Science.gov

Sample records for overcome software brittleness

  1. Towards an Approach to Overcome Software Brittleness

    SciTech Connect

    OSBOURN,GORDON C.

    1999-11-01

    Development of bug-free, high-surety, complex software is quite difficult using current tools. The brittle nature of the programming constructs in popular languages such as C/C++ is one root cause. Brittle commands force the designer to rigidly specify the minutiae of tasks, e.g. using ''for(index=0;index>total;index++)'', rather than specifying the goals or intent of the tasks, e.g. ''ensure that all relevant data elements have been examined''. Specification of task minutiae makes code hard to comprehend, which in turn encourages design errors/limitations and makes future modifications quite difficult. This report describes an LDRD project to seed the development of a surety computer language, for stand-alone computing environments, to be implemented using the swarm intelligence of autonomous agents. The long term vision of this project was to develop a language with the following surety capabilities: (1) Reliability -- Autonomous agents can appropriate y decide when to act and when a task is complete, provide a natural means for avoiding brittle task specifications, and can overcome many hardware glitches. (2) Safety, security -- Watchdog safety and security agents can monitor other agents to prevent unauthorized or dangerous actions. (3) An immune system -- The small chunks of agent code can have an encryption scheme to enable detection and elimination of unauthorized and corrupted agents. This report describes the progress achieved during this small 9 month project and describes lessons learned.

  2. Overcoming the brittleness of glass through bio-inspiration and micro-architecture

    NASA Astrophysics Data System (ADS)

    Mirkhalaf, M.; Dastjerdi, A. Khayer; Barthelat, F.

    2014-01-01

    Highly mineralized natural materials such as teeth or mollusk shells boast unusual combinations of stiffness, strength and toughness currently unmatched by engineering materials. While high mineral contents provide stiffness and hardness, these materials also contain weaker interfaces with intricate architectures, which can channel propagating cracks into toughening configurations. Here we report the implementation of these features into glass, using a laser engraving technique. Three-dimensional arrays of laser-generated microcracks can deflect and guide larger incoming cracks, following the concept of ‘stamp holes’. Jigsaw-like interfaces, infiltrated with polyurethane, furthermore channel cracks into interlocking configurations and pullout mechanisms, significantly enhancing energy dissipation and toughness. Compared with standard glass, which has no microstructure and is brittle, our bio-inspired glass displays built-in mechanisms that make it more deformable and 200 times tougher. This bio-inspired approach, based on carefully architectured interfaces, provides a new pathway to toughening glasses, ceramics or other hard and brittle materials.

  3. Portal for Families Overcoming Neurodevelopmental Disorders (PFOND): Implementation of a Software Framework for Facilitated Community Website Creation by Nontechnical Volunteers

    PubMed Central

    Imam, Tuhina; Lee, Cheryl E; Chen, Shirley Yu; Herman, Adam; Sharma, Balraj; Johal, Gurinder; Gu, Bobby

    2013-01-01

    Background The Portal for Families Overcoming Neurodevelopmental Disorders (PFOND) provides a structured Internet interface for the sharing of information with individuals struggling with the consequences of rare developmental disorders. Large disease-impacted communities can support fundraising organizations that disseminate Web-based information through elegant websites run by professional staff. Such quality resources for families challenged by rare disorders are infrequently produced and, when available, are often dependent upon the continued efforts of a single individual. Objective The project endeavors to create an intuitive Web-based software system that allows a volunteer with limited technical computer skills to produce a useful rare disease website in a short time period. Such a system should provide access to emerging news and research findings, facilitate community participation, present summary information about the disorder, and allow for transient management by volunteers who are likely to change periodically. Methods The prototype portal was implemented using the WordPress software system with both existing and customized supplementary plug-in software modules. Gamification scoring features were implemented in a module, allowing editors to measure progress. The system was installed on a Linux-based computer server, accessible across the Internet through standard Web browsers. Results A prototype PFOND system was implemented and tested. The prototype system features a structured organization with distinct partitions for background information, recent publications, and community discussions. The software design allows volunteer editors to create a themed website, implement a limited set of topic pages, and connect the software to dynamic RSS feeds providing information about recent news or advances. The prototype was assessed by a fraction of the disease sites developed (8 out of 27), including Aarskog-Scott syndrome, Aniridia, Adams-Oliver syndrome

  4. Brittle nails (image)

    MedlinePlus

    Like the skin, the fingernails are a reflection of a person's state of health. Low levels of zinc and iron as well as thyroid problems can cause brittle nails. However, brittle nails are often a normal ...

  5. Brittle diabetes: psychopathological aspects.

    PubMed

    Pelizza, Lorenzo; Bonazzi, Federica; Scaltriti, Sara; Milli, Bruna; Giuseppina, Chierici

    2014-01-01

    Background. The term "brittle" is used to described an uncommon subgroup of type I diabetics whose lives are disrupted by severe glycaemic instability with repeated and prolonged hospitalization. Psychosocial problems are the major perceived underlying causes of brittle behaviour. Aim of this study is a systematic psychopathological assessement of brittleness using specific parameters of general psychopathology and personality traits following the multiaxial format (axis I and II) of the current DSM-IV-TR diagnostic criteria for mental disorders. Methods. Patients comprised 21 brittle type I diabetics and a case-control group of 21 stable diabetics, matched for age, gender, years of education, and diabetes duration. General psychopathology and the DSM-IV-TR personality traits/disorders were assessed using the Syptom Checklist-90-R (SCL-90-R) and the Millon Clinical Multiaxial Inventory-III (MCMI-III). Results. The comparison for SCL-90-R parameters exclusively revealed higher scores in "Phobic Anxiety" subscale in brittle diabetics. No differences in all the other SCL-90-R primary symptom dimensions and in the three SCL-90-R global distress indices were observed between the two diabetic groups, as well as in the all MCMI-III clinical syndrome categories corresponding to DSM-IV-TR specific psychiatric disorders. However, brittle patients presented lower scores in MCMI-III compulsive personality traits and higher scores in paranoid, schizoid, schizotypal, antisocial, borderline, narcissistic, avoidant, dependent, depressive, and passive-aggressive personality traits. Conclusions. In this study, brittle diabetics show no differencies in terms of global severity of psychopathological distress and axis I specific DSM-IV-TR diagnoses in comparison with non-brittle subjects (except for phobic anxiety). Differently, brittle diabetics are characterized from less functional and maladaptive personality features and suffer more frequently and intensively from specific

  6. Fracture of brittle solids

    NASA Technical Reports Server (NTRS)

    Doherty, R. D.; Nash, S. K.

    1990-01-01

    Upon completion of this experiment, the student should be able to give an elementary account of brittle versus ductile failure, conduct a three-point bend test on a tensile testing machine, and statistically analyze experimental data that exhibit inherently wide scatter. The experimental procedure is described.

  7. Brittleness of ceramics

    NASA Technical Reports Server (NTRS)

    Kroupa, F.

    1984-01-01

    The main characteristics of mechanical properties of ceramics are summarized and the causes of their brittleness, especially the limited mobility of dislocations, are discussed. The possibility of improving the fracture toughness of ceramics and the basic research needs relating to technology, structure and mechanical properties of ceramics are stressed in connection with their possible applications in engineering at high temperature.

  8. Overcoming Barriers.

    PubMed

    Neal-Boylan, Leslie; Schmidt, Kari L

    2015-01-01

    Dr. Neal-Boylan's program of scholarship has always focused on nurse workforce issues. She recently published two books related to how nurses work. One (The Nurse's Reality Gap: Overcoming Barriers Between Academic Achievement and Clinical Success; Neal-Boylan, 2013) focused on the experience of new graduates from baccalaureate, master's, and doctoral programs. The second book, The Nurse's Reality Shift: Using Our History to Transform Our Future (Neal-Boylan, 2014), focuses on the problems nursing continues to face throughout our history and has failed to correct. PMID:26200309

  9. Fracture technology for brittle materials

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.

    1988-01-01

    Ceramics materials have the potential for use in high-temperature, fuel-efficient engines. However, because these materials are brittle, their fracture characteristics must be well documented prior to their application. Thus Lewis is working to understand the fracture and strength properties of brittle ceramic and ceramic matrix materials. An understanding of fracture properties aids both designers who are attempting to design high-temperature structures and materials scientists who seek to design more temperature-resistant materials. Both analytical and experimental approaches to fracture analysis are being taken. Methods for testing fracture toughness, crack growth resistance, and strength are being developed. The failure mechanisms at both room and elevated temperatures are also being investigated. Such investigations aid materials scientists in developing better high-temperature materials. Of concern is the anisotropy of ceramic materials and the experimental verification of ceramic design codes that will allow brittle material behavior to be accurately predicted at high temperature.

  10. Battling Brittle Bones

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The accuDEXA(R) Bone Mineral Density Assessment System, manufactured by Schick Technologies, Inc., utilizes "camera on a chip" sensor technology invented and developed by NASA's Jet Propulsion Laboratory. Schick's accuDEXA system offers several advantages over traditional osteoporosis tests, which assess bone density loss in the hip and spine, and require specialized personnel to conduct. With accuDEXA, physicians can test the entire body's bone density at a peripheral site, such as the finger, without applying gels or having patients remove garments. Results are achieved in 30 seconds and printed out in less than a minute, compared to the estimated exam time of 15 minutes for hip and spine density analyses. Schick has also applied the CMOS APS technology to a new software product that performs dental radiography using up to 90 percent less radiation exposure than conventional X-rays. Called Computed Dental Radiography(R), the new digital imaging product utilizes an electronic sensor in place of X-ray film to generate sharp and clear images that appear on a computer screen within 3 seconds, and can be enlarged and enhanced to identify problems.

