Wireless Damage Monitoring of Laminated CFRP Composites using Electrical Resistance Change
2007-02-25
Final report Project Title: Wireless Damage Monitoring of Laminated CFRP composites using Electrical Resistance Change Project number...07 NOV 2007 2. REPORT TYPE 3. DATES COVERED 4. TITLE AND SUBTITLE Wireless Damage Monitoring of Laminated CFRP composites using Electrical...strain measuring sensors into laminated composite structures [12, 13]. This approach, however, may cause reductions in static and fatigue strengths
NASA Astrophysics Data System (ADS)
Yang, In-Young; Kim, Ji-Hoon; Cha, Cheon-Seok; Lee, Kil-Sung; Hsu, David K.; Im, Kwang-Hee
2007-07-01
In particular, CFRP (carbon fiber reinforced plastics) composite materials have found wide applicability because of their inherent design flexibility and improved material properties. CFRP composites were manufactured from uni-direction prepreg sheet in this paper. It is important to assess fiber orientation, material properties and part defect in order to ensure product quality and structural integrity of CFRP because strength and stiffness of composites depend on fiber orientation. It is desirable to perform nondestructive evaluation which is very beneficial. An new method for nondestructively determining the fiber orientation in a composite laminate is presented. A one-sided pitch-catch setup was used in the detection and evaluation of flaws and material anomalies in the unidirectional CFRP composite laminates. Two Rayleigh wave transducers were joined head-to-head and used in the pitch-catch mode on the surface of the composites. The pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composite. Especially, ultrasonic waves were extensively characterized in the CFRP composite laminates both normal to fiber and along to fiber with using a one-sided direction of Rayleigh wave transducers. Also, one-sided ultrasonic measurement was made with using a Rayleigh wave transducers and a conventional scanner was used in an immersion tank for extracting fiber orientation information from the ultrasonic reflection in the unidirectional laminate. Therefore, it is thought that the proposed method is useful to evaluate integrity of CFRP laminates.
Effect of temperatures on impact damage and residual strength of CFRP composite laminates
NASA Astrophysics Data System (ADS)
Im, Kwang-Hee; Cha, Cheon-Seok; Park, Jae-Woung; Cha, Yong-Hun; Yang, In-Young; Jung, Jong-An
2000-05-01
In this paper, the effect of temperature variations (low and high temperatures) was experimentally studied on the impact damages of CFRP laminates. Composite laminates used for this experiment are CF/EPOXY orthotropic laminated plates with two-interfaces [06/906]s and [04/904]s, and CF/PEEK orthotropic laminated plates with two-interfaces [06/906]s. A steel ball launched by the air gun collides against CFRP laminates to generate impact damages. With impact-damaged specimens, nondestructive evaluation (NDE) technique, such as a scanning acoustic microscope (SAM) was performed on the delamination-damaged samples to characterize damage growth using the SAM after impact damages according to the temperatures. Therefore, this study aims experimentally to present the interrelations between the impact energy and impact damages (i.e. delamination area and matrix) of CFRP laminates. (CF/EPOXY, CF/PEEK) subjected to FOD (foreign object damages) under low and high temperatures.
Optimization-Based Monitoring of Laminated CFRP Composites using Electrical Resistance Changes
2009-11-09
ABSTRACT Impact load like a tool drop easily causes a delamination crack in a laminated Carbon Fiber Reinforced Polymer ( CFRP ). The delamination crack...Reinforced Polymer ( CFRP ). The delamination crack causes deterioration of structural reliability of a laminated CFRP . Monitoring of delamination is...Monitoring, Optimization Introduction Laminated Carbon Fiber Reinforced Polymer ( CFRP ) has been increasingly applied to the aerospace primary
One-Sided Measurement Approach on Ultrasonic Beam Path Analysis in CFRP Composite Laminates
NASA Astrophysics Data System (ADS)
Im, K. H.; Hsu, D. K.; Kim, H. J.; Song, S. J.; Dayal, V.; Barnard, D.; Park, J. W.; Lee, K. S.; Yang, Y. J.; Yang, I. Y.
2008-02-01
Composite materials are attractive for a wide range of applications because of high performance engineering structures. In particular, the importance of carbon-fiber reinforced plastics (CFRP) has been generally recognized in both space and civil aircraft industries; so, CFRP composite laminates are widely used. It is very important to detect defects in composite laminates because they cause the mechanical properties (stiffness, strength) of the laminate to be reduced. As well known for ultrasonic technique for evaluating the defect of CFRP composite laminates, a pitch-catch technique was found to be more practical than normal incidence backwall echo of longitudinal wave to arbitrary flaws in the composite, including fiber orientation, low level porosity, ply waviness, and cracks. The measurement depth using Rayleigh probes can be increased by increasing the separation distance of the transmitting and receiving probes. Also, with the aid of the automatic scanner, the one-sided pitch-catch probe was used to produce C-scan images for mapping out the images with beam profiles. Especially pitch-catch beam path was nondestructively characterized for the specimens when measuring a peak-to-peak amplitude and time-of-flight in order to build the beam profile modeling in the unidirectional CFRP composite laminates. Also, the pitch-catch simulation was performed to predict the beam profile trend of wave propagation in the unidirectional CF/Epoxy composite laminates. Therefore, it is found that the experimentally Rayleigh wave variation of pitch-catch ultrasonic signal was consistent with simulated results and one-side ultrasonic measurement might be very useful to detect the defects in CFRP composites.
Influence of terahertz waves on the fiber direction of CFRP composite laminates
NASA Astrophysics Data System (ADS)
Im, Kwang-Hee; Hsu, David K.; Chiou, Chien-Ping; Barnard, Daniel J.; Yang, In-Young; Park, Je-Woong
2013-01-01
The importance of Carbon-fiber reinforced plastics (CFRP) are widely utilized due to more high performance in engineering structures. It was well known that a nondestructive technique would be very beneficial. A new terahertz radiation has been recognized for their importance in technological applications. Recently, T-ray (terahertz ray) advances of technology and instrumentation has provided a probing field on the electromagnetic spectrum. The THz-TDS can be considered as a useful tool using general non-conducting materials; however it is quite limited to conducting materials. In order to solve various material properties, the index of refraction (n) and the absorption coefficient (α) are derived in reflective and transmission configuration using the terahertz time domain spectroscopy. However, the T-ray is limited in order to penetrate a conducting material to some degree. Here, the T-ray would not go through easily the CFRP composite laminates since carbon fibers are electrically conducting while the epoxy matrix is not. So, investigation of terahertz time domain spectroscopy (THz TDS) was made and reflection and transmission configurations were studied for a 48-ply thermoplastic PPS (poly-phenylene sulfide)-based CFRP solid laminate. It is found that the electrical conductivity of CFRP composites depends on the direction of unidirectional fibers. Also, the T-ray could penetrate a CFRP composite laminate a few ply based on the E-filed (Electrical field) of carbon fibers. The terahertz scanning images were made at the angles ranged from 0° to 180° with respect to the nominal fiber axis. So, the images were mapped out based on the electrical field (E-field) direction in the CFRP solid laminates. Also, using two-dimensional spatial Fourier transform, interface C-scan images were transformed into quantitatively angular distribution plots to show the fiber orientation information therein and to predict the orientation of the ply.
Damage Assessment of CFRP [90/±45/0] Composite Laminates over Fatigue Cycles
NASA Astrophysics Data System (ADS)
Ahmadzadeh, G. R.; Shirazi, A.; Varvani-Farahani, A.
2011-12-01
The present paper develops a stiffness-based model to characterize the progressive fatigue damage in quasi-isotropic carbon fiber reinforced polymer (CFRP) [90/±45/0] composite laminates with various stacking sequences. The damage model is constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional plies of 90°, 0° and angle-ply laminates of ±45° as the number of cycles progresses. The proposed model accumulates damages of constituent plies constructing [90/±45/0] laminates by means of weighting factor η 90, η 0 and η 45. These weighting factors were defined based on the damage progress over fatigue cycles within the plies 90°, 0° and ±45° of the composite laminates. Damage model has been verified using CFRP [90/±45/0] laminates samples made of graphite/epoxy 3501-6/AS4. Experimental fatigue damage data of [90/±45/0] composite laminates have fell between the predicted damage curves of 0°, 90° plies and ±45°, 0/±45° laminates over life cycles at various stress levels. Predicted damage results for CFRP [90/±45/0] laminates showed good agreement with experimental data. Effect of stacking sequence on the model of stiffness reduction has been assessed and it showed that proposed fatigue damage model successfully recognizes the changes in mechanism of fatigue damage development in quasi-isotropic composite laminates.
Effects of the shock duration on the response of CFRP composite laminates
NASA Astrophysics Data System (ADS)
Gay, Elise; Berthe, Laurent; Boustie, Michel; Arrigoni, Michel; Buzaud, Eric
2014-11-01
Shock loads induce a local tensile stress within a sample. The location and amplitude of this high strain rate stress can be monitored respectively by the duration and intensity of the shock. The process is applied to carbon fibre reinforced polymer (CFRP) composites, involved in aeronautic or defense industry. This paper describes the response of CFRP laminates of different thicknesses to a shock load normal to the fibres direction. The effects of the shock duration on the wave propagation are key issues of this work. Experiments have been performed on high power laser facilities and on a high power pulsed generator to get a wide range of pulse duration from fs to µs. Numerical simulation provides a comprehensive approach of the wave propagation and tensile stress generation within these complex materials. The main result concerns the relation between the load duration, the tensile stress and the induced delamination within 1, 4 and 8 ply composite laminates.
Detection of Fiber Layer-Up Lamination Order of CFRP Composite Using Thermal-Wave Radar Imaging
NASA Astrophysics Data System (ADS)
Wang, Fei; Liu, Junyan; Liu, Yang; Wang, Yang; Gong, Jinlong
2016-09-01
In this paper, thermal-wave radar imaging (TWRI) is used as a nondestructive inspection method to evaluate carbon-fiber-reinforced-polymer (CFRP) composite. An inverse methodology that combines TWRI with numerical optimization technique is proposed to determine the fiber layer-up lamination sequences of anisotropic CFRP composite. A 7-layer CFRP laminate [0°/45°/90°/0°]_{{s}} is heated by a chirp-modulated Gaussian laser beam, and then finite element method (FEM) is employed to calculate the temperature field of CFRP laminates. The phase based on lock-in correlation between reference chirp signal and the thermal-wave signal is performed to obtain the phase image of TWRI, and the least square method is applied to reconstruct the cost function that minimizes the square of the difference between the phase of TWRI inspection and numerical calculation. A hybrid algorithm that combines the simulation annealing with Nelder-Mead simplex research method is employed to solve the reconstructed cost function and find the global optimal solution of the layer-up sequences of CFRP composite. The result shows the feasibility of estimating the fiber layer-up lamination sequences of CFRP composite with optimal discrete and constraint conditions.
Strengthening and repair of steel-concrete composite girders using CFRP laminates
NASA Astrophysics Data System (ADS)
Tavakkolizadeh, Mohammadreza
The use of advanced composite materials for rehabilitation and repair of deteriorating infrastructure has been embraced worldwide. The conventional techniques for strengthening of substandard bridges are costly, time consuming and labor intensive. A total of 38 specimens made of steel and carbon fibers were prepared and tested to investigate the possibility of galvanic corrosion. Two simulated aggressive environments and three different amounts of epoxy coating were used. Potentiodynamic polarization and galvanic corrosion tests were conducted. The results of the experiments showed the existence of galvanic corrosion however the rate of such corrosion could be decreased significantly by epoxy coating. A total of 21 specimens made of S 5 x 10 A36 steel beams were prepared and tested to determine the effectiveness of CFRP patch on fatigue life of notched beam. The results showed that not only CFRP patch tends to extend the fatigue life of a detail more than three times, but also it decreases the crack growth rate significantly. To investigate the effectiveness of the epoxy bonded CFRP sheets in repair and retrofit of composite girders, a total of six large-scale steel-concrete composite girders made of W 14 x 30 A36 steel beam and 7.5 cm. thick by 91 cm wide concrete slab were prepared and tested. Three different numbers of CFRP layers and three different damage level in Range were considered. The retrofitting test results showed that epoxy bonded CFRP Sheet increased the ultimate load carrying capacity of composite girders and the behavior can be conservatively predicted by traditional methods. The repair test results showed that epoxy bonded CFRP sheet could restore the ultimate load carrying capacity and stiffness of damaged steel-concrete composite girders. The ultimate capacity of the repaired beam was predicted by traditional methods of analysis of steel-concrete composite beams, which was fairly conservative. Guidelines and procedures for design of Steel-Concrete-CFRP
Imaging of Fatigue Damage in CFRP Composite Laminates Using Nonlinear Harmonic Generation
NASA Astrophysics Data System (ADS)
Mattei, Christophe; Marty, Pierre
2003-03-01
In this paper, experimental evidence is presented that suggests a strong nonlinear interaction between acoustic wave and micro-structural damage before the onset of delaminations in fatigued CFRP samples. Sample used were 32 plies quasi-isotropic graphite/epoxy laminate fatigued with a four point bending fatigue. First harmonic images were constructed from the amplitude of the first harmonic normalized by the amplitude of the fundamental. Harmonic imaging technique (HIT) shows a much higher sensitivity to micro-damage than amplitude C-scan. Correlations are established between the image zone where the nonlinear parameter is high and the region where a high density of micro-delamination and matrix cracks is observed.
Damage in woven CFRP laminates under impact loading
NASA Astrophysics Data System (ADS)
Ullah, H.; Harland, A. R.; Silberschmidt, V. V.
2012-08-01
Carbon fibre-reinforced polymer (CFRP) composites used in sports products can be exposed to different in-service conditions such as large dynamic bending deformations caused by impact loading. Composite materials subjected to such loads demonstrate various damage modes such as matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution affects both in-service properties and performance of CFRP that can deteriorate with time. These failure modes need adequate means of analysis and investigation, the major approaches being experimental characterisation and numerical simulations. This research deals with a deformation behaviour and damage in composite laminates due to dynamic bending. Experimental tests are carried out to characterise the behaviour of a woven CFRP material under large-deflection dynamic bending in impact tests carried out to obtain the force-time and absorbed energy profiles for CFRP laminates. Damage in the impacted laminates is analysed using optical microscopy. Numerical simulations are performed to study the deformation behaviour and damage in CFRP for cases of large-deflection bending based on three-dimensional finite-element models implemented in the commercial code Abaqus/Explicit. Multiple layers of bilinear cohesive-zone elements are employed to model the initiation and progression of inter-ply delamination observed in the microscopy studies. The obtained results of simulations show good agreement with experimental data.
NASA Astrophysics Data System (ADS)
Wang, Cheng-Dong; Qiu, Kun-Xian; Chen, Ming; Cai, Xiao-Jiang
2015-03-01
Carbon Fiber Reinforced Plastic (CFRP) composite laminates are widely used in aerospace and aircraft structural components due to their superior properties. However, they are regarded as difficult-to-cut materials because of bad surface quality and low productivity. Drilling is the most common hole making process for CFRP composite laminates and drilling induced delamination damage usually occurs severely at the exit side of drilling holes, which strongly deteriorate holes quality. In this work, the candle stick drill and multi-facet drill are employed to evaluate the machinability of drilling T700/LT-03A CFRP composite laminates in terms of thrust force, delamination, holes diameter and holes surface roughness. S/N ratio is used to characterize the thrust force while an ellipse-shaped delamination model is established to quantitatively analyze the delamination. The best combination of drilling parameters are determined by full consideration of S/N ratios of thrust force and the delamination. The results indicate that candle stick drill will induce the unexpected ellipse-shaped delamination even at its best drilling parameters of spindle speed of 10,000 rpm and feed rate of 0.004 mm/tooth. However, the multi-facet drill cutting at the relative lower feed rate of 0.004 mm/tooth and lower spindle speed of 6000 rpm can effectively prevent the delamination. Comprehensively, holes quality obtained by multi-facet drill is much more superior to those obtained by candle stick drill.
Fabrication of CFRP/Al Active Laminates
NASA Astrophysics Data System (ADS)
Asanuma, Hiroshi; Haga, Osamu; Ohira, Junichiro; Takemoto, Kyosuke; Imori, Masataka
This paper describes fabrication and evaluation of the active laminate. It was made by hot-pressing of an aluminum plate as a high CTE material, a unidirectional CFRP prepreg as a low CTE material and an electric resistance heater, a KFRP prepreg as a low CTE material and an insulator between them, and copper foils as electrodes. In this study, fabricating conditions and performances such as curvature change and output force were examined. Under optimized fabricating conditions, it became clear that 1) the curvature of the active laminate linearly changes as a function of temperature, between room temperature and its hot pressing temperature without hysteresis by electric resistance heating of carbon fiber in the CFRP layer and cooling, and 2) the output force against a fixed punch almost linearly increases with increasing temperature during heating from 313K up to around the glass transition temperature of the epoxy matrix.
Time Domain Reflectometry for Damage Detection of Laminated CFRP plate
2011-08-18
Final Report PROJECT ID: AOARD-10-4112 Title: Time Domain Reflectometry for damage detection of laminated CFRP plate Researcher: Professor Akira...From July/2010 To July/2011 Abstract Recently, high toughness Carbon Fiber Reinforced Polymer ( CFRP ) laminates are used to primary structures. The...tough CFRP yields small fiber breakages when delamination crack is made in many cases. This requires a detection system of fiber breakages at low cost for
Damage in woven CFRP laminates subjected to low velocity impacts
NASA Astrophysics Data System (ADS)
Ullah, H.; Abdel-Wahab, A. A.; Harland, A. R.; Silberschmidt, V. V.
2012-08-01
Carbon fabric-reinforced polymer (CFRP) composites used in sports products can be exposed to different in-service conditions such as large dynamic bending deformations caused by impact loading. Composite materials subjected to such loads demonstrate various damage modes such as matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution in these materials affects both their in-service properties and performance that can deteriorate with time. These processes need adequate means of analysis and investigation, the major approaches being experimental characterisation and non-destructive examination of internal damage in composite laminates. This research deals with a deformation behaviour and damage in woven composite laminates due to low-velocity dynamic out-of-plane bending. Experimental tests are carried out to characterise the behaviour of such laminates under large-deflection dynamic bending in un-notched specimens in Izod tests using a Resil Impactor. A series of low-velocity impact tests is carried out at various levels of impact energy to assess the energy absorbed and force-time response of CFRP laminates. X-ray micro computed tomography (micro-CT) is used to investigate material damage modes in the impacted specimens. X-ray tomographs revealed that through-thickness matrix cracking, inter-ply delamination and intra-ply delamination, such as tow debonding and fabric fracture, were the prominent damage modes.
Analysis of nonlinear deformations and damage in CFRP textile laminates
NASA Astrophysics Data System (ADS)
Ullah, H.; Harland, A. R.; Lucas, T.; Price, D.; Silberschmidt, V. V.
2011-07-01
Carbon fibre-reinforced polymer (CFRP) textile composites are widely used in aerospace, automotive and construction components and structures thanks to their relatively low production costs, higher delamination and impact strength. They can also be used in various products in sports industry. These products are usually exposed to different in-service conditions such as large bending deformation and multiple impacts. Composite materials usually demonstrate multiple modes of damage and fracture due to their heterogeneity and microstructure, in contrast to more traditional homogeneous structural materials like metals and alloys. Damage evolution affects both their in-service properties and performance that can deteriorate with time. These damage modes need adequate means of analysis and investigation, the major approaches being experimental characterisation, numerical simulations and microtomography analysis. This research deals with a deformation behaviour and damage in composite laminates linked to their quasi-static bending. Experimental tests are carried out to characterise the behaviour of woven CFRP material under large-deflection bending. Two-dimensional finite element (FE) models are implemented in the commercial code Abaqus/Explicit to study the deformation behaviour and damage in woven CFRP laminates. Multiple layers of bilinear cohesive-zone elements are employed to model the onset and progression of inter-ply delamination process. X-ray Micro-Computed Tomography (MicroCT) analysis is carried out to investigate internal damage mechanisms such as cracking and delaminations. The obtained results of simulations are in agreement with experimental data and MicroCT scans.
Enhancement of Gas Barrier Properties of CFRP Laminates Fabricated Using Thin-Ply Prepregs
NASA Astrophysics Data System (ADS)
横関, 智弘; 高木, 智宏; 吉村, 彰記; Ogasawara, Toshio; 荻原, 慎二
Composite laminates manufactured using thin-ply prepregs are expected to have superior resistance properties against microcracking compared to those using standard prepregs. In this study, comparative investigations are presented on the microcrack accumulation and gas leakage characteristics of CFRP laminates fabricated using standard and thin-ply prepregs, consisting of high-performance carbon fiber and toughened epoxy, as a fundamental research on the cryogenic composite tanks for future space vehicles. It was shown that laminates using thin-ply prepregs exhibited much higher strain at microcrack initiation compared to those using standard prepregs at room and cryogenic temperatures. In addition, helium gas leak tests using CFRP laminated tubular specimens subjected to quasi-static tension loadings were performed. It was demonstrated that CFRP laminates using thin-ply prepregs have higher gas barrier properties than those using standard prepregs.
Damage Detection of Laminated CFRP Structures using Electric Pulse Wave Transmission
2010-05-05
SUPPLEMENTARY NOTES 14. ABSTRACT For laminated CFRP structures, it is quite difficult to detect internal damage such as delamination, matrix cracks, and...unclassified Abstract. Carbon Fiber Reinforced Polymer ( CFRP ) laminates are applied to many aerospace structures. For these laminated CFRP ...Carbon Fiber Reinforced Polymer ( CFRP ) has been increasingly applied to the aerospace primary structures because of its high specific strength and
NASA Technical Reports Server (NTRS)
Hudson, Tyler B.; Hou, Tan-Hung; Grimsley, Brian W.; Yaun, Fuh-Gwo
2016-01-01
A guided wave-based in-process cure monitoring technique for carbon fiber reinforced polymer (CFRP) composites was investigated at NASA Langley Research Center. A key cure transition point (vitrification) was identified and the degree of cure was monitored using metrics such as amplitude and time of arrival (TOA) of guided waves. Using an automated system preliminarily developed in this work, high-temperature piezoelectric transducers were utilized to interrogate a twenty-four ply unidirectional composite panel fabricated from Hexcel (Registered Trademark) IM7/8552 prepreg during cure. It was shown that the amplitude of the guided wave increased sharply around vitrification and the TOA curve possessed an inverse relationship with degree of cure. The work is a first step in demonstrating the feasibility of transitioning the technique to perform in-process cure monitoring in an autoclave, defect detection during cure, and ultimately a closed-loop process control to maximize composite part quality and consistency.
Homogenized Creep Behavior of CFRP Laminates at High Temperature
NASA Astrophysics Data System (ADS)
Fukuta, Y.; Matsuda, T.; Kawai, M.
In this study, creep behavior of a CFRP laminate subjected to a constant stress is analyzed based on the time-dependent homogenization theory developed by the present authors. The laminate is a unidirectional carbon fiber/epoxy laminate T800H/#3631 manufactured by Toray Industries, Inc. Two kinds of creep analyses are performed. First, 45° off-axis creep deformation of the laminate at high temperature (100°C) is analyzed with three kinds of creep stress levels, respectively. It is shown that the present theory accurately predicts macroscopic creep behavior of the unidirectional CFRP laminate observed in experiments. Then, high temperature creep deformations at a constant creep stress are simulated with seven kinds of off-axis angles, i.e., θ = 0°, 10°, 30°, 45°, 60°, 75°, 90°. It is shown that the laminate has marked in-plane anisotropy with respect to the creep behavior.
Development of High Performance CFRP/Metal Active Laminates
NASA Astrophysics Data System (ADS)
Asanuma, Hiroshi; Haga, Osamu; Imori, Masataka
This paper describes development of high performance CFRP/metal active laminates mainly by investigating the kind and thickness of the metal. Various types of the laminates were made by hot-pressing of an aluminum, aluminum alloys, a stainless steel and a titanium for the metal layer as a high CTE material, a unidirectional CFRP prepreg as a low CTE/electric resistance heating material, a unidirectional KFRP prepreg as a low CTE/insulating material. The aluminum and its alloy type laminates have almost the same and the highest room temperature curvatures and they linearly change with increasing temperature up to their fabrication temperature. The curvature of the stainless steel type jumps from one to another around its fabrication temperature, whereas the titanium type causes a double curvature and its change becomes complicated. The output force of the stainless steel type attains the highest of the three under the same thickness. The aluminum type successfully increased its output force by increasing its thickness and using its alloys. The electric resistance of the CFRP layer can be used to monitor the temperature, that is, the curvature of the active laminate because the curvature is a function of temperature.
NASA Astrophysics Data System (ADS)
Okabe, Tomonaga; Yashiro, Shigeki
This study proposes the cohesive zone model (CZM) for predicting fatigue damage growth in notched carbon-fiber-reinforced composite plastic (CFRP) cross-ply laminates. In this model, damage growth in the fracture process of cohesive elements due to cyclic loading is represented by the conventional damage mechanics model. We preliminarily investigated whether this model can appropriately express fatigue damage growth for a circular crack embedded in isotropic solid material. This investigation demonstrated that this model could reproduce the results with the well-established fracture mechanics model plus the Paris' law by tuning adjustable parameters. We then numerically investigated the damage process in notched CFRP cross-ply laminates under tensile cyclic loading and compared the predicted damage patterns with those in experiments reported by Spearing et al. (Compos. Sci. Technol. 1992). The predicted damage patterns agreed with the experiment results, which exhibited the extension of multiple types of damage (e.g., splits, transverse cracks and delaminations) near the notches.
NASA Astrophysics Data System (ADS)
Kumagai, S.; Shindo, Y.
2004-06-01
The cryogenic fracture behavior of carbon fiber reinforced polymer (CFRP) woven laminates was studied. Experiments and a finite element analysis were conducted on single edge notched CFRP woven laminates subjected to in-plane loading. Damage processes were identified by acoustic emission measurement and digital microscopy.
Effect of anisotropy on fatigue properties of notched CFRP laminates
NASA Astrophysics Data System (ADS)
Murakami, Ri-Ichi; Yamanaka, Keisi; Inaba, Tatsuichi; Takaichi, Hiroshi; Shibayama, Muneaki
1993-04-01
The effect of anisotropy on fatigue properties of notched carbon fiber reinforced plastic laminates has been studied. The off-axis angle of carbon fiber was varied from 0 to 45 deg. The ultimate tensile strength and the tensile elastic modulus drastically decreased when the off-axis angle of carbon fiber increased to 30 deg. When the-off axis angle of carbon fiber increased over 30 deg, these values approached approximately constant values. The maximum tensile strain also increased and saturated to a constant value when the off-axis angle of the carbon fiber increased. The fatigue strength of notched CFRP laminates showed a similar dependence of ultimate tensile strength on the off-axis angle. The decrease of fatigue strength results from the fatigue damage in relation to the off-axis angle. The fatigue damage process was analyzed in terms of AE measurement and fractography. These results indicate that the fatigue damage process of CFRP laminates was significantly affected by the off-axis angle of carbon fiber.
Aluminium/lithium alloy-CFRP hybrid laminate: Fabrication and properties
Freischmidt, G.; Coutts, R.S.P.; Janardhana, M.N.
1993-12-31
Hybrid composite laminates of aluminum and aluminum/lithium alloy sheeting with unidirectional carbon fiber/epoxy plies have been fabricated to produce sheet materials of high strength, low density and reduced fatigue crack growth rate. In an arrangement of one layer of unidirectional carbon fiber reinforced plastic (CFRP) and 2 sheets of 2090-T3 aluminum alloy was used to give a material with a density of 2.20g/cm{sup 3}. Tensile test results gave an ultimate strength of 803MPa, a modulus of 75.7GPa and a 2% offset yield strength of 497MPa. Preliminary fatigue crack growth rate determinations on single edge notch (SEN) specimens show a marked reduction compared to monolithic 2090-T3. Other hybrid laminates using 2024-T3 alloy have also been made and tested. These laminates show reduced tensile properties, however, they appear to have lower fatigue crack growth rates than when using 2090T3 in hybrid form. The fabrication of hybrid laminates included the use of unsupported adhesive film to bond the precured unidirectional carbon fiber composite plies to the aluminum sheeting. This has left a distinct interphase region between the alloy and CFRP which is thought to improve properties through an effective load transfer.
2008-03-01
to measure fatigue limit of the CFRP laminates. Figure 12 shows the results of the fatigue tests. The abscissa is the number of cycles to failure and...monitoring of CFRP composite structures 2007 April – 2008 March Professor Akira Todoroki Department of Mechanical Sciences and Engineering Tokyo...monitoring of CFRP composite structures 5a. CONTRACT NUMBER FA48690714039 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Akira Todoroki 5d
Damage Behavior and Life Prediction in CFRP Cross-Ply Laminates under Fatigue Loading
NASA Astrophysics Data System (ADS)
Tohgo, Keiichiro; Nakagawa, Shuji; Araki, Hiroyasu
This paper deals with fatigue damage and life prediction of CFRP cross-ply laminates. Fatigue tests are carried out on CFRP unidirectional and cross-ply laminates under the on-axis and off-axis directions. On the unidirectional laminate, fiber breakage and fiber-peeling develop before the final fracture under on-axis fatigue, while the final fracture suddenly occurs by cracking along the fiber direction under off-axis fatigue. On the cross-ply laminates, ply-cracking in 90° plies and fiber-peeling in 0° plies develop under on-axis fatigue, while ply-cracking and delamination lead to the final fracture under off-axis fatigue. Based on the comparison of damage behavior and S-N curves between unidirectional and cross-ply laminates, possibility of fatigue life prediction of CFRP cross-ply laminates is discussed.
Hybrid composite laminate structures
NASA Technical Reports Server (NTRS)
Chamis, C. C.; Lark, R. F. (Inventor)
1977-01-01
An invention which relates to laminate structures and specifically to essentially anisotropic fiber composite laminates is described. Metal foils are selectively disposed within the laminate to produce increased resistance to high velocity impact, fracture, surface erosion, and other stresses within the laminate.
A simplified mesoscale model for predicting the mechanical behavior of stitched CFRP laminates
NASA Astrophysics Data System (ADS)
Li, Jun; Wang, Bo; Jiao, Guiqiong
2017-06-01
This paper presents a finite element (FE) analysis of the mechanical responses for stitched CFRP laminates under different mechanical loads. Firstly, the through-thickness stitch was simplified to z-pin like reinforcement with a uniform displacement constraint on the upper and lower surfaces of the laminate. Then, a mesoscale 3D representative volume element (RVE) of the stitched composite was proposed and modeled in the FE code ABAQUS, where the reinforcing stitch, composite layers and interfaces were built. A 3D Hashin damage model and built-in cohesive elements were respectively used to predict the mechanical failure of the stitch and the damageable behavior of cohesive interfaces. Simulation results reveal the progressive damage and rupture processes of the RVE under tensile and shear mechanical loads, and macroscopic nonlinear load-displacement responses of the mesoscale model are also captured.
2012-01-30
ones and the measured data. 4. ATM-2 for the fatigue life prediction of CFRP laminates was expanded to MMF /ATM method for the fatigue life...TECHNICAL APPROACH 1. The procedure of MMF /ATM method combined with our advanced ATM and the micromechanics of failure ( MMF ) developed by Professor...Sung-Kyu Ha and others is proposed for the fatigue life prediction of the structures made of CFRP laminates. 2. The master curves of MMF /ATM
Compression Fracture of CFRP Laminates Containing Stress Intensifications.
Leopold, Christian; Schütt, Martin; Liebig, Wilfried V; Philipkowski, Timo; Kürten, Jonas; Schulte, Karl; Fiedler, Bodo
2017-09-05
For brittle fracture behaviour of carbon fibre reinforced plastics (CFRP) under compression, several approaches exist, which describe different mechanisms during failure, especially at stress intensifications. The failure process is not only initiated by the buckling fibres, but a shear driven fibre compressive failure beneficiaries or initiates the formation of fibres into a kink-band. Starting from this kink-band further damage can be detected, which leads to the final failure. The subject of this work is an experimental investigation on the influence of ply thickness and stacking sequence in quasi-isotropic CFRP laminates containing stress intensifications under compression loading. Different effects that influence the compression failure and the role the stacking sequence has on damage development and the resulting compressive strength are identified and discussed. The influence of stress intensifications is investigated in detail at a hole in open hole compression (OHC) tests. A proposed interrupted test approach allows identifying the mechanisms of damage initiation and propagation from the free edge of the hole by causing a distinct damage state and examine it at a precise instant of time during fracture process. Compression after impact (CAI) tests are executed in order to compare the OHC results to a different type of stress intensifications. Unnotched compression tests are carried out for comparison as a reference. With this approach, a more detailed description of the failure mechanisms during the sudden compression failure of CFRP is achieved. By microscopic examination of single plies from various specimens, the different effects that influence the compression failure are identified. First damage of fibres occurs always in 0°-ply. Fibre shear failure leads to local microbuckling and the formation and growth of a kink-band as final failure mechanisms. The formation of a kink-band and finally steady state kinking is shifted to higher compressive strains
Compression Fracture of CFRP Laminates Containing Stress Intensifications
Schütt, Martin; Philipkowski, Timo; Kürten, Jonas; Schulte, Karl
2017-01-01
For brittle fracture behaviour of carbon fibre reinforced plastics (CFRP) under compression, several approaches exist, which describe different mechanisms during failure, especially at stress intensifications. The failure process is not only initiated by the buckling fibres, but a shear driven fibre compressive failure beneficiaries or initiates the formation of fibres into a kink-band. Starting from this kink-band further damage can be detected, which leads to the final failure. The subject of this work is an experimental investigation on the influence of ply thickness and stacking sequence in quasi-isotropic CFRP laminates containing stress intensifications under compression loading. Different effects that influence the compression failure and the role the stacking sequence has on damage development and the resulting compressive strength are identified and discussed. The influence of stress intensifications is investigated in detail at a hole in open hole compression (OHC) tests. A proposed interrupted test approach allows identifying the mechanisms of damage initiation and propagation from the free edge of the hole by causing a distinct damage state and examine it at a precise instant of time during fracture process. Compression after impact (CAI) tests are executed in order to compare the OHC results to a different type of stress intensifications. Unnotched compression tests are carried out for comparison as a reference. With this approach, a more detailed description of the failure mechanisms during the sudden compression failure of CFRP is achieved. By microscopic examination of single plies from various specimens, the different effects that influence the compression failure are identified. First damage of fibres occurs always in 0°-ply. Fibre shear failure leads to local microbuckling and the formation and growth of a kink-band as final failure mechanisms. The formation of a kink-band and finally steady state kinking is shifted to higher compressive strains
Delamination Monitoring of Quasi-Isotropic CFRP Laminate Using Electric Potential Change Method
NASA Astrophysics Data System (ADS)
Ueda, Masahito; Todoroki, Akira
Real-time detection of delamination in carbon fiber reinforce plastic (CFRP) laminates has been requiring to maintain the structural reliability of aircraft. In this paper, electric potential change method (EPCM) was applied to monitor delaminations in quasi-isotropic CFRP laminate. As the coefficient of thermal expansion and mold shrinkage factor of carbon fiber and epoxy matrix is different, residual stress is developed in the laminate during the fabrication process of curing. The local strain variation due to delaminations was measured by EPCM utilizing the piezoresistivity of the laminate itself. Finite element simulation was performed to investigate the applicability of the method.
Numerical Prediction of Fatigue Damage Progress in Holed CFRP Laminates Using Cohesive Elements
NASA Astrophysics Data System (ADS)
Yashiro, Shigeki; Okabe, Tomonaga
This study presents a numerical simulation to predict damage progress in notched composite laminates under cyclic loading by using a cohesive zone model. A damage-mechanics concept was introduced directly into the fracture process in the cohesive elements in order to express crack growth by cyclic loading. This approach then conformed to the established damage mechanics and facilitated understanding the procedure and reducing computation costs. We numerically investigated the damage progress in holed CFRP cross-ply laminates under tensile cyclic loading and compared the predicted damage patterns with experiment results. The predicted damage patterns agreed with the experiment results that exhibited the extension of multiple types of damage (splits, transverse cracks, and delamination) near the hole. A numerical study indicated that the change in the distribution of in-plane shear stress due to delamination induced the extension of splits and transverse cracks near the hole.
Development of damage suppression system using embedded SMA foil in CFRP laminates
NASA Astrophysics Data System (ADS)
Ogisu, Toshimichi; Nomura, Masato; Ando, Norio; Takaki, Junji; Kobayashi, Masakazu; Okabe, Tomonaga; Takeda, Nobuo
2001-07-01
Some recent studies have suggested possible applications of Shape Memory Alloy (SMA) for a smart health monitoring and suppression of damage growth. The authors have been conducting research and development studies on applications of embedded SMA foil actuators in CFRP laminates as the basic research for next generation aircrafts. First the effective surface treatment for improvement of bonding properties between SMA and CFRP was studied. It was certified that the anodic oxide treatment by 10% NaOH solution was the most effective treatment from the results of peel resistance test and shear strength test. Then, CFRP laminates with embedded SMA foils were successfully fabricated using this effective surface treatment. The damage behavior of quasi-isotropic CFRP laminates with embedded SMA foils was characterized in both quasi-static load-unload and fatigue tests. The relationship between crack density and applied strain was obtained. The recovery stress generated by embedded SMA foils could increase the onset strain of transverse cracking by 0.2%. The onset strain of delmination in CFRP laminates was also increased accordingly. The shear-lag analysis was also conducted to predict the damage evolution in CFRP laminates with embedded SMA foils. The adhesive layers on both sides of SMA foils were treated as shear elements. The theoretical analysis successfully predicted the experimental results.
Cryogenic mechanical response of multilayer satin weave CFRP composites with cracks
NASA Astrophysics Data System (ADS)
Watanabe, S.; Shindo, Y.; Takeda, T.; Narita, F.
2008-07-01
We deal with the thermomechanical response of multilayer satin weave carbon-fiber-reinforced polymer (CFRP) laminates with internal and/or edge cracks and temperature-dependent material properties subjected to tensile loading at cryogenic temperatures. The composite material is assumed to be under the generalized plane strain. Cracks are located in the transverse fiber bundles and extend to the interfaces between two fiber bundles. A finite-element model is employed to study the influence of residual thermal stresses on the mechanical behavior of multilayer CFRP woven laminates with cracks. Numerical calculations are carried out, and Young's modulus and stress distributions near the crack tip are shown graphically.
An application of a neural network to damage identification in CFRP laminates
Byon, O.I.; Fujikawa, Y.
1994-12-31
For the wider use of CFRP, the damage specially in the laminated direction such as transverse cracking, delamination or fiber-matrix debonding should be easily and economically searched and a reasonable non-destructive test method should be also fixed. This paper presents the application of the hierarchical neural network to the damage identification in the CFRP laminated beam and discusses the accuracy and the efficiency of this method. As a result, it is found that the neural network is the very useful and practical non-destructive method as the first approximation of damage identification in the CFRP laminated beam. Even the network is developed through the iterative calculation, this network is fitted for the field measuring because the damage can be identified by the simpler operations of summations and multiplications.
Interaction between pulsed infrared laser and carbon fiber reinforced polymer composite laminates
NASA Astrophysics Data System (ADS)
Liu, Yan-Chi; Wu, Chen-Wu; Song, Hong-Wei; Huang, Chen-Guang
2016-10-01
The Laser drilling processes, in particular the interaction between the pulsed infrared Laser and the target materials were investigated on the CFRP composite laminate. The incremental freezing method was designed to reveal experimentally the temporal patterns of the ablation profiles in the CFRP composite laminates subjected to pulsed Laser irradiation. The temperature characteristics of the specimens were analyzed with Finite Element Method (FEM) and the phase change history studied. The theoretical results match well with the experimental outcome.
NASA Astrophysics Data System (ADS)
Liu, Yan-Chi; Wu, Chen-Wu; Huang, Yi-Hui; Song, Hong-Wei; Huang, Chen-Guang
2017-01-01
The interlaminar damages were investigated on the carbon fiber reinforced polymer (CFRP) composite laminate under laser irradiation. Firstly, the laminated T700/BA9916 composites were exposed to continuous wave laser irradiation. Then, the interface cracking patterns of such composite laminates were examined by optical microscopy and scanning electron microscopy. Finally, the Finite Element Analysis (FEA) was performed to compute the interface stress of the laminates under laser irradiation. And the effects of the laser parameters on the interlaminar damage were discussed.
Damage assessment in CFRP laminates exposed to impact fatigue loading
NASA Astrophysics Data System (ADS)
Tsigkourakos, George; Silberschmidt, Vadim V.; Ashcroft, I. A.
2011-07-01
Demand for advanced engineering composites in the aerospace industry is increasing continuously. Lately, carbon fibre reinforced polymers (CFRPs) became one of the most important structural materials in the industry due to a combination of characteristics such as: excellent stiffness, high strength-to-weight ratio, and ease of manufacture according to application. In service, aerospace composite components and structures are exposed to various transient loads, some of which can propagate in them as cyclic impacts. A typical example is an effect of the wind gusts during flight. This type of loading is known as impact fatigue (IF); it is a repetition of low-energy impacts. Such loads can cause various types of damage in composites: fibre breaking, transverse matrix cracking, de-bonding between fibres and matrix and delamination resulting in reduction of residual stiffness and loss of functionality. Furthermore, this damage is often sub-surface, which reinforces the need for more regular inspection. The effects of IF are of major importance due its detrimental effect on the structural integrity of components that can be generated after relatively few impacts at low force levels compared to those in a standard fatigue regime. This study utilises an innovative testing system with the capability of subjecting specimens to a series of repetitive impacts. The primary subject of this paper is to assess the damaging effect of IF on the behaviour of drilled CFRP specimens, exposed to such loading. A detailed damage analysis is implemented utilising an X-ray micro computed tomography system. The main findings suggested that at early stages of life damage is governed by o degree splits along the length of the specimens resulting in a 20% reduction of stiffness. The final failure damage scenario indicated that transverse crasks in the 90 degree plies are the main reason for complete delamination which can be translated to a 50% stiffness reduction.
Honeycomb-laminate composite structure
NASA Technical Reports Server (NTRS)
Gilwee, W. J., Jr.; Parker, J. A. (Inventor)
1977-01-01
A honeycomb-laminate composite structure was comprised of: (1) a cellular core of a polyquinoxaline foam in a honeycomb structure, and (2) a layer of a noncombustible fibrous material impregnated with a polyimide resin laminated on the cellular core. A process for producing the honeycomb-laminate composite structure and articles containing the honeycomb-laminate composite structure is described.
Development of active CFRP/metal laminates and their demonstrations in complicated forms
NASA Astrophysics Data System (ADS)
Asanuma, H.; Nakata, T.; Tanaka, T.; Imori, M.; Haga, O.
2006-03-01
This paper describes development of high performance CFRP/metal active laminates and demonstrations of them in complicated forms. Various types of the laminates were made by hot-pressing of an aluminum, aluminum alloys, a stainless steel and a titanium for the metal layer as a high CTE material, a unidirectional CFRP prepreg as a low CTE/electric resistance heating material, a unidirectional KFRP prepreg as a low CTE/insulating material. The aluminum and its alloy type laminates have almost the same and the highest room temperature curvatures and they linearly change with increasing temperature up to their fabrication temperature. The curvature of the stainless steel type jumps from one to another around its fabrication temperature, whereas the titanium type causes a double curvature and its change becomes complicated. The output force of the stainless steel type attains the highest of the three under the same thickness. The aluminum type successfully increased its output force by increasing its thickness and using its alloys. The electric resistance of the CFRP layer can be used to monitor the temperature, that is, the curvature of the active laminate because the curvature is a function of temperature. The aluminum type active laminate was made into complicated forms, that is, a hatch, a stack, a coil and a lift types, and their actuation performances were successfully demonstrated.
Post-Impact Fatigue Behavior of Woven and Knitted Fabric CFRP Laminates for Marine Use
NASA Astrophysics Data System (ADS)
Kimpara, Isao; Saito, Hiroshi
In this study, the damage evolution behavior was evaluated. Damage observation was conducted by the integration of non-destructive and direct observation methods. Target reinforcements were T300-3k plain woven fabric (PW) and T700S-12k multi-axial knitted fabric (MA). Impact damage distribution in the CFRP laminate was observed precisely, and three-dimensional damage model was constructed. Compression after impact (CAI) and post impact fatigue (PIF) performances were evaluated. The effect of water absorption on these performances was also evaluated. The effect of water absorption on CAI and PIF performances were small in PW CFRP laminates. Conversely, PIF properties of water-absorbed MA drastically decreased than that of dry ones. CAI strength was not affected by water absorption. PIF performance of dry MA CFRP was fairly higher than that of the others. From the precise observation, some evidences of interfacial deterioration caused by water absorption were confirmed in both PW and MA CFRP laminates.
Fatigue damage development of various CFRP-laminates
NASA Technical Reports Server (NTRS)
Schulte, K.; Baron, CH.
1988-01-01
The chronic strength and fatigue behavior of a woven carbon-fiber reinforced laminate in a balanced eight-shaft satin weave style was compared to nonwoven laminates with an equivalent cross-ply layup. Half the fibers were arranged in the direction of the load and the other half perpendicular to it. Two types of nonwoven laminates consisting of continuous fibers and aligned discontinuous fibers, both produced from carbon fiber prepregs, were studied. The cross-ply laminate with continuous fiber showed the best characteristics with regard to both static strength and fatigue. The similarities and differences in damage mechanisms in the laminates are described.
Fatigue damage development of various CFRP-laminates
NASA Technical Reports Server (NTRS)
Schulte, K.; Baron, CH.
1988-01-01
The chronic strength and fatigue behavior of a woven carbon-fiber reinforced laminate in a balanced eight-shaft satin weave style was compared to nonwoven laminates with an equivalent cross-ply layup. Half the fibers were arranged in the direction of the load and the other half perpendicular to it. Two types of nonwoven laminates consisting of continuous fibers and aligned discontinuous fibers, both produced from carbon fiber prepregs, were studied. The cross-ply laminate with continuous fiber showed the best characteristics with regard to both static strength and fatigue. The similarities and differences in damage mechanisms in the laminates are described.
NASA Astrophysics Data System (ADS)
Choi, Jung-Hun; Kang, Min-Sung; Koo, Jae-Mean; Seok, Chang-Sung; Kim, Hyung-Ick
The fatigue crack propagation of CFRP (carbon fiber reinforced composite material) laminates is of current interest, particularly with regard to their durability under fatigue loading. Recently, carbon fiber reinforced composite materials (Woven fabric) are widely used in various fields of engineering because of its advanced properties. Then, many researchers have studied woven fabric CFRP materials but fatigue crack propagation behaviors for composites have not been still standardized . It shows the different crack propagation behavior according to load and fiber direction. Therefore, there is a need to consider fatigue crack propagation behavior in conformity with fiber arraying direction to load direction at designing structure using woven CFRP materials. In this study, therefore, the fatigue crack propagation for plain woven CFRP composite materials was investigated under two different fiber array direction (fiber arraying direction to load : 0°, 45°). Fatigue crack propagation tests of the woven CFRP composite were conducted under sinusoidal wave-form with stress ratios of 0.3 at a frequency of 10Hz, respectively. As a result of test, fatigue crack propagation rates (da/dN) were plotted against the stress-intensity factor amplitude (ΔK) and other factor. Also we compared ΔK with other factor that considering in-plain anisotropy. All of tests of fatigue crack propagation were carried out under mode I opening loading by using compact tension specimens.
NASA Astrophysics Data System (ADS)
Woizeschke, P.; Vollertsen, F.
2015-09-01
The structural properties of lightweight constructions can be adapted to specific local requirements using multi-material designs. Aluminum alloys and carbon fiber-reinforced plastics (CFRP) are materials of great interest requiring suitable joining techniques in order to transfer the advantages of combining the materials to structural benefits. Thus, the research group "Schwarz-Silber" investigates novel concepts to enable frontal aluminum-CFRP joints using transition structures. In the foil concept titanium foils are used as transition elements. Specimens have been produced using three-layer titanium laminates. In tensile tests, three failure locations have been observed: (1) Al-Ti seam, (2) Ti-CFRP hybrid laminate, and (3) CFRP laminate. In this paper, the fracture mechanisms of these failure modes are investigated by analyzing metallographic micrographs and fracture surfaces as well as by correlating load-displacement curves to video imaging of tensile tests. The results show that the cracking of the CFRP layers can be traced back to an assembly error. The laminate character of the titanium part tends to reduce the Al-Ti seam strength. However, two sub-joint tests demonstrate that the Al-Ti seam can endure loads up to 9.5 kN. The ductile failure behavior of the Ti-CFRP hybrid laminates is caused by plastic deformations of the titanium laminate liners.
NDE and SHM Simulation for CFRP Composites
NASA Technical Reports Server (NTRS)
Leckey, Cara A. C.; Parker, F. Raymond
2014-01-01
Ultrasound-based nondestructive evaluation (NDE) is a common technique for damage detection in composite materials. There is a need for advanced NDE that goes beyond damage detection to damage quantification and characterization in order to enable data driven prognostics. The damage types that exist in carbon fiber-reinforced polymer (CFRP) composites include microcracking and delaminations, and can be initiated and grown via impact forces (due to ground vehicles, tool drops, bird strikes, etc), fatigue, and extreme environmental changes. X-ray microfocus computed tomography data, among other methods, have shown that these damage types often result in voids/discontinuities of a complex volumetric shape. The specific damage geometry and location within ply layers affect damage growth. Realistic threedimensional NDE and structural health monitoring (SHM) simulations can aid in the development and optimization of damage quantification and characterization techniques. This paper is an overview of ongoing work towards realistic NDE and SHM simulation tools for composites, and also discusses NASA's need for such simulation tools in aeronautics and spaceflight. The paper describes the development and implementation of a custom ultrasound simulation tool that is used to model ultrasonic wave interaction with realistic 3-dimensional damage in CFRP composites. The custom code uses elastodynamic finite integration technique and is parallelized to run efficiently on computing cluster or multicore machines.
NASA Astrophysics Data System (ADS)
Evci, C.; Uyandıran, I.
2017-02-01
Impact damage is one of the major concerns that should be taken into account with the new aircraft and spacecraft structures which employ ever-growing use of composite materials. Considering the thermal loads encountered at different altitudes, both low and high temperatures can affect the properties and impact behavior of composite materials. This study aims to investigate the effect of temperature and impactor diameter on the impact behavior and damage development in balanced and symmetrical CFRP laminates which were manufactured by employing vacuum bagging process with autoclave cure. Instrumented drop-weight impact testing system is used to perform the low velocity impact tests in a range of temperatures ranged from 60 down to -50 °C. Impact tests for each temperature level were conducted using three different hemispherical impactor diameters varying from 10 to 20 mm. Energy profile method is employed to determine the impact threshold energies for damage evolution. The level of impact damage is determined from the dent depth on the impacted face and delamination damage detected using ultrasonic C-Scan technique. Test results reveal that the threshold of penetration energy, main failure force and delamination area increase with impactor diameter at all temperature levels. No clear influence of temperature on the critical force thresholds could be derived. However, penetration threshold energy decreased as the temperature was lowered. Drop in the penetration threshold was more obvious with quite low temperatures. Delamination damage area increased while the temperature decreased from +60 °C to -50 °C.
Damage suppression system using embedded SMA (shape memory alloy) foils in CFRP laminate structures
NASA Astrophysics Data System (ADS)
Ogisu, Toshimichi; Shimanuki, Masakazu; Kiyoshima, Satoshi; Takaki, Junji; Takeda, Nobuo
2003-08-01
This paper presents an overview of the demonstrator program with respect to the damage growth suppression effects using embedded SMA foils in CFRP laminates. The damage growth suppression effects were demonstrated for the technical verification in order to apply to aircraft structure. In our previous studies, the authors already confirmed the damage growth suppression effects of CFRP laminates with embedded pre-strained SMA foils through both coupon and structural element tests. It was founded that these effects were obtained by the suppression of the strain energy release rate based on the suppression of the crack opening displacement due to the recovery stress of SMA foils through the detail observation of the damage behavior. In this study, these results were verified using the demonstrator test article, which was 1/3-scaled model of commercial airliner fuselage structure. For the demonstration of damage growth suppression effects, the evaluation area was located in the lower panel, which was dominated in tension load during demonstration. The evaluation area is the integrated stiffened panel including both "smart area" (CFRP laminate with embedded pre-strained SMA foils) and "conventional area" (standard CFRP laminate) for the direct comparison. The demonstration was conducted at 80 degree Celsius in smart area and room temperature (RT) in conventional area during quasi-static load-unload test method. As the test results, the demonstrator test article presented that the damage onset strain in the smart area was improved by 30% for compared with the conventional area. Therefore, the successful technical verification of the damage onset/growth suppression effect using the demonstrator presented the feasibility of the application of smart material and structural system to aircraft structures.
Effect of Circular Hole Notch Size on Strength Characteristics of CFRP/AL7075 Hybrid Composites
NASA Astrophysics Data System (ADS)
Yoon, Han Ki; Park, Joon Soo; Lee, Sang Pill; Park, Yi Hyun; Kong, Yu Sik; Park, Won Jo
As for the properties on both the aluminum and the CFRP which are used to make CFRP/AL7075 hybrid composites, CARALL (carbon reinforced aluminum laminate). In the CARALL specimen for rule of mixture, we were analyzed notched strength by finite element method. The results obtained from FEM notched strength analysis and experimental are as follows; In the unnotch CARALL specimen, the stresses imposed CFRP, epoxy, A17075 obtained by finite element method strength solution for A/C9991, when strain 0.48%, are 392 Mpa, 26 Mpa and 321 Mpa, respectively. The slope of the stress-strain curve by FEM increase in keeping with the hole size and the yield strain decrease to 36% and 55% for A/C9993 and A/C9991 respectively. And an agreement is found between the experimental results and the FEM analytical prediction results.
Some remarks on static, creep and fatigue flexural strength of satin woven CFRP laminates
Miyano, Y.; McMurry, M.K.; Muki, R.
1995-12-31
This paper deals with the time-temperature dependent flexural strength of a satin-woven CFRP laminate having a matrix resin with a high glass transition temperature of T{sub g} = 236/C under static, creep and fatigue loading by 3-point bending tests. Static tests were conducted at various points in a wide range of deflection rates and temperatures. The creep and fatigue tests were carried out at various constant temperatures; the fatigue test was conducted at two frequencies. The results of the experimental study are as follows. The flexural strength of the CFRP laminates for all three loading types is time-temperature dependent even near room temperature well below T{sub g}. The time and temperature superposition principle for the matrix resin also holds for the flexural strength of the CFRP laminates. The fracture modes are almost the same for the three loading types under all conditions tested. Finally, we propose a method for predicting the flexural fatigue strength for a given number of cycles to failure at an arbitrary temperature, frequency and stress ratio based on the current experimental findings and considering the relationships among the static, creep and fatigue flexural strengths.
Experimental Observation on Low Cycle Fatigue Behavior of Symmetric Angle-Ply CFRP Laminate
NASA Astrophysics Data System (ADS)
Sakai, Masahiro; Uda, Nobuhide; Kunoo, Kazuo
Cyclic zero-tension tests for symmetric angle-ply CFRP laminated specimens were carried out to investigate the low cycle fatigue behavior of graphite/epoxy and graphite/PEEK composites. Two types of stacking sequences were tested: [+θ/-θ]4s (Distributed ply) and [+θ4/-θ4]s (Blocked ply), where θ was 30º or 45º. Stress-strain curves of specimens under cyclic loadings were obtained by means of an extensometer. A mechanical ratcheting, which means progressive increase in plastic strain at each cycle, was observed on the cyclic stress-strain curves. Comparing the stress-strain curve of static tensile test with one of the cyclic zero-tension test, we made the assumption that the fatigue failure occurred when the ratcheting strain by cyclic loadings reached the static failure strain. Results of an ultrasonic scanning test revealed that the distributed ply specimens differed from the blocked ply specimens in an internal fatigue damage progress.
2011-08-12
ABSTRACT In this project a polymeric laminate composite was fabricated from a carbon fiber reinforced plastic ( CFRP ) plate and a polyvinylchloride...PVC). The PVC- CFRP laminate worked as a bimorph actuator. Bending behavior of the PVC- CFRP laminate was tested by fully submerging the laminate in a...water bath and also changing the environmental temperature. It is observed that the PVC- CFRP laminate has a number of advantages compared to other
Lightweight optical telescope structures fabricated from CFRP composites
NASA Astrophysics Data System (ADS)
Martin, Robert N.; Romeo, Robert C.
2007-09-01
CFRP (carbon fiber reinforced plastic) is an attractive material for fabrication of optical systems. The stiffness-to-weight ratio of CFRP is high, the coefficient of thermal expansion is low, the structure thermalizes rapidly, and many of the structural properties can be tailored to the application. We have used CFRP and CFRP-aluminum sandwich panels extensively in the structures of astronomical, optical telescopes up to 1.5m diameter aperture. In designing the optical structures, we have chosen some key fabrication techniques with CFRP that take advantage of the mechanical properties. This paper discusses the design and fabrication of 2 major telescope projects. The 1m ULTRA telescope has both the optics and the OTA fabricated from CFRP. This telescope has been recently installed at the SDSU Mt. Laguna Observatory near San Diego. A 1.4m telescope for the Naval Research Lab is being designed and fabricated at CMA. The optics, OTA, and the mount are all being fabricated using CFRP composites. The result is a lightweight structure which can be moved or deployed as necessary.
Characteristic evaluation of CFRP composites under falling weight impact loading
NASA Astrophysics Data System (ADS)
Im, K. H.; Park, N. S.; Hsu, D. K.; Kim, S. K.; Park, J. W.; Yang, I. Y.
2002-05-01
This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of carbon-fiber reinforced plastics (CFRP) laminate plates based on considerations of stress wave propagation theory, which were converted to measurements of load and displacement verses time. The delamination area of impacted specimens for the different ply orientations was measured with an ultrasonic C-scanner to determine the correlation between impact energy and delamination area. The energy absorbed by a quasi-isotropic specimen having four interfaces was higher than that of orthotropic laminates with two interfaces. The more interfaces, the greater the energy absorbed. The absorbed energy of a hybrid specimen containing a CFRP layer was higher than that of normal specimens. Also, a falling weight impact tester was built to evaluate the characteristics and impact strength of CFRPs.
a Region of Interest Computed Tomography Technique for Inspection of CFRP Laminates
NASA Astrophysics Data System (ADS)
Woods, S.; Amos, M.; Cooper, I.; Withers, P.
