show that the plasticity of nano-polycrystal Mg can be enhanced with the introduction of C/A interfaces. For samples 5.2 nm in AB spacing and larger, the superior tensile ductility and nearly perfect plastic flow behavior occur during plastic deformation. The studies indicate that the cooperative interactions between crystalline and amorphous are the main reason for excellent ductility enhancements in C/A Mg/Mgsbnd Al nanocomposites.

Detection of structural changes and mechanical properties of light alloys after severe plastic deformation

NASA Astrophysics Data System (ADS)

Krasnoveikin, V. A.; Kozulin, A. A.; Skripnyak, V. A.

2017-11-01

Severe plastic deformation by equal channel angular pressing has been performed to produce light aluminum and magnesium alloy billets with ultrafine-grained structure. The physical and mechanical properties of the processed alloys are examined by studying their microstructure, measuring microhardness, yield strength, and uniaxial tensile strength. A nondestructive testing technique using three-dimensional X-ray tomography is proposed for detecting internal structural defects and monitoring damage formation in the structure of alloys subjected to severe plastic deformation. The investigation results prove the efficiency of the chosen method and selected mode of producing ultrafine-grained light alloys.

The hidden life of pyrite: how low can it go?

NASA Astrophysics Data System (ADS)

Boyle, Alan; Barrie, Craig; Salter, Michael

2010-05-01

Pyrite is the most abundant sulphide mineral in the Earth's crust, being present in most rock units but only volumetrically important in sulphide ore deposits. Thus, rheological behaviour of pyrite does not have significant implications for crustal deformation as a whole, but it does for deformation of ore deposits. Therefore, understanding pyrite behaviour in ore deposits may help understanding of deformation in rocks where it is of low abundance. Pyrite is a difficult mineral to study because it is both opaque and cubic, two properties that hide most of its microstructure when studied using optical microscopy as well as standard SEM back-scattered electron imaging. Etching can reveal some of the internal secrets of pyrite, but the technique is not universally applicable. The generally accepted view from such studies, coupled with experimental deformation and some TEM studies, is that pyrite is a robust mineral, which, under typical geological strain-rates, deforms by plastic deformation mechanisms above ~425 °C and by brittle or pressure-solution diffusive mechanisms below. Over the last decade or so, the advent of reliable and fast SEM-based electron backscattered diffraction (EBSD) systems, coupled with orientation contrast (OC) imaging techniques, has revolutionised study of microstructure in cubic minerals. Plastic deformation can now be readily identified in pyrite; it is no longer hidden. Freitag et al (2004) documented relatively low temperature (~350 °C) plastic deformation of pyrite from Green's Creek, Alaska, raising the possibility that pyrite deforms plastically at lower temperatures than is generally accepted. In this presentation we describe pyrite microstructures from a series of pyrite-rich polymetallic ore deposits (Parys Mountain, Anglesey; Løkken, Norway; Baia Borsa, Romania), deformed at low temperature metamorphic conditions (~200-420 °C). Our results (Barrie et al. 2009) indicate that pyrite grains in all of the ore deposits studied preserve internal lattice ‘distortion' or ‘bending' indicating plastic deformation mechanisms operated. Many pyrite grains in the ore deposits also contain low-angle (~2°) sub-grain boundaries or ‘dislocation walls', indicating that both dislocation glide and creep deformation mechanisms have operated within the pyrite grains. These results indicate that plastic deformation of pyrite, under geological strain-rates, can go down to as low as ~200 °C suggesting the brittle-ductile transition in pyrite occurs at temperatures potentially as low as ~200 °C; much lower than the generally accepted temperature of ~425 °C. Many pyrite grains in sulphide ore deposits preserve internal chemical zonation of trace elements (e.g. Large et al. 2009). The potential relationship between plastic deformation and trace element distribution in pyrite will be discussed. Barrie, C. D., Boyle, A. P. & Salter, M., 2009. How low can you go? - Extending downwards the limits of plastic deformation in pyrite. Mineralogical Magazine, 73(6), 895-913. Freitag, K., Boyle, A. P., Nelson, E., Hitzman, M., Churchill, J. & Lopez-Pedrosa, M., 2004. The use of electron backscatter diffraction and orientation contrast imaging as tools for sulphide textural studies: example from the Greens Creek deposit (Alaska). Mineralium Deposita, 39, 103-113. Large, R. R., Danyushevsky, L., Hollit, C., Maslennikov, V., Meffre, S., Gilbert, S., Bull, S., Scott, R., Emsbo, P., Thomas, H., Singh, B. & Foster, J., 2009. Gold and Trace Element Zonation in Pyrite Using a Laser Imaging Technique: Implications for the Timing of Gold in Orogenic and Carlin-Style Sediment-Hosted Deposits. Economic Geology, 104(5), 635-668.

Quantum effect on the nucleation of plastic deformation carriers and destruction in crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khon, Yury A., E-mail: khon@ispms.tsc.ru; Kaminskii, Petr P., E-mail: ppk@ispms.tsc.ru

2015-10-27

New concepts on the irreversible crystal deformation as a structure transformation caused by a change in interatomic interactions at fluctuations of the electron density under loading are described. The change in interatomic interactions lead to the excitation of dynamical displacements of atoms. A model and a theory of a deformable pristine crystal taking into account the excitation of thermally activated and dynamical displacements of atoms are suggested. New mechanisms of the nucleation of plastic deformation carriers and destruction in pristine crystals at the real value of the deforming stress are studied.

Crystal plasticity in Cu damascene interconnect lines undergoing electromigration as revealed by synchrotron x-ray microdiffraction

NASA Astrophysics Data System (ADS)

Budiman, A. S.; Nix, W. D.; Tamura, N.; Valek, B. C.; Gadre, K.; Maiz, J.; Spolenak, R.; Patel, J. R.

2006-06-01

Plastic deformation was observed in damascene Cu interconnect test structures during an in situ electromigration experiment and before the onset of visible microstructural damage (voiding, hillock formation). We show here, using a synchrotron technique of white beam x-ray microdiffraction, that the extent of this electromigration-induced plasticity is dependent on the linewidth. In wide lines, plastic deformation manifests itself as grain bending and the formation of subgrain structures, while only grain rotation is observed in the narrower lines. The deformation geometry leads us to conclude that dislocations introduced by plastic flow lie predominantly in the direction of electron flow and may provide additional easy paths for the transport of point defects. Since these findings occur long before any observable voids or hillocks are formed, they may have direct bearing on the final failure stages of electromigration.

Equilibrium stability of a cylindrical body subject to the internal structure of the material and inelastic behaviour of the completely compressed matrix

NASA Astrophysics Data System (ADS)

Gotsev, D. V.; Perunov, N. S.; Sviridova, E. N.

2018-03-01

The mathematical model describing the stress-strain state of a cylindrical body under the uniform radial compression effect is constructed. The model of the material is the porous medium model. The compressed skeleton of the porous medium possesses hardening elastic-plastic properties. Deforming of the porous medium under the specified compressive loads is divided into two stages: elastic deforming of the porous medium and further elastic-plastic deforming of the material with completely compressed matrix. The analytical relations that define the fields of stress and displacement at each stage of the deforming are obtained. The influence of the porosity and other physical, mechanical and geometric parameters of the construction on the size of the plastic zone is evaluated. The question of the ground state equilibrium instability is investigated within the framework of the three-dimensional linearized relationships of the stability theory of deformed bodies.

Behavior of lateral-deformation coefficients during elastoplastic deformation of metals

NASA Astrophysics Data System (ADS)

Zimin, B. A.; Smirnov, I. V.; Sudenkov, Yu. V.

2017-06-01

The results of investigations into variation of the coefficients of lateral deformation (the Poisson ratio) during single-axis tension of samples of steel 12Kh18N10T and St3, titanium VT1, the aluminum alloy D16AM, copper M1, and a magnesium alloy are considered. The technique developed on the basis of the optoacoustic effect and simultaneous measurements of the longitudinal and surface speeds of sound in metallic samples during the tension makes it possible to measure the rates at various stages of the deformation process. The data obtained make it possible to construct the dependences of variation of the lateral-deformation coefficients at all stages of the plastic flow. The correlation of these variations both with known processes of structural reconstructions at various stages of plastic flow and with the process of localization of plastic-shear bands in the aluminum alloy is noted.

Structure and mechanical properties of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation by high-pressure torsion

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2015-04-01

The structural and phase transformations have been studied in aging commercial aluminum-lithium alloy Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg in the as-delivered state and after severe plastic deformation by torsion for 1, 5 and 10 revolutions under a high pressure of 4 GPa. Deformation-induced nanofragmentation and dynamic recrystallization have been found to occur in the alloy. The degree of recrystallization increases with deformation. Nanofragmentation and recrystallization processes are accompanied by the deformation-induced decomposition of solid solution and changes in both the nucleation mechanism of precipitation and the phase composition of the alloy. The influence of a nanostructured nanophase state of the alloy on its mechanical properties (microhardness, plasticity, elastic modulus, and stiffness) is discussed.

Dynamic strength properties of the surface of an ultra-fine-grained aluminum alloy under conditions of high-speed erosion

NASA Astrophysics Data System (ADS)

Kazarinov, N. A.; Evstifeev, A. D.; Petrov, Yu. V.; Lashkov, V. A.

2016-05-01

The influence of severe plastic deformation on the material surface is investigated under highspeed erosion conditions. The AD1 aluminum alloy was tested with the structure changed by severe plastic torsional deformation.

Evaluation of alignment error of micropore X-ray optics caused by hot plastic deformation

NASA Astrophysics Data System (ADS)

Numazawa, Masaki; Ishi, Daiki; Ezoe, Yuichiro; Takeuchi, Kazuma; Terada, Masaru; Fujitani, Maiko; Ishikawa, Kumi; Nakajima, Kazuo; Morishita, Kohei; Ohashi, Takaya; Mitsuda, Kazuhisa; Nakamura, Kasumi; Noda, Yusuke

2018-06-01

We report on the evaluation and characterization of micro-electromechanical system (MEMS) X-ray optics produced by silicon dry etching and hot plastic deformation. Sidewalls of micropores formed by etching through a silicon wafer are used as X-ray reflecting mirrors. The wafer is deformed into a spherical shape to focus parallel incidence X-rays. We quantitatively evaluated a mirror alignment error using an X-ray pencil beam (Al Kα line at 1.49 keV). The deviation angle caused only by the deformation was estimated from angular shifts of the X-ray focusing point before and after the deformation to be 2.7 ± 0.3 arcmin on average within the optics. This gives an angular resolution of 12.9 ± 1.4 arcmin in half-power diameter (HPD). The surface profile of the deformed optics measured using a NH-3Ns surface profiler (Mitaka Kohki) also indicated that the resolution was 11.4 ± 0.9 arcmin in HPD, suggesting that we can simply evaluate the alignment error caused by the hot plastic deformation.

An experimental investigation of energy absorption in TRIP steel under impact three-point bending deformation

NASA Astrophysics Data System (ADS)

Pham, Hang; Iwamoto, Takeshi

2015-09-01

TRIP (Transformation-induced Plasticity) steel is nowadays in widespread use in the automobile industry because of their favorable mechanical properties such as high strength, excellent formability and toughness because of strain-induced martensitic transformation. Moreover, when TRIP steel is applied to the components of the vehicles, it is expected that huge amount of kinetic energy will be absorbed into both plastic deformation and martensitic transformation during the collision. Basically, bending deformation due to buckling is one of the major crash deformation modes of automobile structures. Thus, an investigation of energy absorption during bending deformation at high impact velocity for TRIP steel is indispensable. Although TRIP steel have particularly attracted the recent interest of the scientific community, just few studies can be found on the energy absorption characteristic of TRIP steel, especially at impact loading condition. In present study, experimental investigations of bending deformation behaviors of TRIP steel are conducted in the three-point bending tests for both smooth and pre-cracked specimen. Then, energy absorption characteristic during plastic deformation and fracture process at high impact velocity in TRIP steel will be discussed.

Room temperature deformation mechanisms of alumina particles observed from in situ micro-compression and atomistic simulations.

DOE PAGES

Sarobol, Pylin; Chandross, Michael E.; Carroll, Jay D.; ...

2015-09-22

Aerosol deposition (AD) is a solid-state deposition technology that has been developed to fabricate ceramic coatings nominally at room temperature. Sub-micron ceramic particles accelerated by pressurized gas impact, deform, and consolidate on substrates under vacuum. Ceramic particle consolidation in AD coatings is highly dependent on particle deformation and bonding; these behaviors are not well understood. In this work, atomistic simulations and in situ micro-compressions in the scanning electron microscope, and the transmission electron microscope (TEM) were utilized to investigate fundamental mechanisms responsible for plastic deformation/fracture of particles under applied compression. Results showed that highly defective micron-sized alumina particles, initially containingmore » numerous dislocations or a grain boundary, exhibited no observable shape change before fracture/fragmentation. Simulations and experimental results indicated that particles containing a grain boundary only accommodate low strain energy per unit volume before crack nucleation and propagation. In contrast, nearly defect-free, sub-micron, single crystal alumina particles exhibited plastic deformation and fracture without fragmentation. Dislocation nucleation/motion, significant plastic deformation, and shape change were observed. Simulation and TEM in situ micro-compression results indicated that nearly defect-free particles accommodate high strain energy per unit volume associated with dislocation plasticity before fracture. As a result, the identified deformation mechanisms provide insight into feedstock design for AD.« less

Optimization of In-Situ Shot-Peening-Assisted Cold Spraying Parameters for Full Corrosion Protection of Mg Alloy by Fully Dense Al-Based Alloy Coating

NASA Astrophysics Data System (ADS)

Wei, Ying-Kang; Luo, Xiao-Tao; Li, Cheng-Xin; Li, Chang-Jiu

2017-01-01

Magnesium-based alloys have excellent physical and mechanical properties for a lot of applications. However, due to high chemical reactivity, magnesium and its alloys are highly susceptible to corrosion. In this study, Al6061 coating was deposited on AZ31B magnesium by cold spray with a commercial Al6061 powder blended with large-sized stainless steel particles (in-situ shot-peening particles) using nitrogen gas. Microstructure and corrosion behavior of the sprayed coating was investigated as a function of shot-peening particle content in the feedstock. It is found that by introducing the in-situ tamping effect using shot-peening (SP) particles, the plastic deformation of deposited particles is significantly enhanced, thereby resulting in a fully dense Al6061 coating. SEM observations reveal that no SP particle is deposited into Al6061 coating at the optimization spraying parameters. Porosity of the coating significantly decreases from 10.7 to 0.4% as the SP particle content increases from 20 to 60 vol.%. The electrochemical corrosion experiments reveal that this novel in-situ SP-assisted cold spraying is effective to deposit fully dense Al6061 coating through which aqueous solution is not permeable and thus can provide exceptional protection of the magnesium-based materials from corrosion.

Electron backscatter and X-ray diffraction studies on the deformation and annealing textures of austenitic stainless steel 310S

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nezakat, Majid, E-mail: majid.nezakat@usask.ca

We studied the texture evolution of thermo-mechanically processed austenitic stainless steel 310S. This alloy was cold rolled up to 90% reduction in thickness and subsequently annealed at 1050 °C. At the early stages of deformation, strain-induced martensite was formed from deformed austenite. By increasing the deformation level, slip mechanism was found to be insufficient to accommodate higher deformation strains. Our results demonstrated that twinning is the dominant deformation mechanism at higher deformation levels. Results also showed that cold rolling in unidirectional and cross rolling modes results in Goss/Brass and Brass dominant textures in deformed samples, respectively. Similar texture components aremore » observed after annealing. Thus, the annealing texture was greatly affected by texture of the deformed parent phase and martensite did not contribute as it showed an athermal reversion during annealing. Results also showed that when the fraction of martensite exceeds a critical point, its grain boundaries impeded the movement of austenite grain boundaries during annealing. As a result, recrystallization incubation time would increase. This caused an incomplete recrystallization of highly deformed samples, which led to a rational drop in the intensity of the texture components. - Highlights: •Thermo-mechanical processing through different cold rolling modes can induce different textures. •Martensite reversion is athermal during annealing. •Higher fraction of deformation-induced martensite can increase the annealing time required for complete recrystallization. •Annealing texture is mainly influenced by the deformation texture of austenite.« less

Field Performance of Recycled Plastic Foundation for Pipeline

PubMed Central

Kim, Seongkyum; Lee, Kwanho

2015-01-01

The incidence of failure of embedded pipelines has increased in Korea due to the increasing applied load and the improper compaction of bedding and backfill materials. To overcome these problems, a prefabricated lightweight plastic foundation using recycled plastic was developed for sewer pipelines. A small scale laboratory chamber test and two field tests were conducted to verify its construction workability and performance. From the small scale laboratory chamber test, the applied loads at 2.5% and 5.0% of deformation were 3.45 kgf/cm2 and 5.85 kgf/cm2 for Case S1, and 4.42 kgf/cm2 and 6.43 kgf/cm2 for Case S2, respectively. From the first field test, the vertical deformation of the recycled plastic foundation (Case A2) was very small. According to the analysis based on the PE pipe deformation at the connection (CN) and at the center (CT), the pipe deformation at each part for Case A1 was larger than that for Case A2, which adopted the recycled lightweight plastic foundation. From the second field test, the measured maximum settlements of Case B1 and Case B2 were 1.05 cm and 0.54 cm, respectively. The use of a plastic foundation can reduce the settlement of an embedded pipeline and be an alternative construction method.

In-vitro long term and electrochemical corrosion resistance of cold deformed nitrogen containing austenitic stainless steels in simulated body fluid.

PubMed

Talha, Mohd; Behera, C K; Sinha, O P

2014-07-01

This work was focused on the evaluation of the corrosion behavior of deformed (10% and 20% cold work) and annealed (at 1050 °C for 15 min followed by water quenching) Ni-free high nitrogen austenitic stainless steels (HNSs) in simulated body fluid at 37°C using weight loss method (long term), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Scanning electron microscopy (SEM) was used to understand the surface morphology of the alloys after polarization test. It has been observed that cold working had a significant influence on the corrosion resistant properties of these alloys. The weight loss and corrosion rates were observed to decrease with increasing degree of cold working and nitrogen content in the alloy. The corrosion resistance of the material is directly related to the resistance of the passive oxide film formed on its surface which was enhanced with cold working and nitrogen content. It was also observed that corrosion current densities were decreased and corrosion potentials were shifted to more positive values. By seeing pit morphology under SEM, shallower and smaller pits were associated with HNSs and cold worked samples, indicating that corrosion resistance increases with increasing nitrogen content and degree of cold deformation. X-ray diffraction profiles of annealed as well as deformed alloys were revealed and there is no evidence for formation of martensite or any other secondary phases. Copyright © 2014 Elsevier B.V. All rights reserved.

Analysis of cold worked holes for structural life extension

NASA Technical Reports Server (NTRS)

Wieland, David H.; Cutshall, Jon T.; Burnside, O. Hal; Cardinal, Joseph W.

1994-01-01

Cold working holes for improved fatigue life of fastener holes are widely used on aircraft. This paper presents methods used by the authors to determine the percent of cold working to be applied and to analyze fatigue crack growth of cold worked fastener holes. An elastic, perfectly-plastic analysis of a thick-walled tube is used to determine the stress field during the cold working process and the residual stress field after the process is completed. The results of the elastic/plastic analysis are used to determine the amount of cold working to apply to a hole. The residual stress field is then used to perform damage tolerance analysis of a crack growing out of a cold worked fastener hole. This analysis method is easily implemented in existing crack growth computer codes so that the cold worked holes can be used to extend the structural life of aircraft. Analytical results are compared to test data where appropriate.

Atomistic simulation on the plastic deformation and fracture of bio-inspired graphene/Ni nanocomposites

NASA Astrophysics Data System (ADS)

Yang, Zhenyu; Wang, Dandan; Lu, Zixing; Hu, Wenjun

2016-11-01

Molecular dynamics simulations were performed to investigate the plastic deformation and fracture behaviors of bio-inspired graphene/metal nanocomposites, which have a "brick-and-mortar" nanostructure, consisting of hard graphene single-layers embedded in a soft Ni matrix. The plastic deformation mechanisms of the nanocomposites were analyzed as well as their effects on the mechanical properties with various geometrical variations. It was found that the strength and ductility of the metal matrix can be highly enhanced with the addition of the staggered graphene layers, and the plastic deformation can be attributed to the interfacial sliding, dislocation nucleation, and cracks' combination. The strength of the nanocomposites strongly depends on the length scale of the nanostructure and the interlayer distance as well. In addition, slip at the interface releases the stress in graphene layers, leading to the stress distribution on the graphene more uniform. The present results are expected to contribute to the design of the nanolayered graphene/metal composites with high performance.

Plastic deformation treated as material flow through adjustable crystal lattice

NASA Astrophysics Data System (ADS)

Minakowski, P.; Hron, J.; Kratochvíl, J.; Kružík, M.; Málek, J.

2014-08-01

Looking at severe plastic deformation experiments, it seems that crystalline materials at yield behave as a special kind of anisotropic, highly viscous fluids flowing through an adjustable crystal lattice space. High viscosity provides a possibility to describe the flow as a quasi-static process, where inertial and other body forces can be neglected. The flow through the lattice space is restricted to preferred crystallographic planes and directions causing anisotropy. In the deformation process the lattice is strained and rotated. The proposed model is based on the rate form of the decomposition rule: the velocity gradient consists of the lattice velocity gradient and the sum of the velocity gradients corresponding to the slip rates of individual slip systems. The proposed crystal plasticity model allowing for large deformations is treated as the flow-adjusted boundary value problem. As a test example we analyze a plastic flow of an single crystal compressed in a channel die. We propose three step algorithm of finite element discretization for a numerical solution in the Arbitrary Lagrangian Eulerian (ALE) configuration.

Ultrasound Velocity Measurements in High-Chromium Steel Under Plastic Deformation

NASA Astrophysics Data System (ADS)

Lunev, Aleksey; Bochkareva, Anna; Barannikova, Svetlana; Zuev, Lev

2016-04-01

In the present study, the variation of the propagation velocity of ultrasound in the plastic deformation of corrosion-resistant high-chromium steel 40X13 with ferrite-carbide (delivery status), martensitic (quenched) and sorbitol (after high-temperature tempering) structures have beem studied/ It is found that each state shows its view of the loading curve. In the delivery state diagram loading is substantially parabolic throughout, while in the martensitic state contains only linear strain hardening step and in the sorbitol state the plastic flow curve is three-step. The velocity of ultrasonic surface waves (Rayleigh waves) was measured simultaneously with the registration of the loading curve in the investigated steel in tension. It is shown that the dependence of the velocity of ultrasound in active loading is determined by the law of plastic flow, that is, the staging of the corresponding diagram of loading. Structural state of the investigated steel is not only changing the type of the deformation curve under uniaxial tension, but also changes the nature of ultrasound speed of deformation.

High-Oriented Thermoelectric Nano-Bulk Fabricated from Thermoelectric Ink

NASA Astrophysics Data System (ADS)

Koyano, M.; Mizutani, S.; Hayashi, Y.; Nishino, S.; Miyata, M.; Tanaka, T.; Fukuda, K.

2017-05-01

Printing technology is expected to provide innovative and environmentally friendly processes for thermoelectric (TE) module fabrication. As described in this paper, we propose an orientation control process using plastic deformation at high temperatures and present high-oriented TE nano-bulks fabricated from bismuth telluride (Bi-Te) TE inks using this process. In the case of n-type Bi-Te, surface x-ray diffraction reveals that crystalline grains in the plastic-deformed nano-bulk demonstrate a c-plane orientation parallel to the pressed face. According to the high orientation, electrical resistivity ρ, thermal conductivity κ, and figure of merit ZT show anisotropic behavior. It is noteworthy that ( ZT)// almost reaches unity ( ZT)// ˜1 at 340 K, even at low temperatures of the plastic deformation process. In contrast, the ZT of plastic-deformed p-type nano-bulk indicates isotropic behavior. The difference in the process temperature dependence of ZT suggests that n-type and p-type nano-bulk orientation mechanisms mutually differ.

Structural Transformations in Metallic Materials During Plastic Deformation

NASA Astrophysics Data System (ADS)

Zasimchuk, E.; Turchak, T.; Baskova, A.; Chausov, N.; Hutsaylyuk, V.

2017-03-01

In this paper, the structure formation during the plastic deformation of polycrystalline nickel and aluminum based alloy 2024-T3 is investigated. The possibility of the relaxation and synergetic structure formation is examined. It is shown the deformation softening to be due to the crystallization of the amorphous structure of hydrodynamics flow channels (synergetic structure) HC as micrograins and their subsequent growth. The possible mechanism of micrograins' growth is proposed. The deformation processes change the phase composition of the multiphase alloy 2024-T3. It is shown by the quantitative analysis of the structures which were deformed in different regimes of the alloy samples. A method for increasing of the fatigue life through a dynamic pre-deformation is suggested.

Birefringence and incipient plastic deformation in elastically overdriven [100] CaF2 under shock compression

NASA Astrophysics Data System (ADS)

Li, Y.; Zhou, X. M.; Cai, Y.; Liu, C. L.; Luo, S. N.

2018-04-01

[100] CaF2 single crystals are shock-compressed via symmetric planar impact, and the flyer plate-target interface velocity histories are measured with a laser displacement interferometry. The shock loading is slightly above the Hugoniot elastic limit to investigate incipient plasticity and its kinetics, and its effects on optical properties and deformation inhomogeneity. Fringe patterns demonstrate different features in modulation of fringe amplitude, including birefringence and complicated modulations. The birefringence is attributed to local lattice rotation accompanying incipient plasticity. Spatially resolved measurements show inhomogeneity in deformation, birefringence, and fringe pattern evolutions, most likely caused by the inhomogeneity associated with lattice rotation and dislocation slip. Transiently overdriven elastic states are observed, and the incubation time for incipient plasticity decreases inversely with increasing overdrive by the elastic shock.

Gradient Plasticity Model and its Implementation into MARMOT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barker, Erin I.; Li, Dongsheng; Zbib, Hussein M.

2013-08-01

The influence of strain gradient on deformation behavior of nuclear structural materials, such as boby centered cubic (bcc) iron alloys has been investigated. We have developed and implemented a dislocation based strain gradient crystal plasticity material model. A mesoscale crystal plasticity model for inelastic deformation of metallic material, bcc steel, has been developed and implemented numerically. Continuum Dislocation Dynamics (CDD) with a novel constitutive law based on dislocation density evolution mechanisms was developed to investigate the deformation behaviors of single crystals, as well as polycrystalline materials by coupling CDD and crystal plasticity (CP). The dislocation density evolution law in thismore » model is mechanism-based, with parameters measured from experiments or simulated with lower-length scale models, not an empirical law with parameters back-fitted from the flow curves.« less

The evolution of rifting process in the tectonic history of the Earth

NASA Technical Reports Server (NTRS)

Milanovsky, E. E.; Nikishin, A. M.

1985-01-01

The continental rifting is the response of the lithosphere to the oriented tension. The distribution of viscosity in the lithosphere plays an essential role during all stages of the rifting. The viscosity is a function of the temperature, the lithostatic pressure, the rock composition, the deformation rate and other factors. The temperature is the most important factor. The vertical section of continental lithosphere of the rift zone may be divided into the following layers: the upper crust, in which brittle deformation prevails; the medialcrust, in which the role of plastic deformation increases; the lower crust, in which plastic deformation prevails; and the uppermost plastic part of the mantle overlapping asthenosphere. The depth of the boundaries in the crust layers are mainly controlled by the temperature.

Deformation bands, the LEDS theory, and their importance in texture development: Part II. Theoretical conclusions

NASA Astrophysics Data System (ADS)

Kuhlmann-Wilsdorf, D.

1999-09-01

The facts regarding “regular” deformation bands (DBs) outlined in Part I of this series of articles are related to the low-energy dislocation structure (LEDS) theory of dislocation-based plasticity. They prompt an expansion of the theory by including the stresses due to strain gradients on account of changing selections of slip systems to the previously known dislocation driving forces. This last and until now neglected driving force is much smaller than the components considered hitherto, principally due to the applied stress and to mutual stress-screening among neighbor dislocations. As a result, it permits a near-proof of the LEDS hypothesis, to wit that among all structures which, in principle, are accessible to the dislocations, that one is realized which has the lowest free energy. Specifically, the temperature rises that would result from annihilating the largest DBs amount to only several millidegrees Centigrade, meaning that they, and by implication the entire dislocation structures, are close to thermodynamical equilibrium. This is in stark contrast to the assumption of the presently widespread self-organizing dislocation structures (SODS) modeling that plastic deformation occurs far from equilibrium and is subject to Prigogine’s thermodynamics of energy-flow-through systems. It also holds out promise for future rapid advances in the construction of constitutive equations, since the LEDS hypothesis is the principal basis of the LEDS theory of plastic deformation and follows directly from the second law of thermodynamics in conjunction with Newton’s third law. By contrast, all other known models of metal plasticity are in conflict with the LEDS hypothesis. In regard to texture modeling, the present analysis shows that Taylor’s criterion of minimum plastic work is incorrect and should be replaced by the criterion of minimum free energy in the stressed state. Last, the LEDS hypothesis is but a special case of the more general low-energy structure (LES) hypothesis, applying to plastic deformation independent of the deformation mechanism. It is thus seen that plastic deformation is one of nature’s means to generate order, as a byproduct of the entropy generation when mechanical work is largely converted into heat.

Plasticity of ductile metallic glasses: a self-organized critical state.

PubMed

Sun, B A; Yu, H B; Jiao, W; Bai, H Y; Zhao, D Q; Wang, W H

2010-07-16

We report a close correlation between the dynamic behavior of serrated flow and the plasticity in metallic glasses (MGs) and show that the plastic deformation of ductile MGs can evolve into a self-organized critical state characterized by the power-law distribution of shear avalanches. A stick-slip model considering the interaction of multiple shear bands is presented to reveal complex scale-free intermittent shear-band motions in ductile MGs and quantitatively reproduce the experimental observations. Our studies have implications for understanding the precise plastic deformation mechanism of MGs.

3D microstructural evolution of primary recrystallization and grain growth in cold rolled single-phase aluminum alloys

NASA Astrophysics Data System (ADS)

Adam, Khaled; Zöllner, Dana; Field, David P.

2018-04-01

Modeling the microstructural evolution during recrystallization is a powerful tool for the profound understanding of alloy behavior and for use in optimizing engineering properties through annealing. In particular, the mechanical properties of metallic alloys are highly dependent upon evolved microstructure and texture from the softening process. In the present work, a Monte Carlo (MC) Potts model was used to model the primary recrystallization and grain growth in cold rolled single-phase Al alloy. The microstructural representation of two kinds of dislocation densities, statistically stored dislocations and geometrically necessary dislocations were quantified based on the ViscoPlastic Fast Fourier transform method. This representation was then introduced into the MC Potts model to identify the favorable sites for nucleation where orientation gradients and entanglements of dislocations are high. Additionally, in situ observations of non-isothermal microstructure evolution for single-phase aluminum alloy 1100 were made to validate the simulation. The influence of the texture inhomogeneity is analyzed from a theoretical point of view using an orientation distribution function for deformed and evolved texture.

Improved bonding strength of bioactive cermet Cold Gas Spray coatings.

PubMed

Gardon, M; Concustell, A; Dosta, S; Cinca, N; Cano, I G; Guilemany, J M

2014-12-01

The fabrication of cermet biocompatible coatings by means Cold Gas Spray (CGS) provides prosthesis with outstanding mechanical properties and the required composition for enhancing the bioactivity of prosthetic materials. In this study, hydroxyapatite/Titanium coatings were deposited by means of CGS technology onto titanium alloy substrates with the aim of building-up well-bonded homogeneous coatings. Powders were blended in different percentages and sprayed; as long as the amount of hydroxyapatite in the feedstock increased, the quality of the coating was reduced. Besides, the relation between the particle size distribution of ceramic and metallic particles is of significant consideration. Plastic deformation of titanium particles at the impact eased the anchoring of hard hydroxyapatite particles present at the top surface of the coating, which assures the looked-for interaction with the cells. Coatings were immersed in Hank's solution for 1, 4 and 7 days; bonding strength value was above 60 MPa even after 7 days, which enhances common results of HAp coatings obtained by conventional thermal spray technologies. Copyright © 2014 Elsevier B.V. All rights reserved.

Work Hardening Behavior of 1020 Steel During Cold-Beating Simulation

NASA Astrophysics Data System (ADS)

CUI, Fengkui; LING, Yuanfei; XUE, Jinxue; LIU, Jia; LIU, Yuhui; LI, Yan

2017-03-01

The present research of cold-beating formation mainly focused on roller design and manufacture, kinematics, constitutive relation, metal flow law, thermo-mechanical coupling, surface micro-topography and microstructure evolution. However, the research on surface quality and performance of workpieces in the process of cold-beating is rare. Cold-beating simulation experiment of 1020 steel is conducted at room temperature and strain rates ranging from 2000 to 4000 s-1 base on the law of plastic forming. According to the experimental data, the model of strain hardening of 1020 steel is established, Scanning Electron Microscopy(SEM) is conducted, the mechanism of the work hardening of 1020 steel is clarified by analyzing microstructure variation of 1020 steel. It is found that the strain rate hardening effect of 1020 steel is stronger than the softening effect induced by increasing temperatures, the process of simulation cold-beating cause the grain shape of 1020 steel significant change and microstructure elongate significantly to form a fibrous tissue parallel to the direction of deformation, the higher strain rate, the more obvious grain refinement and the more hardening effect. Additionally, the change law of the work hardening rate is investigated, the relationship between dislocation density and strain, the relationship between work hardening rate and dislocation density is obtained. Results show that the change trend of the work hardening rate of 1020 steel is divided into two stages, the work hardening rate decreases dramatically in the first stage and slowly decreases in the second stage, finally tending toward zero. Dislocation density increases with increasing strain and strain rate, work hardening rate decreases with increasing dislocation density. The research results provide the basis for solving the problem of improving the surface quality and performance of workpieces under cold-beating formation of 1020 steel.

An investigation of the inelastic behaviour of trabecular bone during the press-fit implantation of a tibial component in total knee arthroplasty.

PubMed

Kelly, N; Cawley, D T; Shannon, F J; McGarry, J P

2013-11-01

The stress distribution and plastic deformation of peri-prosthetic trabecular bone during press-fit tibial component implantation in total knee arthroplasty is investigated using experimental and finite element techniques. It is revealed that the computed stress distribution, implantation force and plastic deformation in the trabecular bone is highly dependent on the plasticity formulation implemented. By incorporating pressure dependent yielding using a crushable foam plasticity formulation to simulate the trabecular bone during implantation, highly localised stress concentrations and plastic deformation are computed at the bone-implant interface. If the pressure dependent yield is neglected using a traditional von Mises plasticity formulation, a significantly different stress distribution and implantation force is computed in the peri-prosthetic trabecular bone. The results of the study highlight the importance of: (i) simulating the insertion process of press-fit stem implantation; (ii) implementing a pressure dependent plasticity formulation, such as the crushable foam plasticity formulation, for the trabecular bone; (iii) incorporating friction at the implant-bone interface during stem insertion. Simulation of the press-fit implantation process with an appropriate pressure dependent plasticity formulation should be implemented in the design and assessment of arthroplasty prostheses. Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

Size effects in olivine control strength in low-temperature plasticity regime

NASA Astrophysics Data System (ADS)

Kumamoto, K. M.; Thom, C.; Wallis, D.; Hansen, L. N.; Armstrong, D. E. J.; Goldsby, D. L.; Warren, J. M.; Wilkinson, A. J.