  11. Soft matter: Brittle for breakfast

    NASA Astrophysics Data System (ADS)

    Vandewalle, Nicolas

    2015-10-01

    Crushing a brittle porous medium such as a box of cereal causes the grains to break up and rearrange themselves. A lattice spring model based on simple physical assumptions gives rise to behaviours that are complex enough to reproduce diverse compaction patterns.

  12. Overcoming prejudice.

    PubMed

    Da Silva, J M; Correa, J; Terto, V

    1998-02-01

    People of African descent comprise a large proportion of Brazil's population. While racism exists in the country, it is commonly denied. Most Afro-Brazilians live in poor areas, with poor health care services, sanitation, schools, and transport. Since HIV is linked to poverty, Afro-Brazilians are more affected by HIV than is the overall population. Although Afro-Brazilians contribute to Brazil's culture, they do not benefit from that contribution. Recognizing this considerable social problem, Project Araye was created in 1996 to address issues of race and HIV. Building upon religious and cultural traditions, the project is staffed by Afro-Brazilians who are knowledgeable in both health issues and Afro-Brazilian culture. Project Araye supports a wide range of diverse community leaders in linking sexual health and HIV with other health concerns which affect Afro-Brazilians such as sickle-cell anemia, diabetes, and leprosy. One important challenge has been overcoming the target population's denial of HIV and encouraging Afro-Brazilians to accept that HIV also affects them. Community leaders include religious leaders, rap musicians, artists, and other people respected by various communities. Activities include visits to samba dance schools, Umbanda and Candomble temples, and street youth groups to provide HIV-related information. PMID:12293758

  13. Testing Bonds Between Brittle And Ductile Films

    NASA Technical Reports Server (NTRS)

    Wheeler, Donald R.; Ohsaki, Hiroyuki

    1989-01-01

    Simple uniaxial strain test devised to measure intrinsic shear strength. Brittle film deposited on ductile stubstrate film, and combination stretched until brittle film cracks, then separates from substrate. Dimensions of cracked segments related in known way to tensile strength of brittle film and shear strength of bond between two films. Despite approximations and limitations of technique, tests show it yields semiquantitative measures of bond strengths, independent of mechanical properties of substrates, with results reproducible with plus or minus 6 percent.

  14. Protection of brittle film against cracking

    NASA Astrophysics Data System (ADS)

    Musil, J.; Sklenka, J.; Čerstvý, R.

    2016-05-01

    This article reports on the protection of the brittle Zrsbnd Sisbnd O film against cracking in bending by the highly elastic top film (over-layer). In experiments the Zrsbnd Sisbnd O films with different elemental composition and structure were used. Both the brittle and highly elastic films were prepared by magnetron sputtering using a dual magnetron. The brittle film easily cracks in bending. On the other hand, the highly elastic film exhibits enhanced resistance to cracking in bending. Main characteristic parameters of both the brittle and highly elastic films are given. Special attention is devoted to the effect of the structure (crystalline, amorphous) of both the brittle and highly elastic top film on the resistance of cracking of the brittle film. It was found that (1) both the X-ray amorphous and crystalline brittle films easily crack in bending, (2) the highly elastic film can have either X-ray amorphous or crystalline structure and (3) both the X-ray amorphous and crystalline, highly elastic top films perfectly protect the brittle films against cracking in bending. The structure, mechanical properties and optical transparency of the brittle and highly elastic sputtered Zrsbnd Sisbnd O films are described in detail. At the end of this article, the principle of the low-temperature formation of the highly elastic films is also explained.

  15. Evaluation of the brittleness of the rocks using various brittleness indices

    NASA Astrophysics Data System (ADS)

    Cheon, Dae-Sung; Jung, Yong-Bok; Park, Chan; Park, Eui-Seob

    2015-04-01

    In general, the rock has the feature of drastically reduced bearing capacity during the small strain by the brittle characteristic. Because brittleness is considered as both of inherent property and behavior of materials, various brittleness indices have been proposed and based on these the brittleness degrees of the rock are determined. The brittleness indices are used for evaluating the stability of brittle failure in deep mines or underground excavations, drillability evaluation in the well drilling field, sawability evaluation in the building stone field and others. In recent years there has been utilized as a descriptor of the hydraulic fracturing in shale gas and enhanced geothermal system. In this paper, we estimated the brittleness index of different types of rocks using various brittleness indices proposed by previous researchers and investigated their relationship and applicability. The commonly used brittleness index in Rock Mechanics is the ratio between uniaxial compressive strength and tensile strength. In Reservior Geomechanics, the indices using dynamic elastic modulus and Poisson's ratio calculated from well logging data are generally used. In higher brittleness or brittleness index, the rock shows the following characteristics; low values of elongation of grains, fracture failure, formation of fines and debris, a higher ratio of compressive to tensile strength, higher resilience, higher internal friction angle, formation of cracks in indentation, easy to fracture etc.. The brittleness index showed relatively good relations with rock intrinsic properties such as uniaxial compressive strength, elastic modulus and fracture toughness in particular rock types. The correlation among brittleness index using geophysical logging data was shown. However, it was difficult to find a relationship of the brittleness indices between uses in traditional Rock Mechanics and Reservoir Geomechanics. Since some brittleness indices have no special meaning, a careful

  16. Time-dependent Brittle Deformation in Darley Dale Sandstone

    NASA Astrophysics Data System (ADS)

    Baud, P.; Heap, M. J.; Meredith, P. G.; Bell, A. F.; Main, I. G.

    2008-12-01

    The characterization of time-dependent brittle rock deformation is fundamental to understanding the long- term evolution and dynamics of the Earth's upper crust. The chemical influence of water promotes time- dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Here we report results from a study of time-dependent brittle creep in water- saturated samples of Darley Dale sandstone (initial porosity of 13%). Conventional creep experiments (or 'static fatigue' tests) show that time to failure decreases dramatically with the imposed deviatoric stress. They also suggest the existence of a critical level of damage beyond which localized failure develops. Sample variability results however in significant scattering in the experimental data and numerous tests are needed to clearly define a relation between the strain rate and the applied stress. We show here that stress-stepping experiments provide a means to overcome this problem and that it is possible this way to obtain the strain rate dependence on applied stress with a single test. This allows to study in details the impact of various thermodynamical conditions on brittle creep. The influence of effective stress was investigated in stress-stepping experiments with effective confining pressures of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the expected purely mechanical influence of an elevated effective stress our results also demonstrate that stress corrosion appears to be inhibited at higher effective stresses. The influence of doubling the pore fluid pressure however, whilst maintaining a constant effective stress, is shown to have no effect on the rate of stress corrosion. We then discuss the results in light of acoustic emission hypocentre location data and optical microscope analysis and use our experimental data to validate proposed macroscopic creep laws. Finally, using

  17. Computational brittle fracture using smooth particle hydrodynamics

    SciTech Connect

    Mandell, D.A.; Wingate, C.A.; Schwalbe, L.A.

    1996-10-01

    We are developing statistically based, brittle-fracture models and are implementing them into hydrocodes that can be used for designing systems with components of ceramics, glass, and/or other brittle materials. Because of the advantages it has simulating fracture, we are working primarily with the smooth particle hydrodynamics code SPBM. We describe a new brittle fracture model that we have implemented into SPBM. To illustrate the code`s current capability, we have simulated a number of experiments. We discuss three of these simulations in this paper. The first experiment consists of a brittle steel sphere impacting a plate. The experimental sphere fragment patterns are compared to the calculations. The second experiment is a steel flyer plate in which the recovered steel target crack patterns are compared to the calculated crack patterns. We also briefly describe a simulation of a tungsten rod impacting a heavily confined alumina target, which has been recently reported on in detail.

  18. Overcoming Breastfeeding Challenges

    MedlinePlus Videos and Cool Tools

    ... and Human Services Office on Women's Health Skip Navigation Skip top navigation Home A-Z Health Topics ePublications News About Us Contact Us Text size | Print | Skip left navigation It's Only Natural Planning ahead Overcoming challenges Overcoming ...

  19. Brittleness Effect on Rock Fatigue Damage Evolution

    NASA Astrophysics Data System (ADS)

    Nejati, Hamid Reza; Ghazvinian, Abdolhadi

    2014-09-01

    The damage evolution mechanism of rocks is one of the most important aspects in studying of rock fatigue behavior. Fatigue damage evolution of three rock types (onyx marble, sandstone and soft limestone) with different brittleness were considered in the present study. Intensive experimental tests were conducted on the chosen rock samples and acoustic emission (AE) sensors were used in some of them to monitor the fracturing process. Experimental tests indicated that brittleness strongly influences damage evolution of rocks in the course of static and dynamic loading. AE monitoring revealed that micro-crack density induced by the applied loads during different stages of the failure processes increases as rock brittleness increases. Also, results of fatigue tests on the three rock types indicated that the rock with the most induced micro-cracks during loading cycles has the least fatigue life. Furthermore, the condition of failure surfaces of the studied rocks samples, subjected to dynamic and static loading, were evaluated and it was concluded that the roughness of failure surfaces is influenced by loading types and rock brittleness. Dynamic failure surfaces were rougher than static ones and low brittle rock demonstrate a smoother failure surface compared to high brittle rock.