2011-06-01
Region of Interest (ROI) Computed Tomography (CT) is a radiographic inspection technique that inspects only part of a sample. However, ROI images normally suffer from reconstruction artefacts that can affect the inspection by obscuring defects. This paper describes the development of two data completion methods which minimise the reconstruction artefacts, allowing the technique to be applied without compromising defect detection. The techniques were developed for specific application to inspection of Carbon Fibre Reinforced Plastic (CFRP) laminate panels. The results presented include both fan-beam and cone-beam system geometries.
NASA Astrophysics Data System (ADS)
Khokhar, Zahid R.; Ashcroft, Ian A.; Silberschmidt, Vadim V.
2014-02-01
Laminated carbon fibre-reinforced polymer (CFRP) composites are already well established in structural applications where high specific strength and stiffness are required. Damage in these laminates is usually localised and may involve numerous mechanisms, such as matrix cracking, laminate delamination, fibre de-bonding or fibre breakage. Microstructures in CFRPs are non-uniform and irregular, resulting in an element of randomness in the localised damage. This may in turn affect the global properties and failure parameters of components made of CFRPs. This raises the question of whether the inherent stochasticity of localised damage is of significance in terms of the global properties and design methods for such materials. This paper presents a numerical modelling based analysis of the effect of material randomness on delamination damage in CFRP materials by the implementation of a stochastic cohesive-zone model (CZM) within the framework of the finite-element (FE) method. The initiation and propagation of delamination in a unidirectional CFRP double-cantilever beam (DCB) specimen loaded under mode-I was analyzed, accounting for the inherent microstructural stochasticity exhibited by such laminates via the stochastic CZM. Various statistical realizations for a half-scatter of 50 % of fracture energy were performed, with a probability distribution based on Weibull's two-parameter probability density function. The damaged area and the crack lengths in laminates were analyzed, and the results showed higher values of those parameters for random realizations compared to the uniform case for the same levels of applied displacement. This indicates that deterministic analysis of composites using average properties may be non-conservative and a method based on probability may be more appropriate.
Improvement of Mechanical and Thermal Properties of CFRP Laminates Using Micro-Fibrillated Cellulose
NASA Astrophysics Data System (ADS)
Kim, Hyojin; Suzuki, Tadashi; Takemura, Kenichi
The aim of this study is improvement of mechanical and thermal properties of plain woven carbon fiber (CF) reinforced epoxy with addition of MFC as the additive. Carbon fiber/epoxy laminates with addition 0.3, 0.5, 0.7 and 1wt% of MFC were characterized by flexural test, DSC and TMA. The result represented that the flexural strength improved slightly at 0.3 and 0.5 wt% of MFC, but flexural modulus was not changed, respectively. The glass transition temperature of MFC-CFRP laminates showed the increase according to increase of MFC addition at 0.7 and 1.0 wt%. The coefficient of thermal expansion was decrease by 0.7 wt% of MFC addition.
Study on three dimensional transient thermal stress analysis for laminated composite materials
Matsumoto, Kin`ya; Zako, Masaru
1995-11-01
Transient heat conduction and thermal stress analysis of laminated composite materials are very important because they are hated during manufacturing process. Anisotropy of thermal conductivity has to be considered for heat conduction analysis of composite materials such as FRP. Assuming that heat conducts uniformly in normal direction in thin structures, laminated plates can be modeled as single layers with the equivalent heat conductivities. With this assumption, FEM three dimensional transient heat conduction and thermal stress analysis programs for laminated composite materials are developed. As numerical examples, the heat conduction and thermal stresses of laminated CFRP structure are investigated.
Fabrication technique of SMA/CFRP smart composites
NASA Astrophysics Data System (ADS)
Xu, Ya; Otsuka, Kazuhiro; Toyama, Nobuyuki; Yoshida, Hitoshi; Nagai, Hideki; Oishi, Ryutaro; Kikushima, Yoshihiro; Yuse, Kaori; Akimune, Yoshio; Kishi, Teruo
2003-03-01
In recent years, pre-strained TiNi shape memory alloys (SMA) have been used for fabricating smart structure with carbon fibers reinforced plastics (CFRP). However, since the curing temperature of CFRP is higher than the reverse transformation temperatures of TiNi SMA, special fixture jigs have to be used for keeping the pre-strain during fabrication, which restricted its practical application. We have developed a new method to control the transformation temperatures of SMA by proper thermo-mechanical treatments and composition adjustment, which is suitable to fabricate SMA/CFRP smart composite with a curing temperature of 130C. Furthermore, we tried to develop a new fabrication technique which is also suitable to fabricate SMA/CFRP smart composite with a curing temperature of 180C. It was found that by using cold drawn ultra-thin TiNi wires, TiNi/CFRP composites with a curing temperature of 180C could be fabricated without special fixture jigs. The damage suppression effect by embedded ultra-thin wires in the smart composite was confirmed.
Comparative Study on Flexural Strengthening of RC Beams using CFRP Laminate by Different Techniques
NASA Astrophysics Data System (ADS)
Jeevan, N.; Jagannatha Reddy, H. N.
2017-08-01
This paper presents a detailed study on flexural behaviour of RC beams strengthened using Carbon Fiber Reinforced Polymer (CFRP) laminate. A detailed study was made on strengthened beam using Externally Bonded Laminate (EBL) and Internally Bonded Laminate (IBL) techniques. In IBL technique the laminate is sandwiched between the layers of epoxy mounted on the cover portion by the groove. The beams were designed as under-reinforced section. Totally six beams were casted, out of this two beams were control beams. Strengthened beams were divided into two sets (IBL and EBL) of two beams each. The main aim of this work is to delay the debonding failure in order to enhance the ultimate load carrying capacity for strengthened beams. Four-point bending flexural tests were conducted on specimens up to failure. The experimental results illustrate that, the strengthened beams significantly increases the cracking, working and ultimate load when compared with control beams. IBL technique shows the significant increase in the debonding strain by delaying the beam from debonding failure which in turn enhances the ultimate load by almost 73% compared with control beam and 39% with EBL technique. All the deflection values from the experiments are within the limit of codal provisions. The IBL technique was emerged as the better strengthening technique, which increases almost 41% of working load (Pw) compared with strengthening codes.
TEA CO2 laser machining of CFRP composite
NASA Astrophysics Data System (ADS)
Salama, A.; Li, L.; Mativenga, P.; Whitehead, D.
2016-05-01
Carbon fibre-reinforced polymer (CFRP) composites have found wide applications in the aerospace, marine, sports and automotive industries owing to their lightweight and acceptable mechanical properties compared to the commonly used metallic materials. Machining of CFRP composites using lasers can be challenging due to inhomogeneity in the material properties and structures, which can lead to thermal damages during laser processing. In the previous studies, Nd:YAG, diode-pumped solid-state, CO2 (continuous wave), disc and fibre lasers were used in cutting CFRP composites and the control of damages such as the size of heat-affected zones (HAZs) remains a challenge. In this paper, a short-pulsed (8 μs) transversely excited atmospheric pressure CO2 laser was used, for the first time, to machine CFRP composites. The laser has high peak powers (up to 250 kW) and excellent absorption by both the carbon fibre and the epoxy binder. Design of experiment and statistical modelling, based on response surface methodology, was used to understand the interactions between the process parameters such as laser fluence, repetition rate and cutting speed and their effects on the cut quality characteristics including size of HAZ, machining depth and material removal rate (MRR). Based on this study, process parameter optimization was carried out to minimize the HAZ and maximize the MRR. A discussion is given on the potential applications and comparisons to other lasers in machining CFRP.
NASA Astrophysics Data System (ADS)
Xu, Wei; Cao, Maosen; Li, Ximing; Radzieński, Maciej; Ostachowicz, Wiesław; Bai, Runbo
2017-10-01
Delamination monitoring in carbon fiber reinforced polymer (CFRP) laminated plates is crucial to ensure the integrity and safety of the structures that accommodate the plates. To identify delaminations in CFRP laminated plates, the two-dimensional (2D) curvature mode shape method is a prevailing method that features instant and simultaneous determination of the presence and location of the delamination. However, this method has two noticeable deficiencies in characterizing incipient small-sized delaminations, namely lack of damage sensitivity and inadequate noise robustness. To this end, this study proposes a new dynamics feature of the complex-wavelet 2D curvature mode shape to discriminate small-sized delaminations. This feature is delicately formulated based on the integration of the 2D curvature mode shape with the complex wavelet. The complex-wavelet 2D curvature mode shape is superior to the 2D curvature mode shape by virtue of its stronger damage sensitivity and noise robustness. These merits can be attributed to the adjustable localization and the multi-scale properties of the second-order Gabor wavelet, respectively. Proof of concept of the complex-wavelet 2D curvature mode shape is numerically undertaken in a finite-element laminated CFRP plate with a small-sized delamination, with emphasis on sensitivity to damage and robustness against noise. The applicability of the feature is experimentally validated on a CFRP laminated plate with a small-sized delamination, whose mode shapes are acquired via the non-contact measurement using a scanning laser vibrometer. The numerical and experimental results show that the complex-wavelet 2D curvature mode shape can effectively designate the presence and location of the delaminations in CFRP laminated plates under noisy conditions.
A Model for Piezoresistance Behavior in a CFRP Cross-Ply Laminate with Transverse Cracking
NASA Astrophysics Data System (ADS)
Ogi, Keiji
An electromechanical model is proposed for predicting the resistance change in CFRP cross-ply laminates with transverse cracking loaded in tension. A one-dimensional equivalent circuit model was established for describing the relation between the resistance change and mechanical strain at a given transverse crack density. A shear lag model was employed for obtaining the mechanical strain distribution. The relative resistance change-strain curve was measured for various transverse crack density and the slope and secant of the curve were defined as the gage factor and residual resistance change, respectively. Unknown functions in the model were determined using the measured residual resistance changes. The model can predict the bilinear behavior in the relative resistance change-strain curves during loading/unloading. It is found that the second residual resistance change can be the parameter for predicting transverse crack density because it increases monotonically with transverse crack density compared with the gage factors.
A General Study of Hybrid Composite Laminates.
1977-12-01
appeared to have little effect on the overall properties of a laminate. Hybrid composite laminates obey classical laminate theory and can, in certain ply configurations, develop considerable free edge effect stresses. (Author)
An experimental study of permeability within an out-of-autoclave vacuum-bag-only CFRP laminate
NASA Astrophysics Data System (ADS)
Wallace, Landon F.
The out-of-autoclave vacuum-bag-only (OOA-VBO) manufacturing process is a process that eliminates an autoclave when manufacturing aerospace quality carbon fiber reinforced plastics (CFRP). OOA-VBO pre-impregnated resin tow systems rely on air channel networks that guide unwanted voids out of the laminate. The air path networks can be characterized by measuring the permeability of a pre-cured laminate. Permeability results were successfully obtained for a laminate with a compaction similar to that found in a typical vacuum bagging setup. A study was done to find the relationship between compaction of the laminate and permeability. Permeability was measured as the laminate cured, using a constant temperature ramp rate. An experimental nodal analysis was performed to find the permeability at the midpoint of the in-plane direction.
NASA Astrophysics Data System (ADS)
Melnykowycz, Mark M.; Belloli, Alberto; Ermanni, Paolo; Barbezat, Michel
2006-03-01
In the current study Active Fiber Composites (AFC) utilizing Lead-Zirconate-Titanate (PZT) fibers with Kapton (R) screen printed interdigitated electrodes (IDE) were integrated into carbon fiber reinforced plastic (CFRP) laminates to investigate integration issues associated with smart structures and host laminate integrity. To aid in this goal surrogate or "dummy" AFC (DAFC) using a composite core and Kapton (R) outer layers (to match the longitudinal mechanical and interface properties of the AFC) were employed. These DAFC were used in place of real AFC to expedite test specimen manufacture and evaluation. This allowed efficient investigation of the impact of an integrated AFC-like inclusion on laminate mechanical integrity. Laminates with integrated AFC were additionally tested with signal monitoring to assess AFC health during the test. Investigation into laminate failure was accomplished via a finite element model of the system which was created in ANSYS to investigate failure in the composite plies. Tsai-Wu failure criterion was calculated to investigate laminate failure characteristics. Integration of AFC into CFRP laminates degraded laminate strength by 13.3% using insertion integration and 7.8% using the interlacing integration technique. The finite element model showed that interlacing integration enabled distribution of critical forces over the entire laminate while insertion integration led to critical forces concentrating over the integration region.
Wang, Zhi-Yu; Wang, Qing-Yuan; Liu, Yong-Jie
2015-08-19
Corrugated steel web with inherent high out-of-plane stiffness has a promising application in configuring large span highway bridge girders. Due to the irregularity of the configuration details, the local stress concentration poses a major fatigue problem for the welded flange plates of high strength low alloy structural steels. In this work, the methods of applying CFRP laminate and shot peening onto the surfaces of the tension flanges were employed with the purpose of improving the fatigue strength of such configuration details. The effectiveness of this method in the improvement of fatigue strength has been examined experimentally. Test results show that the shot peening significantly increases hardness and roughness in contrast to these without treatment. Also, it has beneficial effects on the fatigue strength enhancement when compared against the test data of the joints with CFRP strengthening. The stiffness degradation during the loading progress is compared with each treatment. Incorporating the stress acting on the constituent parts of the CFRP laminates, a discussion is made regarding the mechanism of the retrofit and related influencing factors such as corrosion and economic cost. This work could enhance the understanding of the CFRP and shot peening in repairing such welded details and shed light on the reinforcement design of welded joints between corrugated steel webs and flange plates.
Wang, Zhi-Yu; Wang, Qing-Yuan; Liu, Yong-Jie
2015-01-01
Corrugated steel web with inherent high out-of-plane stiffness has a promising application in configuring large span highway bridge girders. Due to the irregularity of the configuration details, the local stress concentration poses a major fatigue problem for the welded flange plates of high strength low alloy structural steels. In this work, the methods of applying CFRP laminate and shot peening onto the surfaces of the tension flanges were employed with the purpose of improving the fatigue strength of such configuration details. The effectiveness of this method in the improvement of fatigue strength has been examined experimentally. Test results show that the shot peening significantly increases hardness and roughness in contrast to these without treatment. Also, it has beneficial effects on the fatigue strength enhancement when compared against the test data of the joints with CFRP strengthening. The stiffness degradation during the loading progress is compared with each treatment. Incorporating the stress acting on the constituent parts of the CFRP laminates, a discussion is made regarding the mechanism of the retrofit and related influencing factors such as corrosion and economic cost. This work could enhance the understanding of the CFRP and shot peening in repairing such welded details and shed light on the reinforcement design of welded joints between corrugated steel webs and flange plates. PMID:28793509
Miyano, Yasushi; Daichou, Noboru; Nakada, Masayuki; Mohri, Michihiro
1996-12-31
The flexural fatigue behavior of two kinds of unidirectional pitch-based CFRP laminates, which have different types of matrix resin, were evaluated at several levels of frequency and temperature. The fatigue behavior of both CFRPs was found to be remarkably dependent on time and temperature. The time-temperature superposition principle for the viscoelastic behavior of the matrix resin holds for the fatigue strength as well as the static strength of the CFRPs. The master curves of fatigue strength for the CFRPs can be divided into three distinct groups of curves, each corresponding to a different mode of fracture. The time and temperature dependence of the fatigue behavior of the CFRP laminates is not only controlled by the viscoelastic behavior of the matrix resin, even though the static behavior is dominated by the viscoelastic behavior of matrix resin.
Numerical and experimental assessments of nonlinear bearing strength properties of CFRP laminates
Kisielewicz, L.T.; Ando, K.; Kenmochi, K.
1994-12-31
Pin connectors are commonly used in a variety of applications using a variety of materials and have attracted a great number of researches both in technological and analytical fields. While for metallic materials both the rheological and structural phenomena of such connectors are well understood and allow to proceed to design and optimization based on analytical methods, the situation is not the same for new materials such as CFRP or other composites. The paper approaches the assessment of bearing strength of such connectors both from the experimental and numerical standpoints and show the capability of the latter to predict this structural strength.
Bond Strength of Composite CFRP Reinforcing Bars in Timber.
Corradi, Marco; Righetti, Luca; Borri, Antonio
2015-07-03
The use of near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars is an interesting method for increasing the shear and flexural strength of existing timber members. This article examines the behaviour of carbon FRP (CFRP) bars in timber under direct pull-out conditions. The objective of this experimental program is to investigate the bond strength between composite bars and timber: bars were epoxied into small notches made into chestnut and fir wood members using a commercially-available epoxy system. Bonded lengths varied from 150 to 300 mm. Failure modes, stress and strain distributions and the bond strength of CFRP bars have been evaluated and discussed. The pull-out capacity in NSM CFRP bars at the onset of debonding increased with bonded length up to a length of 250 mm. While CFRP bar's pull-out was achieved only for specimens with bonded lengths of 150 and 200 mm, bar tensile failure was mainly recorded for bonded lengths of 250 and 300 mm.
Bond Strength of Composite CFRP Reinforcing Bars in Timber
Corradi, Marco; Righetti, Luca; Borri, Antonio
2015-01-01
The use of near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars is an interesting method for increasing the shear and flexural strength of existing timber members. This article examines the behaviour of carbon FRP (CFRP) bars in timber under direct pull-out conditions. The objective of this experimental program is to investigate the bond strength between composite bars and timber: bars were epoxied into small notches made into chestnut and fir wood members using a commercially-available epoxy system. Bonded lengths varied from 150 to 300 mm. Failure modes, stress and strain distributions and the bond strength of CFRP bars have been evaluated and discussed. The pull-out capacity in NSM CFRP bars at the onset of debonding increased with bonded length up to a length of 250 mm. While CFRP bar’s pull-out was achieved only for specimens with bonded lengths of 150 and 200 mm, bar tensile failure was mainly recorded for bonded lengths of 250 and 300 mm. PMID:28793423
The performance of integrated active fiber composites in carbon fiber laminates
NASA Astrophysics Data System (ADS)
Melnykowycz, M.; Brunner, A. J.
2011-07-01
Piezoelectric elements integrated into fiber-reinforced polymer-matrix laminates can provide various functions in the resulting adaptive or smart composite. Active fiber composites (AFC) composed of lead zirconate titanate (PZT) fibers can be used as a component in a smart material system, and can be easily integrated into woven composites. However, the impact of integration on the device and its functionality has not been fully investigated. The current work focuses on the integration and performance of AFC integrated into carbon-fiber-reinforced plastic (CFRP) laminates, focusing on the strain sensor performance of the AFC-CFRP laminate under tensile loading conditions. AFC were integrated into cross-ply CFRP laminates using simple insertion and interlacing of the CFRP plies, with the AFC always placed in the 90° ply cutout area. Test specimens were strained to different strain levels and then cycled with a 0.01% strain amplitude, and the resulting signal from the AFC was monitored. Acoustic emission monitoring was performed during tensile testing to provide insight to the failure characteristics of the PZT fibers. The results were compared to those from past studies on AFC integration; the strain signal of AFC integrated into CFRP was much lower than that for AFC integrated into woven glass fiber laminates. However, the profiles of the degradations of the AFC signal resulting from the strain were nearly identical, showing that the PZT fibers fragmented in a similar manner for a given global strain. The sensor performance recovered upon unloading, which is attributed to the closure of cracks between PZT fiber fragments.
Surface treatment of CFRP composites using femtosecond laser radiation
NASA Astrophysics Data System (ADS)
Oliveira, V.; Sharma, S. P.; de Moura, M. F. S. F.; Moreira, R. D. F.; Vilar, R.
2017-07-01
In the present work, we investigate the surface treatment of carbon fiber-reinforced polymer (CFRP) composites by laser ablation with femtosecond laser radiation. For this purpose, unidirectional carbon fiber-reinforced epoxy matrix composites were treated with femtosecond laser pulses of 1024 nm wavelength and 550 fs duration. Laser tracks were inscribed on the material surface using pulse energies and scanning speeds in the range 0.1-0.5 mJ and 0.1-5 mm/s, respectively. The morphology of the laser treated surfaces was investigated by field emission scanning electron microscopy. We show that, by using the appropriate processing parameters, a selective removal of the epoxy resin can be achieved, leaving the carbon fibers exposed. In addition, sub-micron laser induced periodic surface structures (LIPSS) are created on the carbon fibers surface, which may be potentially beneficial for the improvement of the fiber to matrix adhesion in adhesive bonds between CFRP parts.
NASA Astrophysics Data System (ADS)
Arca, M. A.; Coker, D.
2014-06-01
High mechanical properties and light weight structures of composite materials and advances in manufacturing processes have increased the use of composite materials in the aerospace and wind energy industries as a primary load carrying structures in complex shapes. However, use of composite materials in complex geometries such as L-shaped laminates creates weakness at the radius which causes delamination. Carbon nanotubes (CNTs) is preferred as a toughening materials in composite matrices due to their high mechanical properties and aspect ratios. However, effect of CNTs on curved beam strength (CBS) is not investigated in literature comprehensively. The objective of this study is to investigate the effect of CNT on Mode I and Mode II fracture toughness and CBS. L-shaped beams are fabric carbon/epoxy composite laminates manufactured by hand layup technique. Curved beam composite laminates were subjected to four point bending loading according to ASTM D6415/D6415M-06a. Double cantilever beam (DCB) tests and end notch flexure (ENF) tests were conducted to determine mode-I and mode-II fracture toughness, respectively. Preliminary results show that 3% CNT addition to the resin increased the mode-I fracture toughness by %25 and mode-II fracture toughness by %10 compared to base laminates. In contrast, no effect on curved beam strength was found.
Effect of a Thin Soft Core on the Impact Behaviour of CFRP Laminates
NASA Astrophysics Data System (ADS)
Caprino, Giancarlo; Lopresto, Valentina; Riccio, Massimo; Leone, Claudio
2012-04-01
Low-velocity impact tests were carried out on sandwich plates having CFRP facings and thin rubbery core. Two types of cores, differing in the material nature and thickness, were used. For comparison, similar tests were performed on the monolithic laminate. Various impact parameters, among which indentation, first failure energy, perforation energy, absorbed energy and maximum contact force, were analyzed, to highlight the effect of the core on the material response. The influence of the core on the macroscopic behaviour of the panels was quite limited, except in the elastic phase, where the lower stiffness of the sandwich configurations resulted in a higher energy at first failure. More relevant differences were found from the study of failure modes, carried out combining ultrasonic C-scan and a limited number of microscopic observations. In particular, in correspondence of the energy for barely visible impact damage, besides considerable facing-core debonding, both the facings of the sandwich structures exhibited fibre breakage at their back side.
Mechanical Characterization of CFRP Woven Laminates between Room Temperature and 4K
NASA Astrophysics Data System (ADS)
Kumagai, Susumu; Shindo, Yasuhide; Horiguchi, Katsumi; Takeda, Tomo
In order to evaluate the mechanical properties of T800H/3633 CFRP woven laminates for cryogenic tankage in RLV, tensile and in-plane shear tests were performed at room temperature, liquid nitrogen temperature (77K) and liquid helium temperature (4K). The tensile tests were conducted in accordance with ASTM D 3039 and JIS K 7073. Tensile strength and modulus were evaluated for both the warp and fill directions. A problem was encountered with obtaining acceptable failure of the specimens. We could not achieve failure in the test section. This problem was avoided by using dogbone shaped specimens. A two-dimensional finite element analysis was also used to study the stress distributions within the specimens and to interpret the experimental measurements. The in-plane shear modulus and shear strength were measured by tensile tests on the ±45° specimens (ASTM D 3518 and JIS K 7079). The effects of temperature on the stress-strain responses in tension and in-plane shear are examined. Fracture topography of specimens is also investigated and interpreted.
Rotary ultrasonic machining of CFRP composites: a study on power consumption.
Cong, W L; Pei, Z J; Deines, T W; Srivastava, Anil; Riley, L; Treadwell, C
2012-12-01
Carbon fiber reinforced plastic (CFRP) composites are very difficult to machine. A large number of holes need to be drilled in CFRP for many applications. Therefore, it is important to develop cost-effective drilling processes. CFRP has been drilled by rotary ultrasonic machining (RUM) successfully. The literature has reports about the effects of input variables on output variables (including cutting force, torque, surface roughness, tool wear, and workpiece delamination) in RUM of CFRP. However, there are no reports on power consumption in RUM of CFRP. This paper reports the first study on power consumption in RUM of CFRP. It reports an experimental investigation on effects of input variables (ultrasonic power, tool rotation speed, feedrate, and type of CFRP) on power consumption of each component (including ultrasonic power supply, spindle motor, coolant pump, and air compressor) and the entire RUM system. Copyright © 2012 Elsevier B.V. All rights reserved.
CFRP composite thin-shelled mirrors for future space telescopes
NASA Astrophysics Data System (ADS)
Romeo, Robert C.; Chen, Peter C.
2002-12-01
The need for extremely large aperture telescopes drives the requirement for new materials and novel approaches to mirror production. Many lightweight mirror concepts are currently being persued, some with promise for extending their ability to facilitate 100-meter and larger space telescope primaries. These concepts include some rather unorthodox materials in unique configurations. Past experience in producing extremely thin CFRP composite mirrors, using unidirectional CFRP prepreg tape, has led us to a more novel CFPR material, which could further reduce the mass and cost of their predecessors. We present a carbon-based, ultra-lightweight fleece material, which have been shown to exhibit high specularity and extremely low areal density, 200 grams/m2, at 2-plies, in contrast to more typical unidirectional CFPR material.
Basic mechanics of laminated composite plates
NASA Technical Reports Server (NTRS)
Nettles, Alan T.
1994-01-01
The mechanics of laminated composite materials is presented in a clear manner with only essential derivations included. The constitutive equations in all of their forms are developed and then summarized in a separate section. The effects of hygrothermal effects are included. The prediction of the engineering constants for a laminate are derived. Strength of laminated composites is not covered.
NASA Astrophysics Data System (ADS)
Wu, Qi; Yu, Fengming; Okabe, Yoji; Kobayashi, Satoshi
2015-01-01
In this research, we applied a novel optical fiber sensor, phase-shifted fiber Bragg grating balanced sensor with high sensitivity and broad bandwidth, to acoustic emission (AE) detection in carbon fiber reinforced plastics (CFRPs). AE signals generated in the tensile testing of angle-ply and cross-ply CFRP laminates were both detected by the novel optical fiber sensor and traditional PZT sensors. The cumulative hits detected by both sensors coincided after applying simple data processing to eliminate the noise, and clearly exhibited Kaiser effect and Felicity effect. Typical AE signals detected by both sensors were discussed and were tried to relate to micro CFRP damages observed via microscope. These results demonstrate that this novel optical fiber sensor can reliably detect AE signals from various damages. It has the potential to be used in practical AE detection, as an alternative to the piezoelectric PZT sensor.
Thermal-Mechanical Response of Cracked Satin Weave CFRP Composites at Cryogenic Temperatures
NASA Astrophysics Data System (ADS)
Watanabe, S.; Shindo, Y.; Narita, F.; Takeda, T.
2008-03-01
This paper examines the thermal-mechanical response of satin weave carbon fiber reinforced polymer (CFRP) laminates with internal and/or edge cracks subjected to uniaxial tension load at cryogenic temperatures. Cracks are considered to occur in the transverse fiber bundles and extend through the entire thickness of the fiber bundles. Two-dimentional generalized plane strain finite element models are developed to study the effects of residual thermal stresses and cracks on the mechanical behavior of CFRP woven laminates. A detailed examination of the Young's modulus and stress distributions near the crack tip is carried out which provides insight into material behavior at cryogenic temperatures.
THERMAL-MECHANICAL RESPONSE OF CRACKED SATIN WEAVE CFRP COMPOSITES AT CRYOGENIC TEMPERATURES
Watanabe, S.; Shindo, Y.; Narita, F.; Takeda, T.
2008-03-03
This paper examines the thermal-mechanical response of satin weave carbon fiber reinforced polymer (CFRP) laminates with internal and/or edge cracks subjected to uniaxial tension load at cryogenic temperatures. Cracks are considered to occur in the transverse fiber bundles and extend through the entire thickness of the fiber bundles. Two-dimentional generalized plane strain finite element models are developed to study the effects of residual thermal stresses and cracks on the mechanical behavior of CFRP woven laminates. A detailed examination of the Young's modulus and stress distributions near the crack tip is carried out which provides insight into material behavior at cryogenic temperatures.
Guided Wave Propagation Study on Laminated Composites by Frequency-Wavenumber Technique
NASA Technical Reports Server (NTRS)
Tian, Zhenhua; Yu, Lingyu; Leckey, Cara A. C.
2014-01-01
Toward the goal of delamination detection and quantification in laminated composites, this paper examines guided wave propagation and wave interaction with delamination damage in laminated carbon fiber reinforced polymer (CFRP) composites using frequency-wavenumber (f-kappa) analysis. Three-dimensional elastodynamic finite integration technique (EFIT) is used to acquire simulated time-space wavefields for a CFRP composite. The time-space wavefields show trapped waves in the delamination region. To unveil the wave propagation physics, the time-space wavefields are further analyzed by using two-dimensional (2D) Fourier transforms (FT). In the analysis results, new f-k components are observed when the incident guided waves interact with the delamination damage. These new f-kappa components in the simulations are experimentally verified through data obtained from scanning laser Doppler vibrometer (SLDV) tests. By filtering the new f-kappa components, delamination damage is detected and quantified.
Impact Damage Detection of Toughened CFRP Laminates with Time Domain Reflectometry
2013-01-30
matching with the coaxial cable is cumbersome for actual CFRP structures. CFRP Copper mesh 0 GFRP Directional Coupler Waveform Generator Microstrip ...manufactured by Mini- Circuits (N.Y., USA). The input pulse was 5 Vp-p (peak-to-peak voltage) and the half-band width was 4 ns. 4. Results and discussion
Spatial Evolution of the Thickness Variations over a CFRP Laminated Structure
NASA Astrophysics Data System (ADS)
Davila, Yves; Crouzeix, Laurent; Douchin, Bernard; Collombet, Francis; Grunevald, Yves-Henri
2017-01-01
Ply thickness is one of the main drivers of the structural performance of a composite part. For stress analysis calculations (e.g., finite element analysis), composite plies are commonly considered to have a constant thickness compared to the reality (coefficients of variation up to 9% of the mean ply thickness). Unless this variability is taken into account reliable property predictions cannot be made. A modelling approach of such variations is proposed using parameters obtained from a 16-ply quasi-isotropic CFRP plate cured in an autoclave. A discrete Fourier transform algorithm is used to analyse the frequency response of the observed ply and plate thickness profiles. The model inputs, obtained by a mathematical representation of the ply thickness profiles, permit the generation of a representative stratification considering the spatial continuity of the thickness variations that are in good agreement with the real ply profiles spread over the composite part. A residual deformation FE model of the composite plate is used to illustrate the feasibility of the approach.
Symmetries in laminated composite plates
NASA Technical Reports Server (NTRS)
Noor, A. K.
1976-01-01
The different types of symmetry exhibited by laminated anisotropic fibrous composite plates are identified and contrasted with the symmetries of isotropic and homogeneous orthotropic plates. The effects of variations in the fiber orientation and the stacking sequence of the layers on the symmetries exhibited by composite plates are discussed. Both the linear and geometrically nonlinear responses of the plates are considered. A simple procedure is presented for exploiting the symmetries in the finite element analysis. Examples are given of square, skew and polygonal plates where use of symmetry concepts can significantly reduce the scope and cost of analysis.
Damage of hybrid composite laminates
NASA Astrophysics Data System (ADS)
Haery, Haleh A.; Kim, Ho Sung
2013-08-01
Hybrid laminates consisting of woven glass fabric/epoxy composite plies and woven carbon fabric/epoxy composite plies are studied for fatigue damage and residual strength. A theoretical framework based on the systems approach is proposed as a guide to deal with the complexity involving uncertainties and a large number of variables in the hybrid composite system. A relative damage sensitivity factor expression was developed for quantitative comparisons between non-hybrid and hybrid composites. Hypotheses derived from the theoretical framework were tested and verified. The first hypothesis was that the difference between two different sets of properties produces shear stress in interface between carbon fibre reinforced plastics (CRP) and glass fibre reinforced plastics (GRP), and eventually become a source for CRP/GRP interfacial delamination or longitudinal cracking. The second hypothesis was that inter-fibre bundle delamination occurs more severely to CRP sub-system than GRP sub-system.
Piezoceramics/CFRP composites for active vibration control and shape control of aerospace structures
NASA Astrophysics Data System (ADS)
Herold-Schmidt, Ursula; Schaefer, Wolfgang; Zaglauer, Helmut W.
1996-04-01
The application of piezoceramics/CFRP composites for active control of aerospace structures was investigated in a laboratory scale. Exemplary results are presented for active vibration damping of CFRP plates with integrated PZT sensors and actuators as well as for shape control of an antenna reflector shell using piezoelements.
Machining of fiber-reinforced composite laminates
NASA Astrophysics Data System (ADS)
Won, Myong-Shik
As fiber-reinforced composite laminates are becoming considerably popular in a wide range of applications, the necessity for machining such materials is increasing rapidly. Due to their microscopical inhomogeneity, anisotropy, and highly abrasive nature, composite laminates exhibit some peculiar types of machining damage. Consequently, the machining of composite laminates requires a different approach from that used for metals and offers a challenge from both an academic and application point of view. In the present work, the drilling of composite laminated plates and the edge trimming of tubular composite laminates were investigated through theoretical analyses and their experimental verification. First, a drilling process model using linear elastic fracture mechanics and classical plate bending theory was developed to predict the critical thrust value responsible for the onset of delamination during the drilling of composite laminates with pre-drilled pilot holes. Experiments using stepped drills, which can utilize the effectiveness of such pilot holes, were conducted on composite laminates. Reasonably good agreement was found between the results of the process model and the tests. Second, the development of a model-based intelligent control strategy for the efficient drilling of composite laminates was explored by experiments and analyses. In this investigation, mathematical models were created to relate the drilling forces to cutting parameters and to identify the different process stages. These models predicted the degree of thrust force regulation to prevent delamination. Third, the edge trimming of thin-walled tubular composite laminates was modeled and analyzed for estimating the critical cutting force at the initiation of longitudinal cracking. A series of full-scale edge trimming tests were conducted on tubular composite specimens to assess the current approach and to obtain basic machining data for various composite laminates. The present study provides
Comparison of experimental and analytical results for free vibration of laminated composite plates
Maryuama, Koichi; Narita, Yoshihiro; Ichinomiya, Osamu
1995-11-01
Fibrous composite materials are being increasingly employed in high performance structures, including pressured vessel and piping applications. These materials are usually used in the form of laminated flat or curved plates, and the understanding of natural frequencies and the corresponding mode shapes is essential to a reliable structural design. Although many references have been published on analytical study of laminated composite plates, a limited number of experimental studies have appeared for dealing with vibration characteristics of the plates. This paper presents both experimental and analytical results for the problems. In the experiment, the holographic interferometry is used to measure the resonant frequencies and corresponding mode shapes of six-layered CFRP (carbon fiber reinforced plastic) composite plates. The material constants of a lamina are calculated from fiber and matrix material constants by using some different composite rules. With the calculated constants, the natural frequencies of the laminated CFRP plates are theoretically determined by the Ritz method. From the comparison of two sets of the results, the effect of choosing different composite rules is discussed in the vibration study of laminated composite plates.
On impact damage detection and quantification for CFRP laminates using structural response data only
NASA Astrophysics Data System (ADS)
Sultan, M. T. H.; Worden, K.; Pierce, S. G.; Hickey, D.; Staszewski, W. J.; Dulieu-Barton, J. M.; Hodzic, A.
2011-11-01
The overall purpose of the research is to detect and attempt to quantify impact damage in structures made from composite materials. A study that uses simplified coupon specimens made from a Carbon Fibre-Reinforced Polymer (CFRP) prepreg with 11, 12 and 13 plies is presented. PZT sensors were placed at three separate locations in each test specimen to record the responses from impact events. To perform damaging impact tests, an instrumented drop-test machine was used and the impact energy was set to cover a range of 0.37-41.72 J. The response signals captured from each sensor were recorded by a data acquisition system for subsequent evaluation. The impacted specimens were examined with an X-ray technique to determine the extent of the damaged areas and it was found that the apparent damaged area grew monotonically with impact energy. A number of simple univariate and multivariate features were extracted from the sensor signals recorded during impact by computing their spectra and calculating frequency centroids. The concept of discordancy from the statistical discipline of outlier analysis is employed in order to separate the responses from non-damaging and damaging impacts. The results show that the potential damage indices introduced here provide a means of identifying damaging impacts from the response data alone.
NASA Astrophysics Data System (ADS)
WenQin, Han; Ying, Luo; AiJun, Gu; Yuan, Fuh-Gwo
2016-04-01
Discrimination of acoustic emission (AE) signals related to different damage modes is of great importance in carbon fiber-reinforced plastic (CFRP) composite materials. To gain a deeper understanding of the initiation, growth and evolution of the different types of damage, four types of specimens for different lay-ups and orientations and three types of specimens for interlaminar toughness tests are subjected to tensile test along with acoustic emission monitoring. AE signals have been collected and post-processed, the statistical results show that the peak frequency of AE signal can distinguish various damage modes effectively. After a AE signal were decomposed by Empirical Mode Decomposition (EMD) method, it may separate and extract all damage modes included in this AE signal apart from damage mode corresponding to the peak frequency. Hilbert-Huang Transform (HHT) of AE signals can clearly illustrate the frequency distribution of Intrinsic Mode Functions (IMF) components in time-scale in different damage stages, and can calculate accurate instantaneous frequency for damage modes recognition to help understanding the damage process.
Indentation law for composite laminates
NASA Technical Reports Server (NTRS)
Yang, S. H.
1981-01-01
Static indentation tests are described for glass/epoxy and graphite/epoxy composite laminates with steel balls as the indentor. Beam specimens clamped at various spans were used for the tests. Loading, unloading, and reloading data were obtained and fitted into power laws. Results show that: (1) contact behavior is not appreciably affected by the span; (2) loading and reloading curves seem to follow the 1.5 power law; and (3) unloading curves are described quite well by a 2.5 power law. In addition, values were determined for the critical indentation, alpha sub cr which can be used to predict permanent indentations in unloading. Since alpha sub cr only depends on composite material properties, only the loading and an unloading curve are needed to establish the complete loading-unloading-reloading behavior.
Detection of delamination in composite laminates using small-diameter FBG sensors
NASA Astrophysics Data System (ADS)
Takeda, Shin-ichi; Okabe, Yoji; Takeda, Nobuo
2002-07-01
This paper presents delamination monitoring techniques in composite laminates using small-diameter fiber Bragg grating (FBG) sensors that was developed for embedding in the laminates without inducing any structural defects. First, this FBG sensor was embedded in carbon fiber reinforced plastic (CFRP) cross-ply laminates. The reflection spectra from the FBG sensor were measured at various delamination sizes through a static four-point bending test. From experimental results, the spectrum was found to have two peaks due to the initiation of the delamination. The intensity ratio of these two peaks changed as the delamination size increased. In order to confirm the deformation of the measured spectra, the spectra were calculated theoretically. The calculated result reproduced the change in the measured spectrum very well. Thus, we proposed the intensity ratio of the two peaks as an effective indicator for evaluation of the delamination size. Secondly, detection of the edge delamination in quasi-isotropic CFRP laminates was conducted using the FBG sensor. The reflection spectra were measured at various delamination sizes through fatigue test. The form of the spectrum changed sensitively by growth of the edge delamination. Hence the small-diameter FBG sensor could also be applied to detect the edge delamination in quasi-isotropic composite laminates under cyclic loading.
Effects of Temperature on Mode II Fracture Toughness of Multidirectional CFRP Laminates
NASA Astrophysics Data System (ADS)
Kim, Hyoung Soo; Wang, Wen Xue; Takao, Yoshihiro; Ben, Goichi
End notched flexure (ENF) tests were performed to investigate the effects of temperature and fiber orientation on Mode II interlaminar fracture behavior, GIIC (GII at the crack initiation), of carbon fiber-reinforced epoxy composites, T800H/#3631. The values of GIIC for three kinds of laminates, [012//012], [22.5/-22.5/08/-22.5/22.5//-22.5/22.5/08/22.5/-22.5] and [45/-45/08/-45/45//-45/45/08/45/-45], with a pre-cracked interface, that is // in each laminate, were obtained at three temperatures, i.e. -100°C, 25°C and 150°C. It is shown that GIIC is obviously affected by the temperature and fiber orientation. The scanning electron microscope (SEM) observation was also carried out to investigate the fracture surface. SEM analysis suggested that the decreased Mode II interlaminar fracture toughness for all kinds of specimens at high temperature could be attributed to temperature-induced matrix property change or fiber-matrix interfacial weakening.
Low-cycle and high-cycle fatigue failure process characterization of CFRP cross-ply laminates
Takeda, N.; Ogihara, S.; Kobayashi, A.
1994-12-31
Damage progress in toughened-type CFRP cross-ply laminates under tensile fatigue loading was measured by the replica technique. The damage parameters, the transverse crack density and the delamination ratio, were presented. Based on above data, simple shear-lag analysis combined with the modified Paris law model was conducted to model the damage progress. In addition, a novel power-law model was proposed, which related the cyclic strain range and the number of cycles. The loading-unloading tests were also performed to obtain the Young`s modulus reduction and the permanent strain as functions of the damage state. The shear-lag predictions of the Young`s modulus reduction and the permanent strain showed good agreement with the experimental data, when the interaction between transverse cracking and delamination were taken into account.
Poly-m-aramid nanofiber mats: Production for application as structural modifiers in CFRP laminates
NASA Astrophysics Data System (ADS)
Mazzocchetti, Laura; D'Angelo, Emanuele; Benelli, Tiziana; Belcari, Juri; Brugo, Tommaso Maria; Zucchelli, Andrea; Giorgini, Loris
2016-05-01
Poly(m-phenylene isophtalamide) electrospun nanofibrous membranes were produced to be used as structural reinforcements for carbon fiber reinforced composites production. In order for the polymer to be electrospun, it needs however to be fully solubilized, so the addition of some salts is required to help disrupt the tight macromolecular packing based on intra- and inter-molecular hydrogen bonding. Such salts may also contribute to the electrospinnability of the overall solution, since the provide it with a higher conductivity, whatever the solvent might be. The salt haobwever stays in the final nanofibrous mat. The membranes containing the salt are also observed to be highly hygroscopic, with a water content up to 26%, in the presence of 20%wt LiCl in the nanofibrous mat. When those membranes were interleaved among prepregs to produce a laminates, the obtained composite displayed thermal properties comparable to those of a reference nanofiber-free composite, though the former showed also easier delamination. Hence the removal of the hygroscopic salt was performed, that lead to thinner membranes, whose water content matched that of the pristine polymer. The washing step induced a thinning of the layers and of the fibers diameters, though no fiber shrinking nor membrane macroscopic damages were observed. These preliminary encouraging results thus pave the way to a deeper study of the optimized condition for producing convenient poly(m-phenylene isophtalamide) electrospun nanofibrous membranes to be used for carbon fiber reinforced composites structural modification.
Nonlinear finite element analysis of mechanical characteristics on CFRP composite pressure vessels
NASA Astrophysics Data System (ADS)
Liu, Dong-xia; Liang, Li; Li, Ming
2010-06-01
CFRP(Carbon Fibre Reinforced Plastic) composite pressure vessel was calculated using finite element program of ANSYS for their mechanical characteristics in this paper. The elastic-plastic model and elements of Solid95 were selected for aluminium alloys of gas cylinder. Also liner-elastic model and layer elements of Shell99 were adopted for carbon fibre/epoxy resin. The stress state of CFRP composite pressure vessel was calculated under different internal pressures include pre-stressing pressures, working pressures, test hydraulic pressures, minimum destructive pressures etcetera to determine the size of gas cylinder and layer parameter of carbon fibre. The mechanical characteristics CFRP composite vessel could were using to design and test of gas cylinder. Numerical results showed that finite element model and calculating method were efficient for study of CFRP gas cylinder and useful for engineering design.
Strain measurements inside thick CFRP laminates at the vicinity of bolted joints
NASA Astrophysics Data System (ADS)
Menendez, Jose M.; Guemes, J. Alfredo
1999-05-01
Intracore fiber Bragg gratings have been extensively used as longitudinal strain sensors both bonded and embedded in numerous applications, fulfilling the same task as conventional resistive strain gages. Comparative results obtained in composite laminates with both types of sensors show an excellent correlation in those places where the strain distributions are smooth. In this case, optical sensors offer additional advantages: unnecessary calibration, multiplexing capability, small size, embedding ability, etc. But optical sensors reveal all their potential in those locations where the anisotropy of the composite structural element promotes strong strain distributions, and complex stress fields. In these cases, the analysis of the distorted spectrum of a grating submitted to an intense strain gradient offers a big amount of information, even without using spectrum integration methods. Furthermore, the knowledge of the optical behavior of fiber Bragg gratings submitted to transverse loads allows having additional information about the residual stress field promoted during the manufacturing process, and the stress release due to the machining of the part. This paper demonstrates theoretically and experimentally that fiber Bragg gratings can be valuable tools not only to monitor complete composite structures in service, but to analyze the stress and strain state of those particular configurations in which any kind of information, due to their complexity and high requirements, is essential.
Simulation of Lightning-Induced Delamination in Un-protected CFRP Laminates
NASA Astrophysics Data System (ADS)
Naghipour, P.; Pineda, E. J.; Arnold, S. M.
2016-08-01
Lightning is a major cause of damage in laminated composite aerospace structures during flight. The most significant failure mode induced by lightning is delamination, which might extend well beyond the visible damage zone, and requires sophisticated techniques and equipment to detect. Therefore, it is crucial to develop a numerical tool capable of predicting the damage zone induced from a lightning strike to minimize costly repair acreage and supplement extremely expensive lightning experiments. Herein, a detailed numerical study consisting of a multidirectional composite with user-defined, temperature-dependent, interlaminar elements subjected to a lightning strike is designed, and delamination/damage expansion is studied under specified conditions. It is observed both the size and shape of the delamination zone are strongly dependent on the assumed temperature-dependent fracture toughness; the primary parameter controlling lightning-induced delamination propagation. An accurate estimation of the fracture toughness profile is crucial in order to have a reliable prediction of the delamination zone and avoid sub-critical structural failures.
Shear response and design of RC beams strengthened using CFRP laminates
NASA Astrophysics Data System (ADS)
Singh, Shamsher B.
2013-12-01
The present investigation addresses the shear strengthening of deficient reinforced concrete (RC) beams using carbon fiber-reinforced polymer (CFRP) sheets. The effect of the pattern and orientation of the strengthening fabric on the shear capacity of the strengthened beams were examined. Three beams with various lay-ups of strengthening fabric, 45°, 0°/90°, and 0°/90°/45° were examined, in addition to an unstrengthened control beam. Principal and shear strains were measured at different locations at the critical sections of the strengthened beams corresponding to each applied shear force. Experimental results showing the advantage of beam strengthened using the various lay-ups of CFRP sheets are discussed. It is concluded that Beam-45°, Beam-0°/90°, and Beam-0°/90°/45° show about 25%, 19%, and 40% increases in shear-load carrying capacity in comparison to the control beam, respectively. Also, there exists a critical value of shear force up to which there is no appreciable shear strain in the CFRP sheets/beam. This shear force marks the ultimate shear resistance of the control beam. However, the strengthened beams exhibited significant strength and stiffness even beyond the critical value of the shear force. A design example for shear strengthening shows that the design equations available in the literature underestimate the actual shear strength of the beams.
Fatigue crack growth in aluminum laminate composites
Hoffman, P.B.; Carpenter, R.D.; Gibeling, J.C.
1996-12-31
Fatigue crack growth has been measured in a laminated metal composite (LMC) consisting of alternating layers of AA6090/SiC/25p metal matrix composite (MMC) and AA5182 alloy. This material was tested in both as-pressed (F temper) and aged (T6 temper) conditions. Corresponding crack growth measurements were made in self-laminates of both the MMC and AA5182 materials to examine the role of the interfaces.
Direct Composite Laminate Veneers: Three Case Reports
Korkut, Bora; Yanıkoğlu, Funda; Günday, Mahir
2013-01-01
Re-establishing a patient’s lost dental esthetic appearance is one of the most important topics for contemporary dentistry. New treatment materials and methods have been coming on the scene, day by day, in order to achieve such an aim. Most dentists prefer more conservative and aesthetic approaches, such as direct and indirect laminate veneer restorations, instead of full-ceramic crowns for anteriors where aesthetics is really important. Laminate veneers are restorations which are envisioned to correct existing abnormalities, esthetic deficiencies and discolo-rations. Laminate veneer restorations may be processed in two different ways: direct or indirect. Direct laminate veneers have no need to be prepared in the laboratory and are based on the principle of application of a composite material directly to the prepared tooth surface in the dental clinic. Indirect laminate veneers may be produced from composite materials or ceramics, which are cemented to the tooth with an adhesive resin. In this case report, direct composite laminate veneer technique used for three patients with esthetic problems related to fractures, discolorations and an old prolapsed restoration, is described and six-month follow-ups are discussed. As a conclusion, direct laminate veneer restorations may be a treatment option for patients with the esthetic problems of anterior teeth in cases similar to those reported here. PMID:23875090
Method for fabricating laminated uranium composites
Chapman, L.R.
1983-08-03
The present invention is directed to a process for fabricating laminated composites of uranium or uranium alloys and at least one other metal or alloy. The laminated composites are fabricated by forming a casting of the molten uranium with the other metal or alloy which is selectively positioned in the casting and then hot-rolling the casting into a laminated plate in or around which the casting components are metallurgically bonded to one another to form the composite. The process of the present invention provides strong metallurgical bonds between the laminate components primarily since the bond disrupting surface oxides on the uranium or uranium alloy float to the surface of the casting to effectively remove the oxides from the bonding surfaces of the components.
Thermal buckling of symmetrically laminated composite plates
NASA Technical Reports Server (NTRS)
Meyers, C. A.; Hyer, M. W.
1991-01-01
This paper discusses an investigation into the thermal buckling of symmetrically laminated composite plates. In this study thermal buckling is investigated for laminates under two different simple support conditions, fixed and sliding. These laminates are subjected to the conditions of a uniform temperature change, and a temperature change varying linearly along the length of the plate. The effects of the principal material axes not being aligned with the edges of the plate are also investigated. The buckling response is studied using variational methods, specifically the Trefftz criterion. A Rayleigh-Ritz formulation is used to obtain numerical results from the formulations for the prebuckling response and the buckling response.
Thermal buckling of laminated composite shells
Thangaratnam, R.K.; Palaninathan, R.; Ramachandran, J. )
1990-05-01
The linear buckling analysis of laminated composite cylindrical and conical shells under thermal load using the finite element method is reported here. Critical temperatures are presented for various cases of cross-ply and angly-ply laminated shells. The effects of radius/thickness ratio, number of layers, ratio of coefficients of thermal expansion, and the angle of fiber orientation have been studied. The results indicate that the buckling behavior of laminated shell under thermal load is different from that of mechanically loaded shell with respect to the angle of fiber orientation. 6 refs.
Flexural Upgrading of Steel-Concrete Composite Girders Using Externally Bonded CFRP Reinforcement
NASA Astrophysics Data System (ADS)
Kabir, Mohammad Z.; Eshaghian, M.
2010-04-01
This study focuses on the flexural performance of composite steel-concrete beam girders retrofitted with CFRP. The current work is a numerical study of the load carrying capacity of a section which is strengthened by externally bonding of CFRP to the tension flange. At the primarily stage of the work, the model is verified by published experimental data. The three dimensional interactive failure Tsai-Wu criteria was implemented to retrofitted composite girder in order to identify the failure mode. Then a detailed parametric study is carried out to investigate the effects of geometry parameters and material characteristics on flexural performance of a composite section.
Experimental approach on the collapse mechanism of CFRP composite tubes
NASA Astrophysics Data System (ADS)
Kim, Y. N.; Im, K. H.; Park, J. W.; Yang, I. Y.
2001-04-01
This study is to investigate the energy absorption characteristics of CFRP(Carbon-Fiber Reinforced Plastics) tubes on static and dynamic tests. Axial static compression tests have been carried out using the static testing machine(Shin-gang buckling testing machine) and dynamic compression tests have been utilized using an vertical crushing testing machine. When such tubes are subjected to crushing loads, the response is complex and depends on the interaction between the different mechanisms that could control the crushing process. The collapse characteristics and energy absorption have been examined for various tubes. Energy absorption of the tubes are increased as changes in the lay-up which may increase the modulus of tubes. The results have been varied significantly as a function of ply orientation and interlaminar number. In general, the stacking sequence [0/90] CFRP tubes absorbed more energy than the [15/-15] CFRP tubes.
NASA Astrophysics Data System (ADS)
Jang, Byung-Koog; Xu, Ya; Oishi, Ryutaro; Nagai, Hideki; Yoshida, Hitoshi; Akimune, Yoshio; Otsuka, Kazuhiro; Kishi, Teruo
2002-07-01
The focus of this work is the thermomechanical characterization and effect of damage recovery on the pre-strained SMA wire embedded CFRP composites for developing the smart composites with self-damage control. The SMA utilized in this work is a Ni-45at percent Ti wire with a diameter of 0.4 mm. A steel mold was specially designed to embed the pre-strained TiNi wire into CFRP preperg and prevent their recovery during the cure cycle. TiNi/CFRP composites were fabricated by hot-pressing in the temperature range of 150-180 degrees C by controlling the applied pressure. The overall research is divided into four parts: fabrication of SMA wire embedded CFRP composites, experimental characterization of thermomechanical behavior on SMA wire by electrical heating, recovery effect of self-damage control in composites and sensing effect by detecting the electrical resistance at SMA wire. Compressive recovery force induced by thermomechanical actuation of SMA depends on pre-strained level and volume fraction of TiNi. The hot-pressed TiNi/CFRP specimens were loaded under tensile test in order to induce a transverse crack or partial damage. Specially, transverse crack easily happen at 90 degrees stacking CFRP layers. The damage degree due to generation of transverse cracks is quantified by real-time measurements of electrical resistance of SMA in composites during tensile load. After electrical heating, the generated transverse cracks at composites successfully repaired due to compressive force introduced by pre-strained TiNi wires and resulting in the self-damage recovery effect.
Free edge effects in laminated composites
NASA Technical Reports Server (NTRS)
Herakovich, C. T.
1989-01-01
The fundamental mechanics of free-edge effects in laminated fiber-reinforced composites is examined, reviewing the results of recent experimental and analytical investigations. The derivation of the governing equations for the basic problem is outlined, including the equilibrium and mismatch conditions and the elasticity formulation, and experimental data on axial displacement and shear strain in angle-ply laminates are summarized. Numerical predictions of free-edge deformation and interlaminar and through-thickness stress distributions are presented for cross-ply, angle-ply, and quasi-isotropic laminates, and the mechanisms of edge damage and failure in angle-ply laminates are briefly characterized. Extensive diagrams, drawings, graphs, and photographs are provided.
Composite Laminate With Coefficient of Thermal Expansion Matching D263 Glass
NASA Technical Reports Server (NTRS)
Robinson, David; Rodini, Benjamin
2012-01-01
The International X-ray Observatory project seeks to make an X-ray telescope assembly with 14,000 flexible glass segments. The glass used is commercially available SCHOTT D263 glass. Thermal expansion causes the mirror to distort out of alignment. A housing material is needed that has a matching coefficient of thermal expansion (CTE) so that when temperatures change in the X-ray mirror assembly, the glass and housing pieces expand equally, thus reducing or eliminating distortion. Desirable characteristics of this material include a high stiffness/weight ratio, and low density. Some metal alloys show promise in matching the CTE of D263 glass, but their density is high compared to aluminum, and their stiffness/weight ratio is not favorable. A laminate made from carbon fiber reinforced plastic (CFRP) should provide more favorable characteristics, but there has not been any made with the CTE matching D263 Glass. It is common to create CFRP laminates of various CTEs by stacking layers of prepreg material at various angles. However, the CTE of D263 glass is 6.3 ppm/ C at 20 C, which is quite high, and actually unachievable solely with carbon fiber and resin. A composite laminate has been developed that has a coefficient of thermal expansion identical to that of SCHOTT D263 glass. The laminate is made of a combination of T300 carbon fiber, Eglass, and RS3C resin. The laminate has 50% uni-T300 plies and 50% uni-E-glass plies, with each fiber-layer type laid up in a quasi-isotropic laminate for a total of 16 plies. The fiber volume (percent of fiber compared to the resin) controls the CTE to a great extent. Tests have confirmed that a fiber volume around 48% gives a CTE of 6.3 ppm/ C. This is a fairly simple composite laminate, following well established industry procedures. The unique feature of this laminate is a somewhat unusual combination of carbon fiber with E-glass (fiberglass). The advantage is that the resulting CTE comes out to 6.3 ppm/ C at 20 C, which matches D
Detection of CFRP Composite Manufacturing Defects Using a Guided Wave Approach
NASA Technical Reports Server (NTRS)
Hudson, Tyler B.; Hou, Tan-Hung; Grimsley, Brian W.; Yuan, Fuh-Gwo
2015-01-01
NASA Langley Research Center is investigating a guided-wave based defect detection technique for as-fabricated carbon fiber reinforced polymer (CFRP) composites. This technique will be extended to perform in-process cure monitoring, defect detection and size determination, and ultimately a closed-loop process control to maximize composite part quality and consistency. The overall objective of this work is to determine the capability and limitations of the proposed defect detection technique, as well as the number and types of sensors needed to identify the size, type, and location of the predominant types of manufacturing defects associated with laminate layup and cure. This includes, porosity, gaps, overlaps, through-the-thickness fiber waviness, and in-plane fiber waviness. The present study focuses on detection of the porosity formed from variations in the matrix curing process, and on local overlaps intentionally introduced during layup of the prepreg. By terminating the cycle prematurely, three 24-ply unidirectional composite panels were manufactured such that each subsequent panel had a higher final degree of cure, and lower level of porosity. It was demonstrated that the group velocity, normal to the fiber direction, of a guided wave mode increased by 5.52 percent from the first panel to the second panel and 1.26 percent from the second panel to the third panel. Therefore, group velocity was utilized as a metric for degree of cure and porosity measurements. A fully non-contact guided wave hybrid system composed of an air-coupled transducer and a laser Doppler vibrometer (LDV) was used for the detection and size determination of an overlap By transforming the plate response from the time-space domain to the frequency-wavenumber domain, the total wavefield was then separated into the incident and backscatter waves. The overlap region was accurately imaged by using a zero-lag cross-correlation (ZLCC) imaging condition, implying the incident and backscattered
Finite element analysis when orthogonal cutting of hybrid composite CFRP/Ti
NASA Astrophysics Data System (ADS)
Xu, Jinyang; El Mansori, Mohamed
2015-07-01
Hybrid composite, especially CFRP/Ti stack, is usually considered as an innovative structural configuration for manufacturing the key load-bearing components in modern aerospace industry. This paper originally proposed an FE model to simulate the total chip formation process dominated the hybrid cutting operation. The hybrid composite model was established based on three physical constituents, i.e., Ti constituent, interface and CFRP constituent. Different constitutive models and damage criteria were introduced to replicate the interrelated cutting behaviour of the stack material. The CFRP/Ti interface was modelled as a third phase through the concept of cohesive zone (CZ). Particular attention was made on the comparative studies of the influence of different cutting-sequence strategies on the machining responses induced in hybrid stack cutting. The numerical results emphasized the pivotal role of cutting-sequence strategy on the various machining induced responses including cutting-force generation, machined surface quality and induced interface damage.