2017-12-01

The strength of the lithospheric mantle during deformation by low-temperature plasticity controls a range of geological phenomena, including lithospheric-scale strain localization, the evolution of friction on deep seismogenic faults, and the flexure of tectonic plates. However, constraints on the strength of olivine in this deformation regime are difficult to obtain from conventional rock-deformation experiments, and previous results vary considerably. We demonstrate via nanoindentation that the strength of olivine in the low-temperature plasticity regime is dependent on the length-scale of the test, with experiments on smaller volumes of material exhibiting larger yield stresses. This "size effect" has previously been explained in engineering materials as a result of the role of strain gradients and associated geometrically necessary dislocations in modifying plastic behavior. The Hall-Petch effect, in which a material with a small grain size exhibits a higher strength than one with a large grain size, is thought to arise from the same mechanism. The presence of a size effect resolves discrepancies among previous experimental measurements of olivine, which were either conducted using indentation methods or were conducted on polycrystalline samples with small grain sizes. An analysis of different low-temperature plasticity flow laws extrapolated to room temperature reveals a power-law relationship between length-scale (grain size for polycrystalline deformation and contact radius for indentation tests) and yield strength. This suggests that data from samples with large inherent length scales best represent the plastic strength of the coarse-grained lithospheric mantle. Additionally, the plastic deformation of nanometer- to micrometer-sized asperities on fault surfaces may control the evolution of fault roughness due to their size-dependent strength.

A bioactive coating with submicron-sized titania crystallites fabricated by induction heating of titanium after tensile deformations.

PubMed

Li, Ning-Bo; Xu, Wen-Hua; Xiao, Gui-Yong; Zhao, Jun-Han; Lu, Yu-Peng

2017-11-01

Thermal oxidation technology was widely investigated as one of effective surface modification method for improving the bioactivity and biocompatibility of titanium and its alloys. In this work, the induction heat oxidization method, a fast, efficient, economical and environmental protective technology, was applied to prepare the submicron-morphological oxide coating with variable rutile TiO 2 equiaxed crystallites on the surface of pure Ti substrates after cold-drawing with 10-20% deformations. The results showed the plastic-deformed Ti cylinders recrystallized during induction heating treatment (IHT) for 10-20s which resulted in evolution of microstructures as well as slight improvement of microhardness. The surface characteristics of TiO 2 crystallites in oxidation layers were determined by the microstructural evolutions of Ti substrate in terms of the nucleation and growth of TiO 2 crystallites. Specially, the oxidized surface with 50-75nm roughness and more uniform and finer equiaxed oxide grains remarkablely improved the apatite deposition after bioactive evaluation in 1.5 × SBF for 7 days. This work provided a potential method to create controlled bioactive oxide coatings with submicro-/nano-scaled TiO 2 crystallites on titanium substrate in terms of the role of metallographic microstructure in the formation process of titanium oxides. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effect of tensile twins on the subsequent plastic deformation in rolled Mg-3Al-1Zn alloy

NASA Astrophysics Data System (ADS)

Yoon, Jonghun; Kim, Se-Jong; Lee, Youngseon

2013-12-01

The {101¯2} tensile twins influence plastic flow of magnesium alloys for the subsequent plastic deformation since it contributes to grain refinement and texture hardening between the twinned and untwined regions. This paper investigates the variation of plastic flow of the rolled Mg-3Al-1Zn alloy which is compressed with a small plastic strain at the room temperature to induce the twins in the initial specimen. Subsequent tension and compression along the rolling and transverse direction are conducted with the twin induced specimens in order to examine the effect of the initial tensile twins.

Ductilisation of tungsten (W): Tungsten laminated composites

DOE PAGES

Reiser, Jens; Garrison, Lauren M.; Greuner, Henri; ...

2017-08-02

Here we elucidate the mechanisms of plastic deformation and fracture of tungsten laminated composites. Furthermore our results suggest that the mechanical response of the laminates is governed by the plastic deformation of the tungsten plies. In most cases, the impact of the interlayer is of secondary importance.

Nano-twin Mediated Plasticity in Carbon-containing FeNiCoCrMn High Entropy Alloys

DOE PAGES

Wu, Zhenggang; Bei, Hongbin; Parish, Chad M

2015-06-14

Equiatomic FeNiCoCrMn alloy has been reported to exhibit promising strength and ductility at cryogenic temperature and deformation mediated by nano-twining appeared to be one of the main reasons. We use the FeNiCoCrMn alloy as a base alloy to seek further improvement of its mechanical properties by alloying additional elements, i.e., interstitial carbon. Moreover, the effects of carbon on microstructures, mechanical properties and twinning activities were investigated in two different temperatures (77 and 293 K). With addition of 0.5 at% C, the high entropy alloy still remains entirely single phase face-centered cubic (FCC) crystal structure. We found that these materials canmore » be cold rolled and recrystallized to produce a microstructure with equiaxed grains. Both strain hardening rate and strength are enhanced while high uniform elongations to fracture (~70% at 77 K and ~40% at 293 K) are still maintained. The increased strain hardening and strength could be caused by the promptness of deformation twinning in C-containing high entropy alloys.« less

Effect of the Leveling Conditions on Residual Stress Evolution of Hot Rolled High Strength Steels for Cold Forming

NASA Astrophysics Data System (ADS)

Park, Keecheol; Oh, Kyungsuk

2017-09-01

In order to investigate the effect of leveling conditions on residual stress evolution during the leveling process of hot rolled high strength steels, the in-plane residual stresses of sheet processed under controlled conditions at skin-pass mill and levelers were measured by cutting method. The residual stress was localized near the edge of sheet. As the thickness of sheet was increased, the residual stress occurred region was expanded. The magnitude of residual stress within the sheet was reduced as increasing the deformation occurred during the leveling process. But the residual stress itself was not removed completely. The magnitude of camber occurred at cut plate was able to be predicted by the residual stress distribution. A numerical algorithm was developed for analysing the effect of leveling conditions on residual stress. It was able to implement the effect of plastic deformation in leveling, tension, work roll bending, and initial state of sheet (residual stress and curl distribution). The validity of simulated results was verified from comparison with the experimentally measured residual stress and curl in a sheet.

Strengthening of Aluminum Alloy 2219 by Thermo-mechanical Treatment

NASA Astrophysics Data System (ADS)

Li, Xifeng; Lei, Kun; Song, Peng; Liu, Xinqin; Zhang, Fei; Li, Jianfei; Chen, Jun

2015-10-01

Strengthening of aluminum alloy 2219 by thermo-mechanical treatment has been compared with artificial aging. Three simple deformation modes including pre-stretching, compression, and rolling have been used in thermo-mechanical treatment. The tensile strength, elongation, fracture feature, and precipitated phase have been investigated. The results show that the strengthening effect of thermo-mechanical treatment is better than the one of artificial aging. Especially, the yield strength significantly increases with a small decrease of elongation. When the specimen is pre-stretched to 8.0%, the yield strength reaches 385.0 MPa and increases by 22.2% in comparison to the one obtained in aging condition. The maximum tensile strength of 472.4 MPa is achieved with 4.0% thickness reduction by compression. The fracture morphology reveals locally ductile and brittle failure mechanism, while the coarse second-phase particles distribute on the fracture surface. The intermediate phases θ″ or θ' orthogonally precipitate in the matrix after thermo-mechanical treatment. As compared to artificial aging, the cold plastic deformation increases distribution homogeneity and the volume fraction of θ'' or θ' precipitates. These result in a better strengthening effect.

Study of fatigue crack propagation in Ti-1Al-1Mn based on the calculation of cold work evolution

NASA Astrophysics Data System (ADS)

Plekhov, O. A.; Kostina, A. A.

2017-05-01

The work proposes a numerical method for lifetime assessment for metallic materials based on consideration of energy balance at crack tip. This method is based on the evaluation of the stored energy value per loading cycle. To calculate the stored and dissipated parts of deformation energy an elasto-plastic phenomenological model of energy balance in metals under the deformation and failure processes was proposed. The key point of the model is strain-type internal variable describing the stored energy process. This parameter is introduced based of the statistical description of defect evolution in metals as a second-order tensor and has a meaning of an additional strain due to the initiation and growth of the defects. The fatigue crack rate was calculated in a framework of a stationary crack approach (several loading cycles for every crack length was considered to estimate the energy balance at crack tip). The application of the proposed algorithm is illustrated by the calculation of the lifetime of the Ti-1Al-1Mn compact tension specimen under cyclic loading.

Hydrogen-Induced Plastic Deformation in ZnO

NASA Astrophysics Data System (ADS)

Lukáč, F.; Čížek, J.; Vlček, M.; Procházka, I.; Anwand, W.; Brauer, G.; Traeger, F.; Rogalla, D.; Becker, H.-W.

In the present work hydrothermally grown ZnO single crystals covered with Pd over-layer were electrochemically loaded with hydrogen and the influence of hydrogen on ZnO micro structure was investigated by positron annihilation spectroscopy (PAS). Nuclear reaction analysis (NRA) was employed for determination of depth profile of hydrogen concentration in the sample. NRA measurements confirmed that a substantial amount of hydrogen was introduced into ZnO by electrochemical charging. The bulk hydrogen concentration in ZnO determined by NRA agrees well with the concentration estimated from the transported charge using the Faraday's law. Moreover, a subsurface region with enhanced hydrogen concentration was found in the loaded crystals. Slow positron implantation spectroscopy (SPIS) investigations of hydrogen-loaded crystal revealed enhanced concentration of defects in the subsurface region. This testifies hydrogen-induced plastic deformation of the loaded crystal. Absorbed hydrogen causes a significant lattice expansion. At low hydrogen concentrations this expansion is accommodated by elastic straining, but at higher concentrations hydrogen-induced stress exceeds the yield stress in ZnO and plastic deformation of the loaded crystal takes place. Enhanced hydrogen concentration detected in the subsurface region by NRA is, therefore, due to excess hydrogen trapped at open volume defects introduced by plastic deformation. Moreover, it was found that hydrogen-induced plastic deformation in the subsurface layer leads to typical surface modification: formation of hexagonal shape pyramids on the surface due to hydrogen-induced slip in the [0001] direction.

A Computational Study of Plastic Deformation in AISI 304 Induced by Surface Mechanical Attrition Treatment

NASA Astrophysics Data System (ADS)

Zhang, X. C.; Lu, J.; Shi, S. Q.

2010-05-01

As a technique of grain refinement process by plastic deformation, surface mechanical attrition treatment (SMAT) has been developed to be one of the most effective ways to optimize the mechanical properties of various materials including pure metals and alloys. SMAT can significantly reduce grain size into nanometer regime in the surface layer of bulk materials, providing tremendous opportunities for improving physical, chemical and mechanical properties of the materials. In this work, a computational modeling of the surface mechanical attrition treatment (SMAT) process is presented, in which Johnson-Cook plasticity model and the finite element method were employed to study the high strain rate, elastic-plastic dynamic process of ball impact on a metallic target. AISI 304 steel with low stacking fault energy was chosen as the target material. First, a random impact model was used to analyze the statistic characteristics of ball impact, and then the plastic deformation behavior and residual stress distribution in AISI 304 stainless steel during SMAT were studied. The simulation results show that the compressive residual stress and vertical deformation of the surface structures were directly affected by ball impact frequency, incident impact angle and ball diameter used in SMAT process.

Osteoporosis affects both post-yield microdamage accumulation and plasticity degradation in vertebra of ovariectomized rats

NASA Astrophysics Data System (ADS)

Li, Siwei; Niu, Guodong; Dong, Neil X.; Wang, Xiaodu; Liu, Zhongjun; Song, Chunli; Leng, Huijie

2017-04-01

Estrogen withdrawal in postmenopausal women increases bone loss and bone fragility in the vertebra. Bone loss with osteoporosis not only reduces bone mineral density (BMD), but actually alters bone quality, which can be comprehensively represented by bone post-yield behaviors. This study aimed to provide some information as to how osteoporosis induced by estrogen depletion could influence the evolution of post-yield microdamage accumulation and plastic deformation in vertebral bodies. This study also tried to reveal the part of the mechanisms of how estrogen deficiency-induced osteoporosis would increase the bone fracture risk. A rat bilateral ovariectomy (OVX) model was used to induce osteoporosis. Progressive cyclic compression loading was developed for vertebra testing to elucidate the post-yield behaviors. BMD, bone volume fraction, stiffness degradation, and plastic deformation evolution were compared among rats raised for 5 weeks (ovx5w and sham5w groups) and 35 weeks (ovx35w and sham35w groups) after sham surgery and OVX. The results showed that a higher bone loss in vertebral bodies corresponded to lower stiffness and higher plastic deformation. Thus, osteoporosis could increase the vertebral fracture risk probably through microdamage accumulation and plastic deforming degradation.

A study of microindentation hardness tests by mechanism-based strain gradient plasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Y.; Xue, Z.; Gao, H.

2000-08-01

We recently proposed a theory of mechanism-based strain gradient (MSG) plasticity to account for the size dependence of plastic deformation at micron- and submicron-length scales. The MSG plasticity theory connects micron-scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor's dislocation hardening model to strain gradient plasticity. Here we show that the theory of MSG plasticity, when used to study micro-indentation, indeed reproduces the linear dependence observed in experiments, thus providing an important self-consistent check of the theory. The effects of pileup, sink-in, and the radius of indenter tip have been taken into account in the indentation model.more » In accomplishing this objective, we have generalized the MSG plasticity theory to include the elastic deformation in the hierarchical framework. (c) 2000 Materials Research Society.« less

Developments in Processing by Severe Plastic Deformation at the 3rd Pan American Materials Congress

NASA Astrophysics Data System (ADS)

Figueiredo, Roberto B.; Kawasaki, Megumi; Langdon, Terence G.

2017-10-01

The 3rd Pan American Materials Congress in San Diego, California, February 26-March 2, 2017, provided an opportunity to bring together many participants working in the field of severe plastic deformation. This article provides a brief review of these activities.

Atomic-level deformation of CuxZr100-x metallic glasses under shock loading

NASA Astrophysics Data System (ADS)

Demaske, Brian J.; Wen, Peng; Phillpot, Simon R.; Spearot, Douglas E.

2018-06-01

Plastic deformation mechanisms in CuxZr100-x bulk metallic glasses (MGs) subjected to shock are investigated using molecular dynamics simulations. MGs with Cu compositions between 30 and 70 at. % subjected to shock waves generated via piston velocities that range from 0.125 to 2.0 km/s are considered. In agreement with prior studies, plastic deformation is initiated via formation of localized regions of high von Mises shear strain, known as shear transformation zones (STZs). At low impact velocities, but above the Hugoniot elastic limit, STZ nucleation is dispersed behind the shock front. As impact velocity is increased, STZ nucleation becomes more homogeneous, eventually leading to shock-induced melting, which is identified in this work via high atomic diffusivity. The shear stress necessary to initiate plastic deformation within the shock front is independent of composition at shock intensities near the elastic limit but increases with increasing Cu content at high shock intensities. By contrast, both the flow stress in the plastically deformed MG and the critical shock pressure associated with melting behind the shock front are found to increase with increasing Cu content over the entire range of impact velocities. The evolution of the short-range order in the MG samples during shock wave propagation is analyzed using a polydisperse Voronoi tessellation method. Cu-centered polyhedra with full icosahedral symmetry are found to be most resistant to change under shock loading independent of the MG composition. A saturation is observed in the involvement of select Cu-centered polyhedra in the plastic deformation processes at a piston velocity around 0.75 km/s.

Numerical modeling of axi-symmetrical cold forging process by ``Pseudo Inverse Approach''

NASA Astrophysics Data System (ADS)

Halouani, A.; Li, Y. M.; Abbes, B.; Guo, Y. Q.

2011-05-01

The incremental approach is widely used for the forging process modeling, it gives good strain and stress estimation, but it is time consuming. A fast Inverse Approach (IA) has been developed for the axi-symmetric cold forging modeling [1-2]. This approach exploits maximum the knowledge of the final part's shape and the assumptions of proportional loading and simplified tool actions make the IA simulation very fast. The IA is proved very useful for the tool design and optimization because of its rapidity and good strain estimation. However, the assumptions mentioned above cannot provide good stress estimation because of neglecting the loading history. A new approach called "Pseudo Inverse Approach" (PIA) was proposed by Batoz, Guo et al.. [3] for the sheet forming modeling, which keeps the IA's advantages but gives good stress estimation by taking into consideration the loading history. Our aim is to adapt the PIA for the cold forging modeling in this paper. The main developments in PIA are resumed as follows: A few intermediate configurations are generated for the given tools' positions to consider the deformation history; the strain increment is calculated by the inverse method between the previous and actual configurations. An incremental algorithm of the plastic integration is used in PIA instead of the total constitutive law used in the IA. An example is used to show the effectiveness and limitations of the PIA for the cold forging process modeling.

Twinning-mediated work hardening and texture evolution in CrCoFeMnNi high entropy alloys at cryogenic temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, T. K.; Wu, Z.; Stoica, A. D.

The cryogenic plastic deformation of CrCoFeMnNi high entropy alloy is characterized by three distinct stages based on the change of the work hardening rate. Microstructure and bulk texture at different strain levels were studied by electron backscatter diffraction (EBSD) and neutron diffraction. Our findings indicate that the deformation twins led to the constant work hardening rate at Stage II and resulted in the appearance of <115 >//TA texture component, while the dislocation slip was involved all though the entire plastic deformation. As a result, the twinning-mediated tensile plastic deformation at cryogenic temperature finally induced the strong {111}- < 112 >more » texture component and minor {001} < 110 > texture component accompanied with twinning-induced {115}< 552 > texture component.« less

Twinning-mediated work hardening and texture evolution in CrCoFeMnNi high entropy alloys at cryogenic temperature

DOE PAGES

Liu, T. K.; Wu, Z.; Stoica, A. D.; ...

2017-06-17

The cryogenic plastic deformation of CrCoFeMnNi high entropy alloy is characterized by three distinct stages based on the change of the work hardening rate. Microstructure and bulk texture at different strain levels were studied by electron backscatter diffraction (EBSD) and neutron diffraction. Our findings indicate that the deformation twins led to the constant work hardening rate at Stage II and resulted in the appearance of <115 >//TA texture component, while the dislocation slip was involved all though the entire plastic deformation. As a result, the twinning-mediated tensile plastic deformation at cryogenic temperature finally induced the strong {111}- < 112 >more » texture component and minor {001} < 110 > texture component accompanied with twinning-induced {115}< 552 > texture component.« less

Phyllotactic transformations as plastic deformations of tubular crystals with defects

NASA Astrophysics Data System (ADS)

Beller, Daniel; Nelson, David

Tubular crystals are 2D lattices in cylindrical topologies, which could be realized as assemblies of colloidal particles, and occur naturally in biological microtubules and in single-walled carbon nanotubes. Their geometry can be understood in the language of phyllotaxis borrowed from botany. We study the mechanics of plastic deformations in tubular crystals in response to tensile stress, as mediated by the formation and separation of dislocation pairs in a triangular lattice. Dislocation motion allows the growth of one phyllotactic arrangement at the expense of another, offering a low-energy, stepwise mode of plastic deformation in response to external stresses. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, dislocation glide. The crystal's bending modulus is found to produce simple but important corrections to the tube's deformation mechanics.

Deformation Behavior and Structure of i-Al-Cu-Fe Quasicrystalline Alloy in Vicinity of Nanoindenter Indentation

NASA Astrophysics Data System (ADS)

Shalaeva, E. V.; Selyanin, I. O.; Smirnova, E. O.; Smirnov, S. V.; Novachek, D. D.

2018-02-01

The nanoindentation tests have been carried out for the quasicrystalline polygrain Al62.4Cu25.3Fe12.3 alloy with the icosahedral structure i; the load P-displacement h diagrams have been used to estimate the contributions of plastic deformation (monotonic and intermittent), and the structures of the transverse microscopic sections have been studied in the vicinity of indentations by electron microscopy. It is shown that several systems of deformation bands are formed in the elasto-plastic zone in the vicinity of the indentations along the close-packed planes of the i lattice with the five-fold and two-fold symmetry axes; the bands often begin from cracks and manifest the signs of the dislocation structure. The traces of the phase transformation with the formation of the β-phase areas are observed only in a thin layer under an indenter. The effects of intermittent deformation are up to 50% of the total inelastic deformation and are related to the plastic behavior of the quasicrystal-activation and passage of deformation bands and also the formation of undersurface micro- and nanosized cracks.

Using the two-way shape memory effect of NiTi to control surface texture for cellular mechanotransduction

NASA Astrophysics Data System (ADS)

Liang, Yuan; Qin, Haifeng; Hou, Xiaoning; Doll, Gary L.; Ye, Chang; Dong, Yalin

2018-07-01

Mechanical force can crucially affect form and function of cells, and play critical roles in many diseases. While techniques to conveniently apply mechanical force to cells are limited, we fabricate a surface actuator prototype for cellular mechanotransduction by imparting severe plastic deformation into the surface of shape memory alloy (SMA). Using ultrasonic nanocrystal surface modification (UNSM), a deformation-based surface engineering technique with high controllability, micro surface patterns can be generated on the surface of SMA so that the micro-size cell can conform to the pattern; meanwhile, phase transformation can be induced in the subsurface by severe plastic deformation. By controlling plastic deformation and phase transformation, it is possible to establish a quantitative relation between deformation and temperature. When cells are cultured on the UNSM-treated surface, such surface can dynamically deform in response to external temperature change, and therefore apply controllable mechanical force to cells. Through this study, we demonstrate a novel way to fabricate a low-cost surface actuator that has the potential to be used for high-throughput cellular mechanotransduction.

Plasticity and local adaptation explain lizard cold tolerance.

PubMed

Card, Daren C; Schield, Drew R; Castoe, Todd A

2018-05-01

How does climate variation limit the range of species and what does it take for species to colonize new regions? In this issue of Molecular Ecology, Campbell-Staton et al. () address these broad questions by investigating cold tolerance adaptation in the green anole lizard (Anolis carolinensis) across a latitudinal transect. By integrating physiological data, gene expression data and acclimation experiments, the authors disentangle the mechanisms underlying cold adaptation. They first establish that cold tolerance adaptation in Anolis lizards follows the predictions of the oxygen- and capacity-limited thermal tolerance hypothesis, which states that organisms are limited by temperature thresholds at which oxygen supply cannot meet demand. They then explore the drivers of cold tolerance at a finer scale, finding evidence that northern populations are adapted to cooler thermal regimes and that both phenotypic plasticity and heritable genetic variation contribute to cold tolerance. The integration of physiological and gene expression data further highlights the varied mechanisms that drive cold tolerance adaptation in Anolis lizards, including both supply-side and demand-side adaptations that improve oxygen economy. Altogether, their work provides new insight into the physiological and genetic mechanisms underlying adaptation to new climatic niches and demonstrates that cold tolerance in northern lizard populations is achieved through the synergy of physiological plasticity and local genetic adaptation for thermal performance. © 2018 John Wiley & Sons Ltd.

Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton

NASA Astrophysics Data System (ADS)

Pan, Peng-Zhi; Feng, Xia-Ting; Huang, Xiao-Hua; Cui, Qiang; Zhou, Hui

2009-05-01

This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic material. Mohr-Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and time effects on the behavior of EDZ especially the evolution of permeability around the drift.

Constitutive Law and Flow Mechanism in Diamond Deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong

2012-11-19

Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significantmore » ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.« less

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Superior room-temperature ductility of typically brittle quasicrystals at small sizes

PubMed Central

Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

2016-01-01

The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ∼4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals—dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices. PMID:27515779

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

DOE PAGES

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.; ...

2017-11-30

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Plastic Deformation as a Means to Achieve Stretchable Polymer Semiconductors

NASA Astrophysics Data System (ADS)

O'Connor, Brendan

Developing intrinsically stretchable semiconductors will seamlessly transition traditional devices into a stretchable platform. Polymer semiconductors are inherently soft materials due to the weak van der Waal intermolecular bonding allowing for flexible devices. However, these materials are not typically stretchable and when large strains are applied they either crack or plastically deform. Here, we study the use of repeated plastic deformation as a means of achieving stretchable films. In this talk, critical aspects of polymer semiconductor material selection, morphology and interface properties will be discussed that enable this approach of achieving stretchable films. We show that one can employ high performance donor-acceptor polymer semiconductors that are typically brittle through proper polymer blending to significantly increase ductility to achieve stretchable films. We demonstrate a polymer blend film that can be repeatedly deformed over 65%, while maintaining charge mobility consistently above 0.15 cm2/Vs. During the stretching process we show that the films follow a well-controlled repeated deformation pattern for over 100 stretching cycles.

Mechanisms-based viscoplasticity: Theoretical approach and experimental validation for steel 304L

PubMed Central

Zubelewicz, Aleksander; Oliferuk, Wiera

2016-01-01

We propose a mechanisms-based viscoplasticity approach for metals and alloys. First, we derive a stochastic model for thermally-activated motion of dislocations and, then, introduce power-law flow rules. The overall plastic deformation includes local plastic slip events taken with an appropriate weight assigned to each angle of the plane misorientation from the direction of maximum shear stress. As deformation progresses, the material experiences successive reorganizations of the slip systems. The microstructural evolution causes that a portion of energy expended on plastic deformation is dissipated and the rest is stored in the defect structures. We show that the reorganizations are stable in a homogeneously deformed material. The concept is tested for steel 304L, where we reproduce experimentally obtained stress-strain responses, we construct the Frost-Ashby deformation map and predict the rate of the energy storage. The storage is assessed in terms of synchronized measurements of temperature and displacement distributions on the specimen surface during tensile loading. PMID:27026209

Tensile fracture of coarse-Grained cast austenitic manganese steels

NASA Astrophysics Data System (ADS)

Rittel, D.; Roman, I.

1988-09-01

Tensile fracture of coarse-grained (0.25 to 1 mm) cast austenitic manganese (Hadfield) steels has been investigated. Numerous surface discontinuities nucleate in coarse slip bands, on the heavily deformed surface of tensile specimens. These discontinuities do not propagate radially and final fracture results from central specimen cracking at higher strains. On the microscopic scale, bulk voids nucleate during the entire plastic deformation and they do not coalesce by shear localization (e.g., void-sheet) mechanism. Close voids coalesce by internal necking, whereas distant voids are bridged by means of small voids which nucleate at later stages of the plastic deformation. The high toughness of Hadfield steels is due to their high strain-hardening capacity which stabilizes the plastic deformation, and avoids shear localization and loss of load-bearing capacity. The observed dependence of measured mechanical properties on the specimen’s geometry results from the development of a surface layer which charac-terizes the deformation of this coarse-grained material.

The effect of hydrogenation on strain hardening and deformation mechanisms in <113> single crystals of Hadfield steel

NASA Astrophysics Data System (ADS)

Astafurova, Elena; Maier, Galina; Melnikov, Eugene; Koshovkina, Vera; Moskvina, Valentina; Smirnov, Alexander; Bataev, Vladimir

2015-10-01

The effect of hydrogenation on the strain-hardening behavior and the deformation mechanisms of <113>-oriented single crystals of Hadfield steel was investigated under tension at room temperature. The stages of plastic flow and deformation mechanisms for hydrogen-charged specimens are similar to one in hydrogen-free state: slip → slip + single twinning → slip + multiple twinning. Hydrogen alloying favors to mechanical twinning, micro- and macrolocalization of plastic flow.

Deformation of compound shells under action of internal shock wave loading

NASA Astrophysics Data System (ADS)

Chernobryvko, Marina; Kruszka, Leopold; Avramov, Konstantin

2015-09-01

The compound shells under the action of internal shock wave loading are considered. The compound shell consists of a thin cylindrical shell and two thin parabolic shells at the edges. The boundary conditions in the shells joints satisfy the equality of displacements. The internal shock wave loading is modelled as the surplus pressure surface. This pressure is a function of the shell coordinates and time. The strain rate deformation of compound shell takes place in both the elastic and in plastic stages. In the elastic stage the equations of the structure motions are obtained by the assumed-modes method, which uses the kinetic and potential energies of the cylindrical and two parabolic shells. The dynamic behaviour of compound shells is treated. In local plastic zones the 3-D thermo-elastic-plastic model is used. The deformations are described by nonlinear model. The stress tensor elements are determined using dynamic deformation theory. The deformation properties of materials are influenced by the strain rate behaviour, the influence of temperature parameters, and the elastic-plastic properties of materials. The dynamic yield point of materials and Pisarenko-Lebedev's criterion of destruction are used. The modified adaptive finite differences method of numerical analysis is suggested for those simulations. The accuracy of the numerical simulation is verified on each temporal step of calculation and in the case of large deformation gradients.

Multiscale deformation behavior for multilayered steel by in-situ FE-SEM

NASA Astrophysics Data System (ADS)

Tanaka, Y.; Kishimoto, S.; Yin, F.; Kobayashi, M.; Tomimatsu, T.; Kagawa, K.

2010-03-01

The multi-scale deformation behavior of multi-layered steel during tensile loading was investigated by in-situ FE-SEM observation coupled with multi-scale pattern. The material used was multi-layered steel sheet consisting of martensitic and austenitic stainless steel layers. Prior to in-situ tensile testing, the multi-scale pattern combined with a grid and random dots were fabricated by electron beam lithography on the polished surface in the area of 1 mm2 to facilitate direct observation of multi-scale deformation. Both of the grids with pitches of 10 μm and a random speckle pattern ranging from 200 nm to a few μm sizes were drawn onto the specimen surface at same location. The electron moiré method was applied to measure the strain distribution in the deformed specimens at a millimeter scale and digital images correlation method was applied to measure the in-plane deformation and strain distribution at a micron meter scale acquired before and after at various increments of straining. The results showed that the plastic deformation in the austenitic stainless steel layer was larger than the martensitic steel layer at millimeter scale. However, heterogeneous intrinsic grain-scale plastic deformation was clearly observed and it increased with increasing the plastic deformation.

Effect of Severe Plastic Deformation on Structure and Properties of Al-Sc-Ta and Al-Sc-Ti Alloys

NASA Astrophysics Data System (ADS)

Berezina, Alla; Monastyrska, Tetiana; Davydenko, Olexandr; Molebny, Oleh; Polishchuk, Sergey

2017-03-01

The comparative analysis of the effect of monotonous and non-monotonous severe plastic deformations (SPD) on the structure and properties of aluminum alloys has been carried out. Conventional hydrostatic extrusion (HE) with a constant deformation direction and equal-channel angular hydroextrusion (ECAH) with an abrupt change in the deformation direction were chosen for the cases of monotonous and non-monotonous SPD, respectively. Model cast hypoeutectic Al-0.3%Sc alloys and hypereutectic Al-0.6%Sc alloys with Ta and Ti additives were chosen for studying. It was demonstrated that SPD of the alloys resulted in the segregation of the material into active and inactive zones which formed a banded structure. The active zones were shown to be bands of localized plastic deformation. The distance between zones was found to be independent of the accumulated strain degree and was in the range of 0.6-1 μm. Dynamic recrystallization in the active zones was observed using TEM. The dynamic recrystallization was accompanied by the formation of disclinations, deformation bands, low-angle, and high-angle boundaries, i.e., rotational deformation modes developed. The dynamic recrystallization was more intense during the non-monotonous deformation as compared with the monotonous one, which was confirmed by the reduction of texture degree in the materials after ECAH.

Study on Plastic Deformation Characteristics of Shot Peening of Ni-Based Superalloy GH4079

NASA Astrophysics Data System (ADS)

Zhong, L. Q.; Liang, Y. L.; Hu, H.

2017-09-01

In this paper, the X-ray stress diffractometer, surface roughness tester, field emission scanning electron microscope(SEM), dynamic ultra-small microhardness tester were used to measure the surface residual stress and roughness, topography and surface hardness changes of GH4079 superalloy, which was processed by metallographic grinding, turning, metallographic grinding +shot peening and turning + shot peening. Analysized the effects of shot peening parameters on shot peening plastic deformation features; and the effects of the surface state before shot peening on shot peening plastic deformation characteristics. Results show that: the surface residual compressive stress, surface roughness and surface hardness of GH4079 superalloy were increased by shot peening, in addition, the increment of the surface residual compressive stress, surface roughness and surface hardness induced by shot peening increased with increasing shot peening intensity, shot peening time, shot peening pressure and shot hardness, but harden layer depth was not affected considerably. The more plastic deformation degree of before shot peening surface state, the less increment of the surface residual compressive stress, surface roughness and surface hardness induced by shot peening.

Microstructural record of pressure solution and crystal plastic deformation in carbonate fault rocks from a shallow crustal strike-slip fault, Northern Calcareous Alps (Austria)

NASA Astrophysics Data System (ADS)

Bauer, Helene; Rogowitz, Anna; Grasemann, Benhard; Decker, Kurt

2017-04-01

This study presents microstructural investigations of natural carbonate fault rocks that formed by a suite of different deformation processes, involving hydro-fracturing, dissolution-precipitation creep and cataclasis. Some fault rocks show also clear indications of crystal plastic deformation, which is quite unexpected, as the fault rocks were formed in an upper crustal setting, raising the question of possible strongly localised, low temperature ductile deformation in carbonate rocks. The investigated carbonate fault rocks are from an exhumed, sinistral strike-slip fault at the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Northern Calcareous Alps (Austria). The SEMP fault system formed during eastward lateral extrusion of the Eastern Alps in the Oligocene to Lower Miocene. Based on vitrinite reflectance data form intramontane Teritary basins within the Northern Calcareous Alps, a maximum burial depth of 4 km for the investigated fault segment is estimated. The investigated fault accommodated sinistral slip of several hundreds of meters. Microstructural analysis of fault rocks includes scanning electron microscopy, optical microscopy and electron backscattered diffraction mapping. The data show that fault rocks underwent various stages of evolution including early intense veining (hydro-fracturing) and stylolite formation reworked by localised shear zones. Cross cutting relationship reveals that veins never cross cut clay seams accumulated along stylolites. We conclude that pressure solution processes occured after hydro-fracturing. Clay enriched zones localized further deformation, producing a network of small-scale clay-rich shear zones of up to 1 mm thickness anastomosing around carbonate microlithons, varying from several mm down to some µm in size. Clay seams consist of kaolinit, chlorite and illite matrix and form (sub) parallel zones in which calcite was dissolved. Beside pressure solution, calcite microlithons show also ductile deformation microstructures, including deformation twinning, undulose extinction, subgrain rotation recrystallization and even grain boundary migration. Especially coarse grained calcites from veins localized ductile deformation and record dislocation glide. The investigated fault rocks are excellent examples of frictional, pressure solution and crystal plastic deformation processes. We speculated that crystal plastic deformation typical for higher metamorphic shear zones in marbles, can be either produced under much lower temperature conditions or the temperature necessary for crystal plastic deformation was generated by frictional slip or strain heating within the fault zone.

Metal nanoplates: Smaller is weaker due to failure by elastic instability

NASA Astrophysics Data System (ADS)

Ho, Duc Tam; Kwon, Soon-Yong; Park, Harold S.; Kim, Sung Youb

2017-11-01

Under mechanical loading, crystalline solids deform elastically, and subsequently yield and fail via plastic deformation. Thus crystalline materials experience two mechanical regimes: elasticity and plasticity. Here, we provide numerical and theoretical evidence to show that metal nanoplates exhibit an intermediate mechanical regime that occurs between elasticity and plasticity, which we call the elastic instability regime. The elastic instability regime begins with a decrease in stress, during which the nanoplates fail via global, and not local, deformation mechanisms that are distinctly different from traditional dislocation-mediated plasticity. Because the nanoplates fail via elastic instability, the governing strength criterion is the ideal strength, rather than the yield strength, and as a result, we observe a unique "smaller is weaker" trend. We develop a simple surface-stress-based analytic model to predict the ideal strength of the metal nanoplates, which accurately reproduces the smaller is weaker behavior observed in the atomistic simulations.

Stability of a horizontal well and hydraulic fracture initiation in rocks of the bazhenov formation

NASA Astrophysics Data System (ADS)

Stefanov, Yu. P.; Bakeev, R. A.; Myasnikov, A. V.; Akhtyamova, A. I.; Romanov, A. S.