  20. Fracturing and brittleness index analyses of shales

    NASA Astrophysics Data System (ADS)

    Barnhoorn, Auke; Primarini, Mutia; Houben, Maartje

    2016-04-01

    The formation of a fracture network in rocks has a crucial control on the flow behaviour of fluids. In addition, an existing network of fractures , influences the propagation of new fractures during e.g. hydraulic fracturing or during a seismic event. Understanding of the type and characteristics of the fracture network that will be formed during e.g. hydraulic fracturing is thus crucial to better predict the outcome of a hydraulic fracturing job. For this, knowledge of the rock properties is crucial. The brittleness index is often used as a rock property that can be used to predict the fracturing behaviour of a rock for e.g. hydraulic fracturing of shales. Various terminologies of the brittleness index (BI1, BI2 and BI3) exist based on mineralogy, elastic constants and stress-strain behaviour (Jin et al., 2014, Jarvie et al., 2007 and Holt et al., 2011). A maximum brittleness index of 1 predicts very good and efficient fracturing behaviour while a minimum brittleness index of 0 predicts a much more ductile shale behaviour. Here, we have performed systematic petrophysical, acoustic and geomechanical analyses on a set of shale samples from Whitby (UK) and we have determined the three different brittleness indices on each sample by performing all the analyses on each of the samples. We show that each of the three brittleness indices are very different for the same sample and as such it can be concluded that the brittleness index is not a good predictor of the fracturing behaviour of shales. The brittleness index based on the acoustic data (BI1) all lie around values of 0.5, while the brittleness index based on the stress strain data (BI2) give an average brittleness index around 0.75, whereas the mineralogy brittleness index (BI3) predict values below 0.2. This shows that by using different estimates of the brittleness index different decisions can be made for hydraulic fracturing. If we would rely on the mineralogy (BI3), the Whitby mudstone is not a suitable

  1. The anti-proliferative and anti-angiogenic effect of the methanol extract from brittle star

    PubMed Central

    Baharara, Javad; Amini, Elaheh; Mousavi, Marzieh

    2015-01-01

    Background: Anti-angiogenic therapy is a crucial step in cancer treatment. The discovery of new anti-angiogenic compounds from marine organisms has become an attractive concept in anti-cancer therapy. Because little data correlated to the pro- and anti-angiogenic efficacies of Ophiuroidea, which include brittle star, the current study was designed to explore the anti-angiogenic potential of brittle star methanol extract in vitro and in vivo. Methods: The anti-proliferative effect of brittle star extract on A2780cp cells was examined by MTT assays, and transcriptional expression of VEGF and b-FGF was evaluated by RT-PCR. In an in vivo model, 40 fertilized Ross eggs were divided into control and three experimental groups. The experimental groups were incubated with brittle star extract at concentrations of 25, 50 and 100 µg/ml, and photographed by photo-stereomicroscopy. Ultimately, numbers and lengths of vessels were measured by Image J software. Data were analyzed with SPSS software (p<0.05). Results: Results illustrated that the brittle star extract exerted a dose- and time-dependent anti-proliferative effect on A2780cp cancer cells. In addition, VEGF and b-FGF expression decreased with brittle star methanol extract treatment. Macroscopic evaluations revealed significant changes in the second and third experimental group compared to controls (p<0.05). Conclusion: These finding revealed the anti-angiogenic effects of brittle star methanol extract in vitro and in vivo confer novel insight into the application of natural marine products in angiogenesis-related pathologies. PMID:26989740

  2. Overcoming: A Concept Analysis

    PubMed Central

    Brush, Barbara L.; Kirk, Keri; Gultekin, Laura; Baiardi, Janet M.

    2011-01-01

    This article provides an operational definition of overcoming as a first step in the systematic analysis of the concept. Using the method described by Walker and Avant (2005), the authors identify the attributes and characteristics of overcoming and its theoretical and practical application to nursing. Sample cases from clinical research illustrate the concept further. Further nursing research needs to test the theoretical relationships between overcoming and outcome variables. PMID:21806626

  3. Brittle damage models in DYNA2D

    SciTech Connect

    Faux, D.R.

    1997-09-01

    DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.

  4. High Speed Dynamics in Brittle Materials

    NASA Astrophysics Data System (ADS)

    Hiermaier, Stefan

    2015-06-01

    Brittle Materials under High Speed and Shock loading provide a continuous challenge in experimental physics, analysis and numerical modelling, and consequently for engineering design. The dependence of damage and fracture processes on material-inherent length and time scales, the influence of defects, rate-dependent material properties and inertia effects on different scales make their understanding a true multi-scale problem. In addition, it is not uncommon that materials show a transition from ductile to brittle behavior when the loading rate is increased. A particular case is spallation, a brittle tensile failure induced by the interaction of stress waves leading to a sudden change from compressive to tensile loading states that can be invoked in various materials. This contribution highlights typical phenomena occurring when brittle materials are exposed to high loading rates in applications such as blast and impact on protective structures, or meteorite impact on geological materials. A short review on experimental methods that are used for dynamic characterization of brittle materials will be given. A close interaction of experimental analysis and numerical simulation has turned out to be very helpful in analyzing experimental results. For this purpose, adequate numerical methods are required. Cohesive zone models are one possible method for the analysis of brittle failure as long as some degree of tension is present. Their recent successful application for meso-mechanical simulations of concrete in Hopkinson-type spallation tests provides new insight into the dynamic failure process. Failure under compressive loading is a particular challenge for numerical simulations as it involves crushing of material which in turn influences stress states in other parts of a structure. On a continuum scale, it can be modeled using more or less complex plasticity models combined with failure surfaces, as will be demonstrated for ceramics. Models which take microstructural

  5. Shock-wave properties of brittle solids

    SciTech Connect

    Grady, D.E.

    1995-10-01

    Extensive experimental investigation in the form of large-amplitude, nonlinear wave-profile measurements which manifest the shock strength and equation-of-state properties of brittle solids has been performed. Brittle materials for which a base of dynamic property data is available include Al{sub 2}O{sub 3}, AlN, B{sub 4}C, CaCO{sub 3}, SiC, Si{sub 3}N{sub 4}, SiO{sub 2} (quartz and glass), TiB{sub 2}, WC and ZrO{sub 2}. Planar impact methods and velocity interferometry diagnostics have been used exclusively to provide the high-resolution shock-profile data. These wave-profile data are providing engineering dynamic strength and equation-of-state properties as well as controlled, shock-induced motion histories for the validation of theoretical and Computational models. Of equal importance, such data are providing a window into the physics of a newly emerging understanding of the compression and deformation behavior of high-strength brittle solids. When considered along with a rich assortment of strength and deformation data in the literature, a systematic assessment of this shock-wave data lends strong support for failure waves and concomitant high-confinement dilatancy as a general mechanism of inelastic deformation in the shock compression of ceramics. Phase transformation in selected brittle solids appears to be a critical state phenomenon strongly controlled by kinetics. The risetime and structure of deformation shock waves in brittle solids are controlled by viscous effects which at present are still poorly understood. The shockwave data also suggest that both crystalline plasticity and brittle fracture may play important and interconnected roles in the dynamic failure process.

  6. Origin of brittle cleavage in iridium.

    PubMed

    Cawkwell, Marc J; Nguyen-Manh, Duc; Woodward, Christopher; Pettifor, David G; Vitek, Vaclav

    2005-08-12

    Iridium is unique among the face-centered cubic metals in that it undergoes brittle cleavage after a period of plastic deformation under tensile stress. Atomistic simulation using a quantum-mechanically derived bond-order potential shows that in iridium, two core structures for the screw dislocation are possible: a glissile planar core and a metastable nonplanar core. Transformation between the two core structures is athermal and leads to exceptionally high rates of cross slip during plastic deformation. Associated with this athermal cross slip is an exponential increase in the dislocation density and strong work hardening from which brittle cleavage is a natural consequence. PMID:16099981

  7. Ductile to brittle transition in dynamic fracture of brittle bulk metallic glass

    SciTech Connect

    Wang, G.; Han, Y. N.; Han, B. S.; Wang, W. H.; Xu, X. H.; Ke, F. J.

    2008-05-01

    We report an unusual transition from a locally ductile to a pure brittle fracture in the dynamic fracture of brittle Mg{sub 65}Cu{sub 20}Gd{sub 10} bulk metallic glass. The fractographic evolution from a dimple structure to a periodic corrugation pattern and then to the mirror zone along the crack propagation direction during the dynamic fracture process is discussed within the framework of the meniscus instability of the fracture process zone. This work might provide an important clue in understanding of the energy dissipation mechanism for dynamic crack propagation in brittle glassy materials.

  8. Precision grinding process development for brittle materials

    SciTech Connect

    Blaedel, K L; Davis, P J; Piscotty, M A

    1999-04-01

    High performance, brittle materials are the materials of choice for many of today's engineering applications. This paper describes three separate precision grinding processes developed at Lawrence Liver-more National Laboratory to machine precision ceramic components. Included in the discussion of the precision processes is a variety of grinding wheel dressing, truing and profiling techniques.

  9. Overcoming job stress

    MedlinePlus

    ... page: //medlineplus.gov/ency/patientinstructions/000884.htm Overcoming job stress To use the sharing features on this ... you stay healthy and feel better. Causes of Job Stress Although the cause of job stress is ...