NASA Astrophysics Data System (ADS)
Yamaguchi, Keisuke; Ueda, Takao; Nanasawa, Akira
As a new rehabilitation technique for recovery both of loading ability and durability of concrete structures deteriorated by chloride attack, desalination (electrochemical chloride removal technique from concrete) using CFRP composite electrode bonding to concrete has been developed. In this study, basic application was tried using small RC specimens, and also application to the large-scale RC beams deteriorated by the chloride attack through the long-term exposure in the outdoors was investigated. As the result of bending test of treated specimens, the decrease of strengthening effect with the electrochemical treatment was observed in the case of small specimens using low absorption rate resin for bonding, on the other hand, in the case of large-scale RC beam using 20% absorption rate resin for bonding CFRP composite electrode, enough strengthening effect was obtained by the bending failure of RC beam with the fracture of CFRP board.
NASA Astrophysics Data System (ADS)
Atobe, Satoshi; Nonami, Shunsuke; Hu, Ning; Fukunaga, Hisao
2017-09-01
Foreign object impact events are serious threats to composite laminates because impact damage leads to significant degradation of the mechanical properties of the structure. Identification of the location and force history of the impact that was applied to the structure can provide useful information for assessing the structural integrity. This study proposes a method for identifying impact forces acting on CFRP (carbon fiber reinforced plastic) laminated plates on the basis of the sound radiated from the impacted structure. Identification of the impact location and force history is performed using the sound pressure measured with microphones. To devise a method for identifying the impact location from the difference in the arrival times of the sound wave detected with the microphones, the propagation path of the sound wave from the impacted point to the sensor is examined. For the identification of the force history, an experimentally constructed transfer matrix is employed to relate the force history to the corresponding sound pressure. To verify the validity of the proposed method, impact tests are conducted by using a CFRP cross-ply laminate as the specimen, and an impulse hammer as the impactor. The experimental results confirm the validity of the present method for identifying the impact location from the arrival time of the sound wave detected with the microphones. Moreover, the results of force history identification show the feasibility of identifying the force history accurately from the measured sound pressure using the experimental transfer matrix.
Guided Wave and Damage Detection in Composite Laminates Using Different Fiber Optic Sensors
Li, Fucai; Murayama, Hideaki; Kageyama, Kazuro; Shirai, Takehiro
2009-01-01
Guided wave detection using different fiber optic sensors and their applications in damage detection for composite laminates were systematically investigated and compared in this paper. Two types of fiber optic sensors, namely fiber Bragg gratings (FBG) and Doppler effect-based fiber optic (FOD) sensors, were addressed and guided wave detection systems were constructed for both types. Guided waves generated by a piezoelectric transducer were propagated through a quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate and acquired by these fiber optic sensors. Characteristics of these fiber optic sensors in ultrasonic guided wave detection were systematically compared. Results demonstrated that both the FBG and FOD sensors can be applied in guided wave and damage detection for the CFRP laminates. The signal-to-noise ratio (SNR) of guided wave signal captured by an FOD sensor is relatively high in comparison with that of the FBG sensor because of their different physical principles in ultrasonic detection. Further, the FOD sensor is sensitive to the damage-induced fundamental shear horizontal (SH0) guided wave that, however, cannot be detected by using the FBG sensor, because the FOD sensor is omnidirectional in ultrasound detection and, in contrast, the FBG sensor is severely direction dependent. PMID:22412347
Guided wave and damage detection in composite laminates using different fiber optic sensors.
Li, Fucai; Murayama, Hideaki; Kageyama, Kazuro; Shirai, Takehiro
2009-01-01
Guided wave detection using different fiber optic sensors and their applications in damage detection for composite laminates were systematically investigated and compared in this paper. Two types of fiber optic sensors, namely fiber Bragg gratings (FBG) and Doppler effect-based fiber optic (FOD) sensors, were addressed and guided wave detection systems were constructed for both types. Guided waves generated by a piezoelectric transducer were propagated through a quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate and acquired by these fiber optic sensors. Characteristics of these fiber optic sensors in ultrasonic guided wave detection were systematically compared. Results demonstrated that both the FBG and FOD sensors can be applied in guided wave and damage detection for the CFRP laminates. The signal-to-noise ratio (SNR) of guided wave signal captured by an FOD sensor is relatively high in comparison with that of the FBG sensor because of their different physical principles in ultrasonic detection. Further, the FOD sensor is sensitive to the damage-induced fundamental shear horizontal (SH(0)) guided wave that, however, cannot be detected by using the FBG sensor, because the FOD sensor is omnidirectional in ultrasound detection and, in contrast, the FBG sensor is severely direction dependent.
Experimental micromechanical approach to failure process in CFRP cross-ply laminates
Takeda, N.; Ogihara, S.; Kobayashi, A.
1994-12-31
The microscopic failure process of three different types of cross-ply laminates, (0/90{sub n}/0) (n = 4, 8, 12), was investigated at R.T. and 80 C. Progressive damage parameters, the transverse crack density and the delamination ratio, were measured. A simple modified shear-lag analysis including the thermal residual strains was conducted to predict the transverse crack density as a function of laminate strain, considering the constraint effect, as well as the strength distribution of the transverse layer. The analysis was also extended to the system containing delamination to predict the delamination length. A prediction was also presented for the transverse crack density including the effect of the delamination growth. The prediction showed good agreement with the experimental results.
Finite element analysis of shear deformable laminated composite plates
Kam, T.Y.; Chang, R.R. )
1993-03-01
A shear deformable finite element is developed for the analysis of thick laminated composite plates. The finite element formulation is based on Mindlin's plate theory in which shear correction factors are derived from the exact expressions for orthotropic materials. The element is used to solve a variety of problems on deflection, stress distribution, natural frequency and buckling of laminated composite plates. The effects of material properties, plate aspect ratio, length-to-thickness ratio, number of layers and lamination angle on the mechanical behaviors of laminated composite plates are investigated. Optimal lamination arrangements of layers for laminated composite plates of particular applications are determined.
Lamination residual stresses in fiber composites
NASA Technical Reports Server (NTRS)
Daniel, I. M.; Liber, T.
1975-01-01
An experimental investigation was conducted to determine the magnitude of lamination residual stresses in angle-ply composites and to evaluate their effects on composite structural integrity. The materials investigated were boron/epoxy, boron/polyimide, graphite/low modulus epoxy, graphite/high modulus epoxy, graphite/polyimide and s-glass/epoxy. These materials were fully characterized. Static properties of laminates were also determined. Experimental techniques using embedded strain gages were developed and used to measure residual strains during curing. The extent of relaxation of lamination residual stresses was investigated. It was concluded that the degree of such relaxation is low. The behavior of angle-ply laminates subjected to thermal cycling, tensile load cycling, and combined thermal cycling with tensile load was investigated. In most cases these cycling programs did not have any measurable influence on residual strength and stiffness of the laminates. In the tensile load cycling tests, the graphite/polyimide shows the highest endurance with 10 million cycle runouts at loads up to 90 percent of the static strength.
Fracture modes in notched angleplied composite laminates
NASA Technical Reports Server (NTRS)
Irvine, T. B.; Ginty, C. A.
1984-01-01
The Composite Durability Structural Analysis (CODSTRAN) computer code is used to determine composite fracture. Fracture modes in solid and notched, unidirectional and angleplied graphite/epoxy composites were determined by using CODSTRAN. Experimental verification included both nondestructive (ultrasonic C-Scanning) and destructive (scanning electron microscopy) techniques. The fracture modes were found to be a function of ply orientations and whether the composite is notched or unnotched. Delaminations caused by stress concentrations around notch tips were also determined. Results indicate that the composite mechanics, structural analysis, laminate analysis, and fracture criteria modules embedded in CODSTRAN are valid for determining composite fracture modes.
Impact performance of two bamboo-based laminated composites
Huanrong Liu; Zehui Jiang; Zhengjun Sun; Yan Yan; Zhiyong Cai; Xiubiao Zhang
2017-01-01
The present work aims to determine the impact performance of two bamboo-based laminated composites [bamboo/poplar laminated composite (BPLC) and bamboo/ glass fiber laminated composite (BGFLC)] using lowvelocity impact tests by a drop tower. In addition, fracture characteristics were evaluated using computed tomography (CT). Results showed that BPLC presented better...
Thermal postbuckling behavior of laminated composite plates
Singh, G.; Rao, G.V.; Lyengar, N.G.R. )
1994-06-01
Thermal buckling and postbuckling behavior of shear deformable laminated composite plates is investigated by employing a four-node rectangular C(sup 1) continuous finite element. The investigation reveals that the postbuckling path may not remain stable throughout. It is shown that secondary instabilities coupled with changes in the spatial deformation do take place from the postbuckling path. 15 refs.
Thermal buckling of laminated composite plates
Chen, L.W.; Chen, L.Y.
1987-01-01
Thermal buckling of laminated composite plates subjected to a temperature change is studied. The displacement equations of equilibrium are used and Galerkin's method is employed to determine the critical buckling temperature. Clamped and simply supported boundary conditions are both considered. The effects of various parameters on the thermal buckling are examined. 18 references.
Reliability analysis of continuous fiber composite laminates
NASA Technical Reports Server (NTRS)
Thomas, David J.; Wetherhold, Robert C.
1991-01-01
This paper describes two methods, the maximum distortion energy (MDE) and the principle of independent action (PIA), developed for the analysis of the reliability of a single continuous composite lamina. It is shown that, for the typical laminated plate structure, the individual lamina reliabilities can be combined in order to produce the upper and the lower bounds of reliability for the laminate, similar in nature to the bounds on properties produced from variational elastic methods. These limits were derived for both the interactive and the model failure considerations. Analytical expressions were also derived for the sensitivity of the reliability limits with respect to changes in the Weibull parameters and in loading conditions.
Preliminary evaluation of hybrid titanium composite laminates
NASA Technical Reports Server (NTRS)
Miller, J. L.; Progar, D. J.; Johnson, W. S.; St.clair, T. L.
1994-01-01
In this study, the mechanical response of hybrid titanium composite laminates (HTCL) was evaluated at room and elevated temperatures. Also, the use of an elastic-plastic laminate analysis program for predicting the tensile response from constituent properties was verified. The improvement in mechanical properties achieved by the laminates was assessed by comparing the results of static strength and constant amplitude fatigue tests to those for monolithic titanium sheet. Two HTCL were fabricated with different fiber volume fractions, resin layer thicknesses, and resins. One panel was thicker and was more poorly bonded in comparison to other. Consequently, the former had a lower tensile strength, while fewer cracks grew in this panel and at a slower rate. Both panels showed an improvement in fatigue life of almost two orders of magnitude. The model predictions were also in good agreement with the experimental results for both HTCL panels.
Micro-Cracking Detection in Laminated Composites
NASA Technical Reports Server (NTRS)
Chu, Tsuchin; Leyte, Alma; DiGregorio, Anthony; Russell, Samuel S.; Walker, James L.; Thom, Robert (Technical Monitor)
2002-01-01
Porosity and fatigue cracking are two critical factors that affect the performance and safety of cryogenic fuel tanks and feedlines made from unlined laminated or weaved carbon/epoxy materials. This paper presents the experiments to induce fatigue cracking of laminated composites through thermal cycling as well as the feasibility of using Thermography and Ultrasound Spectroscopy technology (UT) to detect and measure such micro-cracking. Carbon/epoxy laminated composite panels were built and cut into strips. These specimens were partially submerged in liquid nitrogen while subjected to various loads on a test machine. Edges of some specimens were polished and etched to determine the degree of micro-cracking. The rest of specimens were then examined with Thermography and Ultrasound Spectroscopy NDE systems to investigate the feasibility of finding such micro-cracking in the laminated composites. Thermography is utilized to determine changes in thermal diffusivity. The degree of cracking may reduce the apparent thermal diffusivity and therefore change the thermal response on the surface. Thermography testing was conducted on a group of specimens where it is desired to have some correlation between the predetermined stress and the thermography data. Ultrasound Spectroscopy was used to determine peak changes between the pre-stressed and stressed samples. Data from the inspections were analyzed and the results are presented in this paper.
Digital holographic nondestructive testing of laminate composite
NASA Astrophysics Data System (ADS)
Karray, Mayssa; Christophe, Poilane; Gargouri, Mohamed; Picart, Pascal
2016-09-01
Optical digital holographic techniques can be used for nondestructive testing of materials. Digital holographic nondestructive testing essentially measures deformations on the surface of the object. However, there is sufficient sensitivity to detect subsurface and internal defects in metallic and composite specimens. We investigate and discuss the vibration analysis of laminated composite glass-epoxy using time averaging in digital Fresnel holography to visualize the modes of vibration and to test the integrity of the structures of studied materials.
Yelve, Nitesh P; Mitra, Mira; Mujumdar, P M; Ramadas, C
2016-08-01
A new hybrid method based upon nonlinear Lamb wave response in time and frequency domains is introduced to locate a delamination in composite laminates. In Lamb wave based nonlinear method, the presence of damage is shown by the appearance of higher harmonics in the Lamb wave response. The proposed method not only uses this spectral information but also the corresponding temporal response data, for locating the delamination. Thus, the method is termed as a hybrid method. The paper includes formulation of the method and its application to locate a Barely Visible Impact Damage (BVID) induced delamination in a Carbon Fiber Reinforced Polymer (CFRP) laminate. The method gives the damage location fairly well. It is a baseline free method, as it does not need data from the pristine specimen.
Modeling Composite Laminate Crushing for Crash Analysis
NASA Technical Reports Server (NTRS)
Fleming, David C.; Jones, Lisa (Technical Monitor)
2002-01-01
Crash modeling of composite structures remains limited in application and has not been effectively demonstrated as a predictive tool. While the global response of composite structures may be well modeled, when composite structures act as energy-absorbing members through direct laminate crushing the modeling accuracy is greatly reduced. The most efficient composite energy absorbing structures, in terms of energy absorbed per unit mass, are those that absorb energy through a complex progressive crushing response in which fiber and matrix fractures on a small scale dominate the behavior. Such failure modes simultaneously include delamination of plies, failure of the matrix to produce fiber bundles, and subsequent failure of fiber bundles either in bending or in shear. In addition, the response may include the significant action of friction, both internally (between delaminated plies or fiber bundles) or externally (between the laminate and the crushing surface). A figure shows the crushing damage observed in a fiberglass composite tube specimen, illustrating the complexity of the response. To achieve a finite element model of such complex behavior is an extremely challenging problem. A practical crushing model based on detailed modeling of the physical mechanisms of crushing behavior is not expected in the foreseeable future. The present research describes attempts to model composite crushing behavior using a novel hybrid modeling procedure. Experimental testing is done is support of the modeling efforts, and a test specimen is developed to provide data for validating laminate crushing models.
Methods for Preparing Nanoparticle-Containing Thermoplastic Composite Laminates
NASA Technical Reports Server (NTRS)
Gruber, Mark B. (Inventor); Jensen, Brian J. (Inventor); Cano, Roberto J. (Inventor)
2016-01-01
High quality thermoplastic composites and composite laminates containing nanoparticles and/or nanofibers, and methods of producing such composites and laminates are disclosed. The composites comprise a thermoplastic polymer and a plurality of nanoparticles, and may include a fibrous structural reinforcement. The composite laminates are formed from a plurality of nanoparticle-containing composite layers and may be fused to one another via an automated process.
NASA Astrophysics Data System (ADS)
Diaz Montiel, Paulina
Carbon Fiber Reinforced Polymer (CFRP) materials are used in aerospace structures due to their superior mechanical properties and reduced weight. Non-destructive evaluation (NDE) techniques are needed for such materials to detect and measure intra-ply matrix cracking and inter-ply delamination damage without harming or altering their initial configuration. The aim of NDE techniques is to use the composite material as a sensor itself, and to use its intrinsic material properties as measure of damage. Previous literature has shown that CFRP composites are electrically conductive in the fibers direction, and that the fiber-to-fiber contact due to waviness provides electrical conduction in the direction normal to the fibers. When matrix cracking or delamination defects are introduced in the composite, they break the fiber contact network, and this increases the local resistivity of the material. The Electrical Resistance Tomography (ERT) provides a NDE technique that uses these inherent changes in conductive properties of the composite to map its internal damage state. As opposed to other NDE methods, this technique allows the in-situ monitoring and detection on damage, which is particularly desirable for large and complex aerospace structures. This research investigates efficient numerical modeling techniques for inverse identification of delamination damage location and size in composite laminates using ERT based NDE. Identification of damage in composites requires solving the inverse problem that minimizes the difference between the model predicted and the measured change in resistance at specified electrode locations. The direct use of numerical finite element models of the laminate in the inverse identification is computationally expensive and it requires the development of accurate surrogate models. The use of Response Surfaces and Kriging approximations for single-response surrogate modeling is investigated in this work. Since the electrical resistance changes
Progressive delamination in polymer matrix composite laminates: A new approach
NASA Technical Reports Server (NTRS)
Chamis, C. C.; Murthy, P. L. N.; Minnetyan, L.
1992-01-01
A new approach independent of stress intensity factors and fracture toughness parameters has been developed and is described for the computational simulation of progressive delamination in polymer matrix composite laminates. The damage stages are quantified based on physics via composite mechanics while the degradation of the laminate behavior is quantified via the finite element method. The approach accounts for all types of composite behavior, laminate configuration, load conditions, and delamination processes starting from damage initiation, to unstable propagation, and to laminate fracture. Results of laminate fracture in composite beams, panels, plates, and shells are presented to demonstrate the effectiveness and versatility of this new approach.
Laminate analogy for composites enhanced concrete structures
Chamis, C.C.; Gotsis, P.K.
1997-10-01
A new and effective method is described to design composites to repair damage or enhance the overload strength of concrete infrastructures. The method is based on laminate analogy which is derivable from composite mechanics and available in computer codes. It is used to simulate structural sections made from reinforced concrete which are typical in infrastructures as well as select reinforced concrete structures. The structural sections are represented by a number of layers through the thickness where different layers are used for the concrete, for the reinforcing steel in concrete, and for the composite. The reinforced concrete structures are represented with finite elements where the element stiffness parameters are from the structural sections which are represented by the laminate analogy. The load carrying capability of the structure is determined by progressive structural fracture. Results show up to 40 percent improvements for damage and for overload enhancement with relatively small laminate thickness for the structural sections and up to three times for the composite enhanced select structures (arch and dome).
Thermomechanical postbuckling analysis of laminated composite shells
Averill, R.C.; Reddy, J.N.
1993-01-01
The nonlinear response of laminated composite structures subjected to thermal loads is investigated. Analysis is performed using a refined theory and an associated finite element model for geometrically nonlinear analysis of laminated composite shell structures. The model is based on a third-order displacement field which accounts for both transverse shear and transverse normal deformations. Numerical studies of simply-supported plates and cylindrical panels indicate that when the panels are free to expand or contract in the transverse direction, the predicted critical buckling temperatures do not depend significantly upon whether or not transverse normal deformations are explicitly accounted for in the analysis model. However, the critical buckling temperatures are strongly dependent upon whether or not the transverse normal deformations are restrained along the boundaries of the panels. 25 refs.
Rogge, Matthew D; Leckey, Cara A C
2013-09-01
Delaminations in composite laminates resulting from impact events may be accompanied by minimal indication of damage at the surface. As such, inspections are required to ensure defects are within allowable limits. Conventional ultrasonic scanning techniques have been shown to effectively characterize the size and depth of delaminations but require physical contact with the structure and considerable setup time. Alternatively, a non-contact scanning laser vibrometer may be used to measure guided wave propagation in the laminate structure generated by permanently bonded transducers. A local Fourier domain analysis method is presented for processing guided wavefield data to estimate spatially dependent wavenumber values, which can be used to determine delamination depth. The technique is applied to simulated wavefields and results are analyzed to determine limitations of the technique with regards to determining defect size and depth. Based on simulation results, guidelines for application of the technique are developed. Finally, experimental wavefield data is obtained in quasi-isotropic carbon fiber reinforced polymer (CFRP) laminates with impact damage. The recorded wavefields are analyzed and wavenumber is measured to an accuracy of up to 8.5% in the region of shallow delaminations. These results show the promise of local wavenumber domain analysis to characterize the depth of delamination damage in composite laminates. The technique can find application in automated vehicle health assurance systems with potential for high detection rates and greatly reduced operator effort and setup time.
Residual stresses in polymer matrix composite laminates
NASA Technical Reports Server (NTRS)
Hahn, H. T.
1976-01-01
Residual stresses in composites are induced during fabrication and by environmental exposure. The theory formulated can describe the shrinkage commonly observed after a thermal expansion test. Comparison between the analysis and experimental data for laminates of various material systems indicates that the residual stress-free temperature can be lower than the curing temperature, depending on the curing process. Effects of residual stresses on ply failure including the acoustic emission characteristics are discussed.
Delamination stresses in semicircular laminated composite bars
NASA Technical Reports Server (NTRS)
Ko, William L.
1988-01-01
Using anisotropic elasticity theory, delamination stresses in a semicircular laminated composite curved bar subjected to end forces and end moments were calculated, and their radial locations determined. A family of design curves was presented, showing variation of the intensity of delamination stresses and their radial locations with different geometry and different degrees of anisotropy of the curved bar. The effect of anisotropy on the location of peak delamination stress was found to be small.
Compression failure of composite laminates
NASA Technical Reports Server (NTRS)
Pipes, R. B.
1983-01-01
This presentation attempts to characterize the compressive behavior of Hercules AS-1/3501-6 graphite-epoxy composite. The effect of varying specimen geometry on test results is examined. The transition region is determined between buckling and compressive failure. Failure modes are defined and analytical models to describe these modes are presented.
Acousto-Optic Measurements in CFRP Laminates Using Fiber Bragg Grating Sensors
2011-09-01
level. The main objective of this paper is to describe the results of an acousto - optic experiment using FBG sensors and present FR as a potential way of determining accumulated damage in a carbon composite structure.
Nondestructive evaluation of defects in carbon fiber reinforced polymer (CFRP) composites
NASA Astrophysics Data System (ADS)
Ngo, Andrew C. Y.; Goh, Henry K. H.; Lin, Karen K.; Liew, W. H.
2017-04-01
Carbon fiber reinforced polymer (CFRP) composites are increasingly used in aerospace applications due to its superior mechanical properties and reduced weight. Adhesive bonding is commonly used to join the composite parts since it is capable of joining incompatible or dissimilar components. However, insufficient adhesive or contamination in the adhesive bonds might occur and pose as threats to the integrity of the plane during service. It is thus important to look for suitable nondestructive testing (NDT) techniques to detect and characterize the sub-surface defects within the CFRP composites. Some of the common NDT techniques include ultrasonic techniques and thermography. In this work, we report the use of the abovementioned techniques for improved interpretation of the results.
Thermal stresses in thick laminated composite shells
NASA Technical Reports Server (NTRS)
Yuan, F. G.
1993-01-01
The paper provides an analytical formulation to investigate the thermomechanical behavior of thick composite shells subjected to a temperature distribution which varies arbitrarily in the radial direction. For illustrative purposes, shells under uniform temperature change are presented. It is found that thermal twist would occur even for symmetric laminated shells. Under uniform temperature rise, results for off-axis graphite/epoxy shells show that extensional-shear coupling can cause tensile radial stress throughout the shell and tensile hoop stress in the inner region. Laminated graphite/epoxy shells can exhibit negative effective thermal expansion coefficients in the longitudinal and transverse directions. Finally, the stacking sequence has a strong influence on the thermal stress distributions.
NASA Astrophysics Data System (ADS)
Russo, A.; Zuccarello, B.
2007-07-01
The paper presents a theoretical-numerical hybrid method for determining the stresses distribution in composite laminates containing a circular hole and subjected to uniaxial tensile loading. The method is based upon an appropriate corrective function allowing a simple and rapid evaluation of stress distributions in a generic plate of finite width with a hole based on the theoretical stresses distribution in an infinite plate with the same hole geometry and material. In order to verify the accuracy of the method proposed, various numerical and experimental tests have been performed by considering different laminate lay-ups; in particular, the experimental results have shown that a combined use of the method proposed and the well-know point-stress criterion leads to reliable strength predictions for GFRP or CFRP laminates with a circular hole.
Residual stress characterization for laminated composites
NASA Astrophysics Data System (ADS)
Liu, Shao-Chun
With increasing applications of advanced laminated composites, process-induced residual stress has drawn more and more attention in recent years. Efforts have been devoted to understanding residual stress both quantitatively and qualitatively. In the current study, a novel technique called the Cure Referencing Method was developed which has the capability for measuring the residual stress on the symmetric laminated composite plates. It can also differentiate residual stress into two components: one is due to the mismatch of the coefficient of thermal expansion, the other is caused by the matrix chemical curing shrinkage. The chemical curing shrinkage of the polymer matrix was investigated in further detail. A technique was developed to measure the post-gel chemical curing shrinkage which is the portion of curing shrinkage that really induces the residual stress in the polymer matrix composites. Time-dependent material property is another issue associated with polymer matrix composite materials. The data of several short-term tensile creep tests run at different temperature were used to construct a linear viscoelastic: model for describing the behavior of the composites over a long period of time. It was found that physical aging of the polymer matrix needs to be taken into account in order to have a more accurate representation of the long-term behavior. A fair agreement was obtained between the result of the long-term creep test and the master curve constructed from several momentary creep tests.
Interlaminar interaction in paper thermoplastic laminate composites
NASA Astrophysics Data System (ADS)
Prambauer, M.; Paulik, C.; Burgstaller, C.
2016-07-01
Bio-based composites are a research topic since several decades, which aims for sustainable and durable materials. In the scope of this research, many different sources for biobased reinforcements have been investigated. Typical issues associated with the use of such are property variations due to cultivation area and climate, besides the influences of the type, pretreatment and fibre geometry. Another issue can be the availability of such natural fibres. Due to these reasons, we started using paper sheets as reinforcements in laminate composites with thermoplastic materials. In preliminary studies with polypropylene composites, we found good mechanical properties, even higher than could be expected by estimating the composite properties from the constituents by applying simple rule of mixtures type models. We suspect, besides some effect of paper compaction, interlaminar effects to be the reason for this. Therefore, the aim of this work is to investigate the effects of the interfacial interaction on the different paper laminate properties due to different matrix polymers. For this work, we used polypropylene, polyamide 6 and 12 as well as polystyrene. Composites were produced via compression moulding and samples for mechanical testing and density evaluation were cut from the moulded plates. The results from mechanical tests show, that there is a reinforcing effect, regardless of matrix polymer used. Simple rule of mixtures evaluations show, that the different matrices exhibit different degrees of interaction, based on their chemical structure. In addition, also influences due to processing were found.
High-power picosecond laser drilling/machining of carbon fibre-reinforced polymer (CFRP) composites
NASA Astrophysics Data System (ADS)
Salama, A.; Li, L.; Mativenga, P.; Sabli, A.
2016-02-01
The large differences in physical and thermal properties of the carbon fibre-reinforced polymer (CFRP) composite constituents make laser machining of this material challenging. An extended heat-affected zone (HAZ) often occurs. The availability of ultrashort laser pulse sources such as picosecond lasers makes it possible to improve the laser machining quality of these materials. This paper reports an investigation on the drilling and machining of CFRP composites using a state-of-the-art 400 W picosecond laser system. Small HAZs (<25 µm) were obtained on the entry side of 6-mm-diameter hole drilled on sample of 6 mm thickness, whereas no HAZ was seen below the top surface on the cut surfaces. Multiple ring material removal strategy was used. Furthermore, the effect of laser processing parameters such as laser power, scanning speed and repetition rate on HAZ sizes and ablation depth was investigated.
Impact Damage Tolerance of a Carbon Fibre Composite Laminate.
1984-05-01
design of composite structures. 8 CONCLUSIONS These carbon fibre/ epoxy resin laminates are susceptible :: low e ;rt., - .. impact damage, especially...ROYAL AIRCRAFT ESTABLISHMENT0 Technical Report 84049 May 1984 GARTEUR/TP-007 IMPACT DAMAGE TOLERANCE OF A CARBON FIBRE COMPOSITE LAMINATE by DTIC G...007 Received for printing 3 May 1984 IMPACT DAMAGE TOLERANCE OF A CARBON FIBRE COMPOSITE LAMINATE by G. Dorey P. Sigety* K. Stellbrink** W. G. J. ’t
NASA Astrophysics Data System (ADS)
Jumahat, Aidah; Soutis, Constantinos; Hodzic, Alma
2011-02-01
The in-plane shear and compressive properties of unidirectional (UD) HTS40/977-2 carbon fibre-toughened resin (CF/TR) laminates are investigated. Scanning Electron microscopy (SEM) and optical microscopy are used to reveal the failure mechanisms developed during compression. It is found that damage initiates by fibre microbuckling (a fibre instability failure mode) which then is followed by yielding of the matrix to form a fibre kink band zone that leads to final fracture. Analytical models are briefly reviewed and a graphical method, based on the shear response of the composite system, is described in order to estimate the UD compressive strength. Predictions for the HTS40/977-2 system are compared to experimental measurements and to data of five other unidirectional carbon fibre reinforced polymer (CFRP) composites that are currently used in aerospace and other structural applications. It is shown that the estimated values are in a good agreement with the measured results.
Micromechanics of composite laminate compression failures
NASA Technical Reports Server (NTRS)
Guynn, E. Gail; Bradley, Walter L.
1988-01-01
The purpose of this annual progress report is to summarize the work effort and results accomplished from July 1987 through July 1988 on NASA Research Grant NAG1-659 entitled Micromechanics of Composite Laminate Compressive Failure. The report contains: (1) the objective of the proposed research, (2) the summary of accomplishments, (3) a more extensive review of compression literature, (4) the planned material (and corresponding properties) received to date, (5) the results for three possible specimen geometries, experimental procedures planned, and current status of the experiments, and (6) the work planned for the next contract year.
Strength of Bolted Joints in Laminated Composites
1984-03-01
considered (c13ao23=033a0). Under these conditions, in the absence of body forces, the condition of force equilibriui can be expressed as E18 ] (1) Bo2...Conference), ASTM STP 617, 1977, pp 229-242. 14. I.M. Daniel, R.E. Rowlands, and J.B. Whiteside, "Effects of Material and Stacking Sequence on the...Whitney, "Uniaxial Failure of Composite Laminates Containing Stress Concentrations,"Fracture Mechanics of Compo-ites, ASTM STP 593, 1975, pp. 117-142
Torres-Acosta, A.A.; Sagues, A.A.; Sen, R.
1998-12-31
Experiments were performed to determine the possible extent of galvanic corrosion when CFRP and steel are in contact in chloride contaminated concrete. Three concrete environments (water-to-cement (w/c) ratio of 0.41) at relative humidities (RH) of {approx}60%, {approx}80% and {approx}95%, and 14 kg/m{sup 3} chloride were investigated. The CFRP composite potential reached between {minus}180 and {minus}590 mV (vsCSE) when it was in contact with steel at these environments. Results showed significant galvanic action in the 80% RH chloride contaminated concrete (nominal steel current densities as high as 0.3 {micro}A/cm{sup 2}).
Nonlinear laminate analysis for metal matrix fiber composites
NASA Technical Reports Server (NTRS)
Chamis, C. C.; Sinclair, J. H.
1981-01-01
A nonlinear laminate analysis is described for predicting the mechanical behavior (stress-strain relationships) of angleplied laminates in which the matrix is strained nonlinearly by both the residual stress and the mechanical load and in which additional nonlinearities are induced due to progressive fiber fractures and ply relative rotations. The nonlinear laminate analysis (NLA) is based on linear composite mechanics and a piece wise linear laminate analysis to handle the nonlinear responses. Results obtained by using this nonlinear analysis on boron fiber/aluminum matrix angleplied laminates agree well with experimental data. The results shown illustrate the in situ ply stress-strain behavior and synergistic strength enhancement.
Prediction of Composite Laminate Fracture: Micromechanics and Progressive Fracture
NASA Technical Reports Server (NTRS)
Gotsis, P. K.; Chamis, C. C.; Minnetyan, L.
1996-01-01
This report describes an investigation to predict first-ply failure and final fracture in selected composite laminates subjected to inplane loads. The laminates were composed of glass fiber and graphite fibers in epoxy matrices. Failure envelopes based on first-ply failure and laminate fracture were generated for combined loading of these laminates. Predictions were evaluated by micromechanics-based theory and progressive fracture. The results show that, for most cases, combined tensile loading significantly enhanced the laminate fracture stress in comparison to the uniaxial loading.
The Effects of Debonding on the Low-Velocity Impact Response of Steel-CFRP Fibre Metal Laminates
NASA Astrophysics Data System (ADS)
Pärnänen, T.; Vänttinen, A.; Kanerva, M.; Jokinen, J.; Saarela, O.
2016-12-01
The effect of metal-composite debonding on low-velocity impact response, i.e. on contact force-central deflection response, deformation profiles and strains on the free surfaces was studied. We focused on type 2/1 fibre metal laminate specimens made of stainless steel and carbon fibre epoxy layers, and tested them with drop-weight impact and quasi-static indentation loadings. Local strains were measured with strain gauges and full-field strains with a 3-D digital image correlation method. In addition, finite element simulations were performed and the effects of debonding were studied by exploiting cohesive elements. Our results showed that debonding, either the initial debonding or that formed during the loading, lowers the slope of the contact force-central deflection curve during the force increase. The debonding formation during the rebound phase was shown to amplify the rebound of the impact side, i.e. to lower the ultimate post-impact deflection. The free surface strains were studied on the laminate's lower surface at the area outside the debond damage. In terms of in-plane strains, debonding formation during impact and indentation, as well as the initial debonding, lowered the peripheral strain and resulted in a positive change in the radial strain.
Residual stress and crack propagation in laminated composites
Yttergren, R.M.F.; Zeng, K.; Rowcliffe, D.J.
1994-12-31
Residual stress distributions in several laminated ceramic composites were measured by an indentation technique. The material included alumina-zirconia laminated composites, containing strong interfaces, and alumina-porcelain laminated composites with both weak and strong interfaces. The residual stress in these material originates from the mismatch of the thermal properties, differences in elastic properties, and different shrinkage of the laminates during sintering. An experimental technique is presented which gives a direct view of the residual stress state in the materials. Values of residual tensile stress are presented as a function of position relative to the interface in each material.
NASA Astrophysics Data System (ADS)
Amano, Masataro; Okabe, Yoji; Takeda, Nobuo
A Ti-Ni shape memory alloy (SMA) foil and a small-diameter fiber Bragg grating (FBG) sensor were embedded simultaneously into a CFRP cross-ply laminate. When the specimen was heated, the recovery compressive force was generated from the embedded SMA foil, which homogenized the non-uniform strain distribution caused by cracks in the 90° ply. Then, the tensile stress in the 90° ply was relaxed and the occurrence of new transverse cracks was suppressed. This effect was evaluated with the embedded FBG sensor. When the specimen was heated, the deformed reflection spectrum of the FBG returned to its original shape, which suggested that Ti-Ni SMA foil was effective to suppress the damage. However, relaxation of thermal residual tensile stress in the 90° ply was also effective. The result of the 3D FEA suggested that the suppression of damage occurrence and growth was mainly caused by the relaxation of thermal residual tensile stress.
Statistical fatigue of unnotched composite laminates
NASA Technical Reports Server (NTRS)
Yang, J. N.; Jones, D. L.
1980-01-01
A general analytical, phenomenological model is developed for characterizing fatigue damage accumulation in unnotched composite laminates, and experimental results are used to evaluate the model. The fatigue model, which is developed for various types of cyclic loadings, is based on the assumption that the residual strength reduction is a monotonically decreasing function of the fatigue life. Parameters are determined from baseline test data consisting of one set of residual strength data, one set of static strength data, and one set of constant amplitude fatigue life data. Once the parameters are determined, the model is able to predict: (1) the statistical distribution of the fatigue life, and the residual strength under constant and variable amplitude loads, and (2) the effect of periodic proof tests, without any additional experimental data. Experimental test results show that predictions made from the present model agree quite well with the experimental results. The model is also applicable to fatigue of bonded or bolted composite joints.
Permeability After Impact Testing of Composite Laminates
NASA Technical Reports Server (NTRS)
Nettles, A.T.; Munafo, Paul (Technical Monitor)
2002-01-01
Since composite laminates are beginning to be identified for use in reusable launch vehicle propulsion systems, an understanding of their permeance is needed. A foreign object impact event can cause a localized area of permeability (leakage) in a polymer matrix composite and it is the aim of this study to assess a method of quantifying permeability-after-impact results. A simple test apparatus is presented and variables that could affect the measured values of permeability-after-impact were assessed. Once it was determined that valid numbers were being measured, a fiber/resin system was impacted at various impact levels and the resulting permeability measured, first with a leak check solution (qualitative) then using the new apparatus (quantitative). The results showed that as the impact level increased, so did the measured leakage. As the pressure to the specimen was increased, the leak rate was seen to increase in a non-linear fashion for almost all of the specimens tested.
Permeability After Impact Testing of Composite Laminates
NASA Technical Reports Server (NTRS)
Nettles, Alan T.
2003-01-01
Since composite laminates are beginning to be identified for use in reusable launch vehicle propulsion systems, an understanding of their permeance is needed. A foreign object impact event can cause a localized area of permeability (leakage) in a polymer matrix composite and it is the aim of this study to assess a method of quantifying permeability-after-impact results. A simple test apparatus is presented and variables that could affect the measured values of permeability-after-impact were assessed. Once it was determined that valid numbers were being measured, a fiber/resin system was impacted at various impact levels and the resulting permeability measured, first with a leak check solution (qualitative) then using the new apparatus (quantitative). The results showed that as the impact level increased, so did the measured leakage. As the pressure to the specimen was increased, the leak rate was seen to increase in a non-linear fashion for almost all of the specimens tested.
Fracture toughness and impact properties of laminated metal composites
Lesuer, D.R.; Riddle, R.A.; Gogolewski, R.P.; Syn, C.K.; Cunningham, B.J.
1996-03-04
Laminated metal composites consist of alternating metal (or metal matrix composite) layers bonded together. These materials can provide fracture toughness and impact properties superior to those of the component materials. These properties are a function of component material properties, laminate architecture (volume fraction, thickness) and interface properties. Properties are compared for seven lightweight materials.
Failure and deformation analyses of smart laminated composites
NASA Astrophysics Data System (ADS)
Hasan, Z.; Muliana, A.
2012-09-01
The present study focuses on the failure analysis and shape control of smart composite laminates under coupled thermal (hygro), electric, and mechanical stimuli. A linear thermo(hygro)electroelastic constitutive model for transversely isotropic materials is used for each ply in the composite laminate and for the piezoelectric materials that are integrated with laminates of the composite. Piezoelectric materials, such as lead zirconate titanate, and piezoelectric fiber composites, such as an active fiber composite or a microfiber composite, are considered as actuators for controlling unwanted bending deformations to avoid failure in such composite laminates. Due to the high stress concentrations at the interfaces between an active layer and the host structure, which may cause debonding, embedded actuators in which the active material is placed as part of the plies to form geometrically continuous plies are considered in order to minimize the stress concentration while improving the actuation capability. The first-ply failure and the ultimate laminate failure criteria of composite laminates are used to predict the failure stress and mode of the smart composite laminates, where commonly known macroscopic failure criteria, such as the Tsai-Hill, Tsai-Wu, and maximum stress criteria, are employed for each lamina. Piezoelectric materials can be used to prevent the failure from hygrothermal and mechanical loadings by applying an electric voltage in order to counteract laminate deformations. Based on the deformation and failure analyzes of smart composite laminates having various stacking sequences, fiber and matrix constituents, and piezoelectric materials, we could estimate the overall properties and failure envelopes of the laminates, which is useful in the preliminary design of smart composite structures.
Vibration suppression of composite laminated plate with nonlinear energy sink
NASA Astrophysics Data System (ADS)
Zhang, Ye-Wei; Zhang, Hao; Hou, Shuai; Xu, Ke-Fan; Chen, Li-Qun
2016-06-01
The composite laminated plate is widely used in supersonic aircraft. So, there are many researches about the vibration suppression of composite laminated plate. In this paper, nonlinear energy sink (NES) as an effective method to suppress vibration is studied. The coupled partial differential governing equations of the composite laminated plate with the nonlinear energy sink (NES) are established by using the Hamilton principle. The fourth-order Galerkin discrete method is used to truncate the partial differential equations, which are solved by numerical integration method. Meanwhile study about the precise effectiveness of the nonlinear energy sink (NES) by discussing the different installation location of the nonlinear energy sink (NES) at the same speed. The results indicate that the nonlinear energy sink (NES) can significantly suppress the severe vibration of the composite laminated plate with speed wind loadings in to protect the composite laminated plate from excessive vibration.
Effect of Impact Damage and Open Hole on Compressive Strength of Hybrid Composite Laminates
Hiel, C.; Brinson, H.F.
1993-05-01
Impact damage tolerance is a frequently listed design requirement for composites hardware. The effect of impact damage and open hole size on laminate compressive strength was studied on sandwich beam specimens which combine CFRP-GFRP hybrid skins and a syntactic foam core. Three test specimen configurations have been investigated for this study. The first two were sandwich beams which were loaded in pure bending (by four point flexure). One series had a skin damaged by impact, and the second series had a circular hole machined through one of the skins. The reduction of compressive strength with increasing damage (hole) size was compared. Additionally a third series of uniaxially loaded open hole compression coupons were tested to generate baseline data for comparison with both series of sandwich beams.
Effect of Impact Damage and Open Hole on Compressive Strength of Hybrid Composite Laminates
NASA Technical Reports Server (NTRS)
Hiel, Clement; Brinson, H. F.
1993-01-01
Impact damage tolerance is a frequently listed design requirement for composites hardware. The effect of impact damage and open hole size on laminate compressive strength was studied on sandwich beam specimens which combine CFRP-GFRP hybrid skins and a syntactic foam core. Three test specimen configurations have been investigated for this study. The first two were sandwich beams which were loaded in pure bending (by four point flexure). One series had a skin damaged by impact, and the second series had a circular hole machined through one of the skins. The reduction of compressive strength with increasing damage (hole) size was compared. Additionally a third series of uniaxially loaded open hole compression coupons were tested to generate baseline data for comparison with both series of sandwich beams.
Thermo-mechanical response predictions for metal matrix composite laminates
NASA Technical Reports Server (NTRS)
Aboudi, J.; Hidde, J. S.; Herakovich, C. T.
1991-01-01
An analytical micromechanical model is employed for prediction of the stress-strain response of metal matrix composite laminates subjected to thermomechanical loading. The predicted behavior of laminates is based upon knowledge of the thermomechanical response of the transversely isotropic, elastic fibers and the elastic-viscoplastic, work-hardening matrix. The method is applied to study the behavior of silicon carbide/titanium metal matrix composite laminates. The response of laminates is compared with that of unidirectional lamina. The results demonstrate the effect of cooling from a stress-free temperature and the mismatch of thermal and mechanical properties of the constituent phases on the laminate's subsequent mechanical response. Typical results are presented for a variety of laminates subjected to monotonic tension, monotonic shear and cyclic tensile/compressive loadings.
Effect of laminate edge conditions on the formation of microvoids in composite laminates
NASA Astrophysics Data System (ADS)
Anderson, J. P.; Altan, M. C.
2015-05-01
Manufacturing defects such as microvoids are common in thermoset composite components and are known to negatively affect their strength. The resin pressure developed in and the resin flow out from the laminates during cure have been reported to be the primary factors influencing the final void content of a composite component. In this work, the effect of laminate edge conditions during the cure process on the formation of microvoids was experimentally investigated. This was achieved by fabricating eight-ply laminates from TenCate® BT250/7781 prepreg in a hot-press at a constant cure pressure of 170 kPa while limiting the laminate perimeter available for resin flow by 0%, 25%, 50%, 75%, and 100%. The individual plies of these five laminates were conditioned at 99% relative humidity before curing to maximize the moisture present in the lay-up before fabrication. The presence of moisture in the lay-ups was expected to promote void formation and allow the effect of restricting flow at the edges of a laminate to be better identified. The restriction of resin outflow was found to cause the average characteristic void diameter to decrease by 17% and void content to rise by 33%. This phenomenon was identified to be a result of the outflow restriction increasing the number of voids trapped within the laminate and indicates that for laminates cured at low pressures resin outflow is the dominant mechanism for void reduction.
Micromechanical Modeling of Impact Damage Mechanisms in Unidirectional Composite Laminates
NASA Astrophysics Data System (ADS)
Meng, Qinghua; Wang, Zhenqing
2016-12-01
Composite laminates are susceptible to the transverse impact loads resulting in significant damage such as matrix cracking, fiber breakage and delamination. In this paper, a micromechanical model is developed to predict the impact damage of composite laminates based on microstructure and various failure models of laminates. The fiber and matrix are represented by the isotropic and elastic-plastic solid, and their impact failure behaviors are modeled based on shear damage model. The delaminaton failure is modeling by the interface element controlled by cohesive damage model. Impact damage mechanisms of laminate are analyzed by using the micromechanical model proposed. In addition, the effects of impact energy and laminated type on impact damage behavior of laminates are investigated. Due to the damage of the surrounding matrix near the impact point caused by the fiber deformation, the surface damage area of laminate is larger than the area of impact projectile. The shape of the damage area is roughly rectangle or elliptical with the major axis extending parallel to the fiber direction in the surface layer of laminate. The alternating laminated type with two fiber directions is more propitious to improve the impact resistance of laminates.
NASA Astrophysics Data System (ADS)
Yokozeki, Tomohiro; Iwahori, Yutaka; Ishiwata, Shin
This study investigated the thermo-elastic properties and microscopic ply cracking behaviors in carbon fiber reinforced nanotube-dispersed epoxy laminates. The nanocomposite laminates used in this study consisted of traditional carbon fibers and epoxy resin filled with cup-stacked carbon nanotubes (CSCNTs). Thermo-mechanical properties of unidirectional nanocomposite laminates were evaluated, and quasi-static and fatigue tension tests of cross-ply laminates were carried out in order to observe the damage accumulation behaviors of matrix cracks. Clear retardation of matrix crack onset and accumulation was found in composite laminates with CSCNT compared to those without CSCNT. Fracture toughness associated with matrix cracking was evaluated based on the analytical model using the experimental results. It was concluded that the dispersion of CSCNT resulted in fracture toughness improvement and residual thermal strain decrease, and specifically, the former was the main contribution to the retardation of matrix crack formation.
Dynamic delamination in curved composite laminates under quasi-static loading
NASA Astrophysics Data System (ADS)
Uyar, I.; Gozluklu, B.; Coker, D.
2014-06-01
In the wind energy industry, new advances in composite manufacturing technology and high demand for lightweight structures are fostering the use of composite laminates in a wide variety of shapes as primary load carrying elements. However, once a moderately thick laminate takes highly curved shape, such as an L-shape, Interlaminar Normal Stresses (ILNS) are induced together with typical Interlaminar Shear Stresses (ILSS) on the interfaces between the laminas. The development of ILNS promotes mode-I type of delamination propagation in the curved part of the L-shaped structure, which is a problem that has recently raised to the forefront in in-service new composite wind turbines. Delamination propagation in L-shaped laminates can be highly dynamic even though the loading is quasistatic. An experimental study to investigate dynamic delamination under quasi-static loading is carried out using a million fps high speed camera. Simulations of the experiments are conducted with a bilinear cohesive zone model implemented in user subroutine of the commercial FEA code ABAQUS/explicit. The experiments were conducted on a 12-layered woven L-shaped CFRP laminates subjected to shear loading perpendicular to the arm of the specimen with a free-sliding fixture to match the boundary conditions used in the FEA. A single delamination is found to initiate at the 5th interface during a single drop in the load. The delamination is then observed to propagate to the arms at intersonic speed of 2200m/s. The results obtained using cohesive zone models in the numerical simulations were found to be in good agreement with experimental results in terms of load displacement behavior and delamination history.
Non-linear behavior of fiber composite laminates
NASA Technical Reports Server (NTRS)
Hashin, Z.; Bagchi, D.; Rosen, B. W.
1974-01-01
The non-linear behavior of fiber composite laminates which results from lamina non-linear characteristics was examined. The analysis uses a Ramberg-Osgood representation of the lamina transverse and shear stress strain curves in conjunction with deformation theory to describe the resultant laminate non-linear behavior. A laminate having an arbitrary number of oriented layers and subjected to a general state of membrane stress was treated. Parametric results and comparison with experimental data and prior theoretical results are presented.
Reliability analysis of ceramic matrix composite laminates
NASA Technical Reports Server (NTRS)
Thomas, David J.; Wetherhold, Robert C.
1991-01-01
At a macroscopic level, a composite lamina may be considered as a homogeneous orthotropic solid whose directional strengths are random variables. Incorporation of these random variable strengths into failure models, either interactive or non-interactive, allows for the evaluation of the lamina reliability under a given stress state. Using a non-interactive criterion for demonstration purposes, laminate reliabilities are calculated assuming previously established load sharing rules for the redistribution of load as the failure of laminae occur. The matrix cracking predicted by ACK theory is modeled to allow a loss of stiffness in the fiber direction. The subsequent failure in the fiber direction is controlled by a modified bundle theory. Results using this modified bundle model are compared with previous models which did not permit separate consideration of matrix cracking, as well as to results obtained from experimental data.
Simulating Progressive Damage of Notched Composite Laminates with Various Lamination Schemes
NASA Astrophysics Data System (ADS)
Mandal, B.; Chakrabarti, A.
2017-05-01
A three dimensional finite element based progressive damage model has been developed for the failure analysis of notched composite laminates. The material constitutive relations and the progressive damage algorithms are implemented into finite element code ABAQUS using user-defined subroutine UMAT. The existing failure criteria for the composite laminates are modified by including the failure criteria for fiber/matrix shear damage and delamination effects. The proposed numerical model is quite efficient and simple compared to other progressive damage models available in the literature. The efficiency of the present constitutive model and the computational scheme is verified by comparing the simulated results with the results available in the literature. A parametric study has been carried out to investigate the effect of change in lamination scheme on the failure behaviour of notched composite laminates.
The structural response of unsymmetrically laminated composite cylinders
NASA Technical Reports Server (NTRS)
Butler, T. A.; Hyer, M. W.
1989-01-01
The responses of an unsymmetrically laminated fiber-reinforced composite cylinder to an axial compressive load, a torsional load, and the temperature change associated with cooling from the processing temperature to the service temperature are investigated. These problems are considered axisymmetric and the response is studied in the context of linear elastic material behavior and geometrically linear kinematics. Four different laminates are studied: a general unsymmetric laminate; two unsymmetric but more conventional laminates; and a conventional quasi-isotropic symmetric laminate. The responses based on closed-form solutions for different boundary conditions are computed and studied in detail. Particular emphasis is directed at understanding the influence of elastic couplings in the laminates. The influence of coupling decreased from a large effect in the general unsymmetric laminate, to practically no effect in the quasi-isotropic laminate. For example, the torsional loading of the general unsymmetric laminate resulted in a radial displacement. The temperature change also caused a significant radial displacement to occur near the ends of the cylinder. On the other hand, the more conventional unsymmetric laminate and the quasi-isotropic cylinder did not deform radially when subjected to a torsional load. From the results obtained, it is clear the degree of elastic coupling can be controlled and indeed designed into a cylinder, the degree and character of the coupling being dictated by the application.
Extrinsic fracture mechanisms in two laminated metal composites
Lesuer, D.; Syn, C.; Riddle, R.; Sherby, O.
1994-11-29
The crack growth behavior and fracture toughness of two laminated metal composites (6090/SiC/25p laminated with 5182 and ultrahigh-carbon steel laminated with brass) have been studied in both ``crack arrester`` and ``crack divider`` orientations. The mechanisms of crack growth were analyzed and extrinsic toughening mechanisms were found to contribute significantly to the toughness. The influence of laminate architecture (layer thickness and component volume function), component material properties and residual stress on these mechanisms and the resulting crack growth resistance are discussed.
Laminated sheet composites reinforced with modular filament sheet
NASA Technical Reports Server (NTRS)
Reece, O. Y.
1968-01-01
Aluminum and magnesium composite sheet laminates reinforced with low density, high strength modular filament sheets are produced by diffusion bonding and explosive bonding. Both processes are accomplished in normal atmosphere and require no special tooling or cleaning other than wire brushing the metal surfaces just prior to laminating.
Cutting Modeling of Hybrid CFRP/Ti Composite with Induced Damage Analysis
Xu, Jinyang; El Mansori, Mohamed
2016-01-01
In hybrid carbon fiber reinforced polymer (CFRP)/Ti machining, the bi-material interface is the weakest region vulnerable to severe damage formation when the tool cutting from one phase to another phase and vice versa. The interface delamination as well as the composite-phase damage is the most serious failure dominating the bi-material machining. In this paper, an original finite element (FE) model was developed to inspect the key mechanisms governing the induced damage formation when cutting this multi-phase material. The hybrid composite model was constructed by establishing three disparate physical constituents, i.e., the Ti phase, the interface, and the CFRP phase. Different constitutive laws and damage criteria were implemented to build up the entire cutting behavior of the bi-material system. The developed orthogonal cutting (OC) model aims to characterize the dynamic mechanisms of interface delamination formation and the affected interface zone (AIZ). Special focus was made on the quantitative analyses of the parametric effects on the interface delamination and composite-phase damage. The numerical results highlighted the pivotal role of AIZ in affecting the formation of interface delamination, and the significant impacts of feed rate and cutting speed on delamination extent and fiber/matrix failure. PMID:28787824
Cutting Modeling of Hybrid CFRP/Ti Composite with Induced Damage Analysis.
Xu, Jinyang; El Mansori, Mohamed
2016-01-04
In hybrid carbon fiber reinforced polymer (CFRP)/Ti machining, the bi-material interface is the weakest region vulnerable to severe damage formation when the tool cutting from one phase to another phase and vice versa. The interface delamination as well as the composite-phase damage is the most serious failure dominating the bi-material machining. In this paper, an original finite element (FE) model was developed to inspect the key mechanisms governing the induced damage formation when cutting this multi-phase material. The hybrid composite model was constructed by establishing three disparate physical constituents, i.e., the Ti phase, the interface, and the CFRP phase. Different constitutive laws and damage criteria were implemented to build up the entire cutting behavior of the bi-material system. The developed orthogonal cutting (OC) model aims to characterize the dynamic mechanisms of interface delamination formation and the affected interface zone (AIZ). Special focus was made on the quantitative analyses of the parametric effects on the interface delamination and composite-phase damage. The numerical results highlighted the pivotal role of AIZ in affecting the formation of interface delamination, and the significant impacts of feed rate and cutting speed on delamination extent and fiber/matrix failure.
Accurate stress resultants equations for laminated composite deep thick shells
Qatu, M.S.
1995-11-01
This paper derives accurate equations for the normal and shear force as well as bending and twisting moment resultants for laminated composite deep, thick shells. The stress resultant equations for laminated composite thick shells are shown to be different from those of plates. This is due to the fact the stresses over the thickness of the shell have to be integrated on a trapezoidal-like shell element to obtain the stress resultants. Numerical results are obtained and showed that accurate stress resultants are needed for laminated composite deep thick shells, especially if the curvature is not spherical.
Investigation on mechanical behavior of filament-wound CFRP tubes
NASA Astrophysics Data System (ADS)
Zhang, Liangquan; Li, Hui
2011-04-01
Firstly, two types of CFRP tubes are designed using the filament-wound forming technology. These tubes are winded by carbon fibers with a filament winding pattern of [(900/00)2]S. The compression and tensile test are also carried out to investigate the stress-strain relationship, ultimate strength and macroscopic failure mode of the former CFRP tube. The results demonstrate that the former CFRP tube has a much larger ultimate tensile stress and strain than compressive stress and strain. However, the elastic modules of CFRP tubes under tension and compression are similar and the failure mode of these CFRP tubes is brittle under compression and tension. Secondly, the stress and strain analysis method of filament-wound CFRP tube is investigated according to anisotropic elasticity theory and lamination theory of composite material. Then, the strength of carbon-fiber-reinforced plastic tubes is obtained. In addition, the comparison of theoretical analysis results and experimental results shows that the theoretical analysis results are reliable.
Damage growth in composite laminates with interleaves
NASA Technical Reports Server (NTRS)
Goree, James G.
1987-01-01
The influence of placing interleaves between fiber reinforced plies in multilayered composite laminates is investigated. The geometry of the composite is idealized as two dimensional, isotropic, linearly elastic media made of a damaged layer bonded between two half planes and separated by thin interleaves of low extensional and shear moduli. The damage in the layer is taken in the form of a symmetric crack perpendicular to the interface and may extend up to the interface. The case of an H-shaped crack in the form of a broken layer with delamination along the interface is also analyzed. The interleaves are modeled as distributed shear and tension springs. Fourier integral transform techniques are used to develop solutions in terms of singular integral equations. An asymptotic analysis of the integral equations based on Muskhelishvili's techniques reveals logarithmically singular axial stresses in the half plane at the crack tips for the broken layer. For the H shaped crack, similar singularities are found to exist in the axial stresses at the interface crack tips in the layer and the half plane. The solution of the equations is found numerically for the stresses and displacements by using the Hadamard's concept of direct differentiation of Cauchy integrals as well as Gaussian integration techniques.
Design of composite laminates by a Monte Carlo method
NASA Astrophysics Data System (ADS)
Fang, Chin; Springer, George S.
1993-01-01
A Monte Carlo procedure was developed for optimizing symmetric fiber reinforced composite laminates such that the weight is minimum and the Tsai-Wu strength failure criterion is satisfied in each ply. The laminate may consist of several materials including an idealized core, and may be subjected to several sets of combined in-plane and bending loads. The procedure yields the number of plies, the fiber orientation, and the material of each ply and the material and thickness of the core. A user friendly computer code was written for performing the numerical calculations. Laminates optimized by the code were compared to laminates resulting from existing optimization methods. These comparisons showed that the present Monte Carlo procedure is a useful and efficient tool for the design of composite laminates.
Barbero, E.J.