2017-12-01

Three-dimensional numerical modeling of the formation of the stress-strain state in the vicinity of a horizontal well in weakened rocks of the Bazhenov formation is carried out. The influence of the well orientation and plastic deformation on the stress-strain state and the possibility of hydraulic fracturing are considered. It is shown that the deviation of the well from the direction of maximum compression leads to an increase in plastic deformation and a discrepancy between tangential stresses around the well bore and principle stresses in the surrounding medium. In an elastoplastic medium, an increase in the pressure in the well can lead to a large-scale development of plastic deformation, at which no tensile stresses necessary for hydraulic fracturing according to the classical scheme arise. In this case, there occur plastic expansion and fracture of the well.

Evolution of microstructure and mechanical properties of steel in the course of pressing-drawing

NASA Astrophysics Data System (ADS)

Lezhnev, S. N.; Volokitina, I. E.; Volokitin, A. V.

2017-11-01

The combined continuous pressing-drawing process is proposed after a comprehensive analysis of available plastic structure-forming techniques taking into account the promising trends in their development. This combination of severe plastic deformation in equal-channel step die and drawing allows one to obtain a wire of desired size and shape in the cross section with an ultrafine-grained structure after a few deformation cycles. It also enables initial workpieces of any length to be processed and, therefore, allows one to obtain finished products up to several tens of meters in length. The aim of this study is to investigate the effect of new combined pressing-drawing technique of plastic deformation on the structure and mechanical properties of the steel. These studies have shown that the proposed deformation technique has a significant advantage of the techniques currently used to manufacture a steel wire.

Effect of plastic deformation on the magnetic properties and dislocation luminescence of isotopically enriched silicon {sup 29}Si:B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koplak, O. V.; Shteynman, E. A.; Tereschenko, A. N.

2015-09-15

A correlation between the temperature dependences of the D1-line intensity of dislocation luminescence and the magnetic moment of plastically deformed isotopically enriched crystals {sup 29}Si:B is found. It is established that the magnetic susceptibility of the deformed crystals obtained by integration of the spectra of electron spin resonance and the D1-line intensity undergo similar nonmonotonic variations with temperature varying in the range of 20–32 K.

Numerical simulation of elasto-plastic deformation of composites: evolution of stress microfields and implications for homogenization models

NASA Astrophysics Data System (ADS)

González, C.; Segurado, J.; LLorca, J.

2004-07-01

The deformation of a composite made up of a random and homogeneous dispersion of elastic spheres in an elasto-plastic matrix was simulated by the finite element analysis of three-dimensional multiparticle cubic cells with periodic boundary conditions. "Exact" results (to a few percent) in tension and shear were determined by averaging 12 stress-strain curves obtained from cells containing 30 spheres, and they were compared with the predictions of secant homogenization models. In addition, the numerical simulations supplied detailed information of the stress microfields, which was used to ascertain the accuracy and the limitations of the homogenization models to include the nonlinear deformation of the matrix. It was found that secant approximations based on the volume-averaged second-order moment of the matrix stress tensor, combined with a highly accurate linear homogenization model, provided excellent predictions of the composite response when the matrix strain hardening rate was high. This was not the case, however, in composites which exhibited marked plastic strain localization in the matrix. The analysis of the evolution of the matrix stresses revealed that better predictions of the composite behavior can be obtained with new homogenization models which capture the essential differences in the stress carried by the elastic and plastic regions in the matrix at the onset of plastic deformation.

Understanding deformation mechanisms during powder compaction using principal component analysis of compression data.

PubMed

Roopwani, Rahul; Buckner, Ira S

2011-10-14

Principal component analysis (PCA) was applied to pharmaceutical powder compaction. A solid fraction parameter (SF(c/d)) and a mechanical work parameter (W(c/d)) representing irreversible compression behavior were determined as functions of applied load. Multivariate analysis of the compression data was carried out using PCA. The first principal component (PC1) showed loadings for the solid fraction and work values that agreed with changes in the relative significance of plastic deformation to consolidation at different pressures. The PC1 scores showed the same rank order as the relative plasticity ranking derived from the literature for common pharmaceutical materials. The utility of PC1 in understanding deformation was extended to binary mixtures using a subset of the original materials. Combinations of brittle and plastic materials were characterized using the PCA method. The relationships between PC1 scores and the weight fractions of the mixtures were typically linear showing ideal mixing in their deformation behaviors. The mixture consisting of two plastic materials was the only combination to show a consistent positive deviation from ideality. The application of PCA to solid fraction and mechanical work data appears to be an effective means of predicting deformation behavior during compaction of simple powder mixtures. Copyright © 2011 Elsevier B.V. All rights reserved.

Microstructure and Plastic Deformation of the As-Welded Invar Fusion Zones

NASA Astrophysics Data System (ADS)

Yao, D. J.; Zhou, D. R.; Xu, P. Q.; Lu, F. G.

2017-05-01

The as-welded Invar fusion zones were fabricated between cemented carbides and carbon steel using a Fe-Ni Invar interlayer and laser welding method. Three regions in the as-welded Invar fusion zones were defined to compare microstructures, and these were characterized and confirmed by scanning electron microscopy and X-ray diffractometry. The structure and plastic deformation mechanism for initial Invar Fe-Ni alloys and the as-welded Invar fusion zones are discussed. (1) After undergoing high-temperature thermal cycles, the microstructure of the as-welded Invar fusion zones contains γ-(Fe, Ni) solid solution (nickel dissolving in γ-Fe) with a face-centered cubic (fcc) crystal structure and mixed carbides (eutectic colonies, mixed carbides between two adjacent grains). The mixed carbides exhibited larger, coarser eutectic microstructures with a decrease in welding speed and an increase in heat input. (2) The structure of the initial Invar and the as-welded Invar is face-centered cubic γ-(Fe, Ni). (3) The as-welded Invar has a larger plastic deformation than initial Invar with an increase in local strain field and dislocation density. Slip deformation is propagated along the (111) plane. This finding helps us to understand microstructure and the formation of dislocation and plastic deformation when the Invar Fe-Ni alloy undergoes a high-temperature process.

Spring back of infinite honeycomb sheets beyond plastic deformation

NASA Astrophysics Data System (ADS)

Bonfanti, A.; Bhaskar, A.

2015-02-01

Cellular structures are promising for applications where high stiffness and strength are required with the minimal use of material. They are often used in applications where the plastic deformation plays an important role, such as those involving crashworthiness, energy absorption, and stents. The elastic analysis of a honeycomb sheet has been carried out in the past [1]. The present analysis extends this classical work in the elasto-plastic regime. Recoil analysis due to elastic recovery is absent from the published literature. This work aims to develop an analytical model to calculate the spring back for a simplified case, that of an infinite honeycomb sheet. An elastic-perfectly plastic material model is assumed. The recoil for a clamped beam with a load and moment applied at the free edge is analytically calculated first. This is carried out by relating the stress distribution of the cross section to the final deformed shape. The part corresponding to the elastic contribution is subsequently subtracted in order to obtain the final configuration after the external load is removed. This simple elasto-plastic analysis is then incorporated into the analysis of an infinite sheet made of uniform hexagonal cells. The translational symmetry of the lattice is exploited along with the analysis of a beam under tip loading through to plastic stage and recoil. The final shape of the struts upon the removal of the remote stress is completely determined by the plastic deformation which cannot be recovered. The expression for the beam thus obtained is then used to build an analytical model for an infinite honeycomb sheet loaded in both directions.

The use of ion beam cleaning to obtain high quality cold welds with minimal deformation

NASA Technical Reports Server (NTRS)

Sater, B. L.; Moore, T. J.

1978-01-01

This paper describes a variation of cold welding which utilizes an ion beam to clean mating surfaces prior to joining in a vacuum environment. High quality solid state welds were produced with minimal deformation. Due to experimental fixture limitation in applying pressure work has been limited to a few low yield strength materials.

Occurrence of cohesion of metals during combined plastic deformation

NASA Technical Reports Server (NTRS)

Aynbinder, S. G.; Klokova, E. F.

1980-01-01

Experiments were conducted to study the cohesion of metals with surface films of varying thickness and hardness. It was established that the deformation necessary for the occurrence of cohesion is determined by the correlation of mechanical properties of the films and the base metal. The greater the relative hardness of the film the lower the deformation necessary for the occurrence of cohesion. The films are as plastic as the base metal prevent cohesion, since in this case it is impossible for sections of metal to appear that are free of contaminants. The physical perculiarities of metals that determine their capability for coalescence under conditions of dry friction are the relative hardness and plasticity of the oxide films formed on their surface under atmospheric conditions.

The noncontinuum crack tip deformation behavior of surface microcracks

NASA Astrophysics Data System (ADS)

Morris, W. L.

1980-07-01

The crack tip opening displacement (CTOD) of small surface fatigue cracks (lengths of the grain size) in Al 2219-T851 depends upon the location of a crack relative to the grain boundaries. Both CTOD and crack tip closure stress are greatest when the crack tip is a large distance from the next grain boundary in the direction of crack propagation. Contrary to behavioral trends predicted by continuum fracture mechanics, crack length has no detectable effect on the contribution of plastic deformation to CTOD. It is apparent from these observations that the region of significant plastic deformation is confined by the grain boundaries, resulting in a plastic zone size that is insensitive to crack length and to external load.

Discrete dislocation plasticity analysis of loading rate-dependent static friction.

PubMed

Song, H; Deshpande, V S; Van der Giessen, E

2016-08-01

From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length [Formula: see text], the onset of sliding is fully controlled by adhesion while for large contact length [Formula: see text], the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.

Electromigration-induced Plasticity and Texture in Cu Interconnects

NASA Astrophysics Data System (ADS)

Budiman, A. S.; Hau-Riege, C. S.; Besser, P. R.; Marathe, A.; Joo, Y.-C.; Tamura, N.; Patel, J. R.; Nix, W. D.

2007-10-01

Plastic deformation has been observed in damascene Cu interconnect test structures during an in-situ electromigration experiment and before the onset of visible microstructural damage (ie. voiding) using a synchrotron technique of white beam X-ray microdiffraction. We show here that the extent of this electromigration-induced plasticity is dependent on the texture of the Cu grains in the line. In lines with strong <111> textures, the extent of plastic deformation is found to be relatively large compared to our plasticity results in the previous study[1] using another set of Cu lines with weaker textures. This is consistent with our earlier observation that the occurrence of plastic deformation in a given grain can be strongly correlated with the availability of a <112> direction of the crystal in the proximity of the direction of the electron flow in the line (within an angle of 10°). In <111> out-of-plane oriented grains in a damascene interconnect scheme, the crystal plane facing the sidewall tends to be a {110} plane,[2-4] so as to minimize interfacial energy. Therefore, it is deterministic rather than probabilistic that the <111> grains will have a <112> direction nearly parallel to the direction of electron flow. Thus, strong <111> textures lead to more plasticity, as we observe.

Alternate approach for calculating hardness based on residual indentation depth: Comparison with experiments

NASA Astrophysics Data System (ADS)

Ananthakrishna, G.; K, Srikanth

2018-03-01

It is well known that plastic deformation is a highly nonlinear dissipative irreversible phenomenon of considerable complexity. As a consequence, little progress has been made in modeling some well-known size-dependent properties of plastic deformation, for instance, calculating hardness as a function of indentation depth independently. Here, we devise a method of calculating hardness by calculating the residual indentation depth and then calculate the hardness as the ratio of the load to the residual imprint area. Recognizing the fact that dislocations are the basic defects controlling the plastic component of the indentation depth, we set up a system of coupled nonlinear time evolution equations for the mobile, forest, and geometrically necessary dislocation densities. Within our approach, we consider the geometrically necessary dislocations to be immobile since they contribute to additional hardness. The model includes dislocation multiplication, storage, and recovery mechanisms. The growth of the geometrically necessary dislocation density is controlled by the number of loops that can be activated under the contact area and the mean strain gradient. The equations are then coupled to the load rate equation. Our approach has the ability to adopt experimental parameters such as the indentation rates, the geometrical parameters defining the Berkovich indenter, including the nominal tip radius. The residual indentation depth is obtained by integrating the Orowan expression for the plastic strain rate, which is then used to calculate the hardness. Consistent with the experimental observations, the increasing hardness with decreasing indentation depth in our model arises from limited dislocation sources at small indentation depths and therefore avoids divergence in the limit of small depths reported in the Nix-Gao model. We demonstrate that for a range of parameter values that physically represent different materials, the model predicts the three characteristic features of hardness, namely, increase in the hardness with decreasing indentation depth, and the linear relation between the square of the hardness and the inverse of the indentation depth, for all but 150 nm, deviating for smaller depths. In addition, we also show that it is straightforward to obtain optimized parameter values that give good fit to the hardness data for polycrystalline cold worked copper and single crystals of silver.

Characterization of plastic deformation and chemical reaction in titanium-polytetrafluoroethylene mixture

NASA Astrophysics Data System (ADS)

Davis, Jeffery Jon

1998-09-01

The subject of this dissertation is the deformation process of a single metal - polymer system (titanium - polytetrafluoroethylene) and how this process leads to initiation of chemical reaction. Several different kinds of experiments were performed to characterize the behavior of this material to shock and impact. These mechanical conditions induce a rapid plastic deformation of the sample. All of the samples tested had an initial porosity which increased the plastic flow condition. It is currently believed that during the deformation process two important conditions occur: removal of the oxide layer from the metal and decomposition of the polymer. These conditions allow for rapid chemical reaction. The research from this dissertation has provided insight into the complex behavior of plastic deformation and chemical reactions in titanium - polytetrafluoroethylene (PTFE, Teflon). A hydrodynamic computational code was used to model the plastic flow for correlation with the results from the experiments. The results from this work are being used to develop an ignition and growth model for metal/polymer systems. Three sets of experiments were used to examine deformation of the 80% Ti and 20% Teflon materials: drop- weight, gas gun, and split-Hopkinson pressure bar. Recovery studies included post shot analysis of the samples using x-ray diffraction. Lagrangian hydrocode DYNA2D modeling of the drop-weight tests was performed for comparison with experiments. One of the reactions know to occur is Ti + C → TiC (s) which results in an exothermic release. However, the believed initial reactions occur between Ti and fluorine which produces TixFy gases. The thermochemical code CHEETAH was used to investigate the detonation products and concentrations possible during Ti - Teflon reaction. CHEETAH shows that the Ti - fluorine reactions are thermodynamically favorable. This research represents the most comprehensive to date study of deformation induced chemical reaction in metal/polymers.

Simultaneous increase in the strength, plasticity, and corrosion resistance of an ultrafine-grained Ti-4Al-2V pseudo-alpha-titanium alloy

NASA Astrophysics Data System (ADS)

Chuvil'deev, V. N.; Kopylov, V. I.; Nokhrin, A. V.; Bakhmet'ev, A. M.; Sandler, N. G.; Kozlova, N. A.; Tryaev, P. V.; Tabachkova, N. Yu.; Mikhailov, A. S.; Ershova, A. V.; Gryaznov, M. Yu.; Chegurov, M. K.; Sysoev, A. N.; Smirnova, E. S.

2017-05-01

The influence of severe plastic deformation on the structural-phase state of grain boundaries in a Ti-4Al-2V (commercial PT3V grade) pseudo-alpha-titanium alloy has been studied. It is established that increase in the strength, plasticity, and corrosion resistance of this alloy is related to the formation of an ultrafine- grained structure. In particular, it is shown that an increase in the resistance to hot-salt intergranular corrosion is due to diffusion-controlled redistribution of aluminum and vanadium atoms at the grain boundaries of titanium formed during thermal severe plastic deformation.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie; Zheng, Jie

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie; Zheng, Jie

2016-11-01

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie

2017-11-01

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Deformation-driven diffusion and plastic flow in amorphous granular pillars.

PubMed

Li, Wenbin; Rieser, Jennifer M; Liu, Andrea J; Durian, Douglas J; Li, Ju

2015-06-01

We report a combined experimental and simulation study of deformation-induced diffusion in compacted quasi-two-dimensional amorphous granular pillars, in which thermal fluctuations play a negligible role. The pillars, consisting of bidisperse cylindrical acetal plastic particles standing upright on a substrate, are deformed uniaxially and quasistatically by a rigid bar moving at a constant speed. The plastic flow and particle rearrangements in the pillars are characterized by computing the best-fit affine transformation strain and nonaffine displacement associated with each particle between two stages of deformation. The nonaffine displacement exhibits exponential crossover from ballistic to diffusive behavior with respect to the cumulative deviatoric strain, indicating that in athermal granular packings, the cumulative deviatoric strain plays the role of time in thermal systems and drives effective particle diffusion. We further study the size-dependent deformation of the granular pillars by simulation, and find that different-sized pillars follow self-similar shape evolution during deformation. In addition, the yield stress of the pillars increases linearly with pillar size. Formation of transient shear lines in the pillars during deformation becomes more evident as pillar size increases. The width of these elementary shear bands is about twice the diameter of a particle, and does not vary with pillar size.

The effects of cold rolling and the subsequent heat treatments on the shape memory and the superelasticity characteristics of Cu73Al16Mn11 shape memory alloy

NASA Astrophysics Data System (ADS)

Babacan, N.; Ma, J.; Turkbas, O. S.; Karaman, I.; Kockar, B.

2018-01-01

In the present study, the effect of thermo-mechanical treatments on the shape memory and the superelastic characteristics of Cu73Al16Mn11 (at%) shape memory alloy were investigated. 10%, 50% and 70% cold rolling and subsequent heat treatment processes were conducted to achieve strengthening via grain size refinement. 70% grain size reduction compared to the homogenized condition was obtained using 70% cold rolling and subsequent recrystallization heat treatment technique. Moreover, 10% cold rolling was applied to homogenized specimen to reveal the influence of the low percentage cold rolling reduction with no heat treatment on shape memory properties of Cu73Al16Mn11 (at%) alloy. Stress free transformation temperatures, monotonic tension and superelasticity behaviors of these samples were compared with those of the as-aged sample. Isobaric heating-cooling experiments were also conducted to see the dimensional stability of the samples as a function of applied stress. The 70% grain-refined sample exhibited better dimensional stability showing reduced residual strain levels upon thermal cycling under constant stress compared with the as-aged material. However, no improvement was achieved with grain size reduction in the superelasticity experiments. This distinctive observation was attributed to the difference in the magnitude of the stress levels achieved during two different types of experiments which were the isobaric heating-cooling and superelasticity tests. Intergranular fracture due to the stress concentration overcame the strengthening effect via grain refinement in the superelasticity tests at higher stress values. On the other hand, the strength of the material and resistance of material against plastic deformation upon phase transformation were increased as a result of the grain refinement at lower stress values in the isobaric heating-cooling experiments.

Measurement of installation deformation of the acetabulum during prosthetic replacement of a hip joint using digital image correlation

NASA Astrophysics Data System (ADS)

Lei, Dong; Bai, Pengxiang; Zhu, Feipeng

2018-01-01

Nowadays, acetabulum prosthesis replacement is widely used in clinical medicine. However, there is no efficient way to evaluate the implantation effect of the prosthesis. Based on a modern photomechanics technique called digital image correlation (DIC), the evaluation method of the installation effect of the acetabulum was established during a prosthetic replacement of a hip joint. The DIC method determines strain field by comparing the speckle images between the undeformed sample and the deformed counterpart. Three groups of experiments were carried out to verify the feasibility of the DIC method on the acetabulum installation deformation test. Experimental results indicate that the installation deformation of acetabulum generally includes elastic deformation (corresponding to the principal strain of about 1.2%) and plastic deformation. When the installation angle is ideal, the plastic deformation can be effectively reduced, which could prolong the service life of acetabulum prostheses.

Effects of anisotropy and irradiation on the deformation behavior of Zircaloy 2. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pelloux, R.M.; Ballinger, R.; Lucas, G.

1979-01-01

An experimental program investigated the effects of texture anisotropy and irradiation on the mechanical behavior of Zircaloy-2. Short time and time dependent mechanical behavior were considered. Irradiation effects were simulated through the use of 4.75 MeV protons. The temperature ranges investigated were 298/sup 0/K and 573 to 673/sup 0/K. Both cold worked-stress relieved and annealed material were used in this experimental program. Short time yield behavior of different crystallographic textures was determined by uniaxial and plane strain tests in the temperature range 298/sup 0/K and 573 to 673/sup 0/K. Monotonic flow loci were constructed for each texture. Yield behavior ismore » a strong function of the crystallographic texture number f at all temperatures investigated. The rotation of texture with increasing plastic strain was investigated as a function of initial texture at 298/sup 0/K and 623/sup 0/K. The rate of texture rotation df/epsilon/sub p/ was found to be a unique function of the initial texture for plastic strains less than 0.08. Time dependent mechanical behavior was investigated in the range 573 to 673/sup 0/K using constant load creep and stress relaxation tests. The tensile creep strength is proportional to the resolved fraction of basal poles in the test direction. In variable stress and temperature tests, the time-hardening rule was found to be inapplicable. The strain-hardening rule was applied with success to data obtained at temperatures less than or equal to 648/sup 0/K. Irradiation creep tests were conducted in vacuum at 598/sup 0/K and 102 to 241 MPa on 80..mu..m thick Zircaloy-2 foil specimens in both the recrystallized and cold worked-stress relieved condition. In the irradiation creep tests irradiation hardening and enhanced irradiation creep were observed. Radiation hardening effects were significant in annealed material but were attenuated in cold worked-stress relieved material.« less

Modeling multiscale evolution of numerous voids in shocked brittle material.

PubMed

Yu, Yin; Wang, Wenqiang; He, Hongliang; Lu, Tiecheng

2014-04-01

The influence of the evolution of numerous voids on macroscopic properties of materials is a multiscale problem that challenges computational research. A shock-wave compression model for brittle material, which can obtain both microscopic evolution and macroscopic shock properties, was developed using discrete element methods (lattice model). Using a model interaction-parameter-mapping procedure, qualitative features, as well as trends in the calculated shock-wave profiles, are shown to agree with experimental results. The shock wave splits into an elastic wave and a deformation wave in porous brittle materials, indicating significant shock plasticity. Void collapses in the deformation wave were the natural reason for volume shrinkage and deformation. However, media slippage and rotation deformations indicated by complex vortex patterns composed of relative velocity vectors were also confirmed as an important source of shock plasticity. With increasing pressure, the contribution from slippage deformation to the final plastic strain increased. Porosity was found to determine the amplitude of the elastic wave; porosity and shock stress together determine propagation speed of the deformation wave, as well as stress and strain on the final equilibrium state. Thus, shock behaviors of porous brittle material can be systematically designed for specific applications.

Deformation behavior of human enamel and dentin-enamel junction under compression.

PubMed

Zaytsev, Dmitry; Panfilov, Peter

2014-01-01

Deformation behavior under uniaxial compression of human enamel and dentin-enamel junction (DEJ) is considered in comparison with human dentin. This deformation scheme allows estimating the total response from all levels of the hierarchical composite material in contrast with the indentation, which are limited by the mesoscopic and microscopic scales. It was shown for the first time that dental enamel is the strength (up to 1850MPa) hard tissue, which is able to consider some elastic (up to 8%) and plastic (up to 5%) deformation under compression. In so doing, it is almost undeformable substance under the creep condition. Mechanical properties of human enamel depend on the geometry of sample. Human dentin exhibits the similar deformation behavior under compression, but the values of its elasticity (up to 40%) and plasticity (up to 18%) are much more, while its strength (up to 800MPa) is less in two times. Despite the difference in mechanical properties, human enamel is able to suppress the cracking alike dentin. Deformation behavior under the compression of the samples contained DEJ as the same to dentin. This feature allows a tooth to be elastic-plastic (as dentin) and wear resistible (as enamel), simultaneously. © 2013 Elsevier B.V. All rights reserved.

Transfer of a cold atmospheric pressure plasma jet through a long flexible plastic tube

NASA Astrophysics Data System (ADS)

Kostov, Konstantin G.; Machida, Munemasa; Prysiazhnyi, Vadym; Honda, Roberto Y.

2015-04-01

This work proposes an experimental configuration for the generation of a cold atmospheric pressure plasma jet at the downstream end of a long flexible plastic tube. The device consists of a cylindrical dielectric chamber where an insulated metal rod that serves as high-voltage electrode is inserted. The chamber is connected to a long (up to 4 m) commercial flexible plastic tube, equipped with a thin floating Cu wire. The wire penetrates a few mm inside the discharge chamber, passes freely (with no special support) along the plastic tube and terminates a few millimeters before the tube end. The system is flushed with Ar and the dielectric barrier discharge (DBD) is ignited inside the dielectric chamber by a low frequency ac power supply. The gas flow is guided by the plastic tube while the metal wire, when in contact with the plasma inside the DBD reactor, acquires plasma potential. There is no discharge inside the plastic tube, however an Ar plasma jet can be extracted from the downstream tube end. The jet obtained by this method is cold enough to be put in direct contact with human skin without an electric shock. Therefore, by using this approach an Ar plasma jet can be generated at the tip of a long plastic tube far from the high-voltage discharge region, which provides the safe operation conditions and device flexibility required for medical treatment.

Semantic modeling of plastic deformation of polycrystalline rock

NASA Astrophysics Data System (ADS)

Babaie, Hassan A.; Davarpanah, Armita

2018-02-01

We have developed the first iteration of the Plastic Rock Deformation (PRD) ontology by modeling the semantics of a selected set of deformational processes and mechanisms that produce, reconfigure, displace, and/or consume the material components of inhomogeneous polycrystalline rocks. The PRD knowledge model also classifies and formalizes the properties (relations) that hold between instances of the dynamic physical and chemical processes and the rock components, the complex physio-chemical, mathematical, and informational concepts of the plastic rock deformation system, the measured or calculated laboratory testing conditions, experimental procedures and protocols, the state and system variables, and the empirical flow laws that define the inter-relationships among the variables. The ontology reuses classes and properties from several existing ontologies that are built for physics, chemistry, biology, and mathematics. With its flexible design, the PRD ontology is well positioned to incrementally develop into a model that more fully represents the knowledge of plastic deformation of polycrystalline rocks in the future. The domain ontology will be used to consistently annotate varied data and information related to the microstructures and the physical and chemical processes that produce them at different spatial and temporal scales in the laboratory and in the solid Earth. The PRDKB knowledge base, when built based on the ontology, will help the community of experimental structural geologists and metamorphic petrologists to coherently and uniformly distribute, discover, access, share, and use their data through automated reasoning and integration and query of heterogeneous experimental deformation data that originate from autonomous rock testing laboratories.

Influence of Plastic Deformation on Martensitic Transformation During Hot Stamping of Complex Structure Auto Parts

NASA Astrophysics Data System (ADS)

Shen, Yuhan; Song, Yanli; Hua, Lin; Lu, Jue

2017-04-01

The ultra-high strength steel auto parts manufactured by hot stamping are widely applied for weight reduction and safety improvement. During the hot stamping process, hot forming and quenching are performed in one step wherein plastic deformation and phase transformation simultaneously take place and affect each other. Thereinto, the influence of deformation on martensitic transformation is of great importance. In the present paper, the influence of plastic deformation on martensitic transformation during hot stamping of complex structure auto parts was investigated. For this purpose, a B-pillar reinforced panel in B1500HS steel was manufactured by hot stamping, and the process was simulated by finite element software based on a thermo-mechanical-metallurgical coupled model. Considering various deformation degrees, the microstructures and mechanical properties at four typical locations of the hot stamped B-pillar reinforced panel were detected. The results show that the martensitic content and the microhardness increase with the increase in the deformation amount. There are two reasons causing this phenomenon: (1) the increase in mechanical driving force and (2) the increased probability of the martensitic nucleation at crystal defects. The x-ray diffraction analysis indicates the carbon enrichment in retained austenite which results from the carbon diffusion during the low-carbon martensite formation. Furthermore, the carbon content decreases with the increase in the deformation amount, because the deformation of austenite suppresses the carbon diffusion.

Effect of Severe Plastic Deformation on Structure and Properties of Al-Sc-Ta and Al-Sc-Ti Alloys.

PubMed

Berezina, Alla; Monastyrska, Tetiana; Davydenko, Olexandr; Molebny, Oleh; Polishchuk, Sergey

2017-12-01

The comparative analysis of the effect of monotonous and non-monotonous severe plastic deformations (SPD) on the structure and properties of aluminum alloys has been carried out. Conventional hydrostatic extrusion (HE) with a constant deformation direction and equal-channel angular hydroextrusion (ECAH) with an abrupt change in the deformation direction were chosen for the cases of monotonous and non-monotonous SPD, respectively. Model cast hypoeutectic Al-0.3%Sc alloys and hypereutectic Al-0.6%Sc alloys with Ta and Ti additives were chosen for studying. It was demonstrated that SPD of the alloys resulted in the segregation of the material into active and inactive zones which formed a banded structure. The active zones were shown to be bands of localized plastic deformation. The distance between zones was found to be independent of the accumulated strain degree and was in the range of 0.6-1 μm. Dynamic recrystallization in the active zones was observed using TEM. The dynamic recrystallization was accompanied by the formation of disclinations, deformation bands, low-angle, and high-angle boundaries, i.e., rotational deformation modes developed. The dynamic recrystallization was more intense during the non-monotonous deformation as compared with the monotonous one, which was confirmed by the reduction of texture degree in the materials after ECAH.

PROCESS SIMULATION OF COLD PRESSING OF ARMSTRONG CP-Ti POWDERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabau, Adrian S; Gorti, Sarma B; Peter, William H

A computational methodology is presented for the process simulation of cold pressing of Armstrong CP-Ti Powders. The computational model was implemented in the commercial finite element program ABAQUSTM. Since the powder deformation and consolidation is governed by specific pressure-dependent constitutive equations, several solution algorithms were developed for the ABAQUS user material subroutine, UMAT. The solution algorithms were developed for computing the plastic strain increments based on an implicit integration of the nonlinear yield function, flow rule, and hardening equations that describe the evolution of the state variables. Since ABAQUS requires the use of a full Newton-Raphson algorithm for the stress-strainmore » equations, an algorithm for obtaining the tangent/linearization moduli, which is consistent with the return-mapping algorithm, also was developed. Numerical simulation results are presented for the cold compaction of the Ti powders. Several simulations were conducted for cylindrical samples with different aspect ratios. The numerical simulation results showed that for the disk samples, the minimum von Mises stress was approximately half than its maximum value. The hydrostatic stress distribution exhibits a variation smaller than that of the von Mises stress. It was found that for the disk and cylinder samples the minimum hydrostatic stresses were approximately 23 and 50% less than its maximum value, respectively. It was also found that the minimum density was noticeably affected by the sample height.« less

Deep focus earthquakes in the laboratory

NASA Astrophysics Data System (ADS)

Schubnel, Alexandre; Brunet, Fabrice; Hilairet, Nadège; Gasc, Julien; Wang, Yanbin; Green, Harry W., II

2014-05-01

While the existence of deep earthquakes have been known since the 1920's, the essential mechanical process responsible for them is still poorly understood and remained one of the outstanding unsolved problems of geophysics and rock mechanics. Indeed, deep focus earthquake occur in an environment fundamentally different from that of shallow (<100 km) earthquakes. As pressure and temperature increase with depth however, intra-crystalline plasticity starts to dominate the deformation regime so that rocks yield by plastic flow rather than by brittle fracturing. Olivine phase transitions have provided an attractive alternative mechanism for deep focus earthquakes. Indeed, the Earth mantle transition zone (410-700km) is the locus of the two successive polymorphic transitions of olivine. Such scenario, however, runs into the conceptual barrier of initiating failure in a pressure (P) and temperature (T) regime where deviatoric stress relaxation is expected to be achieved through plastic flow. Here, we performed laboratory deformation experiments on Germanium olivine (Mg2GeO4) under differential stress at high pressure (P=2-5GPa) and within a narrow temperature range (T=1000-1250K). We find that fractures nucleate at the onset of the olivine to spinel transition. These fractures propagate dynamically (i.e. at a non-negligible fraction of the shear wave velocity) so that intense acoustic emissions are generated. Similar to deep-focus earthquakes, these acoustic emissions arise from pure shear sources, and obey the Gutenberg-Richter law without following Omori's law. Microstructural observations prove that dynamic weakening likely involves superplasticity of the nanocrystalline spinel reaction product at seismic strain rates. Although in our experiments the absolute stress value remains high compared to stresses expected within the cold core of subducted slabs, the observed stress drops are broadly consistent with those calculated for deep earthquakes. Constant differential stress conditions at failure over a wide range of confinement (2-5GPa) strongly suggest that transformational faulting is largely independent of normal stress and thus involves non-frictional processes. We suggest that rupture nucleation is controlled by dislocation density and spinel nucleation kinetics, while propagation is controlled by superplastic flow. High stress and high dislocation density conditions can be met in a cold subducting slab full of metastable olivine, due to stress concentrations at the micro and mesoscopic scales because of buckling, folding, and/or inherited fractures. This is particularly true in the Tonga-Kermadec region for instance, for which the largest catalog of deep focus earthquake is available.

The relationship between strain geometry and geometrically necessary dislocations

NASA Astrophysics Data System (ADS)

Hansen, Lars; Wallis, David

2016-04-01

The kinematics of past deformations are often a primary goal in structural analyses of strained rocks. Details of the strain geometry, in particular, can help distinguish hypotheses about large-scale tectonic phenomena. Microstructural indicators of strain geometry have been heavily utilized to investigate large-scale kinematics. However, many of the existing techniques require structures for which the initial morphology is known, and those structures must undergo the same deformation as imposed macroscopically. Many deformed rocks do not exhibit such convenient features, and therefore the strain geometry is often difficult (if not impossible) to ascertain. Alternatively, crystallographic textures contain information about the strain geometry, but the influence of strain geometry can be difficult to separate from other environmental factors that might affect slip system activity and therefore the textural evolution. Here we explore the ability for geometrically necessary dislocations to record information about the deformation geometry. It is well known that crystallographic slip due to the motion of dislocations yields macroscopic plastic strain, and the mathematics are established to relate dislocation glide on multiple slip systems to the strain tensor of a crystal. This theoretical description generally assumes that dislocations propagate across the entire crystal. However, at any point during the deformation, dislocations are present that have not fully transected the crystal, existing either as free dislocations or as dislocations organized into substructures like subgrain boundaries. These dislocations can remain in the lattice after deformation if the crystal is quenched sufficiently fast, and we hypothesize that this residual dislocation population can be linked to the plastic strain geometry in a quantitative manner. To test this hypothesis, we use high-resolution electron backscatter diffraction to measure lattice curvatures in experimentally deformed single crystals and aggregates of olivine for which the strain geometry is known. Tested geometries include constrictional strain, flattening strain, and plane strain. We use measured lattice curvatures to calculate the densities and spatial distributions of geometrically necessary dislocations. Dislocation densities are calculated for each of the major dislocation types in olivine. These densities are then used to estimate the plastic strain geometry under the assumption that the population of geometrically necessary dislocations accurately represents the relative activity of different dislocations during deformation. Our initial results demonstrate compelling relationships between the imposed strain geometry and the calculated plastic strain geometry. In addition, the calculated plastic strain geometry is linked to the distribution of crystallographic orientations, giving insight into the nature of plastic anisotropy in textured olivine aggregates. We present this technique as a new microstructural tool for assessing the kinematic history of deformed rocks.

Plastic Deformation of Micromachined Silicon Diaphragms with a Sealed Cavity at High Temperatures

PubMed Central

Ren, Juan; Ward, Michael; Kinnell, Peter; Craddock, Russell; Wei, Xueyong

2016-01-01

Single crystal silicon (SCS) diaphragms are widely used as pressure sensitive elements in micromachined pressure sensors. However, for harsh environments applications, pure silicon diaphragms are hardly used because of the deterioration of SCS in both electrical and mechanical properties. To survive at the elevated temperature, the silicon structures must work in combination with other advanced materials, such as silicon carbide (SiC) or silicon on insulator (SOI), for improved performance and reduced cost. Hence, in order to extend the operating temperatures of existing SCS microstructures, this work investigates the mechanical behavior of pressurized SCS diaphragms at high temperatures. A model was developed to predict the plastic deformation of SCS diaphragms and was verified by the experiments. The evolution of the deformation was obtained by studying the surface profiles at different anneal stages. The slow continuous deformation was considered as creep for the diaphragms with a radius of 2.5 mm at 600 °C. The occurrence of plastic deformation was successfully predicted by the model and was observed at the operating temperature of 800 °C and 900 °C, respectively. PMID:26861332

Design of an Orthodontic Torque Simulator for Measurement of Bracket Deformation

NASA Astrophysics Data System (ADS)

Melenka, G. W.; Nobes, D. S.; Major, P. W.; Carey, J. P.