  10. Overcoming breastfeeding problems

    MedlinePlus

    Plugged milk ducts; Nipple soreness when breastfeeding; Breastfeeding - overcoming problems; Let-down reflex ... Breastfeeding (nursing) your baby can be a good experience for both the mother and the baby. It ...

  11. Johanna and Tommy: Two Preschoolers in Sweden with Brittle Bones.

    ERIC Educational Resources Information Center

    Millde, Kristina; Brodin, Jane

    Information is presented for caregivers of Swedish children with osteogenesis imperfecta (brittle bones) and their families. Approximately five children with brittle bones are born in Sweden annually. Two main types of brittle bone disease have been identified: congenita and tarda. Typical symptoms include numerous and unexpected fractures, bluish…

  12. Fracture in compression of brittle solids

    NASA Technical Reports Server (NTRS)

    1983-01-01

    The fracture of brittle solids in monotonic compression is reviewed from both the mechanistic and phenomenological points of view. The fundamental theoretical developments based on the extension of pre-existing cracks in general multiaxial stress fields are recognized as explaining extrinsic behavior where a single crack is responsible for the final failure. In contrast, shear faulting in compression is recognized to be the result of an evolutionary localization process involving en echelon action of cracks and is termed intrinsic.

  13. Fabrication of brittle materials -- current status

    SciTech Connect

    Scattergood, R.O.

    1988-12-01

    The research initiatives in the area of precision fabrication will be continued in the upcoming year. Three students, T. Bifano (PhD), P. Blake (PhD) and E. Smith (MS), finished their research programs in the last year. Sections 13 and 14 will summarize the essential results from the work of the Materials Engineering students Blake and Smith. Further details will be presented in forthcoming publications that are now in preparation. The results from Bifano`s thesis have been published in adequate detail and need not be summarized further. Three new students, S. Blackley (MS), H. Paul (PhD), and S. Smith (PhD) have joined the program and will continue the research efforts in precision fabrication. The programs for these students will be outlined in Sections 15 and 16. Because of the success of the earlier work in establishing new process models and experimental techniques for the study of diamond turning and diamond grinding, the new programs will, in part, build upon the earlier work. This is especially true for investigations concerned with brittle materials. The basic understanding of material response of nominally brittle materials during machining or grinding operations remains as a challenge. The precision fabrication of brittle materials will continue as an area of emphasis for the Precision Engineering Center.

  14. Overcoming the Polyester Image.

    ERIC Educational Resources Information Center

    Regan, Dorothy

    1988-01-01

    Urges community colleges to overcome their image problem by documenting the colleges' impact on their communities. Suggests ways to determine what data should be collected, how to collect the information, and how it can be used to empower faculty, staff, and alumni to change the institution's image. (DMM)

  15. Controlled crack growth specimen for brittle systems

    NASA Technical Reports Server (NTRS)

    Calomino, Anthony M.; Brewer, David N.

    1990-01-01

    A pure Mode 1 fracture specimen and test procedure has been developed which provides extended, stable, through-thickness crack growth in ceramics and other brittle, nonmetallic materials. Fixed displacement loading, applied at the crack mouth, promotes stable crack extension by reducing the stored elastic strain energy. Extremely fine control of applied displacements is achieved by utilizing the Poisson's expansion of a compressively loaded cylindrical pin. Stable cracks were successfully grown in soda-lime glass and monolithic Al2O3 for lengths in excess of 20 mm without uncontrollable catastrophic failure.

  16. Aerogel: Tile Composites Toughen a Brittle Superinsulation

    NASA Technical Reports Server (NTRS)

    White, Susan; Rasky, Daniel; Arnold, James O. (Technical Monitor)

    1998-01-01

    Pure aerogels, though familiar in the laboratory for decades as exotic lightweight insulators with unusual physical properties, have had limited industrial applications due to their low strength and high brittleness. Composites formed of aerogels and the ceramic fiber matrices like those used as space shuttle tiles bypass the fragility of pure aerogels and can enhance the performance of space shuttle tiles in their harsh operating environment. Using a layer of aerogel embedded in a tile may open up a wide range of applications where thermal insulation, gas convection control and mechanical strength matter.

  17. Controlled crack growth specimen for brittle systems

    NASA Technical Reports Server (NTRS)

    Calomino, Anthony M.; Brewer, David N.

    1992-01-01

    A pure Mode 1 fracture specimen and test procedure has been developed which provides extended, stable, through-thickness crack growth in ceramics and other brittle, nonmetallic materials. Fixed displacement loading, applied at the crack mouth, promotes stable crack extension by reducing the stored elastic strain energy. Extremely fine control of applied displacements is achieved by utilizing the Poisson's expansion of a compressively loaded cylindrical pin. Stable cracks were successfully grown in soda-lime glass and monolithic Al2O3 for lengths in excess of 2O mm without uncontrollable catastrophic failure.

  18. Brittle and semi-brittle behaviours of a carbonate rock: influence of water and temperature

    NASA Astrophysics Data System (ADS)

    Nicolas, A.; Fortin, J.; Regnet, J. B.; Dimanov, A.; Guéguen, Y.

    2016-07-01

    Inelastic deformation can either occur with dilatancy or compaction, implying differences in porosity changes, failure and petrophysical properties. In this study, the roles of water as a pore fluid, and of temperature, on the deformation and failure of a micritic limestone (white Tavel limestone, porosity 14.7 per cent) were investigated under triaxial stresses. For each sample, a hydrostatic load was applied up to the desired confining pressure (from 0 up to 85 MPa) at either room temperature or at 70 °C. Two pore fluid conditions were investigated at room temperature: dry and water saturated. The samples were deformed up to failure at a constant strain rate of ˜10-5 s-1. The experiments were coupled with ultrasonic wave velocity surveys to monitor crack densities. The linear trend between the axial crack density and the relative volumetric strain beyond the onset of dilatancy suggests that cracks propagate at constant aspect ratio. The decrease of ultrasonic wave velocities beyond the onset of inelastic compaction in the semi-brittle regime indicates the ongoing interplay of shear-enhanced compaction and crack development. Water has a weakening effect on the onset of dilatancy in the brittle regime, but no measurable influence on the peak strength. Temperature lowers the confining pressure at which the brittle-semi-brittle transition is observed but does not change the stress states at the onset of inelastic compaction and at the post-yield onset of dilatancy.

  19. Atomistic simulations of brittle crack growth.

    SciTech Connect

    Hoyt, Jeffrey John

    2007-04-01

    Ceramic materials such as lead zirconium titanates (PZT), low temperature co-fired ceramics and silica glasses are used in several of Sandia's mission critical components. Brittle fracture, either during machining and processing or after many years in service, remains a serious reliability and cost issue. Despite its technological importance, brittle fracture remains poorly understand, especially the onset and propagation of sub-critical cracks. However, some insights into the onset of fracture can be gleaned from the atomic scale structure of the amorphous material. In silica for example, it is well known [1] that the Si-O-Si bonds are relatively weak and, in angle distribution functions determined from scattering experiments, the bonds exhibit a wide spread around a peak at 150. By contrast the O-Si-O bonds are strong with a narrow peak in the distribution around the 109 dictated by the SiO{sub 4} tetrahedron. In addition, slow energy release in silica, as deduced from dissolution experiments, depends on the distribution of 3-fold and higher rings in the amorphous structure. The purpose of this four month LDRD project was to investigate the atomic structure of silica in the bulk and in the vicinity of a crack tip using molecular dynamics simulations. Changes in the amorphous structure in the neighborhood of an atomically sharp tip may provide important clues as to the initiation sites and the stress intensity required to propagate a sub-critical crack.

  20. Phase field approximation of dynamic brittle fracture

    NASA Astrophysics Data System (ADS)

    Schlüter, Alexander; Willenbücher, Adrian; Kuhn, Charlotte; Müller, Ralf

    2014-11-01

    Numerical methods that are able to predict the failure of technical structures due to fracture are important in many engineering applications. One of these approaches, the so-called phase field method, represents cracks by means of an additional continuous field variable. This strategy avoids some of the main drawbacks of a sharp interface description of cracks. For example, it is not necessary to track or model crack faces explicitly, which allows a simple algorithmic treatment. The phase field model for brittle fracture presented in Kuhn and Müller (Eng Fract Mech 77(18):3625-3634, 2010) assumes quasi-static loading conditions. However dynamic effects have a great impact on the crack growth in many practical applications. Therefore this investigation presents an extension of the quasi-static phase field model for fracture from Kuhn and Müller (Eng Fract Mech 77(18):3625-3634, 2010) to the dynamic case. First of all Hamilton's principle is applied to derive a coupled set of Euler-Lagrange equations that govern the mechanical behaviour of the body as well as the crack growth. Subsequently the model is implemented in a finite element scheme which allows to solve several test problems numerically. The numerical examples illustrate the capabilities of the developed approach to dynamic fracture in brittle materials.

  1. Brittle dynamic damage due to earthquake rupture

    NASA Astrophysics Data System (ADS)

    Bhat, Harsha; Thomas, Marion

    2016-04-01

    The micromechanical damage mechanics formulated by Ashby and Sammis, 1990, and generalized by Deshpande and Evans 2008 has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated new crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative. Incorporating this feature produces additional strain-rate sensitivity in the constitutive response. The model is also experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over wide range of strain rates. We then implement this constitutive response to understand the role of dynamic brittle off-fault damage on earthquake ruptures. We show that off-fault damage plays an important role in asymmetry of rupture propagation and is a source of high-frequency ground motion in the near source region.