1989-01-01
In this study, a computational model for accurate analysis of composite laminates and laminates with including delaminated interfaces is developed. An accurate prediction of stress distributions, including interlaminar stresses, is obtained by using the Generalized Laminate Plate Theory of Reddy in which layer-wise linear approximation of the displacements through the thickness is used. Analytical as well as finite-element solutions of the theory are developed for bending and vibrations of laminated composite plates for the linear theory. Geometrical nonlinearity, including buckling and postbuckling are included and used to perform stress analysis of laminated plates. A general two dimensional theory of laminated cylindrical shells is also developed in this study. Geometrical nonlinearity and transverse compressibility are included. Delaminations between layers of composite plates are modelled by jump discontinuity conditions at the interfaces. The theory includes multiple delaminations through the thickness. Geometric nonlinearity is included to capture layer buckling. The strain energy release rate distribution along the boundary of delaminations is computed by a novel algorithm. The computational models presented herein are accurate for global behavior and particularly appropriate for the study of local effects.
Xu, Wei; Cao, Maosen; Ding, Keqin; Radzieński, Maciej; Ostachowicz, Wiesław
2017-01-01
Carbon fiber reinforced polymer laminates are increasingly used in the aerospace and civil engineering fields. Identifying cracks in carbon fiber reinforced polymer laminated beam components is of considerable significance for ensuring the integrity and safety of the whole structures. With the development of high-resolution measurement technologies, mode-shape-based crack identification in such laminated beam components has become an active research focus. Despite its sensitivity to cracks, however, this method is susceptible to noise. To address this deficiency, this study proposes a new concept of multi-resolution modal Teager–Kaiser energy, which is the Teager–Kaiser energy of a mode shape represented in multi-resolution, for identifying cracks in carbon fiber reinforced polymer laminated beams. The efficacy of this concept is analytically demonstrated by identifying cracks in Timoshenko beams with general boundary conditions; and its applicability is validated by diagnosing cracks in a carbon fiber reinforced polymer laminated beam, whose mode shapes are precisely acquired via non-contact measurement using a scanning laser vibrometer. The analytical and experimental results show that multi-resolution modal Teager–Kaiser energy is capable of designating the presence and location of cracks in these beams under noisy environments. This proposed method holds promise for developing crack identification systems for carbon fiber reinforced polymer laminates. PMID:28773016
Xu, Wei; Cao, Maosen; Ding, Keqin; Radzieński, Maciej; Ostachowicz, Wiesław
2017-06-15
Carbon fiber reinforced polymer laminates are increasingly used in the aerospace and civil engineering fields. Identifying cracks in carbon fiber reinforced polymer laminated beam components is of considerable significance for ensuring the integrity and safety of the whole structures. With the development of high-resolution measurement technologies, mode-shape-based crack identification in such laminated beam components has become an active research focus. Despite its sensitivity to cracks, however, this method is susceptible to noise. To address this deficiency, this study proposes a new concept of multi-resolution modal Teager-Kaiser energy, which is the Teager-Kaiser energy of a mode shape represented in multi-resolution, for identifying cracks in carbon fiber reinforced polymer laminated beams. The efficacy of this concept is analytically demonstrated by identifying cracks in Timoshenko beams with general boundary conditions; and its applicability is validated by diagnosing cracks in a carbon fiber reinforced polymer laminated beam, whose mode shapes are precisely acquired via non-contact measurement using a scanning laser vibrometer. The analytical and experimental results show that multi-resolution modal Teager-Kaiser energy is capable of designating the presence and location of cracks in these beams under noisy environments. This proposed method holds promise for developing crack identification systems for carbon fiber reinforced polymer laminates.
Fracture behavior of thick, laminated graphite/epoxy composites
NASA Technical Reports Server (NTRS)
Harris, C. E.; Morris, D. H.
1984-01-01
The effect of laminate thickness on the fracture behavior of laminated graphite epoxy (T300/5208) composites was studied. The predominantly experimental research program included the study of the 0/+ or - 45/90 sub ns and 0/90 sub ns laminates with thickness of 8, 32, 64, 96 and 120 plies and the 0/+ or - 45 sub ns laminate with thickness of 6, 30, 60, 90 and 120 plies. The research concentrated on the measurement of fracture toughness utilizing the center-cracked tension, compact tension and three point bend specimen configurations. The development of subcritical damage at the crack tip was studied nondestructively using enhanced X-ray radiography and destructively using the laminate deply technique. The test results showed fracture toughness to be a function of laminate thickness. The fracture toughness of the 0 + or - 45/90 sub ns and 0/90 sub ns laminates decreased with increasing thickness and asymptotically approached lower bound values of 30 ksi square root of in. (1043 MPa square root of mm and 25 ksi square root of in (869 MPa square root of mm respectively. In contrast to the other two laminates, the fracture toughness of the 0/+ or - 45 sub ns laminate increased sharply with increasing thickness but reached an upper plateau value of 40 ksi square root of in (1390 MPa square root of mm) at 30 plies. Fracture toughness was independent of crack size for both thin and thick laminates for all three laminate types except for the 0/90 sub 2s laminate which spilt extensively. The center cracked tension, three point bend and compact tension specimens gave comparable results.
Design of laminated composite plates for maximum shear buckling loads
Chang, R.R.; Chu, K.H.; Kam, T.Y.
1993-12-01
The optimal lamination arrangements of laminated composite plates with maximum shear buckling loads are studied via a multi-start global optimization technique. A previously proposed shear deformable finite element is used to evaluate the positive and negative shear buckling loads of laminated composite plates in the optimal design process. Optimal lay-ups of thin as well as moderately thick composite plates with global maximum positive or negative shear buckling loads are determined utilizing the multi-start global optimal design technique. A number of examples of the optimal shear buckling design of symmetrically and antisymmetrically laminated composite plates with various material properties, length-to-thickness ratios, aspect ratios and different numbers of layer groups are given to illustrate the trends of optimal layer orientations of the plates. Since the existence of in-plane axial force is possible, the effects of axial compressive load on the optimal layer orientations for maximum shear buckling load are also investigated.
Laminated metals composites fracture and ballistic impact behavior
Lesuer, D.R.; Syn, C.K.; Sherby, O.D.; Wadsworth, J.
1998-01-20
Recent advances in the fracture and ballistic impact response of laminated metal composites (LMCs) are reviewed. The laminate structure can provide significant improvements to these properties relative to the component materials. Typical fracture and ballistic impact properties in LMCs are illustrated for systems containing Al alloys and Al matrix composites. The unique mechanisms operating in a layered structure that contribute to fracture or ballistic impact resistance are discussed. The influence of laminate architecture, component material properties and interface strength on mechanisms and properties are briefly reviewed for these Al-based LMCs.
Stress analysis in laminated composites with fastener holes
Iarve, E.V.
1995-12-31
Spline approximation approach has been extended for three-dimensional stress analysis in composite laminates with elastic fastener holes. Contact problem describing the interaction between laminated composite and an elastic bolt has been solved by using variational approach and Lagrangian multiplier method. Rigorous criterion for definition of the contact zone size is derived from variational principle. Representative problems such as: bearing loading with zero and 4% clearance rigid bolt and filled hole tension problems were solved for homogeneous plates.
Support Assembly for Composite Laminate Materials During Roll Press Processing
NASA Technical Reports Server (NTRS)
Catella, Luke A.
2011-01-01
A composite laminate material is supported during the roll press processing thereof by an assembly having: first and second perforated films disposed adjacent to first and second opposing surfaces of a mixture of uncured resin and fibers defining the composite laminate material, a gas permeable encasement surrounding the mixture and the first and second films, a gas impervious envelope sealed about the gas permeable encasement, and first and second rigid plates clamped about the gas impervious envelope.
Progressive Fracture of Laminated Composite Stiffened Plate
NASA Technical Reports Server (NTRS)
Gotsis, Pascalis K.; Chamis, Christos C.; David, Kostantinos; Abdi, Frank
2007-01-01
Laminated fiber-reinforced composite stiffened plate with [0/90/plus or minus 45]s plies made of S-Glass/epoxy are evaluated via computational simulation to study damage and fracture progression. The loads are pressure and temperature which varies from 21 to 65.5 C (case I) and from 143.3 to 21 C (case II). An integrated computer code is used for the simulation of the damage progression. Results show that damage initiation begins at low load level, with matrix cracking at the 0 deg. (bottom and top) plies, fiber fracture at the bottom (0 deg.) ply and interply delamination at the top (0 deg. ) ply. Increasing the applied pressure, the damage growth is expended resulting in fracture through the thickness of the structure. At this stage, 90 percent of the plies damage at applied pressure 15.306 MPa for the case I and 15.036 MPa for the case II. After this stage the cracks propagate rapidly and the structure collapses.
CFRP composite optical telescope assembly for the 1 m ULTRA project
NASA Astrophysics Data System (ADS)
Martin, Robert N.; Romeo, Robert C.
2006-06-01
The focus of the ULTRA Project is to develop and test Ultra-Lightweight Technology for Research applications in Astronomy. The ULTRA project is a collaborative effort involving the private firm Composite Mirror Applications, Inc (CMA) and 3 universities: University of Kansas, San Diego State University, and Dartmouth College. Funding for ULTRA is predominately from a NSF three year MRI program grant to CMA and KU with additional support from CMA, KU and SDSU. The goal of the ULTRA program is to demonstrate that a viable alternative exists to traditional glass mirror and steel telescope technology by designing, fabricating and testing a research telescope constructed from carbon fiber reinforced plastic (CFRP) materials. In particular, a 1m diameter, Cassegrain telescope optics set and optical tube assembly (OTA) are being designed and fabricated by CMA. The completed telescope will be deployed at SDSU's Mt Laguna Observatory in a refurbished structure (new dome and mount provided via KU and SDSU). We expect that a successful completion and testing of this project will lead to future use of CFRP technology in larger telescopes and segmented telescopes. This paper describes the OTA (optical tube assembly) that has been developed for the ULTRA project. The mirror technology is described in another paper in this conference. A poster describes the ULTRA project overview in more detail.
Residual stresses and their effects in composite laminates
NASA Technical Reports Server (NTRS)
Hahn, H. T.; Hwang, D. G.
1983-01-01
Residual stresses in composite laminates are caused by the anisotropy in expansional properties of constituent unidirectional plies. The effect of these residual stresses on dimensional stability is studied through the warping of unsymmetric (0 sub 4/90 sub 4)sub T graphite/epoxy laminates while their effect on ply failure is analyzed for (0/90)sub 2s Kevlar 49/epoxy laminate. The classical laminated plate theory is used to predict the warping of small and large panels. The change of warping does not indicate a noticeable stress relaxation at 75 C while it is very sensitive to moisture content and hence to environment. A prolonged gellation at the initial cure temperature reduces residual stresses while postcure does not. The matrix/interface cracking in dry (0/90)sub 2s Kevlar 49/epoxy laminate is shown to be the result of the residual stress exceeding the transverse strength.
The strength of laminated composite materials under repeated impact loading
NASA Technical Reports Server (NTRS)
Rotem, Assa
1988-01-01
When low velocity and energy impact is exerted on a laminated composite material, in a perpendicular direction to the plane of the laminate, invisible damage may develop. It is shown analytically and experimentally that the invisible damage occurs during the first stage of contact between the impactor and the laminate and is a result of the contact stresses. However, the residual flexural strength changes only slightly, because it depends mainly on the outer layers, and these remain undamaged. Repeated impact intensifies the damage inside the laminate and causes larger bending under equivalent impact load. Finally, when the damage is most severe, even though it is still invisible, the laminate fails because of bending on the tension side. If the repeated impact is halted before final fracture occurs the residual strength and modulus would decrease by a certain amount.
Matrix cracking in laminated composites under monotonic and cyclic loadings
NASA Technical Reports Server (NTRS)
Allen, David H.; Lee, Jong-Won
1991-01-01
An analytical model based on the internal state variable (ISV) concept and the strain energy method is proposed for characterizing the monotonic and cyclic response of laminated composites containing matrix cracks. A modified constitution is formulated for angle-ply laminates under general in-plane mechanical loading and constant temperature change. A monotonic matrix cracking criterion is developed for predicting the crack density in cross-ply laminates as a function of the applied laminate axial stress. An initial formulation for a cyclic matrix cracking criterion for cross-ply laminates is also discussed. For the monotonic loading case, a number of experimental data and well-known models are compared with the present study for validating the practical applicability of the ISV approach.
The strength of laminated composite materials under repeated impact loading
NASA Technical Reports Server (NTRS)
Rotem, Assa
1988-01-01
When low velocity and energy impact is exerted on a laminated composite material, in a perpendicular direction to the plane of the laminate, invisible damage may develop. It is shown analytically and experimentally that the invisible damage occurs during the first stage of contact between the impactor and the laminate and is a result of the contact stresses. However, the residual flexural strength changes only slightly, because it depends mainly on the outer layers, and these remain undamaged. Repeated impact intensifies the damage inside the laminate and causes larger bending under equivalent impact load. Finally, when the damage is most severe, even though it is still invisible, the laminate fails because of bending on the tension side. If the repeated impact is halted before final fracture occurs the residual strength and modulus would decrease by a certain amount.
Residual stresses and their effects in composite laminates
NASA Technical Reports Server (NTRS)
Hahn, H. T.; Hwang, D. G.
1983-01-01
Residual stresses in composite laminates are caused by the anisotropy in expansional properties of constituent unidirectional plies. The effect of these residual stresses on dimensional stability is studied through the warping of unsymmetric (0 sub 4/90 sub 4)sub T graphite/epoxy laminates while their effect on ply failure is analyzed for (0/90)sub 2s Kevlar 49/epoxy laminate. The classical laminated plate theory is used to predict the warping of small and large panels. The change of warping does not indicate a noticeable stress relaxation at 75 C while it is very sensitive to moisture content and hence to environment. A prolonged gellation at the initial cure temperature reduces residual stresses while postcure does not. The matrix/interface cracking in dry (0/90)sub 2s Kevlar 49/epoxy laminate is shown to be the result of the residual stress exceeding the transverse strength.
Matrix cracking in laminated composites under monotonic and cyclic loadings
NASA Technical Reports Server (NTRS)
Allen, David H.; Lee, Jong-Won
1991-01-01
An analytical model based on the internal state variable (ISV) concept and the strain energy method is proposed for characterizing the monotonic and cyclic response of laminated composites containing matrix cracks. A modified constitution is formulated for angle-ply laminates under general in-plane mechanical loading and constant temperature change. A monotonic matrix cracking criterion is developed for predicting the crack density in cross-ply laminates as a function of the applied laminate axial stress. An initial formulation for a cyclic matrix cracking criterion for cross-ply laminates is also discussed. For the monotonic loading case, a number of experimental data and well-known models are compared with the present study for validating the practical applicability of the ISV approach.
Progressive Failure Analysis Methodology for Laminated Composite Structures
NASA Technical Reports Server (NTRS)
Sleight, David W.
1999-01-01
A progressive failure analysis method has been developed for predicting the failure of laminated composite structures under geometrically nonlinear deformations. The progressive failure analysis uses C(exp 1) shell elements based on classical lamination theory to calculate the in-plane stresses. Several failure criteria, including the maximum strain criterion, Hashin's criterion, and Christensen's criterion, are used to predict the failure mechanisms and several options are available to degrade the material properties after failures. The progressive failure analysis method is implemented in the COMET finite element analysis code and can predict the damage and response of laminated composite structures from initial loading to final failure. The different failure criteria and material degradation methods are compared and assessed by performing analyses of several laminated composite structures. Results from the progressive failure method indicate good correlation with the existing test data except in structural applications where interlaminar stresses are important which may cause failure mechanisms such as debonding or delaminations.
Defect detection and evaluation of ultrasonic infrared thermography for aerospace CFRP composites
NASA Astrophysics Data System (ADS)
Yang, Bo; Huang, Yaoda; Cheng, Long
2013-09-01
The ultrasonic infrared thermography Non-destructive Testing is introduced for detecting the impact damage of a CFRP specimen for Unmanned Aerial Vehicles. The characteristics of thermal images with damage are particularly analyzed. A Local Binary Fitting (LBF) model based on a non-Gaussian kernel function is used to segment the defect edge. In view of the discontinuity of defect in thermal images due to multilayered structure of composite materials, defect merging algorithms are proposed including time domain and space domain methods by using a few thermal images, and the defect geometric distortion during camera imaging is also compensated. The defect in the composite material can be quantitatively analyzed after the defect reconstruction. The experimental result has shown that the proposed algorithm can effectively detect and evaluate the impact damage of thermal images and the accuracy of quantitative assessment is correspondingly increased.
Computational Modeling of Micro-Crack Induced Attenuation in CFRP Composites
NASA Technical Reports Server (NTRS)
Roberts, R. A.; Leckey, C. A. C.
2012-01-01
A computational study is performed to determine the contribution to ultrasound attenuation in carbon fiber reinforced polymer composite laminates of linear elastic scattering by matrix micro-cracking. Multiple scattering approximations are benchmarked against exact computational approaches. Results support linear scattering as the source of observed increased attenuation in the presence of micro-cracking.
Computational modeling of micro-crack induced attenuation in CFRP composites
NASA Astrophysics Data System (ADS)
Roberts, R. A.; Leckey, C. A. C.
2013-01-01
A computational study is performed to determine the contribution to ultrasound attenuation in carbon fiber reinforced polymer composite laminates of linear elastic scattering by matrix micro-cracking. Multiple scattering approximations are benchmarked against exact computational approaches. Results support linear scattering as the source of observed increased attenuation in the presence of micro-cracking.
Prediction of microcracking in composite laminates under thermomechanical loading
NASA Technical Reports Server (NTRS)
Maddocks, Jason R.; Mcmanus, Hugh L.
1995-01-01
Composite laminates used in space structures are exposed to both thermal and mechanical loads. Cracks in the matrix form, changing the laminate thermoelastic properties. An analytical methodology is developed to predict microcrack density in a general laminate exposed to an arbitrary thermomechanical load history. The analysis uses a shear lag stress solution in conjunction with an energy-based cracking criterion. Experimental investigation was used to verify the analysis. Correlation between analysis and experiment is generally excellent. The analysis does not capture machining-induced cracking, or observed delayed crack initiation in a few ply groups, but these errors do not prevent the model from being a useful preliminary design tool.
Interlaminar stresses in composite laminates: A perturbation analysis
NASA Technical Reports Server (NTRS)
Hsu, P. W.; Herakovich, C. T.
1976-01-01
A general method of solution for an elastic balanced symmetric composite laminate subject to a uniaxial extension was developed based upon a perturbation analysis of a limiting free body containing an interfacial plane. The solution satisfies more physical requirements and boundary conditions than previous investigations, and predicts smooth continuous interlaminar stresses with no instabilities. It determines the finite maximum intensity for the interlaminar normal stress in all laminates, provides mathematical evidences for the singular stresses in angle-ply laminates, suggests the need for the experimental determination of an important problem parameter, and introduces a viable means for solving related problems of practical interest.
Axisymmetric vibrations of laminated composite conical shells with varying thickness
Shikanai, G.; Suzuki, K.; Kojima, M.
1995-11-01
An exact solution procedure is presented for solving axisymmetric free vibrations of laminated composite conical shells with varying thickness. Based on the classical lamination theory neglecting shear deformation and rotary inertia, equations of motion and boundary conditions are obtained from the stationary conditions of the Lagrangian. The equations of motion are solved exactly by using a power series expansion for symmetrically laminated, cross-ply conical shells. Numerical studies are made for conical shells having both ends clamped to show the effects of the number of laminae, stacking sequences and other parameters upon the frequencies.
Vibration analysis of rotating thin laminated composite shell of revolution
Suzuki, K.; Shikanai, G.; Takayama, K.
1995-11-01
An exact solution procedure is presented for solving free vibrations of a rotating thin laminated composite shell of revolution having meridionally constant curvature. Based on the classical lamination theory, equations of motion and boundary conditions are obtained from the stationally conditions of the Lagrangian. The equations of motion are solved exactly by using a power series expansion for symmetrically laminated, cross-ply shells. Frequencies and mode shapes of the shells having both ends clamped and both ends freely supported are presented showing their variations with rotating angular velocity, number of laminae and other parameters.
Adhesive Wear Performance of CFRP Multilayered Polyester Composites Under Dry/wet Contact Conditions
NASA Astrophysics Data System (ADS)
Danaelan, D.; Yousif, B. F.
The tribo-performance of a new engineering composite material based on coconut fibers was investigated. In this work, coconut fibers reinforced polyester (CFRP) composites were developed. The tribo-experiments were conducted by using pin-on-disc machine under dry and wet sliding contact condition against smooth stainless steel counterface. Worn surfaces were observed using optical microscope. Friction coefficient and specific wear rate were presented as a function of sliding distance (0-0.6 km) at different sliding velocities (0.1-0.28 m/s). The effect of applied load and sliding velocity was evaluated. The results showed that all test parameters have significant influence on friction and wear characteristics of the composites. Moreover, friction coefficient increased as the normal load and speed increased, the values were about 0.7-0.9 under dry contact condition. Meanwhile, under wet contact condition, there was a great reduction in the friction coefficient, i.e. the values were about 0.1-0.2. Furthermore, the specific wear rates were found to be around 2-4 (10-3) mm3/Nm under dry contact condition and highly reduced under wet condition. In other words, the presence of water as cleaner and polisher assisted to enhance the adhesive wear performance of CFRP by about 10%. The images from optical microscope showed evidence of adhesive wear mode with transition to abrasive wear mode at higher sliding velocities due to third body abrasion. On the other hand, optical images for wet condition showed less adhesive wear and smooth surfaces.
Nonlinear analysis of laminated fibrous composites. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Renieri, G. D.; Herakovich, C. T.
1976-01-01
A computerized analysis of the nonlinear behavior of fibrous composite laminates including axial loading, thermal loading, temperature dependent properties, and edge effects is presented. Ramberg-Osgood approximations are used to represent lamina stress-strain behavior and percent retention curves are employed to model the variation of properties with temperature. Balanced, symmetric laminates comprised of either boron/epoxy, graphite/epoxy, or borsic-aluminum are analyzed using a quasi-three-dimensional finite element analysis. Results are presented for the interlaminar stress distributions in cross-ply, angle-ply, and more complex laminates. Nonlinear stress-strain curves for a variety of composite laminates in tension and compression are obtained and compared to other existing theories and experimental results.
Design and Ballistic Performance of Hybrid Composite Laminates
NASA Astrophysics Data System (ADS)
Ćwik, Tomasz K.; Iannucci, Lorenzo; Curtis, Paul; Pope, Dan
2017-06-01
This paper presents an initial design assessment of a series of novel, cost-effective, and hybrid composite materials for applications involving high velocity impacts. The proposed hybrid panels were designed in order to investigate various physical phenomenon occurring during high velocity impact on compliant laminates from a previous study on Dyneema® and Spectra®. In the first, screening phase of the study twenty different hybrid composite laminates were impacted with 20 mm Fragment Simulating Projectiles at 1 km/s striking velocity. The best performing concepts were put forward to phase II with other hybrid concepts involving shear thickening fluids, commonly used in low velocity impacts. The results indicated that it is possible to design hybrid laminates of similar ballistic performance as the reference Dyneema® laminate, but with lower material costs. The optimal hybrid concept involves a fibre reinforced Polypropylene front and a Dyneema® backing.
Fatigue of notched fiber composite laminates. Part 1: Analytical model
NASA Technical Reports Server (NTRS)
Mclaughlin, P. V., Jr.; Kulkarni, S. V.; Huang, S. N.; Rosen, B. W.
1975-01-01
A description is given of a semi-empirical, deterministic analysis for prediction and correlation of fatigue crack growth, residual strength, and fatigue lifetime for fiber composite laminates containing notches (holes). The failure model used for the analysis is based upon composite heterogeneous behavior and experimentally observed failure modes under both static and fatigue loading. The analysis is consistent with the wearout philosophy. Axial cracking and transverse cracking failure modes are treated together in the analysis. Cracking off-axis is handled by making a modification to the axial cracking analysis. The analysis predicts notched laminate failure from unidirectional material fatique properties using constant strain laminate analysis techniques. For multidirectional laminates, it is necessary to know lamina fatique behavior under axial normal stress, transverse normal stress and axial shear stress. Examples of the analysis method are given.
Design and Ballistic Performance of Hybrid Composite Laminates
NASA Astrophysics Data System (ADS)
Ćwik, Tomasz K.; Iannucci, Lorenzo; Curtis, Paul; Pope, Dan
2016-10-01
This paper presents an initial design assessment of a series of novel, cost-effective, and hybrid composite materials for applications involving high velocity impacts. The proposed hybrid panels were designed in order to investigate various physical phenomenon occurring during high velocity impact on compliant laminates from a previous study on Dyneema® and Spectra®. In the first, screening phase of the study twenty different hybrid composite laminates were impacted with 20 mm Fragment Simulating Projectiles at 1 km/s striking velocity. The best performing concepts were put forward to phase II with other hybrid concepts involving shear thickening fluids, commonly used in low velocity impacts. The results indicated that it is possible to design hybrid laminates of similar ballistic performance as the reference Dyneema® laminate, but with lower material costs. The optimal hybrid concept involves a fibre reinforced Polypropylene front and a Dyneema® backing.
Fracture behavior of hybrid composite laminates
NASA Technical Reports Server (NTRS)
Kennedy, J. M.
1983-01-01
The tensile fracture behavior of 15 center-notched hybrid laminates was studied. Three basic laminate groups were tested: (1) a baseline group with graphite/epoxy plies, (2) a group with the same stacking sequence but where the zero-deg plies were one or two plies of S-glass or Kevlar, and (3) a group with graphite plies but where the zero-deg plies were sandwiched between layers of perforated Mylar. Specimens were loaded linearly with time; load, far field strain, and crack opening displacement (COD) were monitored. The loading was stopped periodically and the notched region was radiographed to reveal the extent and type of damage (failure progression). Results of the tests showed that the hybrid laminates had higher fracture toughnesses than comparable all-graphite laminates. The higher fracture toughness was due primarily to the larger damage region at the ends of the slit; delamination and splitting lowered the stress concentration in the primary load-carrying plies. A linear elastic fracture analysis, which ignored delamination and splitting, underestimated the fracture toughness. For almost all of the laminates, the tests showed that the fracture toughness increased with crack length. The size of the damage region at the ends of the slit and COD measurements also increased with crack length.
Damage Tolerance of Composite Laminates from an Empirical Perspective
NASA Technical Reports Server (NTRS)
Nettles, Alan T.
2009-01-01
Damage tolerance consists of analysis and experimentation working together. Impact damage is usually of most concern for laminated composites. Once impacted, the residual compression strength is usually of most interest. Other properties may be of more interest than compression (application dependent). A damage tolerance program is application specific (not everyone is building aircraft). The "Building Block Approach" is suggested for damage tolerance. Advantage can be taken of the excellent fatigue resistance of damaged laminates to save time and costs.
Nonlinear effects on composite laminate thermal expansion
NASA Technical Reports Server (NTRS)
Hashin, Z.; Rosen, B. W.; Pipes, R. B.
1979-01-01
Analyses of Graphite/Polyimide laminates shown that the thermomechanical strains cannot be separated into mechanical strain and free thermal expansion strain. Elastic properties and thermal expansion coefficients of unidirectional Graphite/Polyimide specimens were measured as a function of temperature to provide inputs for the analysis. The + or - 45 degrees symmetric Graphite/Polyimide laminates were tested to obtain free thermal expansion coefficients and thermal expansion coefficients under various uniaxial loads. The experimental results demonstrated the effects predicted by the analysis, namely dependence of thermal expansion coefficients on load, and anisotropy of thermal expansion under load. The significance of time dependence on thermal expansion was demonstrated by comparison of measured laminate free expansion coefficients with and without 15 day delay at intermediate temperature.
Electron radiation effects on Mode II interlaminar fracture toughness of GFRP and CFRP composites
Takeda, N.; Tohdoh, M.; Takahashi, K.
1989-01-01
The degradation properties of epoxy-based fiber-reinforced-plastics (FRP) composites irradiated by high-energy electrons were studied using the Mode II interlaminar fracture toughness G/sub IIc/, measured by end-notched flexure tests. The radiation-induced degradation mechanisms were investigated through G/sub IIc/ and the scanning electron micrographs of fracture surfaces. For GFRP, the significant decrease in G/sub IIc/ was found. Debonding of glass fibers and epoxy matrix (or degradation of silane coupling agents) plays an important role in degradation in addition to resin degradation. Thus, the improvement of the radiation resistance of fiber-resin interfaces as well as matrix itself is of supreme importance in order to increase the radiation resistance of GFRP. For CFRP, on the other hand, no degradation in fiber-resin interfaces was found and the slight decrease in G/sub IIc/ seems to be due to the resin degradation. 18 references, 6 figures.
Matt, Howard M.
2006-01-01
To monitor in-flight damage and reduce life-cycle costs associated with CFRP composite aircraft, an autonomous built-in structural health monitoring (SHM) system is preferred over conventional maintenance routines and schedules. This thesis investigates the use of ultrasonic guided waves and piezoelectric transducers for the identification and localization of damage/defects occurring within critical components of CFRP composite aircraft wings, mainly the wing skin-to-spar joints. The guided wave approach for structural diagnostics was demonstrated by the dual application of active and passive monitoring techniques. For active interrogation, the guided wave propagation problem was initially studied numerically by a semi-analytical finite element method, which accounts for viscoelastic damping, in order to identify ideal mode-frequency combinations sensitive to damage occurring within CFRP bonded joints. Active guided wave tests across three representative wing skin-to-spar joints at ambient temperature were then conducted using attached Macro Fiber Composite (MFC) transducers. Results from these experiments demonstrate the importance of intelligent feature extraction for improving the sensitivity to damage. To address the widely neglected effects of temperature on guided wave base damage identification, analytical and experimental analyses were performed to characterize the influence of temperature on guided wave signal features. In addition, statistically-robust detection of simulated damage in a CFRP bonded joint was successfully achieved under changing temperature conditions through a dimensionally-low, multivariate statistical outlier analysis. The response of piezoceramic patches and MFC transducers to ultrasonic Rayleigh and Lamb wave fields was analytically derived and experimentally validated. This theory is useful for designing sensors which possess optimal sensitivity toward a given mode-frequency combination or for predicting the frequency dependent
Interlaminate Deformation in Thermoplastic Composite Laminates: Experimental-Numerical Correlation
NASA Astrophysics Data System (ADS)
Shen, M.; Tong, J.; Wang, S.; Fang, Y.
2010-06-01
The interlaminar deformation behaviors of thermoplastic AS4/PEEK composite laminates subjected to static tensile loading are investigated by means of microscopic moiré interferometry with high spatial resolution. The fully threedimensional orthotropic elastic-plastic analysis of interlaminar deformation for the thermoplastic laminates is developed in this paper, and used to simulate the stress-strain curves of tensile experiment for its angle-ply laminates. Under uniaxial tensile loading, the 3D orthotropic elastic-plastic FE analysis and microscopic moiré interferometry of interlaminar deformations are carried out for the [±25]S4 laminates. The quantitative local-filed experimental results of interlaminar shear strain and displacements at freeedge surface of the laminate are compared with corresponding numerical results of the orthotropic elastic-plastic FE model. It is indicated that the numerical tensile stressstrain curves of angle-ply laminates computed with 3D orthotropic elastic-plastic model are agree with experimental results. The numerical interlaminar displacement U and shear strain γxz are also consistent with the experimental results obtained by moiré interferometry. It is expected the elastic-plastic interlaminar stresses and deformations analysis for the optimal design and application of AS4/PEEK laminates and its structures.
Damage Processes and Fracture Surface Morphology in Laminated Composites
1990-08-01
Morphology in Laminated Composites 6. AUTHOR(S) M Bryan H. Fortson 2 PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION rijREPORT...LAMINATED COMPOSITES Approved: Erian A. Armanios, Chairman Stephq D. Antolovich Victor L. Berdichevsky Georgedyrdomateas Charles E. Uenr’( ’-6 Date...Introduction 2.2 Descriptions of Delam-ination 2.3 Analyses of Short-Bea- m Tests 2.4 Relevant Work in Materials Science 2.5 Survey of Composite Specimen
A higher order theory of laminated composite cylindrical shells
NASA Technical Reports Server (NTRS)
Krishna Murthy, A. V.; Reddy, T. S. R.
1986-01-01
A new higher order theory has been proposed for the analysis of composite cylindrical shells. The formulation allows for arbitrary variation of inplane displacements. Governing equations are presented in the form of a hierarchy of sets of partial differential equations. Each set describes the shell behavior to a certain degree of approximation. The natural frequencies of simply-supported isotropic and laminated shells and stresses in a ring loaded composite shell have been determined to various orders of approximation and compared with three dimensional solutions. These numerical studies indicate the improvements achievable in estimating the natural frequencies and the interlaminar shear stresses in laminated composite cylinders.
Three dimensional inelastic finite element analysis of laminated composites
NASA Technical Reports Server (NTRS)
Griffin, O. H., Jr.; Kamat, M. P.
1980-01-01
Formulations of the inelastic response of laminated composites to thermal and mechanical loading are used as the basis for development of the computer NALCOM (Nonlinear Analysis of Laminated Composites) computer program which uses a fully three dimensional isoparametric finite element with 24 nodes and 72 degrees of freedom. An incremental solution is performed with nonlinearities introduced as pseudoloads computed for initial strains. Equilibrium iteration may be performed at every step. Elastic and elastic-plastic response of boron/epoxy and graphite/epoxy graphite/epoxy and problems of curing 0/90 sub s Gr/Ep laminates with and without circular holes are analyzed. Mechanical loading of + or - 45sub s Gr/Ep laminates is modeled and symmetry conditions which exist in angle-ply laminates are discussed. Results are compared to experiments and other analytical models when possible. All models are seen to agree reasonably well with experimetnal results for off-axis tensile coupons. The laminate analyses show the three dimensional effects which are present near holes and free corners.
Vibration analysis of composite laminate plate excited by piezoelectric actuators.
Her, Shiuh-Chuan; Lin, Chi-Sheng
2013-03-01
Piezoelectric materials can be used as actuators for the active vibration control of smart structural systems. In this work, piezoelectric patches are surface bonded to a composite laminate plate and used as vibration actuators. A static analysis based on the piezoelectricity and elasticity is conducted to evaluate the loads induced by the piezoelectric actuators to the host structure. The loads are then employed to develop the vibration response of a simply supported laminate rectangular plate excited by piezoelectric patches subjected to time harmonic voltages. An analytical solution of the vibration response of a simply supported laminate rectangular plate under time harmonic electrical loading is obtained and compared with finite element results to validate the present approach. The effects of location and exciting frequency of piezoelectric actuators on the vibration response of the laminate plate are investigated through a parametric study. Numerical results show that modes can be selectively excited, leading to structural vibration control.
Vibration Analysis of Composite Laminate Plate Excited by Piezoelectric Actuators
Her, Shiuh-Chuan; Lin, Chi-Sheng
2013-01-01
Piezoelectric materials can be used as actuators for the active vibration control of smart structural systems. In this work, piezoelectric patches are surface bonded to a composite laminate plate and used as vibration actuators. A static analysis based on the piezoelectricity and elasticity is conducted to evaluate the loads induced by the piezoelectric actuators to the host structure. The loads are then employed to develop the vibration response of a simply supported laminate rectangular plate excited by piezoelectric patches subjected to time harmonic voltages. An analytical solution of the vibration response of a simply supported laminate rectangular plate under time harmonic electrical loading is obtained and compared with finite element results to validate the present approach. The effects of location and exciting frequency of piezoelectric actuators on the vibration response of the laminate plate are investigated through a parametric study. Numerical results show that modes can be selectively excited, leading to structural vibration control. PMID:23529121
Thermal buckling and postbuckling of symmetrically laminated composite plates
NASA Technical Reports Server (NTRS)
Meyers, C. A.; Hyer, M. W.
1991-01-01
The thermal buckling and postbuckling response of symmetrically laminated composite plates are discussed. Using variational methods in conjunction with a Rayleigh-Ritz formulation, thermal buckling and postbuckling are investigated for two laminates, a (+/- 45/0/90) and a (+/- 45/02), under two different simple support conditions, fixed and sliding. These laminates are subjected to the condition of a uniform temperature change. The effects of the principal material axis not being aligned with the edges of the plate, referred to here as material axis skewing, are also investigated. Although differences between buckling temperatures for the two support conditions were small, support conditions can have a large influence on thermal postbuckling response. In general, plates with fixed simple supports deflect more than plates with sliding simple supports. In addition, support conditions can influence modal interaction. Skewing of the material axis decreases the buckling temperatures of both laminates and, like fixed support conditions, causes increased postbuckling deflections. Skewing also influences modal interaction.
Modelling of thick composites using a layerwise laminate theory
NASA Technical Reports Server (NTRS)
Robbins, D. H., Jr.; Reddy, J. N.
1993-01-01
The layerwise laminate theory of Reddy (1987) is used to develop a layerwise, two-dimensional, displacement-based, finite element model of laminated composite plates that assumes a piecewise continuous distribution of the tranverse strains through the laminate thickness. The resulting layerwise finite element model is capable of computing interlaminar stresses and other localized effects with the same level of accuracy as a conventional 3D finite element model. Although the total number of degrees of freedom are comparable in both models, the layerwise model maintains a 2D-type data structure that provides several advantages over a conventional 3D finite element model, e.g. simplified input data, ease of mesh alteration, and faster element stiffness matrix formulation. Two sample problems are provided to illustrate the accuracy of the present model in computing interlaminar stresses for laminates in bending and extension.
Contact analysis for riveted and bolted joints of composite laminates
NASA Astrophysics Data System (ADS)
Ye, Tian-Qi; Li, Wei; Shen, Guanqing
The computational strategy and numerical technique developed are demonstrated to be efficient for the analysis of riveted and bolted joints of composite laminates. The 3D contact analysis provides more accurate results for the evaluation of strength of the mechanically fastened joints in the composite structures. The method described can be extended to multibody contact problems, it has been implemented in the computer codes.
Finite element analyses of wood laminated composite poles
Cheng Piao; Todd F. Shupe; R.C. Tang; Chung Y. Hse
2005-01-01
Finite element analyses using ANSYS were conducted on orthotropic, polygonal, wood laminated composite poles subjected to a body force and a concentrated load at the free end. Deflections and stress distributions of small-scale and full-size composite poles were analyzed and compared to the results obtained in an experimental study. The predicted deflection for both...
Damage Precursor Investigation of Fiber-Reinforced Composite Materials Under Fatigue Loads
2013-09-01
Damage Detection of CFRP Laminates Using Electrical Resistance Measurement and Neural Network. Composite Structures 1999, 47.1, 525–530. Sharma, R...Normal Stress States of Transversely Loaded UD- CFRP from Viewpoint of Failure Initiation. Composites Science and Technology 2009, 69.11, 1726–1734
Design and optimization of the CFRP mirror components
NASA Astrophysics Data System (ADS)
Wei, Lei; Zhang, Lei; Gong, Xiaoxue
2017-09-01
As carbon fiber reinforced polymer (CFRP) material has been developed and demonstrated as an effective material in lightweight telescope reflector manufacturing recently, the authors of this article have extended to apply this material on the lightweight space camera mirror design and fabrication. By CFRP composite laminate design and optimization using finite element method (FEM) analysis, a spherical mirror with φ316 mm diameter whose core cell reinforcement is an isogrid configuration is fabricated. Compared with traditional ways of applying ultra-low-expansion glass (ULE) on the CFRP mirror surface, the method of nickel electroplating on the surface effectively reduces the processing cost and difficulty of the CFRP mirror. Through the FEM analysis, the first order resonance frequency of the CFRP mirror components reaches up to 652.3 Hz. Under gravity affection coupling with +5°C temperature rising, the mirror surface shape root-mean-square values (RMS) at the optical axis horizontal state is 5.74 nm, which meets mechanical and optical requirements of the mirror components on space camera.
Hybrid Titanium Composite Laminates: A New Aerospace Material
NASA Technical Reports Server (NTRS)
Johnson, W. S.; Cobb, Ted Q.; Lowther, Sharon; St.Clair, T. L.
1998-01-01
In the realm of aerospace design and performance, there are few boundaries in the never-ending drive for increased performance. This thirst for ever-increased performance of aerospace equipment has driven the aerospace and defense industries into developing exotic, extremely high-performance composites that are pushing the envelope in terms of strength-to-weight ratios, durability, and several other key measurements. To meet this challenge of ever-increasing improvement, engineers and scientists at NASA-Langley Research Center (NASA-LaRC) have developed a high-temperature metal laminate based upon titanium, carbon fibers, and a thermoplastic resin. This composite, known as the Hybrid Titanium Composite Laminate, or HTCL, is the latest chapter in a significant, but relatively short, history of metal laminates.
Mechanisms of compressive failure in woven composites and stitched laminates
NASA Technical Reports Server (NTRS)
Cox, B. N.; Dadkhah, M. S.; Inman, R. V.; Morris, W. L.; Schroeder, S.
1992-01-01
Stitched laminates and angle interlock woven composites have been studied in uniaxial, in-plane, monotonic compression. Failure mechanisms have been found to depend strongly on both the reinforcement architecture and the degree of constraint imposed by the loading grips. Stitched laminates show higher compressive strength, but are brittle, possessing no load bearing capacity beyond the strain for peak load. Post-mortem inspection shows a localized shear band of buckled and broken fibers, which is evidently the product of an unstably propagating kink band. Similar shear bands are found in the woven composites if the constraint of lateral displacements is weak; but, under strong constraint, damage is not localized but distributed throughout the gauge section. While the woven composites tested are weaker than the stitched laminates, they continue to bear significant loads to compressive strains of approx. 15 percent, even when most damage is confined to a shear band.
Investigating Delamination Migration in Composite Tape Laminates
NASA Technical Reports Server (NTRS)
Ratcliffe, James G.; DeCarvalho, Nelson V.
2014-01-01
A modification to a recently developed test specimen designed to investigate migration of a delamination between neighboring ply interfaces in tape laminates is presented. The specimen is a cross-ply laminated beam consisting of 40 plies with a polytetrafluoroethylene insert spanning part way along its length. The insert is located between a lower 0-degree ply (specimen length direction) and a stack of four 90-degree plies (specimen width direction). The modification involved a stacking sequence that promotes stable delamination growth prior to migration, and included a relocation of the insert from the specimen midplane to the interface between plies 14 and 15. Specimens were clamped at both ends onto a rigid baseplate and loaded on their upper surface via a piano hinge assembly, resulting in a predominantly flexural loading condition. Tests were conducted with the load-application point positioned at various locations along a specimen's span. This position affected the sequence of damage events during a test.
Nondimensional impact models for composite laminates
NASA Technical Reports Server (NTRS)
Sankar, B. V.; Nguyen, P. T.; Ku, C.
1990-01-01
The equations governing the problem of low-velocity impact of a simply supported rectangular laminated plate are nondimensionalized such that the problem is defined in terms of five dimensionless parameters. A parametric study using the Graeco-Latin Factorial Plan is performed. Semi-empirical formulas for maximum impact force, impact duration, and maximum back surface strains are obtained. It is found that some of the simple impact models provide the bounds for the case of impact on a finite extent plate.
Ultrasonic nondestructive evaluation of graphite epoxy composite laminates
NASA Technical Reports Server (NTRS)
Miller, James G.
1990-01-01
Quantitative ultrasonic techniques are summarized with applications to the measurement of frequency-dependent attenuation and backscatter and to the NDE of composite laminates. Results are listed for the ultrasonic NDE of graphite-epoxy composite laminates including impact and fatigue damage as well as porosity. The methods reviewed include transmission measurements of attenuation, reconstructive tomography based on attenuation, estimating attenuation from backscattered ultrasound, and backscatter approaches. Phase-sensitive and -insensitive detection techniques are mentioned such as phase cancellation at piezoelectric receiving transducers and acoustoelectric effects. The techniques permit the NDE of the parameters listed in inhomogeneous media and provide both images from the transmission mode and in the reflection mode.
Laminated structures and methods and compositions for producing same
Fumei, Giancarlo J.; Karabedian, James A.
1977-04-05
Methods for bonding two substrates, one of which is polymeric, which comprise coating the surface of at least one substrate with an adhesive composition comprising a major component which is an adhesive for the first substrate and a minor disperse phase which is a solution of a polymer in a solvent for the polymeric substrate and contacting the coated surface of the one substrate with the surface of the other substrate, together with adhesive compositions useful for joining such substrates, laminates so formed, and articles comprised of such laminates.
Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Smeltzer, Stanley S., III
2000-01-01
An analytical, parametric study of the attenuation of bending boundary layers or edge effects in balanced and unbalanced, symmetrically and unsymmetrically laminated thin cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize and quantify the effects of laminate orthotropy and laminate anisotropy on the bending boundary-layer decay length in a very general and encompassing manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all the laminate constructions considered, the results show that the differences between results that were obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that in some cases neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and in other cases it results in an overestimation.
Current Distribution Characteristics of CFRP Panels
NASA Astrophysics Data System (ADS)
Yamamoto, Kazuo
CFRP (Carbon Fiber Reinforced Plastic) is widely used in the structures of aircrafts, automobiles, wing turbines, and rockets because of its qualities of high mechanical strength, low weight, fatigue resistance, and dimensional stability. However, these structures are often at risk of being struck by lightning. When lightning strikes such structures and lightning current flows through the CFRP, it may be structurally damaged because of the impact of the lightning strike or ignitions between layers. If there are electronic systems near the CFRP, they may break down or malfunction because of the resulting electromagnetic disturbance. In fact, the generation mechanisms of these breakdowns and malfunctions depend on the current distribution in the CFRP. Hence, it is critical to clarify the current distribution in various kinds of CFRPs. In this study, two kinds of CFRP panels—one composed of quasi-isotropic lamination layers and the other composed of 0°/90° lamination layers of unidirectional CFRP prepregs—are used to investigate the dependence of current distribution on the nature of the lamination layers. The current distribution measurements and simulations for CFRP panels are compared with those for a same-sized aluminum plate. The knowledge of these current distribution characteristics would be very useful for designing the CFRP structures of aircrafts, automobiles, wing turbines, rockets, etc. in the future.
Self-sensing and self-actuating CFRP structure using partially flexible composites
NASA Astrophysics Data System (ADS)
Kumagai, Keisuke; Todoroki, A.; Matsuzaki, Ryosuke
2008-03-01
For Unmanned aerial vehicles, a morphing wing is desired to improve the maneuverability and reduce the total weight of structures. Our research group has developed a foldable composite structure for a morphing wing skin plate by using Carbon Fiber Reinforced Plastics (CFRP). The material system is called Partially Flexible Composites (PFC). In the present paper, PFC is introduced and a self-sensing system of the PFC is investigated. Since carbon fibers have electrical conductivity, damages of the PFC can be detected by monitoring electrical resistance changes of the PFC. This method is called Electrical Resistance Changes Method. An electrical resistance model of the PFC is built and a relationship of ratio of fiber fractures and electrical resistance changes is obtained. Then, to investigate the performance of the PFC, cyclic-bending tests are conducted. Damages of the PFC caused by cyclic-bending are detected by using ERCM. As a result, the PFC with more than 10mm-long flexible part has almost no damage; the stiffness of the structure remains unchanged. After that, a McKibben pneumatic artificial muscles actuator is made and it is founded that this can be applied to the PFC as an actuator. This actuator consists of a silicon rubber and a carbon fiber that are the same as the material of flexible part of the PFC. This enables us to make actuator-integrated composite structures. In the present study, the applicability of the McKibben pneumatic artificial muscles actuator is investigated.
Damage prediction in cross-plied curved composite laminates
NASA Technical Reports Server (NTRS)
Martin, Roderick H.; Jackson, Wade C.
1991-01-01
Analytical and experimental work is detailed which is required to predict delamination onset and growth in a curved cross plied composite laminate subjected to static and fatigue loads. The composite used was AS4/3501/6, graphite/epoxy. Analytically, a closed form stress analysis and 2-D and 3-D finite element analyses were conducted to determine the stress distribution in an undamaged curved laminate. The finite element analysis was also used to determine values of strain energy release rate at a delamination emanating from a matrix crack in a 90 deg ply. Experimentally, transverse tensile strength and fatigue life were determined from flat 90 deg coupons. The interlaminar tensile strength and fatigue life were determined from double cantilevered beam specimens. Cross plied curved laminates were tested statically and in fatigue to give a comparison to the analytical predictions. A comparison of the fracture mechanics life prediction technique and the strength based prediction technique is given.
Compression and compression fatigue testing of composite laminates
NASA Technical Reports Server (NTRS)
Porter, T. R.
1982-01-01
The effects of moisture and temperature on the fatigue and fracture response of composite laminates under compression loads were investigated. The structural laminates studied were an intermediate stiffness graphite-epoxy composite (a typical angle ply laimna liminate had a typical fan blade laminate). Full and half penetration slits and impact delaminations were the defects examined. Results are presented which show the effects of moisture on the fracture and fatigue strength at room temperature, 394 K (250 F), and 422 K (300 F). Static tests results show the effects of defect size and type on the compression-fracture strength under moisture and thermal environments. The cyclic tests results compare the fatigue lives and residual compression strength under compression only and under tension-compression fatigue loading.
Fatigue Damage in CFRP Woven Fabric Composites through Dynamic Modulus Measurements
Chiaki Miyasaka; K. L. Telschow
2004-07-01
Advanced fiber reinforced composite materials offer substantial advantages over metallic materials for the structural applications subjected to fatigue loading. With the increasing use of these composites, it is required to understand their mechanical response to cyclic loading (1)-(4). Our major concern in this work is to macroscopically evaluate the damage development in composites during fatigue loading. For this purpose, we examine what effect the fatigue damage may have on the material properties and how they can be related mathematically to each other. In general, as the damage initiates in composite materials and grows during cyclic loading, material properties such as modulus, residual strength and strain would vary and, in many cases, they may be significantly reduced because of the progressive accumulation of cracks. Therefore, the damage can be characterized by the change in material properties, which is expected to be available for non-destructive evaluation of the fatigue damage development in composites. Here, the tension-tension fatigue tests are firstly conducted on the plain woven fabric carbon fiber composites for different loading levels. In the fatigue tests, the dynamic elastic moduli are measured on real-time, which will decrease with an increasing number of cycles due to the degradation of stiffness. Then, the damage function presenting the damage development during fatigue loading is determined from the dynamic elastic moduli thus obtained, from which the damage function is formulated in terms of a number of cycles and an applied loading level. Finally, the damage function is shown to be applied for predicting the remaining lifetime of the CFRP composites subjected to two-stress level fatigue loading.
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Hopkins, Dale A.
1993-01-01
The boundary element method is utilized to analyze the effects of fiber/matrix interfaces on the micromechanical behavior of laminated composites as well as the elastic behavior of woven composites. Effective composite properties are computed for laminated SiC/RBSN and SiC/Ti-15-3 composites, as well as a woven SiC/SiC composite. The properties calculated using the computerized tool BEST-CMS match the experimental results well.
NASA Astrophysics Data System (ADS)
Lepedat, Karin; Wagner, Robert; Lang, Jürgen
The use of phenolic resin for the impregnation of a carrier material such as paper or fabric based on either organic or inorganic fibers was and still is one of the most important application areas for liquid phenolic resins. Substrates like paper, cotton, or glass fabric impregnated with phenolic resins are used as core layers for decorative and technical laminates and for many other different industrial applications. Nowadays, phenolic resins for decorative laminates used for furniture, flooring, or in the construction and transportation industry have gained significant market share. The Laminates chapter mainly describes the manufacture of decorative laminates especially the impregnation and pressing process with special emphasis to new technological developments and recent trends. Moreover, the different types of laminates are introduced, combined with some brief comments as they relate to the market for decorative surfaces.
NASA Astrophysics Data System (ADS)
Park, Yurim; Shrestha, Pratik; Kwon, Hyunseok; Kim, Jin-Hyuk; Kwon, Heejung; Kim, Chun-Gon
2016-04-01
Applications of composite materials in aerospace structures is increasing due to the outstanding properties, however, monitoring such composite structures exposed to harsh environments is still a posing issue. Low Earth orbit space structures are exposed to property degradation and damage from high-degree vacuum, ultraviolet radiation, thermal cycling, and atomic oxygen attack which are detrimental to composite materials. In this study, FBG sensors for embedding in CFRP composite plates in different thickness locations to provide health and damage monitoring of the material exposed to such environments regarding the overall health of the material with a focus on the exposed surface are explored in comparison to conventional FBG sensors.
NASA Astrophysics Data System (ADS)
Williams, Kevin Vaughan
Rapid growth in use of composite materials in structural applications drives the need for a more detailed understanding of damage tolerant and damage resistant design. Current analytical techniques provide sufficient understanding and predictive capabilities for application in preliminary design, but current numerical models applicable to composites are few and far between and their development into well tested, rigorous material models is currently one of the most challenging fields in composite materials. The present work focuses on the development, implementation, and verification of a plane-stress continuum damage mechanics based model for composite materials. A physical treatment of damage growth based on the extensive body of experimental literature on the subject is combined with the mathematical rigour of a continuum damage mechanics description to form the foundation of the model. The model has been implemented in the LS-DYNA3D commercial finite element hydrocode and the results of the application of the model are shown to be physically meaningful and accurate. Furthermore it is demonstrated that the material characterization parameters can be extracted from the results of standard test methodologies for which a large body of published data already exists for many materials. Two case studies are undertaken to verify the model by comparison with measured experimental data. The first series of analyses demonstrate the ability of the model to predict the extent and growth of damage in T800/3900-2 carbon fibre reinforced polymer (CFRP) plates subjected to normal impacts over a range of impact energy levels. The predicted force-time and force-displacement response of the panels compare well with experimental measurements. The damage growth and stiffness reduction properties of the T800/3900-2 CFRP are derived using published data from a variety of sources without the need for parametric studies. To further demonstrate the physical nature of the model, a IM6
Analysis of damage in composite laminates under bending
NASA Astrophysics Data System (ADS)
Kuriakose, Sunil
The focus of this research was damage formation in composite laminates subjected to bending. Matrix cracking and internal delamination are common damage modes before final failure for a composite laminate under thermo-mechanical loading. Two configurations of cross-ply laminates, namely [0m/90 n]s and [90m/0n]s, were considered for the study. Approximate analytical solutions for the stress states in the two laminates subjected to constant bending moment, with matrix cracks in the 90° layers, were derived using a variational approach. The evolution of matrix cracking under monotonically increasing load was studied for a number of composite materials. The analytical predictions showed an initial stage of rapid matrix crack multiplication followed by a slowing down in the crack multiplication. In the case of [0m/90n] s laminate, 0° ply failure in tension or compression was found to be likely even at the initial stages of matrix cracking for laminates with thin 90° layer. The 0° ply failure is delayed for laminates with thicker 90° layer. The analytical model for the stress state in the [90m/0 n]s laminate was extended to include delamination from the matrix crack-tip along the 0/90 interface. The bending moment required to initiate crack-tip delamination was computed as a function of the crack density. By comparing this result with matrix crack evolution, the relative dominance of the two modes of damage could be determined. The critical crack density beyond which delamination dominates matrix cracking is obtained from the analysis. The critical crack density is interpreted as the stage beyond which growth of delamination rather than matrix cracking is likely to occur. Parametric studies conducted by varying the laminate configuration showed that the critical crack density for delamination onset strongly depends on the thickness of the 90° layer and the distance of the 90° layer from the laminate mid-plane. Quasi-static growth of delamination under monotonic
High resolution imaging of impacted CFRP composites with a fiber-optic laser-ultrasound scanner.
Pelivanov, Ivan; Ambroziński, Łukasz; Khomenko, Anton; Koricho, Ermias G; Cloud, Gary L; Haq, Mahmoodul; O'Donnell, Matthew
2016-06-01
Damage induced in polymer composites by various impacts must be evaluated to predict a component's post-impact strength and residual lifetime, especially when impacts occur in structures related to human safety (in aircraft, for example). X-ray tomography is the conventional standard to study an internal structure with high resolution. However, it is of little use when the impacted area cannot be extracted from a structure. In addition, X-ray tomography is expensive and time-consuming. Recently, we have demonstrated that a kHz-rate laser-ultrasound (LU) scanner is very efficient both for locating large defects and evaluating the material structure. Here, we show that high-quality images of damage produced by the LU scanner in impacted carbon-fiber reinforced polymer (CFRP) composites are similar to those produced by X-ray tomograms; but they can be obtained with only single-sided access to the object under study. Potentially, the LU method can be applied to large components in-situ.
Theoretical modeling and experimental analyses of laminated wood composite poles
Cheng Piao; Todd F. Shupe; Vijaya Gopu; Chung Y. Hse
2005-01-01
Wood laminated composite poles consist of trapezoid-shaped wood strips bonded with synthetic resin. The thick-walled hollow poles had adequate strength and stiffness properties and were a promising substitute for solid wood poles. It was necessary to develop theoretical models to facilitate the manufacture and future installation and maintenance of this novel...
Mechanical properties of small-scale wood laminated composite poles
Cheng Piao; Todd F. Shupe; Chung Y. Hse
2004-01-01
Power companies in the United States consume millions of solid wood poles every year. These poles are from high-valued trees that are becoming more expensive and less available. wood laminated composite poles (LCP) are a novel alternative to solid wood poles. LCP consists of trapezoid wood strips that are bonded by a synthetic resin. The wood strips can be made from...
Interface fracture and composite deformation of model laminates
NASA Astrophysics Data System (ADS)
Fox, Matthew R.