2013-12-01

The design and testing of an orthodontic torque simulator that reproduces the effect of archwire rotation on orthodontic brackets is described. This unique device is capable of simultaneously measuring the deformation and loads applied to an orthodontic bracket due to archwire rotation. Archwire rotation is used by orthodontists to correct the inclination of teeth within the mouth. This orthodontic torque simulator will provide knowledge of the deformation and loads applied to orthodontic bracket that will aide clinicians by describing the effect of archwire rotation on brackets. This will also impact that design on new archwirebracket systems by providing an assessment of performance. Deformation of the orthodontic bracket tie wings is measured using a digital image correlation process to measure elastic and plastic deformation. The magnitude of force and moments applied to the bracket though the archwire is also measured using a six-axis load cell. Initial tests have been performed on two orthodontic brackets of varying geometry to demonstrate the measurement capability of the orthodontic torque simulator. The demonstration experiment shows that a Damon Q bracket had a final plastic deformation after a single loading of 0.022 mm while the Speed bracket deformed 0.071 mm. This indicates that the Speed bracket plastically deforms 3.2 times more than the Damon Q bracket for similar magnitude of applied moment. The demonstration experiment demonstrates that bracket geometry affect the deformation of orthodontic brackets and this difference can be detected using the orthodontic torque simulator.

Inelastic deformation and phenomenological modeling of aluminum including transient effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, C.W.

A review was made of several phenomenological theories which have recently been proposed to describe the inelastic deformation of crystalline solids. Hart's deformation theory has many advantages, but there are disagreements with experimental deformation at stress levels below yield. A new inelastic deformation theory was proposed, introducing the concept of microplasticity. The new model consists of five deformation elements: a friction element representing a deformation element controlled by dislocation glide, a nonrecoverable plastic element representing the dislocation leakage rate over the strong dislocation barriers, a microplastic element representing the dislocation leakage rate over the weak barriers, a short range anelasticmore » spring element representing the recoverable anelastic strain stored by piled-up dislocations against the weak barriers, and a long range anelastic spring element representing the recoverable strain stored by piled-up dislocations against the strong barriers. Load relaxation and tensile testing in the plastic range were used to determine the material parameters for the plastic friction elements. The short range and long range anelastic moduli and the material parameters for the kinetics of microplasticity were determined by the measurement of anelastic loops and by performing load relaxation tests in the microplastic region. Experimental results were compared with a computer simulation of the transient deformation behavior of commercial purity aluminum. An attempt was made to correlate the material parameters and the microstructure from TEM. Stability of material parameters during inelastic deformation was discussed and effect of metallurgical variables was examined experimentally. 71 figures, 5 tables.« less

Plastic behavior of polycrystalline copper at optical scales of deformation

NASA Astrophysics Data System (ADS)

Domber, Jeanette Leah

Microplasticity is permanent deformation that occurs below the proportional limit of a material. For precision deployable optical spacecraft, it is unknown how microplasticity will affect the performance of the precision structure. An examination of the rolling of thin film optical reflectors indicates a strong dependence of the post-deployed shape on the strain hardening exponent of the material. However, confirmation of the valid extension of the constitutive model used to predict the deployed shape to microscopic strain regimes is necessary. The primary objective of this thesis is threefold: determine the relationship between stress and strain at nano to microstrain levels for representative materials; determine if the relationship between microscopic and macroscopic plastic behavior can be accurately characterized by the Ramberg-Osgood strain hardening constitutive model with a single set of material parameters; and determine if dislocation motion is the root cause of microplastic behavior at room temperature. The test apparatus, with a dynamic force range of 40,000 to 1, measures strains from 0.01 to 1000 parts per million (ppm) of cylindrical amorphous quartz and cold-worked and annealed tempered polycrystalline copper specimen. Elastic behavior in all three materials was consistent with typical values. However, plastic responses were larger than expected. Stresses on the order of 10 to 10,000 kPa (1.45 to 1450 psi) produced permanent strain in all three types of materials ranging from 0.01 to 1 ppm, some of which was attributable to a systematic error in the measurement. Extrapolating macroplastic behavior to lower stress and strain values underestimates the amount of microplasticity observed in the material. Therefore, material property characterization is required at all strain levels that are of concern for a particular application. The similarity in the levels of measured permanent strain for a given stress level between the as-drawn and annealed copper is consistent with the observed dislocation substructure of the two materials, which is also similar. This uniformity indicates that microplastic behavior at room temperature is driven by dislocation glide.

Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

NASA Astrophysics Data System (ADS)

Kovaleva, Elizaveta; Klötzli, Urs; Wheeler, John; Habler, Gerlinde

2018-02-01

This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains have axis oriented parallel to the foliation plane, with the majority of deformed grains having axis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems <100>{010} and < 1 bar 10>{110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system <100>{001} and rotation axis [010]. The slip system < 1 bar 10>{110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the crust, and, possibly, the timing of deformation, if the isotopic systems of deformed zircon were reset.

Modelling highly deformable metal extrusion using SPH

NASA Astrophysics Data System (ADS)

Prakash, Mahesh; Cleary, Paul W.

2015-05-01

Computational modelling is often used to reduce trial extrusions through accurate defect prediction. Traditionally, metal extrusion is modelled using mesh based finite element methods. However, large plastic deformations can lead to heavy re-meshing and numerical diffusion. Here we use the mesh-less smoothed particle hydrodynamics method since it allows simulation of large deformations without re-meshing and the tracking of history dependent properties such as plastic strain making it suitable for defect prediction. The variation in plastic strain and deformation for aluminium alloy in a cylindrical 3D geometry with extrusion ratio and die angle is evaluated. The extrusion process is found to have three distinct phases consisting of an initial sharp rise in extrusion force, a steady phase requiring constant force and terminating in a sharp decline in force as metal is completely extruded. Deformation and plastic strain increased significantly with extrusion ratio but only moderately with die angle. Extrusion force increased by 150 % as the extrusion ratio increased from 2:1 to 4:1 but had only a marginal change with die angle. A low strain zone in the centre of the extruded product was found to be a function of extrusion ratio but was persistent and did not vary with die angle. Simulation of a complex 3D building industry component showed large variations in plastic strain along the length of the product at two scales. These were due to change in metal behaviour as extrusion progressed from phase 1 to phase 2. A stagnation zone at the back of the die was predicted that could lead to the "funnel" or "pipe" defect.

Postharvest conservation of the tuberous roots of Pachyrhizus Ahipa (Wedd) Parodi.

PubMed

Mussury, Rosilda M; Scalon, Silvana P Q; Silva, Magaiver A; Silva, Tatiane F; Gomes, Hellen; Gassi, Rosimeire

2013-01-01

This paper aimed to evaluate the effects of storage periods on the conservation of Pachyrhizus ahipa roots at different temperatures and packaging materials. The roots were harvested, washed, packed in PVC, plastic bags, without wrappings (control) and stored in polystyrene trays in refrigerators, or cold chambers, or at room temperature. Total titratable acidity (TTA), total soluble solids (TSS), pH, as well as their ash, lipid, total carbohydrate and protein (dry basis) contents were analyzed. The lowest loss of root fresh weight was observed in the cold chamber and plastic bags. The TTA remained higher among roots stored in the cold chamber and in PVC packaging. The lowest TSS contents were observed for roots stored in the cold chamber, and these did not vary among the packing materials. The average carbohydrate content percentage for all treatments was 84.9%. The percentage of lipids was highest in roots stored at room temperature while protein and ash contents were highest in roots under refrigeration. The best storage conditions for roots are plastic bags packaging in a cold chamber, with the roots retaining appropriate quality for commercialization for up to 30 days.

Recrystallization and grain growth phenomena in a particle-reinforced aluminum composite

NASA Astrophysics Data System (ADS)

van Aken, D. C.; Krajewski, P. E.; Vyletel, G. M.; Allison, J. E.; Jones, J. W.

1995-06-01

Recrystallization and grain growth in a 2219/TiC/15p composite were investigated as functions of the amount of deformation and deformation temperature. Both cold and hot deformed samples were annealed at the normal solution treatment temperature of 535 °C. It was shown that large recrystallized grain diameters, relative to the interparticle spacing, could be produced in a narrow range of deformation for samples cold-worked and those hot-worked below 450 °C. For cold-worked samples, between 4 to 6 pct deformation, the recrystallized grain diameters varied from 530 to 66 μm as the amount of deformation increased. Subsequent grain growth was not observed in these recrystallized materials and noncompact grain shapes were observed. For deformations greater than 15 pct, recrystallized grain diameters less than the interparticle spacing were observed and subsequent grain growth produced a pinned grain diameter of 27 μm. The pinned grain diameter agreed well with an empirical model based on three dimensional (3-D) Monte Carlo simulations of grain growth and particle pinning in a two-phase material. Tensile properties were determined as a function of grain size, and it was shown that grain size had a weak influence on yield strength. A maximum in the yield strength was observed at a grain size larger than the normal grain growth and particle-pinned diameter.

Structure and mechanical properties of a high-carbon steel subjected to severe deformation

NASA Astrophysics Data System (ADS)

Gorkunov, E. S.; Zadvorkin, S. M.; Goruleva, L. S.; Makarov, A. V.; Pecherkina, N. L.

2017-10-01

The structure and mechanical properties of a high-carbon eutectic steel subjected to the cold plastic deformation by hydrostatic extrusion in a wide range of true strain have been studied. Using scanning and transmission electron microscopy, it has been shown that the formation of cellular, fragmented, and submicrocrystalline structures occurs in the ferritic constituent of the pearlite structure of the steel upon extrusion. This is a consequence of the occurrence of dynamic recovery and continuous dynamic and post-dynamic recrystallization, which cause a decrease in the density of free dislocations at the true strain of more than 1.62. The partial dissolution of the carbide phase is also observed. It has been found that, at a true strain of up to 0.81, the strength properties of the investigated steel are determined mainly by subgrain, dislocation, and precipitation mechanisms of the strengthening; in the deformation range of 0.81-1.62, the role of the grainboundary strengthening increases. At strains above 1.62, grain-boundary strengthening is a prevailing mechanism in the formation of the level of strength properties of the extruded U8A steel. The ultimate tensile strength and yield stress over the entire strain range only uniquely correlate with the density of highangle boundaries; the dependences of the strength characteristics on other structural parameters are not monotonic.

Uncovering the true nature of deformation microstructures using 3D analysis methods

NASA Astrophysics Data System (ADS)

Ferry, M.; Quadir, M. Z.; Afrin, N.; Xu, W.; Loeb, A.; Soe, B.; McMahon, C.; George, C.; Bassman, L.

2015-08-01

Three-dimensional electron backscatter diffraction (3D EBSD) has emerged as a powerful technique for generating 3D crystallographic information in reasonably large volumes of a microstructure. The technique uses a focused ion beam (FIB) as a high precision serial sectioning device for generating consecutive ion milled surfaces of a material, with each milled surface subsequently mapped by EBSD. The successive EBSD maps are combined using a suitable post-processing method to generate a crystallographic volume of the microstructure. The first part of this paper shows the usefulness of 3D EBSD for understanding the origin of various structural features associated with the plastic deformation of metals. The second part describes a new method for automatically identifying the various types of low and high angle boundaries found in deformed and annealed metals, particularly those associated with grains exhibiting subtle and gradual variations in orientation. We have adapted a 2D image segmentation technique, fast multiscale clustering, to 3D EBSD data using a novel variance function to accommodate quaternion data. This adaptation is capable of segmenting based on subtle and gradual variation as well as on sharp boundaries within the data. We demonstrate the excellent capabilities of this technique with application to 3D EBSD data sets generated from a range of cold rolled and annealed metals described in the paper.

Effects of Process Parameters on Copper Powder Compaction Process Using Multi-Particle Finite Element Method

NASA Astrophysics Data System (ADS)

Güner, F.; Sofuoğlu, H.

2018-01-01

Powder metallurgy (PM) has been widely used in several industries; especially automotive and aerospace industries and powder metallurgy products grow up every year. The mechanical properties of the final product that is obtained by cold compaction and sintering in powder metallurgy are closely related to the final relative density of the process. The distribution of the relative density in the die is affected by parameters such as compaction velocity, friction coefficient and temperature. Moreover, most of the numerical studies utilizing finite element approaches treat the examined environment as a continuous media with uniformly homogeneous porosity whereas Multi-Particle Finite Element Method (MPFEM) treats every particles as an individual body. In MPFEM, each of the particles can be defined as an elastic- plastic deformable body, so the interactions of the particles with each other and the die wall can be investigated. In this study, each particle was modelled and analyzed as individual deformable body with 3D tetrahedral elements by using MPFEM approach. This study, therefore, was performed to investigate the effects of different temperatures and compaction velocities on stress distribution and deformations of copper powders of 200 µm-diameter in compaction process. Furthermore, 3-D MPFEM model utilized von Mises material model and constant coefficient of friction of μ=0.05. In addition to MPFEM approach, continuum modelling approach was also performed for comparison purposes.

[Effects of covering the windowpane with plastic film on microclimate and sunshine of the living room in a cold region].

PubMed

Peng, G H

1990-05-01

Experiments were made to ascertain the effects of covering windowpane with plastic film in Hulunbeir region on microclimate and sunshine intensity in the living room. It was found that a good regulative effect on the room microclimate resulted by covering the windowpane with plastic film in the cold region. The room temperature rose distinctly. No evident effects were found on ultra-violet radiation and illumination. But the concentration of carbon dioxide increased to some extent. Attention should be paid to ventilation of the room.

The mechanics of solids in the plastically-deformable state

NASA Technical Reports Server (NTRS)

Mises, R. V.

1986-01-01

The mechanics of continua, which is based on the general stress model of Cauchy, up to the present has almost exclusively been applied to liquid and solid elastic bodies. Saint-Venant has developed a theory for the plastic or remaining form changes of solids, but it does not give the required number of equations for determining motion. A complete set of equations of motion for plastic deformable bodies is derived. This is done within the framework of Cauch mechanics. And it is supported by certain experimental facts which characterize the range of applications.

Modeling of surface effects in crystalline materials within the framework of gradient crystal plasticity

NASA Astrophysics Data System (ADS)

Peng, Xiang-Long; Husser, Edgar; Huang, Gan-Yun; Bargmann, Swantje

2018-03-01

A finite-deformation gradient crystal plasticity theory is developed, which takes into account the interaction between dislocations and surfaces. The model captures both energetic and dissipative effects for surfaces penetrable by dislocations. By taking advantage of the principle of virtual power, the surface microscopic boundary equations are obtained naturally. Surface equations govern surface yielding and hardening. A thin film under shear deformation serves as a benchmark problem for validation of the proposed model. It is found that both energetic and dissipative surface effects significantly affect the plastic behavior.

Size-dependent plastic deformation of twinned nanopillars in body-centered cubic tungsten

NASA Astrophysics Data System (ADS)

Xu, Shuozhi; Startt, Jacob K.; Payne, Thomas G.; Deo, Chaitanya S.; McDowell, David L.

2017-05-01

Compared with face-centered cubic metals, twinned nanopillars in body-centered cubic (BCC) systems are much less explored partly due to the more complicated plastic deformation behavior and a lack of reliable interatomic potentials for the latter. In this paper, the fault energies predicted by two semi-empirical interatomic potentials in BCC tungsten (W) are first benchmarked against density functional theory calculations. Then, the more accurate potential is employed in large scale molecular dynamics simulations of tensile and compressive loading of twinned nanopillars in BCC W with different cross sectional shapes and sizes. A single crystal, a twinned crystal, and single crystalline nanopillars are also studied as references. Analyses of the stress-strain response and defect nucleation reveal a strong tension-compression asymmetry and a weak pillar size dependence in the yield strength. Under both tensile and compressive loading, plastic deformation in the twinned nanopillars is dominated by dislocation slip on {110} planes that are nucleated from the intersections between the twin boundary and the pillar surface. It is also found that the cross sectional shape of nanopillars affects the strength and the initial site of defect nucleation but not the overall stress-strain response and plastic deformation behavior.

Quantitative Analyses of the Modes of Deformation in Engineering Thermoplastics

NASA Astrophysics Data System (ADS)

Landes, B. G.; Bubeck, R. A.; Scott, R. L.; Heaney, M. D.

1998-03-01

Synchrotron-based real-time small-angle X-ray scattering (RTSAXS) studies have been performed on rubber-toughened engineering thermoplastics with amorphous and semi-crystalline matrices. Scattering patterns are measured at successive time intervals of 3 ms were analyzed to determine the plastic strain due to crazing. Simultaneous measurements of the absorption of the primary beam by the sample permits the total plastic strain to be concurrently computed. The plastic strain due to other deformation mechanisms (e.g., particle cavitation and macroscopic shear yield can be determined from the difference between the total and craze-derived plastic strains. The contribution from macroscopic shear deformation can be determined from video-based optical data measured simultaneously with the X-ray data. These types of time-resolved experiments result in the generation of prodigious quantities of data, the analysis of which can considerably delay the determination of key results. A newly developed software package that runs in WINDOWSa 95 permits the rapid analysis of the relative contributions of the deformation modes from these time-resolved experiments. Examples of using these techniques on ABS-type and QUESTRAa syndiotactic polystyrene type engineering resins will be given.

Cell response to nanocrystallized metallic substrates obtained through severe plastic deformation.

PubMed

Bagherifard, Sara; Ghelichi, Ramin; Khademhosseini, Ali; Guagliano, Mario

2014-06-11

Cell-substrate interface is known to control the cell response and subsequent cell functions. Among the various biophysical signals, grain structure, which indicates the repeating arrangement of atoms in the material, has also proved to play a role of significant importance in mediating the cell activities. Moreover, refining the grain size through severe plastic deformation is known to provide the processed material with novel mechanical properties. The potential application of such advanced materials as biomedical implants has recently been evaluated by investigating the effect of different substrate grain sizes on a wide variety of cell activities. In this review, recent advances in biomedical applications of severe plastic deformation techniques are highlighted with special attention to the effect of the obtained nano/ultra-fine-grain size on cell-substrate interactions. Various severe plastic deformation techniques used for this purpose are discussed presenting a brief description of the mechanism for each process. The results obtained for each treatment on cell morphology, adhesion, proliferation, and differentiation, as well as the in vivo studies, are discussed. Finally, the advantages and challenges regarding the application of these techniques to produce multifunctional bio-implant materials are addressed.

Sessile dislocations by reactions in NiAl severely deformed at room temperature

DOE PAGES

Geist, D.; Gammer, C.; Rentenberger, C.; ...

2015-02-05

B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a(110) dislocations by dislocationmore » reactions; the a(110) dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a(110) dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.« less

The Surface Layer Mechanical Condition and Residual Stress Forming Model in Surface Plastic Deformation Process with the Hardened Body Effect Consideration

NASA Astrophysics Data System (ADS)

Mahalov, M. S.; Blumenstein, V. Yu

2017-10-01

The mechanical condition and residual stresses (RS) research and computational algorithms creation in complex types of loading on the product lifecycle stages relevance is shown. The mechanical state and RS forming finite element model at surface plastic deformation strengthening machining, including technological inheritance effect, is presented. A model feature is the production previous stages obtained transformation properties consideration, as well as these properties evolution during metal particles displacement through the deformation space in the present loading step.

The Special Features of the Deformation Behavior of an Ultrafine-Grained Aluminum Alloy of the Al-Mg-Li System at Room Temperature

NASA Astrophysics Data System (ADS)

Naydenkin, E. V.; Mishin, I. P.; Ivanov, K. V.

2015-04-01

The special features of the deformation behavior of an ultrafine-grained aluminum alloy produced by severe plastic deformation are investigated. Unlike ultrafine-grained pure aluminum, the second-phase particles precipitated in the bulk and at the grain boundaries of the alloy are shown to hinder the development of grain boundary sliding and plastic strain localization. This increases the length of the strain hardening stage and uniformity of elongation of a heterogeneous aluminum alloy specimen as compared to pure aluminum.

A Versatile Method for Nanostructuring Metals, Alloys and Metal Based Composites

NASA Astrophysics Data System (ADS)

Gurau, G.; Gurau, C.; Bujoreanu, L. G.; Sampath, V.

2017-06-01

A new severe plastic deformation method based on High Pressure Torsion is described. The method patented as High Speed High Pressure Torsion (HSHPT) shows a wide scope and excellent adaptability assuring large plastic deformation degree on metals, alloys even on hard to deform or brittle alloys. The paper present results obtained on aluminium, magnesium, titan, iron and coper alloys. In addition capability of HSHPT to process metallic composites is described. OM SEM, TEM, DSC, RDX and HV investigation methods were employed to confirm fine and ultrafine structure.

AFM study of the plastic deformation behavior of poly-synthetically-twinned (PST) titanium aluminide crystals

NASA Astrophysics Data System (ADS)

Chen, Yali

The plastic deformation behavior of PST TiAl crystals was investigated using AFM techniques to reveal the effects of lamellar structure on the deform mechanisms of two-phase TiAl materials. PST crystals with a nominal composition of Ti52Al48 (atomic percent) were grown by the floating zone method and at various orientations deformed in compression at room temperature. Atomic Force Microscopy (AFM) was employed to investigate the deformation structure on the free surfaces. The deformation of the PST crystals is highly anisotropic and the deformation mechanism changes dramatically with sample orientation. When the angle between the loading axis and the lamellar interfaces is below 20°, the gamma lamellae deform by dislocation slip and twinning on planes oblique to the lamellar interfaces, but the Burgers vectors or the resultant shear vectors are parallel to the lamellar interfaces inside each lamella. When the angle is between 20° and 80° the gamma phase deforms by shear on planes parallel to the lamellar interfaces. Some domains deform by a combination of ordinary dislocation slip and twinning. In the domains where twinning cannot be activated, slip occurs by ordinary dislocations or superdislocations. When the loading axis is nearly perpendicular to the lamellar interfaces ordinary dislocation slip and twinning on slip planes inclined with the lamellar interfaces are dominant and the shear is trans-lamellar. The three deformation modes are termed as A, B and N type deformation modes respectively. In the A type mode the alpha2 lamellae concomitantly deform by prismatic slip. In the other two modes, the alpha2 phase does not deform and acts as strong obstacles to the transfer of deformation. Abundant misfit dislocations are emitted from the lamellar interfaces which is beneficial for the plastic deformation. On the other hand, the lamellar interfaces strongly impede trans-lamellar deformation and channel the deformation inside each lamella. The inhomogeneous coherency stresses at the lamellar interfaces also lead to heterogeneous deformation of PST crystals. The deformation behavior of the lamellar grains produces remarkable strain incompatibility in lamellar polycrystals and deteriorates the deformability.

Comparison of dislocation density tensor fields derived from discrete dislocation dynamics and crystal plasticity simulations of torsion

DOE PAGES

Jones, Reese E.; Zimmerman, Jonathan A.; Po, Giacomo; ...

2016-02-01

Accurate simulation of the plastic deformation of ductile metals is important to the design of structures and components to performance and failure criteria. Many techniques exist that address the length scales relevant to deformation processes, including dislocation dynamics (DD), which models the interaction and evolution of discrete dislocation line segments, and crystal plasticity (CP), which incorporates the crystalline nature and restricted motion of dislocations into a higher scale continuous field framework. While these two methods are conceptually related, there have been only nominal efforts focused at the global material response that use DD-generated information to enhance the fidelity of CPmore » models. To ascertain to what degree the predictions of CP are consistent with those of DD, we compare their global and microstructural response in a number of deformation modes. After using nominally homogeneous compression and shear deformation dislocation dynamics simulations to calibrate crystal plasticity ow rule parameters, we compare not only the system-level stress-strain response of prismatic wires in torsion but also the resulting geometrically necessary dislocation density fields. To establish a connection between explicit description of dislocations and the continuum assumed with crystal plasticity simulations we ascertain the minimum length-scale at which meaningful dislocation density fields appear. Furthermore, our results show that, for the case of torsion, that the two material models can produce comparable spatial dislocation density distributions.« less

The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

NASA Astrophysics Data System (ADS)

Ji, L. K.; Xu, T.; Zhang, J. M.; Wang, H. T.; Tong, M. X.; Zhu, R. H.; Zhou, G. S.

2017-07-01

Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10-5, 1.25 × 10-4, 2.5 × 10-3, and 1.25 × 10-2 s-1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10-3 s-1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10-5 s-1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10-3 s-1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.

An Auxetic structure configured as oesophageal stent with potential to be used for palliative treatment of oesophageal cancer; development and in vitro mechanical analysis.

PubMed

Ali, Murtaza N; Rehman, Ihtesham Ur

2011-11-01

Oesophageal cancer is the ninth leading cause of malignant cancer death and its prognosis remains poor. Dysphagia which is an inability to swallow is a presenting symptom of oesophageal cancer and is indicative of incurability. The goal of this study was to design and manufacture an Auxetic structure film and to configure this film as an Auxetic stent for the palliative treatment of oesophageal cancer, and for the prevention of dysphagia. Polypropylene was used as a material for its flexibility and non-toxicity. The Auxetic (rotating-square geometry) structure was made by laser cutting the polypropylene film. This flat structure was welded together to form a tubular form (stent), by an adjustable temperature control soldering iron station: following this, an annealing process was also carried out to ease any material stresses. Poisson's ratio was estimated and elastic and plastic deformation of the Auxetic structure was evaluated. The elastic and plastic deformation behaviours of the Auxetic polypropylene film were evaluated by applying repetitive uniaxial tensile loads. Observation of the structure showed that it was initially elastically deformed, thereafter plastic deformation occurred. This research discusses a novel way of fabricating an Auxetic structure (rotating-squares connected together through hinges) on Polypropylene films, by estimating the Poisson's ratio and evaluating the plastic deformation relevant to the expansion behaviour of an Auxetic stent within the oesophageal lumen.

Analysis of Plastic Flow Instability During Superplastic Deformation of the Zn-Al Eutectoid Alloy Modified with 2 wt.% Cu

NASA Astrophysics Data System (ADS)

Ramos-Azpeitia, Mitsuo; Elizabeth Martínez-Flores, E.; Hernandez-Rivera, Jose Luis; Torres-Villaseñor, Gabriel

2017-11-01

The aim of this work is to analyze the plastic flow instability in Zn-21Al-2Cu alloy deformed under 10-3 s-1 and 513 K, which are optimum conditions for inducing superplastic behavior in this alloy. An evaluation using the Hart and Wilkinson-Caceres criteria showed that the limited stability of plastic flow observed in this alloy is related to low values of the strain-rate sensitivity index ( m) and the strain-hardening coefficient ( γ), combined with the tendency of these parameters to decrease depending on true strain ( ɛ). The reduction in m and γ values could be associated with the early onset of plastic instability and with microstructural changes observed as function of the strain. Grain growth induced by deformation seems to be important during the first stage of deformation of this alloy. However, when ɛ > 0.4 this growth is accompanied by other microstructural rearrangements. These results suggest that in this alloy, a grain boundary sliding mechanism acts to allow a steady superplastic flow only for ɛ < 0.4. For ɛ values between 0.4 and 0.7, observed occurrences of microstructural changes and severe neck formation lead to the supposition that there is a transition in the deformation mechanism. These changes are more evident when ɛ > 0.7 as another mechanism is thought to take over.

Influence of combined thermomechanical treatment on impurity segregation in ferritic-martensitic and austenitic stainless steels

NASA Astrophysics Data System (ADS)

Ilyin, A. M.; Neustroev, V. S.; Shamardin, V. K.; Shestakov, V. P.; Tazhibaeva, I. L.; Krivchenkoa, V. A.

2000-12-01

In this study 13Cr2MoVNb ferritic-martensitic steel (FMS) and 16Cr15Ni3MoNb austenitic stainless steel (ASS) tensile specimens were subjected to standard heat treatments and divided into two groups. Specimens in group 1 (FMS only) were aged at 400°C in a stress free and in an elastically stressed state with a tensile load (100 MPa) then doped with hydrogen in an electrolytic cell. Specimens in group 2 were subjected to cold work (up to 10%) and exposed to short-time heating at 500° for 0.5 h. All specimens were fractured at room temperature in an Auger spectrometer and Auger analysis of the fracture surfaces was performed in situ after fracturing. A noticeable increase of N and P segregation levels and a widening of the depth distribution on the grain boundary facets were observed in the FMS after aging in the stressed state. Cold-worked FMS and ASS showed a ductile dimple mode of fracture, but relatively high levels of S, P and N were observed on the dimple surfaces. We consider the origin of such effects in terms of the stressed state and plastic-deformation-enhanced segregation.

Solid state consolidation nanocrystalline copper-tungsten using cold spray

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hall, Aaron Christopher; Sarobol, Pylin; Argibay, Nicolas

It is well known that nanostructured metals can exhibit significantly improved properties compared to metals with conventional grain size. Unfortunately, nanocrystalline metals typically are not thermodynamically stable and exhibit rapid grain growth at moderate temperatures. This severely limits their processing and use, making them impractical for most engineering applications. Recent work has shown that a number of thermodynamically stable nanocrystalline metal alloys exist. These alloys have been prepared as powders using severe plastic deformation (e.g. ball milling) processes. Consolidation of these powders without compromise of their nanocrystalline microstructure is a critical step to enabling their use as engineering materials. Wemore » demonstrate solid-state consolidation of ball milled copper-tantalum nanocrystalline metal powder using cold spray. Unfortunately, the nanocrystalline copper-tantalum powder that was consolidated did not contain the thermodynamically stable copper-tantalum nanostructure. Nevertheless, this does this demonstrates a pathway to preparation of bulk thermodynamically stable nanocrystalline copper-tantalum. Furthermore, it demonstrates a pathway to additive manufacturing (3D printing) of nanocrystalline copper-tantalum. Additive manufacturing of thermodynamically stable nanocrystalline metals is attractive because it enables maximum flexibility and efficiency in the use of these unique materials.« less

Study of the Production of a Metallic Coating on Natural Fiber Composite Through the Cold Spray Technique

NASA Astrophysics Data System (ADS)

Astarita, Antonello; Boccarusso, Luca; Durante, Massimo; Viscusi, Antonio; Sansone, Raffaele; Carrino, Luigi

2018-02-01

The deposition of a metallic coating on hemp-PLA (polylactic acid) laminate through the cold spray technique was studied in this paper. A number of different combinations of the deposition parameters were tested to investigate the feasibility of the process. The feasibility of the process was proved when processing conditions are properly set. The bonding mechanism between the substrate and the first layer of particles was studied through scanning electron microscope observations, and it was found that the polymeric matrix experiences a huge plastic deformation to accommodate the impinging particles; conversely a different mechanism was observed when metallic powders impact against a previously deposited metallic layer. The difference between the bonding mechanism and the growth of the coating was also highlighted. Depending on the spraying parameters, four different processing conditions were highlighted and discussed, and as a result the processing window was defined. The mechanical properties of the composite panel before and after the deposition were also investigated. The experiments showed that when properly carried out, the deposition process does not affect the strength of the panel; moreover, no improvements were observed because the contribution of the coating is negligible with respect to one of the reinforcement fibers.

Influence of laser irradiation on deposition characteristics of cold sprayed Stellite-6 coatings

NASA Astrophysics Data System (ADS)

Li, Bo; Jin, Yan; Yao, Jianhua; Li, Zhihong; Zhang, Qunli; Zhang, Xin

2018-03-01

Depositing hard materials such as Stellite-6 solely by cold spray (CS) is challengeable due to limited ability of plastic deformation. In this study, the deposition of Stellite-6 powder was achieved by supersonic laser deposition (SLD) which combines CS with synchronous laser irradiation. The surface morphology, deposition efficiency, track shape of Stellite-6 coatings produced over a range of laser irradiation temperatures were examined so as to reveal the effects of varying laser energy inputting on the deposition process of high strength material. The microstructure, phase composition and wear/corrosion resistant properties of the as-deposited Stellite-6 coatings were also investigated. The experimental results demonstrate that the surface flatness and deposition efficiency increase with laser irradiation temperature due to the softening effect induced by laser heating. The as-deposited Stellite-6 tracks show asymmetric shapes which are influenced by the relative configuration of powder stream and laser beam. The SLD coatings can preserve the original microstructure and phase of the feedstock material due to relatively low laser energy inputting, which result in the superior wear/corrosion resistant properties as compared to the counterpart prepared by laser cladding.

Nature of the ``yield tooth'' under torsion in plastic-deformed whiskers

NASA Astrophysics Data System (ADS)

Bataronov, I. L.; Belikov, A. M.; Drozhzhin, A. I.; Roshchupkin, A. M.

1987-07-01

The plastic torsion of whiskers with high Peierls barriers has been studied. As the samples for the studies we chose p-type germanium whiskers with <111> growth axis. The diameter of the whisker was (5 60)·10-6 m and the gauge length was (1 4)·10-3 m. The whiskers were dislocation-free in the initial state. Within the framework of the continuum model developed by us for the plastic deformation of whiskers under torsion, we analyze the anomalies of the torsional stress-strain diagram under different testing conditions and with preliminary deformation. The “flow tooth” during the torsion of a whisker is attributable to the nonuniform distribution of dislocations over the cross section of the whisker and high barriers to the dislocation motion.

Studying damage accumulation in martensitic corrosion-resistant steel under cold radial reduction

NASA Astrophysics Data System (ADS)

Karamyshev, A. P.; Nekrasov, I. I.; Nesterenko, A. V.; Parshin, V. S.; Smirnov, S. V.; Shveikin, V. P.; Fedulov, A. A.

2017-12-01

Cold radial reduction of specimens made of the Kh17N2 corrosion-resistant martensitic steel is studied on a lever-type radial-forging machine (RFM). The mechanical properties of the deformed specimens, the "damage accumulation - strain" relation in the specimens are obtained with the application of hydrostatic and fractographic methods for fractured specimens. The damage of the Kh17N2 corrosion-resistant steel is evaluated as a result of an experimental study considering the data of simulation by a complex finite element model of cold deformation on a lever-type RFM.

Influence of voids distribution on the deformation behavior of nanocrystalline palladium

NASA Astrophysics Data System (ADS)

Bachurin, D. V.

2018-07-01

Uniaxial deformation of three-dimensional nanocrystalline palladium containing porosity in the form of voids was investigated by means of molecular dynamics method. Simulations were performed at temperature of 300 K and at a constant strain rate of 108s-1. Two cases of voids distribution were considered: random and at triple or quadrupole junctions. It has been revealed that both the voids distribution and subsequent annealing at elevated temperature influence the deformation behavior of nanocrystalline palladium. In particular, the presence of voids at grain junctions results in a reduction of the Young's modulus and more pronounced softening effect during plastic deformation. The subsequent annealing evokes shrinkage of voids and strengthening effect. Contribution of grain boundary accommodation processes into both elastic and plastic deformation of nanocrystalline materials is discussed.

MAGNETIC MEASUREMENT OF THE PLASTIC STRESS-STRAIN CURVE OF MULTICRYSTALLINE NICKEL (in German)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwink, Ch.; Zankl, G.

1962-01-01

Ballistic measurements of the coercive force H/sub c/ and the initial permeability mu /sub alpha / were made on nlckel wires, and their dependence on plastic tensile deformation was followed. The results are shown graphically. H/ sub c/ and 1/ mu /sub alpha / start to increase at a given tensile stress with the introduction of plastic expansion and increases almost linearly with the tensile stress applied. At a tensile stress of 7.2 plus or minus 0.5 kp/mm/sup 2/ both curves have noticable bends. The bend point is related by a special process to the plastic deformation of the multicrystallinemore » material. (J.S.R.)« less

Some aspects of the stability of the plane deformation mode of filaments of finite stiffness beyond the elasticity limits

NASA Astrophysics Data System (ADS)

Shimanovskii, A. V.