  2. Isotropic MD simulations of dynamic brittle fracture

    SciTech Connect

    Espanol, P.; Rubio, M.A.; Zuniga, I.

    1996-12-01

    The authors present results obtained by molecular dynamics simulations on the propagation of fast cracks in triangular 2D lattices. Their aim is to simulate Mode 1 fracture of brittle isotropic materials. They propose a force law that respects the isotropy of the material. The code yields the correct imposed sound c{sub {parallel}}, shear c{sub {perpendicular}} and surface V{sub R} wave speeds. Different notch lengths are systematically studied. They observed that initially the cracks are linear and always branch at a particular critical velocity c* {approx} 0.8V{sub R} and that this occurs when the crack tip reaches the position of a front emitted from the initial crack tip and propagating at a speed c = 0.68V{sub R}.

  3. Reliability Analysis of Brittle, Thin Walled Structures

    SciTech Connect

    Jonathan A Salem and Lynn Powers

    2007-02-09

    One emerging application for ceramics is diesel particulate filters being used order to meet EPA regulations going into effect in 2008. Diesel particulates are known to be carcinogenic and thus need to be minimized. Current systems use filters made from ceramics such as mullite and corderite. The filters are brittle and must operate at very high temperatures during a burn out cycle used to remove the soot buildup. Thus the filters are subjected to thermal shock stresses and life time reliability analysis is required. NASA GRC has developed reliability based design methods and test methods for such applications, such as CARES/Life and American Society for Testing and Materials (ASTM) C1499 “Standard Test Method for Equibiaxial Strength of Ceramics.”

  4. Brittle failure kinetics model for concrete

    SciTech Connect

    Silling, S.A.

    1997-03-01

    A new constitutive model is proposed for the modeling of penetration and large stress waves in concrete. Rate effects are incorporated explicitly into the damage evolution law, hence the term brittle failure kinetics. The damage variable parameterizes a family of Mohr-Coulomb strength curves. The model, which has been implemented in the CTH code, has been shown to reproduce some distinctive phenomena that occur in penetration of concrete targets. Among these are the sharp spike in deceleration of a rigid penetrator immediately after impact. Another is the size scale effect, which leads to a nonlinear scaling of penetration depth with penetrator size. This paper discusses the theory of the model and some results of an extensive validation effort.

  5. Fracture process zone of brittle composites

    SciTech Connect

    Yu, C.

    1992-01-01

    An experimental-numerical analysis was used to study the fracture process zone (FPZ) trailing the crack tip in brittle composites. Two major parts are included in this dissertation. Part 1 is a static mode 1 fracture analysis of ceramic matrix composites. Part 2 is a mixed mode 1 and mode 2 dynamic fracture analysis of concrete. In Part 1, the FPZ which trailed a stably growing crack in SiC(w)/Al2O3 ceramic matrix composite was investigated through a hybrid experimental-numerical analysis. Surface displacements on the sides of three-point bend and wedge loaded-double cantilever beam (WL-DCB) specimens with chevron notch starter cracks were measured with moire interferometry during crack growth. The three-point bend specimens were precracked by the single edge precrack bend (SEPB) method. The experimental data was then input to two and three dimensional finite element models of the three-point bend and WL-DCB specimens, respectively, to determine by an inverse analysis the crack closure stress (CCS) versus crack opening displacement (COD) relations for SiC(w)/Al2O3. Energy dissipation rates in the trailing process zone plus the matrix fracture and fiber breakage accounted for about 80 percent of the release energy rate with the remainder being dissipated through the frontal process zone. In Part 2, a hybrid experimental-numerical procedure was used to analyze rapid crack growth in an impact loaded three-point bend concrete specimen with an offset straight precrack. Two-beam dynamic moire interferometry was used to record eight sequential moire patterns of the horizontal or vertical displacements by a ultra-high speed camera with an exposure of 2 microseconds and a framing rate of 100,000 frames/sec. The fracture responses of ceramic composites and concrete were both characterized by FPZ models which are the dominant fracture energy dissipation mechanism in this type of brittle composite.

  6. Overcoming associative learning.

    PubMed

    Haselgrove, Mark

    2016-08-01

    Thorndike (1898, 1911) rejected the idea that animal behavior was the consequence of reasoning, and suggested instead that the gradual acquisition of associations formed the basis of behavior-a contention that has had a significant impact on the development of animal learning theory. Despite this, comparative psychology provides a number of examples of behaviors that have been considered to be above and beyond the explanation of associative-, or reinforcement-learning mechanisms. These behaviors have motivated some researchers to propose higher-order cognitive abilities in animals, including (but not limited to) reasoning, sensitivity to ambiguity, and metacognition. However, other authors have questioned this claim, and provided alternative explanations for these behaviors from an associative perspective. With relevant examples, the steps that must be taken in order to overcome an associative explanation of behavior are described. (PsycINFO Database Record PMID:26986019

  7. Magnetic fabric of brittle fault rocks

    NASA Astrophysics Data System (ADS)

    Pomella, Hannah

    2014-05-01

    The anisotropy of magnetic susceptibility (AMS) has been recognized as a highly sensitive indicator of rock fabric and is widely employed in the field of structural geology. Brittle faults are often characterized by fault breccia and gouge, fault rocks with clast-in-matrix textures. A noteworthy property of both gouge and breccia is the often observed presence of a fabric that is defined by the preferred orientation of clasts and grains in the matrix. In the very fine-grained gouge and in the matrix of the breccia the fabric is not visible in the field or in thin sections but can probably be detected by AMS analyses. For the present study different kinds of brittle fault rocks have been sampled on two faults with known tectonic settings, in order to allow for a structural interpretation of the measured AMS signal. The measurements were carried out with an AGICO MFK1-FA Kappabridge and a CS4 furnace apparatus at the Institute of Geology, University of Innsbruck. Fault gouge was sampled on the Naif fault located in the Southern Alps, E of Meran, South Tyrol, Italy. Along this fault the Permian Granodiorite overthrusts the Southalpine basement and its Permomesozoic cover. The Neoalpine thrust fault is characterised by a wide cataclastic zone and an up to 1 m thick fault gouge. The gouge was sampled using paleomagnetic sample boxes. Heating experiments indicate that the magnetic fabric is dominated by paramagnetic minerals (>95%). The samples provide a magnetic susceptibility in the range of +10*E-5 [SI]. The K-min axis of the magnetic ellipsoid corresponds approximately to the pol of the fault plane measured in the field. However the whole magnetic ellipsoid shows a variation in the inclination compared to the structural data. Fine-grained ultracataclasites were sampled on the Assergi fault, located in the Abruzzi Apennines, NE of L'Aquila, Italy. This normal fault was active in historical time and crosscuts limestones as well as talus deposits. An up to 20 cm thick

  8. Brittle and compaction creep in porous sandstone

    NASA Astrophysics Data System (ADS)

    Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip

    2015-04-01

    Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate

  9. Theory of friction based on brittle fracture

    USGS Publications Warehouse

    Byerlee, J.D.

    1967-01-01

    A theory of friction is presented that may be more applicable to geologic materials than the classic Bowden and Tabor theory. In the model, surfaces touch at the peaks of asperities and sliding occurs when the asperities fail by brittle fracture. The coefficient of friction, ??, was calculated from the strength of asperities of certain ideal shapes; for cone-shaped asperities, ?? is about 0.1 and for wedge-shaped asperities, ?? is about 0.15. For actual situations which seem close to the ideal model, observed ?? was found to be very close to 0.1, even for materials such as quartz and calcite with widely differing strengths. If surface forces are present, the theory predicts that ?? should decrease with load and that it should be higher in a vacuum than in air. In the presence of a fluid film between sliding surfaces, ?? should depend on the area of the surfaces in contact. Both effects are observed. The character of wear particles produced during sliding and the way in which ?? depends on normal load, roughness, and environment lend further support to the model of friction presented here. ?? 1967 The American Institute of Physics.

  10. Modeling failure in brittle porous ceramics

    NASA Astrophysics Data System (ADS)

    Keles, Ozgur

    Brittle porous materials (BPMs) are used for battery, fuel cell, catalyst, membrane, filter, bone graft, and pharmacy applications due to the multi-functionality of their underlying porosity. However, in spite of its technological benefits the effects of porosity on BPM fracture strength and Weibull statistics are not fully understood--limiting a wider use. In this context, classical fracture mechanics was combined with two-dimensional finite element simulations not only to account for pore-pore stress interactions, but also to numerically quantify the relationship between the local pore volume fraction and fracture statistics. Simulations show that even the microstructures with the same porosity level and size of pores differ substantially in fracture strength. The maximum reliability of BPMs was shown to be limited by the underlying pore--pore interactions. Fracture strength of BMPs decreases at a faster rate under biaxial loading than under uniaxial loading. Three different types of deviation from classic Weibull behavior are identified: P-type corresponding to a positive lower tail deviation, N-type corresponding to a negative lower tail deviation, and S-type corresponding to both positive upper and lower tail deviations. Pore-pore interactions result in either P-type or N-type deviation in the limit of low porosity, whereas S-type behavior occurs when clusters of low and high fracture strengths coexist in a fracture data.