Model laminates were studied to improve the understanding of composite mechanical behavior. NiAl/Mo and NiAl/Cr model laminates, with a series of interfaces, were bonded at 1100°C. Reaction layers were present in all laminates, varying in thickness with bonding conditions. Interface fracture strengths and resistances were determined under primarily mode II loading conditions using a novel technique, the asymmetrically-loaded shear (ALS) test, in which one layer of the laminate was loaded in compression, producing a stable interface crack. The NiAl/Mo interface was also fractured in four-point bending. A small amount of plasticity was found to play a role in crack initiation. During steady-state mode II interface fracture of NiAl/Mo model laminates, large-scale slip was observed near the crack tip in the NiAl adjacent to the interface. After testing, the local slope and curvature of the interface were characterized at intervals along the interface and at slip locations to qualitatively describe local stresses present at and just ahead of the crack tip. The greatest percentage of slip occurred where closing forces on the crack tip were below the maximum value and were decreasing with crack growth. A mechanism for crack propagation is presented describing the role of large-scale slip in crack propagation. The mechanical response of structural laminates in 3-D stress states, as would be present in a polycrystalline aggregate composed of lamellar grains, are lacking. In order to understand the response of laminates composed of hard and soft phases, Pb/Zn laminates were prepared and tested in compression with varying lamellar orientation relative to the loading axis. A model describing the mechanical response in a general state assuming elastic-perfectly plastic isotropic layers was developed. For the 90° laminate, a different approach was applied, using the friction hill concepts used in forging analyses. With increasing ratios of cross-sectional radius to layer
Multiscale modeling of damage in multidirectional composite laminates
NASA Astrophysics Data System (ADS)
Singh, Chandra Veer
The problem of damage accumulation in laminated composite materials has received much attention due to their widespread application in the aerospace, automotive, civil, and sports industries. In the aerospace industry, composites are used to make light weight and efficient structural components. In the Boeing 787, for example, more than 50% of the structure is made of composite materials. Although there have been significant developments in analyzing cross-ply laminates, none of the present approaches provides reasonable predictions for multidirectional laminates in which intralaminar cracks may form in multiple orientations. Nevertheless, the prediction of damage accumulation and its effect on structural performance is a very difficult problem due to complexity of the cracking processes. This study presents a synergistic damage mechanics (SDM) methodology to analyze damage behavior in multidirectional composite laminates with intralaminar cracks in plies of multiple orientations. SDM combines the strengths of micro-damage mechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to these cracks. The micromechanics is performed on a representative unit cell using a three-dimensional finite element analysis to calculate the crack opening displacement accounting for the influence of the surrounding plies, the so-called constraint effect. This information is then incorporated in the CDM formulation dealing with laminates containing cracks in different ply orientations through a 'constraint parameter'. Following CDM, a separate damage mode is defined for each type of crack and the expressions for engineering moduli of the damaged laminate are then derived in terms of crack density and the constraint parameter. The SDM methodology is implemented for [0 m/+/- thetan/0 m/2]s laminates containing cracks in +/-theta plies. It is then extended to [0m /+/- thetan/90 r]s and [0m/90 r/+/- thetan] s laminates with cracks additionally in the
Design, fabrication, and characterization of laminated hydroxyapatite-polysulfone composites
NASA Astrophysics Data System (ADS)
Wilson, Clifford Adams, II
There exists a need to develop devices that can be used to replace hard tissues, such as bone, in load-bearing areas of the body. An ideal hard tissue replacement device is one that stimulates growth of natural tissues, and is slowly resorbed by the body. The implant is also required to have elastic modulus, strength, and toughness values similar to the tissues being replaced. Hydroxyapatite (HA) is the primary mineral phase of bone and has the potential for use in biomedical applications because it stimulates cell growth and is resorbable. Unfortunately, HA is a relatively low strength, low toughness material, which limits its application to only low load-bearing regions of the body. In order to apply HA to greater load-bearing areas of the body, strength and toughness must be improved through the formation of a composite structure. The goal of this study to show that a composite structure formed from HA and a biocompatible polymer can be fabricated with strength and toughness values that are within the range necessary for load-bearing biomedical applications. Therefore, Polysulfone-HA composites were developed and tested. Polysulfone (PSu) is a hard, glassy polymer that has been shown to be biocompatible. Composites were fabricated through a combination of tape casting, solvent casting, and lamination. Monolithic HA and laminate specimens were tested in biaxial flexure. A unique laminate theory solution was developed to characterize stress distributions for laminates. Failure loads, failure stress, work of fracture, and apparent toughness were compared for the laminates against monolithic HA specimens. Initial testing results showed that laminates had a failure stress of 60 +/- 10, which is a 170% improvement over the 22 +/- 2 MPa failure stress for monolithic HA. The work of fracture was improved by 5500% from 11 +/- 2 for the monolithic HA to 612 +/- 240 for the laminates. Work of fracture values gave the laminates an apparent fracture toughness of 7.2 MPa•m1
Boundary layer thermal stresses in angle-ply composite laminates
NASA Technical Reports Server (NTRS)
Wang, S. S.; Choi, I.
1979-01-01
Boundary-layer thermal stress singularities and distributions of angle-ply composite laminates under uniform thermal loading are investigated through a system of sixth-order governing partial differential equations developed with the aid of the anisotropic elasticity field equations and Lekhnitskii's complex stress functions. Results are presented for cases of various angle-ply graphite/epoxy laminates, and it is shown that the boundary-layer thickness depends on the degree of anisotropy of each individual lamina, thermomechanical properties of each ply, and the relative thickness of adjacent layers.
The fatigue behavior of composite laminates under various mean stresses
NASA Technical Reports Server (NTRS)
Rotem, A.
1991-01-01
A method is developed for predicting the S-N curve of a composite laminate which is subjected to an arbitrary stress ratio, R (minimum stress/maximum stress). The method is based on the measuring of the S-N behavior of two distinct cases, tension-tension and compression-compression fatigue loadings. Using these parameters, expressions are formulated that estimate the fatigue behavior under any stress ratio loading. Experimental results from the testing of graphite/epoxy laminates, with various structures, are compared with the predictions and show good agreement.
Fracture behavior of unidirectional boron/aluminum composite laminates
NASA Technical Reports Server (NTRS)
Jones, F. W.; Goree, J. G.
1983-01-01
An experimental investigation of the fracture behavior of unidirectional boron/aluminum composite laminates was conducted in order to verify the results of mathematical models. These models predict the fiber stresses and displacements and the amount of damage growth in a center-notched lamina as a function of the applied remote stress and the matrix and fiber material properties. A brittle lacquer coating was used to detect the yielding in the matrix while X-ray techniques were used to determine the number of broken fibers in the laminate. The notched strengths and the amounts of damage found in the specimens agreed well with those predicted by the models. It was shown that for thin laminates the amount of damage and the fiber displacements do not depend strongly on the number of plies for a given notch width.
A comparison of simple shear characterization methods for composite laminates
NASA Technical Reports Server (NTRS)
Yeow, Y. T.; Brinson, H. F.
1977-01-01
Various methods for the shear stress-strain characterization of composite laminates are examined, and their advantages and limitations are briefly discussed. Experimental results and the necessary accompanying analysis are then presented and compared for three simple shear characterization procedures. These are the off-axis tensile test method, the + or - 45 degs tensile test method and the 0 deg/90 degs symmetric rail shear test method. It is shown that the first technique indicates that the shear properties of the G/E laminates investigated are fundamentally brittle in nature while the latter two methods tend to indicate that the G/E laminates are fundamentally ductile in nature. Finally, predictions of incrementally determined tensile stress-strain curves utilizing the various different shear behavior methods as input information are presented and discussed.
Nonlinear temperature dependent failure analysis of finite width composite laminates
NASA Technical Reports Server (NTRS)
Nagarkar, A. P.; Herakovich, C. T.
1979-01-01
A quasi-three dimensional, nonlinear elastic finite element stress analysis of finite width composite laminates including curing stresses is presented. Cross-ply, angle-ply, and two quasi-isotropic graphite/epoxy laminates are studied. Curing stresses are calculated using temperature dependent elastic properties that are input as percent retention curves, and stresses due to mechanical loading in the form of an axial strain are calculated using tangent modulii obtained by Ramberg-Osgood parameters. It is shown that curing stresses and stresses due to tensile loading are significant as edge effects in all types of laminate studies. The tensor polynomial failure criterion is used to predict the initiation of failure. The mode of failure is predicted by examining individual stress contributions to the tensor polynomial.
Tension fatigue analysis and life prediction for composite laminates
NASA Technical Reports Server (NTRS)
Obrien, T. K.; Rigamonti, M.; Zanotti, C.
1988-01-01
A tension fatigue life prediction methodology for composite laminates is presented. Tension fatigue tests were conducted on quasi-isotropic and orthotropic glass epoxy, graphite epoxy, and glass/graphite epoxy hybrid laminates. Edge delamination onset data were used to generate plots of strain energy release rate as a function of cycles to delamination onset. These plots were then used along with strain energy release rate analyses of delaminations initiating at matrix cracks to predict local delamination onset. Stiffness loss was measured experimentally to account for the accumulation of matrix cracks and for delamination growth. Fatigue failure was predicted by comparing the increase in global strain resulting from stiffness loss to the decrease in laminate failure strain resulting from delaminations forming at matrix cracks through the laminate thickness. Good agreement between measured and predicted lives indicated that the through-thickness damage accumulation model can accurately describe fatigue failure for laminates where the delamination onset behavior in fatigue is well characterized, and stiffness loss can be monitored in real time to account for damage growth.
Effect of microcracks on the thermal expansion of composite laminates
NASA Technical Reports Server (NTRS)
Bowles, D. E.
1984-01-01
A finite element analysis was used to quantitatively predict the effect of matrix microcracks in the 90 deg plies of graphite/epoxy composites on the coefficient of thermal expansion in the 0 deg direction, alpha (y) (perpendicular to the cracks). Results were generated for (0m/90n)s, (0/+ or 45/90)s and (0/90/ + or - 45)s graphite/epoxy laminate configurations. Analytical predictions were compared with experimental results for the two quasi-isotropic laminate configurations. Both analytical and experimental results showed that microcracks reduced the effective stiffness of the 90 deg plies, thus causing the laminates, thermal response to be more like that of a (0) laminate. The change in alpha(y) was a function of lamina material properties, microcrack density, fiber orientation, and stacking sequence. A combination of classical lamination theory and finite element analysis was used to predict the effect of microcracks in both the 90 deg and 0 deg plies. Analytical results showed that the addition of microcracks in the 0 deg plies do affect alpha(y), but to a lesser extent than those in the 90 deg plies.
Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Smeltzer, Stanley S., III
2000-01-01
A study of the attenuation of bending boundary layers in balanced and unbalanced, symmetrically and unsymmetrically laminated cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize the effects of laminate orthotropy and anisotropy on the bending boundary-layer decay length in a very general manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all laminates considered, the results show that the differences between results obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that, in some cases, neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and, in other cases, results in an overestimation.
Transient response of a laminated composite plate
NASA Technical Reports Server (NTRS)
Datta, S. K.; Ju, T. H.; Bratton, R. L.; Shah, A. H.
1992-01-01
Results are presented from an investigation of the effect of layering on transient wave propagation in a laminated cross-ply plate, giving attention to the case of 2D plane strain in the case where a line vertical force is applied on a free surface of the plate; the line may be either parallel or perpendicular to the fibers in a ply. The results are in both the time and frequency domains for the normal stress component in the x direction, at a point on the surface of the plate on which the force is applied. Comparative results are also presented for a homogeneous plate whose properties are the static effective ones, when the number of plies is large.
A Shear Deformable Shell Element for Laminated Composites
NASA Technical Reports Server (NTRS)
Chao, W. C.; Reddy, J. N.
1984-01-01
A three-dimensional element based on the total Lagrangian description of the motion of a layered anisotropic composite medium is developed, validated, and used to analyze layered composite shells. The element contains the following features: geometric nonlinearity, dynamic (transient) behavior, and arbitrary lamination scheme and lamina properties. Numerical results of nonlinear bending, natural vibration, and transient response are presented to illustrate the capabilities of the element.
Laminated thermoplastic composite material from recycled high density polyethylene
NASA Technical Reports Server (NTRS)
Liu, Ping; Waskom, Tommy L.
1994-01-01
The design of a materials-science, educational experiment is presented. The student should understand the fundamentals of polymer processing and mechanical property testing of materials. The ability to use American Society for Testing and Materials (ASTM) standards is also necessary for designing material test specimens and testing procedures. The objectives of the experiment are (1) to understand the concept of laminated composite materials, processing, testing, and quality assurance of thermoplastic composites and (2) to observe an application example of recycled plastics.
A Design Tool for Robust Composite Structures
2010-06-01
related goal is to compare the blast response of Dyneema® laminates with that of a carbon fiber reinforced polymer ( CFRP ) composite. (iii) To identify...embedded Dyneema® composite layers, both below and above the ballistic limit. 16 6. Hybrid Dyneema®/Carbon Fiber Reinforced Polymer Matrix Composites...of Dyneema® fibers to carbon fiber reinforced polymer ( CFRP ) composites. The study focuses specifically on 3D orthogonal weaves with carbon employed
Exact solutions for laminated composite cylindrical shells in cylindrical bending
NASA Technical Reports Server (NTRS)
Yuan, F. G.
1992-01-01
Analytic elasticity solutions for laminated composite cylindrical shells under cylindrical bending are presented. The material of the shell is assumed to be general cylindrically anisotropic. Based on the theory of cylindrical anisotropic elasticity, coupled governing partial differential equations are developed. The general expressions for the stresses and displacements in the laminated composite cylinders are discussed. The closed form solutions based on Classical Shell Theory (CST) and Donnell's (1933) theory are also derived for comparison purposes. Three examples illustrate the effect of radius-to-thickness ratio, coupling and stacking sequence. The results show that, in general, CST yields poor stress and displacement distributions for thick-section composite shells, but converges to the exact elasticity solution as the radius-to-thickness ratio increases. It is also shown that Donnell's theory significantly underestimates the stress and displacement response.
Vibration suppression for laminated composite plates with arbitrary boundary conditions
NASA Astrophysics Data System (ADS)
Li, J.; Narita, Y.
2013-11-01
An analysis of vibration suppression for laminated composite plates subject to active constrained layer damping under various boundary conditions is presented. Piezoelectric-fiber-reinforced composites (PFRCs) are used as active actuators, and the effect of PFRC patches on vibration control is reported here. An analytical approach is expanded to analyze the vibration of laminated composites with arbitrary boundary conditions. By using Hamilton's principle and the Rayleigh-Ritz method, the equation of motion for the resulting electromechanical coupling system is derived. A velocity feedback control rule is employed to obtain an effective active damping in the vibration control. The orientation effect of piezoelectric fibers in the PFRC patches on the suppression of forced vibrations is also investigated.
Bolted joints in a laminated composite strut design expert system
NASA Astrophysics Data System (ADS)
Wu, C. M. L.
A knowledge-based expert system for the design and analysis of composite laminated struts with bolted joints is described. This system is part of a Composite Design Expert System aimed at performing analysis and design of composite laminated plates and struts and at assessing designs. The system uses a minimum weight optimization that satisfies the failure criteria of local and overall buckling, and a stress/strain failure criterion. Emphasis is placed on the formulation for the minimum weight optimization of struts with bolted joints. Attention is also given to a procedure for optimizing a strut to be fitted in a given length of a gap and the assessment of competing strut designs.
Developments in impact damage modeling for laminated composite structures
NASA Technical Reports Server (NTRS)
Dost, Ernest F.; Avery, William B.; Swanson, Gary D.; Lin, Kuen Y.
1991-01-01
Damage tolerance is the most critical technical issue for composite fuselage structures studied in the Advanced Technology Composite Aircraft Structures (ATCAS) program. The objective here is to understand both the impact damage resistance and residual strength of the laminated composite fuselage structure. An understanding of the different damage mechanisms which occur during an impact event will support the selection of materials and structural configurations used in different fuselage quadrants and guide the development of analysis tools for predicting the residual strength of impacted laminates. Prediction of the damage state along with the knowledge of post-impact response to applied loads will allow for engineered stacking sequencies and structural configurations; intelligent decisions on repair requirements will also result.
Edge delamination in angle-ply composite laminates, part 5
NASA Technical Reports Server (NTRS)
Wang, S. S.
1981-01-01
A theoretical method was developed for describing the edge delamination stress intensity characteristics in angle-ply composite laminates. The method is based on the theory of anisotropic elasticity. The edge delamination problem is formulated using Lekhnitskii's complex-variable stress potentials and an especially developed eigenfunction expansion method. The method predicts exact orders of the three-dimensional stress singularity in a delamination crack tip region. With the aid of boundary collocation, the method predicts the complete stress and displacement fields in a finite-dimensional, delaminated composite. Fracture mechanics parameters such as the mixed-mode stress intensity factors and associated energy release rates for edge delamination can be calculated explicity. Solutions are obtained for edge delaminated (theta/-theta theta/-theta) angle-ply composites under uniform axial extension. Effects of delamination lengths, fiber orientations, lamination and geometric variables are studied.
Contact law and impact responses of laminated composites
NASA Technical Reports Server (NTRS)
Sun, C. T.; Yang, S. H.
1980-01-01
Static identation tests were performed to determine the law of contact between a steel ball and glass/epoxy and graphite/epoxy laminated composites. For both composites the power law with an index of 1.5 was found to be adequate for the loading curve. Substantial permanent deformations were noted after the unloading. A high order beam finite element was used to compute the dynamic contact force and response of the laminated composite subjected to the impact of an elastic sphere. This program can be used with either the classical Hertzian contact law or the measured contact law. A simple method is introduced for estimating the contact force and contact duration in elastic impacts.
Thermoviscoelastic characterization and prediction of Kevlar/epoxy composite laminates
NASA Technical Reports Server (NTRS)
Gramoll, K. C.; Dillard, D. A.; Brinson, H. F.
1990-01-01
The thermoviscoelastic characterization of Kevlar 49/Fiberite 7714A epoxy composite lamina and the development of a numerical procedure to predict the viscoelastic response of any general laminate constructed from the same material were studied. The four orthotropic material properties, S sub 11, S sub 12, S sub 22, and S sub 66, were characterized by 20 minute static creep tests on unidirectional (0) sub 8, (10) sub 8, and (90) sub 16 lamina specimens. The Time-Temperature Superposition-Principle (TTSP) was used successfully to accelerate the characterization process. A nonlinear constitutive model was developed to describe the stress dependent viscoelastic response for each of the material properties. A numerical procedure to predict long term laminate properties from lamina properties (obtained experimentally) was developed. Numerical instabilities and time constraints associated with viscoelastic numerical techniques were discussed and solved. The numerical procedure was incorporated into a user friendly microcomputer program called Viscoelastic Composite Analysis Program (VCAP), which is available for IBM PC type computers. The program was designed for ease of use. The final phase involved testing actual laminates constructed from the characterized material, Kevlar/epoxy, at various temperatures and load level for 4 to 5 weeks. These results were compared with the VCAP program predictions to verify the testing procedure and to check the numerical procedure used in the program. The actual tests and predictions agreed for all test cases which included 1, 2, 3, and 4 fiber direction laminates.
Methods of making metallic glass foil laminate composites
Vianco, Paul T.; Fisher, Robert W.; Hosking, Floyd M.; Zanner, Frank J.
1996-01-01
A process for the fabrication of a rapidly solidified foil laminate composite. An amorphous metallic glass foil is flux treated and coated with solder. Before solidification of the solder the foil is collected on a take-up spool which forms the composite into a solid annular configuration. The resulting composite exhibits high strength, resiliency and favorable magnetic and electrical properties associated with amorphous materials. The composite also exhibits bonding strength between the foil layers which significantly exceeds the bulk strength of the solder alone.
Methods of making metallic glass foil laminate composites
Vianco, P.T.; Fisher, R.W.; Hosking, F.M.; Zanner, F.J.
1996-08-20
A process for the fabrication of a rapidly solidified foil laminate composite. An amorphous metallic glass foil is flux treated and coated with solder. Before solidification of the solder the foil is collected on a take-up spool which forms the composite into a solid annular configuration. The resulting composite exhibits high strength, resiliency and favorable magnetic and electrical properties associated with amorphous materials. The composite also exhibits bonding strength between the foil layers which significantly exceeds the bulk strength of the solder alone. 6 figs.
The lightweight structure design of a CFRP mirror
NASA Astrophysics Data System (ADS)
Ding, Jiaoteng; Xu, Liang; Ma, Zhen; Xie, Yongjie; Luo, Yao; Wang, Yongjie; Pang, Zhihai
2016-10-01
The advantage of Carbon Fiber Reinforced Polymer (CFRP) is obvious as a common space material for low density, low thermal expansion coefficient and high specific stiffness characteristics, it is the ideal material choice for space optical reflector. Mirror structure with honeycomb can achieve high rates of lightweight, as well as high specific stiffness. For Φ300mm CFRP mirror, accounting of the actual process properties of CFRP, mirror panels laminated based on thermal stability design, honeycomb fabricated using one innovative inlaying-grafting design method. Finally, lightweight structure design of the CFRP primary mirror completed, the thermal stability result of the Φ300mm CFRP mirror achieved is 10nm°C.
Modeling Unidirectional Composite Laminates Using XFEM
2015-06-30
various composite constructions. Furthermore, the effects of different loading scenarios are not well understood. Although FRPs show...loading condition on the composite cylinder was exterior hydrostatic pressure—a particularly useful loading condition because of its widespread effect on...displacement ( , ). Once a bond initially breaks, it will not reconnect with subsequent contact. In order to investigate the effects
3D Guided Wave Motion Analysis on Laminated Composites
NASA Technical Reports Server (NTRS)
Tian, Zhenhua; Leckey, Cara; Yu, Lingyu
2013-01-01
Ultrasonic guided waves have proved useful for structural health monitoring (SHM) and nondestructive evaluation (NDE) due to their ability to propagate long distances with less energy loss compared to bulk waves and due to their sensitivity to small defects in the structure. Analysis of actively transmitted ultrasonic signals has long been used to detect and assess damage. However, there remain many challenging tasks for guided wave based SHM due to the complexity involved with propagating guided waves, especially in the case of composite materials. The multimodal nature of the ultrasonic guided waves complicates the related damage analysis. This paper presents results from parallel 3D elastodynamic finite integration technique (EFIT) simulations used to acquire 3D wave motion in the subject laminated carbon fiber reinforced polymer composites. The acquired 3D wave motion is then analyzed by frequency-wavenumber analysis to study the wave propagation and interaction in the composite laminate. The frequency-wavenumber analysis enables the study of individual modes and visualization of mode conversion. Delamination damage has been incorporated into the EFIT model to generate "damaged" data. The potential for damage detection in laminated composites is discussed in the end.
On the mechanics of thin-walled laminated composite beams
NASA Astrophysics Data System (ADS)
Barbero, Ever J.; Lopez-Anido, Roberto; Davalos, Julio F.
1993-01-01
A formal engineering approach of the mechanics of thin-walled laminated beams based on kinematic assumptions consistent with Timoshenko beam theory is presented. Thin-walled composite beams with open or closed cross section subjected to bending and axial load are considered. A variational formulation is employed to obtain a comprehensive description of the structural response. Beam stiffness coefficients, which account for the cross section geometry and for the material anisotropy, are obtained. An explicit expression for the static shear correction factor of thin-walled composite beams is derived from energy equivalence. A numerical example involving a laminated I-beam is used to used to demonstrate the capability of the model for predicting displacements and ply stresses.
Modelling low velocity impact induced damage in composite laminates
NASA Astrophysics Data System (ADS)
Shi, Yu; Soutis, Constantinos
2017-12-01
The paper presents recent progress on modelling low velocity impact induced damage in fibre reinforced composite laminates. It is important to understand the mechanisms of barely visible impact damage (BVID) and how it affects structural performance. To reduce labour intensive testing, the development of finite element (FE) techniques for simulating impact damage becomes essential and recent effort by the composites research community is reviewed in this work. The FE predicted damage initiation and propagation can be validated by Non Destructive Techniques (NDT) that gives confidence to the developed numerical damage models. A reliable damage simulation can assist the design process to optimise laminate configurations, reduce weight and improve performance of components and structures used in aircraft construction.
Piezoelectrically strained bistable laminates with macro fiber composites
NASA Astrophysics Data System (ADS)
Lee, Andrew J.; Moosavian, Amin; Inman, Daniel J.
2017-04-01
The bistability and snap through capability of an unsymmetric laminate consisting of only Macro Fiber Composites (MFC) are investigated. The non-linear analysis predicts two cylindrically stable configurations when strain anisotropy is piezoelectrically induced within a [0MFC/90MFC]T laminate. This is achieved by bonding two MFCs in their actuated states and releasing the voltage post cure to create in-plane residual stresses. The minimization of total potential energy with the Rayleigh-Ritz method are used to analytically model the resulting laminate. A finite element analysis is conducted in MSC Nastran using the piezoelectric-thermal analogy approach to verify the analytical results. The effects of adhesive properties, bonding cure cycles, MFC layup, and its geometry on the curvatures, displacements, and bifurcation voltages are characterized. Finally, the snap through and reverse snap through capabilities with piezoelectric actuation are demonstrated. This adaptive laminate functions as both the actuator and the primary structure and allows large deformations under a non-continuous energy input. Its snap through capability allows full configuration control necessary in morphing applications.
Thermal buckling and postbuckling of symmetrically laminated composite plates
Meyers, C.A.; Hyer, M.W. )
1991-12-01
The thermal buckling and postbuckling response of symmetrically laminated composite plates are discussed. Using variational methods in conjunction with a Rayleigh-Ritz formulation, thermal buckling and postbuckling are investigated for two laminates, a ({plus minus} 45/0/90) and a ({plus minus} 45/02), under two different simple support conditions, fixed and sliding. These laminates are subjected to the condition of a uniform temperature change. The effects of the principal material axis not being aligned with the edges of the plate, referred to here as material axis skewing, are also investigated. Although differences between buckling temperatures for the two support conditions were small, support conditions can have a large influence on thermal postbuckling response. In general, plates with fixed simple supports deflect more than plates with sliding simple supports. In addition, support conditions can influence modal interaction. Skewing of the material axis decreases the buckling temperatures of both laminates and, like fixed support conditions, causes increased postbuckling deflections. Skewing also influences modal interaction. 8 refs.
Delamination failure in a unidirectional curved composite laminate
NASA Technical Reports Server (NTRS)
Martin, Roderick H.
1990-01-01
Delamination failure in a unidirectional curved composite laminate was investigated. The curved laminate failed unstably by delaminations developing around the curved region of the laminate at different depths through the thickness until virtually all bending stiffness was lost. Delamination was assumed to initiate at the location of the highest radial stress in the curved region. A closed form curved beam elasticity solution and a 2-D finite element analysis (FEA) were conducted to determine this location. The variation in the strain energy release rate, G, with delamination growth was then determined using the FEA. A strength-based failure criteria adequately predicted the interlaminar tension failure which caused initial delamination onset. Using the G analysis the delamination was predicted to extend into the arm and leg of the laminate, predominantly in mode I. As the initial delamination grew arould the curved region, the maximum radial stress in the newly formed inner sublaminate increased to a level sufficient to cause a new delamination to initiate in the sublaminate with no increase in applied load. This failure progression was observed experimentally.
Permeability of Impacted Coated Composite Laminates
NASA Technical Reports Server (NTRS)
Johnson, W. S.; Findley, Benjamin
2002-01-01
Composite materials are being considered for use on future generations of Reusable Launch Vehicles (RLVs) for both fuel tanks and fuel feedlines. Through the use of composite materials NASA can reduce the overall weight of the vehicle dramatically. This weight savings can then be translated into an increase in the weight of payload sent into orbit, reducing the cost per pound of payload. It is estimated that by switching to composite materials for fuel tanks the weight of the tanks can be reduced by 40 percent, which translates to a total vehicle weight savings of 14 percent. In this research, carbon/epoxy composites were studied for fuel feedline applications. There are concerns about using composite materials for feedlines and fuel tanks because these materials are extremely vulnerable to impact in the form of inadvertent bumping or dropped tools both during installation and maintenance. Additionally, it has been found that some of the sample feedlines constructed have had leaks, and thus there may be a need to seal preexisting leaks in the composite prior to usage.
A life prediction model for laminated composite structural components
NASA Technical Reports Server (NTRS)
Allen, David H.
1990-01-01
A life prediction methodology for laminated continuous fiber composites subjected to fatigue loading conditions was developed. A summary is presented of research completed. A phenomenological damage evolution law was formulated for matrix cracking which is independent of stacking sequence. Mechanistic and physical support was developed for the phenomenological evolution law proposed above. The damage evolution law proposed above was implemented to a finite element computer program. And preliminary predictions were obtained for a structural component undergoing fatigue loading induced damage.
Flexible matrix composite laminated disk/ring flywheel
NASA Technical Reports Server (NTRS)
Gupta, B. P.; Hannibal, A. J.
1984-01-01
An energy storage flywheel consisting of a quasi-isotropic composite disk overwrapped by a circumferentially wound ring made of carbon fiber and a elastometric matrix is proposed. Through analysis it was demonstrated that with an elastomeric matrix to relieve the radial stresses, a laminated disk/ring flywheel can be designed to store a least 80.3 Wh/kg or about 68% more than previous disk/ring designs. at the same time the simple construction is preserved.
Evaluation of micro-damage accumulation in holed plain-woven CFRP composite under fatigue loading
NASA Astrophysics Data System (ADS)
Ying, Jia; Nishikawa, Masaaki; Hojo, Masaki
2014-03-01
Fluorescence method was used to detect the micro-damage caused by fatigue in a plain-woven carbon fiber reinforced polymer (CFRP). Fluorescence measurement is a method which estimates micro-damage by measuring fluorescent intensity change inside materials. The principle is, larger micro-damage means larger plastic strain, thus more space in that damaged spot which allows more fluorescent dyes coming in the material. By detecting fluorescent intensity in CFRP layer by layer using confocal laser microscopy, micro-damage can be estimated. Results show that there's a good relationship between micro-damage and fluorescent intensity gradient.
NASA Astrophysics Data System (ADS)
Harris, Jason; Barjasteh, Ehsan
2017-04-01
The study focuses on the formation of artificial neural pathways for the use of structural health monitoring in prosthesis by means of Fiber Bragg Grating (FBG) optic sensors to detect shifts in strain. Implementation of these fibers are embedded into carbon fiber reinforced polymer (CFRP) based structures. CFRP was considered for its wide use application in ankle-foot prosthesis, which undergoes high loads of stress and wear.. This method acts as a system of early detection which could prevent the prosthesis from critical failure due to previously undetected interior defects, further improving the patient's well being.
Nonlinear probabilistic finite element models of laminated composite shells
NASA Technical Reports Server (NTRS)
Engelstad, S. P.; Reddy, J. N.
1993-01-01
A probabilistic finite element analysis procedure for laminated composite shells has been developed. A total Lagrangian finite element formulation, employing a degenerated 3-D laminated composite shell with the full Green-Lagrange strains and first-order shear deformable kinematics, forms the modeling foundation. The first-order second-moment technique for probabilistic finite element analysis of random fields is employed and results are presented in the form of mean and variance of the structural response. The effects of material nonlinearity are included through the use of a rate-independent anisotropic plasticity formulation with the macroscopic point of view. Both ply-level and micromechanics-level random variables can be selected, the latter by means of the Aboudi micromechanics model. A number of sample problems are solved to verify the accuracy of the procedures developed and to quantify the variability of certain material type/structure combinations. Experimental data is compared in many cases, and the Monte Carlo simulation method is used to check the probabilistic results. In general, the procedure is quite effective in modeling the mean and variance response of the linear and nonlinear behavior of laminated composite shells.
Resin infusion of layered metal/composite hybrid and resulting metal/composite hybrid laminate
NASA Technical Reports Server (NTRS)
Cano, Roberto J. (Inventor); Grimsley, Brian W. (Inventor); Weiser, Erik S. (Inventor); Jensen, Brian J. (Inventor)
2009-01-01
A method of fabricating a metal/composite hybrid laminate is provided. One or more layered arrangements are stacked on a solid base to form a layered structure. Each layered arrangement is defined by a fibrous material and a perforated metal sheet. A resin in its liquid state is introduced along a portion of the layered structure while a differential pressure is applied across the laminate structure until the resin permeates the fibrous material of each layered arrangement and fills perforations in each perforated metal sheet. The resin is cured thereby yielding a metal/composite hybrid laminate.
An experimental investigation on the three-point bending behavior of composite laminate
NASA Astrophysics Data System (ADS)
A, Azzam; W, Li
2014-08-01
The response of composite laminate structure to three-point bending load was investigated by subjecting two types of stacking sequences of composite laminate structure by using electronic universal tester (Type: WDW-20) machine. Optical microscope was selected in order to characterize bending damage, delamination, and damage shapes in composite laminate structures. The results showed that the [0/90/-45/45]2s exhibits a brittle behavior, while other laminates exhibit a progressive failure mode consisting of fiber failure, debonding (splitting), and delamination. The [45/45/90/0]2s laminate has a highly nonlinear load- displacement curve due to compressive yielding.
1991-06-07
strength of laminated composite structure was composed by P.Y. Tang , for the Naval Ocean Systems Center, San Diego in 1989.2 The researcher deduced that...of ’P. Y. Tang , Development of a Progressive Failure Model for Strength of Laminated Composite Structure (San Diego: Naval Oceans System Center, 1989...macromechanics, composite material behavior is studied ssP, y. Tang , Development of a Progressive Failure Model for Strength. of Laminated Composite Structure
Ballistic damage in hybrid composite laminates
NASA Astrophysics Data System (ADS)
Phadnis, Vaibhav A.; Pandya, Kedar S.; Naik, Niranjan K.; Roy, Anish; Silberschmidt, Vadim V.
2015-07-01
Ballistic damage of hybrid woven-fabric composites made of plain-weave E-glass- fabric/epoxy and 8H satin-weave T300 carbon-fabric/epoxy is studied using a combination of experimental tests, microstructural studies and finite-element (FE) analysis. Ballistic tests were conducted with a single-stage gas gun. Fibre damage and delamination were observed to be dominating failure modes. A ply-level FE model was developed, with a fabric-reinforced ply modelled as a homogeneous orthotropic material with capacity to sustain progressive stiffness degradation due to fibre/matrix cracking, fibre breaking and plastic deformation under shear loading. Simulated damage patterns on the front and back faces of fabric-reinforced composite plates provided an insight into their damage mechanisms under ballistic loading.
Performance of soft dielectric laminated composites
NASA Astrophysics Data System (ADS)
Gei, Massimiliano; Springhetti, Roberta; Bortot, Eliana
2013-10-01
This paper contains a thorough investigation of the performance of electrically activated layered soft dielectric composite actuators under plane deformation. Noting that the activation can be induced by controlling either the voltage or the surface charge, the overall behaviour of the system is obtained via homogenization at large strains, taking either the macroscopic electric field or the macroscopic electric displacement field as independent electrical variables. The performance of a two-phase composite actuator compared to that of the homogeneous case is highlighted for few boundary-value problems and for different values of stiffness and permittivity ratios between constituents being significant for applications, where the soft matrix is reinforced by a relatively small volume fraction of a stiff and high-permittivity phase. For charge-controlled devices, it is shown that some composite layouts admit, on one hand, the occurrence of pull-in/snap-through instabilities that can be exploited to design release-actuated systems, and on the other hand, the possibility of thickening at increasing surface charge density.
Thermoviscoelastic characterization and predictions of Kevlar/epoxy composite laminates
Gramoll, K.C.
1988-01-01
This study consisted of two main parts, the thermoviscoelastic characterization of Kevlar 49/Fiberite 7714A epoxy composite lamina and the development of a numerical procedure to predict the viscoelastic response of any general laminate constructed from the same material. The four orthotropic material properties, S{sub 11}, S{sub 12}, S{sub 22}, and S{sub 66}, were characterized by 20-minute static creep tests on unidirectional ((0){sub s}, (10){sub s}, and (90){sub 16}) lamina specimens. A new numerical procedure to predict long-term laminate properties from lamina properties (obtained experimentally) was developed. Numerical instabilities and time constraints associated with viscoelastic numerical techniques were discussed and solved. The numerical procedure was incorporated into a user-friendly microcomputer program called Viscoelastic Composite Analysis Program (VCAP), which is available for IBM PC type computers. The program was designed for ease of use and includes graphics, menus, help messages, etc. The final phase of the study involved testing actual laminates constructed from the characterized material, Kevlar/epoxy, at various temperature and load levels for 4 to 5 weeks.
Stability and morphing characteristics of bistable composite laminates
NASA Astrophysics Data System (ADS)
Tawfik, Samer A.
The focus of the current research is to investigate the potential of using bistable unsymmetric cross-ply laminated composites as a means for achieving structures with morphed characteristics. To this end, an investigation of the design space for laminated composites exhibiting bistable behavior is undertaken and the key parameters controlling their behavior are identified. For this purpose a nonlinear Finite Element methodology using ABAQUS(TM) code is developed to predict both the cured shapes and the stability characteristics of unsymmetric cross-ply laminates. In addition, an experimental program is developed to validate the analytically predicted results through comparison with test data. A new method is proposed for attaching piezoelectric actuators to a bistable panel in order to preserve its favorable stability characteristics as well as optimizing the actuators performance. The developed nonlinear FE methodology is extended to predict the actuation requirements of bistable panels. Actuator requirements, predicted using the nonlinear FE analysis, are found to be in agreement with the test results. The current research also explores the potential for implementing bistable panels for Uninhabited Aerial Vehicle (UAV) wing configuration. To this end, a set of bistable panels is manufactured by combining symmetric and unsymmetric balanced and unbalanced stacking sequence and their stability characteristics are predicted. A preliminary analysis of the aerodynamic characteristics of the manufactured panels is carried out and the aerodynamic benefits of manufactured bistable panel are noted.
Buckling of laminated composite plates subject to nonuniform in-plane edge loads
Kam, T.Y.; Chu, K.H.
1995-08-01
The buckling of laminated composite plates subjected to nonuniform in-plane edge loads is studied using a shear deformable finite element. The finite element formulation is based on Mindlin`s plate theory in which shear correction factors are derived from the exact expressions for orthotropic materials. Buckling testing of laminated composite plates with different lamination arrangements using the strain measurement technique is performed. The test results indicate that the proposed linear finite element method is unable to predict the buckling strength of imperfect laminated composite plates. The applications of the proposed finite element method are demonstrated by determining the optimal lamination arrangements of symmetrically laminated angle-ply plates comprised of different numbers of layer groups subject to various types of edge loads for attaining the maximum buckling strength. The so obtained optimal fiber angles and number of layer groups of the plates may be useful for practical buckling design of laminated composite plates.
Analysis of delamination growth in compressively loaded composite laminates
NASA Astrophysics Data System (ADS)
Tratt, Matthew D.
The present analytical and empirical study of composite structure delamination has attempted to predict the threshold stress for the initiation of delamination growth in compressively loaded composite laminates. The strain-energy release-rate distributions around circular delaminations are computed via MSC/NASTRAN analysis in conjunction with a virtual crack-opening technique. Static compression tests were conducted on specimens of graphite fiber-reinforced epoxy having circular delaminations of various sizes. Computed delamination growth threshold-stress prediction results were at substantial variance with the test data, but confirmed trends and gave qualitative insight into quasi-static delamination growth.
Analysis of shear test method for composite laminates
NASA Technical Reports Server (NTRS)
Bergner, H. W., Jr.; Davis, J. G., Jr.; Herakovich, C. T.
1977-01-01
An elastic plane stress finite element analysis of the stress distributions in four flat test specimens for in-plane shear response of composite materials subjected to mechanical or thermal loads is presented. The shear test specimens investigated include: slotted coupon, cross beam, losipescu, and rail shear. Results are presented in the form of normalized shear contour plots for all three in-plane stess components. It is shown that the cross beam, losipescu, and rail shear specimens have stress distributions which are more than adequate for determining linear shear behavior of composite materials. Laminate properties, core effects, and fixture configurations are among the factors which were found to influence the stress distributions.
Pulse propagation in a laminated composite plate and nondestructive evaluation
NASA Technical Reports Server (NTRS)
Ju, T. H.; Datta, S. K.
1992-01-01
The surface response of a laminated composite plate with delamination cracks has been studied in this paper. The objective of this study is to analyze the surface response both in the time and frequency domains due to delamination cracks at different depths in a cross-ply composite plate. For reasons of simplicity, attention has been focused here on two-dimensional (plane-strain) motions. The source of excitation is taken to be a line vertical force acting perpendicular to the fibers in a lamina. Numerical results are presented, showing peak responses at certain resonance frequencies. A comparison of these results with those for a uniaxial graphite epoxy plate shows characteristic differences.
Design of multiple-ply laminated composite tapered beams
NASA Technical Reports Server (NTRS)
Rodriguez, P.
1993-01-01
A study of a special case of symmetric laminated composite cantilever beams is presented. The approach models beams that are tapered both in depth and width and investigates the effect of the ply layup angle and the ply taper on bending and interlaminar shearing stresses. For the determination of stresses and deflections, the beam stiffness matrices are expressed as linear functions of the beam length. Using classical lamination theory (CLT) the stiffness matrices are determined and assembled at strategic locations along the length of the beam. They are then inverted and necessary stiffness parameters are obtained numerically and extracted for determination of design information at each location chosen. Several ply layup configurations are investigated, and design considerations are presented based on the findings. Finally, recommendations for the design of these beams are presented, and a means for anticipating the location of highest stresses is offered.
Experimental determination of material constants of a hybrid composite laminate
Ihekweazu, S.N.; Lari, S.B.; Unanwa, C.O.
1999-07-01
This paper discusses the results of the experimental study that was conducted in order to determine the material properties of a hybrid composite laminate made from Fiberite material MXM-7714/120 (a fabric prepreg consisting of woven Kevlar{reg_sign} 49 reinforcement impregnated with Fiberite 250 F (121 C) curing 7714 epoxy resin) and HYE-2448AIE (a 250 F (121 C) curing epoxy resin impregnated unidirectional graphite tape). First, each of the materials that comprise the hybrid laminate was fabricated separately according to ASTM-D-3039 specification in order to determine their material properties. The materials were then hybridized and the properties were determined. Data from this experiment reveal that a new class of material that can meet desired specifications can be created through hybridization. The data also revealed that the properties of the materials bonded together as a hybrid complement the properties of the constituent members of the hybrid.
On the enhancement of impact damage tolerance of composite laminates
NASA Technical Reports Server (NTRS)
Nettles, A. T.; Lance, D. G.
1993-01-01
This paper examines the use of a thin layer of Ultra High Molecular Weight Polyethylene (UHMWPE) on the outer surface of carbon/epoxy composite materials as a method of improving impact resistance and damage tolerance through hybridization. Flat 16-ply laminates as well as honeycomb sandwich structures with eight-ply facesheets were tested in this study. Instrumented drop-weight impact testing was used to inflict damage upon the specimens. Evaluation of damage resistance included instrumented impact data, visual examination, C-scanning and compression after impact (CAI) testing. The results show that only one lamina of UHMWPE did not improve the damage tolerance (strength retention) of the 16-ply flat laminate specimens or the honeycomb sandwich beams, however, a modest gain in impact resistance (detectable damage) was found for the honeycomb sandwich specimens that contained an outer layer of UHMWPE.
Iosipescu shear properties of graphite fabric/epoxy composite laminates
NASA Technical Reports Server (NTRS)
Walrath, D. E.; Adams, D. F.
1985-01-01
The Iosipescu shear test method is used to measure the in-plane and interlaminar shear properties of four T300 graphite fabric/934 epoxy composite materials. Different weave geometries tested include an Oxford weave, a 5-harness satin weave, an 8-harness satin weave, and a plain weave with auxiliary warp yarns. Both orthogonal and quasi-isotropic layup laminates were tested. In-plane and interlaminar shear properties are obtained for laminates of all four fabric types. Overall, little difference in shear properties attributable to the fabric weave pattern is observed. The auxiliary warp material is significantly weaker and less stiff in interlaminar shear parallel to its fill direction. A conventional strain gage extensometer is modified to measure shear strains for use with the Iosipescu shear test. While preliminary results are encouraging, several design iterations failed to produce a reliable shear transducer prototype. Strain gages are still the most reliable shear strain transducers for use with this test method.
Failure analysis of composite laminates including biaxial compression
NASA Technical Reports Server (NTRS)
Tennyson, R. C.; Elliott, W. G.
1983-01-01
This report describes a continued effort on the development and application of the tensor polynomial failure criterion for composite laminate analysis. In particular, emphasis is given to the design, construction and testing of a cross-beam laminate configuration to obtain "pure' biaxial compression failure. The purpose of this test case was to provide to permit "closure' of the cubic form of the failure surface in the 1-2 compression-compression quadrant. This resulted in a revised set of interaction strength parameters and the construction of a failure surface which can be used with confidence for strength predictions, assuming a plane stress state exists. Furthermore, the problem of complex conjugate roots which can occur in some failure regions is addressed and an "engineering' interpretation is provided. Results are presented illustrating this behavior and the methodology for overcoming this problem is discussed.
On the enhancement of impact damage tolerance of composite laminates
NASA Technical Reports Server (NTRS)
Nettles, A. T.; Lance, D. G.
1993-01-01
This paper examines the use of a thin layer of Ultra High Molecular Weight Polyethylene (UHMWPE) on the outer surface of carbon/epoxy composite materials as a method of improving impact resistance and damage tolerance through hybridization. Flat 16-ply laminates as well as honeycomb sandwich structures with eight-ply facesheets were tested in this study. Instrumented drop-weight impact testing was used to inflict damage upon the specimens. Evaluation of damage resistance included instrumented impact data, visual examination, C-scanning and compression after impact (CAI) testing. The results show that only one lamina of UHMWPE did not improve the damage tolerance (strength retention) of the 16-ply flat laminate specimens or the honeycomb sandwich beams, however, a modest gain in impact resistance (detectable damage) was found for the honeycomb sandwich specimens that contained an outer layer of UHMWPE.
NASA Astrophysics Data System (ADS)
Kundalwal, S. I.; Kumar, R. Suresh; Ray, M. C.
2013-10-01
This paper deals with the investigation of active constrained layer damping (ACLD) of smart laminated continuous fuzzy fiber reinforced composite (FFRC) shells. The distinct constructional feature of a novel FFRC is that the uniformly spaced short carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of the continuous carbon fiber reinforcements. The constraining layer of the ACLD treatment is considered to be made of vertically/obliquely reinforced 1-3 piezoelectric composite materials. A finite element (FE) model is developed for the laminated FFRC shells integrated with the two patches of the ACLD treatment to investigate the damping characteristics of the laminated FFRC shells. The effect of variation of the orientation angle of the piezoelectric fibers on the damping characteristics of the laminated FFRC shells has been studied when the piezoelectric fibers are coplanar with either of the two mutually orthogonal vertical planes of the piezoelectric composite layer. It is revealed that radial growth of CNTs on the circumferential surfaces of the carbon fibers enhances the attenuation of the amplitude of vibrations and the natural frequencies of the laminated FFRC shells over those of laminated base composite shells without CNTs.
Metal-ceramic laminate composite magnetoelectric gradiometer.
Bedekar, V; Bichurin, M I; Ivanov, S N; Pukinski, Y J; Priya, S
2010-03-01
Gradiometer resembles in functionality a magnetic field sensor where it measures the magnetic field gradient and its sensitivity is determined by the ability to quantify differential voltage change with respect to a reference value. Magnetoelectric (ME) gradiometer designed in this study is based upon the nickel (Ni)-Pb(Zr,Ti)O(3) (PZT) composites and utilizes the ring-dot piezoelectric transformer structure working near the resonance as the basis. The samples had the ring-dot electrode pattern printed on the top surface of PZT, where ring acts as the input while dot acts as the output. There is an insulation gap between the input and output section of 1.2 mm. The generated magnetic field due to converse ME effect interacts with the external applied magnetic field producing flux gradient, which is detected through the frequency shift and output voltage change in gradiometer structure. The measurements of output voltage dependence on applied magnetic field clearly illustrate that the proposed design can provide high sensitivity and bandwidth.
An experimental investigation on orthogonal cutting of hybrid CFRP/Ti stacks
NASA Astrophysics Data System (ADS)
Xu, Jinyang; El Mansori, Mohamed
2016-10-01
Hybrid CFRP/Ti stack has been widely used in the modern aerospace industry owing to its superior mechanical/physical properties and excellent structural functions. Several applications require mechanical machining of these hybrid composite stacks in order to achieve dimensional accuracy and assembly performance. However, machining of such composite-to-metal alliance is usually an extremely challenging task in the manufacturing sectors due to the disparate natures of each stacked constituent and their respective poor machinability. Special issues may arise from the high force/heat generation, severe subsurface damage and rapid tool wear. To study the fundamental mechanisms controlling the bi-material machining, this paper presented an experimental study on orthogonal cutting of hybrid CFRP/Ti stack by using superior polycrystalline diamond (PCD) tipped tools. The utilized cutting parameters for hybrid CFRP/Ti machining were rigorously adopted through a compromise selection due to the disparate machinability behaviors of the CFRP laminate and Ti alloy. The key cutting responses in terms of cutting force generation, machined surface quality and tool wear mechanism were precisely addressed. The experimental results highlighted the involved five stages of CFRP/Ti cutting and the predominant crater wear and edge fracture failure governing the PCD cutting process.
On Poisson's ratio for metal matrix composite laminates. [aluminum boron composites
NASA Technical Reports Server (NTRS)
Herakovich, C. T.; Shuart, M. J.
1978-01-01
The definition of Poisson's ratio for nonlinear behavior of metal matrix composite laminates is discussed and experimental results for tensile and compressive loading of five different boron-aluminum laminates are presented. It is shown that there may be considerable difference in the value of Poisson's ratio as defined by a total strain or an incremental strain definition. It is argued that the incremental definition is more appropriate for nonlinear material behavior. Results from a (0) laminate indicate that the incremental definition provides a precursor to failure which is not evident if the total strain definition is used.
NASA Technical Reports Server (NTRS)
Nettles, Alan T.
1994-01-01
Delaminations in laminated composite materials can degrade the compressive strength of these materials. Delaminations can form as a result of impact damage or processing flaws. In order to better understand the effects of these delaminations on the compressive behavior of laminated composite plates, programs have been conducted to assess the criticality of prescribed delaminations of known size, shape, and location on the compression strength of laminated composites. A review of these programs is presented along with highlights of pertinent findings from each.
Effect of laminate thickness and specimen configuration on the fracture of laminated composites
NASA Technical Reports Server (NTRS)
Harris, C. E.; Morris, D. H.
1986-01-01
Attention is given to the effect of laminate thickness on graphite/epoxy laminates in the present measurements of fracture toughness in center cracked tension specimens, compact tension specimens, and three-point bend specimens. Crack tip damage development prior to fracture is also studied. The results obtained show fracture toughness to be a function of laminate thickness, being in all cases independent of crack size. The fracture surface of all thick laminates was uniform in the interior and self-similar with the starter notch. With only one exception, the fracture toughness of the thicker laminates was relatively independent of specimen configuration.
NASA Astrophysics Data System (ADS)
Philp, Wayne R.; Pierce, S. Gareth; Gachagan, Anthony; McNab, Alistair; Hayward, Gordon; Culshaw, Brian
1996-04-01
Glass reinforced plastic (GRP) and carbon fibre reinforced plastic (CF'RP) laminates are durable, versatile and light-weight materials which are progressively replacing metals traditionally used in aerospace, automobile, rail, gas-storage and many other industries. If these composite structures were to debond, fracture or seriously degrade whilst in-service, public injury or catastrophic failure could result. Therefore, in-service condition monitoring techniques for composite structures are most significant and are of immediate importance.
NASA Astrophysics Data System (ADS)
Nakada, Masakazu; Maeda, M.; Hirohata, T.; Morita, M.; Miyano, Y.
1997-03-01
A prediction method of fatigue strength of polymer composites for an arbitrary frequency, stress ratio and temperature was proposed. The method is based upon the four hypotheses, (A) same failure mechanism for static, creep and fatigue failure, (b) same time-temperature superposition principle for all failure strengths, (C) linear cumulative damage law for monotone loading and (D) linear dependence of fatigue strength upon stress ratio. Flexural static, creep and fatigue tests at various temperatures were conducted in the transverse direction of two kinds of unidirectional CFRP laminates, which are T300/2500 and T300/PEEK. The validity of the prediction method and the applicability of the hypotheses for the flexural fatigue strength in the transverse direction of unidirectional CFRP laminates were discussed.
NASA Astrophysics Data System (ADS)
Kumar, Deepak; Roy, Rene; Kweon, Jin-Hwe; Choi, Jin-ho
2016-06-01
Sub-laminate damage in the form of matrix cracking and delamination was simulated by using interface cohesive elements in the finite element (FE) software ABAQUS. Interface cohesive elements were inserted parallel to the fiber orientation in the transverse ply with equal spacing (matrix cracking) and between the interfaces (delamination). Matrix cracking initiation in the cohesive elements was based on stress traction separation laws and propagated under mixed-mode loading. We expanded the work of Shi et al. (Appl. Compos. Mater. 21, 57-70 2014) to include delamination and simulated additional [45/-45/0/90]s and [02/90n]s { n = 1,2,3} CFRP laminates and a [0/903]s GFRP laminate. Delamination damage was quantified numerically in terms of damage dissipative energy. We observed that transverse matrix cracks can propagate to the ply interface and initiate delamination. We also observed for [0/90n/0] laminates that as the number of 90° ply increases past n = 2, the crack density decreases. The predicted crack density evolution compared well with experimental results and the equivalent constraint model (ECM) theory. Empirical relationships were established between crack density and applied stress by linear curve fitting. The reduction of laminate elastic modulus due to cracking was also computed numerically and it is in accordance with reported experimental measurements.
An orthotropic laminate composite containing a layer with a crack
NASA Technical Reports Server (NTRS)
Arin, K.
1974-01-01
A laminate composite containing an orthotropic layer with a crack situated normal to the interfaces, and bonded to two orthotropic half-planes of dissimilar materials was considered. The solutions for two different classes of orthotropic materials are presented. In each case, the problem was first reduced to a system of dual integral equations, then to a singular integral equation which was subsequently solved numerically for the stress intensity factors at the tip of the crack. The effect of the material properties on the stress intensity factor was investigated. The generalized plane stress and the plane strain were treated simultaneously.
Analytical and Experimental Characterization of Damage Processes in Composite Laminates
1988-06-01
INDIVIDUAL 221L TELEPHONE NUMBER 2.6IESMO L~~~.CoL(In do~? A( meA0 ode) 00 FORM 1473, 83 APR EDITION OF I JAN 73 IS OBSOLETE. ABSTRACT This report...Mechanics of Metal Matrix Composite Laminates," Strain Localization and Size Effect Due to Cracking and Damage, edited by J. Mazars and Z.P. Bazant , Elsevier...Effect Due to Cracking and Damage, edited by J. Mazars and Z.P. Bazant , Elsevier Scientific Publishers, London, 1988. 17 14. Kaveh-Ahangar, A., Ph.D
Low velocity impact analysis of composite laminated plates
NASA Astrophysics Data System (ADS)
Zheng, Daihua
2007-12-01
In the past few decades polymer composites have been utilized more in structures where high strength and light weight are major concerns, e.g., aircraft, high-speed boats and sports supplies. It is well known that they are susceptible to damage resulting from lateral impact by foreign objects, such as dropped tools, hail and debris thrown up from the runway. The impact response of the structures depends not only on the material properties but also on the dynamic behavior of the impacted structure. Although commercial software is capable of analyzing such impact processes, it often requires extensive expertise and rigorous training for design and analysis. Analytical models are useful as they allow parametric studies and provide a foundation for validating the numerical results from large-scale commercial software. Therefore, it is necessary to develop analytical or semi-analytical models to better understand the behaviors of composite structures under impact and their associated failure process. In this study, several analytical models are proposed in order to analyze the impact response of composite laminated plates. Based on Meyer's Power Law, a semi-analytical model is obtained for small mass impact response of infinite composite laminates by the method of asymptotic expansion. The original nonlinear second-order ordinary differential equation is transformed into two linear ordinary differential equations. This is achieved by neglecting high-order terms in the asymptotic expansion. As a result, the semi-analytical solution of the overall impact response can be applied to contact laws with varying coefficients. Then an analytical model accounting for permanent deformation based on an elasto-plastic contact law is proposed to obtain the closed-form solutions of the wave-controlled impact responses of composite laminates. The analytical model is also used to predict the threshold velocity for delamination onset by combining with an existing quasi
a Study of 954-2A/IM7 Composite Laminates Containing a Central Hole
NASA Astrophysics Data System (ADS)
Kim, Hyungwon
Predicting microcracking properties of the composite laminates in nonuniform stress conditions was the subject in this paper. The uniform stress field meant the stresses were independent of the width direction. The material was the 954-2A/IM7 laminates containing a central hole. Microcracks initiated at the edge of the hole and propagated into the laminate. Because the tensile stress concentration decreased with distance, the microcracks were arrested before the edge of the laminate. Because carbon fiber composites were opaque, a x-ray method was used to detect the length of the propagating microcracks. The microcracking at the near edge of the hole could be reasonably predicted by considering the local laminate stresses and the microcracking toughness measured in unnotched laminates. However, the data away from the hole did not agree with the predictions. The local microcrack density was always much higher than that predicted by the local laminate stress.
NASA Technical Reports Server (NTRS)
Saravanos, Dimitris A.
1996-01-01
Mechanics for the analysis of laminated composite shells with piezoelectric actuators and sensors are presented. A new mixed-field laminate theory for piezoelectric shells is formulated in curvilinear coordinates which combines single-layer assumptions for the displacements and a layerwise representation for the electric potential. The resultant coupled governing equations for curvilinear piezoelectric laminates are described. Structural mechanics are subsequently developed and an 8-node finite-element is formulated for the static and dynamic analysis of adaptive composite structures of general laminations containing piezoelectric layers. Evaluations of the method and comparisons with reported results are presented for laminated piezoelectric-composite plates, a closed cylindrical shell with a continuous piezoceramic layer and a laminated composite semi-circular cantilever shell with discrete cylindrical piezoelectric actuators and/or sensors.
Computational modeling of progressive failure and damage in composite laminates
NASA Astrophysics Data System (ADS)
Basu, Shiladitya
Current and future aerospace systems utilize an ever-increasing amount of fiber reinforced composite laminates in various mission critical structural components making it imperative to understand their damage tolerance capacity under a multitude of loading envelopes. Their comparatively low strength under predominantly axial compressive loading severely limits the design loads of such structures. In the current work, a mechanism based lamina level computational methodology is developed for progressive failure analysis (PFA) of composite laminates beyond initial failure. A combination of analytical and micromechanical studies are used to identify the underlying mechanism of failure under predominantly compressive loading. Under such loading, the class of carbon fiber reinforced laminates considered in this thesis fails by fiber kinking. Results from an analytical study dispel the notion of a fixed compressive strength and show that it is a function of the in-situ geometric and material properties and stress state. These observations and finite element based micromechanical studies have identified the in-situ fiber rotation in the presence of initial fiber misalignment and the degradation of the in-situ shear modulus due to microcracking as the two main drivers of the kinking failure mechanism. A previously developed thermodynamics based lamina constitutive model is utilized to develop a PFA methodology for laminated composites. Laminae are assumed to be damaged by microcraking that is manifested in the degradation of the shear modulus and the transverse modulus. The amount of irrecoverable energy, expressed as a thermodynamic state variable S, provides a measure of the damage state inside a lamina. Lamina level coupon tests are used to obtain relations between S and the degrading moduli. These relations in conjunction with the lamina elastic constants and the geometric information such as the lamina thickness and the lamina lay-up are used as the PFA inputs. Damage
Ancient and Modern Laminated Composites - From the Great Pyramid of Gizeh to Y2K
Wadsworth, J.; Lesuer, D.R.