A method for calculating the plane bending of elastic-plastic filaments of finite stiffness is proposed on the basis of plastic flow theory. The problem considered is shown to reduce to relations similar to Kirchhoff equations for elastic work. Expressions are obtained for determining the normalized stiffness characteristics for the cross section of a filament with plastic regions containing beam theory equations as a particular case. A study is made of the effect of the plastic region size on the position of the elastic deformation-unloading interface and on the normalized stiffness of the filament cross section. Calculation results are presented in graphic form.

Finite element solutions for crack-tip behavior in small-scale yielding

NASA Technical Reports Server (NTRS)

Tracey, D. M.

1976-01-01

The subject considered is the stress and deformation fields in a cracked elastic-plastic power law hardening material under plane strain tensile loading. An incremental plasticity finite element formulation is developed for accurate analysis of the complete field problem including the extensively deformed near tip region, the elastic-plastic region, and the remote elastic region. The formulation has general applicability and was used to solve the small scale yielding problem for a set of material hardening exponents. Distributions of stress, strain, and crack opening displacement at the crack tip and through the elastic-plastic zone are presented as a function of the elastic stress intensity factor and material properties.

Treatment of plastic deformation of the forearm in young adults with double-level osteotomies: case reports.

PubMed

Moon, Edward S; Howlett, John; Wiater, Brett P; Trumble, Thomas E

2011-04-01

Plastic deformation of the forearm is a rare injury in young adults that occurs when a slow bending or rotational force is applied to the arm, most commonly in the setting of an industrial workplace accident. There are currently no guidelines for treatment of the residual forearm deformity that often results in limitations of forearm supination and pronation. We present 2 cases demonstrating that deformity correction with single cortex, double-level osteotomies combined with rigid plate fixation and early range of motion exercise that results in good functional outcomes. Copyright © 2011 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Analysis of fluid-structure interaction in a frame pipe undergoing plastic deformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khamlichi, A.; Jezequel, L.; Jacques, Y.

1995-11-01

Water hammer pressure waves of sufficiently large magnitude can cause plastic flexural deformations in a frame pipe. In this study, the authors propose a modelization of this problem based on plane wave approximation for the fluid equations and approximation of the structure motion by a single-degree-of-freedom elastic-plastic oscillator. Direct analytical integration of elastic-plastic equations through pipe sections, then over the pipe length is performed in order to identify the oscillator parameters. Comparison of the global load-displacement relationship obtained with the finite element solution was considered and has shown good agreement. Fluid-structure coupling is achieved by assuming elbows to act likemore » plane monopole sources, where localized jumps of fluid velocity occur and where net pressure forces are exerted on the structure. The authors have applied this method to analyze the fluid-structure interaction in this range of deformations. Energy exchange between the fluid and the structure and energy dissipation are quantified.« less

Insights from the Lattice-Strain Evolution on Deformation Mechanisms in Metallic-Glass-Matrix Composites

DOE PAGES

Jia, Haoling; Zheng, Lili; Li, Weidong; ...

2015-02-18

In this paper, in situ high-energy synchrotron X-ray diffraction experiments and micromechanics-based finite element simulations have been conducted to examine the lattice-strain evolution in metallic-glass-matrix composites (MGMCs) with dendritic crystalline phases dispersed in the metallic-glass matrix. Significant plastic deformation can be observed prior to failure from the macroscopic stress–strain curves in these MGMCs. The entire lattice-strain evolution curves can be divided into elastic–elastic (denoting deformation behavior of matrix and inclusion, respectively), elastic–plastic, and plastic–plastic stages. Characteristics of these three stages are governed by the constitutive laws of the two phases (modeled by free-volume theory and crystal plasticity) and geometric informationmore » (crystalline phase morphology and distribution). The load-partitioning mechanisms have been revealed among various crystalline orientations and between the two phases, as determined by slip strain fields in crystalline phase and by strain localizations in matrix. Finally, implications on ductility enhancement of MGMCs are also discussed.« less

Evolution of plastic deformation and its effect on mechanical properties of laser additive repaired Ti64ELI titanium alloy

NASA Astrophysics Data System (ADS)

Zhao, Zhuang; Chen, Jing; Tan, Hua; Lin, Xin; Huang, Weidong

2017-07-01

In this paper, laser additive manufacturing (LAM) technology with powder feeding has been employed to fabricate 50%LAMed specimens (i.e. the volume fraction of the laser deposited zone was set to 50%). With aid of the 3D-DIC technique, the tensile deformation behavior of 50%LAMed Ti64ELI titanium alloy was investigated. The 50%LAMed specimen exhibits a significant characteristic of strength mismatch due to the heterogeneous microstructure. The tensile fracture of 50%LAMed specimen occurs in WSZ (wrought substrate zone), but the tensile strength is slightly higher and the plastic elongation is significantly lower than that of the wrought specimen. The 3D-DIC results shows that the 50%LAMed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and the maximal strain is invariably concentrated in WSZ. The ABAQUS simulation indicates that, the LDZ (laser deposited zone) can constrain the plastic deformation of the WSZ and biaxial stresses develop at the interface after yielding.

Numerical Simulation of Pipeline Deformation Caused by Rockfall Impact

PubMed Central

Liang, Zheng; Han, Chuanjun

2014-01-01

Rockfall impact is one of the fatal hazards in pipeline transportation of oil and gas. The deformation of oil and gas pipeline caused by rockfall impact was investigated using the finite element method in this paper. Pipeline deformations under radial impact, longitudinal inclined impact, transverse inclined impact, and lateral eccentric impact of spherical and cube rockfalls were discussed, respectively. The effects of impact angle and eccentricity on the plastic strain of pipeline were analyzed. The results show that the crater depth on pipeline caused by spherical rockfall impact is deeper than by cube rockfall impact with the same volume. In the inclined impact condition, the maximum plastic strain of crater caused by spherical rockfall impact appears when incidence angle α is 45°. The pipeline is prone to rupture under the cube rockfall impact when α is small. The plastic strain distribution of impact crater is more uneven with the increasing of impact angle. In the eccentric impact condition, plastic strain zone of pipeline decreases with the increasing of eccentricity k. PMID:24959599

Microstructural evolution of bainitic steel severely deformed by equal channel angular pressing.

PubMed

Nili-Ahmadabadi, M; Haji Akbari, F; Rad, F; Karimi, Z; Iranpour, M; Poorganji, B; Furuhara, T

2010-09-01

High Si bainitic steel has been received much of interest because of combined ultra high strength, good ductility along with high wear resistance. In this study a high Si bainitic steel (Fe-0.22C-2.0Si-3.0Mn) was used with a proper microstructure which could endure severe plastic deformation. In order to study the effect of severe plastic deformation on the microstructure and properties of bainitic steel, Equal Channel Angular Pressing was performed in two passes at room temperature. Optical, SEM and TEM microscopies were used to examine the microstructure of specimens before and after Equal Channel Angular Pressing processing. X-ray diffraction was used to measure retained austenite after austempering and Equal Channel Angular Pressing processing. It can be seen that retained austenite picks had removed after Equal Channel Angular Pressing which could attributed to the transformation of austenite to martensite during severe plastic deformation. Enhancement of hardness values by number of Equal Channel Angular Pressing confirms this idea.

Parameter determination of hereditary models of deformation of composite materials based on identification method

NASA Astrophysics Data System (ADS)

Kayumov, R. A.; Muhamedova, I. Z.; Tazyukov, B. F.; Shakirzjanov, F. R.

2018-03-01

In this paper, based on the analysis of some experimental data, a study and selection of hereditary models of deformation of reinforced polymeric composite materials, such as organic plastic, carbon plastic and a matrix of film-fabric composite, was pursued. On the basis of an analysis of a series of experiments it has been established that organo-plastic samples behave like viscoelastic bodies. It is shown that for sufficiently large load levels, the behavior of the material in question should be described by the relations of the nonlinear theory of heredity. An attempt to describe the process of deformation by means of linear relations of the theory of heredity leads to large discrepancies between the experimental and calculated deformation values. The use of the theory of accumulation of micro-damages leads to much better description of the experimental results. With the help of the hierarchical approach, a good approximation of the experimental values was successful only in the first three sections of loading.

Multiple deformation mechanisms operating at seismogenic depths: Tectonic pseudotachylyte and associated deformation from the central Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Prante, M. R.; Evans, J. P.

2012-12-01

Description and identification of fault-related deformation products that are diagnostic of seismic slip have implications for the energy budget of earthquakes, fault strength, and fault-rock assemblages. We describe tectonic pseduotachylyte, cataclastic rocks, crystal-plastic deformation, and hydrothermal alteration form faults exhumed from seismogenic depths in the Volcanic Lakes area, in northern Sequoia and Kings Canyon National Park, CA, USA. Fault rock protoliths include Mesozoic granite and granodiorite plutonic and limited metasedimentary and metavolcanic rocks. These plutonic and metamorphic rocks are cross-cut by the E-W striking, steeply dipping, left-lateral strike-slip Granite Pass (GPF) and Glacier Lakes faults (GLF). Cross-cutting relationships and microstructural data suggest that the GPF is the oldest fault in the area and preserves evidence for coeval brittle and plastic crystal deformation, and hydrothermal fluid-flow. Tectonic pseudotachylyte from the area has been dated using the 40Ar/39Ar method at 76.6 ± 0.3 Ma; when placed into a thermochronologic framework for the plutonic host rock it can be inferred that the pseudotachylyte formed at depths between 2.4-6.0 km with ambient temperatures between 110-160°C. Exceptionally well preserved tectonic pseudotachylyte from the GLF and GPF contain evidence for a frictional melt origin including: 1) plagioclase spherulites and microlites, 2) injection vein morphology, 3) amygdules, 4) viscous flow banding and folds, and 5) embayed and corroded clasts. Pseudotachylyte from the GPF and GLF is associated with brittle and plastic deformation in the damage zone of the faults. Evidence for plastic deformation includes undulose extinction, deformation lamellae, subgrain development, and grain boundary bulging in quartz; and limited undulose extinction in feldspar. Additionally, abundant hydrothermal alteration and mineralization has been documented in the GPF and GLF fault zones, including, chlorite pseudomorphs after biotite and alteration of mafic phases to epidote, sericite and calcite alteration of albite, and calcite and chlorite filled veins. Cross-cutting calcite veins contain fine-grained calcite with abundant twins up to 20 μm-thick. Multiple pseudotachylyte injection veins and reworked pseudotachylyte in cataclastic rock suggest multiple earthquakes along the GPF and GLF at depths favorable to pseudotachylyte formation. Abundant hydrothermal alteration and cross-cutting calcite veins with thick (> 1 μm) twins is consistent with ambient temperatures between 170 and 200°C. These temperatures are generally consistent with the reported ambient temperature conditions during pseudotachylyte formation. Crystal-plastic deformation of quartz and feldspar in the GPF and GLF zones is consistent with deformation at temperatures between 200-400°C. Frictional melt and associated brittle and plastic deformation, and fluid alteration are presumed to have occurred at similar temperature conditions and may be coeval. These results have important implication for understanding energy sinks associated with seismic slip and the conditions of tectonic pseudotachylyte formation.

Simulation study of the effect of strain rate on the mechanical properties and tensile deformation of gold nanowire

NASA Astrophysics Data System (ADS)

Shi, Guo-Jie; Wang, Jin-Guo; Hou, Zhao-Yang; Wang, Zhen; Liu, Rang-Su

2017-09-01

The mechanical properties and deformation mechanisms of Au nanowire during the tensile processes at different strain rates are revealed by the molecular dynamics method. It is found that the Au nanowire displays three distinct types of mechanical behaviors when tensioning at low, medium and high strain rates, respectively. At the low strain rate, the stress-strain curve displays a periodic zigzag increase-decrease feature, and the plastic deformation is resulted from the slide of dislocation. The dislocations nucleate, propagate, and finally annihilate in every decreasing stages of stress, and the nanowire always can recover to FCC-ordered structure. At the medium strain rate, the stress-strain curve gently decreases during the plastic process, and the deformation is contributed from sliding and twinning. The dislocations formed in the yield stage do not fully propagate and further escape from the nanowire. At the high strain rate, the stress-strain curve wave-like oscillates during the plastic process, and the deformation is resulted from amorphization. The FCC atoms quickly transform into disordered amorphous structure in the yield stage. The relative magnitude between the loading velocity of strain and the propagation velocity of phonons determines the different deformation mechanisms. The mechanical behavior of Au nanowire is similar to Ni, Cu and Pt nanowires, but their deformation mechanisms are not completely identical with each other.

Mechanical and time-dependent behavior of wood-plastic composites subjected to tension and compression

Treesearch

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2012-01-01

The thermoplastics within wood—plastic composites (WPCs) are known to experience significant time-dependent deformation or creep. In some formulations, creep deformation can be twice as much as the initial quasi-static strain in as little as 4 days. While extensive work has been done on the creep behavior of pure polymers, little information is available on the...

Effect of hot plastic deformation on the structural state of a Al-10%SiC composite

NASA Astrophysics Data System (ADS)

Pugacheva, N. B.; Vichuzhanin, D. I.; Michurov, N. S.; Smirnov, A. S.

2017-12-01

The paper studies the microstructure of honeycomb aluminum matrix composites with a granulated Al-Zn-Cu-Mg alloy matrix filled SiC particles amounting to 10 vol % after hot plastic deformation at near-solidus temperatures. It demonstrates the possibility of the collapse of the SiC filler network and the formation of filler clusters separated from each other.

Estimation Model for Magnetic Properties of Stamped Electrical Steel Sheet

NASA Astrophysics Data System (ADS)

Kashiwara, Yoshiyuki; Fujimura, Hiroshi; Okamura, Kazuo; Imanishi, Kenji; Yashiki, Hiroyoshi

Less deterioration in magnetic properties of electrical steel sheets in the process of stamping out iron-core are necessary in order to maintain its performance. First, the influence of plastic strain and stress on magnetic properties was studied by test pieces, in which plastic strain was added uniformly and residual stress was not induced. Because the influence of plastic strain was expressed by equivalent plastic strain, at each equivalent plastic strain state the influence of load stress was investigated. Secondly, elastic limit was determined about 60% of macroscopic yield point (MYP), and it was found to agree with stress limit inducing irreversible deterioration in magnetic properties. Therefore simulation models, where beyond elastic limit plastic deformation begins and magnetic properties are deteriorated steeply, are proposed. Besides considered points in the deformation analysis are strain-rate sensitivity of flow stress, anisotropy under deformation, and influence of stress triaxiality on fracture. Finally, proposed models have been shown to be valid, because magnetic properties of 5mm width rectangular sheets stamped out from non-oriented electrical steel sheet (35A250 JIS grade) can be estimated with good accuracy. It is concluded that the elastic limit must be taken into account in both stamping process simulation and magnetic field calculation.

Microstructure characterization based on the type of deformed grains in cold-rolled, Cu-added, bake-hardenable steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, J.S.; Kim, S.I.; Choi, S.-H., E-mail: shihoon@sunchon.ac.kr

2014-06-01

The electron backscatter diffraction technique has been used to characterize the microstructure of deformed grains in cold-rolled, Cu-added, bake-hardenable steel. A new scheme based on the kind and number of average orientations, as determined from a unique grain map of the deformed grains, was developed in order to classify deformed grains by type. The α-fiber components, γ-fiber components and random orientations, those which could not be assigned to either γ-fiber or α-fiber components, were used to define the average orientation of unique grains within individual deformed grains. The microstructures of deformed grains in as-rolled specimens were analyzed based on themore » Taylor factor, stored energy, and misorientation. The relative levels and distributions of the Taylor factor, the stored energy and the misorientation were examined in terms of the types of deformed grains. - Highlights: • We characterized the microstructure of Cu-added BH steel using EBSD. • A new scheme was developed in order to classify deformed grains by type. • Stored energy and misorientation are strongly dependent on the type of deformed grains. • Microstructure was examined in terms of the types of deformed grains.« less

Influence of deformation on structural-phase state of weld material in St3 steel

NASA Astrophysics Data System (ADS)

Smirnov, Alexander; Kozlov, Eduard; Ababkov, Nicolay; Popova, Natalya; Nikonenko, Elena; Ozhiganov, Yevgeniy; Zboykova, Nadezhda; Koneva, Nina

2016-01-01

The structural-phase condition of the weld material subjected to the plastic deformation was investigated using the translucent diffraction electron microscopy method. The investigations were carried out near the joint of the weld and the base metal. The seam was done by the method of manual arc welding without artificial defects. The St3 steel was taken as the welded material. Influence of the plastic deformation on morphology, phase composition, defect structure and its parameters of weld metal was revealed. All investigations were done at the distance of 0.5 mm from the joint of the weld and the base metal at the deformation degrees from 0 to 5% and after destruction of a sample. It was established that deformation of the sample did not lead to qualitative changes in the structure (the structure is still presented by ferrite-pearlite mixture) but changed the quantitative parameters of the structure, namely, with the increase of plastic deformation a part of the pearlite component becomes more and more imperfect. In the beginning it turns into the destroyed pearlite then into ferrite, the volume fraction of pearlite is decreased. The polarization of dislocation structure takes place but it doesn't lead to the internal stresses that can destroy the sample.

Macroscopic tensile plasticity by scalarizating stress distribution in bulk metallic glass

PubMed Central

Gao, Meng; Dong, Jie; Huan, Yong; Wang, Yong Tian; Wang, Wei-Hua

2016-01-01

The macroscopic tensile plasticity of bulk metallic glasses (BMGs) is highly desirable for various engineering applications. However, upon yielding, plastic deformation of BMGs is highly localized into narrow shear bands and then leads to the “work softening” behaviors and subsequently catastrophic fracture, which is the major obstacle for their structural applications. Here we report that macroscopic tensile plasticity in BMG can be obtained by designing surface pore distribution using laser surface texturing. The surface pore array by design creates a complex stress field compared to the uniaxial tensile stress field of conventional glassy specimens, and the stress field scalarization induces the unusual tensile plasticity. By systematically analyzing fracture behaviors and finite element simulation, we show that the stress field scalarization can resist the main shear band propagation and promote the formation of larger plastic zones near the pores, which undertake the homogeneous tensile plasticity. These results might give enlightenment for understanding the deformation mechanism and for further improvement of the mechanical performance of metallic glasses. PMID:26902264

Behaviour of thin-walled cold-formed steel members in eccentric compression

NASA Astrophysics Data System (ADS)

Ungureanu, Viorel; Kotełko, Maria; Borkowski, Łukasz; Grudziecki, Jan

2018-01-01

Thin-walled cold-formed steel structures are usually made of members of class 4 cross-sections. Since these sections are prematurely prone to local or distortional buckling and due to the fact they do not have a real post-elastic capacity, the failure at ultimate stage of those members, either in compression or bending, always occurs by forming a local plastic mechanism. The present paper investigates the evolution of the plastic mechanisms and the possibility to use them to characterise the ultimate strength of short thin-walled cold-formed steel members subjected to eccentric compression about minor axis, particularly for members with lipped channel cross-section. Five different types of plastic mechanisms for members in compression with different eccentricities are identified and examined on the basis of FE numerical simulations. Preliminary results of experimental validation of numerical results are presented. The research is based on previous studies and some new investigations of the authors.

EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nanstad, Randy K; Sokolov, Mikhail A; Merkle, John Graham

2007-01-01

To enable determination of the fracture toughness reference temperature, T0, with reactor pressure vessel surveillance specimens, the precracked Charpy (PCVN) three-point bend, SE(B), specimen is of interest. Compared with the 25-mm (1 in.) thick compact, 1TC(T), specimen, tests with the PCVN specimen (10x10x55 mm) have resulted in T0 temperatures as much as 40 XC lower (a so-called specimen bias effect). The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory developed a two-part project to evaluate the C(T) versus PCVN differences, (1) calibration experiments concentrating on test practices, and (2) a matrix of transition range tests with various specimenmore » geometries and sizes, including 1T SE(B) and 1TC(T). The test material selected was a plate of A533 grade B class 1 steel. The calibration experiments included assessment of the computational validity of J-integral determinations, while the constraint characteristics of various specimen types and sizes were evaluated using key curves and notch strength determinations. The results indicate that J-integral solutions for the small PCVN specimen are comparable in terms of J-integral validity with 1T bend specimens. Regarding constraint evaluations, Phase I deformation is defined where plastic deformation is confined to crack tip plastic zone development, whereas Phase II deformation is defined where plastic hinging deformation develops. In Phase II deformation, the 0.5T SE(B) B B specimen (slightly larger than the PCVN specimen) consistently showed the highest constraint of all SE(B) specimens evaluated for constraint comparisons. The PCVN specimen begins the Phase II type of deformation at relatively low KR levels, with the result that KJc values above about 70 MPa m from precracked Charpy specimens are under extensive plastic hinging deformation.« less

How tough is bone? Application of elastic-plastic fracture mechanics to bone.

PubMed

Yan, Jiahau; Mecholsky, John J; Clifton, Kari B

2007-02-01

Bone, with a hierarchical structure that spans from the nano-scale to the macro-scale and a composite design composed of nano-sized mineral crystals embedded in an organic matrix, has been shown to have several toughening mechanisms that increases its toughness. These mechanisms can stop, slow, or deflect crack propagation and cause bone to have a moderate amount of apparent plastic deformation before fracture. In addition, bone contains a high volumetric percentage of organics and water that makes it behave nonlinearly before fracture. Many researchers used strength or critical stress intensity factor (fracture toughness) to characterize the mechanical property of bone. However, these parameters do not account for the energy spent in plastic deformation before bone fracture. To accurately describe the mechanical characteristics of bone, we applied elastic-plastic fracture mechanics to study bone's fracture toughness. The J integral, a parameter that estimates both the energies consumed in the elastic and plastic deformations, was used to quantify the total energy spent before bone fracture. Twenty cortical bone specimens were cut from the mid-diaphysis of bovine femurs. Ten of them were prepared to undergo transverse fracture and the other 10 were prepared to undergo longitudinal fracture. The specimens were prepared following the apparatus suggested in ASTM E1820 and tested in distilled water at 37 degrees C. The average J integral of the transverse-fractured specimens was found to be 6.6 kPa m, which is 187% greater than that of longitudinal-fractured specimens (2.3 kPa m). The energy spent in the plastic deformation of the longitudinal-fractured and transverse-fractured bovine specimens was found to be 3.6-4.1 times the energy spent in the elastic deformation. This study shows that the toughness of bone estimated using the J integral is much greater than the toughness measured using the critical stress intensity factor. We suggest that the J integral method is a better technique in estimating the toughness of bone.

Effect of material inhomogeneity on the cyclic plastic deformation behavior at the microstructural level: micromechanics-based modeling of dual-phase steel

NASA Astrophysics Data System (ADS)

Paul, Surajit Kumar

2013-07-01

The microstructure of dual-phase (DP) steels typically consists of a soft ferrite matrix with dispersed islands of hard martensite phase. Due to the composite effect of ferrite and martensite, DP steels exhibit a unique combination of strain hardening, strength and ductility. A microstructure-based micromechanical modeling approach is adopted in this work to capture the tensile and cyclic plastic deformation behavior of DP steel. During tensile straining, strain incompatibility between the softer ferrite matrix and the harder martensite phase arises due to a difference in the flow characteristics of these two phases. Microstructural-level inhomogeneity serves as the initial imperfection, triggering strain incompatibility, strain partitioning and finally shear band localization during tensile straining. The local deformation in the ferrite phase is constrained by adjacent martensite islands, which locally results in stress triaxiality development in the ferrite phase. As the martensite distribution varies within the microstructure, the stress triaxiality also varies in a band within the microstructure. Inhomogeneous stress and strain distribution within the softer ferrite phase arises even during small tensile straining because of material inhomogeneity. The magnitude of cyclic plastic deformation within the softer ferrite phase also varies according to the stress distribution in the first-quarter cycle tensile loading. Accumulation of tensile/compressive plastic strain with number of cycles is noted in different locations within the ferrite phase during both symmetric stress and strain controlled cycling. The basic mode of cyclic plastic deformation in an inhomogeneous material is cyclic strain accumulation, i.e. ratcheting. Microstructural inhomogeneity results in cyclic strain accumulation in the aggregate DP material even in symmetric stress cycling.

The effect of hydrogen on the parameters of plastic deformation localization in low carbon steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lunev, Aleksey G., E-mail: agl@ispms.tsc.ru, E-mail: nadjozhkin@ispms.tsc.ru; Nadezhkin, Mikhail V., E-mail: agl@ispms.tsc.ru, E-mail: nadjozhkin@ispms.tsc.ru; Shlyakhova, Galina V., E-mail: shgv@ispms.tsc.ru

2014-11-14

In the present study, the effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested polycrystals of low-carbon steel Fe-0.07%C has been studied using double exposure speckle photography technique. The main parameters of plastic flow localization at various stages of deformation hardening have been determined in polycrystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at a controlled constant cathode potential. Also, the effect of hydrogen on changing of microstructure by using optical microscopy has been demonstrated.

Nanosized carbon modifier used to control plastic deformations of asphalt concrete

NASA Astrophysics Data System (ADS)

Vysotskaya, M. A.; Shekhovtsova, S. Yu; Barkovsky, D. V.

2018-03-01

Aspects related to plastic track, the formation of which directly depends on the properties of the binder in the composition of asphalt concrete, are considered in this article. The effect of primary carbon nanomaterials on the quality of polymer and bitumen binder in comparison with the traditional binder including cross-linking agent is evaluated. The influence of binders on the resistance to the track formation of type B asphalt concrete is studied. To quantify the service life of surfacing, a calculation method based on the criteria for the resistance of surfacing material to plastic deformations is used.

Correlation between elastic and plastic deformations of partially cured epoxy networks

NASA Astrophysics Data System (ADS)

Müller, Michael; Böhm, Robert; Geller, Sirko; Kupfer, Robert; Jäger, Hubert; Gude, Maik

2018-05-01

The thermo-mechanical behavior of polymer matrix materials is strongly dependent on the curing reaction as well as temperature and time. To date, investigations of epoxy resins and their composites mainly focused on the elastic domain because plastic deformation of cross-linked polymer networks was considered as irrelevant or not feasible. This paper presents a novel approach which combines both elastic and plastic domain. Based on an analytical framework describing the storage modulus, analogous parameter combinations are defined in order to reduce complexity when variations in temperature, strain rate and degree of cure are encountered.

Detection of plasticity mechanisms in an energetic molecular crystal through shock-like 3D unidirectional compressions: A Molecular Dynamics study

NASA Astrophysics Data System (ADS)

Lafourcade, Paul; Denoual, Christophe; Maillet, Jean-Bernard

2017-06-01

TATB crystal structure consists in graphitic-like sheets arranged in the a-b plane where a, b and c define the edge vectors of the unit cell. This type of stacking provides the TATB monocrystal very anisotropic physical, chemical and mechanical properties. In order to explore which mechanisms are involved in TATB plasticity, we use a Molecular Dynamics code in which the overall deformation is prescribed as a function of time, for any deformation path. Furthermore, a computation of the Green-Lagrange strain tensor is proposed, which helps reveal various defects and plasticity mechanisms. Through prescribed large strain of shock-like deformations, a three-dimensional characterization of TATB monocrystal yield stress has been obtained, confirming the very anisotropic behavior of this energetic material. Various plasticity mechanisms are triggered during these simulations, including counter intuitive defects onset such as gliding along transveral planes containing perfect dislocations and twinning. Gliding in the a-b plane occurs systematically and does not lead to significant plastic behavior, in accordance with a previous study on dislocation core structures for this plane, based on a coupling between the Peierls-Nabarro-Galerkin method and Molecular Dynamics simulations.

Crystal plasticity assisted prediction on the yield locus evolution and forming limit curves

NASA Astrophysics Data System (ADS)

Lian, Junhe; Liu, Wenqi; Shen, Fuhui; Münstermann, Sebastian

2017-10-01

The aim of this study is to predict the plastic anisotropy evolution and its associated forming limit curves of bcc steels purely based on their microstructural features by establishing an integrated multiscale modelling approach. Crystal plasticity models are employed to describe the micro deformation mechanism and correlate the microstructure with mechanical behaviour on micro and mesoscale. Virtual laboratory is performed considering the statistical information of the microstructure, which serves as the input for the phenomenological plasticity model on the macroscale. For both scales, the microstructure evolution induced evolving features, such as the anisotropic hardening, r-value and yield locus evolution are seamlessly integrated. The predicted plasticity behaviour by the numerical simulations are compared with experiments. These evolutionary features of the material deformation behaviour are eventually considered for the prediction of formability.

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Moore, John A.; Barton, Nathan R.; Florando, Jeff; Mulay, Rupalee; Kumar, Mukul

2017-10-01

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material’s structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V’s mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments or lower fidelity models. The results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.

The influence of severe plastic deformation by high pressure torsion on structure and mechanical properties of Hadfield steel single crystals

NASA Astrophysics Data System (ADS)

Zakharova, G. G.; Astafurova, E. G.

2010-07-01

Hadfield steel single crystals have been deformed by high pressure torsion at room temperature (P=5GPa) for 1, 2, 3 revolutions. The resulting microstructure has been studied by means of transmission electron microscopy (TEM) and X-ray analysis. The size of fragments decreases with increasing number of revolutions due to interaction of slip dislocations, microbands and thin twins. As a result of severe plastic deformation, the microhardness of the Hadfield steel has been increased, and a portion of epsilon, α' martensite has been found.

Electromigration-induced plastic deformation in passivated metal lines

NASA Astrophysics Data System (ADS)

Valek, B. C.; Bravman, J. C.; Tamura, N.; MacDowell, A. A.; Celestre, R. S.; Padmore, H. A.; Spolenak, R.; Brown, W. L.; Batterman, B. W.; Patel, J. R.

2002-11-01

We have used scanning white beam x-ray microdiffraction to study microstructural evolution during an in situ electromigration experiment on a passivated Al(Cu) test line. The data show plastic deformation and grain rotations occurring under the influence of electromigration, seen as broadening, movement, and splitting of reflections diffracted from individual metal grains. We believe this deformation is due to localized shear stresses that arise due to the inhomogeneous transfer of metal along the line. Deviatoric stress measurements show changes in the components of stress within the line, including relaxation of stress when current is removed.

Strain Hardening of Hadfield Manganese Steel

NASA Astrophysics Data System (ADS)

Adler, P. H.; Olson, G. B.; Owen, W. S.

1986-10-01

The plastic flow behavior of Hadfield manganese steel in uniaxial tension and compression is shown to be greatly influenced by transformation plasticity phenomena. Changes in the stress-strain (σ-ɛ) curves with temperature correlate with the observed extent of deformation twinning, consistent with a softening effect of twinning as a deformation mechanism and a hardening effect of the twinned microstructure. The combined effects give upward curvature to the σ-ɛ curve over extensive ranges of plastic strain. A higher strain hardening in compression compared with tension appears to be consistent with the observed texture development. The composition dependence of stacking fault energy computed using a thermodynamic model suggests that the Hadfield composition is optimum for a maximum rate of deformation twinning. Comparisons of the Hadfield steel with a Co-33Ni alloy exhibiting similar twinning kinetics, and an Fe-21Ni-lC alloy deforming by slip indicate no unusual strain hardening at low strains where deformation is controlled by slip, but an unusual amount of structural hardening associated with the twin formation in the Hadfield steel. A possible mechanism of anomalous twin hardening is discussed in terms of modified twinning behavior (pseudotwinning) in nonrandom solid solutions.

Sectional Finite Element Analysis on Viscous Pressure Forming of Sheet Metal

NASA Astrophysics Data System (ADS)

Liu, Jianguang; Wang, Zhongjin; Liu, Yan

2007-05-01

Viscous pressure forming (VPF) is a recently developed sheet flexible-die forming process, which uses a kind of semi-solid, flowable and viscous material as pressure-carrying medium that typically applied on one side of the sheet metal or on both sides of sheet metal. Different from traditional sheet metal forming processes in which sheet metal is the unique deformation-body, VPF is a coupling process of visco-elastoplastic bulk deformation of viscous medium and elasto-plastic deformation of sheet metal. A sectional finite element model for the coupled deformation between visco-elastoplastic body and elasto-plastic sheet metal was proposed to analyze VPF. The resolution of the Updated Lagrangian formulation is based on a static approach. By using static-explicit time integration strategy, the deformation of elasto-plastic sheet metal and visco-elastoplastic body can keep stable. The frictional contact between sheet metal and visco-elastoplastic body is treated by penalty function method. Using the proposed algorithm, sheet metal viscous pressure bulging (VPB) process is analyzed and compared with experiments. A good agreement between numerical simulation results and experimental ones proved the efficiency and stability of this algorithm.

SU-F-J-68: Deformable Dose Accumulation for Voxel-Based Dose Tracking of PTV Cold Spots for Adaptive Radiotherapy of the Head and Neck

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, C; Chetty, I; Mao, W

Purpose: To utilize deformable dose accumulation (DDA) to determine how cold spots within the PTV change over the course of fractionated head and neck (H&N) radiotherapy. Methods: Voxel-based dose was tracked using a DDA platform. The DDA process consisted of B-spline-based deformable image registration (DIR) and dose accumulation between planning CT’s and daily cone-beam CT’s for 10 H&N cancer patients. Cold spots within the PTV (regions receiving less than the prescription, 70 Gy) were contoured on the cumulative dose distribution. These cold spots were mapped to each fraction, starting from the first fraction to determine how they changed. Spatial correlationmore » between cold spot regions over each fraction, relative to the last fraction, was computed using the Jaccard index Jk (Mk,N), where N is the cold spot within the PTV at the end of the treatment, and Mk the same region for fraction k. Results: Figure 1 shows good spatial correlation between cold spots, and highlights expansion of the cold spot region over the course of treatment, as a result of setup uncertainties, and anatomical changes. Figure 2 shows a plot of Jk versus fraction number k averaged over 10 patients. This confirms the good spatial correlation between cold spots over the course of treatment. On average, Jk reaches ∼90% at fraction 22, suggesting that possible intervention (e.g. reoptimization) may mitigate the cold spot region. The cold spot, D99, averaged over 10 patients corresponded to a dose of ∼65 Gy, relative to the prescription dose of 70 Gy. Conclusion: DDA-based tracking provides spatial dose information, which can be used to monitor dose in different regions of the treatment plan, thereby enabling appropriate mid-treatment interventions. This work is supported in part by Varian Medical Systems, Palo Alto, CA.« less

The effect of plastic strain on the evolution of crystallographic texture in Zircaloy-2

NASA Astrophysics Data System (ADS)

Ballinger, R. G.; Lucas, G. E.; Pelloux, R. M.

1984-09-01

The evolution of crystallographic texture during plastic deformation was investigated in Zircaloy-2 using X-ray and metallographic techniques. Inverse pole figures, the resolved fraction of basal poles, and the volume fraction of twinned material, were determined as a function of plastic strain for several strain paths and initial textures at 298 K and 623 K. Incremental transverse platic strain ratios ( R) were mesured as a function of plastic strain. Texture rotation occurs early in the deformation process, after as little as 1.5% plastic strain. For compressive plastic strains, the resolved fraction of basal poles increases in the direction parallel to the strain axis. For tensile plastic strains, the resolved fraction of basal poles decreases in the direction parallel to the strain axis. The rate of change of the resolved fraction of basal poles with plastic strain is a function of the initial resolved fraction of basal poles. The texture rotation can be explained by considering the operation of the principal tensile twinning systems, {101¯2}<1¯011>.

Texture and structure contribution to low-temperature plasticity enhancement of Mg-Al-Zn-Mn Alloy MA2-1hp after ECAP and annealing

NASA Astrophysics Data System (ADS)

Serebryany, V. N.; D'yakonov, G. S.; Kopylov, V. I.; Salishchev, G. A.; Dobatkin, S. V.