  11. ON THE BRITTLENESS OF ENAMEL AND SELECTED DENTAL MATERIALS

    PubMed Central

    Park, S.; Quinn, J. B; Romberg, E.; Arola, D.

    2008-01-01

    Although brittle material behavior is often considered undesirable, a quantitative measure of “brittleness” is currently not used in assessing the clinical merits of dental materials. Objective To quantify and compare the brittleness of human enamel and common dental restorative materials used for crown replacement. Methods Specimens of human enamel were prepared from the 3rd molars of “young” (18≤age≤25) and “old” (50≤age) patients. The hardness, elastic modulus and apparent fracture toughness were characterized as a function of distance from the DEJ using indentation approaches. These properties were then used in estimating the brittleness according to a model that accounts for the competing dissipative processes of deformation and fracture. The brittleness of selected porcelain, ceramic and Micaceous Glass Ceramic (MGC) dental materials was estimated and compared with that of the enamel. Results The average brittleness of the young and old enamel increased with distance from the DEJ. For the old enamel the average brittleness increased from approximately 300 µm−1 at the DEJ to nearly 900 µm−1 at the occlusal surface. While there was no significant difference between the two age groups at the DEJ, the brittleness of the old enamel was significantly greater (and up to 4 times higher) than that of the young enamel near the occlusal surface. The brittleness numbers for the restorative materials were up to 90% lower than that of young occlusal enamel. Significance The brittleness index could serve as a useful scale in the design of materials used for crown replacement, as well as a quantitative tool for characterizing degradation in the mechanical behavior of enamel. PMID:18436299

  12. An experimental investigation of wave propagation in fractured brittle material

    NASA Astrophysics Data System (ADS)

    Patel, Bibhuti Bhusan

    An experimental method for visualizing and analyzing the propagation of plate stress waves in a brittle plate is developed. A procedure has been developed to cast Break-Away glass (a low molecular weight polystyrene material) plate specimens in an open mold. The specimens are loaded with short duration (200 [...]s) stress pulses on one edge by an electromagnetic stress wave generator. The propagating stress waves generate out-of-plane deformations on the specimen surface, which are observed using Twyman-Green interferometry. The fringe patterns created by the propagating stress waves are captured using a high speed camera - pulsing laser combination at 4[...]s intervals.A generalized "Fringe Analysis Procedure" is developed to subtract the reference interferogram from the subsequent interferograms. The "Fringe Analysis Procedure" employs a fringe edge detection algorithm to obtain the sharp edge lines of the fringes in an interferogram. A digitizer is used to extract points on these edge lines and assign them fringe numbers. The "griddata" option in the commercial software "Matlab" is utilized to interpolate the deformation field on to the nodes of a uniform grid. The field values at these nodes in the reference image are then subtracted from corresponding values in the subsequent images to obtain the actual deformation patterns generated by the propagating stress waves. The "Fringe Analysis Procedure" has eliminated the subjective element introduced by human judgment in manual fringe tracing procedures.The developed experimental method and the image analysis technique is used to investigate the propagation of stress waves in Break-Away glass plate specimens.

  13. Dependence of tablet brittleness on tensile strength and porosity.

    PubMed

    Gong, Xingchu; Chang, Shao-Yu; Osei-Yeboah, Frederick; Paul, Shubhajit; Perumalla, Sathyanarayana Reddy; Shi, Limin; Sun, Wei-Jhe; Zhou, Qun; Sun, Changquan Calvin

    2015-09-30

    An analysis of data collected from 25 sets of diverse pharmaceutical powders has identified that an exponential growth function satisfactorily describes the relationship between tablet brittleness and tablet porosity while a power law function well describes the relationship between tablet brittleness and tensile strength. These equations have the potential to facilitate better characterization of tablet mechanical properties and to guide the design and optimization of pharmaceutical tablet products. PMID:26226338

  14. Universal behaviour in compressive failure of brittle materials.

    PubMed

    Renshaw, C E; Schulson, E M

    2001-08-30

    Brittle failure limits the compressive strength of rock and ice when rapidly loaded under low to moderate confinement. Higher confinement or slower loading results in ductile failure once the brittle-ductile transition is crossed. Brittle failure begins when primary cracks initiate and slide, creating wing cracks at their tips. Under little to no confinement, wing cracks extend and link together, splitting the material into slender columns which then fail. Under low to moderate confinement, wing crack growth is restricted and terminal failure is controlled by the localization of damage along a narrow band. Early investigations proposed that localization results from either the linkage of wing cracks or the buckling of microcolumns created between adjacent wing cracks. Observations of compressive failure in ice suggest a mechanism whereby localization initiates owing to the bending-induced failure of slender microcolumns created between sets of secondary cracks emanating from one side of a primary crack. Here we analyse this mechanism, and show that it leads to a closed-form, quantitative model that depends only on independently measurable mechanical parameters. Our model predictions for both the brittle compressive strength and the brittle-ductile transition are consistent with data from a variety of crystalline materials, offering quantitative evidence for universal processes in brittle failure and for the broad applicability of the model. PMID:11528475

  15. Ultrasonic Apparatus for Pulverizing Brittle Material

    NASA Technical Reports Server (NTRS)

    Sherrit, Stewart; Bao, Xiaoqi; Bar-Cohen, Yoseph; Dolgin, Benjamin; Chang, Zensheu

    2004-01-01

    The figure depicts an apparatus that pulverizes brittle material by means of a combination of ultrasonic and sonic vibration, hammering, and abrasion. The basic design of the apparatus could be specialized to be a portable version for use by a geologist in collecting powdered rock samples for analysis in the field or in a laboratory. Alternatively, a larger benchtop version could be designed for milling and mixing of precursor powders for such purposes as synthesis of ceramic and other polycrystalline materials or preparing powder samples for x-ray diffraction or x-ray fluorescence measurements to determine crystalline structures and compositions. Among the most attractive characteristics of this apparatus are its light weight and the ability to function without need for a large preload or a large power supply: It has been estimated that a portable version could have a mass <0.5 kg, would consume less than 1 W h of energy in milling a 1-cm3 volume of rock, and could operate at a preload <10 N. The basic design and principle of operation of this apparatus are similar to those of other apparatuses described in a series of prior NASA Tech Briefs articles, the two most relevant being Ultrasonic/ Sonic Drill/Corers With Integrated Sensors (NPO-20856), Vol. 25, No. 1 (January 2001), page 38 and Ultrasonic/ Sonic Mechanisms for Deep Drilling and Coring (NPO-30291), Vol. 27, No. 9 (September 2003), page 65. As before, vibrations are excited by means of a piezoelectric actuator, an ultrasonic horn, and a mass that is free to move axially over a limited range. As before, the ultrasonic harmonic motion of the horn drives the free-mass in a combination of ultrasonic harmonic and lower-frequency hammering motion. In this case, the free-mass is confined within a hollow cylinder that serves as a crushing chamber, and the free-mass serves as a crushing or milling tool. The hammering of the free-mass against a material sample at the lower end of the chamber grinds the sample into

  16. Intermittent single point machining of brittle materials

    SciTech Connect

    Marsh, E

    1999-12-07

    A series of tests were undertaken to explore diamond tool wear in the intermittent cutting of brittle materials, specifically silicon. The tests were carried out on a plain way No. 3 Moore machine base equipped as a flycutter with a motorized Professional Instruments 4R air bearing spindle. The diamond tools were made by Edge Technologies with known crystal orientation and composition and sharpened with either an abrasive or chemical process, depending on the individual test. The flycutting machine configuration allowed precise control over the angle at which the tool engages the anisotropic silicon workpiece. In contrast, the crystallographic orientation of the silicon workpiece changes continuously during on-axis turning. As a result, it is possible to flycut a workpiece in cutting directions that are known to be easy or hard. All cuts were run in the 100 plane of the silicon, with a slight angle deliberately introduced to ensure that the 100 plane is engaged in ''up-cutting'' which lengthens the tool life. A Kistler 9256 dynamometer was used to measure the cutting forces in order to gain insight into the material removal process and tool wear during testing. The dynamometer provides high bandwidth force measurement with milli-Newton resolution and good thermal stability. After many successive passes over the workpiece, it was observed that the cutting forces grow at a rate that is roughly proportional to the degradation of the workpiece surface finish. The exact relationship between cutting force growth and surface finish degradation was not quantified because of the problems associated with measuring surface finish in situ. However, a series of witness marks were made during testing in an aluminum sample that clearly show the development of wear flats on the tool nose profile as the forces grow and the surface finish worsens. The test results show that workpieces requiring on the order of two miles of track length can be made with low tool wear and excellent

  17. Brittle and semibrittle creep in a low porosity carbonate rock

    NASA Astrophysics Data System (ADS)

    Nicolas, Aurélien; Fortin, Jérôme; Regnet, Jean-Baptiste; Dimanov, Alexandre; Guéguen, Yves

    2016-04-01

    The mechanical behavior of limestones at room temperature is brittle at low confining pressure and becomes semi-brittle with the increase of the confining pressure. The brittle behavior is characterized by a macroscopic dilatancy due to crack propagation, leading to a stress drop when cracks coalesce at failure. The semi-brittle behavior is characterized by diffuse deformation due to intra-crystalline plasticity (dislocation movements and twinning) and microcracking. The aim of this work is to examine the influence of pore fluid and time on the mechanical behavior. Constant strain rate triaxial deformation experiments and stress-stepping creep experiments were performed on white Tavel limestone (porosity 14.7%). Elastic wave velocity evolutions were recorded during each experiment and inverted to crack densities. Constant strain rate triaxial experiments were performed for confining pressure in the range of 5-90 MPa. For Pc≤55 MPa our results show that the behavior is brittle. In this regime, water-saturation decreases the differential stress at the onset of crack propagation and enhances macroscopic dilatancy. For Pc≥70 MPa, the behavior is semi-brittle. Inelastic compaction is due to intra-crystalline plasticity and micro-cracking. However, in this regime, our results show that water-saturation has no clear effect at the onset of inelastic compaction. Stress stepping creep experiments were performed in a range of confining pressures crossing the brittle-ductile transition. In the brittle regime, the time-dependent axial deformation is coupled with dilatancy and a decrease of elastic wave velocities, which is characteristic of crack propagation and/or nucleation. In the semi-brittle regime, the first steps are inelastic compactant because of plastic pore collapse. But, following stress steps are dilatant because of crack nucleation and/or propagation. However, our results show that the axial strain rate is always controlled by plastic phenomena, until the last

  18. Constrained molecular dynamics for quantifying intrinsic ductility versus brittleness

    NASA Astrophysics Data System (ADS)

    Tanguy, D.