2000-03-14
Laminated metal composites have been cited in antiquity; for example, a steel laminate that may date as far back as 2750 B.C., was found in the Great Pyramid in Gizeh in 1837. A laminated shield containing bronze, tin, and gold layers, is described in detail by Homer. Well-known examples of steel laminates, such as an Adze blade, dating to 400 B.C. can be found in the literature. The Japanese sword is a laminated composite at several different levels and Merovingian blades were composed of laminated steels. Other examples are also available, including composites from China, Thailand, Indonesia, Germany, Britain, Belgium, France, and Persia. The concept of lamination to provide improved properties has also found expression in modern materials. Of particular interest is the development of laminates including high carbon and low carbon layers. These materials have unusual properties that are of engineering interest; they are similar to ancient welded Damascus steels. The manufacture of collectable knives, labeled ''welded Damascus'', has also been a focus of contemporary knifemakers. Additionally, in the Former Soviet Union, laminated composite designs have been used in engineering applications. Each of the above areas will be briefly reviewed, and some of the metallurgical principles will be described that underlie improvement in properties by lamination. Where appropriate, links are made between these property improvements and those that may have been present in ancient artifacts.
Experimental Verification of Computational Models for Laminated Composites
NASA Technical Reports Server (NTRS)
Harris, Charles E.; Coats, Timothy W.; Glaessgen, Edward H.
1999-01-01
The objective of the research reported herein is to develop a progressive damage methodology capable of predicting the residual strength of continuous fiber-reinforced, laminated, polymer matrix composites with through-penetration damage. The fracture behavior of center-notch tension panels with thin crack-like slits was studied. Since fibers are the major load-carrying constituent in polymer matrix composites, predicting the residual strength of a laminate requires a criterion for fiber fracture. The effects on fiber strain due to other damage mechanisms such as matrix cracking and delaminations must also be modeled. Therefore, the research herein examines the damage mechanisms involved in translaminate fracture and identifies the toughening mechanisms responsible for damage growth resistance in brittle epoxy matrix systems. The mechanics of matrix cracking and fiber fracture are discussed as is the mathematical framework for the progressive damage model developed by the authors. The progressive damage analysis algorithms have been implemented into a general purpose finite element code developed by NASA, the Computational Structural Mechanics Testbed (COMET). Damage growth is numerically simulated and the analytical residual strength predictions are compared to experimental results for a variety of notched panel configurations and materials systems.
Integrated piezoceramic transducers for imaging damage in composite laminates
NASA Astrophysics Data System (ADS)
Ng, C. T.; Veidt, M.; Rajic, N.
2009-07-01
This paper presents a two-phase imaging methodology to characterise damage in composite laminates utilising Lamb waves generated by integrated piezoceramic transducers. The proposed methodology uses the transducers to sequentially scan the composite laminates before and after the presence of damage by transmitting and receiving Lamb wave pulses. In phase one the damage localisation image is reconstructed by analysing the cross-correlation of the wavelet extracted information from scatter signals with the excitation pulse for each transducer pair. A potential damage area is then reconstructed by superimposing the image observed from each actuator and sensor signal path. In phase two Lamb wave diffraction tomography is used to reconstruct an image quantifying size and shape of the damage based on the same set of measurement data and identified damage location in phase one. The two-phase imaging approach together with the modified diffraction tomography reconstruction algorithm enables a significant reduction of the required number of transducers without the need to know the damage location in advance. Numerical and experimental results are presented to demonstrate the efficiency, accuracy and sensitivity of the proposed methodology.
Strain Rate Sensitivity of Graphite/Polymer Laminate Composites
NASA Astrophysics Data System (ADS)
Syed, Izhar H.; Brar, N. S.
2002-07-01
Strain rate sensitivities of Graphite/Epoxy and Graphite/Peek laminate composites are investigated by measuring their stress-strain response at strain rates of 0.001/s, 0.1/s, and 400/s. Tension specimens of the composite laminates are fabricated in a dog-bone shape. Stress-strain data at quasi-static rates of 0.001/s and 0.1/s are obtained using a servohydraulic test system. High strain rate data are produced with a Direct Tension Split Hopkinson Bar (DTSHB). A tensile stress pulse is generated in the DTSHB by impacting a stopper flange at the end of the incident bar with an aluminum/polymeric tube launched around the incident bar. The failure (flow) tensile stress of Graphite/Epoxy increases from 240 MPa to 280±10 MPa (ɛ = 0.06) when the strain rate is raised from 0.001/s to 400/s. For Graphite/Peek, failure (flow) tension stress increases from 175 MPa at a strain rate of 0.001/s to 270±20 MPa at a strain rate of 400/s.
Suppression of interlaminar damage in carbon/epoxy laminates by use of interleaf layers
Tanimoto, Toshio . Dept. of Materials Science Ceramic Technology)
1994-10-15
Carbon fiber reinforced plastics (CFRP) have been widely used as a structural material. In general, fiber orientation angle of each lamina in these laminates is variously chosen in order to taylor a material which meets the particular requirement for the material properties in arbitrary direction of laminate. Quasi-isotropic lamination, in which the laminate consisted of laminae with fiber orientation of 0[degree], +45[degree], [minus]45[degree] and 90[degree] to loading axis, is most commonly employed in the actual application. However, quasi-isotropic carbon/epoxy laminates are known to develop the interlaminar stress concentrations near the free edge region. These laminates have a strong tendency to delaminate near the edges when subjected to axial in-plane loading. Such a free edge delamination under loading in the plane of the laminate is a unique problem to laminated composites. This paper summarizes the author's investigation which was performed to reduce the free edge interlaminar stresses in the laminate by incorporating interleaf films between plies and thus to improve the mechanical properties of these materials. In their previous work, the authors have shown that these laminates exhibit a high vibration damping capability. Loss factor values for these CFRP/interleaf laminates which were measured in cantilever beam tests, are 5 to 50 times as large as that for conventional CFRP. In this paper, discussion will be provided on the mechanical properties of the interleaved quasi-isotropic carbon/epoxy laminate, [0/[+-]45/90][sub s], with a special emphasis on the optimum design of interply locations to incorporate the interleaf films for the particular requirement such as static strength, elastic modulus, fatigue resistance and so on.
Tensile and impact behavior of laminated composites based on ultrahigh carbon steel
Lee, S.
1988-01-01
The goal was to develop metal-laminated composites for high strength and high strength and high toughness and centered on three major objectives. The first one was to develop a laminated composite, based on ultrahigh carbon steel (UHCS), which can be selectively heat treated to achieve alternating hard UHCS and soft interleaf layers. The second was to maintain sharp and discrete interlayer boundaries in the UHCS laminated composite after selective heat treatment with no interdiffusion of carbon. The third was to achieve high notch-impact toughness in the selectively heat-treated laminated composite. Five laminated composites were investigated. They are UHCS/Fe-3%Si, UHCS/Hadfield manganese steel (HMS), UHCS/9%Ni-2%Si steel, UHCS/brass and UHCS/304 stainless steel (304ss). All five laminated composites were selectively heat treated to achieve the desired objective of alternating hard and soft layers. Charpy V-notch impact tests were performed on the first four laminates. Each laminate showed a lower ductile-to-brittle transition temperature (DBTT) than those obtained in the monolithic UHS and the monolithic interleaf material making up the laminate.
Fiber optic sensor for continuous health monitoring in CFRP composite materials
NASA Astrophysics Data System (ADS)
Rippert, Laurent; Papy, Jean-Michel; Wevers, Martine; Van Huffel, Sabine
2002-07-01
An intensity modulated sensor, based on the microbending concept, has been incorporated in laminates produced from a C/epoxy prepreg. Pencil lead break tests (Hsu-Neilsen sources) and tensile tests have been performed on this material. In this research study, fibre optic sensors will be proven to offer an alternative for the robust piezoelectric transducers used for Acoustic Emission (AE) monitoring. The main emphasis has been put on the use of advanced signal processing techniques based on time-frequency analysis. The signal Short Time Fourier Transform (STFT) has been computed and several robust noise reduction algorithms, such as Wiener adaptive filtering, improved spectral subtraction filtering, and Singular Value Decomposition (SVD) -based filtering, have been applied. An energy and frequency -based detection criterion is put forward to detect transient signals that can be correlated with Modal Acoustic Emission (MAE) results and thus damage in the composite material. There is a strong indication that time-frequency analysis and the Hankel Total Least Squares (HTLS) method can also be used for damage characterization. This study shows that the signal from a quite simple microbend optical sensor contains information on the elastic energy released whenever damage is being introduced in the host material by mechanical loading. Robust algorithms can be used to retrieve and analyze this information.
Microcracking in composite laminates under thermal and mechanical loading. Thesis
NASA Technical Reports Server (NTRS)
Maddocks, Jason R.
1995-01-01
Composites used in space structures are exposed to both extremes in temperature and applied mechanical loads. Cracks in the matrix form, changing the laminate thermoelastic properties. The goal of the present investigation is to develop a predictive methodology to quantify microcracking in general composite laminates under both thermal and mechanical loading. This objective is successfully met through a combination of analytical modeling and experimental investigation. In the analysis, the stress and displacement distributions in the vicinity of a crack are determined using a shear lag model. These are incorporated into an energy based cracking criterion to determine the favorability of crack formation. A progressive damage algorithm allows the inclusion of material softening effects and temperature-dependent material properties. The analysis is implemented by a computer code which gives predicted crack density and degraded laminate properties as functions of any thermomechanical load history. Extensive experimentation provides verification of the analysis. AS4/3501-6 graphite/epoxy laminates are manufactured with three different layups to investigate ply thickness and orientation effects. Thermal specimens are cooled to progressively lower temperatures down to -184 C. After conditioning the specimens to each temperature, cracks are counted on their edges using optical microscopy and in their interiors by sanding to incremental depths. Tensile coupons are loaded monotonically to progressively higher loads until failure. Cracks are counted on the coupon edges after each loading. A data fit to all available results provides input parameters for the analysis and shows them to be material properties, independent of geometry and loading. Correlation between experiment and analysis is generally very good under both thermal and mechanical loading, showing the methodology to be a powerful, unified tool. Delayed crack initiation observed in a few cases is attributed to a
Ceysson, O.; Salvia, M.; Vincent, L.
1996-04-15
Carbon fiber reinforced plastics (CFRP) offer high specific mechanical properties (performance vs weight ratio). Since carbon fibers are electrical conductors ({rho} = 2.10{sup {minus}5} {Omega}.m), the measurement of the variations of electrical resistance appears to be a valuable technique for damage detection. In the case of CFRP samples, conductivity is not isotropic but depends on the orientation of the carbon fibers. The electrical conduction of (0{degree}) unidirectional (UD) CFRP parallel to the fibers is due to the current flow along the fibers. This can be modeled using the parallel resistance approach. In this present work, the variation of the electrical conductivity can be taken as an indicator of the evolution of various types of damage in classical longitudinal UD but also in ({+-} 45{degree}) CFRP laminates. By comparison with a more classical non-destructive technique such as Acoustic Emission, it has been shown that it is possible that the electrical resistance measurement allows one to monitor in-situ the evolution of various internal damage nucleation and growth in CFRP such as fiber fractures, intraply matrix cracks and interply delaminations.
Linear versus nonlinear theories for laminated composite plates and shells
Qatu, M.S.
1995-11-01
Linear and nonlinear shear-deformation theories for laminated composite plates and shells are discussed in this paper. The emphasis here is on the range of validity for each class of theories. The finite element method is used to determine the maximum stresses for a wide range of statically loaded plate and shell panels with various thickness ratios. This paper concludes that for the vast majority of composite materials and for moderately thick plates and shells, stresses normally reach the maximum allowable stress before nonlinear terms can become important. This has been demonstrated by showing that for the limiting case of shear deformation theories (in which the minimum span length (or radius) to thickness ratio is 20), the material usually fails before the maximum deflection reaches the magnitude of the thickness (where nonlinear terms start to become significant).
Analysis of laminated composite shells under internal pressure
NASA Technical Reports Server (NTRS)
Yuan, F. G.
1991-01-01
A closed form solution is presented that predicts the response of filament wound composite shells subjected to internal pressure. The material of the shell is assumed to be general cylindrically anisotropic. Based on the theory of cylindrical anisotropic elasticity coupled differential equations are developed using Lekhnitskii's stress function approach. Two composite systems, graphite/epoxy and glass/epoxy, are selected to demonstrate the influence of degree of material anisotropy and fiber orientations on the axial and induced twisting deformation. Detailed stress distributions of (45) off-axis unidirectional and (45/-45)s symmetric angle-ply fiber-reinforced laminated shells are shown to illustrate the effect of radius-to-thickness ratio and stacking sequence.
Esthetic Rehabilitation of Anterior Teeth with Laminates Composite Veneers
Riva, Giancarlo
2014-01-01
No- or minimal-preparation veneers associated with enamel preservation offer predictable results in esthetic dentistry; indirect additive anterior composite restorations represent a quick, minimally invasive, inexpensive, and repairable option for a smile enhancement treatment plan. Current laboratory techniques associated with a strict clinical protocol satisfy patients' restorative and esthetic needs. The case report presented describes minimal invasive treatment of four upper incisors with laminate nanohybrid resin composite veneers. A step-by-step protocol is proposed for diagnostic evaluation, mock-up fabrication and trial, teeth preparation and impression, and adhesive cementation. The resolution of initial esthetic issues, patient satisfaction, and nice integration of indirect restorations confirmed the success of this anterior dentition rehabilitation. PMID:25013730
Fatigue Life Methodology for Tapered Composite Flexbeam Laminates
NASA Technical Reports Server (NTRS)
Murri, Gretchen B.; OBrien, T. Kevin; Rousseau, Carl Q.
1997-01-01
The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to non-linear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse displacement. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.
Fatigue Life Methodology for Tapered Composite Flexbeam Laminates
NASA Technical Reports Server (NTRS)
Murri, Gretchen B.; O''Brien, T. Kevin; Rousseau, Carl Q.
1997-01-01
The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delamination fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to nonlinear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axial-tension and transverse cyclic bending loads. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen. Continued cycling resulted in multiple delaminations. A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed. The global responses of the model and test specimens agreed very well in terms of the transverse flexbeam tip-displacement and flapping angle. The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode 2, whereas delamination growth toward the thin region was almost completely mode 1. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.
Quantitative Percussion Diagnostics For Evaluating Bond Integrity Between Composite Laminates
NASA Astrophysics Data System (ADS)
Poveromo, Scott Leonard
Conventional nondestructive testing (NDT) techniques used to detect defects in composites are not able to determine intact bond integrity within a composite structure and are costly to use on large and complex shaped surfaces. To overcome current NDT limitations, a new technology was utilized based on quantitative percussion diagnostics (QPD) to better quantify bond quality in fiber reinforced composite materials. Experimental results indicate that this technology is capable of detecting 'kiss' bonds (very low adhesive shear strength), caused by the application of release agents on the bonding surfaces, between flat composite laminates bonded together with epoxy adhesive. Specifically, the local value of the loss coefficient determined from quantitative percussion testing was found to be significantly greater for a release coated panel compared to that for a well bonded sample. Also, the local value of the probe force or force returned to the probe after impact was observed to be lower for the release coated panels. The increase in loss coefficient and decrease in probe force are thought to be due to greater internal friction during the percussion event for poorly bonded specimens. NDT standards were also fabricated by varying the cure parameters of an epoxy film adhesive. Results from QPD for the variable cure NDT standards and lap shear strength measurements taken of mechanical test specimens were compared and analyzed. Finally, experimental results have been compared to a finite element analysis to understand the visco-elastic behavior of the laminates during percussion testing. This comparison shows how a lower quality bond leads to a reduction in the percussion force by biasing strain in the percussion tested side of the panel.
Development of an Advanced Continuum Theory for Composite Laminates. Phase 1
1990-06-27
and cylindric~l laminates was considered. 14. SBJEC TERM 4IS. NUMBER OF PAGES Cosserat Composite Theory for Composite Laminates 250 16. PRICE CODE 17...aerospace, structural, power and propulsion application offer significant advantages in terms I of efficiency and cost. A widespread and efficient...composite. The mechani- 3 cal behavior of such materials is termed mechanics of composite materials. More specifically, a composite material is one in which
A new approach of FEM for laminated composite plates and shells
NASA Astrophysics Data System (ADS)
Xie, Zhicheng; Li, Rufeng; Dong, Chunying; Qian, Zhendong
1991-03-01
A new approach of FEM for modeling laminated composite plates and shells is developed by extending the Mindlin theory, overcoming difficulties usually encountered in studies of these structures. The new model uses the in-plane displacements, the deflection of the film, and the shear strains in a k-th ply as independent variables. It is shown that the model avoids the 'shear locking' in thin plates and shells and yields more accurate results on the distribution of transverse shear stress through the thickness than can be obtained by previous theories. Numerical examples are presented of laminated plates, axisymmetric laminated composite shells under arbitrary loads, and delamination buckling of laminated plates.
NASA Astrophysics Data System (ADS)
Yang, Zhiyong; Zhang, Jianbao; Xie, Yongjie; Zhang, Boming; Sun, Baogang; Guo, Hongjun
2017-03-01
Carbon fiber reinforced polymer, CFRP, composite materials have been used to fabricate space mirror. Usually the composite space mirror can completely replicate the high-precision surface of mould by replication process, but the actual surface accuracy of replicated space mirror is always reduced, still needed further study. We emphatically studied the error caused by layup and curing on the surface accuracy of space mirror through comparative experiments and analyses, the layup and curing influence factors include curing temperature, cooling rate of curing, method of prepreg lay-up, and area weight of fiber. Focusing on the four factors, we analyzed the error influence rule and put forward corresponding control measures to improve the surface figure of space mirror. For comparative analysis, six CFRP composite mirrors were fabricated and surface profile of mirrors were measured. Four guiding control measures were described here. Curing process of composite space mirror is our next focus.
Laminate behavior for SiC fiber-reinforced reaction-bonded silicon nitride matrix composites
NASA Technical Reports Server (NTRS)
Bhatt, Ramakrishna T.; Phillips, Ronald E.
1990-01-01
The room temperature mechanical properties of SiC fiber reinforced reaction-bonded silicon nitride matrix composite laminates (SiC/RBSN) have been measured. The laminates contained approx 30 volume fraction of aligned 142-micron diameter SiC fiber in a porous RBSN matrix. Three types of laminate studied were unidirectional: (1) (0) sub 8, (2) (10) sub 8, and (3) (45) sub 8, and (90) sub 8; cross plied laminates (0 sub 2/90 sub 2); and angle plied laminates: (+45 sub 2/-45 sub 2). Each laminate contained eight fiber plies. Results of the unidirectionally reinforced composites tested at various angles to the reinforcement direction indicate large anisotropy in in-plane properties. In addition, strength properties of these composites along the fiber direction were independent of specimen gage length and were unaffected by notches normal to the fiber direction. Splitting parallel to the fiber at the notch tip appears to be the dominant crack blunting mechanism responsible for notch insensitive behavior of these composites. In-plane properties of the composites can be improved by 2-D laminate construction. Mechanical property results for (0 sub 2/90 sub 2) sub s and (+45/-45 sub 2) sub s laminates showed that their matrix failure strains were similar to that for (0) sub 8 laminates, but their primary elastic moduli, matrix cracking strengths, and ultimate composite strengths were lower. The elastic properties of unidirectional, cross-ply, and angle-ply composites can be predicted from modified constitutive equations and laminate theory. Further improvements in laminate properties may be achieved by reducing the matrix porosity and by optimizing the bond strength between the SiC fiber and RBSN matrix.
Laminate behavior for SiC fiber-reinforced reaction-bonded silicon nitride matrix composites
NASA Technical Reports Server (NTRS)
Rhatt, R. T.; Phillips, R. E.
1988-01-01
The room temperature mechanical properties of SiC fiber reinforced reaction-bonded silicon nitride matrix composite laminates (SiC/RBSN) have been measured. The laminates contained approx 30 volume fraction of aligned 142-micron diameter SiC fiber in a porous RBSN matrix. Three types of laminate studied were unidirectional: (1) (0) sub 8, (2) (10) sub 8, and (3) (45) sub 8, and (90) sub 8; cross plied laminates (0 sub 2/90 sub 2); and angle plied laminates: (+45 sub 2/-45 sub 2). Each laminate contained eight fiber plies. Results of the unidirectionally reinforced composites tested at various angles to the reinforcement direction indicate large anisotropy in in-plane properties. In addition, strength properties of these composites along the fiber direction were independent of specimen gage length and were unaffected by notches normal to the fiber direction. Splitting parallel to the fiber at the notch tip appears to be the dominant crack blunting mechanism responsible for notch insensitive behavior of these composites. In-plane properties of the composites can be improved by 2-D laminate construction. Mechanical property results for (0 sub 2/90 sub 2)sub s and (+45/-45 sub 2) sub s laminates showed that their matrix failure strains were similar to that for (0) sub 8 laminates, but their primary elastic moduli, matrix cracking strengths, and ultimate composite strengths were lower. The elastic properties of unidirectional, cross-ply, and angle-ply composites can be predicted from modified constitutive equations and laminate theory. Further improvements in laminate properties may be achieved by reducing the matrix porosity and by optimizing the bond strength between the SiC fiber and RBSN matrix.
A New Approach to Fibrous Composite Laminate Strength Prediction
NASA Technical Reports Server (NTRS)
Hart-Smith, L. J.
1990-01-01
A method of predicting the strength of cross-plied fibrous composite laminates is based on expressing the classical maximum-shear-stress failure criterion for ductile metals in terms of strains. Starting with such a formulation for classical isotropic materials, the derivation is extended to orthotropic materials having a longitudinal axis of symmetry, to represent the fibers in a unidirectional composite lamina. The only modification needed to represent those same fibers with properties normalized to the lamina rather than fiber is a change in axial modulus. A mirror image is added to the strain-based lamina failure criterion for fiber-dominated failures to reflect the cutoffs due to the presence of orthogonal fibers. It is found that the combined failure envelope is now identical with the well-known maximum-strain failure model in the tension-tension and compression-compression quadrants but is truncated in the shear quadrants. The successive application of this simple failure model for fibers in the 0/90 degree and +/- 45 degree orientations, in turn, is shown to be the necessary and sufficient characterization of the fiber-dominated failures of laminates made from fibers having the same tensile and compressive strengths. When one such strength is greater than the other, the failure envelope is appropriately truncated for the lesser direct strain. The shear-failure cutoffs are now based on the higher axial strain to failure since they occur at lower strains than and are usually not affected by such mechanisms as microbuckling. Premature matrix failures can also be covered by appropriately truncating the fiber failure envelope. Matrix failures are excluded from consideration for conventional fiber/polymer composites but the additional features needed for a more rigorous analysis of exotic materials are covered. The new failure envelope is compared with published biaxial test data. The theory is developed for unnotched laminates but is easily shrunk to incorporate
Irradiation effects in tungsten-copper laminate composite
Garrison, L. M.; Katoh, Yutai; Snead, Lance L.; Byun, Thak Sang; Reiser, Jens; Rieth, Michael
2016-09-19
Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410–780 °C and fast neutron fluences of 0.02–9.0 × 10^{25} n/m^{2}, E > 0.1 MeV, 0.0039–1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22 °C. After only 0.0039 dpa this was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22 °C. In conclusion, tor elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.
Irradiation effects in tungsten-copper laminate composite
Garrison, L. M.; Katoh, Yutai; Snead, Lance L.; ...
2016-09-19
Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410–780 °C and fast neutron fluences of 0.02–9.0 × 1025 n/m2, E > 0.1 MeV, 0.0039–1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22 °C. After only 0.0039 dpa thismore » was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22 °C. In conclusion, tor elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.« less
Irradiation effects in tungsten-copper laminate composite
Garrison, L. M.; Katoh, Y.; Snead, L. L.; Byun, T. S.; Reiser, J.; Rieth, M.
2016-12-01
Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410-780°C and fast neutron fluences of 0.02-9.0×1025 n/m2, E>0.1 MeV, 0.0039-1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22°C. After only 0.0039 dpa this was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22°C. For elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.
Irradiation effects in tungsten-copper laminate composite
NASA Astrophysics Data System (ADS)
Garrison, L. M.; Katoh, Y.; Snead, L. L.; Byun, T. S.; Reiser, J.; Rieth, M.
2016-12-01
Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410-780 °C and fast neutron fluences of 0.02-9.0 × 1025 n/m2, E > 0.1 MeV, 0.0039-1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22 °C. After only 0.0039 dpa this was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22 °C. For elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.
Irradiation effects in tungsten-copper laminate composite
Garrison, L. M.; Katoh, Yutai; Snead, Lance L.; Byun, Thak Sang; Reiser, Jens; Rieth, Michael
2016-09-19
Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410–780 °C and fast neutron fluences of 0.02–9.0 × 10^{25} n/m^{2}, E > 0.1 MeV, 0.0039–1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22 °C. After only 0.0039 dpa this was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22 °C. In conclusion, tor elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.
Influence of residual stresses on the tensile strength of composite-metal sandwich laminates
NASA Technical Reports Server (NTRS)
Herakovich, C. T.; Wong, D. M.
1977-01-01
The tensile strength of boron-epoxy/aluminum sandwich laminates is discussed relative to the residual thermal stresses generated by curing and bonding at elevated temperatures. It is shown that the sandwich laminates investigated exhibit three dinstinct modes of failure, depending upon the fiber orientation of the composite. Sandwich laminates with moderate to high percentage of 0-deg fibers exhibit early failures initiated by edge effect; laminates with moderate to high percentage of 90-deg fibers fail according to a first-ply failure criterion; laminates with moderate to high percentages of plus or minus 45 deg plies fail at strains equal to or greater than the failure strain of the corresponding all-composite laminate.
Influence of residual stresses on the tensile strength of composite-metal sandwich laminates
NASA Technical Reports Server (NTRS)
Herakovich, C. T.; Wong, D. M.
1977-01-01
The tensile strength of boron-epoxy/aluminum sandwich laminates is discussed relative to the residual thermal stresses generated by curing and bonding at elevated temperatures. It is shown that the sandwich laminates investigated exhibit three dinstinct modes of failure, depending upon the fiber orientation of the composite. Sandwich laminates with moderate to high percentage of 0-deg fibers exhibit early failures initiated by edge effect; laminates with moderate to high percentage of 90-deg fibers fail according to a first-ply failure criterion; laminates with moderate to high percentages of plus or minus 45 deg plies fail at strains equal to or greater than the failure strain of the corresponding all-composite laminate.
Composite laminates with negative through-the-thickness Poisson's ratios
NASA Technical Reports Server (NTRS)
Herakovich, C. T.
1984-01-01
A simple analysis using two dimensional lamination theory combined with the appropriate three dimensional anisotropic constitutive equation is presented to show some rather surprising results for the range of values of the through-the-thickness effective Poisson's ratio nu sub xz for angle ply laminates. Results for graphite-epoxy show that the through-the-thickness effective Poisson's ratio can range from a high of 0.49 for a 90 laminate to a low of -0.21 for a + or - 25s laminate. It is shown that negative values of nu sub xz are also possible for other laminates.
Composite laminates with negative through-the-thickness Poisson's ratios
NASA Technical Reports Server (NTRS)
Herakovich, C. T.
1984-01-01
A simple analysis using two-dimensional lamination theory combined with the appropriate three-dimensional anisotropic constitutive equation is presented to show some rather surprising results for the range of values of the through-the-thickness effective Poisson's ratio nu sub xz for angle ply laminates. Results for graphite-epoxy show that the through-the-thickness effective Poisson's ratio can range from a high of 0.49 for a 90 laminate to a low of -0.21 for a + or - 25s laminate. It is shown that negative values of nu sub xz are also possible for other laminates.
Experimental investigation of defect criticality in FRP laminate composites
NASA Astrophysics Data System (ADS)
Joyce, Peter James
1999-11-01
This work examines the defect criticality of fiber reinforced polymer Composites. The objective is to determine the sensitivity of the finished composite to various process-induced defects. This work focuses on two different classes of process-induced defects; (1) fiber waviness in high performance carbon-fiber reinforced unidirectional composites and (2) void volume in low cost glass-fabric reinforced composites. The role of fiber waviness in the compressive response of unidirectional composites has been studied by a number of other investigators. Because of difficulties associated with producing real composites with varying levels of fiber waviness, most experimental studies of fiber waviness have evaluated composites with artificially induced fiber waviness. Furthermore, most experimental studies have been concentrated on the effects of out-of-plane fiber waviness. The objective of this work is to evaluate the effects of in-plane fiber waviness naturally occurring in autoclave consolidated thermoplastic laminates. The first phase of this project involved the development of a simple technique for measuring the resulting fiber waviness levels. An experimental investigation of the compression strength reduction in composites with in-plane fiber waviness followed. The experimental program included carbon-fiber reinforced thermoplastic composites manufactured from prepreg tape by hand layup, and carbon-fiber and glass-fiber reinforced composites manufactured from an experimental powder towpreg by filament winding and autoclave consolidation. The compression specimens exhibited kink band failure in the prepreg composite and varying amounts of longitudinal splitting and kink banding in the towpreg composites. The compression test results demonstrated the same trend as predicted by microbudding theory but the overall quantitative correlation was poor. The second thrust of this research evaluated void effects in resin transfer molded composites. Much of the existing
NASA Technical Reports Server (NTRS)
Shuart, M. J.; Williams, J. G.
1984-01-01
The response and failure of a + or - 45s class laminate was studied by transparent fiberglass epoxy composite birefringent material. The birefringency property allows the laminate stress distribution to be observed during the test and also after the test if permanent residual stresses occur. The location of initial laminate failure and of the subsequent failure propagation are observed through its transparency characteristics. Experimental results are presented.
Factors Influencing Progressive Failure Analysis Predictions for Laminated Composite Structure
NASA Technical Reports Server (NTRS)
Knight, Norman F., Jr.
2008-01-01
Progressive failure material modeling methods used for structural analysis including failure initiation and material degradation are presented. Different failure initiation criteria and material degradation models are described that define progressive failure formulations. These progressive failure formulations are implemented in a user-defined material model for use with a nonlinear finite element analysis tool. The failure initiation criteria include the maximum stress criteria, maximum strain criteria, the Tsai-Wu failure polynomial, and the Hashin criteria. The material degradation model is based on the ply-discounting approach where the local material constitutive coefficients are degraded. Applications and extensions of the progressive failure analysis material model address two-dimensional plate and shell finite elements and three-dimensional solid finite elements. Implementation details are described in the present paper. Parametric studies for laminated composite structures are discussed to illustrate the features of the progressive failure modeling methods that have been implemented and to demonstrate their influence on progressive failure analysis predictions.
Static aeroelastic behavior of an adaptive laminated piezoelectric composite wing
NASA Technical Reports Server (NTRS)
Weisshaar, T. A.; Ehlers, S. M.
1990-01-01
The effect of using an adaptive material to modify the static aeroelastic behavior of a uniform wing is examined. The wing structure is idealized as a laminated sandwich structure with piezoelectric layers in the upper and lower skins. A feedback system that senses the wing root loads applies a constant electric field to the piezoelectric actuator. Modification of pure torsional deformaton behavior and pure bending deformation are investigated, as is the case of an anisotropic composite swept wing. The use of piezoelectric actuators to create an adaptive structure is found to alter static aeroelastic behavior in that the proper choice of the feedback gain can increase or decrease the aeroelastic divergence speed. This concept also may be used to actively change the lift effectiveness of a wing. The ability to modify static aeroelastic behavior is limited by physical limitations of the piezoelectric material and the manner in which it is integrated into the parent structure.
Prediction of residual tensile strength of transversely impacted composite laminates
NASA Technical Reports Server (NTRS)
Lal, K. M.
1982-01-01
The response to low velocity impact of graphite-epoxy T300/5208 composite laminates is discussed. Steel balls of 3/8 inch, 5/8 inch, and 1 inch diameter were the projectiles. Impact energy was limited to 1.2 joules. Impacted specimens were ultrasonically C scanned to determine the impact damaged region. The threshold value of impact energy for impact damage was found to be approximately 0.3 joules. A model was developed to predict the tensile residual strength of impact damaged specimens from fracture mechanics concepts. Impacted specimens were tested in tension to provide a fracture data base. The experimental results agreed well with the predictions from fracture mechanics. In this study, the maximum impact velocity used to simulate the low velocity transverse impact from common objects like tool drops was 10 m/s.
Vibration testing of impact-damaged composite laminates
NASA Technical Reports Server (NTRS)
Grady, Joseph E.; Meyn, Erwin H.
1989-01-01
A new test is described that can be used to measure changes in the vibration properties of impact damaged composite materials. Impact-induced delamination was observed to significantly affect natural frequencies of vibration and damping properties in cross-ply graphite/epoxy laminates. Natural frequencies are shown to drop by as much as half of their original value, and modal damping ratios can increase by a factor of up to eight when large amounts of damage are present. A simple finite element model of the damaged impact specimens was used to predict the effect of delamination on certain vibration properties. A comparison of the finite element calculations with the experimental measurements suggests that delamination was the dominant mechanism of flexural stiffness loss resulting from the transverse impact.
Fatigue damage mechanisms in boron-aluminium composite laminates
NASA Technical Reports Server (NTRS)
Dvorak, G. J.; Johnson, W. S.
1980-01-01
The relationship between fatigue and shakedown in metal matrix composites is investigated theoretically and experimentally for unidirectional and laminated 6061 Al-B materials. It is shown that no fatigue damage takes place if the applied stress range is such that the material remains elastic, or shakes down, i.e., resumes elastic cyclic straining after a small number of plastic strain cycles. Fatigue damage occurs only in specimens subjected to stress ranges which cause sustained cyclic plastic straining in the aluminum matrix. If the applied stress range is smaller than that required for fatigue failure, after about 10 to the 6th cycles a saturation damage state is reached which remains essentially unchanged with increasing number of cycles.
A physically based failure criterion for laminated composites
NASA Astrophysics Data System (ADS)
Kroll, L.; Hufenbach, W.
1999-07-01
The stress and strain fields in laminated composites can be described realistically with the help of a refined theory of elasticity for anisotropic materials. In contrast, the respective failure characteristics cannot be predicted satisfactorily based on the commonly used failure criteria. The main disadvantage of these generalized failure criteria, such as the quadratic failure criteria of Sakharov, Azzi/Tsai, Tsai/Wu, etc., is that they combine fundamentally different fracture mechanisms of the homogenized UD layer in one approximation by an interpolation polynomial. A completely different method for the formulation of realistic failure criteria, taking into account the heterogeneous anisotropic material structure relevant to the fracture, is based on the Mohr hypothesis for brittle materials that in fact only the stresses in the fracture plane induce failure. This physically based failure criterion not only considers the decisive eifference between the fiber fracture and the interfiber fracture, but also characterizes further fracture types in the plane parallel to the fibers.
On the strain energy of laminated composite plates
NASA Technical Reports Server (NTRS)
Atilgan, Ali R.; Hodges, Dewey H.
1991-01-01
The present effort to obtain the asymptotically correct form of the strain energy in inhomogeneous laminated composite plates proceeds from the geometrically nonlinear elastic theory-based three-dimensional strain energy by decomposing the nonlinear three-dimensional problem into a linear, through-the-thickness analysis and a nonlinear, two-dimensional analysis analyzing plate formation. Attention is given to the case in which each lamina exhibits material symmetry about its middle surface, deriving closed-form analytical expressions for the plate elastic constants and the displacement and strain distributions through the plate's thickness. Despite the simplicity of the plate strain energy's form, there are no restrictions on the magnitudes of displacement and rotation measures.
Static aeroelastic behavior of an adaptive laminated piezoelectric composite wing
NASA Technical Reports Server (NTRS)
Weisshaar, T. A.; Ehlers, S. M.
1990-01-01
The effect of using an adaptive material to modify the static aeroelastic behavior of a uniform wing is examined. The wing structure is idealized as a laminated sandwich structure with piezoelectric layers in the upper and lower skins. A feedback system that senses the wing root loads applies a constant electric field to the piezoelectric actuator. Modification of pure torsional deformaton behavior and pure bending deformation are investigated, as is the case of an anisotropic composite swept wing. The use of piezoelectric actuators to create an adaptive structure is found to alter static aeroelastic behavior in that the proper choice of the feedback gain can increase or decrease the aeroelastic divergence speed. This concept also may be used to actively change the lift effectiveness of a wing. The ability to modify static aeroelastic behavior is limited by physical limitations of the piezoelectric material and the manner in which it is integrated into the parent structure.
An Enriched Shell Element for Delamination Simulation in Composite Laminates
NASA Technical Reports Server (NTRS)
McElroy, Mark
2015-01-01
A formulation is presented for an enriched shell finite element capable of delamination simulation in composite laminates. The element uses an adaptive splitting approach for damage characterization that allows for straightforward low-fidelity model creation and a numerically efficient solution. The Floating Node Method is used in conjunction with the Virtual Crack Closure Technique to predict delamination growth and represent it discretely at an arbitrary ply interface. The enriched element is verified for Mode I delamination simulation using numerical benchmark data. After determining important mesh configuration guidelines for the vicinity of the delamination front in the model, a good correlation was found between the enriched shell element model results and the benchmark data set.
The nonlinear viscoelastic response of resin matrix composite laminates
NASA Technical Reports Server (NTRS)
Hiel, C.; Cardon, A. H.; Brinson, H. F.
1984-01-01
Possible treatments of the nonlinear viscoelastic behavior of materials are reviewed. A thermodynamic based approach, developed by Schapery, is discussed and used to interpret the nonlinear viscoelastic response of a graphite epoxy laminate, T300/934. Test data to verify the analysis for Fiberite 934 neat resin as well as transverse and shear properties of the unidirectional T300/934 composited are presented. Long time creep characteristics as a function of stress level and temperature are generated. Favorable comparisons between the traditional, graphical, and the current analytical approaches are shown. A free energy based rupture criterion is proposed as a way to estimate the life that remains in a structure at any time.
On the role of CFRP reinforcement for wood beams stiffness
NASA Astrophysics Data System (ADS)
Ianasi, A. C.
2015-11-01
In recent years, carbon fiber composites have been increasingly used in different ways in reinforcing structural elements. Specifically, the use of composite materials as a reinforcement for wood beams under bending loads requires paying attention to several aspects of the problem such as the number of the composite layers applied on the wood beams. Study consolidation of composites revealed that they are made by bonding fibrous material impregnated with resin on the surface of various elements, to restore or increase the load carrying capacity (bending, cutting, compression or torque) without significant damage of their rigidity. Fibers used in building applications can be fiberglass, aramid or carbon. Items that can be strengthened are concrete, brick, wood, steel and stone, and in terms of structural beams, walls, columns and floors. This paper describes an experimental study which was designed to evaluate the effect of composite material on the stiffness of the wood beams. It proposes a summary of the fundamental principles of analysis of composite materials and the design and use. The type of reinforcement used on the beams is the carbon fiber reinforced polymer (CFRP) sheet and plates and also an epoxy resin for bonding all the elements. Structural epoxy resins remain the primary choice of adhesive to form the bond to fiber-reinforced plastics and are the generally accepted adhesives in bonded CFRP-wood connections. The advantages of using epoxy resin in comparison to common wood-laminating adhesives are their gap-filling qualities and the low clamping pressures that are required to form the bond between carbon fiber plates or sheets and the wood beams. Mechanical tests performed on the reinforced wood beams showed that CFRP materials may produce flexural displacement and lifting increases of the beams. Observations of the experimental load-displacement relationships showed that bending strength increased for wood beams reinforced with CFRP composite plates
Interlocked fabric and laminated fabric Kevlar 49/epoxy composites
Guess, T.R.; Reedy, E.D. Jr.
1988-01-01
The mechanical behavior of a novel interlocked fabric reinforced Kevlar 49/epoxy composite has been measured and compared to those of a laminated Kevlar 49 fabric composite (which served as a reference material). Both composites were 5.0 mm thick, contained the same 50% in-plane fiber volume fraction and were fabricated in a similar manner using the same Dow DER 332 epoxy, Jeffamine T403-hardened resin system. The reference material (Material 1) was reinforced with seven plies of Dupont style 1033 Kevlar 49 fabric. A photomicrograph of a section polished parallel to one of the fiber directions is shown. The interlocked fabric was designed and woven for Sandia National Laboratories by Albany International Research Co., Dedham, MA. The main design criterion was to duplicate a sewn through-the-thickness fabric used in preliminary studies. The interlocked fabric composite (Material 2) contains roughly 4% by volume of through-the-thickness fiber reinforcement for the purpose of improving interlaminar strength. A photomicrograph of a section showing the warp-aligned binder yarns interlocking the six fabric plies together is shown. 2 refs., 8 figs.
Experimental Design on Laminated Veneer Lumber Fiber Composite: Surface Enhancement
NASA Astrophysics Data System (ADS)
Meekum, U.; Mingmongkol, Y.
2010-06-01
Thick laminate veneer lumber(LVL) fibre reinforced composites were constructed from the alternated perpendicularly arrayed of peeled rubber woods. Glass woven was laid in between the layers. Native golden teak veneers were used as faces. In house formulae epoxy was employed as wood adhesive. The hand lay-up laminate was cured at 150° C for 45 mins. The cut specimen was post cured at 80° C for at least 5 hours. The 2k factorial design of experimental(DOE) was used to verify the parameters. Three parameters by mean of silane content in epoxy formulation(A), smoke treatment of rubber wood surface(B) and anti-termite application(C) on the wood surface were analysed. Both low and high levels were further subcategorised into 2 sub-levels. Flexural properties were the main respond obtained. ANOVA analysis of the Pareto chart was engaged. The main effect plot was also testified. The results showed that the interaction between silane quantity and termite treatment is negative effect at high level(AC+). Vice versa, the interaction between silane and smoke treatment was positive significant effect at high level(AB+). According to this research work, the optimal setting to improve the surface adhesion and hence flexural properties enhancement were high level of silane quantity, 15% by weight, high level of smoked wood layers, 8 out of 14 layers, and low anti termite applied wood. The further testes also revealed that the LVL composite had superior properties that the solid woods but slightly inferior in flexibility. The screw withdrawn strength of LVL showed the higher figure than solid wood. It is also better resistance to moisture and termite attack than the rubber wood.
Fatigue Damage Mechanisms in Advanced Hybrid Titanium Composite Laminates
NASA Technical Reports Server (NTRS)
Johnson, W. Steven; Rhymer, Donald W.; St.Clair, Terry L. (Technical Monitor)
2000-01-01
Hybrid Titanium Composite Laminates (HTCL) are a type of hybrid composite laminate with promise for high-speed aerospace applications, specifically designed for improved damage tolerance and strength at high-temperature (350 F, 177 C). However, in previous testing, HTCL demonstrated a propensity to excessive delamination at the titanium/PMC interface following titanium cracking. An advanced HTCL has been constructed with an emphasis on strengthening this interface, combining a PETI-5/IM7 PMC with Ti-15-3 foils prepared with an alkaline-perborate surface treatment. This paper discusses how the fatigue capabilities of the "advanced" HTCL compare to the first generation HTCL which was not modified for interface optimization, in both tension-tension (R = 0.1) and tension-compression (R=-0.2). The advanced HTCL under did not demonstrate a significant improvement in fatigue life, in either tension-tension or tension-compression loading. However, the advanced HTCL proved much more damage tolerant. The R = 0.1 tests revealed the advanced HTCL to increase the fatigue life following initial titanium ply damage up to 10X that of the initial HTCL at certain stress levels. The damage progression following the initial ply damage demonstrated the effect of the strengthened PMC/titanium interface. Acetate film replication of the advanced HTCL edges showed a propensity for some fibers in the adjacent PMC layers to fail at the point of titanium crack formation, suppressing delamination at the Ti/PMC interface. The inspection of failure surfaces validated these findings, revealing PMC fibers bonded to the majority of the titanium surfaces. Tension compression fatigue (R = -0.2) demonstrated the same trends in cycles between initial damage and failure, damage progression, and failure surfaces. Moreover, in possessing a higher resistance to delamination, the advanced HTCL did not exhibit buckling following initial titanium ply cracking under compression unlike the initial HTCL.
NASA Technical Reports Server (NTRS)
Lesar, Douglas E.
1992-01-01
The performance of the NASTRAN CQUAD4 membrane and plate element in the analysis of undamped natural vibration modes of thin fiber reinforced composite plates was evaluated. The element provides natural frequency estimates that are comparable in accuracy to alternative formulations, and, in most cases, deviate by less than 10 percent from experimentally measured frequencies. The predictions lie within roughly equal accuracy bounds for the two material types treated (GFRP and CFRP), and for the ply layups considered (unidirectional, cross-ply, and angle-ply). Effective elastic lamina moduli had to be adjusted for fiber volume fraction to attain this level of frequency. The lumped mass option provides more accurate frequencies than the consistent mass option. This evaluation concerned only plates with L/t ratios on the order of 100 to 150. Since the CQUAD4 utilizes first-order corrections for transverse laminate shear stiffness, the element should provide useful frequency estimates for plate-like structures with lower L/t. For plates with L/t below 20, consideration should be given to idealizing with 3-D solid elements. Based on the observation that natural frequencies and mode shapes are predicted with acceptable engineering accuracy, it is concluded that CQUAD4 should be a useful and accurate element for transient shock and steady state vibration analysis of naval ship
The in situ transverse lamina strength of composite laminates
NASA Technical Reports Server (NTRS)
Flaggs, D. L.
1983-01-01
The objective of the work reported in this presentation is to determine the in situ transverse strength of a lamina within a composite laminate. From a fracture mechanics standpoint, in situ strength may be viewed as constrained cracking that has been shown to be a function of both lamina thickness and the stiffness of adjacent plies that serve to constrain the cracking process. From an engineering point of view, however, constrained cracking can be perceived as an apparent increase in lamina strength. With the growing need to design more highly loaded composite structures, the concept of in situ strength may prove to be a viable means of increasing the design allowables of current and future composite material systems. A simplified one dimensional analytical model is presented that is used to predict the strain at onset of transverse cracking. While it is accurate only for the most constrained cases, the model is important in that the predicted failure strain is seen to be a function of a lamina's thickness d and of the extensional stiffness bE theta of the adjacent laminae that constrain crack propagation in the 90 deg laminae.
Effects of changes in composite lamina properties on laminate coefficient of thermal expansion
NASA Technical Reports Server (NTRS)
Tompkins, Stephen S.; Funk, Joan G.
1992-01-01
An analytical study of the effects of changes in composite lamina properties on the laminate coefficient of thermal expansion, CTE, has been made. Low modulus graphite/epoxy (T300/934) and high modulus graphite/epoxy (P75/934, P100/934, P120/934), graphite/aluminum (P100/Al), and graphite/glass (HMS/Gl) composite materials were considered in quasi-isotropic and near-zero CTE laminate configurations. The effects of changes in lamina properties on the laminate CTE strongly depend upon the type of composite material as well as the laminate configuration. A 10 percent change in the lamina transverse CTE resulted in changes as large as 0.22 ppm/C in the laminate CTE of a quasi-isotropic Gr/934 laminates. No significant differences were observed in the sensitivities of the laminate CTEs of the P100/934 and P120/934 composite materials due to identical changes in lamina properties. Large changes in laminate CTE can also result from measured temperature and radiation effects on lamina properties.
Effects of changes in composite lamina properties on laminate coefficient of thermal expansion
NASA Technical Reports Server (NTRS)
Tompkins, Stephen S.; Funk, Joan G.
1992-01-01
An analytical study of the effects of changes in composite lamina properties on the laminate coefficient of thermal expansion, CTE, has been made. Low modulus graphite/epoxy (T300/934) and high modulus graphite/epoxy (P75/934, P100/934, P120/934), graphite/aluminum (P100/Al), and graphite/glass (HMS/Gl) composite materials were considered in quasi-isotropic and near-zero CTE laminate configurations. The effects of changes in lamina properties on the laminate CTE strongly depend upon the type of composite material as well as the laminate configuration. A 10 percent change in the lamina transverse CTE resulted in changes as large as 0.22 ppm/C in the laminate CTE of a quasi-isotropic Gr/934 laminates. No significant differences were observed in the sensitivities of the laminate CTEs of the P100/934 and P120/934 composite materials due to identical changes in lamina properties. Large changes in laminate CTE can also result from measured temperature and radiation effects on lamina properties.
NASA Astrophysics Data System (ADS)
Rodriguez-Cobo, L.; Marques, A. T.; Lopez-Higuera, J. M.; Santos, J. L.; Frazão, O.
2013-05-01
Several easy-to-manufacture designs based on a pair of Fiber Bragg Gratings structure embedded in Carbon Fiber Reinforced Plastic (CFRP) have been explored. These smart composites can be used for strain and temperature discrimination. A Finite Elements Analysis and Matlab software were used to study the mechanical responses and its optical behaviors. The results exhibited different sensitivity and using a matrix method it is possible to compensate the thermal drift in a real application keeping a simple manufacture process.
Failure mode interaction in fiber reinforced laminated composites
NASA Astrophysics Data System (ADS)
Prabhakar, Pavana
A novel computational modeling framework to predict the compressive strength of fiber reinforced polymer matrix composite (FRPC) laminates has been presented. The model development has been motivated by a set of experimental results on the compression response of two different FRPCs. The model accounts for failure mode interaction between kink-banding and interface fracture (or delamination), which are observed in the experimental results. To reduce the size of the computational model, those interfaces that are most susceptible to delamination are first determined through a free-edge stress analysis. Furthermore, 0-axis layers, which are passive in the failure process are represented through an equivalent homogenized model, but the microstructural features of the on-axis layers (zero plies) are retained in the computational model. The predictions of the model matched well with the experimental observations, and they were found to accurately account for failure mechanism interactions. Therefore, this model has the potential to replace the need to carry out large numbers of tests to obtain the compressive strength allowable for FRPC laminates, the latter allowable being an essential element in the design of lightweight FRPC aerostructures. Furthermore, the thesis presents a new computational model to predict fiber/matrix splitting failure, a failure mode that is frequently observed in in-plane tensile failure of FRPC's. By considering a single lamina, this failure mechanism was seamlessly modeled through the development of a continuum-decohesive nite element (CDFE). The CDFE was motivated by the variational multiscale cohesive method (VMCM) presented earlier by Rudraraju et al. (2010) at the University of Michigan. In the CDFE, the transition from a continuum to a non-continuum is modeled directly (physically) without resorting to enrichment of the shape functions of the element. Thus, the CDFE is a natural merger between cohesive elements and continuum elements. The
Behavior of curved laminated composite panels and shells under axial compression
NASA Astrophysics Data System (ADS)
Abramovich, H.; Bisagni, C.
2015-10-01
The buckling and post-buckling behavior of curved cylindrical stringer-stiffened laminated composite and metal panels had been investigated both numerically and experimentally. The results were compared to those of cylindrical stringer-stiffened laminated composite shells to yield a way of determining the optimal structure to be used for axial compression loading. For the present tested structures, the composite panels showed the best load-weight ratio.
Characterization of the Effect of Fiber Undulation on Strength and Stiffness of Composite Laminates
2015-03-01
Characterization of the Effect of Fiber Undulation on Strength and Stiffness of Composite Laminates by Todd C Henry, Jaret C Riddick, Ryan P...Proving Ground, MD 21005-5069 ARL-TR-7249 March 2015 Characterization of the Effect of Fiber Undulation on Strength and Stiffness of Composite ...SUBJECT TERMS composite , laminate, fiber undulation, driveshaft, FMC, microbuckling 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT
Toughening mechanisms in Al/Al-SiC laminated metal composites
Lesuer, D.R.; Wadsworth, J.; Riddle, R.A.; Syn, C.K.; Lewandowski, J.J.; Hunt, W.H. Jr.
1996-12-31
The fracture toughness of laminated metal composites consisting of alternating layers of a metal matrix composite (Al6090/SiC/25p) and a monolithic aluminum alloy (Al5182) has been studied as a function of the volume fraction of the component materials. Finite element simulations of the fracture toughness tests have been used to study the mechanisms of crack growth and extrinsic toughening. The mechanisms responsible for toughening in laminated metal composites are described.
Development of a realistic stress analysis for fatigue analysis of notched composite laminates
NASA Technical Reports Server (NTRS)
Humphreys, E. A.; Rosen, B. W.
1979-01-01
A finite element stress analysis which consists of a membrane and interlaminar shear spring analysis was developed. This approach was utilized in order to model physically realistic failure mechanisms while maintaining a high degree of computational economy. The accuracy of the stress analysis predictions is verified through comparisons with other solutions to the composite laminate edge effect problem. The stress analysis model was incorporated into an existing fatigue analysis methodology and the entire procedure computerized. A fatigue analysis is performed upon a square laminated composite plate with a circular central hole. A complete description and users guide for the computer code FLAC (Fatigue of Laminated Composites) is included as an appendix.
NASA Astrophysics Data System (ADS)
Hwang, Joon S.; Kim, Seung J.
2002-06-01
In this paper, an experimental study was performed to investigate the possibility of a new NDE system - Tapping Sound Analysis (TSA). The tapping sound and contact force of healthy laminated composite structure and defective laminated composite structure were measured using tapping device. The feature extraction method based on the wavelet packet transform was used to extract features from the tapping sound. Comparing the feature of the tapping sound of healthy structure and defective structure, a feature index could be derived, which indicates the existence of defect inside the laminated composite structure. Using the feature index, the difference between the tapping sound data of the present specimens could be expressed as a single value.
The experimental behavior of spinning pretwisted laminated composite plates
NASA Technical Reports Server (NTRS)
Kosmatka, John B.; Lapid, Alex J.
1993-01-01
The purpose of the research is to gain an understanding of the material and geometric couplings present in advanced composite turbo-propellers. Twelve pre-twisted laminated composite plates are tested. Three different ply lay-ups (2 symmetric and 1 asymmetric) and four different geometries (flat and 30x pre-twist about the mid-chord, quarter-chord, and leading edge) distinguish each plate from one another. Four rotating and non-rotating tests are employed to isolate the material and geometric couplings of an advanced turbo propeller. The first series of tests consist of non-rotating static displacement, strain, and vibrations. These tests examine the effects of ply lay-up and geometry. The second series of tests consist of rotating displacement, strain, and vibrations with various pitch and sweep settings. These tests utilize the Dynamic Spin Rig Facility at the NASA Lewis Research Center. The rig allows the spin testing of the plates in a near vacuum environment. The tests examine how the material and plate geometry interact with the pitch and sweep geometry of an advanced turbo-propeller.
Dynamic variational asymptotic procedure for laminated composite shells
NASA Astrophysics Data System (ADS)
Lee, Chang-Yong
Unlike published shell theories, the main two parts of this thesis are devoted to the asymptotic construction of a refined theory for composite laminated shells valid over a wide range of frequencies and wavelengths. The resulting theory is applicable to shells each layer of which is made of materials with monoclinic symmetry. It enables one to analyze shell dynamic responses within both long-wavelength, low- and high-frequency vibration regimes. It also leads to energy functionals that are both positive definiteness and sufficient simplicity for all wavelengths. This whole procedure was first performed analytically. From the insight gained from the procedure, a finite element version of the analysis was then developed; and a corresponding computer program, DVAPAS, was developed. DVAPAS can obtain the generalized 2-D constitutive law and recover accurately the 3-D results for stress and strain in composite shells. Some independent works will be needed to develop the corresponding 2-D surface analysis associated with the present theory and to continue towards full verification and validation of the present process by comparison with available published works.
Buckling characteristic of multi-laminated composite elliptical cylindrical shells
NASA Astrophysics Data System (ADS)
Kassegne, Samuel Kinde; Chun, Kyoung-Sik
2015-03-01
Fiber-reinforced composite materials continue to experience increased adoption in aerospace, marine, automobile, and civil structures due to their high specific strength, high stiffness, and light weight. This increased use has been accompanied by applications involving non-traditional configurations such as compression members with elliptical cross-sections. To model such shapes, we develop and report an improved generalized shell element called 4EAS-FS through a combination of enhanced assumed strain and the substitute shear strain fields. A flat shell element has been developed by combining a membrane element with drilling degree-of-freedom and a plate bending element. We use the element developed to determine specifically buckling loads and mode shapes of composite laminates with elliptical cross-section including transverse shear deformations. The combined influence of shell geometry and elliptical cross-sectional parameters, fiber angle, and lay-up on the buckling loads of an elliptical cylinder is examined. It is hoped that the critical buckling loads and mode shapes presented here will serve as a benchmark for future investigations.
Bioinspired Transparent Laminated Composite Film for Flexible Green Optoelectronics.
Lee, Daewon; Lim, Young-Woo; Im, Hyeon-Gyun; Jeong, Seonju; Ji, Sangyoon; Kim, Yong Ho; Choi, Gwang-Mun; Park, Jang-Ung; Lee, Jung-Yong; Jin, Jungho; Bae, Byeong-Soo
2017-07-19
Herein, we report a new version of a bioinspired chitin nanofiber (ChNF) transparent laminated composite film (HCLaminate) made of siloxane hybrid materials (hybrimers) reinforced with ChNFs, which mimics the nanofiber-matrix structure of hierarchical biocomposites. Our HCLaminate is produced via vacuum bag compressing and subsequent UV-curing of the matrix resin-impregnated ChNF transparent paper (ChNF paper). It is worthwhile to note that this new type of ChNF-based transparent substrate film retains the strengths of the original ChNF paper and compensates for ChNF paper's drawbacks as a flexible transparent substrate. As a result, compared with high-performance synthetic plastic films, such as poly(ethylene terephthalate), poly(ether sulfone), poly(ethylene naphthalate), and polyimide, our HCLaminate is characterized to exhibit extremely smooth surface topography, outstanding optical clarity, high elastic modulus, high dimensional stability, etc. To prove our HCLaminate as a substrate film, we use it to fabricate flexible perovskite solar cells and a touch-screen panel. As far as we know, this work is the first to demonstrate flexible optoelectronics, such as flexible perovskite solar cells and a touch-screen panel, actually fabricated on a composite film made of ChNF. Given its desirable macroscopic properties, we envision our HCLaminate being utilized as a transparent substrate film for flexible green optoelectronics.