2013-05-01

Equal channel angular pressing (ECAP) in magnesium alloys due to severe plastic shear deformations provides both grain refinement and the slope of the initial basal texture at 40°-50° to the pressing direction. These changes in microstructure and texture contribute to the improvement of low-temperature plasticity of the alloys. Quantitative texture X-ray diffraction analysis and diffraction of backscattered electrons are used to study the main textural and structural factors responsible for enhanced low-temperature plasticity based on the example of magnesium alloy MA2-1hp of the Mg-Al-Zn-Mn system. The possible mechanisms of deformation that lead to this positive effect are discussed.

Size-Tuned Plastic Flow Localization in Irradiated Materials at the Submicron Scale

NASA Astrophysics Data System (ADS)

Cui, Yinan; Po, Giacomo; Ghoniem, Nasr

2018-05-01

Three-dimensional discrete dislocation dynamics (3D-DDD) simulations reveal that, with reduction of sample size in the submicron regime, the mechanism of plastic flow localization in irradiated materials transitions from irradiation-controlled to an intrinsic dislocation source controlled. Furthermore, the spatial correlation of plastic deformation decreases due to weaker dislocation interactions and less frequent cross slip as the system size decreases, thus manifesting itself in thinner dislocation channels. A simple model of discrete dislocation source activation coupled with cross slip channel widening is developed to reproduce and physically explain this transition. In order to quantify the phenomenon of plastic flow localization, we introduce a "deformation localization index," with implications to the design of radiation-resistant materials.

Interaction of heat production, strain rate and stress power in a plastically deforming body under tensile test

NASA Technical Reports Server (NTRS)

Paglietti, A.

1982-01-01

At high strain rates the heat produced by plastic deformation can give rise to a rate dependent response even if the material has rate independent constitutive equations. This effect has to be evaluated when interpreting a material test, or else it could erroneously be ascribed to viscosity. A general thermodynamic theory of tensile testing of elastic-plastic materials is given in this paper; it is valid for large strain at finite strain rates. It enables discovery of the parameters governing the thermodynamic strain rate effect, provides a method for proper interpretation of the results of the tests of dynamic plasticity, and suggests a way of planning experiments in order to detect the real contribution of viscosity.

Amplified effect of mild plastic anisotropy on residual stress and strain anisotropy

DOE PAGES

Prime, Michael B.

2017-07-01

Axisymmetric indentation of a geometrically axisymmetric disk produced residual stresses by non-uniform plastic deformation. The 2024 aluminum plate used to make the disk exhibited mild plastic anisotropy with about 10% lower strength in the transverse direction compared to the rolling and through-thickness directions. Residual stresses and strains in the disk were measured with neutron diffraction, slitting, the contour method, x-ray diffraction and hole drilling. Surprisingly, the residual-stress anisotropy measured in the disk was about 40%, the residual-strain anisotropy was an impressive 100%, and the residual stresses were higher in the weaker direction. The high residual stress anisotropy relative to themore » mild plastic anisotropy and the direction of the highest stress are explained by considering the mechanics of indentation: constraint on deformation provided by the material surrounding the indentation and preferential deformation in the most compliant direction for incremental deformation. By contrast, the much larger anisotropy in residual strain compared to that in residual stress is independent of the fabrication process and is instead explained by considering Hookean elasticity. For Poisson's ratio of 1/3, the relationship simplifies to the residual strain anisotropy equaling the square of the residual stress anisotropy, which matches the observed results (2 ≈ 1.4^2). Furthermore, a lesson from this study is that to accurately predict residual stresses and strains, one must be wary of seemingly reasonable simplifying assumptions such as neglecting mild plastic anisotropy.« less

Amplified effect of mild plastic anisotropy on residual stress and strain anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prime, Michael B.

Axisymmetric indentation of a geometrically axisymmetric disk produced residual stresses by non-uniform plastic deformation. The 2024 aluminum plate used to make the disk exhibited mild plastic anisotropy with about 10% lower strength in the transverse direction compared to the rolling and through-thickness directions. Residual stresses and strains in the disk were measured with neutron diffraction, slitting, the contour method, x-ray diffraction and hole drilling. Surprisingly, the residual-stress anisotropy measured in the disk was about 40%, the residual-strain anisotropy was an impressive 100%, and the residual stresses were higher in the weaker direction. The high residual stress anisotropy relative to themore » mild plastic anisotropy and the direction of the highest stress are explained by considering the mechanics of indentation: constraint on deformation provided by the material surrounding the indentation and preferential deformation in the most compliant direction for incremental deformation. By contrast, the much larger anisotropy in residual strain compared to that in residual stress is independent of the fabrication process and is instead explained by considering Hookean elasticity. For Poisson's ratio of 1/3, the relationship simplifies to the residual strain anisotropy equaling the square of the residual stress anisotropy, which matches the observed results (2 ≈ 1.4^2). Furthermore, a lesson from this study is that to accurately predict residual stresses and strains, one must be wary of seemingly reasonable simplifying assumptions such as neglecting mild plastic anisotropy.« less

Features of plastic deformation and fracture of dispersion-strengthened V–Cr–Zr–W alloy depending on temperature of tension

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ditenberg, Ivan A.; Grinyaev, Konstantin V.; Tyumentsev, Alexander N.

2015-10-27

Influence of tension temperature on features of plastic deformation and fracture of V–4.23Cr–1.69Zr–7.56W alloy was investigated by scanning and transmission electron microscopy. It is shown that temperature increase leads to activation of the recovery processes, which manifests in the coarsening of microstructure elements, reducing the dislocation density, relaxation of continuous misorientations.

Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laplanche, Guillaume; Bonneville, J.; Varvenne, C.

To reveal the operating mechanisms of plastic deformation in an FCC high-entropy alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, σ y, the activation volume varies from ~60 b3 at 77 K to ~360 b 3 at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with σ - σ y (Haasenmore » plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-strengthened alloy. Lastly, these results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms.« less

Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy

DOE PAGES

Laplanche, Guillaume; Bonneville, J.; Varvenne, C.; ...

2017-10-06

To reveal the operating mechanisms of plastic deformation in an FCC high-entropy alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, σ y, the activation volume varies from ~60 b3 at 77 K to ~360 b 3 at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with σ - σ y (Haasenmore » plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-strengthened alloy. Lastly, these results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms.« less

Influences of rolling method on deformation force in cold roll-beating forming process

NASA Astrophysics Data System (ADS)

Su, Yongxiang; Cui, Fengkui; Liang, Xiaoming; Li, Yan

2018-03-01

In process, the research object, the gear rack was selected to study the influence law of rolling method on the deformation force. By the mean of the cold roll forming finite element simulation, the variation regularity of radial and tangential deformation was analysed under different rolling methods. The variation of deformation force of the complete forming racks and the single roll during the steady state under different rolling modes was analyzed. The results show: when upbeating and down beating, radial single point average force is similar, the tangential single point average force gap is bigger, the gap of tangential single point average force is relatively large. Add itionally, the tangential force at the time of direct beating is large, and the dire ction is opposite with down beating. With directly beating, deformation force loading fast and uninstall slow. Correspondingly, with down beating, deformat ion force loading slow and uninstall fast.

The effects of perturbations on the strain distribution in numerical simulations - elasto-viscoplastic modeling of boudinage as a case study

NASA Astrophysics Data System (ADS)

Peters, Max; Karrech, Ali; Poulet, Thomas; Herwegh, Marco; Regenauer-Lieb, Klaus

2014-05-01

During necking of a mechanically stiffer layer embedded in a weaker matrix, relatively large amounts of strain localize in small areas. As this deformation style appears under distinct geological conditions, necking phenomena, e.g. boudinaged veins, are associated with a variety of deformation modes. So far, there exists rather limited knowledge about the origin of instabilities and their role as precursory structures, i.e. strong localization of elastic energy affecting further plastic deformation (e.g. Regenauer-Lieb & Yuen, 1998; 2004; Karrech et al., 2011a). We applied the finite element solver ABAQUS in order to investigate the 2-D strain distribution in layers including different mechanical material properties during plane strain co-axial deformation. First, linear perturbation analyses were performed in order to evaluate the imperfection sensitivity in the elastic and viscous regimes. We perform a classical modal analysis to determine the natural mode shapes and frequencies of our geological structure during arbitrary vibrations. This analysis aims at detecting the eigenmodes of the geological structure, which are sinusoidal vibrations with geometry specific natural modal shapes and frequencies. The eigenvalues represent the nodal points where the onset of (visco)-elasto-plastic localization can initiate in the structure (Rice, 1977). The eigenmodes, eigenvalues and eigenvectors are highly sensitive to the layer-box' aspect ratio and differences in Young's moduli, or effective viscosity, respectively. Boundary effect-free strain propagation occurs for layer-box aspect ratios smaller than 1:10. Second, these preloading structures were used as seeds for imperfections in elasto-viscoplastic numerical modeling of continuous necking of a coarse-grained mineral layer embedded in a finer-grained matrix (pinch-and-swell type of boudinage), following the thermo-mechanical coupling of grain size evolutions by Herwegh et al. (in press). The evolution of symmetric necks seems to coincide with the transition from dislocation to diffusion creep dominated viscous flow with dramatic grain size reduction and grain growth from swell to neck, respectively, at relatively high extensional strains. Strain propagates from initial stress concentrations in the layer (necks) at an angle of 45° into the matrix, in form of conjugate shear band sets. Preliminary results show that pre-calculated eigenmodes (and corresponding imperfection sizes) amplify these concentrations and lead to a significant reduction of computational time for individual simulations. Moreover, the strain imperfections seeded around the pre-calculated distribution severely change the geometry of necking structures and amount of accommodated plastic strain. We reveal that elastic stress concentrations control localized visco-plastic deformation, which is expressed in the plastic strain energy increase in necking structures. These findings underline the importance of the transient (elasticity and strain hardening) deformation regimes as triggers for plastic deformation and the need for thermodynamics-based (total) energy considerations. REFERENCES Herwegh, M., Poulet, T., Karrech, A. and Regenauer-Lieb, K. (in press). From transient to steady state deformation and grain size: A thermodynamic approach using elasto-visco-plastic numerical modeling. Journal of Geophysical Research. Karrech, A., Regenauer-Lieb, K. and Poulet, T. (2011a). A Damaged visco-plasticity model for pressure and temperature sensitive geomaterials. Journal of Engineering Science 49. Regenauer-Lieb, K., Yuen, D., 1998: Rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere. Geophysical Research Letters, 25. Regenauer-Lieb, K., Yuen, D., 2004. Positive feedback of interacting ductile faults from coupling of equation of state, rheology and thermal-mechanics. Physics of the Earth and Planetary Interiors, 142. Rice, J. R. (1977). The localization of plastic deformation. Theoretical and Applied Mechanics. W. T. Koiter. Amsterdam, North-Holland: 207-220.

Three Distinct Deformation Behaviors of Cementite Lamellae in a Cold-Drawn Pearlitic Wire

NASA Astrophysics Data System (ADS)

Xin, Tuo; Liu, Guiju; Liang, Wenshuang; Cai, Rongsheng; Feng, Honglei; Li, Chen; Li, Jian; Wang, Yiqian

2018-03-01

High-resolution transmission electron microscopy is used to investigate the deformation behaviors of cementite lamellae in the heavily cold-drawn piano wires. Three distinct morphologies of cementite are observed, namely, complete lamella, partly-broken lamella and nearly-disappeared lamella. For the complete cementite lamella, it remains a single-crystalline structure. For the partly-broken cementite lamella, polycrystalline structure and neck-down region appear to release the residual strain. The lattice expansion of ferrite takes place in two perpendicular directions indicating that the carbon atoms dissolve from cementite into ferrite lattices. An orientation relationship is found between ferrite and cementite phases in the cold-drawn pearlitic wire.

Discontinuous precipitation at the deformation band in copper alloy

NASA Astrophysics Data System (ADS)

Han, Seung Zeon; Ahn, Jee Hyuk; You, Young Soo; Lee, Jehyun; Goto, Masahiro; Kim, Kwangho; Kim, Sangshik

2018-01-01

The Cu-Ni-Si alloy is known as a precipitation hardening alloy, where the Ni2Si intermetallic compound is precipitated in the matrix during aging. There are two types of precipitation of Ni2Si: continuous and discontinuous cellular. The discontinuous cellular precipitation is generally initiated at interfaces especially grain boundaries in the matrix. To observe the grain boundary effect on the discontinuous precipitation, a large-grained Cu-Ni-Si-Ti alloy was intentionally fabricated by unidirectional solidification and plastically deformed by groove rolling. While discontinuous cellular precipitation has been generally known to occur only at the high angled grain boundaries in the alloys, we found that it was also generated inside the grains, at the deformation bands formed by plastic deformation.

Soft sediment deformation structures in the Maastrichtian Ajali Formation Western Flank of Anambra Basin, Southern Nigeria

NASA Astrophysics Data System (ADS)

Olabode, Solomon Ojo

2014-01-01

Soft sediment deformation structures were recognized in the Maastrichtian shallow marine wave to tide influenced regressive sediments of Ajali Formation in the western flank of Anambra basin, southern Nigerian. The soft sediment deformation structures were in association with cross bedded sands, clay and silt and show different morphological types. Two main types recognised are plastic deformations represented by different types of recumbent folds and injection structure represented by clastic dykes. Other structures in association with the plastic deformation structures include distorted convolute lamination, subsidence lobes, pillars, cusps and sand balls. These structures are interpreted to have been formed by liquefaction and fluidization mechanisms. The driving forces inferred include gravitational instabilities and hydraulic processes. Facies analysis, detailed morphologic study of the soft sediment deformation structures and previous tectonic history of the basin indicate that the main trigger agent for deformation is earthquake shock. The soft sediment deformation structures recognised in the western part of Anambra basin provide a continuous record of the tectonic processes that acted on the regressive Ajali Formation during the Maastrichtian.

Deformation Mechanisms in Tube Billets from Zr-1%Nb Alloy under Radial Forging

NASA Astrophysics Data System (ADS)

Perlovich, Yuriy; Isaenkova, Margarita; Fesenko, Vladimir; Krymskaya, Olga; Zavodchikov, Alexander

2011-05-01

Features of the deformation process by cold radial forging of tube billets from Zr-1%Nb alloy were reconstructed on the basis of X-ray data concerning their structure and texture. The cold radial forging intensifies grain fragmentation in the bulk of billet and increases significantly the latent hardening of potentially active slip systems, so that operation only of the single slip system becomes possible. As a result, in radially-forged billets unusual deformation and recrystallization textures arise. These textures differ from usual textures of α-Zr by the mutual inversion of crystallographic axes, aligned along the axis of tube.

Modeling Near-Crack-Tip Plasticity from Nano- to Micro-Scales

NASA Technical Reports Server (NTRS)

Glaessgen, Edward H.; Saether, Erik; Hochhalter, Jake D.; Yamakov, Vesselin I.

2010-01-01

Several efforts that are aimed at understanding the plastic deformation mechanisms related to crack propagation at the nano-, meso- and micro-length scales including atomistic simulation, discrete dislocation plasticity, strain gradient plasticity and crystal plasticity are discussed. The paper focuses on discussion of newly developed methodologies and their application to understanding damage processes in aluminum and its alloys. Examination of plastic mechanisms as a function of increasing length scale illustrates increasingly complex phenomena governing plasticity

Study of soft magnetic iron cobalt based alloys processed by powder injection molding

NASA Astrophysics Data System (ADS)

Silva, Aline; Lozano, Jaime A.; Machado, Ricardo; Escobar, Jairo A.; Wendhausen, Paulo A. P.

As a near net shape process, powder injection molding (PIM) opens new possibilities to process Fe-Co alloys for magnetic applications. Due to the fact that PIM does not involve plastic deformation of the material during processing, we envisioned the possibility of eliminating vanadium (V), which is generally added to Fe-Co alloys to improve the ductility in order to enable its further shaping by conventional processes such as forging and cold rolling. In our investigation we have found out two main futures related to the elimination of V, which lead to a cost-benefit gain in manufacturing small magnetic components where high-saturation induction is needed at low frequencies. Firstly, the elimination of V enables the achievement of much better magnetic properties when alloys are processed by PIM. Secondly, a lower sintering temperature can be used when the alloy is processed starting with elemental Fe and Co powders without the addition of V.

Low-temperature creep of austenitic stainless steels

NASA Astrophysics Data System (ADS)

Reed, R. P.; Walsh, R. P.

2017-09-01

Plastic deformation under constant load (creep) in austenitic stainless steels has been measured at temperatures ranging from 4 K to room temperature. Low-temperature creep data taken from past and unreported austenitic stainless steel studies are analyzed and reviewed. Creep at cryogenic temperatures of common austenitic steels, such as AISI 304, 310 316, and nitrogen-strengthened steels, such as 304HN and 3116LN, are included. Analyses suggests that logarithmic creep (creep strain dependent on the log of test time) best describe austenitic stainless steel behavior in the secondary creep stage and that the slope of creep strain versus log time is dependent on the applied stress/yield strength ratio. The role of cold work, strain-induced martensitic transformations, and stacking fault energy on low-temperature creep behavior is discussed. The engineering significance of creep on cryogenic structures is discussed in terms of the total creep strain under constant load over their operational lifetime at allowable stress levels.

The effect of mechanical stress on electric resistance of nanographite-epoxy composites

NASA Astrophysics Data System (ADS)

Vovchenko, L.; Lazarenko, A.; Matzui, L.; Zhuravkov, A.

2012-03-01

The in-plane electric resistance Ra of composite materials (CMs) thermoexfoliated graphite(TEG)-epoxy resin(ED) under compression along compacting C-axis has been investigated by four-probe method. TEG content was 5-75 wt%. It was shown that specimens prepared by cold pressing are denser and reveal lower values of electric resistivity in comparison with specimens prepared by pouring. It was found that compression of the specimens leads to plastic deformation of specimens (εpl) and essential irreversible decrease of electric resistance during the first cycle of loading (up to 50 MPa), especially for the poured specimens with low density. Within the proposed model the contact resistance Rk between graphite particles in CM has been evaluated and it was shown that it increased with the decrease in TEG content in CM and depends on compacting method of CMs and the dispersity of graphite filler.

Understanding thermally activated plastic deformation behavior of Zircaloy-4

NASA Astrophysics Data System (ADS)

Kumar, N.; Alomari, A.; Murty, K. L.

2018-06-01

Understanding micromechanics of plastic deformation of existing materials is essential for improving their properties further and/or developing advanced materials for much more severe load bearing applications. The objective of the present work was to understand micromechanics of plastic deformation of Zircaloy-4, a zirconium-based alloy used as fuel cladding and channel (in BWRs) material in nuclear reactors. The Zircaloy-4 in recrystallized (at 973 K for 4 h) condition was subjected to uniaxial tensile testing at a constant cross-head velocity at temperatures in the range 293 K-1073 K and repeated stress relaxation tests at 293 K, 573 K, and 773 K. The minimum in the total elongation was indicative of dynamic strain aging phenomenon in this alloy in the intermediate temperature regime. The yield stress of the alloy was separated into effective and athermal components and the transition from thermally activated dislocation glide to athermal regime took place at around 673 K with the athermal stress estimated to be 115 MPa. The activation volume was found to be in the range of 40 b3 to 160 b3. The activation volume values and the data analyses using the solid-solution models in literature indicated dislocation-solute interaction to be a potential deformation mechanism in thermally activated regime. The activation energy calculated at 573 K was very close to that found for diffusivity of oxygen in α-Zr that was suggestive of dislocations-oxygen interaction during plastic deformation. This type of information may be helpful in alloy design in selecting different elements to control the deformation behavior of the material and impart desired mechanical properties in those materials for specific applications.

Mechanisms of Plastic Deformation in Collagen Networks Induced by Cellular Forces.

PubMed

Ban, Ehsan; Franklin, J Matthew; Nam, Sungmin; Smith, Lucas R; Wang, Hailong; Wells, Rebecca G; Chaudhuri, Ovijit; Liphardt, Jan T; Shenoy, Vivek B

2018-01-23

Contractile cells can reorganize fibrous extracellular matrices and form dense tracts of fibers between neighboring cells. These tracts guide the development of tubular tissue structures and provide paths for the invasion of cancer cells. Here, we studied the mechanisms of the mechanical plasticity of collagen tracts formed by contractile premalignant acinar cells and fibroblasts. Using fluorescence microscopy and second harmonic generation, we quantified the collagen densification, fiber alignment, and strains that remain within the tracts after cellular forces are abolished. We explained these observations using a theoretical fiber network model that accounts for the stretch-dependent formation of weak cross-links between nearby fibers. We tested the predictions of our model using shear rheology experiments. Both our model and rheological experiments demonstrated that increasing collagen concentration leads to substantial increases in plasticity. We also considered the effect of permanent elongation of fibers on network plasticity and derived a phase diagram that classifies the dominant mechanisms of plasticity based on the rate and magnitude of deformation and the mechanical properties of individual fibers. Plasticity is caused by the formation of new cross-links if moderate strains are applied at small rates or due to permanent fiber elongation if large strains are applied over short periods. Finally, we developed a coarse-grained model for plastic deformation of collagen networks that can be employed to simulate multicellular interactions in processes such as morphogenesis, cancer invasion, and fibrosis. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Use of first derivative of displacement vs. force profiles to determine deformation behavior of compressed powders.

PubMed

Gharaibeh, Shadi F; Aburub, Aktham

2013-03-01

Displacement (D) vs. force (F) profiles obtained during compaction of powders have been reported by several researchers. These profiles are usually used to obtain mechanical energies associated with the compaction of powders. In this work, we obtained displacement-force data associated with the compression of six powders; Avicel PH101, Avicel PH301, pregelatinized corn starch, anhydrous lactose, dicalcium phosphate, and mannitol. The first three powders are known to deform predominantly by plastic behavior while the later ones are known to deform predominantly by brittle fracture. Displacement-force data was utilized to perform in-die Heckel analysis and to calculate the first derivative (dD/dF) of displacement-force plots. First derivative results were then plotted against mean force (F') at each point and against 1/F' at compression forces between 1 and 20 kN. Results of the in-die Heckle analysis are in very good agreement with the known deformation behavior of the compressed materials. First derivative plots show that materials that deform predominantly by plastic behavior have first derivative values (0.0006-0.0016 mm/ N) larger than those of brittle materials (0.0004 mm/N). Moreover, when dD/dF is plotted against 1/F' for each powder, a linear correlation can be obtained (R2=>0.98). The slopes of the dD/dF vs. 1/F' plots for plastically deforming materials are relatively larger than those for materials that deform by brittle behavior. It is concluded that first derivative plots of displacement-force profiles can be used to determine deformation behavior of powders.

Structural Crashworthiness and Failure

DTIC Science & Technology

1993-04-16

body motion occurs. This rigid -plastic idealization for dynamically loaded structures is based upon the fact that the plastic deformation of a...in general, for any tensor variable x, i represents the convective derivative. It should be noted that the rigid body rotation is included in the...clamped, impulsively loaded, rigid - plastic beam.’ (a) First phase of motion with stationary transverse plastic hinges at A and E and stationary plastic

Assessment of cold welding properties of the internal conical interface of two commercially available implant systems.

PubMed

Norton, M R

1999-02-01

The cone-screw abutment has been shown to diminish micromovement by reducing the burden of component loosening and fracture. However, anecdotal concern for cold welding of cone-screw joints in implant design has been identified as a potential source for lack of retrievability. This comparative study evaluated the loosening torque, as a percentage of tightening torque, for the ITI Straumann and Astra Tech (3.5 and 4.0 mm diameters) implant systems, which use an 8-degree and 11-degree internal cone, respectively. Implants and abutments from each system were mounted in a torque device, and a range of tightening torques was applied. Loosening torques were then measured, and the influence of conus angle, interfacial surface area, saliva contamination, and time delay to loosening were all assessed. The loosening torque only exceeded tightening torque at the highest levels, just before component failure, when plastic deformation was expected. For all clinically relevant levels of torque, both in a dry environment and with components bathed in artificial saliva at 37 degrees C, loosening torque was always seen to be 80% to 90% of tightening torque, demonstrating that cold welding does not occur. There was a high correlation between loosening and tightening torque for all systems tested, but no statistical difference when comparing wet versus dry or comparing individual data for each system. It can be concluded that for clinically relevant levels of tightening torque, no problems are anticipated with respect to retrievability.

In situ strain profiling of elastoplastic bending in Ti-6Al-4V alloy by synchrotron energy dispersive x-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croft, M.; National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973; Shukla, V.

Elastic and plastic strain evolution under four-point bending has been studied by synchrotron energy dispersive x-ray diffraction. Measured strain profiles across the specimen thickness showed an increasing linear elastic strain gradient under increasing four-point bending load up to approx2 kN. The bulk elastic modulus of Ti-6Al-4V was determined as 118 GPa. The onset of plastic deformation was found to set in at a total in-plane strain of approx0.008, both under tension and compression. Plastic deformation under bending is initiated in the vicinity of the surface and at a stress of 1100 MPa, and propagates inward, while a finite core regionmore » remains elastically deformed up to 3.67 kN loading. The onset of the plastic regime and the plastic regime itself has been verified by monitoring the line broadening of the (100) peak of alpha-Ti. The effective compression/tension stress-strain curve has been obtained from the scaling collapse of strain profile data taken at seven external load levels. A similar multiple load scaling collapse of the plastic strain variation has also been obtained. The level of precision in strain measurement reported herein was evaluated and found to be 1.5x10{sup -5} or better.« less

Molecular dynamics simulation of the plastic behavior anisotropy of shock-compressed monocrystal nickel

NASA Astrophysics Data System (ADS)

Chen, Ya-Zhou; Zhou, Liu-Cheng; He, Wei-Feng; Sun, Yu; Li, Ying-Hong; Jiao, Yang; Luo, Si-Hai

2017-01-01

Molecular dynamics simulations were used to study the plastic behavior of monocrystalline nickel under shock compression along the [100] and [110] orientations. The shock Hugoniot relation, local stress curve, and process of microstructure development were determined. Results showed the apparent anisotropic behavior of monocrystalline nickel under shock compression. The separation of elastic and plastic waves was also obvious. Plastic deformation was more severely altered along the [110] direction than the [100] direction. The main microstructure phase transformed from face-centered cubic to body-centered cubic and generated a large-scale and low-density stacking fault along the family of { 111 } crystal planes under shock compression along the [100] direction. By contrast, the main mechanism of plastic deformation in the [110] direction was the nucleation of the hexagonal, close-packed phase, which generated a high density of stacking faults along the [110] and [1̅10] directions.

Viscoelasticity and plasticity mechanisms of human dentin

NASA Astrophysics Data System (ADS)

Borodin, E. N.; Seyedkavoosi, S.; Zaitsev, D.; Drach, B.; Mikaelyan, K. N.; Panfilov, P. E.; Gutkin, M. Yu.; Sevostianov, I.

2018-01-01

Theoretical models of viscoelastic behavior and plastic deformation mechanisms of human dentin are considered. Using the linear viscoelasticity theory in which creep and relaxation kernels have the form of fraction-exponential functions, numerical values of instantaneous and long-time Young's moduli and other characteristics of dentin viscoelasticity under uniaxial compression are found. As dentin plastic deformation mechanisms, mutual collagen fiber sliding in the region of contact of their side surfaces, separation of these fibers from each other, and irreversible tension of some collagen fibers, are proposed. It is shown that the second mechanism activation requires a smaller stress than that for activating others. The models of plastic zones at the mode I crack tip, which correspond to these mechanisms, are studied. It is shown that the plastic zone size can increase from a few hundreds of nanometers to hundreds of micrometers with increasing applied stress.

A study on the plasticity of soda-lime silica glass via molecular dynamics simulations.

PubMed

Urata, Shingo; Sato, Yosuke

2017-11-07

Molecular dynamics (MD) simulations were applied to construct a plasticity model, which enables one to simulate deformations of soda-lime silica glass (SLSG) by using continuum methods. To model the plasticity, stress induced by uniaxial and a variety of biaxial deformations was measured by MD simulations. We found that the surfaces of yield and maximum stresses, which are evaluated from the equivalent stress-strain curves, are reasonably represented by the Mohr-Coulomb ellipsoid. Comparing a finite element model using the constructed plasticity model to a large scale atomistic model on a nanoindentation simulation of SLSG reveals that the empirical method is accurate enough to evaluate the SLSG mechanical responses. Furthermore, the effect of ion-exchange on the SLSG plasticity was examined by using MD simulations. As a result, it was demonstrated that the effects of the initial compressive stress on the yield and maximum stresses are anisotropic contrary to our expectations.

A study on the plasticity of soda-lime silica glass via molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Urata, Shingo; Sato, Yosuke

2017-11-01

Molecular dynamics (MD) simulations were applied to construct a plasticity model, which enables one to simulate deformations of soda-lime silica glass (SLSG) by using continuum methods. To model the plasticity, stress induced by uniaxial and a variety of biaxial deformations was measured by MD simulations. We found that the surfaces of yield and maximum stresses, which are evaluated from the equivalent stress-strain curves, are reasonably represented by the Mohr-Coulomb ellipsoid. Comparing a finite element model using the constructed plasticity model to a large scale atomistic model on a nanoindentation simulation of SLSG reveals that the empirical method is accurate enough to evaluate the SLSG mechanical responses. Furthermore, the effect of ion-exchange on the SLSG plasticity was examined by using MD simulations. As a result, it was demonstrated that the effects of the initial compressive stress on the yield and maximum stresses are anisotropic contrary to our expectations.

Elastic-plastic deformation of a metal-matrix composite coupon with a center slot

NASA Technical Reports Server (NTRS)

Post, D.; Czarnek, R.; Joh, D.; Jo, J.; Guo, Y.

1985-01-01

A comprehensive experimental analysis of deformations of the surface of a metal-matrix specimen is reported. The specimen is a 6-ply 0 + or - 45 sub s boron-aluminum tensile coupon with a central slot. Moire interferometry is used for high-sensitivity whole-field measurements of in-plane displacements. Normal and shear strains are calculated from displacement gradients. Displacement fields are analyzed at various load levels from 15% to 95% of the failure load. Deformations of the boron fibers could be distinguished from those of the matrix. Highly localized plastic slip zones occur tangent to the ends of the slot. Shear strains and concurrent transverse compressive strains in the slip zones reach approximately 10% and 1%, respectively. Upon unloading, elastic recovery in surrounding regions causes a reverse plastic shear strain in the slip zone of about 4%. Longitudinal normal strains on the unslotted ligament peak at the slot boundary at about 1% strain. The strain concentration factor at the end of the slot decreases with load level and the advance of plasticity.

Room- and Low-Temperature Deformation of Multilayered Fiberglass Plastics Reinforced with a Fabric of Sateen Weave

NASA Astrophysics Data System (ADS)

Kucher, N. K.; Dveyrin, A. Z.; Zarazovskii, M. N.; Zemtsov, M. P.

2004-05-01

The regularities of elastic deformation of multilayered fiberglass plastics reinforced with a fabric of sateen weave are studied. The effect of cooling to 77 K on the averaged elastic characteristics of the orthotropic material is analyzed. The efficiency of mathematical modeling in calculating the stiffness and compliance parameters of the woven composites based on the geometry and mechanical properties of their constituents is investigated.

USSR and Eastern Europe Scientific Abstracts. Engineering and Equipment. Number 26

DTIC Science & Technology

1976-11-10

harbor in- volves a sea sector and a river sector. The author indicates the hypotheses taken into consideration, including the number of berths in the...river and sea sectors, the arrivals of sea - and river-going ships, and ship operation time. Also indicated is the system of equations describing...diffusion for plastic deformation by torsion is greater than plastic deformation by tension. The main energy diffusion mechanism is microplastic

LWH and ACH Helmet Hardware Study

DTIC Science & Technology

2015-11-30

stiffer and stronger than Kevlar panels, does not plastically deform (and therefore Figure 11. Typical ductile fracture surface resulting from a...striker from deflecting. The substrate is ¼ inch thick fiberglass plate supported on a base plate of 5083 aluminum alloy . Figure 13. Close ups of...project. We note that the impact damage to the top of the screw heads, is entirely plastic deformation of the slot and top of the head, and is clearly

LWH & ACH Helmet Hardware Study

DTIC Science & Technology

2015-11-30

stiffer and stronger than Kevlar panels, does not plastically deform (and therefore Figure 11. Typical ductile fracture surface resulting from a...striker from deflecting. The substrate is ¼ inch thick fiberglass plate supported on a base plate of 5083 aluminum alloy . Figure 13. Close ups of...project. We note that the impact damage to the top of the screw heads, is entirely plastic deformation of the slot and top of the head, and is clearly

Structure of Al-Fe alloys prepared by different methods after severe plastic deformation under pressure

NASA Astrophysics Data System (ADS)

Dobromyslov, A. V.; Taluts, N. I.

2017-06-01

Al-Fe alloys prepared by casting, rapid quenching from the melt, and mechanical alloying from elemental powders have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and microhardness measurements in the initial state and after severe plastic deformation by high-pressure torsion using Bridgman anvils. The relationship between the phase composition, microstructure, and the microhardness of the investigated alloys has been established.

Use of multiscale zirconium alloy deformation models in nuclear fuel behavior analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montgomery, Robert; Tomé, Carlos; Liu, Wenfeng

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. CASL has endeavored to improve upon this approach by incorporating a microstructurally-based, atomistically-informed, zirconium alloy mechanical deformation analysis capability into the BISON-CASL engineering scale fuel performance code. Specifically, the viscoplastic self-consistent (VPSC) polycrystal plasticity modeling approach, developed bymore » Lebensohn and Tome´ [2], has been coupled with BISON-CASL to represent the mechanistic material processes controlling the deformation behavior of the cladding. A critical component of VPSC is the representation of the crystallographic orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON-CASL and provides initial results utilizing the coupled functionality.« less

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawrence, Samantha K.; Somerday, Brian P.; Ingraham, Mathew Duffy

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases ~20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yieldingmore » in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.« less

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, John A.; Barton, Nathan R.; Florando, Jeff

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

DOE PAGES

Lawrence, Samantha K.; Somerday, Brian P.; Ingraham, Mathew Duffy; ...

2018-04-11

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases ~20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yieldingmore » in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.« less

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE PAGES

Moore, John A.; Barton, Nathan R.; Florando, Jeff; ...

2017-08-24

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Johnson, R D; Young, A P; Schwope, A D

1956-01-01

This report describes the results of a comprehensive study of plastic deformation of aluminum single crystals over a wide range of temperatures. The results of constant-stress creep tests have been reported for the temperature range from 400 degrees to 900 degrees F. For these tests, a new capacitance-type extensometer was designed. This unit has a range of 0.30 inch over which the sensitivity is very nearly linear and can be varied from as low a sensitivity as is desired to a maximum of 20 microinches per millivolt with good stability. Experiments were carried out to investigate the effect of small amounts of prestraining, by two different methods, on the creep and tensile properties of these aluminum single crystals. From observations it has been concluded that plastic deformation takes place predominantly by slip which is accompanied by the mechanisms of kinking and polygonization.

Atomistic basis for the plastic yield criterion of metallic glass.

PubMed

Schuh, Christopher A; Lund, Alan C

2003-07-01

Because of their disordered atomic structure, amorphous metals (termed metallic glasses) have fundamentally different deformation mechanisms compared with polycrystalline metals. These different mechanisms give metallic glasses high strength, but the extent to which they affect other macroscopic deformation properties is uncertain. For example, the nature of the plastic-yield criterion is a point of contention, with some studies reporting yield behaviour roughly in line with that of polycrystalline metals, and others indicating strong fundamental differences. In particular, it is unclear whether pressure- or normal stress-dependence needs to be included in the plastic-yield criterion of metallic glasses, and how such a dependence could arise from their disordered structure. In this work we provide an atomic-level explanation for pressure-dependent yield in amorphous metals, based on an elementary unit of deformation. This simple model compares favourably with new atomistic simulations of metallic glasses, as well as existing experimental data.