    2007-10-01

    Evaluating the critical load levels for intrinsic ductility and brittle propagation is a first, but necessary, step for modeling semibrittle crack propagation. In the most general case, the calculations have to be fully atomistic because the details of the crack tip structure cannot be captured by continuum mechanics. In this paper, we present a method to explore ductile and brittle configurations, within the same force field, giving a quantitative estimate of the proximity of a transition from intrinsic ductility to brittleness. The shear localization is characterized by a centrosymmetry criterion evaluated on each atom in the vicinity of the crack tip. This provides an efficient order parameter to track the nucleation and propagation of dislocations. We show that it can be used as a holonomic constraint within molecular dynamics simulations, giving a precise control over plasticity during crack propagation. The equations of motion are derived and applied to crack propagation in the [112¯] direction of an fcc crystal loaded in mode I along [111]. The critical loads for dislocation emission and for brittle propagation are computed. The key point is that the generalized forces of constraint are not dissipative. Therefore, they do not spoil the critical elastic energy release rates (the Griffith criterion is preserved). As an example of the possibilities of the method, the response of blunted tips is investigated for three configurations: a slab of vacancies, an elliptical hole, and a circular hole. Brittle propagation by an alternative mechanism to cleavage, called “vacancy injection,” is reported.

  19. Brittle failure mode plots for compressional and extensional tectonic regimes

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    1998-05-01

    Equations governing different macroscopic modes of brittle rock failure (extensional fracturing, extensional-shear fracturing, compressional shear failure and reshear of existing faults) can be represented on plots of differential stress vs effective vertical stress for a set of material properties. Such plots can be constructed for different tectonic regimes and correlated to depth for particular fluid pressure conditions, allowing easy evaluation of the physical controls on brittle rock failure, and ready comparison of the fields occupied by the three failure modes in different tectonic settings. They emphasize the relative ease, in terms of differential stress and fluid-pressure levels, of deforming a rock mass by brittle fracturing and faulting in extensional regimes compared with compressional. Aside from their relevance to general structural mechanics, these generic failure plots have wide-ranging application to understanding the initial development and progressive evolution of fault-fracture systems, both in sedimentary basins and as hosting structures for hydrothermal mineralization in different tectonic settings.

  20. Brittle and ductile friction and the physics of tectonic tremor

    USGS Publications Warehouse

    Daub, E.G.; Shelly, D.R.; Guyer, R.A.; Johnson, P.A.

    2011-01-01

    Observations of nonvolcanic tremor provide a unique window into the mechanisms of deformation and failure in the lower crust. At increasing depths, rock deformation gradually transitions from brittle, where earthquakes occur, to ductile, with tremor occurring in the transitional region. The physics of deformation in the transition region remain poorly constrained, limiting our basic understanding of tremor and its relation to earthquakes. We combine field and laboratory observations with a physical friction model comprised of brittle and ductile components, and use the model to provide constraints on the friction and stress state in the lower crust. A phase diagram is constructed that characterizes under what conditions all faulting behaviors occur, including earthquakes, tremor, silent transient slip, and steady sliding. Our results show that tremor occurs over a range of ductile and brittle frictional strengths, and advances our understanding of the physical conditions at which tremor and earthquakes take place. Copyright ?? 2011 by the American Geophysical Union.

  1. Cuttability Assessment of Selected Rocks Through Different Brittleness Values

    NASA Astrophysics Data System (ADS)

    Dursun, Arif Emre; Gokay, M. Kemal

    2016-04-01

    Prediction of cuttability is a critical issue for successful execution of tunnel or mining excavation projects. Rock cuttability is also used to determine specific energy, which is defined as the work done by the cutting force to excavate a unit volume of yield. Specific energy is a meaningful inverse measure of cutting efficiency, since it simply states how much energy must be expended to excavate a unit volume of rock. Brittleness is a fundamental rock property and applied in drilling and rock excavation. Brittleness is one of the most crucial rock features for rock excavation. For this reason, determination of relations between cuttability and brittleness will help rock engineers. This study aims to estimate the specific energy from different brittleness values of rocks by means of simple and multiple regression analyses. In this study, rock cutting, rock property, and brittleness index tests were carried out on 24 different rock samples with different strength values, including marble, travertine, and tuff, collected from sites around Konya Province, Turkey. Four previously used brittleness concepts were evaluated in this study, denoted as B 1 (ratio of compressive to tensile strength), B 2 (ratio of the difference between compressive and tensile strength to the sum of compressive and tensile strength), B 3 (area under the stress-strain line in relation to compressive and tensile strength), and B 9 = S 20, the percentage of fines (<11.2 mm) formed in an impact test for the Norwegian University of Science and Technology (NTNU) model as well as B 9p (B 9 as predicted from uniaxial compressive, Brazilian tensile, and point load strengths of rocks using multiple regression analysis). The results suggest that the proposed simple regression-based prediction models including B 3, B 9, and B 9p outperform the other models including B 1 and B 2 and can be used for more accurate and reliable estimation of specific energy.

  2. In the Initiation of Brittle Compressive Failure: Lessons From Ice

    NASA Astrophysics Data System (ADS)

    Renshaw, C. E.; Schulson, E. M.

    2001-12-01

    Brittle failure limits the compressive strength of rock and ice when rapidly loaded under low to moderate confinement. Higher confinement or slower loading results in ductile failure once the brittle-ductile transition is crossed. It is well established that the macroscopic brittle failure of rock, concrete and other brittle materials under compression is preceded by the initiation and sliding of microscopic primary cracks, creating wing cracks at their tips. In laboratory samples, microcracks begin to nucleate more or less uniformly throughout the sample at compressions equal to about 1/5 to 1/3 the terminal failure stress. Under little to no confinement, wing cracks extend and link together, splitting the material into slender columns which then fail. Under low to moderate confinement, wing crack growth is restricted and terminal failure is controlled by the localization of damage along discrete bands of intense damage inclined by approximately 30 degrees to the direction of the most compressive stress. Earlier investigators proposed that localization results from either the linkage of wing cracks or the buckling of microcolumns created between adjacent wing cracks. Observations of compressive failure in ice suggest a new mechanism whereby localization initiates due to the bending-induced failure of slender microcolumns created between sets of secondary cracks emanating from one side of a primary crack. Analysis of this mechanism leads to a closed-form, quantitative model that only depends on independently measureable mechanical parameters. We show that model predictions for both the brittle compressive strength and the brittle-ductile transition are consistent with data from a variety of crystalline materials.

  3. Towards a software profession

    NASA Technical Reports Server (NTRS)

    Berard, Edward V.

    1986-01-01

    An increasing number of programmers have attempted to change their image. They have made it plain that they wish not only to be taken seriously, but they also wish to be regarded as professionals. Many programmers now wish to referred to as software engineers. If programmers wish to be considered professionals in every sense of the word, two obstacles must be overcome: the inability to think of software as a product, and the idea that little or no skill is required to create and handle software throughout its life cycle. The steps to be taken toward professionalization are outlined along with recommendations.

  4. Finite element model for brittle fracture and fragmentation

    DOE PAGESBeta

    Li, Wei; Delaney, Tristan J.; Jiao, Xiangmin; Samulyak, Roman; Lu, Cao

    2016-06-01

    A new computational model for brittle fracture and fragmentation has been developed based on finite element analysis of non-linear elasticity equations. The proposed model propagates the cracks by splitting the mesh nodes alongside the most over-strained edges based on the principal direction of strain tensor. To prevent elements from overlapping and folding under large deformations, robust geometrical constraints using the method of Lagrange multipliers have been incorporated. In conclusion, the model has been applied to 2D simulations of the formation and propagation of cracks in brittle materials, and the fracture and fragmentation of stretched and compressed materials.

  5. A Weibull characterization for tensile fracture of multicomponent brittle fibers

    NASA Technical Reports Server (NTRS)

    Barrows, R. G.

    1977-01-01

    Necessary to the development and understanding of brittle fiber reinforced composites is a means to statistically describe fiber strength and strain-to-failure behavior. A statistical characterization for multicomponent brittle fibers is presented. The method, which is an extension of usual Weibull distribution procedures, statistically considers the components making up a fiber (e.g., substrate, sheath, and surface) as separate entities and taken together as in a fiber. Tensile data for silicon carbide fiber and for an experimental carbon-boron alloy fiber are evaluated in terms of the proposed multicomponent Weibull characterization.