Integration of active fiber composite (AFC) sensors/actuators into glass/epoxy laminates
NASA Astrophysics Data System (ADS)
Melnykowycz, Mark M.; Kornmann, Xavier; Huber, Christian; Brunner, Andreas J.; Barbezat, Michel
2005-05-01
In the current study Active Fiber Composites (AFC) utilizing Lead-Zirconate-Titanate (PZT) fibers with Kapton screen printed interdigitated electrodes (IDE) were integrated into orthotropic glass fiber reinforced plastic (GFRP) laminates to investigate integration issues associated with smart structures and host laminate integrity. To aid in this goal surrogate or "Dummy" AFC (DAFC) were designed using a GFRP core and Kapton outer layers to match the longitudinal mechanical and interface properties of the AFC. These DAFC were used in place of real AFC to expedite test specimen manufacture and evaluation. This allowed efficient investigation of the impact of an integrated AFC-like inclusion on laminate mechanical integrity. Two integration techniques, cutout and simple insertion were investigated using DAFC, with little difference seen between the integrity of laminates prepared using these two methods. Using this testing scheme the influence of device placement in relation to position extending away from the laminate symmetric axis was found to have an effect on laminate integrity in tensile loading. As the DAFC were placed far from the laminate symmetry axis, the ultimate tensile strength and strain of the laminates decreased in a linear manner while the Young's modulus of the laminates remained constant. Similar trends were observed with integrated AFC specimens. The performance of integrated AFC was characterized using monotonic cyclic tensile loading with increasing strain levels. A transition region was observed between strains of 0.05%-0.50%, with a dramatic decrease in AFC sensitivity from a maximum to minimum value.
Mesophase pitch-based carbon fiber for improved inflammability of CFRP
Nakagoshi, Akira; Tomonoh, Shigeki; Sakamoto, Yosihiro
1995-10-01
Carbon Fiber Reinforced Plastics (CFRP) are extensively used because of their favorable physical properties such as high strength-to-weight ratio and small thermal expansion. However, flammability of CFRP has limited their application especially in the transportation and industrial field. Exposed to flame, CFRP laminates made of PAN-based carbon fibers burst into flame in short time, while CFRP laminates made from mesophase pitch-based carbon fibers don`t burst into flame. This paper describes the experimental results of local heating test by gas burner. When the flame temperature was 1,000 C, a CFRP laminate made from PAN-based carbon fiber burned within 40 sec. Under the same condition, a CFRP laminate made from mesophase pitch-based carbon fiber didn`t burn in 10 min. The matrix resin of both laminates was 250 F curable epoxy resin. This behavior mainly depends upon the thermal conductivity of the carbon fibers. The mesophase pitch-based carbon fibers have high thermal conductivity, so they can diffuse thermal energy and lower laminate surface temperature. On the other hand, PAN-based carbon fibers have low thermal conductivity, so they can`t diffuse thermal energy enough, and the laminates made from them burn easily. Mechanical properties of CFRP during local heating test in comparison with Aluminum plate are also discussed.
Graphite/epoxy Composite Laminates with Co-cured Interlaminar Damping Layers
NASA Technical Reports Server (NTRS)
Pereira, J. Michael
1993-01-01
Damped composite laminates were fabricated by co-curing viscoelastic damping film with graphite/epoxy prepreg plies. The dynamic response of the damped plates was measured using an impulse response technique and compared with the response of similar undamped laminates. Modal damping was computed from the frequency response data. Micrographs of the damped laminates showed that the damping layers retained their integrity during the fabrication process. The layers significantly increased the damping in the composite laminates. The use of the constrained viscoelastic film as an integral part of composite structures appears to be a feasible approach to passive vibration control. Composite plates manufactured with co-cured damping layers may have commercial applications in cases where light weight, strength, and vibration and noise reduction are important considerations.
Superplasticity in an ultrahigh carbon steel-aluminum bronze laminated composite
Tsai, H.C.; Higashi, K.; Sherby, O.D.
1993-12-31
Metal laminated composites based on ultrahigh carbon steel (UHCS) and aluminum bronze can be readily prepared by solid state bonding procedures at relatively low temperatures (670 to 700{degree}C). This is attributed to the fine grain size present in each component. No apparent interdiffusion occurs between the UHCS and aluminum bronze layers either during the solid state bonding steps or during superplastic flow below the transformation temperature of UHCS (770{degree}C). Interdiffusion does occur between the UHCS and aluminum bronze layers when the laminated composite is heated above 770{degree}C as a result of the dissolution of the iron carbides to form austenite. It is shown that a high strain-rate-sensitivity exponent (m = 0.5) can be achieved in the UHCS/bronze laminated composite at elevated temperatures (750 to 850{degree}C) and at low strain rates. High elongations are observed in the laminated composite under these conditions, with a maximum elongation of 650% noted at 750{degree}C. The UHCS/bronze laminated composite shows different mechanical characteristics from a UHCS/brass laminated composite. Brass readily cracks at elevated temperature and prevents the achievement of high elongations in a UHCS/brass composite even when the strain-rate-sensitivity is high. The aluminum bronze is fine-grained and does not form cracks during elevated temperature deformation.
BILAM: a composite laminate failure-analysis code using bilinear stress-strain approximations
McLaughlin, P.V. Jr.; Dasgupta, A.; Chun, Y.W.
1980-10-01
The BILAM code which uses constant strain laminate analysis to generate in-plane load/deformation or stress/strain history of composite laminates to the point of laminate failure is described. The program uses bilinear stress-strain curves to model layer stress-strain behavior. Composite laminates are used for flywheels. The use of this computer code will help to develop data on the behavior of fiber composite materials which can be used by flywheel designers. In this program the stress-strain curves are modelled by assuming linear response in axial tension while using bilinear approximations (2 linear segments) for stress-strain response to axial compressive, transverse tensile, transverse compressive and axial shear loadings. It should be noted that the program attempts to empirically simulate the effects of the phenomena which cause nonlinear stress-strain behavior, instead of mathematically modelling the micromechanics involved. This code, therefore, performs a bilinear laminate analysis, and, in conjunction with several user-defined failure interaction criteria, is designed to provide sequential information on all layer failures up to and including the first fiber failure. The modus operandi is described. Code BILAM can be used to: predict the load-deformation/stress-strain behavior of a composite laminate subjected to a given combination of in-plane loads, and make analytical predictions of laminate strength.
Evaluation of a Progressive Failure Analysis Methodology for Laminated Composite Structures
NASA Technical Reports Server (NTRS)
Sleight, David W.; Knight, Norman F., Jr.; Wang, John T.
1997-01-01
A progressive failure analysis methodology has been developed for predicting the nonlinear response and failure of laminated composite structures. The progressive failure analysis uses C plate and shell elements based on classical lamination theory to calculate the in-plane stresses. Several failure criteria, including the maximum strain criterion, Hashin's criterion, and Christensen's criterion, are used to predict the failure mechanisms. The progressive failure analysis model is implemented into a general purpose finite element code and can predict the damage and response of laminated composite structures from initial loading to final failure.
Composite laminates with spatially varying fiber orientations - 'Variable stiffness panel concept'
NASA Technical Reports Server (NTRS)
Guerdal, Zafer; Olmedo, Reynaldo
1992-01-01
A solution has been obtained to the plane elasticity problem for a symmetrically laminated composite panel with spatially varying fiber orientations. Since variation of the fiber angles along the length of a composite laminate results in stiffness properties that change as a function of location, the laminates are called variable stiffness panels. An analysis of the stiffness variation and its effect on the elastic response of the panel is presented here. A numerical solution has been obtained using an iterative collocation technique. Corresponding closed-form solutions are given for three different sets of boundary conditions. Two of the cases considered have exact solutions and thus serve to validate the numerical model.
NASA Technical Reports Server (NTRS)
Chiang, C. K.; Xue, David Y.; Mei, Chuh
1993-01-01
A finite element formulation is presented for determining the large-amplitude free and steady-state forced vibration response of arbitrarily laminated anisotropic composite thin plates using the Discrete Kirchhoff Theory (DKT) triangular elements. The nonlinear stiffness and harmonic force matrices of an arbitrarily laminated composite triangular plate element are developed for nonlinear free and forced vibration analyses. The linearized updated-mode method with nonlinear time function approximation is employed for the solution of the system nonlinear eigenvalue equations. The amplitude-frequency relations for convergence with gridwork refinement, triangular plates, different boundary conditions, lamination angles, number of plies, and uniform versus concentrated loads are presented.
Improvement of Delamination Resistance in Composite Laminates with Nano-Interlayers (Preprint)
2006-01-01
AFRL-ML-WP-TP-2006-409 IMPROVEMENT OF DELAMINATION RESISTANCE IN COMPOSITE LAMINATES WITH NANO - INTERLAYERS (PREPRINT) Sangwook Sihn, Jin W...IMPROVEMENT OF DELAMINATION RESISTANCE IN COMPOSITE LAMINATES WITH NANO -INTERLAYERS (PREPRINT) 5c. PROGRAM ELEMENT NUMBER 62102F 5d. PROJECT NUMBER...is a nano -interlayer which can be fabricated in the form of either a thin film of nano -modified epoxy reinforced with vapor grown nanofibers or a
NASA Astrophysics Data System (ADS)
Xiang, S.; Wang, J.; Ai, Y. T.; Li, G.-Ch.
2015-11-01
The buckling of simply supported laminated composite plates is studied using various higher-order shear deformation theories. A Navier-type analytical method is used to solve the governing differential equations. The critical buckling loads of simply supported laminated composite plates under a uniaxial buckling load are calculated. The present results are compared with available published results to verify the accuracy of the higher-order shear deformation theories considered.
The compact tension, C(T), specimen in laminated composite testing
Minnetyan, L.; Chamis, C.C.
1997-12-31
Use of the compact tension, C(T), specimens in laminated composites testing is investigated by considering two examples. A new computational methodology that scales up constituent material properties, stress, and strain limits to the structure level is used to evaluate damage propagation stages as well as the structural fracture load. Damage initiation, growth, accumulation, progressive fracture, and ultimate fracture modes are identified. Specific dependences of C(T) specimen test characteristics on laminate configuration and composite constituent properties are quantified.
A new analysis for the static strength of bolted joint in composite laminates
NASA Astrophysics Data System (ADS)
Liu, Ping; Zhang, Kaida
1992-04-01
A new finite element program was developed for analyzing the static strength of bolted joint in composite laminates. Two fracture models were introduced in estimating the failure of mechanical joints. Theoretical results of ultimate stress as well as failure propagation were given for 21 different orientations of T300/648 Carbon/epoxy composite laminates. These results are in satisfactory agreement with the test data.
Processing and Evaluation of 3D-Reinforced Needled Composite Laminate
2012-09-01
This report documents the fabrication and test of a woven glass /epoxy composite laminate that was reinforced in the through- thickness direction with...the in-plane strength of woven glass materials. Because the processing parameters were arbitrarily chosen, these experiments should be considered as...delamination resistance of composite laminates. The tufting process uses a hollow needle to insert glass or carbon threads comprised of typically
Refined Zigzag Theory for Laminated Composite and Sandwich Plates
NASA Technical Reports Server (NTRS)
Tessler, Alexander; DiSciuva, Marco; Gherlone, Marco
2009-01-01
A refined zigzag theory is presented for laminated-composite and sandwich plates that includes the kinematics of first-order shear deformation theory as its baseline. The theory is variationally consistent and is derived from the virtual work principle. Novel piecewise-linear zigzag functions that provide a more realistic representation of the deformation states of transverse-shear-flexible plates than other similar theories are used. The formulation does not enforce full continuity of the transverse shear stresses across the plate s thickness, yet is robust. Transverse-shear correction factors are not required to yield accurate results. The theory is devoid of the shortcomings inherent in the previous zigzag theories including shear-force inconsistency and difficulties in simulating clamped boundary conditions, which have greatly limited the accuracy of these theories. This new theory requires only C(sup 0)-continuous kinematic approximations and is perfectly suited for developing computationally efficient finite elements. The theory should be useful for obtaining relatively efficient, accurate estimates of structural response needed to design high-performance load-bearing aerospace structures.
Transverse cracking and stiffness reduction in composite laminates
NASA Astrophysics Data System (ADS)
Yuan, F. G.; Selek, M. C.
1993-09-01
A study of transverse cracking mechanism in composite laminates is presented using a singular hybrid finite element model. The model provides the global structural response as well as the precise local crack-tip stress fields. An elasticity basis for the problem is established by employing Lekhnitskii's complex variable potentials and method of eigenfunction expansion. Stress singularities associated with the transverse crack are obtained by decomposing the deformation into the symmetric and antisymmetric modes and proper boundary conditions. A singular hybrid element is thereby formulated based on the variational principle of a modified hybrid functional to incorporate local crack singularities. Axial stiffness reduction due to transverse cracking is studied. The results are shown to be in very good agreement with the existing experimental data. Comparison with simple shear lag analysis is also given. The effects of stress intensity factors and strain energy density on the increase of crack density are analyzed. The results reveal that the parameters approach definite limits when crack densities are saturated, an evidence of the existence of characteristic damage state.
Experimental study of Lamb wave propagation in composite laminates
NASA Astrophysics Data System (ADS)
Wang, Lei; Yuan, F. G.
2006-03-01
This paper focuses on the existence of higher-order Lamb wave modes that can be observed from piezoelectric sensors by the excitation of ultrasonic frequencies from piezoelectric actuators. Using three-dimensional (3-D) elasticity theory, the exact dispersion relations governed by transcendental equations are numerically solved for an infinite number of possible wave modes. For symmetric laminates, a robust method by imposing boundary conditions on mid-plane and top surface is developed to separate wave modes. Then both phase and group velocity dispersions of Lamb waves in composites are obtained. Meanwhile three characteristic wave curves including velocity, slowness, and wave curves are introduced to analyze the angular dependency of Lamb wave propagation at a given frequency. In the experiments, two surface-mounted piezoelectric actuators are operated corporately to excite either symmetric or anti-symmetric wave modes with narrow banded excitation signals, and a Gabor wavelet transform is used to extract group velocities from arrival times of Lamb wave received by a piezoelectric sensor. In comparison with the results from the theory and experiment, it is confirmed that the higher-order Lamb waves can be excited from piezoelectric actuators and the measured group velocities agree well with those from 3-D elasticity theory.
The influence of hole size in static strength and fatigue for CFRP composite materials
Yip, M.C.; Perng, T.B.
1993-12-31
The influence of hole size in static strength and fatigue property will be investigated. Carbon/Epoxy laminate is selected as testing materials which are widely used in aircraft industry. The arrangement of fiber orientation is [0{sup 0}/+45{sup 0}/{minus}45{sup 0}/90{sup 0}]{sub 2s}. The basic mechanical properties of smooth and notched specimens were detected. The strength of notched specimens are applied to compare with Whitney-Nuismer stress criterion. For average stress criteria, the theoretical value is in good agreement with experimental data for the parameter a{sub 0} is chosen 1.5 mm. For point stress criteria, the best choice of parameter do is 2.4 mm, but the agreement of experimental data is poorer than the average stress one. The characteristic curve of tension-tension fatigue for smooth and notched laminate were investigated. The notched specimens has a 1 mm diameter circular hole at the center, the stress ratio of fatigue test is 0.1. It is obvious that the data distribution of smooth specimens is more scatter than notched specimens. On the other hand, the reduction of modulus during fatigue process was inspected. After fatigue damage, the influence of hole size on residual strength for a quasi-isotropic laminate was investigated. It is found that residual strength of damaged specimens are higher than undamaged one in some fatigue damage range. When the maximum applied load of fatigue test is chosen 90 percent of static strength, it is seen that the influence is obviously in residual strength. The increment of strength decreases with hole size increasing. When the maximum applied load of fatigue test is chosen 80 percent of static strength, the influence is less than the previous case. The Whitney-Nuismer Average Stress Criteria is extended to predict the residual strength after fatigue. A good prediction can be shown by using the extended criteria.
A tension-mode fracture model for bolted joints in laminated composites
Schulz, K.C.; Packman, P.F.; Eisenmann, J.R.
1995-06-01
A failure prediction model for bolted joints in generally orthotropic laminated composite plates that fail in the tension mode under bearing loading conditions has been developed. The plate is analyzed as a bulk orthotropic plate whose material properties are determined through the application of classical lamination theory to facilitate practical application of the model. Ply-by-ply laminated analysis is not required. Fracture mechanics concepts are applied to a pseudo-flaw which is related to the physical cracking of the laminate at the joint. The maximum circumferential stress concept is extended to orthotropic materials where both the fracture toughness and stress intensity vary with orientation. Excellent correlation between experimental tests conducted on single-bolt joints for two laminate layups and analytical prediction was found.
Compression strength failure mechanisms in unidirectional composite laminates containing a hole
NASA Technical Reports Server (NTRS)
Johnson, Eric R.
1993-01-01
Experiments on graphite-epoxy laminated plates containing unloaded small holes show that these laminates are notch insensitive. That is, the uniaxial strength of these laminates with small holes exceeds the strength predicted by a point stress criterion using the stress concentration factor for the in-plane stress field. Laminates containing large holes exhibit notch sensitive behavior and consequently their strength is reasonably well predicted by the stress concentration effect. This hole size effect is manifested both in tension and in compression. Apparently, some mechanism must cause in-plane stress relief for laminates containing small holes. The purpose of this research was to study the influence of geometric nonlinearity on the micromechanical response of a filamentary composite material in the presence of a strain gradient caused by a discontinuity such as a hole. A mathematical model was developed at the micromechanical level to investigate this geometrically nonlinear effect.
A Higher-Order Bending Theory for Laminated Composite and Sandwich Beams
NASA Technical Reports Server (NTRS)
Cook, Geoffrey M.
1997-01-01
A higher-order bending theory is derived for laminated composite and sandwich beams. This is accomplished by assuming a special form for the axial and transverse displacement expansions. An independent expansion is also assumed for the transverse normal stress. Appropriate shear correction factors based on energy considerations are used to adjust the shear stiffness. A set of transverse normal correction factors is introduced, leading to significant improvements in the transverse normal strain and stress for laminated composite and sandwich beams. A closed-form solution to the cylindrical elasticity solutions for a wide range of beam aspect ratios and commonly used material systems. Accurate shear stresses for a wide range of laminates, including the challenging unsymmetric composite and sandwich laminates, are obtained using an original corrected integration scheme. For application of the theory to a wider range of problems, guidelines for finite element approximations are presented.
Tensile stress-strain behavior of hybrid composite laminates
NASA Technical Reports Server (NTRS)
Kennedy, J. M.
1983-01-01
A study was made of the stress-strain response of several hybrid laminates, and the damage was correlated with nonlinear stress-strain response and ultimate strength. The fibers used in the laminates were graphite, S-glass, and Kevlar. Some laminates with graphite fibers had perforated Mylar film between plies, which lowered the interlaminar bond strength. The laminate configurations were chosen to be like those of buffer strips in large panels and fracture coupons. Longitudinal and transverse specimens were loaded in tension to failure. Some specimens were radiographed to reveal damage due to edge effects. Stress-strain response is discussed in terms of damage shown by the radiographs. Ultimate strengths are compared with simple failure criteria, one of which account for damage.
Tensile stress-strain behavior of hybrid composite laminates
NASA Technical Reports Server (NTRS)
Kennedy, J. M.
1983-01-01
A study was made of the stress-strain response of several hybrid laminates, and the damage was correlated with nonlinear stress-strain response and ultimate strength. The fibers used in the laminates were graphite, S-glass, and Kevlar. Some laminates with graphite fibers had perforated Mylar film between plies, which lowered the interlaminar bond strength. The laminate configurations were chosen to be like those of buffer strips in large panels and fracture coupons. Longitudinal and transverse specimens were loaded in tension to failure. Some specimens were radiographed to reveal damage due to edge effects. Stress-strain response is discussed in terms of damage shown by the radiographs. Ultimate strengths are compared with simple failure criteria, one of which account for damage.
Characterization of delamination onset and growth in a composite laminate
NASA Technical Reports Server (NTRS)
Obrien, T. K.
1981-01-01
The onset and growth of delaminations in unnotched (+ or - 30/+ or - 30/90/90 bar) sub S graphite epoxy laminates is described quantitatively. These laminates, designed to delaminate at the edges under tensile loads, were tested and analyzed. Delamination growth and stiffness loss were monitored nondestructively. Laminate stiffness decreased linearly with delamination size. The strain energy release rate, G, associated with delamination growth, was calculated from two analyses. A critical G for delamination onset was determined, and then was used to predict the onset of delaminations in (+45 sub n/-45 sub n/o sub n/90 sub n) sub s (n=1,2,3) laminates. A delamination resistance curve (R curve) was developed to characterize the observed stable delamination growth under quasi static loading. A power law correlation between G and delamination growth rates in fatigue was established.
NASA Technical Reports Server (NTRS)
Sobel, Larry; Buttitta, Claudio; Suarez, James
1993-01-01
Probabilistic predictions based on the Integrated Probabilistic Assessment of Composite Structures (IPACS) code are presented for the material and structural response of unnotched and notched, 1M6/3501-6 Gr/Ep laminates. Comparisons of predicted and measured modulus and strength distributions are given for unnotched unidirectional, cross-ply, and quasi-isotropic laminates. The predicted modulus distributions were found to correlate well with the test results for all three unnotched laminates. Correlations of strength distributions for the unnotched laminates are judged good for the unidirectional laminate and fair for the cross-ply laminate, whereas the strength correlation for the quasi-isotropic laminate is deficient because IPACS did not yet have a progressive failure capability. The paper also presents probabilistic and structural reliability analysis predictions for the strain concentration factor (SCF) for an open-hole, quasi-isotropic laminate subjected to longitudinal tension. A special procedure was developed to adapt IPACS for the structural reliability analysis. The reliability results show the importance of identifying the most significant random variables upon which the SCF depends, and of having accurate scatter values for these variables.
NASA Technical Reports Server (NTRS)
Sobel, Larry; Buttitta, Claudio; Suarez, James
1993-01-01
Probabilistic predictions based on the Integrated Probabilistic Assessment of Composite Structures (IPACS) code are presented for the material and structural response of unnotched and notched, 1M6/3501-6 Gr/Ep laminates. Comparisons of predicted and measured modulus and strength distributions are given for unnotched unidirectional, cross-ply, and quasi-isotropic laminates. The predicted modulus distributions were found to correlate well with the test results for all three unnotched laminates. Correlations of strength distributions for the unnotched laminates are judged good for the unidirectional laminate and fair for the cross-ply laminate, whereas the strength correlation for the quasi-isotropic laminate is deficient because IPACS did not yet have a progressive failure capability. The paper also presents probabilistic and structural reliability analysis predictions for the strain concentration factor (SCF) for an open-hole, quasi-isotropic laminate subjected to longitudinal tension. A special procedure was developed to adapt IPACS for the structural reliability analysis. The reliability results show the importance of identifying the most significant random variables upon which the SCF depends, and of having accurate scatter values for these variables.
Compression response of thick layer composite laminates with through-the-thickness reinforcement
NASA Technical Reports Server (NTRS)
Farley, Gary L.; Smith, Barry T.; Maiden, Janice
1992-01-01
Compression and compression-after-impact (CAI) tests were conducted on seven different AS4-3501-6 (0/90) 0.64-cm thick composite laminates. Four of the seven laminates had through-the-thickness (TTT) reinforcement fibers. Two TTT reinforcement methods, stitching and integral weaving, and two reinforcement fibers, Kevlar and carbon, were used. The remaining three laminates were made without TTT reinforcements and were tested to establish a baseline for comparison with the laminates having TTT reinforcement. Six of the seven laminates consisted of nine thick layers whereas the seventh material was composed of 46 thin plies. The use of thick-layer material has the potential for reducing structural part cost because of the reduced part count (layers of material). The compression strengths of the TTT reinforced laminates were approximately one half those of the materials without TTT reinforcements. However, the CAI strengths of the TTT reinforced materials were approximately twice those of materials without TTT reinforcements. The improvement in CAI strength is due to an increase in interlaminar strength produced by the TTT reinforcement. Stitched laminates had slightly higher compression and CAI strengths than the integrally woven laminates.
Zhamu, Aruna; Shi, Jinjun; Guo, Jiusheng; Jang, Bor Z
2014-05-20
An electrically conductive laminate composition for fuel cell flow field plate or bipolar plate applications. The laminate composition comprises at least a thin metal sheet having two opposed exterior surfaces and a first exfoliated graphite composite sheet bonded to the first of the two exterior surfaces of the metal sheet wherein the exfoliated graphite composite sheet comprises: (a) expanded or exfoliated graphite and (b) a binder or matrix material to bond the expanded graphite for forming a cohered sheet, wherein the binder or matrix material is between 3% and 60% by weight based on the total weight of the first exfoliated graphite composite sheet. Preferably, the first exfoliated graphite composite sheet further comprises particles of non-expandable graphite or carbon in the amount of between 3% and 60% by weight based on the total weight of the non-expandable particles and the expanded graphite. Further preferably, the laminate comprises a second exfoliated graphite composite sheet bonded to the second surface of the metal sheet to form a three-layer laminate. Surface flow channels and other desired geometric features can be built onto the exterior surfaces of the laminate to form a flow field plate or bipolar plate. The resulting laminate has an exceptionally high thickness-direction conductivity and excellent resistance to gas permeation.
A novel damage index for fatigue damage detection in a laminated composites using Lamb waves
NASA Astrophysics Data System (ADS)
Seki, Daigo
A well-established structural health monitoring (SHM) technique, the Lamb wave based approach, is used for fatigue damage identification in a laminated composite. A novel damage index, 'normalized correlation moment' (NCM) which is composed of the nth moment of the cross correlation of the baseline and comparison waves, was used as damage index for monitoring damage in composites and compared with the signal difference coefficient (SDC) which is one of the most commonly used damage indices. Composite specimens were fabricated by the hand layup method by followed by compression. Piezo electric disks mounted on composite specimens were used as actuators and sensors. Three point bending fatigue tests were carried out on an intact composite laminate and a delaminated composite laminate with [06/904/06] orientation. Finite element analysis was performed to test the validity of SDC and NCM for fatigue damage.
NASA Technical Reports Server (NTRS)
Saravanos, D. A.; Hopkins, D. A.
1995-01-01
Analytical and experimental work is presented on the damped free-vibration of delaminated laminates and beams. A laminate theory is developed where the unknown kinematic perturbations induced by a delamination crack are treated as additional degrees of freedom. The generalized stiffness, inertia and damping matrices of the laminate are formulated. An analytical solution is developed for the prediction of natural frequencies, modes and modal damping in composite beams with delamination cracks. Evaluations of the mechanics on various cantilever beams with a central delamination are performed. Experimental results for the modal frequencies and damping of composite beams with a single delamination are also presented and correlations between analytical predictions and measured data are shown. The effects of delamination vary based on crack size, laminate configuration, and mode order. The implications of the mechanics in developing delamination detection techniques are also discussed.
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.
2000-01-01
A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were implemented into a mechanics of materials based micromechanics method. In the current work, the computation of the effective inelastic strain in the micromechanics model was modified to fully incorporate the Poisson effect. The micromechanics equations were also combined with classical laminate theory to enable the analysis of symmetric multilayered laminates subject to in-plane loading. A quasi-incremental trapezoidal integration method was implemented to integrate the constitutive equations within the laminate theory. Verification studies were conducted using an AS4/PEEK composite using a variety of laminate configurations and strain rates. The predicted results compared well with experimentally obtained values.
Fracture behavior of unidirectional boron/aluminum composite laminates
NASA Technical Reports Server (NTRS)
Goree, J. G.; Jones, W. F.
1983-01-01
An experiment was conducted to verify the results of mathematical models which predict the stresses and displacements of fibers and the amount of damage growth in a center-notched lamina as a function of the applied remote stress and the matrix and fiber material properties. A brittle lacquer coating was used to detect the yielding in the matrix while X-ray techniques were used to determine the number of broken fibers in the laminate. The notched strengths and the amounts of damage found in the specimens agree well with those predicted by the mathematical model. It is shown that the amount of damage and the crack opening displacement does not depend strongly on the number of plies in the laminate for a given notch width. By heat-treating certain laminates to increase the yield stress of the alumina matrix, the effect of different matrix properties on the fracture behavior was investigated. The stronger matrix is shown to weaken the notched laminate by decreasing the amount of matrix damage, thereby making the laminate more notch sensitive.
Ablation behaviors of carbon reinforced polymer composites by laser of different operation modes
NASA Astrophysics Data System (ADS)
Wu, Chen-Wu; Wu, Xian-Qian; Huang, Chen-Guang
2015-10-01
Laser ablation mechanism of Carbon Fiber Reinforced Polymer (CFRP) composite is of critical meaning for the laser machining process. The ablation behaviors are investigated on the CFRP laminates subject to continuous wave, long duration pulsed wave and short duration pulsed wave lasers. Distinctive ablation phenomena have been observed and the effects of laser operation modes are discussed. The typical temperature patterns resulted from laser irradiation are computed by finite element analysis and thereby the different ablation mechanisms are interpreted.
NASA Astrophysics Data System (ADS)
Xie, Jiawen
Delamination is a common failure mode in composite (fiber reinforced and layered) structures subject to low-velocity impacts by foreign objects. To maximize the design capacity, it is important to have reliable tools to predict delamination evolution in laminated composites. The focus of this research is to analyze flexural responses and delamination evolution in laminated composites subject to flexural loading. Analytical solutions were derived from linear elasticity theory and structural mechanics of beam and plate configurations. Formulations and evaluations of the proposed analytical approaches were validated by comparing with results of finite element (FE) simulations in similar settings and published experiment data. Two-dimensional (2D) elasticity theory for laminated panels was extended to analyze elastodynamic responses of pristine panels and quasi-static responses of pre-delaminated panels. A highlight of the approach is exact solutions of displacement and stress fields it provides. Further investigations showed that the 2D elasticity theory is not amenable to a closed-form solution for laminates containing off-axis angle plies due to three-dimensional (3D) states of stress. Closed-form solutions of cohesive zone modeling (CZM) were developed for popular delamination toughness tests of laminated beams. A laminate was modeled as an assembly of two sub-laminates connected by a virtual deformable layer with infinitesimal thickness. Comprehensive parametric studies were performed, offering a deeper understanding of CZM. The studies were further simplified so that closed-form expressions can be obtained, serving as a quick estimation of the flexural responses and the process zone lengths. Analytical CZM solutions were extended analyze quasi-static impact tests of laminated composite plates with arbitrary stacking sequences, aiming to predict critical load, critical interfaces and extent of delamination at that interface. The Rayleigh-Ritz method was used to
A model for inter-laminar shear stress in laminated composites
NASA Astrophysics Data System (ADS)
Zaki, W.; Nguyen, V.; Umer, R.
2017-02-01
The paper presents an analytical model for the estimation of shear stress at the interface of adhesively bonded layers in laminated composites. For this purpose, a new shear stress function is proposed that accounts for the influence of shear lag in laminates assembled using adhesive layers of different types and thicknesses. In addition to the estimation of interfacial stress, the function can be used to determine the difference in normal strains and axial displacements in adjoining layers.
Effect of stacking sequence on the coefficients of mutual influence of composite laminates
NASA Astrophysics Data System (ADS)
Dupir (Hudișteanu, I.; Țăranu, N.; Axinte, A.
2016-11-01
Fiber reinforced polymeric (FRP) composites are nowadays widely used in engineering applications due to their outstanding features, such as high specific strength and specific stiffness as well as good corrosion resistance. A major advantage of fibrous polymeric composites is that their anisotropy can be controlled through suitable choice of the influencing parameters. The unidirectional fiber reinforced composites provide much higher longitudinal mechanical properties compared to the transverse ones. Therefore, composite laminates are formed by stacking two or more laminas, with different fiber orientations, as to respond to complex states of stresses. These laminates experience the effect of axial-shear coupling, which is caused by applying normal or shear stresses, implying shear or normal strains, respectively. The normal-shear coupling is expressed by the coefficients of mutual influence. They are engineering constants of primary interest for composite laminates, since the mismatch of the material properties between adjacent layers can produce interlaminar stresses and/or plies delamination. The paper presents the variation of the in-plane and flexural coefficients of mutual influence for three types of multi-layered composites, with different stacking sequences. The results are obtained using the Classical Lamination Theory (CLT) and are illustrated graphically in terms of fiber orientations, for asymmetric, antisymmetric and symmetric laminates. Conclusions are formulated on the variation of these coefficients, caused by the stacking sequence.
Design Optimization of Laminated Composite Structures Using Explicit Finite Element Analysis
NASA Astrophysics Data System (ADS)
Mika, Krista
Laminated composite materials are used in aerospace, civil and mechanical structural systems due to their superior material properties compared to the constituent materials as well as in comparison to traditional materials such as metals. Laminate structures are composed of multiple orthotropic material layers bonded together to form a single performing part. As such, the layup design of the material largely influences the structural performance. Optimization techniques such as the Genetic Algorithm (GA), Differential Evolution (DE), the Method of Feasible Directions (MFD), and others can be used to determine the optimal laminate composite material layup. In this thesis, sizing, shape and topology design optimization of laminated composites is carried out. Sizing optimization, such as the layer thickness, topology optimization, such as the layer orientation and material and the number of layers present, and shape optimization of the overall composite part contribute to the design optimization process of laminates. An optimization host program written in C++ has been developed to implement the optimization methodology of both population based and numerical gradient based methods. The performance of the composite structural system is evaluated through explicit finite element analysis of shell elements carried out using LS-DYNA. Results from numerical examples demonstrate that optimization design processes can significantly improve composite part performance through implementation of optimum material layup and part shape.
Effect of angle-ply orientation on compression strength of composite laminates
DeTeresa, S J; Hoppel, C P
1999-03-01
An experimental program was initiated to investigate the effect of angle-ply orientations on the compressive strength (X{sub 1C}) of 0{degree} plies in fiber reinforced composite laminates. Graphite fiber-reinforced epoxy test coupons with the generic architecture [0{sub 2}/{+-}{theta}] (where {theta} varied between 0{degree} and 90{degree}) and for the quasi-isotropic architecture were evaluated. The effective compressive strength of the 0{degree} plies varied considerably. The results were related to the Poisson's ratios of the laminates with high Poisson's ratios leading to high transverse tensile strains in the test coupons and lower than expected strengths. Specimens with the [O{sub 2}/{+-}30] architecture had both the highest Poisson's ratio and the lowest calculated ply-level compression strength for the 0{degree} plies. This work has implications in the selection of composite failure criterion for compression performance, design of test coupons for acceptance testing, and the selection of laminate architectures for optimum combinations of compressive and shear behavior. Two commonly used composite failure criteria, the maximum stress and the Tsai-Wu, predict significantly different laminate strengths depending on the Poisson's ratio of the laminate. This implies that the biaxial stress state in the laminate needs to be carefully considered before backing out unidirectional properties.
NASA Astrophysics Data System (ADS)
Panda, Satyajit; Ray, M. C.
2009-08-01
This paper deals with the geometrically nonlinear dynamic analysis of functionally graded (FG) laminated composite plates integrated with a patch of active constrained layer damping (ACLD) treatment. The constraining layer of the ACLD treatment is considered to be made of the piezoelectric fiber reinforced composite (PFRC) material. Each layer of the substrate FG laminated composite plate is made of fiber-reinforced composite material in which the fibers are longitudinally aligned in the plane parallel to the top or bottom surface of the layer and the layer is assumed to be graded in the thickness direction by way of varying the fiber orientation angle across its thickness according to a power-law. The novelty of the present work is that, unlike the traditional laminated composite plates, the FG laminated composite plates are constructed in such a way that the continuous variation of material properties and stresses across the thickness of the plates is achieved. The constrained viscoelastic layer of the ACLD treatment is modeled using the Golla-Hughes-McTavish (GHM) method. Based on the first-order shear deformation (FSDT) theory, a finite element model has been developed to model the open-loop and closed-loop nonlinear dynamics of the overall FG laminated composite plates. Both symmetric and asymmetric FG laminated composite plates are considered as the substrate plates for presenting the numerical results. The analysis suggests the potential use of the ACLD treatment with its constraining layer made of the PFRC material for active control of geometrically nonlinear forced vibrations of FG laminated composite plates. The effect of piezoelectric fiber orientation in the active constraining PFRC layer on the damping characteristics of the overall FG plates is also investigated.
NASA Technical Reports Server (NTRS)
Tompkins, S. S.; Funk, J. G.
1992-01-01
An analytical study of the sensitivity of the laminate coefficient of thermal expansion, CTE, to changes in lamina elastic properties has been made. High modulus graphite/epoxy (P75/934, P100/934, P120/934), graphite/aluminum (P100/Al), and graphite/glass (HMS/Gl) composite materials were considered in quasi-isotropic, low thermal stress, and 'near-zero' thermal expansion laminate configurations. The effects of a positive or negative 10 percent change in lamina properties on laminate CTE is strongly dependent upon both the composite material and the laminate configuration. A 10 percent change in all of the lamina properties had very little effect on the laminate CTE of the HMS/Gl composite laminates investigated. The sensitivity and direction of change in the laminate CTE of Gr/934 depended very strongly on the fiber properties. A 10 percent change in the lamina transverse CTE resulted in changes as large as 0.216 ppm/C in the laminate CTE of a quasi-isotropic Gr/934 laminate. No significant difference was observed in the sensitivity of the laminate CTE of the P100/934 and P120/934 composite materials due to changes in lamina properties. Large changes in laminate CTE can result from measured temperature and radiation effects on lamina properties.
NASA Technical Reports Server (NTRS)
Tompkins, S. S.; Funk, J. G.
1992-01-01
An analytical study of the sensitivity of the laminate coefficient of thermal expansion, CTE, to changes in lamina elastic properties has been made. High modulus graphite/epoxy (P75/934, P100/934, P120/934), graphite/aluminum (P100/Al), and graphite/glass (HMS/Gl) composite materials were considered in quasi-isotropic, low thermal stress, and 'near-zero' thermal expansion laminate configurations. The effects of a positive or negative 10 percent change in lamina properties on laminate CTE is strongly dependent upon both the composite material and the laminate configuration. A 10 percent change in all of the lamina properties had very little effect on the laminate CTE of the HMS/Gl composite laminates investigated. The sensitivity and direction of change in the laminate CTE of Gr/934 depended very strongly on the fiber properties. A 10 percent change in the lamina transverse CTE resulted in changes as large as 0.216 ppm/C in the laminate CTE of a quasi-isotropic Gr/934 laminate. No significant difference was observed in the sensitivity of the laminate CTE of the P100/934 and P120/934 composite materials due to changes in lamina properties. Large changes in laminate CTE can result from measured temperature and radiation effects on lamina properties.
Thermal buckling and postbuckling of symmetrically laminated composite plates. Interim Report No. 84
Meyers, C.A.; Hyer, M.W.; Shuart, M.J.
1991-02-01
An investigation into thermal buckling and postbuckling of symmetrically laminated composite plates is discussed. Thermal buckling is investigated for laminates under two different simple support conditions, fixed and sliding. These laminates are subjected to the conditions of a uniform temperature change and a linearly varying temperature change and nonlinear response to imperfections in the form of a thermal gradient through the thickness of the plate and a lack of initial flatness are also studied. The buckling response is studied using variational methods, specifically the Trefftz criterion. Postbuckling and responses to imperfections are studied using nonlinear equilibrium conditions. A Rayleigh-Ritz formulation is used to obtain numerical results from the formulations for the prebuckling response, the buckling response, and the postbuckling and imperfection responses. The analyses are applied to graphite-reinforced materials with (+ or {minus} 45/0{sub 2})s and (+ or {minus} 45/0/90)s lamination sequences. Numerical results are obtained for these laminates and also for the case of these laminates being rotated 30 deg inplane. For the first laminate, for example, such a rotation results in a (+75/{minus}15/30{sub 2})s stacking sequence. Such skewing of the principal material directions may be encountered when using fiber-reinforced materials in a structurally tailored design. In addition, the influence on thermal buckling of a lack of ideal boundary conditions in the form of boundary compliance and thermal expansion, which would occur in any real set-up, are investigated.
Reinforcement of composite laminate free edges with U-shaped caps
NASA Technical Reports Server (NTRS)
Howard, W. E.; Gossard, T., Jr.; Jones, R. M.
1986-01-01
Generalized plane strain finite element analysis is used to predict reduction of interlaminar normal stresses when a U-shaped cap is bonded to the edge of a laminate. Three-dimensional composite material failure criteria are used in a progressive laminate failure analysis to predict failure loads of laminates with different edge cap designs. In an experimental program, symmetric 11-layer graphite-epoxy laminates with a one-layer cap of Kevlar-epoxy cloth are shown to be 130 to 140 percent stronger than uncapped laminates under static tensile and tension-tension fatigue loading. In addition, the coefficient of variation of the static tensile failure load decreases from 24 to 8 percent when edge caps are added. The predicted failure load calculated with the finite element results is 10 percent lower than the actual failure load. For both capped and uncapped laminates, actual failure loads are much lower than those predicted using classical lamination theory stresses and a two-dimensional failure criterion. Possible applications of the free edge reinforcement concept are described, and future research is suggested.
Ozcan, M; Mese, A
2009-01-01
This study evaluated the effect of conventional versus ultrasonic cementation techniques on the fracture strength of resin composite laminates. In addition, the failure modes were assessed. Window-type preparations 1 mm above the cemento-enamel junction were made on intact human maxillary central incisors (N=60) of similar size with a depth cutting bur. All the prepared teeth were randomly assigned to six experimental groups (10/per group). Using a highly filled polymeric material (Estenia), laminates were produced and finished. The standard thickness of laminates in original tooth form was achieved using the impression molds made prior to tooth preparation. A three-step bonding procedure and dual polymerized resin composite cement (Panavia F 2.0) was employed. The cementation surfaces of the laminates were conditioned (CoJet-Sand, 30 microm SiO2) and silanized (ESPE-Sil). Laminates in Groups 1, 2, 3, 4 and 5 were cemented by five different operators under finger pressure and Group 6 was cemented ultrasonically (Amdent). After excess removal, the laminates were light polymerized. The specimens were stored in water at 37 degrees C for one month prior to the fracture test (universal testing machine, 1 mm/minute). Failure types were classified as: a) Cohesive failure within the composite laminate (Type A), b) Adhesive failure between the tooth and laminate (Type B) and c) Chipping of the laminate with enamel exposure (Type C). No significant difference was found among the mean fracture strength values of the laminates in all the experimental groups (ANOVA, p=0.251). The mean fracture strength values in descending order were: 513 +/- 197, 439 +/- 125, 423 +/- 163, 411 +/- 126, 390 +/- 94, 352 +/- 117 N for Groups 2, 5, 4, 3, 1 and 6, respectively. The majority of failure types was Type A (30/60). While Type B failure was not observed in Group 6 (0/10), Group 1 presented a more frequent incidence of this failure (6/10). The two cementation techniques did not effect the
NASA Astrophysics Data System (ADS)
Lakshminarayana, A.; Vijayakumar, R.; Krishnamohana Rao, G.
2016-09-01
The progressive failure analysis of symmetrically laminated composite plate [0°/+45°/-45°/90°]2s with circular or elliptical cutout under uniform uniaxial compression loading is carried out using finite element method. Hashin's failure criterion is used to predict the lamina failure. A parametric study has been carried out to study the effect of elliptical / circular cutout orientation, cutout size and plate thickness on the ultimate failure load of laminated composite plate under uni-axial compression loading. It is noticed that elliptical cutout orientation has influence on the strength of the notched composite plates. It is observed that the laminate size of the elliptical/circular cutout and plate thickness has substantial influence on the ultimate failure load of notched composite plates.
High Strain Rate Characterization of Laminate Composites Using Direct-Tension Split Hopkinson Bar
NASA Astrophysics Data System (ADS)
Akkala, S.; Hommeida, A.; Brar, N. S.
1999-06-01
Data on high strain rate response of laminate composites is required to numerically simulate penetration/perforation events. Tension specimens of laminate composites can only be fabricated in dog-bone shape and, therefore, a direct tension Hopkinson bar configuration is more appropriate for acquiring high strain data. Launching a 6.35-mm wall thickness aluminum tube around 25.4 diameter aluminum incident bar produces the tension pulse in the incident bar. Ends of the composite specimens in the dog-bone configuration are placed in specially designed grips, which are screwed in the incident and transmitter bars. The configuration allows testing of specimens with threaded ends. Stress-strain data on 6061-T6 aluminum and titanium 6-4 at a strain rate of 10^3/s agree with the published data. High strain rate data on laminate composite specimens reinforced with graphite and glass fibers will be presented.
Elasticity solutions for a class of composite laminate problems with stress singularities
NASA Technical Reports Server (NTRS)
Wang, S. S.
1983-01-01
A study on the fundamental mechanics of fiber-reinforced composite laminates with stress singularities is presented. Based on the theory of anisotropic elasticity and Lekhnitskii's complex-variable stress potentials, a system of coupled governing partial differential equations are established. An eigenfunction expansion method is introduced to determine the orders of stress singularities in composite laminates with various geometric configurations and material systems. Complete elasticity solutions are obtained for this class of singular composite laminate mechanics problems. Homogeneous solutions in eigenfunction series and particular solutions in polynomials are presented for several cases of interest. Three examples are given to illustrate the method of approach and the basic nature of the singular laminate elasticity solutions. The first problem is the well-known laminate free-edge stress problem, which has a rather weak stress singularity. The second problem is the important composite delamination problem, which has a strong crack-tip stress singularity. The third problem is the commonly encountered bonded composite joints, which has a complex solution structure with moderate orders of stress singularities.
Nonlinear Temperature Dependent Failure Analysis of Finite Width Composite Laminates.
1979-12-01
tangent modulii obtained by Ramberg-Osgood parameters. It is shown that a’ring stresses and stresses due to tensile loading are significant as edge ... effect in all types of laminate studies. The tensor polynomial failure criterion is used to predict the initiation of failure. The mode of failure is
Effect of preload on the fatigue and static strength of composite laminates with defects
NASA Technical Reports Server (NTRS)
Porter, T. R.; Smith, G. T.
1977-01-01
The effect of a preload cycle on the structural performance of three graphite/epoxy composite laminates was studied. The layups studied were a laminate typical of general purpose structures (L1), a laminate representative of a filament wound tank (L2), and a laminate representative of turboengine fan blades. The effects of three sizes of simulated initial defects were studied. The tests developed static strength data, fatigue to failure data, and residual static data after application of a predetermined number of fatigue cycles. For L1 specimens, there was a slight trend for the static strength to be greater for preloaded specimens. After application of cyclic loading, however, the influence of preloading was insignificant. In L2 and L3 specimens there was no consistent difference in the static or fatigue results between preloaded and nonpreloaded specimens.
Prediction of Composite Laminate Strength Properties Using a Refined Zigzag Plate Element
NASA Technical Reports Server (NTRS)
Barut, Atila; Madenci, Erdogan; Tessler, Alexander
2013-01-01
This study presents an approach that uses the refined zigzag element, RZE(exp2,2) in conjunction with progressive failure criteria to predict the ultimate strength of composite laminates based on only ply-level strength properties. The methodology involves four major steps: (1) Determination of accurate stress and strain fields under complex loading conditions using RZE(exp2,2)-based finite element analysis, (2) Determination of failure locations and failure modes using the commonly accepted Hashin's failure criteria, (3) Recursive degradation of the material stiffness, and (4) Non-linear incremental finite element analysis to obtain stress redistribution until global failure. The validity of this approach is established by considering the published test data and predictions for (1) strength of laminates under various off-axis loading, (2) strength of laminates with a hole under compression, and (3) strength of laminates with a hole under tension.
Maeda, Takenori
1995-11-01
This paper presents an experimental method for the determination of the bending and torsional rigidities of advanced fiber composite laminates with the aid of laser holographic interferometry. The proposed method consists of a four-point bending test and a resonance test. The bending rigidity ratio (D{sub 12}/D{sub 22}) can be determined from the fringe patterns of the four-point bending test. The bending rigidities (D{sub 11} and D{sub 22}) and the torsional rigidity (D{sub 66}) are calculated from the natural frequencies of cantilever plates of the resonance test. The test specimens are carbon/epoxy cross-ply laminates. The adequacy of the experimental method is confirmed by comparing the measured rigidities with the theoretical values obtained from classical lamination theory (CLT) by using the measured tensile properties. The results show that the present method can be used to evaluate the rigidities of orthotropic laminates with reasonably good accuracy.
Mechanical properties of small-scale laminated wood composite poles: effects of taper and webs
Cheng Piao; Todd F. Shupe; R.C. Tang; Chung Y. Hse
2006-01-01
Laminated hollow wood composite poles represent an efficient utilization of the timber resource and a promising alternative for solid poles that are commonly used in the power transmission and telecommunication lines. The objective of this study was to improve the performance of composite poles by introducing the bio-mimicry concept into the design of hollow wood...
Cheng Piao; Todd F. Shupe; R.C. Tang; Chung Y. Hse
2008-01-01
Tapered composite poles with biomimicry features as in bamboo are a new generation of wood laminated composite poles that may some day be considered as an alternative to solid wood poles that are widely used in the transmission and telecommunication fields. Five finite element models were developed with ANSYS to predict and assess the performance of five types of...
Taha, N A; Palamara, J E; Messer, H H
2012-08-01
To evaluate the open laminate technique using glass ionomer cements (GIC) in association with a low shrink composite for restoring root filled premolars. Extensive MOD cavities plus endodontic access and root filling were performed in intact extracted maxillary premolars. Three restoration types were evaluated: (1) resin composite alone; (2) resin-modified GIC (RM-GIC) open laminate plus resin composite; (3) conventional GIC open laminate plus resin composite (n=8 for all groups and tests). Three tests were conducted to assess restorations: (A) inward cusp deflection during light curing, using DCDTs; (B) fracture strength using a ramped oblique load at 45° to the long axis in a servohydraulic testing machine in comparison with intact and unrestored teeth; (C) proximal marginal leakage using methylene blue dye and the effect of thermocycling. Data were analysed using 1-way ANOVA for cuspal deflection and fracture strength and Fisher's exact test for leakage. Laminate restorations resulted in significantly less cuspal deflection compared with resin composite (4.2±1.2 μm for RM-GIC and 5.1±2.3 μm for conventional GIC vs. 12.2±2.6 μm for composite, P<0.001). Fracture strength was not significantly different among all groups. Failure with all restorations was predominantly adhesive at the tooth-restoration interface. The two laminate groups showed significantly better marginal seal than composite alone, but sealing ability of conventional GIC deteriorated after thermocycling. Laminate restoration of root filled teeth had beneficial effects in terms of reducing cuspal deflection and marginal seal, with acceptable fracture strength. Copyright © 2012 Elsevier Ltd. All rights reserved.
Kahali Moghaddam, Maryam; Breede, Arne; Brauner, Christian; Lang, Walter
2015-01-01
The production of large and complex parts using fiber composite materials is costly due to the frequent formation of voids, porosity and waste products. By embedding different types of sensors and monitoring the process in real time, the amount of wastage can be significantly reduced. This work focuses on developing a knowledge-based method to improve and ensure complete impregnation of the fibers before initiation of the resin cure. Piezoresistive and capacitive pressure sensors were embedded in fiber composite laminates to measure the real-time the pressure values inside the laminate. A change of pressure indicates resin infusion. The sensors were placed in the laminate and the resin was infused by vacuum. The embedded piezoresistive pressure sensors were able to track the vacuum pressure in the fiber composite laminate setup, as well as the arrival of the resin at the sensor. The pressure increase due to closing the resin inlet was also measured. In contrast, the capacitive type of sensor was found to be inappropriate for measuring these quantities. The following study demonstrates real-time monitoring of pressure changes inside the fiber composite laminate, which validate the use of Darcy’s law in porous media to control the resin flow during infusion. PMID:25825973
Moghaddam, Maryam Kahali; Breede, Arne; Brauner, Christian; Lang, Walter
2015-03-27
The production of large and complex parts using fiber composite materials is costly due to the frequent formation of voids, porosity and waste products. By embedding different types of sensors and monitoring the process in real time, the amount of wastage can be significantly reduced. This work focuses on developing a knowledge-based method to improve and ensure complete impregnation of the fibers before initiation of the resin cure. Piezoresistive and capacitive pressure sensors were embedded in fiber composite laminates to measure the real-time the pressure values inside the laminate. A change of pressure indicates resin infusion. The sensors were placed in the laminate and the resin was infused by vacuum. The embedded piezoresistive pressure sensors were able to track the vacuum pressure in the fiber composite laminate setup, as well as the arrival of the resin at the sensor. The pressure increase due to closing the resin inlet was also measured. In contrast, the capacitive type of sensor was found to be inappropriate for measuring these quantities. The following study demonstrates real-time monitoring of pressure changes inside the fiber composite laminate, which validate the use of Darcy's law in porous media to control the resin flow during infusion.
NASA Astrophysics Data System (ADS)
Yin, J. J.; Li, S. L.; Yao, X. L.; Chang, F.; Li, L. K.; Zhang, X. H.
2016-08-01
In order to analyze the lightning strike ablation damage characteristic of composite laminate with fastener, based on the energy-balance relationship in lightning strike, mathematical analysis model of ablation damage of composite laminate with fastener was constructed. According to the model, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate with fastener suffered from lightning current was established based on ABAQUS, and lightning strike ablation damage characteristic was analyzed. Analytical results reveal that lightning current could conduct through the thickness direction of the laminate due to the existence of metallic fastener, and then distribute to all layers, finally conducted in-the-plane of each layer, conductive ability of different layup orientations depend on potential distribution and in-the-plane electrical conductivity along potential gradient declining direction; different potential boundaries correspond to different potential distribution in each layer, and result in conductive ability of different layup orientations was changed, then caused different lightning strike ablation damage distribution. According to the investigation in this paper, we can recognize the lightning strike ablation damage characteristic of composite laminate with fastener qualitatively.
Analytical method for analyzing c-channel stiffener made of laminate composite
NASA Astrophysics Data System (ADS)
Kumton, Tattchapong
Composite materials play the important role in the aviation industry. Conventional materials such as aluminum were replaced by composite material on the main structures. The objective of this study focuses on development of analytical method to analyze the laminated composite structure with C-channel cross-section. A lamination theory base closed-form solution was developed to analysis ply stresses on the C-channel cross-section. The developed method contains the effects of coupling due to unsymmetrical of both laminate and structural configuration levels. The present method also included the expression of the sectional properties such as centroid, axial and bending stiffnesses of cross-section. The results obtain from analytical method showed an excellent agreement with finite element results.
NASA Technical Reports Server (NTRS)
Moncada, Albert M.; Chattopadhyay, Aditi; Bednarcyk, Brett A.; Arnold, Steven M.
2008-01-01
Predicting failure in a composite can be done with ply level mechanisms and/or micro level mechanisms. This paper uses the Generalized Method of Cells and High-Fidelity Generalized Method of Cells micromechanics theories, coupled with classical lamination theory, as implemented within NASA's Micromechanics Analysis Code with Generalized Method of Cells. The code is able to implement different failure theories on the level of both the fiber and the matrix constituents within a laminate. A comparison is made among maximum stress, maximum strain, Tsai-Hill, and Tsai-Wu failure theories. To verify the failure theories the Worldwide Failure Exercise (WWFE) experiments have been used. The WWFE is a comprehensive study that covers a wide range of polymer matrix composite laminates. The numerical results indicate good correlation with the experimental results for most of the composite layups, but also point to the need for more accurate resin damage progression models.
Equivalent circuit method for resonant magnetoelectric effect in disk-shaped laminated composites
NASA Astrophysics Data System (ADS)
Zhang, Ru; Wu, Gaojian; Zhang, Ning
2015-01-01
A theoretical model based on equivalent circuit analytical method has been presented for the magnetoelectric (ME) effect in disk-shaped laminated composites. The derived expressions for the ME voltage coefficient can be used to describe the frequency response of ME effect under both open circuit and finite electrical resistance load conditions. It was shown that the resonance frequency and resonant ME voltage coefficient increase with the increase in electrical resistance load in disk-shaped ME laminated composite, which is consistent with the observations for plate-shaped one. The theoretical results show good agreement with the experimental results in Tb0.3Dy0.7Fe1.92 (Terfenol-D)/Pb(Zr,Ti)O3 (PZT)/Terfenol-D disk-shaped sandwich laminated composite. This work is significant for designing ME devices and their signal-processing and electronic circuits.
Determination of Fracture Parameters for Multiple Cracks of Laminated Composite Finite Plate
NASA Astrophysics Data System (ADS)
Srivastava, Amit Kumar; Arora, P. K.; Srivastava, Sharad Chandra; Kumar, Harish; Lohumi, M. K.
2017-08-01
A predictive method for estimation of stress state at zone of crack tip and assessment of remaining component lifetime depend on the stress intensity factor (SIF). This paper discusses the numerical approach for prediction of first ply failure load (FL), progressive failure load, SIF and critical SIF for multiple cracks configurations of laminated composite finite plate using finite element method (FEM). The Hashin and Chang failure criterion are incorporated in ABAQUS using subroutine approach user defined field variables (USDFLD) for prediction of progressive fracture response of laminated composite finite plate, which is not directly available in the software. A tensile experiment on laminated composite finite plate with stress concentration is performed to validate the numerically predicted subroutine results, shows excellent agreement. The typical results are presented to examine effect of changing the crack tip distance (S), crack offset distance (H), and stacking fiber angle (θ) on FL, and SIF .
Constructing of cure monitoring system with piezoelectric ceramics for composite laminate
NASA Astrophysics Data System (ADS)
Oshima, Nobuo; Inoue, Kouichi; Motogi, Shinya; Fukuda, Takehito
2003-08-01
The cure monitoring system with piezoelectric ceramics is constructed. An embedded type piezoelectric ceramics sensor with flat lead wires is developed. And the piezoelectric ceramics is embedded into composite laminate. A dummy piezoelectric ceramics is set in the autoclave oven. The impedance of the piezoelectric ceramics which is embedded in the composite laminate and that of the dummy piezoelectric ceramics are measured by a LCR meter. The piezoelectric ceramics have strong temperature dependency. The temperature dependency of the impedance of piezoelectric ceramics is corrected by the information from the dummy piezoelectric ceramics. A dielectric sensor is also embedded in the composite laminate as a reference sensor for the degree of cure. The change in calculated cure index shows good correspondence with change in the log ion viscosity which is measured by the dielectric cure monitoring sensor.
Dynamic analysis of tapered laminated composite magnetorheological elastomer (MRE) sandwich plates
NASA Astrophysics Data System (ADS)
Babu, V. Ramesh; Vasudevan, R.
2016-03-01
In the present study, the dynamic performance of the sandwich plate with magneto rheological elastomer (MRE) as the core layer and tapered laminated composite plates as the face layers is investigated. Various MRE tapered laminated composite sandwich plate models are formulated by dropping-off the plies longitudinally in top and bottom composite layers to yield tapered plates as the face layers and uniform MRE layer as the core layer. The governing equations of motion of tapered composite MRE sandwich plates are derived using classical laminated plate theory and solved numerically. Further, silicon based MRE is being fabricated and tested to obtain the shear and loss moduli using MR rheometer. The efficacy of the finite element formulation is validated by carrying out experiments on the various prototypes of tapered composite silicon based MRE sandwich plates and comparing the results in terms of natural frequencies obtained at various magnetic fields with those obtained numerically and with available literature. Also, the effects of magnetic field, taper angle of the top and bottom layers, aspect ratio, ply orientations and various end conditions on the various dynamic properties of tapered laminated composite MRE sandwich plate are investigated. Further, the transverse vibration responses of three different tapered composite MRE based sandwich plates under harmonic force excitation are analyzed at various magnetic fields.