Dynamic strength of cylindrical fiber-glass shells and basalt plastic shells under multiple explosive loading

NASA Astrophysics Data System (ADS)

Syrunin, M. A.; Fedorenko, A. G.

2006-08-01

We have shown experimentally that, for cylindrical shells made of oriented fiberglass platic and basalt plastic there exists a critical level of deformations, at which a structure sustains a given number of explosions from the inside. The magnitude of critical deformation for cylindrical fiberglass shells depends linearly on the logarithm of the number of loads that cause failure. For a given type of fiberglass, there is a limiting level of explosive action, at which the number of loads that do not lead to failure can be sufficiently large (more than ˜ 102). This level is attained under loads, which are an order of magnitude lower than the limiting loads under a single explosive action. Basalt plastic shells can be repeatedly used even at the loads, which cause deformation by ˜ 30-50% lower than the safe value ˜ 3.3.5% at single loading.

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

NASA Astrophysics Data System (ADS)

Lawrence, S. K.; Somerday, B. P.; Ingraham, M. D.; Bahr, D. F.

2018-04-01

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases 22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases 20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yielding in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal a direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.

Molecular dynamics modeling and simulation of void growth in two dimensions

NASA Astrophysics Data System (ADS)

Chang, H.-J.; Segurado, J.; Rodríguez de la Fuente, O.; Pabón, B. M.; LLorca, J.

2013-10-01

The mechanisms of growth of a circular void by plastic deformation were studied by means of molecular dynamics in two dimensions (2D). While previous molecular dynamics (MD) simulations in three dimensions (3D) have been limited to small voids (up to ≈10 nm in radius), this strategy allows us to study the behavior of voids of up to 100 nm in radius. MD simulations showed that plastic deformation was triggered by the nucleation of dislocations at the atomic steps of the void surface in the whole range of void sizes studied. The yield stress, defined as stress necessary to nucleate stable dislocations, decreased with temperature, but the void growth rate was not very sensitive to this parameter. Simulations under uniaxial tension, uniaxial deformation and biaxial deformation showed that the void growth rate increased very rapidly with multiaxiality but it did not depend on the initial void radius. These results were compared with previous 3D MD and 2D dislocation dynamics simulations to establish a map of mechanisms and size effects for plastic void growth in crystalline solids.

North America-Pacific plate boundary, an elastic-plastic megashear - Evidence from very long baseline interferometry

NASA Technical Reports Server (NTRS)

Ward, Steven N.

1988-01-01

Data obtained by Mark III VLBI measurements of radio signals from permanent and mobile VLBI sites for 5.5 years of observations, starting in October 1982, were used to derive a picture of the earth crust deformation near the North America-Pacific plate boundary. The data, which included the vector positions of the VLBI sites and their rate of change, were used for comparison with a number of lithospheric deformation models based upon the concept that the motions of points near the North America-Pacific plate boundary are a linear combination of North America and Pacific velocities. The best of these models were found to fit 95 percent of the variance in 139 VLBI length and transverse velocity observations. Instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the San Andreas Fault; some of this deformation will be recovered through elastic rebound, while the rest will be permanently set through plastic processes. Because the VLBI data have not been collected for a significant fraction of the earthquake cycle, they cannot discriminate between elastic and plastic behaviors.

Preparation, deformation, and failure of functional Al-Sn and Al-Sn-Pb nanocrystalline alloys

NASA Astrophysics Data System (ADS)

Noskova, N. I.; Vil'Danova, N. F.; Filippov, Yu. I.; Churbaev, R. V.; Pereturina, I. A.; Korshunov, L. G.; Korznikov, A. V.

2006-12-01

Changes in the structure, hardness, mechanical properties, and friction coefficient of Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb (wt %) alloys subjected to severe plastic deformation by equal-channel angular pressing (with a force of 40 tonne) and by shear at a pressure of 5 GPa have been studied. The transition into the nanocrystalline state was shown to occur at different degrees of plastic deformation. The hardness exhibits nonmonotonic variations, namely, first it increases and subsequently decreases. The friction coefficient of the Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys quenched from the melt was found to be 0.33; the friction coefficients of these alloys in the submicrocrystalline state (after equal-channel angular pressing) equal 0.24, 0.32, and 0.35, respectively. The effect of disintegration into nano-sized powders was found to occur in the Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys after severe plastic deformation to ɛ = 6.4 and subsequent short-time holding.

Thermodynamically consistent relations involving plasticity, internal energy and thermal effects.

PubMed

Schreyer, H L; Maudlin, P J

2005-11-15

Experimental data associated with plastic deformations indicate that the temperature is less than that predicted from dissipation based on plastic work. To obtain reasonable correlation between theoretical and experimental results, the plastic work is often multiplied by a constant beta. This paper provides an alternative thermodynamic framework in which it is proposed that there is an additional internal energy associated with dislocation pile-up or increase in dislocation density. The form of this internal energy follows from experimental data that relates flow stress to dislocation density and to equivalent plastic strain. The result is that beta is not a constant but a derived function. Representative results for beta and temperature as functions of effective plastic strain are provided for both an uncoupled and a coupled thermoplastic theory. In addition to providing features that are believed to be representative of many metals, the formulation can be used as a basis for more advanced theories such as those needed for large deformations and general forms of internal energy.

Nature and mechanisms of elastic deformations for a rock mass with several workings. [Deviations from superposition of individual effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yagunov, A.S.; Seryakov, V.M.

1985-07-01

This paper presents results of a study which indicates that as a result of the solution for a nonuniform rock mass by the FEM it is established that, first, from the direction of the hanging wall of workings and at the surface, the nature of elastic deformation of the rock is equivalent to that observed under natural conditions, and from the direction of the lying wall of workings and close to their ends there is short-lived rotational creation of elastic displacements, extinguished as plastic deformation develops. Second, the superposition principle, taken as the basis for algebraic summation of displacements andmore » deformations due to individual workings, is not entirely observed in their joint effect on the rock mass in the elastic stage, and with plastic and shear deformation of rocks (partial or complete), depending on their bedding conditions.« less

Interfacial diffusion aided deformation during nanoindentation

DOE PAGES

Samanta, Amit; E., Weinan

2015-07-06

Nanoindentation is commonly used to quantify the mechanical response of material surfaces. Despite its widespread use, a detailed understanding of the deformation mechanisms responsible for plasticity during these experiments has remained elusive. Nanoindentation measurements often show stress values close to a material’s ideal strength which suggests that dislocation nucleation and subsequent dislocation activity dominates the deformation. However, low strain-rate exponents and small activation volumes have also been reported which indicates high temperature sensitivity of the deformation processes. Using an order parameter aided temperature accelerated sampling technique called adiabatic free energy dynamics [J. B. Abrams and M. E. Tuckerman, J. Phys.more » Chem. B, 112, 15742 (2008)], and molecular dynamics we have probed the diffusive mode of deformation during nanoindentation. Localized processes such as surface vacancy and ad-atom pair formation, vacancy diffusion are found to play an important role during indentation. Furthermore, our analysis suggests a change in the dominant deformation mode from dislocation mediated plasticity to diffusional flow at high temperatures, slow indentation rates and small indenter tip radii.« less

Elasticity and anelasticity of microcrystalline aluminum samples having various deformation and thermal histories

NASA Astrophysics Data System (ADS)

Betekhtin, V. I.; Kadomtsev, A. G.; Kardashev, B. K.

2006-08-01

The effect of the amplitude of vibrational deformation on the elastic modulus and internal friction of microcrystalline aluminum samples produced by equal-channel angular pressing was studied. The samples have various deformation and thermal histories. The elastic and inelastic (microplastic) properties of the samples are investigated. As the degree of plastic deformation increases, the Young’s modulus E, the amplitude-independent decrement δi, and the microplastic flow stress σ increase. As the annealing temperature increases, the quantities δi and σ decrease noticeably and the modulus E exhibits a more complex behavior. The experimental data are discussed under the assumption that the dislocation mobility depends on both the spectrum of point defects and the internal stresses, whose level is determined by the degree of plastic deformation and the temperature of subsequent annealing. The concept of internal stresses is also used to analyze the data on the effect of the degree of deformation and annealing on the rupture strength of the samples.

Experimental and numerical investigation on laser-assisted bending of pre-loaded metal plate

NASA Astrophysics Data System (ADS)

Nowak, Zdzisław; Nowak, Marcin; Widłaszewski, Jacek; Kurp, Piotr

2018-01-01

The laser forming technique has an important disadvantage, which is the limitation of plastic deformation generated by a single laser beam pass. To increase the plastic deformation it is possible to apply external forces in the laser forming process. In this paper, we investigate the influence of external pre-loads on the laser bending of steel plate. The pre-loads investigated generate bending towards the laser beam. The thermal, elastic-plastic analysis is performed using the commercial nonlinear finite element analysis package ABAQUS. The focus of the paper is to identify how this pattern of the pre-load influence the final bend angle of the plate.

Ultra fine grained Ti prepared by severe plastic deformation

NASA Astrophysics Data System (ADS)

Lukáč, F.; Čížek, J.; Knapp, J.; Procházka, I.; Zháňal, P.; Islamgaliev, R. K.

2016-01-01

The positron annihilation spectroscopy was employed for characterisation of defects in pure Ti with ultra fine grained (UFG) structure. UFG Ti samples were prepared by two techniques based on severe plastic deformation (SPD): (i) high pressure torsion (HPT) and (ii) equal channel angular pressing (ECAP). Although HPT is the most efficient technique for grain refinement, the size of HPT-deformed specimens is limited. On the other hand, ECAP is less efficient in grain refinement but enables to produce larger samples more suitable for industrial applications. Characterisation of defects by positron annihilation spectroscopy was accompanied by hardness testing in order to monitor the development of mechanical properties of UFG Ti.

Structure of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation and long-term storage

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2015-11-01

Structural and phase transformations in commercial aging aluminum-lithium Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg alloy have been studied after severe plastic deformation by high-pressure torsion (at a pressure of 4 GPa with 1, 5, and 10 revolutions of the anvil) and natural aging (roomtemperature storage) for 1 week and 2 years. It has been found that, in this case, the process of static recrystallization is achieved in the alloy, the degree of which increases with an increasing degree of deformation and time of storage.

Development of ultrafine-grained microstructure in Al-Cu-Mg alloy through equal-channel angular pressing

NASA Astrophysics Data System (ADS)

Sai Anuhya, Danam; Gupta, Ashutosh; Nayan, Niraj; Narayana Murty, S. V. S.; Manna, R.; Sastry, G. V. S.

2014-08-01

Al-Cu-Mg alloys are extensively used for riveting applications in aerospace industries due to their relatively high shear strength coupled with high plasticity. The significant advantage of using V65 aluminum alloy ((Al-4Cu-0.2Mg) for rivet application also stems from its significantly slower natural aging kinetics, which gives operational flexibility to carryout riveting operation even after 4 days of solution heat treatment, in contrast to its equivalent alloy AA2024.Rivets are usually made by cold heading of wire rods. In order to form a defect free rivet head, grain size control in wire rods is essential at each and every stage of processing right from casting onwards upto the final wire drawing stage. Wire drawing is carried out at room temperature to reduce diameter as well as impart good surface finish. In the present study, different microstructures in V65 alloy bars were produced by rolling at different temperatures (room temperature to 523K) and subsequently deformed by equal channel angular pressing (ECAP) at 423K upto an equivalent strain of 7. ECAP was carried out to study the effect of initial microstructure on grain refinement and degree of deformation on the evolution of ultrafine grain structure. The refinement of V65 alloy by ECAP is significantly influenced by Initial microstructure but amount of deformation strongly affects the evolution processes as revealed by optical microscopy and transmission electron microscopy.

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE PAGES

Gao, Yanfei

2015-11-30

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Yanfei

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Foam rheology at large deformation

NASA Astrophysics Data System (ADS)

Géminard, J.-C.; Pastenes, J. C.; Melo, F.

2018-04-01

Large deformations are prone to cause irreversible changes in materials structure, generally leading to either material hardening or softening. Aqueous foam is a metastable disordered structure of densely packed gas bubbles. We report on the mechanical response of a foam layer subjected to quasistatic periodic shear at large amplitude. We observe that, upon increasing shear, the shear stress follows a universal curve that is nearly exponential and tends to an asymptotic stress value interpreted as the critical yield stress at which the foam structure is completely remodeled. Relevant trends of the foam mechanical response to cycling are mathematically reproduced through a simple law accounting for the amount of plastic deformation upon increasing stress. This view provides a natural interpretation to stress hardening in foams, demonstrating that plastic effects are present in this material even for minute deformation.

Grain refinement and Lattice Imperfections in Commercial Aluminum Alloy Processed by Severe Plastic Deformation

NASA Astrophysics Data System (ADS)

Charfeddine, Saifeddine; Zehani, Karim; Besais, Lotfi; Korchef, Atef

2014-08-01

In the present work, investigations on the microstructure of an aluminum alloy that had been subjected to severe plastic deformation (SPD) by equal channel angular pressing (ECAP), filing and ball milling, were carried out using X-ray diffraction and scanning electron microscopy. SPD leads to lattice distortions, increased dislocation density and an intensive refinement of the microstructure. The refinement and lattice imperfections of the material are greatly affected by the deformation modes and loading performance occurring during SPD. During the milling, the dislocation annihilation increases at higher strains thereby resulting in a smaller crystallite size. After ECAP, the material manifests a strong shear texture and anisotropy of the deformation behavior. Strain anisotropy is less pronounced in filed and ball milled powder particles.

Deformation Twins in Nanocrystalline Body-Centered Cubic Mo as Predicted by Molecular Dynamics Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael Tonks; Bulent biner; Yongfeng Zhang

2012-10-01

This work studies deformation twins in nanocrystalline body-centered cubic Mo, including the nucleation and growth mechanisms as well as their effects on ductility, through molecular dynamics simulations. The deformation processes of nanocrystalline Mo are simulated using a columnar grain model with three different orientations. The deformation mechanisms identified, including dislocation slip, grain-boundary-mediated plasticity, deformation twins and martensitic transformation, are in agreement with previous studies. In (1 1 0) columnar grains, the deformation is dominated by twinning, which nucleates primarily from the grain boundaries by successive emission of twinning partials and thickens by jog nucleation in the grain interiors. Upon arrestmore » by a grain boundary, the twin may either produce continuous plastic strain across the grain boundary by activating compatible twinning/slip systems or result in intergranular failure in the absence of compatible twinning/slip systems in the neighboring grain. Multiple twinning systems can be activated in the same grain, and the competition between them favors those capable of producing continuous deformation across the grain boundary.« less

Electrical Conductivity, Thermal Stability, and Lattice Defect Evolution During Cyclic Channel Die Compression of OFHC Copper

NASA Astrophysics Data System (ADS)

Satheesh Kumar, S. S.; Raghu, T.

2015-02-01

Oxygen-free high-conductivity (OFHC) copper samples are severe plastically deformed by cyclic channel die compression (CCDC) technique at room temperature up to an effective plastic strain of 7.2. Effect of straining on variation in electrical conductivity, evolution of deformation stored energy, and recrystallization onset temperatures are studied. Deformation-induced lattice defects are quantified using three different methodologies including x-ray diffraction profile analysis employing Williamson-Hall technique, stored energy based method, and electrical resistivity-based techniques. Compared to other severe plastic deformation techniques, electrical conductivity degrades marginally from 100.6% to 96.6% IACS after three cycles of CCDC. Decrease in recrystallization onset and peak temperatures is noticed, whereas stored energy increases and saturates at around 0.95-1.1J/g after three cycles of CCDC. Although drop in recrystallization activation energy is observed with the increasing strain, superior thermal stability is revealed, which is attributed to CCDC process mechanics. Low activation energy observed in CCDC-processed OFHC copper is corroborated to synergistic influence of grain boundary characteristics and lattice defects distribution. Estimated defects concentration indicated continuous increase in dislocation density and vacancy with strain. Deformation-induced vacancy concentration is found to be significantly higher than equilibrium vacancy concentration ascribed to hydrostatic stress states experienced during CCDC.

Microstructural Changes During Plastic Deformation and Corrosion Properties of Biomedical Co-20Cr-15W-10Ni Alloy Heat-Treated at 873 K

NASA Astrophysics Data System (ADS)

Ueki, Kosuke; Ueda, Kyosuke; Nakai, Masaaki; Nakano, Takayoshi; Narushima, Takayuki

2018-04-01

Microstructural changes were observed during the plastic deformation of ASTM F90 Co-20Cr-15W-10Ni (mass pct) alloy heat-treated at 873 K (600 °C) for 14.4 ks, and analyzed by electron backscatter diffraction and in situ X-ray diffraction techniques. The obtained results revealed that the area fraction of the ɛ-phase (f ɛ ) in the as-received alloy was higher than that in the heat-treated alloy in the low-to-middle strain region (≤ 50 pct), whereas the f ɛ of the heat-treated alloy was higher than that of the as-received alloy at the fracture point. During plastic deformation, the ɛ-phase was preferentially formed at the twin boundaries of the heat-treated alloy rather than at the grain boundaries. According to the transmission electron microscopy observations, the thin ɛ-phase layer formed due to the alloy heat treatment acted as the origin of deformation twinning, which decreased the stress concentration at the grain boundaries. The results of anodic polarization testing showed that neither the heat treatment at 873 K (600 °C) nor plastic deformation affected the alloy corrosion properties. To the best of our knowledge, this is the first study proving that the formation of a thin ɛ-phase layer during the low-temperature heat treatment of the studied alloy represents an effective method for the enhancement of the alloy ductility without sacrificing its strength and corrosion properties.

Microstructural Changes During Plastic Deformation and Corrosion Properties of Biomedical Co-20Cr-15W-10Ni Alloy Heat-Treated at 873 K

NASA Astrophysics Data System (ADS)

Ueki, Kosuke; Ueda, Kyosuke; Nakai, Masaaki; Nakano, Takayoshi; Narushima, Takayuki

2018-06-01

Microstructural changes were observed during the plastic deformation of ASTM F90 Co-20Cr-15W-10Ni (mass pct) alloy heat-treated at 873 K (600 °C) for 14.4 ks, and analyzed by electron backscatter diffraction and in situ X-ray diffraction techniques. The obtained results revealed that the area fraction of the ɛ-phase ( f ɛ ) in the as-received alloy was higher than that in the heat-treated alloy in the low-to-middle strain region (≤ 50 pct), whereas the f ɛ of the heat-treated alloy was higher than that of the as-received alloy at the fracture point. During plastic deformation, the ɛ-phase was preferentially formed at the twin boundaries of the heat-treated alloy rather than at the grain boundaries. According to the transmission electron microscopy observations, the thin ɛ-phase layer formed due to the alloy heat treatment acted as the origin of deformation twinning, which decreased the stress concentration at the grain boundaries. The results of anodic polarization testing showed that neither the heat treatment at 873 K (600 °C) nor plastic deformation affected the alloy corrosion properties. To the best of our knowledge, this is the first study proving that the formation of a thin ɛ-phase layer during the low-temperature heat treatment of the studied alloy represents an effective method for the enhancement of the alloy ductility without sacrificing its strength and corrosion properties.

Ultrafine-Grained Pure Ti Processed by New SPD Scheme Combining Drawing with Shear

NASA Astrophysics Data System (ADS)

Raab, A. G.; Bobruk, E. V.; Raab, G. I.

2018-05-01

The paper displays the results of the studies and analysis of a promising severe plastic deformation scheme that implements the conditions of a non-monotonous impact during shear drawing of long-length bulk metal materials. The paper describes the efficiency of the proposed severe plastic deformation technique to form a gradient ultrafine-grained state in rod-shaped billets on the example of commercially pure Ti and its further development for future industrial applications.

Dislocation-mediated trapping of deuterium in tungsten under high-flux high-temperature exposures

NASA Astrophysics Data System (ADS)

Bakaeva, A.; Terentyev, D.; De Temmerman, G.; Lambrinou, K.; Morgan, T. W.; Dubinko, A.; Grigorev, P.; Verbeken, K.; Noterdaeme, J. M.

2016-10-01

The effect of severe plastic deformation on the deuterium retention in tungsten exposed to high-flux low-energy plasma (flux ∼1024 m-2 s-1, energy ∼50 eV and fluence up to 5 × 1025 D/m2) was studied experimentally in a wide temperature range (460-1000 K) relevant for application in ITER. The desorption spectra in both reference and plastically-deformed samples were deconvoluted into three contributions associated with the detrapping from dislocations, deuterium-vacancy clusters and pores. As the exposure temperature increases, the positions of the release peaks in the plastically-deformed material remain in the same temperature range but the peak amplitudes are altered as compared to the reference material. The desorption peak attributed to the release from pores (i.e. cavities and bubbles) was suppressed in the plastically deformed samples for the low-temperature exposures, but became dominant for exposures above 700 K. The observed strong modulation of the deuterium storage in "shallow" and "deep" traps, as well as the reduction of the integral retention above 700 K, suggest that the dislocation network changes its role from "trapping sites" to "diffusion channels" above a certain temperature. The major experimental observations of the present work are in line with recent computational assessment based on atomistic and mean field theory calculations available in literature.

The Evolution of Second-Phase Particles in 6111 Aluminum Alloy Processed by Hot and Cold Rolling

NASA Astrophysics Data System (ADS)

Zhang, Lixin; Wang, Yihan; Ni, Song; Chen, Gang; Li, Kai; Du, Yong; Song, Min

2018-03-01

The evolution of coarse Al9.9Fe2.65Ni1.45 phase, spherical Al12(Mn,Fe)3Si phase and rod-like Q phase in a 6111 aluminum alloy during hot and cold rolling deformation processes was systematically investigated in this work. The results showed that the coarse Al9.9Fe2.65Ni1.45 particles are mainly distributed at the grain boundaries, accompanied by the co-formation of Al12(Fe,Mn)3Si phase and Mg2Si phase, while the spherical Al12(Mn,Fe)3Si particles are mainly distributed in the grain interiors. Hot rolling has little effects on the size and distribution of both phases, but cold deformation can severely decrease the size of the particles by breaking the particles into small pieces. In addition, the temperature of 450 °C is not high enough for the dissolution of Q phase in the Al matrix, but the Q particles can be broken into small pieces due to the stress concentration during both hot and cold rolling deformation. In addition, the influences of phase evolution, dislocations and recrystallization on the mechanical properties evolution were also discussed.

Modeling Mantle Shear Zones, Melt Focusing and Stagnation - Are Non Volcanic Margins Really Magma Poor?

NASA Astrophysics Data System (ADS)

Lavier, L. L.; Muntener, O.

2011-12-01

Mantle peridotites from ocean-continent transition zones (OCT's) and ultraslow spreading ridges question the commonly held assumption of a simple link between mantle melting and MORB. 'Ancient' and partly refertilized mantle in rifts and ridges illustrates the distribution of the scale of upper mantle heterogeneity even on a local scale. Upwelling of partial melts that enter the conductive lithospheric mantle inevitably leads to freezing of the melt and metasomatized lithosphere. Field data and petrology demonstrates that ancient, thermally undisturbed, pyroxenite-veined subcontinental mantle blobs formed parts of the ocean floor next to thinned continental crust. Similar heterogeneity might be created in the oceanic lithosphere where the thermal boundary layer (TBM) is thick and veined with metasomatic assemblages. This cold, ancient, 'subcontinental domain' is separated by ductile shear zones (or some other form of permeability barriers) from an infiltrated ('hot') domain dominated by refertilized spinel and/or plagioclase peridotite. The footwall of these mantle shear zones display complex refertilization processes and high-temperature deformation. We present numerical models that illustrate the complex interplay of km-scale refertilization with active deformation and melt focusing on top of the mantle. Melt lubricated shear zones focus melt flow in shear fractures (melt bands) occurring along grain boundaries. Continuous uplift and cooling leads to crystallization, and crystal plastic deformation prevails in the subsolidus state. Below 800oC if water is present deformation by shearing of phyllosilicates may become prevalent. We develop physical boundary conditions for which stagnant melt beneath a permeability barrier remains trapped rather than being extracted to the surface via melt-filled fractures. We explore the parameter space for fracturing and drainage and development of anastomozing impermeable shear zones. Our models might be useful to constrain the conditions and enigmatic development of magma-poor and magma rich margins.

Effect of Post-deformation Annealing Treatment on the Microstructural Evolution of a Cold-Worked Corrosion-Resistant Superalloy (CRSA) Steel

NASA Astrophysics Data System (ADS)

Mirzaei, A.; Zarei-Hanzaki, A.; Mohamadizadeh, A.; Lin, Y. C.

2018-03-01

The post-deformation annealing treatments of a commercial cold-worked corrosion-resistant superalloy steel (Sanicro 28 steel) were carried out at different temperatures in the range of 900-1100 °C for different holding durations of 5, 10, and 15 min. The effects of post-deformation annealing time and temperature on the microstructural evolution and subsequent mechanical properties of the processed Sanicro 28 steel were investigated. The observations indicated that twin-twin hardening in cold deformation condition mainly correlates with abundant nucleation of mechanical twins in multiple directions resulting in considerable strain hardening behavior. Microstructural investigations showed that the static recrystallization takes place after isothermal holding at 900 °C for 5 min. Increasing the annealing temperature from 900 to 1050 °C leads to recrystallization development and grain refinement in the as-recrystallized state. In addition, an increase in annealing duration from 5 to 15 min leads to subgrain coarsening and subsequently larger recrystallized grains size. The occurrence of large proportion of the grain refinement, which is achieved in the first annealing stage at 1050 °C after 5 min, is considered as the main factor for the maximum elongation at this stage.

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

NASA Astrophysics Data System (ADS)

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.; Higginbotham, A.; Lazicki, A.; Lee, H. J.; Nagler, B.; Park, H.-S.; Remington, B. A.; Rudd, R. E.; Sliwa, M.; Suggit, M.; Swift, D.; Tavella, F.; Zepeda-Ruiz, L.; Wark, J. S.

2017-10-01

Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.

We report that pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation ismore » challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. Lastly, the techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.« less

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

DOE PAGES

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.; ...

2017-10-25

We report that pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation ismore » challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. Lastly, the techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.« less

Rapid Grain Size Reduction in the Upper Mantle at a Plate Boundary

NASA Astrophysics Data System (ADS)

Kidder, S. B.; Scott, J.; Prior, D. J.; Lubicich, E. J.

2017-12-01

A few spinel peridotite xenoliths found near the Alpine Fault, New Zealand, exhibit a mylonitic texture and, locally, an extremely fine 30 micron grain size. The harzburgite xenoliths were emplaced in a 200 km-long elongate dike zone interpreted as a gigantic tension fracture or Reidel shear associated with Alpine Fault initiation 25 Ma. The presence of thin ( 1 mm) ultramylonite zones with px-ol phase mixing and fine grain sizes, minimal crustal-scale strain associated with the dike swarm, and the absence of mylonites at four of the five xenolith localities associated with the dike swarm indicate that upper mantle deformation was highly localized. Strings of small, recrystallized grains (planes in 3D) are found in the interiors of olivine porphyroclasts. In some cases, bands 1-2 grains thick are traced from the edges of olivine grains and terminate in their interiors. Thicker zones of recrystallized grains are also observed crossing olivine porphyroclasts without apparent offset of the unrecrystallized remnants of the porphyroclasts. We suggest a brittle-plastic origin for these features since the traditional recrystallization mechanisms associated with dislocation creep require much more strain than occurred within these porphyroclasts. Analogous microstructures in quartz and feldspar in mid-crust deformation zones are attributed to brittle-plastic processes. We hypothesize that such fine-grained zones were the precursors of the observed, higher-strain ultramylonite zones. Given the size of the new grains preserved in the porphyroclasts ( 100 micron) and a moho temperature > 650°C, grain growth calculations indicate that the observed brittle-plastic deformation occurred <10,000 yrs. prior to eruption. It is likely then that either brittle-plastic deformation was coeval with the ductile shearing occurring in the ultramylonite bands, or possibly, if deformation can be separated into brittle-plastic (early) and ductile (later) phases, that the entire localization process was very rapid (<10,000 yrs). In either case we interpret that semi-brittle deformation was a key process responsible for rapid localization in this initiating plate-scale mantle shear zone.

An investigation into the mechanism for enhanced mechanical properties in friction stir welded AA2024-T3 joints coated with cold spraying

NASA Astrophysics Data System (ADS)

Li, N.; Li, W. Y.; Yang, X. W.; Feng, Y.; Vairis, A.

2018-05-01

Using cold spraying (CS), a surface layer with a modified microstructure and enhanced mechanical properties was formed on a 3.2 mm thick friction stir welded (FSWed) AA2024-T3 joint. The combined effect of "shot peening effect (SPE)" and "heat flow effect (HFE)" during CS were used to enhance joint mechanical properties. The microstructure evolution of the FSWed AA2024-T3 joints in the surface layer following CS coatings and their effect on mechanical properties were systematically characterized with electron back-scattered diffraction, transmission electron microscopy, differential scanning calorimetry and mechanical tests. Based on these experiments, a grain refinement, finer and more S phases, and improved amount of Guinier-Preston-Bagaryatsky (GPB) zones produced by CS treatments are proposed. The deposition of aluminum coating on the joint, lead to hardness recovery in the stir zone and the development of two low hardness zones as the density of GPB increased. The tensile properties of FSWed AA2024-T3 joints improved with the application of the aluminum coatings. Experiments and analysis of the enhanced mechanical properties mechanism indicate that SPE with a high plastic deformation and HFE with an intensive heat flow are necessary for the production of refined grains and increased numbers of GPB zones.

Experimental and Numerical Study of the Influence of Substrate Surface Preparation on Adhesion Mechanisms of Aluminum Cold Spray Coatings on 300M Steel Substrates

NASA Astrophysics Data System (ADS)

Nastic, A.; Vijay, M.; Tieu, A.; Rahmati, S.; Jodoin, B.

2017-10-01

The effect of substrate surface topography on the creation of metallurgical bonds and mechanical anchoring points has been studied for the cold spray deposition of pure aluminum on 300M steel substrate material. The coatings adhesion strength showed a significant decrease from 31.0 ± 5.7 MPa on polished substrates to 6.9 ± 2.0 MPa for substrates with roughness of 2.2 ± 0.5 μm. Strengths in the vicinity of 45 MPa were reached for coatings deposited onto forced pulsed waterjet treated surfaces with roughnesses larger than 33.8 μm. Finite element analysis has confirmed the sole presence of mechanical anchoring in coating adhesion strength for all surface treatment except polished surfaces. Grit embedment has been shown to be non-detrimental to coating adhesion for the current deposited material combination. The particle deformation process during impacts has been studied through finite element analysis using the Preston-Tonks-Wallace (PTW) constitutive model. The obtained equivalent plastic strain (PEEQ), temperature, contact pressure and velocity vector were correlated to the particle ability to form metallurgical bonds. Favorable conditions for metallurgical bonding were found to be highest for particles deposited on polished substrates, as confirmed by fracture surface analysis.

Effect of cold deformation on the recrystallization behavior of FePd alloy at the ordering temperature using electron backscatter diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Hung-Pin; Chen, Yen-Chun; Chen, Delphic

2014-08-15

In this study, the evolution of the recrystallization texture and microstructure was investigated after annealing of 50% and 90% cold-rolled FePd alloy at 530 °C. The FePd alloy was produced by vacuum arc melting in an atmosphere of 97% Ar and 3% H{sub 2}. The specimens were cold rolled to achieve 50% and 90% reduction in thickness. Electron backscatter diffraction measurements were performed on the rolling direction–normal direction section. With increased deformation from 50% to 90%, recrystallized texture transition occurs. For the 50% cold-rolled alloy, the preferred orientation is (0 1 0) [11 0 1], which is close to themore » cubic orientation after 400 h of annealing. For the 90% cold-rolled alloy, the orientation changes to (0 5 4) [22–4 5] after 16 h of annealing. - Highlights: • Texture and microstructure in cold-rolled FePd alloy was investigated during annealing using EBSD. • The recrystallized texture of 50% cold-rolled FePd is (0 1 0) [11 0 1] at 530 °C for 400 hours. • The recrystallized texture of 90% cold-rolled FePd is changed to (0 5 4) [22–4 5] at 530 °C after 16 hours.« less

The Role of Epibionts of Bacteria of the Genus Pseudoalteromonas and Cellular Proteasomes in the Adaptive Plasticity of Marine Cold-Water Sponges.

PubMed

Kravchuk, O I; Lavrov, A I; Finoshin, A D; Gornostaev, N G; Georgiev, A A; Abaturova, S B; Mikhailov, V S; Lyupina, Yu V

2018-03-01

It was found that cells of different color morphs of the cold-water marine sponges Halichondria panicea (Pallas, 1766) of the class Demospongiae differ in the content of epibionts of bacteria of the genus Pseudoalteromonas. The sponge cells with elevated levels of epibionts of bacteria of the genus Pseudoalteromonas showed an increased expression of Hsp70 proteins but had a reduced level of the proteasomal catalytic beta 5 subunit, which was accompanied by a change in their activity. Probably, epibionts of bacteria of the genus Pseudoalteromonas may affect the ubiquitin-proteasome system in the cells of cold-water marine sponges and, thereby, ensure their adaptive plasticity.

Distortion-free foamed-plastic parts

NASA Technical Reports Server (NTRS)

Hogenson, P. A.; Jackson, R. G.

1979-01-01

In process for molding foamed-plastic products, gases that are formed as byproducts of foaming reaction escape through perforated die. Thus, volatiles are not trapped in pockets that can deform and weaken the molded part.

Elasto-limited plastic analysis of structures for probabilistic conditions

NASA Astrophysics Data System (ADS)

Movahedi Rad, M.

2018-06-01

With applying plastic analysis and design methods, significant saving in material can be obtained. However, as a result of this benefit excessive plastic deformations and large residual displacements might develop, which in turn might lead to unserviceability and collapse of the structure. In this study, for deterministic problem the residual deformation of structures is limited by considering a constraint on the complementary strain energy of the residual forces. For probabilistic problem the constraint for the complementary strain energy of the residual forces is given randomly and critical stresses updated during the iteration. Limit curves are presented for the plastic limit load factors. The results show that these constraints have significant effects on the load factors. The formulations of the deterministic and probabilistic problems lead to mathematical programming which are solved by the use of nonlinear algorithm.

MANTLE CONVECTION, PLATE TECTONICS, AND VOLCANISM ON HOT EXO-EARTHS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Summeren, Joost; Conrad, Clinton P.; Gaidos, Eric, E-mail: summeren@hawaii.edu

Recently discovered exoplanets on close-in orbits should have surface temperatures of hundreds to thousands of Kelvin. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many hundreds to thousands of Kelvin between permanent day and night sides. We investigated the effect of elevated surface temperature and strong surface temperature contrasts for Earth-mass planets on the (1) pattern of mantle convection, (2) tectonic regime, and (3) rate and distribution of partial melting, using numerical simulations of mantle convection with a composite viscous/pseudo-plastic rheology. Our simulations indicate thatmore » if a close-in rocky exoplanet lacks an atmosphere to redistribute heat, a {approx}>400 K surface temperature contrast can maintain an asymmetric degree 1 pattern of mantle convection in which the surface of the planet moves preferentially toward subduction zones on the cold night side. The planetary surface features a hemispheric dichotomy, with plate-like tectonics on the night side and a continuously evolving mobile lid on the day side with diffuse surface deformation and vigorous volcanism. If volcanic outgassing establishes an atmosphere and redistributes heat, plate tectonics is globally replaced by diffuse surface deformation and volcanism accelerates and becomes distributed more uniformly across the planetary surface.« less

Investigation of Thermal Hardening of the FCC Material Containing Strengthening Particles with an L12 Superstructure

NASA Astrophysics Data System (ADS)

Daneyko, O. I.; Kulaeva, N. A.; Kovalevskaya, C. A.; Kolupaeva, S. N.