Carbon laminates with RE doped optical fibre sensors
NASA Astrophysics Data System (ADS)
Miluski, Piotr; Kochanowicz, Marcin; Żmojda, Jacek; Silva, AbíLio P.; Reis, Paulo N. B.; Dorosz, Dominik
2016-11-01
A new type of luminescent optical fibre sensor for structural health monitoring of composite laminates (CFRP) is proposed. The Nd3+ doped multi-core doubleclad fibre incorporated in composite structure was used as a distributed temperature sensor. The change of luminescence intensity (Nd3+ ions) at the wavelength of 880 nm (4F3/2 → 4I9/2) and 1060 nm (4F3/2 → 4I11/2) was used for internal temperature monitoring. The special construction of optical fibre was used as it assures an efficient pumping mechanism and, at same time, it increases the measuring sensitivity. The linear response with relative sensitivity 0.015 K-1 was obtained for temperature range from 30 up to 75ºC. The manufacturing process of CFRP with embedded optical fibre sensor is also discussed.
Behaviour study of thick laminated composites: Experimentation and finite element analyses
NASA Astrophysics Data System (ADS)
Duchaine, Francois
In today's industries, it is common practice to utilize composite materials in very large and thick structures like bridge decks, high pressure vessels, wind turbine blades and aircraft parts to mention a few. Composite materials are highly favoured due to their physical characteristics: low weight, low cost, adaptable mechanical properties, high specific strength and stiffness. The use of composite materials for large structures has however raised several concerns in the prediction of the behaviour of thick laminated composite parts. A lack of knowledge and experience in the use of composite materials during the design, sizing and manufacturing of thick composite parts can lead to catastrophic events. In this thesis, it was supposed that the elastic material properties may vary with the laminate thickness. In order to measure the influence of the thickness on nine orthotropic elastic material properties (E1, E2, E3, nu12, nu 13, nu23, G12, G13 and G23), three categories of thickness have been defined using a comparison between the classical lamination theory (CLT), different beam theories and a numerical 3D solid finite element analysis (FEA) model. The defined categories are: thin laminates for thicknesses below 6 mm (0.236"), moderately thick laminates for thicknesses up to 16 mm (0.630") and thick laminates for thicknesses above 16 mm (0.630"). For three different thicknesses (thin -- 1.5 mm, moderately thick -- 10 mm and thick -- 20 mm), the influence of the thickness on the orthotropic elastic material properties of unidirectional (UD) fibreglass/epoxy laminates has been measured. A torsion test on rectangular bar is also proposed to measure the influence of the thickness on G13 and G23. The nine elastic material properties, in function of the thickness, have been used in CLT and 3D solid FEA model in order to predict the axial Young's modulus and Poisson's ratios of cross-ply and quasi-isotropic laminates. Experimental results have also been obtained for
NASA Technical Reports Server (NTRS)
Riddick, J. C.; Gates, T. S.; Frankland, S.-J. V.
2005-01-01
A multi-scale method to predict the stiffness and stability properties of carbon nanotube-reinforced laminates has been developed. This method is used in the prediction of the buckling behavior of laminated carbon nanotube-polyethylene composites formed by stacking layers of carbon nanotube-reinforced polymer with the nanotube alignment axes of each layer oriented in different directions. Linking of intrinsic, nanoscale-material definitions to finite scale-structural properties is achieved via a hierarchical approach in which the elastic properties of the reinforced layers are predicted by an equivalent continuum modeling technique. Solutions for infinitely long symmetrically laminated nanotube-reinforced laminates with simply-supported or clamped edges subjected to axial compression and shear loadings are presented. The study focuses on the influence of nanotube volume fraction, length, orientation, and functionalization on finite-scale laminate response. Results indicate that for the selected laminate configurations considered in this study, angle-ply laminates composed of aligned, non-functionalized carbon nanotube-reinforced lamina exhibit the greatest buckling resistance with 1% nanotube volume fraction of 450 nm uniformly-distributed carbon nanotubes. In addition, hybrid laminates were considered by varying either the volume fraction or nanotube length through-the-thickness of a quasi-isotropic laminate. The ratio of buckling load-to-nanotube weight percent for the hybrid laminates considered indicate the potential for increasing the buckling efficiency of nanotube-reinforced laminates by optimizing nanotube size and proportion with respect to laminate configuration.
Three-Dimensional Elastoplastic Finite Element Analysis of Laminated Composites.
1980-11-01
effect near an edge is known as the free edge effect . In an effort to evaluate interlaminar stresses and the influence of the stacking sequence on...addition, the interlaminar normal stress was found to be an edge effect , restricted to a region near the free edge approximately equal to the laminate...noted that the presence of interlaminar stresses might be considered an edge effect restricted to a small region near the free edge. In their work of
Fracture Analysis of Matrix Cracking in Laminated Composites.
1985-01-01
several Interfaces. For the laminate shown here, however, onset of edge delamination at 90% of the laminte ,iltimate strength appeir3 t’ be the first...situated ii the laminte mid-plane, the initial delamination growth is primarily of mode-I. To predict the associated delamination onset, it is necessary to...ang) ................................................ 1 E. I. DuPONT COMPANY, Textile Fibers Department, Chestnut Run Location/CR701), Wilmington, DE
Dual mode fracture of composite laminates penetrated by spherical projectiles
NASA Astrophysics Data System (ADS)
Czarnecki, G. J.
The basic for delamination initiation and propagation within an impacted laminate was studied, with an explanation provided for the fracture mode transformation along the projectile's path. Post-impact observations of graphite/epoxy (AS4/3501-6) laminates penetrated by steel spheres (0.5-inch diameter) reveal a fracture mode, similar to shear plugging adjacent to the impacted surface. This fracture mode is contrasted with that of delamination adjacent to the rear surface. The sudden transition from shear plugging to delamination is believed to occur when the projectile interacts with the returning impact-generated tensile wave. To demonstrate the transition, results are presented from ballistically impacted laminates containing a series of imbedded carbon stress and constantan strain gages. Results are based on impact velocities of 1300, 1850, and 2380 f/s. Transverse stress waves are shown capable of creating delamination until attenuated by a local zone of compressed material associated with the on-coming projectile. Based on experimental results, the location of the fracture mode transition plane is predicted both graphically and through a simple equation of motion.
A spectral element for laminated composite beams: theory and application to pyroshock analysis
NASA Astrophysics Data System (ADS)
Ruotolo, R.
2004-02-01
In this article a spectral element for anisotropic, laminated composite beams is developed. Firstly, the axial-bending coupled equations of motion are derived under the assumptions of the First order Shear Deformation Theory, then the spectral element matrix is formulated. The proposed spectral element is validated by comparing, with corresponding results from the scientific literature, natural frequencies of a number of both orthotropic and anisotropic laminated composite beams and the dynamic response of an anisotropic cantilever beam to high frequency transients. Finally, the application of the proposed element to the evaluation of the dynamic response to a simulated pyroshock of an idealized satellite structure made of sandwich beams is shown.
NASA Technical Reports Server (NTRS)
Shuart, M. J.; Williams, J. G.
1984-01-01
An experimental study is reported in which a nondestructive technique involving the use of a transparent fiberglass-epoxy composite birefringent material has been used to investigate compression failure mechanisms in graphite-epoxy laminates. It is shown that the birefringency and transparency of the fiberglass-epoxy material permits regions of high stress to be located and the mechanisms of local failure propagation to be identified within the laminate. The material may also be useful for studying stress fields and for identifying failure initiation and propagation mechanisms in a wide variety of composite-structure problems.
Estimation of the Residual Fatigue Life of Laminated Composites Under a Multistage Cyclic Loading
NASA Astrophysics Data System (ADS)
Strizhius, V.
2016-11-01
Problems on estimation of the residual fatigue life of laminated composites under a multistage regular cyclic loading (with a constant amplitude at each loading stage) are among the most frequently ones encountered in the practice of fatigue life estimations of laminated composites. There are several methods for solving these problems, but their use not always gives results of acceptable accuracy. To improve the accuracy of such estimations for the type of cyclic loading mentioned, a special model of nonlinear accumulation of fatigue damage is proposed.
Detection of acoustic emission from composite laminates using PVF2 transducers
NASA Technical Reports Server (NTRS)
Stiffler, R.; Henneke, E. G., II; Herakovich, C. T.
1983-01-01
Polyvinylidene fluoride (PVF2), a semicrystalline polymer exhibiting piezoelectricity, is presently used as a sensing transducer in acoustic emission (AE) monitoring of several different composite laminate materials in order to obtain both quasi-static and fatigue loading results. AE signals obtained from PVF2 transducers are compared with those obtained by standard AE sensors. It is noted that PVF2 transducers may, through the application of spectral signal analysis, be able to distinguish between two distinct failure modes which have been observed in two composite laminates of the same material, but employing different lamina stacking sequences.
Microcracking in Composite Laminates: Simulation of Crack-Induced Ultrasound Attenuation
NASA Technical Reports Server (NTRS)
Leckey, C. A. C.; Rogge, M. D.; Parker, F. R.
2012-01-01
Microcracking in composite laminates is a known precursor to the growth of inter-ply delaminations and larger scale damage. Microcracking can lead to the attenuation of ultrasonic waves due to the crack-induced scattering. 3D elastodynamic finite integration technique (EFIT) has been implemented to explore the scattering of ultrasonic waves due to microcracks in anisotropic composite laminates. X-ray microfocus computed tomography data was directly input into the EFIT simulation for these purposes. The validated anisotropic 3D EFIT code is shown to be a useful tool for exploring the complex multiple-scattering which arises from extensive microcracking.
On the elastic properties of fiber composite laminates with statistically dispersed ply orientations
NASA Technical Reports Server (NTRS)
Robinson, E. Y.
1972-01-01
Structural application of advanced composite filamentary materials requires lamination of the basic orthotropic plies into angle-ply laminates. The resulting elastic and strength properties depend on the pattern of orientation and are influenced by inevitable errors and inaccuracy in placement of the angle plies. Reviewed is the effect on elastic properties of orientation dispersion. The conventional constitutive relations are recast in a homologous form to account for orientation dispersion by addition of a single parameter. Graphical results are presented to show the behavior of the most important advanced composite materials. The results are directly useful for estimating effects of manufacturing inaccuracy and for design of partially oriented reinforced structures.
NASA Technical Reports Server (NTRS)
Robinson, E. Y.
1973-01-01
Structural application of advanced composite filamentary materials requires lamination of the basic orthotropic plies into angle-ply laminates. This article reviews the effect on elastic properties of orientation dispersion. The conventional constitutive relations are recast in a homologous form to account for uniform orientation dispersion by addition of a single parameter. Graphical results are presented to show the behavior of the most important advanced composite materials. The results are directly useful for estimating effects of manufacturing inaccuracy and for design of partially oriented reinforced structures.
A {3,2}-Order Bending Theory for Laminated Composite and Sandwich Beams
NASA Technical Reports Server (NTRS)
Cook, Geoffrey M.; Tessler, Alexander
1998-01-01
A higher-order bending theory is derived for laminated composite and sandwich beams thus extending the recent {1,2}-order theory to include third-order axial effect without introducing additional kinematic variables. The present theory is of order {3,2} and includes both transverse shear and transverse normal deformations. A closed-form solution to the cylindrical bending problem is derived and compared with the corresponding exact elasticity solution. The numerical comparisons are focused on the most challenging material systems and beam aspect ratios which include moderate-to-thick unsymmetric composite and sandwich laminates. Advantages and limitations of the theory are discussed.
Novel method for joining CFRP to aluminium
NASA Astrophysics Data System (ADS)
Möller, F.; Thomy, C.; Vollertsen, F.; Schiebel, P.; Hoffmeister, C.; Herrmann, A. S.
The current state of the art in joining of carbon-fibre reinforced composites (CFRP) to metals such as aluminium is - for the case of aircraft structures, e.g.- riveting or bolting. However, to reduce structural weight and improve structural performance, integral, load-bearing aluminium-CFRP-structures are desirable. To produce such structures, a novel joint configuration together with an appropriate thermal, laser-based joining process is suggested by the authors. In this paper, the joint configuration (based on CFRP-Ti-aluminium joints) and the laser beam conduction welding process will be presented, and first specimens obtained will be discussed with respect to their properties. It will be shown that the novel approach is in principle suitable to produce load-bearing CFRP-aluminium structures.
NASA Astrophysics Data System (ADS)
Adim, B.; Daouadji, T. Hassaine; Abbes, B.
2016-11-01
The buckling analysis of anti-symmetric cross-ply laminated composite plates under different boundary conditions is examined by using a refined higher order exponential shear deformation theory. The theory, which has strong similarity with classical plate theory in many aspects, accounts for a quadratic variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The number of independent unknowns in the present theory is four, as against five in other shear deformation theories. In this investigation, the equations of motion for simply supported thick laminated rectangular plates are derived and obtained through the use of Hamilton's principle. The closed-form solutions of anti-symmetric cross-ply and angle-ply laminates are obtained using Navier solution. Numerical results for critical buckling loads anti-symmetric cross-ply laminated composite plates are presented. The validity of the present study is demonstrated by comparison with other higher-order solutions reported in the literature. It can be concluded that the proposed theory is accurate and simple in solving the buckling behaviors of anti-symmetric cross-ply laminated composite plates under different boundary conditions
NASA Astrophysics Data System (ADS)
Tseng, Kevin K.; Tinker, Michael L.; Lassiter, John O.; Wang, Liangsheng
2004-07-01
An important way of increasing the payload in a reusable launch vehicle (RLV) is to replace heavy metallic materials by lightweight composite laminates. Engineers and scientists have studied many metallic materials thoroughly, due to the long history of practical usage in many aerospace and aeronautical structures. Compared to metallic materials, composite laminates are a relatively new material and therefore require more attention to ensure the safety and reliability. Among various parts and systems of the RLV, this study focuses on tanks containing cryogenic fuel. Historically, aluminum alloys have been used as the materials to construct fuel tanks for launch vehicles. To replace aluminum alloys with composite laminates or honeycomb materials, engineers have to make sure that the composites are free of defects before, during, and after launch. In addition to robust design and manufacturing procedures, the performance of the composite structures needs to be evaluated constantly. In recent years, the impedance-based health monitoring technique has shown its promise in many applications. This technique makes use of the special properties of smart piezoelectric materials to identify the change of material properties due to the nucleation and progression of damage. A major advantage of this technique is that the procedure is nondestructive in nature and does not perturb the properties and performance of the materials and structures. This paper reports the results of applying the impedance-based nondestructive testing technique to the damage identification of composite laminates at cryogenic temperature. These materials have potential application for fuel tanks in future RLV"s.
Impedance-based structural health monitoring for composite laminates in cryogenic environments
NASA Astrophysics Data System (ADS)
Tseng, Kevin K.; Tinker, Michael L.; Lassiter, John O.; Eckel, Justin T.
2003-08-01
An important way of increasing the payload in a reusable launch vehicle (RLV) is to replace heavy metallic materials by lightweight composite laminates. Compared to metallic materials, composite laminates are a relatively new class of materials and therefore require more attention to ensure the safety and reliability when they are used. Among various parts and systems of the RLV, this study focuses on tanks containing cryogenic fuel. Historically, aluminum alloys have been used as the materials to construct fuel tanks for launch vehicles. To replace aluminum alloys with composite laminates or honeycomb materials, engineers have to make sure that the composites are free of defects before, during, and after launch. In addition, the performance of the composite structures needs to be evaluated constantly. In recent years, the impedance-based health monitoring technique has shown its promise in many applications. A major advantage of this technique is that the procedure is nondestructive in nature and does not perturb the properties and performance of the materials and structures. This paper reports the results of applying the impedance-based nondestructive testing technique to the damage identification of composite laminates at cryogenic temperature. These materials have potential application for fuel tanks in future RLV"s. Regular and single-crystal piezoceramic sensor/actuators are tested to assess their performance under cryogenic temperature.
2011-11-01
Development of an engineering model for predicting the off-axis ratcheting behavior of a unidirectional CFRP laminate has been attempted. For this purpose...accumulation of ratcheting strain occurs in the unidirectional CFRP laminate, regardless of fiber orientation, and the off-axis ratcheting behavior is similar...allows adequately predicting the off-axis ratcheting behavior of the unidirectional CFRP laminate for different stress ratios as well as for different
The high velocity impact loading on symmetrical and woven hybrid composite laminates
NASA Astrophysics Data System (ADS)
Jin, Martin; Richardson, Mel; Zhang, Zhong Yi
2007-07-01
Space structures use fibre composite materials, due to their lightweight. This paper examines the impact response of symmetrical and hybrid composite laminates. Special attention is given to the stacking sequences used. The experimental study of structures has always provided a major contribution to our understanding. Even with the formidable growth in the use and capacity of computing power the need for experimental measurement is as compelling as ever. The design of hybrid composite structures is complicated by the number of design variables and the interaction of the constituents is the composite system. Since it is desirable to experimentally test the design and it is not practical to test a full scale model, the structural/material similitude concept is used to create a small scale model with a similar structural response. In the current study, experimental investigations were carried out to determine the response of four different combinations of hybrid laminates to low-velocity impact loading using an instrumented impact testing machine. Hybrid laminates were fabricated with twill weave carbon fabric and plain weave S2-glass fabric using vacuum assisted resin molding process with SC-15 epoxy resin system. Response of carbon/epoxy and glass/epoxy laminates was also investigated to compare with that of hybrid samples. Square laminates of size 100 mm and nominal thickness of 3 mm were subjected to low-velocity impact loading at four energy levels of 10, 20, 30 and 40 J. Results of the study indicate that there is considerable improvement in the load carrying capability of hybrid composites as compared to carbon/epoxy laminates with slight reduction in stiffness.
Stochastic-Strength-Based Damage Simulation of Ceramic Matrix Composite Laminates
NASA Technical Reports Server (NTRS)
Nemeth, Noel N.; Mital, Subodh K.; Murthy, Pappu L. N.; Bednarcyk, Brett A.; Pineda, Evan J.; Bhatt, Ramakrishna T.; Arnold, Steven M.
2016-01-01
The Finite Element Analysis-Micromechanics Analysis Code/Ceramics Analysis and Reliability Evaluation of Structures (FEAMAC/CARES) program was used to characterize and predict the progressive damage response of silicon-carbide-fiber-reinforced reaction-bonded silicon nitride matrix (SiC/RBSN) composite laminate tensile specimens. Studied were unidirectional laminates [0] (sub 8), [10] (sub 8), [45] (sub 8), and [90] (sub 8); cross-ply laminates [0 (sub 2) divided by 90 (sub 2),]s; angled-ply laminates [plus 45 (sub 2) divided by -45 (sub 2), ]s; doubled-edge-notched [0] (sub 8), laminates; and central-hole laminates. Results correlated well with the experimental data. This work was performed as a validation and benchmarking exercise of the FEAMAC/CARES program. FEAMAC/CARES simulates stochastic-based discrete-event progressive damage of ceramic matrix composite and polymer matrix composite material structures. It couples three software programs: (1) the Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC), (2) the Ceramics Analysis and Reliability Evaluation of Structures Life Prediction Program (CARES/Life), and (3) the Abaqus finite element analysis program. MAC/GMC contributes multiscale modeling capabilities and micromechanics relations to determine stresses and deformations at the microscale of the composite material repeating-unit-cell (RUC). CARES/Life contributes statistical multiaxial failure criteria that can be applied to the individual brittle-material constituents of the RUC, and Abaqus is used to model the overall composite structure. For each FEAMAC/CARES simulation trial, the stochastic nature of brittle material strength results in random, discrete damage events that incrementally progress until ultimate structural failure.
NASA Technical Reports Server (NTRS)
Shuart, M. J.
1985-01-01
The short-wavelength buckling (or the microbuckling) and the interlaminar and inplane shear failures of multi-directional composite laminates loaded in uniaxial compression are investigated. A laminate model is presented that idealizes each lamina. The fibers in the lamina are modeled as a plate, and the matrix in the lamina is modeled as an elastic foundation. The out-of-plane w displacement for each plate is expressed as a trigonometric series in the half-wavelength of the mode shape for laminate short-wavelength buckling. Nonlinear strain-displacement relations are used. The model is applied to symmetric laminates having linear material behavior. The laminates are loaded in uniform end shortening and are simply supported. A linear analysis is used to determine the laminate stress, strain, and mode shape when short-wavelength buckling occurs. The equations for the laminate compressive stress at short-wavelength buckling are dominated by matrix contributions.
Roach, Dennis Patrick; Rackow, Kirk A.
2004-06-01
The FAA's Airworthiness Assurance NDI Validation Center, in conjunction with the Commercial Aircraft Composite Repair Committee, developed a set of composite reference standards to be used in NDT equipment calibration for accomplishment of damage assessment and post-repair inspection of all commercial aircraft composites. In this program, a series of NDI tests on a matrix of composite aircraft structures and prototype reference standards were completed in order to minimize the number of standards needed to carry out composite inspections on aircraft. Two tasks, related to composite laminates and non-metallic composite honeycomb configurations, were addressed. A suite of 64 honeycomb panels, representing the bounding conditions of honeycomb construction on aircraft, was inspected using a wide array of NDI techniques. An analysis of the resulting data determined the variables that play a key role in setting up NDT equipment. This has resulted in a set of minimum honeycomb NDI reference standards that include these key variables. A sequence of subsequent tests determined that this minimum honeycomb reference standard set is able to fully support inspections over the full range of honeycomb construction scenarios found on commercial aircraft. In the solid composite laminate arena, G11 Phenolic was identified as a good generic solid laminate reference standard material. Testing determined matches in key velocity and acoustic impedance properties, as well as, low attenuation relative to carbon laminates. Furthermore, comparisons of resonance testing response curves from the G11 Phenolic NDI reference standard was very similar to the resonance response curves measured on the existing carbon and fiberglass laminates. NDI data shows that this material should work for both pulse-echo (velocity-based) and resonance (acoustic impedance-based) inspections.
Simulation Based Investigation of Hidden Delamination Damage Detection in CFRP Composites
NASA Technical Reports Server (NTRS)
Leckey, Cara A. C.; Parker, F. Raymond
2013-01-01
Guided wave (GW) based damage detection methods have shown promise in structural health monitoring (SHM) and hybrid SHM-nondestructive evaluation (NDE) techniques. Much previous GW work in the aerospace field has been primarily focused on metallic materials, with a growing focus on composite materials. The work presented in this paper demonstrates how realistic three-dimensional (3D) GW simulations can aid in the development of GW based damage characterization techniques for aerospace composites. 3D elastodynamic finite integration technique is implemented to model GW interaction with realistic delamination damage. A local wavenumber technique is applied to simulation data in order to investigate the detectability of hidden delamination damage to enable accurate characterization of damage extent.
NASA Astrophysics Data System (ADS)
Davila, Yves; Crouzeix, Laurent; Douchin, Bernard; Collombet, Francis; Grunevald, Yves-Henri
2017-08-01
Reinforcement angle orientation has a significant effect on the mechanical properties of composite materials. This work presents a methodology to introduce variable reinforcement angles into finite element (FE) models of composite structures. The study of reinforcement orientation variations uses meta-models to identify and control a continuous variation across the composite ply. First, the reinforcement angle is measured through image analysis techniques of the composite plies during the lay-up phase. Image analysis results show that variations in the mean ply orientations are between -0.5 and 0.5° with standard deviations ranging between 0.34 and 0.41°. An automatic post-treatment of the images determines the global and local angle variations yielding good agreements visually and numerically between the analysed images and the identified parameters. A composite plate analysed at the end of the cooling phase is presented as a case of study. Here, the variation in residual strains induced by the variability in the reinforcement orientation are up to 28% of the strain field of the homogeneous FE model. The proposed methodology has shown its capabilities to introduce material and geometrical variability into FE analysis of layered composite structures.
NASA Astrophysics Data System (ADS)
Bloyer, Donald Ray, Jr.
The fracture and cyclic fatigue properties of ductile phase reinforced brittle matrix laminated composites have been investigated through the examination of the effect of layer orientation and reinforcement layer thickness on niobium metal reinforced Nbsb3Al intermetallic laminates. Two laminate orientations, the crack arrester and crack divider, were prepared with layer thickness combinations of 50 mum Nb/200 mum Nbsb3Al, 125 mum Nb/500 mum Nbsb3Al, and 250 mum Nb/1000 mum Nbsb3A1. This gave a nominally constant reinforcement volume fraction of 0.2. The fracture and resistance-curve behavior of these laminates has been compared with similarly reinforced in situ particulate and microlaminate composites. The high aspect ratio of the Nb laminates led to improved toughness in the Nbsb3Al matrix by a factor of 10-20. Laminate orientation had a small effect on crack growth resistance, and properties were optimal in the arrester as compared to the divider orientation. In addition, thicker Nb layers yielded improved fracture toughness. The high fracture toughness observed in these laminates resulted from large crack tip shielding zones formed by bridging Nb layers in the crack wake. These zones were of sufficient size that large scale bridging conditions generally dominated. R-curve modeling using weight function methods allowed simple approximations of the bridging traction functions which were then used to make small scale bridging predictions of the steady state toughness for each laminate. Promising fatigue crack growth resistance properties were observed for the Nb/Nbsb3Al laminates evaluated under cyclic loading conditions. The laminates provided significantly better fatigue resistance than both Nbsb3Al and Nb/Nbsb3Al particulate composites. For a given composite layer thickness, the arrester orientation showed improved cyclic crack growth resistance as compared to divider orientation. The enhanced fatigue behavior of these composites resulted from extrinsic
Shah, D.K.; Chen, D.J.; Chan, W.S.
1994-12-31
This paper applies the finite element least-square extrapolation and smoothing technique to demonstrate its advantages in evaluation of interfacial stress distributions in composite laminates. The analysis uses the quasi-3D finite element modeling technique and complete 3-D analysis using ABAQUS to investigate the stress distributions in graphite/epoxy laminates. Linear (2 point integration) and quadratic (3 point integration) least square fits in 8-node quadrilaterals and 20 node solid isoparametric elements are demonstrated. The evaluation of transformation matrix from gaussian stresses to nodal stresses was performed using symbolic mathematics on `Mathematica`. The results show that use of extrapolation and smoothing offer better estimates of stress distributions and the interfacial stresses in composite laminates.
NASA Astrophysics Data System (ADS)
Deng, Yan; Chen, Xiuhua; Wang, Hai
2015-12-01
This paper investigates the elastic and failure behavior of textile composite laminates by using an analytical multi-scale correlating approach. The analyses are performed under the four scale levels, i.e. the laminate scale, representative unit cell (RUC) scale, tow architecture scale and fiber/matrix scale levels. The correlation between different scales is derived based on the continuum mechanics and homogenization method from which the stress and strain fields in multiple scales can be obtained concurrently. Effective modulus and ultimate failure strengths of different textile composite (plain weave, twill weave and satin weave) laminates are predicted solely from the corresponding constituent properties, braid geometrical parameters and lay-up. The damage and failure mechanisms at the constituent level are also determined by the micromechanical failure criteria. All the predicted results compare favorably with available experimental data. Parametric studies are also performed to examine the effect of various mechanical and geometrical parameters on the resulting mechanical properties.
NASA Technical Reports Server (NTRS)
Rotem, Assa
1990-01-01
Laminated composite materials tend to fail differently under tensile or compressive load. Under tension, the material accumulates cracks and fiber fractures, while under compression, the material delaminates and buckles. Tensile-compressive fatigue may cause either of these failure modes depending on the specific damage occurring in the laminate. This damage depends on the stress ratio of the fatigue loading. Analysis of the fatigue behavior of the composite laminate under tension-tension, compression-compression, and tension-compression had led to the development of a fatigue envelope presentation of the failure behavior. This envelope indicates the specific failure mode for any stress ratio and number of loading cycles. The construction of the fatigue envelope is based on the applied stress-cycles to failure (S-N) curves of both tensile-tensile and compressive-compressive fatigue. Test results are presented to verify the theoretical analysis.
NASA Technical Reports Server (NTRS)
Librescu, Liviu
1990-01-01
Within this research project, the following topics were studied: (1) foundation of the refined theory of flat cross-ply laminated composite flat and curved panels as well as their static and dynamic response analysis; (2) foundation of a geometrically-nonlinear shear-deformable theory of composite laminated flat panels including the effect of initial geometric imperfections and its application in the postbuckling analysis; (3) the study of the dynamic response of shear deformable elastic laminated composite panels to deterministic time-dependent external excitations as the sonic boom and explosive blast type-loadings; (4) the study of the dynamic response of shear deformable elastic laminated composite panels to random excitation as e.g. the one produced by a jet noise or by any time-dependent external excitation whose characteristics are expressed in a statistical sense; and (5) the dynamic stability of fiber-reinforced composite flat panels whose materials (due to e.g. an ambient high temperature field) exhibit a time-dependent physical behavior.
NASA Technical Reports Server (NTRS)
Wang, S. S.
1985-01-01
A three-dimensional hybrid-stress finite element analysis of composite laminates containing cutouts and cracks is presented. Fully three-dimensional, hexahedral isoparametric elements of the hybrid-stress model are formulated on the basis of the Hellinger-Reissner variational principle. Traction-free edges, cutouts, and crack surfaces are modeled by imposition of exact traction boundary conditions along element surfaces. Special boundary and surface elements are constructed by introducing proper constraints on assumed stress functions. The Lagrangian multiplier technique is used to enforce ply-interface continuity conditions in hybrid bimaterial composite elements for modeling the interface region in a composite laminate. Two examples are given to illustrate the capability of the present method of approach: (1) the well-known delamination problem in an angle-ply laminate, and (2) the important problem of a composite laminate containing a circular hole. Results are presented in detail for each case. Implications of interlaminar and intralaminar crack initiation, growth and fracture in composites containing cracks and cutouts are discussed.
NASA Astrophysics Data System (ADS)
Song, Jun Hee; Kim, Hak Kun; Kim, Sam Yeon
2014-07-01
Laminated fiber-reinforced composites can be applied to an insulating structure of a nuclear fusion device. It is necessary to investigate the interlaminar fracture characteristics of the laminated composites for the assurance of design and structural integrity. The three methods used to prepare the glass fiber reinforced plastic composites tested in this study were vacuum pressure impregnation, high pressure laminate (HPL), and prepreg laminate. We discuss the design criteria for safe application of composites and the shear-compressive test methods for evaluating mechanical properties of the material. Shear-compressive tests could be performed successfully using series-type test jigs that were inclined 0°, 30°, 45°, 60°, and 75° to the normal axis. Shear strength depends strongly on the applied compressive stress. The design range of allowable shear stress was extended by use of the appropriate composite fabrication method. HPL had the largest design range, and the allowable interlaminar shear stress was 0.254 times the compressive stress.
Characterization and Formability of Titanium/Aluminum Laminate Composites Fabricated by Hot Pressing
NASA Astrophysics Data System (ADS)
Qin, Liang; Wang, Hui; Cui, Shengqiang; Wu, Qian; Fan, Minyu; Yang, Zonghui; Tao, Jie
2017-07-01
The Ti/Al laminate composites were prepared by hot pressing to investigate the forming performance due to the corresponding potential applications in both the aerospace and auto industry. The bonding interface morphology and element distributions were characterized by SEM and EDS. The phase constituent was detected by XRD. It was observed that these composites presented good bonding interfaces between Ti and Al layers, and no low-sized voids and intermetallic compounds formed at the interface. In addition, the formability of these laminate composites was studied by the uniaxial tension tests, the limit drawing ratio (LDR) and the forming limit curve (FLC) experiments, respectively. The results indicated that the flow stress increased along with the strain rate increment. A constitutive equation was developed for deformation behavioral description of these laminate composites. The LDR value was 1.8, and the most susceptible region to present cracks was located at the punch profile radius. The forming limit curve of the laminate composites was located between the curves of titanium and aluminum and intersected with the major strain line at approximately 0.31. The macroscopic cracks of the FLC sample demonstrated a saw-toothed crack feature.
The engineering of construction specifications for externally bonded FRP composites
NASA Astrophysics Data System (ADS)
Yang, Xinbao
This dissertation, consisting of six technical papers, presents the results of research on the theme of developing engineering and the construction specifications for externally bonded FRP composites. For particular, the work focuses on three critical aspects of the performance of FRP systems: fiber misalignment, corner radius, and lap splice length. Based on both experimental and theoretical investigations, the main contribution of this work is the development of recommendations on fiber misalignment limit, minimum corner radius, lap splice length to be used as guidance in the construction practice of FRP strengthening of concrete structures. The first three papers focus on the strength and stiffness degradation of CFRP laminates from fiber misalignment. It was concluded that misalignment affects strength more than stiffness. In practice, when all fibers in a laminate can be regarded as through fibers, it is recommended to use a reduction factor for strength and no reduction factor for stiffness to account for fiber misalignment. Findings from concrete beams strengthened with misaligned CFRP laminates verified these recommendations. The fourth and fifth papers investigate the effect of corner radius on the mechanical properties of CFRP laminates wrapped around a rectangular cross section. A unique reusable test device was fabricated to determine fiber stress and radial stress of CFRP laminates with different corner radii. Comparison performed with finite element analyses shows that the test method and the reusable device were viable and the stress concentration needs to be considered in FRP laminate wrapped corners. A minimum of 1.0 in. corner radius was recommended for practice. The sixth paper summarizes the research on the lap splice length of FRP laminates under static and repeated loads. Although a lap splice length of 1.5 in. is sufficient for CFRP laminates to develop the ultimate static tensile strength, a minimum of 4.0 in. is recommended in order to
1982-12-01
FATIGUE BEHAVIOR of POLYMER MATRIX COMPOSITE MATERIALS , 4 " .’* .. . . ". ... .. ... . . ~December 1982 41 .. FINAL REPORT .Army Research Office I I...DEPARTMENT REPORT UWME-DR-201-108-1 LAMINATE ANALYSES, MICROMECHANICAL CREEP RESPONSE, AND FATIGUE BEHAVIOR OF POLYMER MATRIX COMPOSITE MATERIALS...Behavior of Polymer Matrix Composite 16 Sept. 1979 - 30 Nov. 1982 Materials 6 PERFORMING ORG. REPORT NUMBER UWME-DR-201-108-1 7. AUTHOR(.) S. CONTRACT
Effect of High Temperature on the Tensile Behavior of CFRP and Cementitious Composites
NASA Technical Reports Server (NTRS)
Toutanji, Houssam A.
1999-01-01
Concrete and other composite manufacturing processes are continuing to evolve and become more and more suited for use in non-Earth settings such as the Moon and Mars. The fact that structures built in lunar environments would experience a range of effects from temperature extremes to bombardment by micrometeorites and that all the materials for concrete production exist on the Moon means that concrete appears to be the most feasible building material. it can provide adequate shelter from the harshness of the lunar environment and at the same time be a cost effective building material. With a return to the Moon planned by NASA to occur after the turn of the century, it will be necessary to include concrete manufacturing as one of the experiments to be conducted in one of the coming missions. Concrete's many possible uses and possibilities for manufacturing make it ideal for lunar construction. The objectives of this research are summarized as follows: i) study the possibility of concrete production on the Moon or other planets, ii) study the effect of high temperature on the tensile behavior of concrete, and iii) study the effect of high temperature on the tensile behavior of carbon fiber reinforced with inorganic polymer composites. Literature review indicates that production of concrete on the Moon or other planets is feasible using the indigenous materials. Results of this study has shown that both the tensile strength and static elastic modulus of concrete decreased with a rise in temperature from 200 to 500 C. The addition of silica fume to concrete showed higher resistance to high temperatures. Carbon fiber reinforced inorganic polymer (CFRIP) composites seemed to perform well up to 300 C. However, a significant reduction in strength was observed of about 40% at 400 C and up to 80% when the specimens were exposed to 700 C.
Effect of High Temperature on the Tensile Behavior of CFRP and Cementitious Composites
NASA Technical Reports Server (NTRS)
Toutanji, Houssam A.
1999-01-01
Concrete and other composite manufacturing processes are continuing to evolve and become more and more suited for use in non-Earth settings such as the Moon and Mars. The fact that structures built in lunar environments would experience a range of effects from temperature extremes to bombardment by micrometeorites and that all the materials for concrete production exist on the Moon means that concrete appears to be the most feasible building material. it can provide adequate shelter from the harshness of the lunar environment and at the same time be a cost effective building material. With a return to the Moon planned by NASA to occur after the turn of the century, it will be necessary to include concrete manufacturing as one of the experiments to be conducted in one of the coming missions. Concrete's many possible uses and possibilities for manufacturing make it ideal for lunar construction. The objectives of this research are summarized as follows: i) study the possibility of concrete production on the Moon or other planets, ii) study the effect of high temperature on the tensile behavior of concrete, and iii) study the effect of high temperature on the tensile behavior of carbon fiber reinforced with inorganic polymer composites. Literature review indicates that production of concrete on the Moon or other planets is feasible using the indigenous materials. Results of this study has shown that both the tensile strength and static elastic modulus of concrete decreased with a rise in temperature from 200 to 500 C. The addition of silica fume to concrete showed higher resistance to high temperatures. Carbon fiber reinforced inorganic polymer (CFRIP) composites seemed to perform well up to 300 C. However, a significant reduction in strength was observed of about 40% at 400 C and up to 80% when the specimens were exposed to 700 C.
NASA Technical Reports Server (NTRS)
Choi, Sukjoo; Sankar, Bhavani; Ebaugh, Newton C.
2005-01-01
A micromechanics method is developed to investigate microcrack propagation in a liquid hydrogen composite tank at cryogenic temperature. The unit cell is modeled using square and hexagonal shapes depends on fiber and matrix layout from microscopic images of composite laminates. Periodic boundary conditions are applied to the unit cell. The temperature dependent properties are taken into account in the analysis. The laminate properties estimated by the micromechanics method are compared with empirical solutions using constituent properties. The micro stresses in the fiber and matrix phases based on boundary conditions in laminate level are calculated to predict the formation of microcracks in the matrix. The method is applied to an actual liquid hydrogen storage system. The analysis predicts micro stresses in the matrix phase are large enough to cause microcracks in the composite. Stress singularity of a transverse crack normal to a ply-interface is investigated to predict the fracture behavior at cryogenic conditions using analytical and finite element analysis. When a transverse crack touches a ply-interface of a composite layer with same fiber orientation, the stress singularity is equal to 1/2. When the transverse crack propagates to a stiffer layer normal to the ply-direction, the singularity becomes less than 1/2 and vice versa. Finite element analysis is performed to predict the fracture toughness of a laminated beam subjected to fracture loads measured by four-point bending tests at room and cryogenic temperatures. As results, the fracture load at cryogenic temperature is significantly lower than that at room temperature. However, when thermal stresses are taken into consideration, for both cases of room and cryogenic temperatures, the difference of the fracture toughness becomes insignificant. The result indicates fracture toughness is a characteristic property, which is independent to temperature changes. The experimental analysis is performed to
Effect of Electrospun Nanofibers on the Short Beam Strength of Laminated Fiberglass Composite
NASA Astrophysics Data System (ADS)
Shinde, Dattaji K.
High specific modulus and strength are the most desirable properties for the material used in structural applications. Composite materials exhibit these properties and over the last decade, their usage has increased significantly, particularly in automotive, defense, and aerospace applications. The major cause of failures in composite laminates is due to delaminations. Delamination in composite laminates can occur due to fatigue, low velocity impact and other loadings modes. Conventional methods like "through-the-thickness stitching" or "Z-Pinning" have limitations for improving flexural and interlaminar properties in woven composites due to the fact that while improving interlaminar properties, the presence of stitches or Z pins affects in-plane properties. This study investigates the flexural behavior of fiberglass composites interleaved with non-woven Tetra Ethyl Orthosilicate (TEOS) electrsopsun nanofibers (ENFs). TEOS ENFs were manufactured using an electrospinning technique and then sintered. Nanoengineered beams were fabricated by interleaving TEOS ENFs between the laminated fiberglass composites to improve the flexural properties. TEOS ENFs, resin film, and failed fiberglass laminated composites with and without nanofibers were characterized using SEM Imaging and ASTM standard testing methods. A hybrid composite was made by interleaving a non-woven sheet of TEOS ENFs between the fiberglass laminates with additional epoxy resin film and fabricated using the out of autoclave vacuum bagging method. Four commonly used stacking sequences of fiberglass laminates with and without nanofibers were used to study the progressive failure and deformation mechanics under flexural loadings. The experimental study has shown significant improvements in short beam strength and strain energy absorption in the nanoengineered laminated fiberglass composites before complete failure. The modes were investigated by performing detailed fractographic examination of failed specimens
A higher-order theory for geometrically nonlinear analysis of composite laminates
NASA Technical Reports Server (NTRS)
Reddy, J. N.; Liu, C. F.
1987-01-01
A third-order shear deformation theory of laminated composite plates and shells is developed, the Navier solutions are derived, and its finite element models are developed. The theory allows parabolic description of the transverse shear stresses, and therefore the shear correction factors of the usual shear deformation theory are not required in the present theory. The theory also accounts for the von Karman nonlinear strains. Closed-form solutions of the theory for rectangular cross-ply and angle-ply plates and cross-ply shells are developed. The finite element model is based on independent approximations of the displacements and bending moments (i.e., mixed finite element model), and therefore, only C sup o -approximation is required. The finite element model is used to analyze cross-ply and angle-ply laminated plates and shells for bending and natural vibration. Many of the numerical results presented here should serve as references for future investigations. Three major conclusions resulted from the research: First, for thick laminates, shear deformation theories predict deflections, stresses and vibration frequencies significantly different from those predicted by classical theories. Second, even for thin laminates, shear deformation effects are significant in dynamic and geometrically nonlinear analyses. Third, the present third-order theory is more accurate compared to the classical and firt-order theories in predicting static and dynamic response of laminated plates and shells made of high-modulus composite materials.
Low-speed impact damage in filament-wound CFRP composite pressure vessels
Matemilola, S.A.; Stronge, W.J.
1997-11-01
Quasi-static and impact tests were conducted on filament-wound carbon fiber composite pressure vessels to study factors that affect burst pressure. Observed damage included fiber microbuckling, matrix cracking, and delamination. Fiber microbuckling of the outer surface layer near the impact point was the main factor that reduced the burst pressure of the vessels. This type of damage was visually detectable on the surface. For similar levels of missile kinetic energy, the impact damage to filament-wound composite pressure vessels depends on size and shape of the colliding body in the contact area. Burst pressure for a damaged vessel decreases with the ratio of axial length of damaged fibers 1, to vessel wall thickness h, up to a ratio l/h = 3; beyond this length of damaged section the burst pressure was independent of length of damage. Strain measurements near the region of loading showed that damage related to fiber microbuckling is sensitive to strain rate. At locations where impact damage was predominantly due to fiber microbuckling, the failure strain was about six times the strain for microbuckling during quasi-static loading.
Scaling of low-velocity impact for symmetric composite laminates
NASA Technical Reports Server (NTRS)
Sankar, Bhavani V.
1992-01-01
The equations governing the problem of low-velocity impact of a simply supported rectangular midplane-symmetric laminated plate are nondimensionalized such that the problem is defined in terms of five dimensionless parameters. A parametric study using the Graeco-Latin Factorial Plan is performed. Semi-empirical formulas for maximum impact force, impact duration, and maximum back surface strains are obtained. It is found that some of the simple impact models provide the bounds for the case of impact on a finite extent plate. A one parameter model is derived for impacts of short duration.
Fatigue of notched fiber composite laminates - Analytical and experimental evaluation
NASA Technical Reports Server (NTRS)
Kulkarni, S. V.; Rosen, B. W.; Mclaughlin, P. V., Jr.; Pipes, R. B.
1977-01-01
Axial cracking in the load direction and transverse cracking across notched boron/epoxy laminate specimens subjected to tension/tension fatigue loading are studied both theoretically and experimentally. The fatigue analysis, which allows for the computation of residual strength and the determination of the preferred mode of crack propagation, is reviewed; static and fatigue data for boron/epoxy lamina are investigated with the aim of characterizing fatigue growth and residual strength as a function of the number of load cycles. It is suggested that correlation between the theory and the experiment may be limited by lack of a capability to predict the growth of delaminations.
Acoustic emission monitoring of unstable damage growth in CFRP composites under tension
NASA Astrophysics Data System (ADS)
Mills-Dadson, B.; Tran, D.; Asamene, K.; Whitlow, T.; Sundaresan, M.
2017-02-01
Composite structural members experience extensive and complex damage that accumulate in a relatively steady pace as the structure is quasi-statically loaded. This damage progression which starts as matrix cracks, delaminations, and random fiber breaks, turns unstable when groups of adjacent fibers, ranging from four to ten fibers fail together, after about 85% of ultimate strength, as reported in the literature. Identifying this critical damage that precedes the final fracture has been difficult even in laboratory specimens. There is little consensus on successful use of AE signals to differentiate failure modes. The inability of AE patterns to identify failure modes is likely caused by the limited frequency bandwidth of available AE sensors, and the high attenuation seen in AE signals particularly in the frequency range likely to be associated with fiber fractures. As a part of this study new acoustic emission sensors capable of measuring frequencies to 2 MHz were developed. In addition, composite specimens were instrumented with sufficient number of sensors to capture high frequency signals before they are attenuated. Unidirectional, cross-ply, and quasi-isotropic carbon-epoxy composite tensile specimens were monitored while they were statically loaded to failure. Distinctly different signals corresponding to the three failure modes could be observed. High frequency acoustic emission signals with frequencies well in excess of 1MHz, mostly seen in the last 20% of the loading cycle. Signals with frequencies in the range of 300 kHz to 700 kHz and duration of the order of 50 microseconds, were observed in cross ply and quasi-isotropic specimens, and are believed to be from matrix cracks. Fewer events with frequencies below 300 kHz and duration that exceeded about 200 microseconds are believed to be from delaminations. An important observation in this study is the appearance of groups of near identical waveforms, which are believed to be from clusters of adjacent
NASA Technical Reports Server (NTRS)
Howard, W. E.; Gossard, Terry, Jr.; Jones, Robert M.
1989-01-01
The present generalized plane-strain FEM analysis for the prediction of interlaminar normal stress reduction when a U-shaped cap is bonded to the edge of a composite laminate gives attention to the highly variable transverse stresses near the free edge, cap length and thickness, and a gap under the cap due to the manufacturing process. The load-transfer mechanism between cap and laminate is found to be strain-compatibility, rather than shear lag. In the second part of this work, the three-dimensional composite material failure criteria are used in a progressive laminate failure analysis to predict failure loads of laminates with different edge-cap designs; symmetric 11-layer graphite-epoxy laminates with a one-layer cap of kevlar-epoxy are shown to carry 130-140 percent greater loading than uncapped laminates, under static tensile and tension-tension fatigue loading.
Wang, S.S.; Srinivasan, S.; Su, K.B.; Dunham, M.G.
1994-12-31
Recent advances in fiber-composites manufacturing and structural efficiency requirements have led to the consideration of large isogrid-stiffened fiber-composite laminate shells for various aeronautical and space structural applications. Very little information, if any, on buckling and postbuckling of these grid-stiffened shells is currently available in the literature. In this paper, a combined analytical and experimental study is reported on the buckling and postbuckling behavior of these filament-wound fiber-composite laminate shells constructed with continuous-filament isogrid stiffeners made of the same composite material system. Solutions from linear bifurcation and geometric nonlinear postbuckling analyses have been obtained for stiffened composite shells, monocoque shells and isogrid stiffeners. Experiments have been conducted in parallel to the analyses, and buckling loads and postbuckling deformation characteristics have been studied for these structures.
Structural properties of laminated Douglas fir/epoxy composite material
Spera, D.A. . Lewis Research Center); Esgar, J.B. ); Gougeon, M.; Zuteck, M.D. )
1990-05-01
This publication contains a compilation of static and fatigue and strength data for laminated-wood material made from Douglas fir and epoxy. Results of tests conducted by several organizations are correlated to provide insight into the effects of variables such as moisture, size, lamina-to-lamina joint design, wood veneer grade, and the ratio of cyclic stress to steady stress during fatigue testing. These test data were originally obtained during development of wood rotor blades for large-scale wind turbines of the horizontal-axis (propeller) configuration. Most of the strength property data in this compilation are not found in the published literature. Test sections ranged from round cylinders 2.25 in. in diameter to rectangular slabs 6 in. by 24 in. in cross section and approximately 30 ft long. All specimens were made from Douglas fir veneers 0.10 in. thick, bonded together with the WEST epoxy system developed for fabrication and repair of wood boats. Loading was usually parallel to the grain. Size effects (reduction in strength with increase in test volume) are observed in some of the test data, and a simple mathematical model is presented that includes the probability of failure. General characteristics of the wood/epoxy laminate are discussed, including features that make it useful for a wide variety of applications. 9 refs.
Lamination residual stresses in hybrid composites, part 1
NASA Technical Reports Server (NTRS)
Daniel, I. M.; Liber, T.
1976-01-01
An experimental investigation was conducted to study lamination residual stresses for various material and loading parameters. The effects of hybridization on residual stresses and residual properties after thermal cycling under load were determined in angle-ply graphite/Kevlar/epoxy and graphite/S-glass/epoxy laminates. Residual strains in the graphite plies are not appreciably affected by the type and number of hybridizing plies. Computed residual stresses at room temperature in the S-glass plies reach values up to seventy-five percent of the transverse strength of the material. Computed residual stresses in the graphite plies exceed the static strength by approximately ten percent. In the case of Kevlar plies, computed residual stresses far exceed the static strength indicating possible early failure of these plies. Static testing of the hybrids above indicates that failure is governed by the ultimate strain of the graphite plies. In thermally cycled hybrids, in general, residual moduli were somewhat lower and residual strengths were higher than initial values.
Structural properties of laminated Douglas fir/epoxy composite material
NASA Technical Reports Server (NTRS)
Spera, David A.; Esgar, Jack B.; Gougeon, Meade; Zuteck, Michael D.
1990-01-01
This publication contains a compilation of static and fatigue strength data for laminated-wood material made from Douglas fir and epoxy. Results of tests conducted by several organizations are correlated to provide insight into the effects of variables such as moisture, size, lamina-to-lamina joint design, wood veneer grade, and the ratio of cyclic stress to steady stress during fatigue testing. These test data were originally obtained during development of wood rotor blades for large-scale wind turbines of the horizontal-axis (propeller) configuration. Most of the strength property data in this compilation are not found in the published literature. Test sections ranged from round cylinders 2.25 in. in diameter to rectangular slabs 6 by 24 in. in cross section and approximately 30 ft. long. All specimens were made from Douglas fir veneers 0.10 in. thick, bonded together with the WEST epoxy system developed for fabrication and repair of wood boats. Loading was usually parallel to the grain. Size effects (reduction in strength with increase in test volume) are observed in some of the test data, and a simple mathematical model is presented that includes the probability of failure. General characteristics of the wood/epoxy laminate are discussed, including features that make it useful for a wide variety of applications.
Interface Effects on the Fracture Mechanism of a High-Toughness Aluminum-Composite Laminate
NASA Astrophysics Data System (ADS)
Cepeda-Jiménez, C. M.; Pozuelo, M.; García-Infanta, J. M.; Ruano, O. A.; Carreño, F.
2009-01-01
The microstructure and the mechanical properties of a multilayer composite laminate based on aluminum 7075 and 2024 alloys produced by hot roll bonding were examined. The composite laminate has been tested at room temperature under Charpy-impact tests, three-point bend tests, and shear tests on the interfaces. The toughness of the post-rolling tempered and T6-treated composite laminate, measured by impact- absorbed energy in the crack-arrester orientation, was more than 20 times higher than that of the monolithic Al 7075 alloy and 7 times higher than that of Al 2024 alloy. The outstanding toughness increase of the composite laminate in the post-rolling tempered and T6-treated condition is mainly due to the mechanism of “interface predelamination.” By this fracture mechanism, the interfaces are debonded before the main crack reaches them, warranting delamination in all interfaces. Therefore, delamination and crack renucleation in every layer are responsible for the improvement in toughness.
Analysis of laminated, composite, circular cylindrical shells with general boundary conditions
NASA Technical Reports Server (NTRS)
Srinivas, S.
1974-01-01
This report develops: (1) a refined approximate theory for the static and dynamic analyses of finite, laminated, composite, circular cylindrical shells with general boundary conditions; (2) an exact three-dimensional analysis of simply supported, laminated, composite, circular cylindrical shells, and (3) a thin-shell theory for laminated, composite, circular cylindrical shells. In the refined approximate theory the displacements are assumed piecewise linear across the thickness and the effects of transverse shear deformations and transverse normal stress are included. A variational approach is followed to obtain the governing differential equations and boundary conditions. A general solution of the governing differential equations is also presented. The results obtained by using the refined approximate theory and the thin-shell theory are compared with the exact results for the case of free vibrations of simply supported, laminated, composite, circular cylindrical shells. The refined approximate theory is very accurate, even for thick shells with short nodal distances, whereas thin-shell theory is reasonably accurate only for thin shells at moderate nodal distances and wave number less than 2.
Impact damage and burst of filament-wound CFRP composite pressure vessel
Matemilola, S.A.; Stronge, W.J.
1996-12-31
Quasi-static and impact tests were conducted on filament-wound carbon fiber composite pressure vessels to study factors that affect burst pressure. Observed damage include fiber microbuckling, matrix cracking, and delamination. For vessels that were not pressurized during test, both the matrix cracking and fiber breakage were restricted to the outer layer, whereas in the case of an internally pressurized vessel struck by a wedge nose shaped impactor these cracks extended into the second layer. Fiber microbuckling of the outer surface layer near the impact point was the main factor that degraded the burst pressure of the vessels. This type of damage was visually detectable on the surface. For an unpressurized vessel it appeared as a pair of cracks radiating from the periphery of contact region. On the other hand, for a pressurized vessel circumferential microbuckling developed within the contact region. The burst pressure for a damaged vessel decreased as the ratio of axial length of the buckled fibers l, to vessel thickness h, increased, up to a ratio {ell}/h {approx} 3, beyond which the burst pressure became constant. Strain measurements near the region of loading showed that fiber microbuckling occurred, the failure strain value at a strain rate of 104 s{sup {minus}1} was about six times the microbuckling strain for quasi-static loading.
Ning, Fuda; Wang, Hui; Cong, Weilong; Fernando, P K S C
2017-04-01
Rotary ultrasonic machining (RUM) has been investigated in machining of brittle, ductile, as well as composite materials. Ultrasonic vibration amplitude, as one of the most important input variables, affects almost all the output variables in RUM. Numerous investigations on measuring ultrasonic vibration amplitude without RUM machining have been reported. In recent years, ultrasonic vibration amplitude measurement with RUM of ductile materials has been investigated. It is found that the ultrasonic vibration amplitude with RUM was different from that without RUM under the same input variables. RUM is primarily used in machining of brittle materials through brittle fracture removal. With this reason, the method for measuring ultrasonic vibration amplitude in RUM of ductile materials is not feasible for measuring that in RUM of brittle materials. However, there are no reported methods for measuring ultrasonic vibration amplitude in RUM of brittle materials. In this study, ultrasonic vibration amplitude in RUM of brittle materials is investigated by establishing a mechanistic amplitude model through cutting force. Pilot experiments are conducted to validate the calculation model. The results show that there are no significant differences between amplitude values calculated by model and those obtained from experimental investigations. The model can provide a relationship between ultrasonic vibration amplitude and input variables, which is a foundation for building models to predict other output variables in RUM.
Process-induced residual stresses and dimensional distortions in advanced laminated composites
NASA Astrophysics Data System (ADS)
Niu, Xiaokai
Process induced residual stresses can degrade the performance of composite structures by consuming a significant portion of the strength in certain plies. Cracking due to overload of these plies can then lead to degradation by environmental effects. A technique called cure referencing method (CRM) has been developed for determining the residual stresses in flat laminated composites. In this technique a diffraction grating used for moire interferometry is transferred onto a composite laminate from a master autoclave tool during the curing process. This transfer takes place at the cure temperature where the matrix solidifies from the liquid state. After cure and upon cooling, the deformation of the composite is recorded with moire interferometry using the tool grating as the reference. The deformation of the composite is then a function of the thermal contraction due to the temperature difference from the cure temperature to room temperature and the deformation caused by chemical shrinkage. These measurements are first conducted on a unidirectional lamina. Using a specially designed oven, the thermal contraction component of the deformation is separated from the overall deformation. For flat multidirectional symmetrical laminates, the residual stresses in each layer and the in-plane dimensional distortions of the laminate are then calculated from the unidirectional information, constitutive equations, equilibrium equations, and compatibility conditions. Several assumptions, which are similar to those used in laminate theory, are also adopted. An independent method called shadow moire is used to validate CRM. The shadow moire method is used to measure the curvature of asymmetrical laminates while the lamination theory is used to calculate the curvature from lamina strain information measured with CRM. Good agreement validates the CRM. In addition, process induced strains on multi-directional composites were measured with the CRM. The validation of CRM and the
Thermally-induced, geometrically nonlinear response of symmetrically laminated composite plates
NASA Technical Reports Server (NTRS)
Meyers, C. A.; Hyer, M. W.
1992-01-01
This paper discusses the thermally-induced geometrically nonlinear response of symmetrically laminated composite plates. The plate response is due to a temperature increase that is uniform in the plane of the plate but has a slight gradient through the thickness. The case of a completely uniform temperature increase but with an initial out-of-plane imperfection in the plate is also considered. Because they are closely allied problems, thermal buckling and postbuckling are discussed. Using variational methods in conjunction with a Rayleigh-Ritz formulation, these responses are investigated for two laminates, a (+/- 45/0/90)s and a (+/- 45/02)s, under two different simple support conditions.
Simulating Initial and Progressive Failure of Open-Hole Composite Laminates under Tension
NASA Astrophysics Data System (ADS)
Guo, Zhangxin; Zhu, Hao; Li, Yongcun; Han, Xiaoping; Wang, Zhihua
2016-12-01
A finite element (FE) model is developed for the progressive failure analysis of fiber reinforced polymer laminates. The failure criterion for fiber and matrix failure is implemented in the FE code Abaqus using user-defined material subroutine UMAT. The gradual degradation of the material properties is controlled by the individual fracture energies of fiber and matrix. The failure and damage in composite laminates containing a central hole subjected to uniaxial tension are simulated. The numerical results show that the damage model can be used to accurately predicte the progressive failure behaviour both qualitatively and quantitatively.