2015-07-01

A mathematical model of plastic deformation of dispersion-hardened materials with an fcc matrix containing strengthening particles with an L12 superstructure having a coherent relationship with the matrix is presented. The model is based on the balance equations of deformation defects of different types with taking into account their transformation during plastic deformation. The influence of scale characteristics of the hardening phase, temperature, and deformation rate on the evolution of the dislocation subsystem and strain hardening of an alloy with an fcc matrix hardened by particles with an L12 super structure is studied. A temperature anomaly of mechanical properties is found for the materials with different fcc matrices (Al,Cu, Ni). It is shown that the temperature anomaly is more pronounced for the material with larger volume fraction of the hardening phase.

Calculation of cracking under pulsed heat loads in tungsten manufactured according to ITER specifications

NASA Astrophysics Data System (ADS)

Arakcheev, A. S.; Skovorodin, D. I.; Burdakov, A. V.; Shoshin, A. A.; Polosatkin, S. V.; Vasilyev, A. A.; Postupaev, V. V.; Vyacheslavov, L. N.; Kasatov, A. A.; Huber, A.; Mertens, Ph; Wirtz, M.; Linsmeier, Ch; Kreter, A.; Löwenhoff, Th; Begrambekov, L.; Grunin, A.; Sadovskiy, Ya

2015-12-01

A mathematical model of surface cracking under pulsed heat load was developed. The model correctly describes a smooth brittle-ductile transition. The elastic deformation is described in a thin-heated-layer approximation. The plastic deformation is described with the Hollomon equation. The time dependence of the deformation and stresses is described for one heating-cooling cycle for a material without initial plastic deformation. The model can be applied to tungsten manufactured according to ITER specifications. The model shows that the stability of stress-relieved tungsten deteriorates when the base temperature increases. This proved to be a result of the close ultimate tensile and yield strengths. For a heat load of arbitrary magnitude a stability criterion was obtained in the form of condition on the relation of the ultimate tensile and yield strengths.

Procedures for experimental measurement and theoretical analysis of large plastic deformations

NASA Technical Reports Server (NTRS)

Morris, R. E.

1974-01-01

Theoretical equations are derived and analytical procedures are presented for the interpretation of experimental measurements of large plastic strains in the surface of a plate. Orthogonal gage lengths established on the metal surface are measured before and after deformation. The change in orthogonality after deformation is also measured. Equations yield the principal strains, deviatoric stresses in the absence of surface friction forces, true stresses if the stress normal to the surface is known, and the orientation angle between the deformed gage line and the principal stress-strain axes. Errors in the measurement of nominal strains greater than 3 percent are within engineering accuracy. Applications suggested for this strain measurement system include the large-strain-stress analysis of impact test models, burst tests of spherical or cylindrical pressure vessels, and to augment small-strain instrumentation tests where large strains are anticipated.

A micromechanical constitutive model for anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals

NASA Astrophysics Data System (ADS)

Yu, Chao; Kang, Guozheng; Kan, Qianhua

2015-09-01

Based on the experimental observations on the anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals done by Gall and Maier (2002), a crystal plasticity based micromechanical constitutive model is constructed to describe such anisotropic cyclic deformation. To model the internal stress caused by the unmatched inelastic deformation between the austenite and martensite phases on the plastic deformation of austenite phase, 24 induced martensite variants are assumed to be ellipsoidal inclusions with anisotropic elasticity and embedded in the austenite matrix. The homogeneous stress fields in the austenite matrix and each induced martensite variant are obtained by using the Mori-Tanaka homogenization method. Two different inelastic mechanisms, i.e., martensite transformation and transformation-induced plasticity, and their interactions are considered in the proposed model. Following the assumption of instantaneous domain growth (Cherkaoui et al., 1998), the Helmholtz free energy of a representative volume element of a NiTi shape memory single crystal is established and the thermodynamic driving forces of the internal variables are obtained from the dissipative inequalities. The capability of the proposed model to describe the anisotropic cyclic deformation of super-elastic NiTi single crystals is first verified by comparing the predicted results with the experimental ones. It is concluded that the proposed model can capture the main quantitative features observed in the experiments. And then, the proposed model is further used to predict the uniaxial and multiaxial transformation ratchetting of a NiTi single crystal.

Phase transformation dependence on initial plastic deformation mode in Si via nanoindentation

DOE PAGES

Wong, Sherman; Haberl, Bianca; Williams, James S.; ...

2016-09-30

Silicon in its diamond-cubic phase is known to phase transform to a technologically interesting mixture of the body-centred cubic and rhombohedral phases under nanoindentation pressure. In this study, we demonstrate that during plastic deformation the sample can traverse two distinct pathways, one that initially nucleates a phase transformation while the other initially nucleates crystalline defects. These two pathways remain distinct even after sufficient pressure is applied such that both deformation mechanisms are present within the sample. Here, it is further shown that the indents that initially nucleate a phase transformation generate larger, more uniform volumes of the phase transformed materialmore » than indents that initially nucleate crystalline defects.« less

Mechanisms of grain refinement in aluminum alloys in the process of severe plastic deformation

NASA Astrophysics Data System (ADS)

Kaibyshev, R. O.; Mazurina, I. A.; Gromov, D. A.

2006-01-01

A study of the mechanisms of grain refinement in the process of severe plastic deformation of two aluminum alloys, i.e., 2219 bearing nanometric particles of Al3Zr and low-alloy Al-3% Cu, is described. The alloys are deformed by the method of equal channel angular pressing at 250°C to a maximum strain degree of about 12. The angles of (sub)grain boundaries in alloy 2219 are determined with the help of transmission electron microscopy by the method of Kikuchi lines. The evolution of the microstructure in alloy Al-3% Cu is studied with the help of grain-boundary maps obtained by the method of electron back-scattered diffraction.

Plastic deformation at surface during unlubricated sliding

NASA Technical Reports Server (NTRS)

Yamamoto, T.; Buckley, D. H.

1982-01-01

The plastic deformation and wear of 304 stainless-steel surface slid against an aluminum oxide rider were observed by using a scanning electron microscope and an optical microscope. Experiments were conducted in a vacuum of 0.000001 Pa and in an environment of 0.0005 Pa chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step-shaped protuberances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. These observations result from both adhesion and an adhesive wear mechanism.

Finite Deformations and Internal Forces in Elastic-Plastic Crystals: Interpretations From Nonlinear Elasticity and Anharmonic Lattice Statics

DTIC Science & Technology

2009-09-01

Sec. 2, while the latter ase—which implicitly includes the effects of image forces of efects in neighboring volume elements—may be more practical rom...versetzungen und eigenspannungen,” Arch . Ration. Mech. Anal., 4, pp. 273–334. 25 Lee, E. H., 1969, “Elastic-Plastic Deformation at Finite Strains,” ASME J...Rev., 73, pp. 373–382. 27 Kroner, E., and Seeger, A., 1959, “Nicht-Lineare Elastizitatstheorie der Verset- zungen und Eigenspannungen,” Arch . Ration

Hydrogen Induced Intergranular Cracking of Nickel-Base Alloys.

DTIC Science & Technology

1982-02-01

alloys are discussed. Experimental The steel used in the present investigation is a fully bainitic 2 1/4 Cr-lMo pressure vessel steel , ASTM A542 Class 3...Appendix A describes recent experiments performed in order to study the influence of plastic deformation on hydrogen transport in a 214 Cr-lMo steel (8...PLASTIC DEFORMATION ON HYDROGEN TRANSPORT IN 2 1/4 Cr-lMo STEEL M. Kurkela, G.S. Frankel, and R.M. Latanision Department of Materials Science and

Electrical resistance oscillations during plastic deformation in A Ti-Al-Nb-Zr alloy at 4·2 K

NASA Astrophysics Data System (ADS)

Nikiforenko, V. N.; Lavrentev, F. F.

1986-10-01

The serrated plastic flow in titanium alloy containing 5% Al, 2·5% Zr and 2% Nb has been investigated by measuring its electrical resistance and applying selective chemical etching. The electrical resistance was found to oscillate under active deformation at 4·2 K. Analysis of the possible causes seems to indicate a dominant role of break by dislocation pile-ups through obstacles, viz second phase precipitates and grain boundaries.

European Conference on Molecular Beam Epitaxy and Related Growth Methods (6th) Held in Tampere, Finland on 21-14 April 1991

DTIC Science & Technology

1991-04-24

2X2) structure caracteristic of a cation rich surface. During the growth we observe intense RHEED oscillations, which show that the growth of Hg...layer which then suffers plastic deformation when the energy stored in the epilayer (proportional to its thickness) is sufficient to create dislocations...table I we present the variation of the in plane lattice mismatch vs. layerthickness. Plastic deformation of the layer starts around 4 to 5 ML, which can

Local microstructure evolution at shear bands in metallic glasses with nanoscale phase separation

PubMed Central

He, Jie; Kaban, Ivan; Mattern, Norbert; Song, Kaikai; Sun, Baoan; Zhao, Jiuzhou; Kim, Do Hyang; Eckert, Jürgen; Greer, A. Lindsay

2016-01-01

At room temperature, plastic flow of metallic glasses (MGs) is sharply localized in shear bands, which are a key feature of the plastic deformation in MGs. Despite their clear importance and decades of study, the conditions for formation of shear bands, their structural evolution and multiplication mechanism are still under debate. In this work, we investigate the local conditions at shear bands in new phase-separated bulk MGs containing glassy nanospheres and exhibiting exceptional plasticity under compression. It is found that the glassy nanospheres within the shear band dissolve through mechanical mixing driven by the sharp strain localization there, while those nearby in the matrix coarsen by Ostwald ripening due to the increased atomic mobility. The experimental evidence demonstrates that there exists an affected zone around the shear band. This zone may arise from low-strain plastic deformation in the matrix between the bands. These results suggest that measured property changes originate not only from the shear bands themselves, but also from the affected zones in the adjacent matrix. This work sheds light on direct visualization of deformation-related effects, in particular increased atomic mobility, in the region around shear bands. PMID:27181922

DYCAST: A finite element program for the crash analysis of structures

NASA Technical Reports Server (NTRS)

Pifko, A. B.; Winter, R.; Ogilvie, P.

1987-01-01

DYCAST is a nonlinear structural dynamic finite element computer code developed for crash simulation. The element library contains stringers, beams, membrane skin triangles, plate bending triangles and spring elements. Changing stiffnesses in the structure are accounted for by plasticity and very large deflections. Material nonlinearities are accommodated by one of three options: elastic-perfectly plastic, elastic-linear hardening plastic, or elastic-nonlinear hardening plastic of the Ramberg-Osgood type. Geometric nonlinearities are handled in an updated Lagrangian formulation by reforming the structure into its deformed shape after small time increments while accumulating deformations, strains, and forces. The nonlinearities due to combined loadings are maintained, and stiffness variation due to structural failures are computed. Numerical time integrators available are fixed-step central difference, modified Adams, Newmark-beta, and Wilson-theta. The last three have a variable time step capability, which is controlled internally by a solution convergence error measure. Other features include: multiple time-load history tables to subject the structure to time dependent loading; gravity loading; initial pitch, roll, yaw, and translation of the structural model with respect to the global system; a bandwidth optimizer as a pre-processor; and deformed plots and graphics as post-processors.

Stability of surface plastic flow in large strain deformation of metals

NASA Astrophysics Data System (ADS)

Viswanathan, Koushik; Udapa, Anirduh; Sagapuram, Dinakar; Mann, James; Chandrasekar, Srinivasan

We examine large-strain unconstrained simple shear deformation in metals using a model two-dimensional cutting system and high-speed in situ imaging. The nature of the deformation mode is shown to be a function of the initial microstructure state of the metal and the deformation geometry. For annealed metals, which exhibit large ductility and strain hardening capacity, the commonly assumed laminar flow mode is inherently unstable. Instead, the imposed shear is accommodated by a highly rotational flow-sinuous flow-with vortex-like components and large-amplitude folding on the mesoscale. Sinuous flow is triggered by a plastic instability on the material surface ahead of the primary region of shear. On the other hand, when the material is extensively strain-hardened prior to shear, laminar flow again becomes unstable giving way to shear banding. The existence of these flow modes is established by stability analysis of laminar flow. The role of the initial microstructure state in determining the change in stability from laminar to sinuous / shear-banded flows in metals is elucidated. The implications for cutting, forming and wear processes for metals, and to surface plasticity phenomena such as mechanochemical Rehbinder effects are discussed.

New design strategy for reversible plasticity shape memory polymers with deformable glassy aggregates.

PubMed

Lin, Tengfei; Tang, Zhenghai; Guo, Baochun

2014-12-10

Reversible plasticity shape memory (RPSM) is a new concept in the study of shape memory performance behavior and describes a phenomenon in which shape memory polymers (SMPs) can undergo a large plastic deformation at room temperature and subsequently recover their original shape upon heating. To date, RPSM behavior has been demonstrated in only a few polymers. In the present study, we implement a new design strategy, in which deformable glassy hindered phenol (AO-80) aggregates are incorporated into an amorphous network of epoxidized natural rubber (ENR) cured with zinc diacrylate (ZDA), in order to achieve RPSM properties. We propose that AO-80 continuously tunes the glass transition temperature (Tg) and improves the chain mobility of the SMP, providing traction and anchoring the ENR chains by intermolecular hydrogen bonding interactions. The RPSM behavior of the amorphous SMPs is characterized, and the results demonstrate good fixity at large deformations (up to 300%) and excellent recovery upon heating. Large energy storage capacities at Td in these RPSM materials are demonstrated compared with those achieved at elevated temperature in traditional SMPs. Interestingly, the further revealed self-healing properties of these materials are closely related to their RPSM behavior.

Shock wave absorber having a deformable liner

DOEpatents

Youngdahl, C.K.; Wiedermann, A.H.; Shin, Y.W.; Kot, C.A.; Ockert, C.E.

1983-08-26

This invention discloses a shock wave absorber for a piping system carrying liquid. The absorber has a plastically deformable liner defining the normal flow boundary for an axial segment of the piping system, and a nondeformable housing is spaced outwardly from the liner so as to define a gas-tight space therebetween. The flow capacity of the liner generally corresponds to the flow capacity of the piping system line, but the liner has a noncircular cross section and extends axially of the piping system line a distance between one and twenty times the diameter thereof. Gas pressurizes the gas-tight space equal to the normal liquid pressure in the piping system. The liner has sufficient structural capacity to withstand between one and one-half and two times this normal liquid pressures; but at greater pressures it begins to plastically deform initially with respect to shape to a more circular cross section, and then with respect to material extension by circumferentially stretching the wall of the liner. A high energy shock wave passing through the liner thus plastically deforms the liner radially into the gas space and progressively also as needed in the axial direction of the shock wave to minimize transmission of the shock wave beyond the absorber.

Forecasting Low-Cycle Fatigue Performance of Twinning-Induced Plasticity Steels: Difficulty and Attempt

NASA Astrophysics Data System (ADS)

Shao, C. W.; Zhang, P.; Zhang, Z. J.; Liu, R.; Zhang, Z. F.

2017-12-01

We find the existing empirical relations based on monotonic tensile properties and/or hardness cannot satisfactorily predict the low-cycle fatigue (LCF) performance of materials, especially for twinning-induced plasticity (TWIP) steels. Given this, we first identified the different deformation mechanisms under monotonic and cyclic deformation after a comprehensive study of stress-strain behaviors and microstructure evolutions for Fe-Mn-C alloys during tension and LCF, respectively. It is found that the good tensile properties of TWIP steel mainly originate from the large activation of multiple twinning systems, which may be attributed to the grain rotation during tensile deformation; while its LCF performance depends more on the dislocation slip mode, in addition to its strength and plasticity. Based on this, we further investigate the essential relations between microscopic damage mechanism (dislocation-dislocation interaction) and cyclic stress response, and propose a hysteresis loop model based on dislocation annihilation theory, trying to quickly assess the LCF resistance of Fe-Mn-C steels as well as other engineering materials. It is suggested that the hysteresis loop and its evolution can provide significant information on cyclic deformation behavior, e.g., (point) defect multiplication and vacancy aggregation, which may help estimate the LCF properties.

Stochastic dislocation kinetics and fractal structures in deforming metals probed by acoustic emission and surface topography measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vinogradov, A.; Laboratory of Hybrid Nanostructured Materials, NITU MISiS, Moscow 119490; Yasnikov, I. S.

2014-06-21

We demonstrate that the fractal dimension (FD) of the dislocation population in a deforming material is an important quantitative characteristic of the evolution of the dislocation structure. Thus, we show that peaking of FD signifies a nearing loss of uniformity of plastic flow and the onset of strain localization. Two techniques were employed to determine FD: (i) inspection of surface morphology of the deforming crystal by white light interferometry and (ii) monitoring of acoustic emission (AE) during uniaxial tensile deformation. A connection between the AE characteristics and the fractal dimension determined from surface topography measurements was established. As a commonmore » platform for the two methods, the dislocation density evolution in the bulk was used. The relations found made it possible to identify the occurrence of a peak in the median frequency of AE as a harbinger of plastic instability leading to necking. It is suggested that access to the fractal dimension provided by AE measurements and by surface topography analysis makes these techniques important tools for monitoring the evolution of the dislocation structure during plastic deformation—both as stand-alone methods and especially when used in tandem.« less

Temperature-dependent plastic hysteresis in highly confined polycrystalline Nb films

NASA Astrophysics Data System (ADS)

Waheed, S.; Hao, R.; Zheng, Z.; Wheeler, J. M.; Michler, J.; Balint, D. S.; Giuliani, F.

2018-02-01

In this study, the effect of temperature on the cyclic deformation behaviour of a confined polycrystalline Nb film is investigated. Micropillars encapsulating a thin niobium interlayer are deformed under cyclic axial compression at different test temperatures. A distinct plastic hysteresis is observed for samples tested at elevated temperatures, whereas negligible plastic hysteresis is observed for samples tested at room temperature. These results are interpreted using planar discrete dislocation plasticity incorporating slip transmission across grain boundaries. The effect of temperature-dependent grain boundary energy and dislocation mobility on dislocation penetration and, consequently, the size of plastic hysteresis is simulated to correlate with the experimental results. It is found that the decrease in grain boundary energy barrier caused by the increase in temperature does not lead to any appreciable change in the cyclic response. However, dislocation mobility significantly affects the size of plastic hysteresis, with high mobilities leading to a larger hysteresis. Therefore, it is postulated that the experimental observations are predominantly caused by an increase in dislocation mobility as the temperature is increased above the critical temperature of body-centred cubic niobium.

Numerical Modeling of Tube Forming by HPTR Cold Pilgering Process

NASA Astrophysics Data System (ADS)

Sornin, D.; Pachón-Rodríguez, E. A.; Vanegas-Márquez, E.; Mocellin, K.; Logé, R.

2016-09-01

For new fast-neutron sodium-cooled Generation IV nuclear reactors, the candidate cladding materials for the very strong burn-up are ferritic and martensitic oxide dispersion strengthened grades. Classically, the cladding tube is cold formed by a sequence of cold pilger milling passes with intermediate heat treatments. This process acts upon the geometry and the microstructure of the tubes. Consequently, crystallographic texture, grain sizes and morphologies, and tube integrity are highly dependent on the pilgering parameters. In order to optimize the resulting mechanical properties of cold-rolled cladding tubes, it is essential to have a thorough understanding of the pilgering process. Finite Element Method (FEM) models are used for the numerical predictions of this task; however, the accuracy of the numerical predictions depends not only on the type of constitutive laws but also on the quality of the material parameters identification. Therefore, a Chaboche-type law which parameters have been identified on experimental observation of the mechanical behavior of the material is used here. As a complete three-dimensional FEM mechanical analysis of the high-precision tube rolling (HPTR) cold pilgering of tubes could be very expensive, only the evolution of geometry and deformation is addressed in this work. The computed geometry is compared to the experimental one. It is shown that the evolution of the geometry and deformation is not homogeneous over the circumference. Moreover, it is exposed that the strain is nonhomogeneous in the radial, tangential, and axial directions. Finally, it is seen that the dominant deformation mode of a material point evolves during HPTR cold pilgering forming.

Orientation Dependence of the Deformation Microstructure of Ta-4%W after Cold-Rolling

NASA Astrophysics Data System (ADS)

Zhang, J.; Ma, G. Q.; Godfrey, A.; Shu, D. Y.; Chen, Q.; Wu, G. L.

2017-07-01

One of the common features of deformed face-centered cubic metals with medium to high stacking fault energy is the formation of geometrically necessary dislocation boundaries. The dislocation boundary arrangements in refractory metals with body-centered cubic crystal structure are, however, less well known. To address this issue a Ta-4%W alloy was cold rolled up to 70% in thickness in the present work. The resulting deformation microstructures were characterized by electron back-scattering diffraction and the dislocation boundary arrangements in each grain were revealed using sample-frame misorientation axis maps calculated using an in-house code. The maps were used to analyze the slip pattern of individual grains after rolling, revealing an orientation dependence of the slip pattern.

Small-scale plasticity critically needs a new mechanics description

NASA Astrophysics Data System (ADS)

Ngan, Alfonso H. W.

2013-06-01

Continuum constitutive laws describe the plastic deformation of materials as a smooth, continuously differentiable process. However, provided that the measurement is done with a fine enough resolution, the plastic deformation of real materials is often found to comprise discrete events usually nanometric in size. For bulk-sized specimens, such nanoscale events are minute compared with the specimen size, and so their associated strain changes are negligibly small, and this is why the continuum laws work well. However, when the specimen size is in the micrometer scale or smaller, the strain changes due to the discrete events could be significant, and the continuum description would be highly unsatisfactory. Yet, because of the advent of microtechnology and nanotechnolgy, small-sized materials will be increasingly used, and so there is a strong need to develop suitable replacement descriptions for plasticity of small materials. As the occurrence of the discrete plastic events is also strongly stochastic, their satisfactory description should also be one of a probabilistic, rather than deterministic, nature.

Mapping Viscoelastic and Plastic Properties of Polymers and Polymer-Nanotube Composites using Instrumented Indentation

PubMed Central

Gayle, Andrew J.; Cook, Robert F.

2016-01-01

An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes. PMID:27563168

Study on the Strain Hardening Behaviors of TWIP/TRIP Steels

NASA Astrophysics Data System (ADS)

Huang, T. T.; Dan, W. J.; Zhang, W. G.

2017-10-01

Due to the complex coupling of twinning-induced plasticity (TWIP), transformation-induced plasticity (TRIP), and dislocation glide in TWIP/TRIP steels, it is difficult as well as essential to build a comprehensive strain hardening model to describe the interactions between different deformation mechanisms ( i.e., deformation twinning, martensitic transformation, and dislocation glide) and the resulted strain hardening behaviors. To address this issue, a micromechanical model is established in this paper to predict the deformation process of TWIP/TRIP steels considering both TWIP and TRIP effects. In the proposed model, the generation of deformation twinning and martensitic transformation is controlled by the stacking fault energy (SFE) of the material. In the thermodynamic calculation of SFE, deformation temperature, chemical compositions, microstrain, and temperature rise during deformation are taken into account. Varied by experimental results, the developed model can predict the stress-strain response and strain hardening behaviors of TWIP/TRIP steels precisely. In addition, the improved strength and enhanced strain hardening in Fe-Mn-C TWIP/TRIP steels due to the increased carbon content is also analyzed, which consists with literature.

Mechanical evolution of transpression zones affected by fault interactions: Insights from 3D elasto-plastic finite element models

NASA Astrophysics Data System (ADS)

Nabavi, Seyed Tohid; Alavi, Seyed Ahmad; Mohammadi, Soheil; Ghassemi, Mohammad Reza

2018-01-01

The mechanical evolution of transpression zones affected by fault interactions is investigated by a 3D elasto-plastic mechanical model solved with the finite-element method. Ductile transpression between non-rigid walls implies an upward and lateral extrusion. The model results demonstrate that a, transpression zone evolves in a 3D strain field along non-coaxial strain paths. Distributed plastic strain, slip transfer, and maximum plastic strain occur within the transpression zone. Outside the transpression zone, fault slip is reduced because deformation is accommodated by distributed plastic shear. With progressive deformation, the σ3 axis (the minimum compressive stress) rotates within the transpression zone to form an oblique angle to the regional transport direction (∼9°-10°). The magnitude of displacement increases faster within the transpression zone than outside it. Rotation of the displacement vectors of oblique convergence with time suggests that transpression zone evolves toward an overall non-plane strain deformation. The slip decreases along fault segments and with increasing depth. This can be attributed to the accommodation of bulk shortening over adjacent fault segments. The model result shows an almost symmetrical domal uplift due to off-fault deformation, generating a doubly plunging fold and a 'positive flower' structure. Outside the overlap zone, expanding asymmetric basins subside to 'negative flower' structures on both sides of the transpression zone and are called 'transpressional basins'. Deflection at fault segments causes the fault dip fall to less than 90° (∼86-89°) near the surface (∼1.5 km). This results in a pure-shear-dominated, triclinic, and discontinuous heterogeneous flow of the transpression zone.

High Strain Rate and Shock-Induced Deformation in Metals

NASA Astrophysics Data System (ADS)

Ravelo, Ramon

2012-02-01

Large-scale non-equilibrium molecular Dynamics (MD) simulations are now commonly used to study material deformation at high strain rates (10^9-10^12 s-1). They can provide detailed information-- such as defect morphology, dislocation densities, and temperature and stress profiles, unavailable or hard to measure experimentally. Computational studies of shock-induced plasticity and melting in fcc and bcc single, mono-crystal metals, exhibit generic characteristics: high elastic limits, large directional anisotropies in the yield stress and pre-melting much below the equilibrium melt temperature for shock wave propagation along specific crystallographic directions. These generic features in the response of single crystals subjected to high strain rates of deformation can be explained from the changes in the energy landscape of the uniaxially compressed crystal lattice. For time scales relevant to dynamic shock loading, the directional-dependence of the yield strength in single crystals is shown to be due to the onset of instabilities in elastic-wave propagation velocities. The elastic-plastic transition threshold can accurately be predicted by a wave-propagation stability analysis. These strain-induced instabilities create incipient defect structures, which can be quite different from the ones, which characterize the long-time, asymptotic state of the compressed solid. With increase compression and strain rate, plastic deformation via extended defects gives way to amorphization associated with the loss in shear rigidity along specific deformation paths. The hot amorphous or (super-cooled liquid) metal re-crystallizes at rates, which depend on the temperature difference between the amorphous solid and the equilibrium melt line. This plastic-amorphous transition threshold can be computed from shear-waves stability analyses. Examples from selected fcc and bcc metals will be presented employing semi-empirical potentials of the embedded atom method (EAM) type as well as results from density functional theory calculations.

Modeling dislocation generation in high pressure Czochralski growth of indium phosphide single crystals

NASA Astrophysics Data System (ADS)

Pendurti, Srinivas

InP is an important material for opto-electronic and high speed electronics applications. Its main use today is as the substrate material for epitaxy to produce GaInAsP lasers. The present technology for growing bulk InP is the high pressure Czochralski process. Bulk InP grown through this technique suffers from presence of a high density of line defects or dislocations, which are produced by thermal stresses the material goes through during its growth in the high temperature furnace. Modeling of these thermal stresses and the resulting plastic deformation, giving rise to dislocation densities, entails simulation of the entire thermal history of the crystal during its growth in the furnace, and studying the deformation of the crystal through suitable visco-plastic constitutive equations. Accordingly, a suitable visco-plastic model for deformation of InP was constructed, integrated with the ABAQUS finite element code, and verified through experimental data for uniaxial constant strain rate deformation tests available in literature. This was then coupled with a computation fluid dynamics model, predicting the entire temperature history in the furnace during crystal growth, to study the plastic deformation and dislocation density evolution in the crystal during growth. Growth in a variety of conditions was simulated and those conditions that generate minimum dislocation density identified. Macroscopic controllable parameters that affect the dislocation densities the most, have also been delineated. It was found that the strength of gas convection in the Czochralski furnace has the strongest effect on the dislocation densities in the fully grown crystal. Comparison of the simulated dislocation densities on wafers, with experimentally recorded etch pit profiles on as-grown crystals was reasonable. Finally some limitations in the work are discussed and avenues for future work identified.

Weld residual stresses and plastic deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rybicki, E.; Shiratori, M.

1989-01-01

Residual stresses due to welding can play a primary role in the performance of piping systems and pressure vessels. The stresses are high, in the range of the yield stress of the material, and can influence the fatigue and fracture behavior as well as component service life. Thus, it is important to have an understanding of weld residual stresses. The papers in this section address the important topic of residual stresses and failure analysis. The paper by Boyles reviews computer simulation in the prediction and analysis of fatigue, fracture, and creep of welded structures. The growing use of expert systemsmore » for these purposes is also covered. Karisson, et al, determine the deformations and stresses during the butt-welding of a pipe. The determination of residual deformations and stresses is also presented. Oddy, Goldak, and McDill propose a method to incorporate transformation plasticity in a finite element program. A three-dimensional analysis of a short longitudinal pipe weld in a typical pressure vessel steel is presented. Chaaban, Morin, Ma, and Bazergui study the influence of ligament thickness, strain hardening, expansion sequence, and level of applied expansion pressure on the interference fit in a model of a tube-to-tubesheet joint in a heat exchanger. This section contains papers dealing with models for plastic deformation. Imatani, Teraura, and Inoue formulate a viscoplastic constitutive model based on an anisotropic yield criterion. Comparisons with experimental results obtained using thin walled tubular specimens made from SUS 304 stainless steel show that the present yield criterion adequately accounts for prior deformation history. Niitsu, Horiguchi, and Ikegami investigate the plastic behavior of S25C mild steel tubular specimens subjected to combined axial and torsional loading at both constant and variable temperatures.« less

Simulation of finite-strain inelastic phenomena governed by creep and plasticity

NASA Astrophysics Data System (ADS)

Li, Zhen; Bloomfield, Max O.; Oberai, Assad A.

2017-11-01

Inelastic mechanical behavior plays an important role in many applications in science and engineering. Phenomenologically, this behavior is often modeled as plasticity or creep. Plasticity is used to represent the rate-independent component of inelastic deformation and creep is used to represent the rate-dependent component. In several applications, especially those at elevated temperatures and stresses, these processes occur simultaneously. In order to model these process, we develop a rate-objective, finite-deformation constitutive model for plasticity and creep. The plastic component of this model is based on rate-independent J_2 plasticity, and the creep component is based on a thermally activated Norton model. We describe the implementation of this model within a finite element formulation, and present a radial return mapping algorithm for it. This approach reduces the additional complexity of modeling plasticity and creep, over thermoelasticity, to just solving one nonlinear scalar equation at each quadrature point. We implement this algorithm within a multiphysics finite element code and evaluate the consistent tangent through automatic differentiation. We verify and validate the implementation, apply it to modeling the evolution of stresses in the flip chip manufacturing process, and test its parallel strong-scaling performance.

Gradient-type modeling of the effects of plastic recovery and surface passivation in thin films

NASA Astrophysics Data System (ADS)

Liu, Jinxing; Kah Soh, Ai

2016-08-01

The elasto-plastic responses of thin films subjected to cyclic tension-compression loading and bending are studied, with a focus on Bauschinger and size effects. For this purpose, a model is established by incorporating plastic recovery into the strain gradient plasticity theory we proposed recently. Elastic and plastic parts of strain and strain gradient, which are determined by the elasto-plastic decomposition according to the associative rule, are assumed to have a degree of material-dependent reversibility. Based on the above assumption, a dislocation reversibility-dependent rule is built to describe evolutions of different deformation components under cyclic loadings. Furthermore, a simple strategy is provided to implement the passivated boundary effects by introducing a gradual change to relevant material parameters in the yield function. Based on this theory, both bulge and bending tests under cyclic loading conditions are investigated. By comparing the present predictions with the existing experimental data, it is found that the yield function is able to exhibit the size effect, the Bauschinger effect, the influence of surface passivation and the hysteresis-loop phenomenon. Thus, the proposed model is deemed helpful in studying plastic deformations of micron-scale films.

Auxetic hexachiral structures with wavy ligaments for large elasto-plastic deformation

NASA Astrophysics Data System (ADS)

Zhu, Yilin; Wang, Zhen-Pei; Hien Poh, Leong

2018-05-01

The hexachiral structure is in-plane isotropic in small deformation. When subjected to large elasto-plastic deformation, however, the hexachiral structure tends to lose its auxeticity and/or isotropy—properties which are desirable in many potential applications. The objective of this study is to improve these two mechanical properties, without significantly compromising the effective yield stress, in the regime with significant material and geometrical nonlinearity effects. It is found that the deformation mechanisms underlying the auxeticity and isotropy properties of a hexachiral structure are largely influenced by the extent of rotation of the central ring in a unit cell. To facilitate the development of this deformation mechanism, an improved design with wavy ligaments is proposed. The improved performance of the proposed hexachiral structure is demonstrated. An initial study on possible applications as a protective material is next carried out, where the improved hexachiral design is shown to exhibit higher specific energy absorption capacity compared to the original design, as well as standard honeycomb structures.

Transition of temporal scaling behavior in percolation assisted shear-branching structure during plastic deformation

DOE PAGES

Ren, Jingli; Chen, Cun; Wang, Gang; ...

2017-03-22

This study explores the temporal scaling behavior induced shear-branching structure in response to variant temperatures and strain rates during plastic deformation of Zr-based bulk metallic glass (BMG). The data analysis based on the compression tests suggests that there are two states of shear-branching structures: the fractal structure with a long-range order at an intermediate temperature of 223 K and a larger strain rate of 2.5 × 10 –2 s –1; the disordered structure dominated at other temperature and strain rate. It can be deduced from the percolation theory that the compressive ductility, ec, can reach the maximum value at themore » intermediate temperature. Furthermore, a dynamical model involving temperature is given for depicting the shear-sliding process, reflecting the plastic deformation has fractal structure at the temperature of 223 K and strain rate of 2.5 × 10 –2 s –1.« less

Plastic deformation of B2-NiTi - is it slip or twinning?

NASA Astrophysics Data System (ADS)

Sehitoglu, H.; Wu, Y.; Alkan, S.; Ertekin, E.

2017-06-01

The work addresses two main questions that have baffled the shape memory research community. Firstly, the superb ductility of B2-NiTi cannot be solely attributed to slip on {0 1 1} planes, because there are not a sufficient number of independent slip systems under arbitrary deformations. We show unequivocally, upon diffraction measurements and local strain field traces, that deformation twinning on {1 1 4} planes that can provide additional systems to accommodate plastic flow is activated. Secondly, the slip direction on the {0 1 1} planes has not been established in NiTi with certainty. It is proved precisely to be in ?0 0 1? direction based on crystallographic shear analysis producing the specific strain tensor components (measured at mesoscale with digital image correlation, DIC). Based on the single-crystal experiments, the CRSSs (critical resolved shear stress) are established as 250 and 330 MPa for slip and twinning, respectively. The results have implications in devising correct crystal plasticity formulations for shape memory alloys.

Elementary model of severe plastic deformation by KoBo process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gusak, A.; Storozhuk, N.; Danielewski, M., E-mail: daniel@agh.edu.pl

2014-01-21

Self-consistent model of generation, interaction, and annihilation of point defects in the gradient of oscillating stresses is presented. This model describes the recently suggested method of severe plastic deformation by combination of pressure and oscillating rotations of the die along the billet axis (KoBo process). Model provides the existence of distinct zone of reduced viscosity with sharply increased concentration of point defects. This zone provides the high extrusion velocity. Presented model confirms that the Severe Plastic Deformation (SPD) in KoBo may be treated as non-equilibrium phase transition of abrupt drop of viscosity in rather well defined spatial zone. In thismore » very zone, an intensive lateral rotational movement proceeds together with generation of point defects which in self-organized manner make rotation possible by the decrease of viscosity. The special properties of material under KoBo version of SPD can be described without using the concepts of nonequilibrium grain boundaries, ballistic jumps and amorphization. The model can be extended to include different SPD processes.« less