  6. Computer Software.

    ERIC Educational Resources Information Center

    Kay, Alan

    1984-01-01

    Discusses the nature and development of computer software. Programing, programing languages, types of software (including dynamic spreadsheets), and software of the future are among the topics considered. (JN)

  7. Fracture mechanics applied to the machining of brittle materials

    SciTech Connect

    Hiatt, G.D.; Strenkowski, J.S.

    1988-12-01

    Research has begun on incorporating fracture mechanics into a model of the orthogonal cutting of brittle materials. Residual stresses are calculated for the machined material by a combination of Eulerian and Lagrangian finite element models and then used in the calculation of stress intensity factors by the Green`s Function Method.

  8. Brittle fracture of old storage tanks can be prevented

    SciTech Connect

    DeWit, J

    1990-02-19

    To see how the fundamentals of brittle fracture play a part in the catastrophic failure of older storage tanks, this article examines and compares four tanks that failed due to brittle fracture. These tanks are: a 42.7-m dia. by 16.5-m high crude oil tank with a floating roof that collapsed in February 1952 at the refinery in Fawley, U.K., during a water test; a 45.7-m dia. by 14.64-m high gas oil tank with a fixed roof that collapsed in March 1952 at a refinery in Fawley; a 45-m dia. by 12.5-m high fuel oil tank with a fixed roof that collapsed in December 1970 at a power station in The Netherlands; and a 36.6-m dia. by 14.64-m high fuel oil tank with a fixed roof that collapsed in January 1988 at a terminal near Pittsburgh. Investigations, experience, and test work show that a brittle fracture in a tank shell is always caused by a combination of specific factors. Important factors that directly influence brittle fracture are discussed.

  9. Macroscopic shock plasticity of brittle material through designed void patterns

    NASA Astrophysics Data System (ADS)

    Jiang, Tailong; Yu, Yin; He, Hongliang; Li, Yongqiang; Huan, Qiang; Wu, Jiankui

    2016-03-01

    The rapid propagation and coalescence of cracks and catastrophic fractures, which occur often under shock compression, compromise a brittle material's design function and restrict its scope of practical application. The shock plasticity of brittle materials can be improved significantly by introducing and designing its microstructure, which can help reduce or delay failure. We used a lattice-spring model, which can describe elastic deformation and brittle fracture of modeled material accurately, to study the influence of void distributions (random, square, hexagonal, and triangular void patterns) on the macroscopic shock response and the mesoscopic deformation feature of brittle materials. Calculated results indicate that the void patterns dominate two inelastic deformation stages on the Hugoniot stress-strain curves (the collapse deformation stage and the slippage deformation stage). It shows that the strain localization is not strong and that the broken media are closer to a round bulk when the samples exist in random and triangular void patterns. This favors an increase in deformation during the slippage deformation stage. For the samples with square and hexagonal void patterns, the strain localization is strong and the broken media are closer to columnar bulks, which favors an increase in deformation during the collapse deformation stage.

  10. Brittle-to-Ductile Transition in Metallic Glass Nanowires.

    PubMed

    Şopu, D; Foroughi, A; Stoica, M; Eckert, J

    2016-07-13

    When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure. PMID:27248329

  11. Overcoming Exclusion through Adult Learning.

    ERIC Educational Resources Information Center

    Nash, Ian; Walshe, John

    Strategies for overcoming exclusion through adult learning were identified through case studies of 19 initiatives in the following countries: Belgium; Mexico; the Netherlands; Norway; Portugal; and the United Kingdom. The study programs involved a diverse array of formal, nonformal, and informal public sector, community, and enterprise-based…

  12. Overcoming Roadblocks to Healthy Eating

    MedlinePlus

    ... National Institute on Aging at NIH Search form Search this site Menu Get Started Try These Exercises Go to My Go4Life Get Free Stuff Be a Partner Overcoming Roadblocks to Healthy Eating Sometimes it’s hard to make smart food choices . Here are some suggestions from Go4Life ...

  13. Overcoming Prejudices: An Invitational Approach.

    ERIC Educational Resources Information Center

    Reed, Charlotte

    1996-01-01

    Offers an invitational model for overcoming prejudices. The model, based on the five-step approach of M. Haberman (1994) and the conflict management plan of W. W. Purkey (1992) proposes an effective and sensitive method for dealing with prejudice and discrimination in the schools. (SLD)

  14. Helping Young Children Overcome Shyness.

    ERIC Educational Resources Information Center

    Malouff, John

    This paper examines shyness--its causes and its impact on children--and presents several strategies based on social learning theory for parents and teachers to help young children overcome shyness. The paper also describes a personal application of these strategies on a young girl. The strategies presented for parents and teachers are: (1) tell…

  15. Brittle to Ductile Transition in Densified Silica Glass

    PubMed Central

    Yuan, Fenglin; Huang, Liping

    2014-01-01

    Current understanding of the brittleness of glass is limited by our poor understanding and control over the microscopic structure. In this study, we used a pressure quenching route to tune the structure of silica glass in a controllable manner, and observed a systematic increase in ductility in samples quenched under increasingly higher pressure. The brittle to ductile transition in densified silica glass can be attributed to the critical role of 5-fold Si coordination defects (bonded to 5 O neighbors) in facilitating shear deformation and in dissipating energy by converting back to the 4-fold coordination state during deformation. As an archetypal glass former and one of the most abundant minerals in the Earth's crest, a fundamental understanding of the microscopic structure underpinning the ductility of silica glass will not only pave the way toward rational design of strong glasses, but also advance our knowledge of the geological processes in the Earth's interior. PMID:24849328

  16. A partial skeletal proteome of the brittle star Ophiocoma wendtii

    NASA Astrophysics Data System (ADS)

    Seaver, Ryan W.

    The formation of mineralized tissue was critical to the evolution and diversification of metazoans and remains functionally significant in most animal lineages. Of special importance is the protein found occluded within the mineral matrix, which facilitates the process of biomineralization and modulates the final mineral structure. These skeletal matrix proteins have well been described in several species, including the sea urchin Stronglyocentrotus purpuratus, an important model organism. Biomineralization research is limited in other echinoderm classes. This research encompasses the first description of mineral matrix proteins in a member of the echinoderm class Ophiuroidea. This work describes the skeletal matrix proteins of the brittle star Ophiocoma wendtii using bioinformatic and proteomic techniques. General characteristics of matrix protein are described and a number of candidate biomineralization related genes have been identified, cloned, and sequenced. The unique evolutionary and biochemical properties of brittle star skeletal matrix proteins are also described.

  17. The Brittle-Ductile Transition - A Self-Consistent Approach.

    NASA Astrophysics Data System (ADS)

    Hobbs, B.; Regenauer-Lieb, K.; Ord, A.; Yuen, D. A.

    2006-12-01

    The brittle-ductile transition (BDT) in the Earth is commonly viewed as a switch between two different constitutive behaviors, plastic and viscous, and is represented in models by various formulations. We show that thermal-mechanical coupling leads to a self consistent view where the BDT emerges naturally within one constitutive framework once a critical temperature is attained. Viscous folding occurs above this temperature and brittle fracturing below. Seismic activity is maximised at the BDT. Orogenesis emerges as a thermal-mechanical decoupling near the BDT during flexing of the lithosphere with the development of "crocodile" -like structures, fold-nappe systems and far-travelled thrust sheets. For quartz- feldspar composite materials this transition lies in a critical range of 500 K to 580 K.

  18. Reliability-based failure analysis of brittle materials

    NASA Technical Reports Server (NTRS)

    Powers, Lynn M.; Ghosn, Louis J.

    1989-01-01

    The reliability of brittle materials under a generalized state of stress is analyzed using the Batdorf model. The model is modified to include the reduction in shear due to the effect of the compressive stress on the microscopic crack faces. The combined effect of both surface and volume flaws is included. Due to the nature of fracture of brittle materials under compressive loading, the component is modeled as a series system in order to establish bounds on the probability of failure. A computer program was written to determine the probability of failure employing data from a finite element analysis. The analysis showed that for tensile loading a single crack will be the cause of total failure but under compressive loading a series of microscopic cracks must join together to form a dominant crack.

  19. Ductile-to-brittle transition in spallation of metallic glasses

    SciTech Connect

    Huang, X.; Ling, Z.; Dai, L. H.

    2014-10-14

    In this paper, the spallation behavior of a binary metallic glass Cu{sub 50}Zr{sub 50} is investigated with molecular dynamics simulations. With increasing the impact velocity, micro-voids induced by tensile pulses become smaller and more concentrated. The phenomenon suggests a ductile-to-brittle transition during the spallation process. Further investigation indicates that the transition is controlled by the interaction between void nucleation and growth, which can be regarded as a competition between tension transformation zones (TTZs) and shear transformation zones (STZs) at atomic scale. As impact velocities become higher, the stress amplitude and temperature rise in the spall region increase and micro-structures of the material become more unstable. Therefore, TTZs are prone to activation in metallic glasses, leading to a brittle behavior during the spallation process.

  20. Comparing the Bending Stiffness Measurements of Brittle Paper

    NASA Astrophysics Data System (ADS)

    Hall, Andrea; McGath, Molly; McGuiggan, Patricia

    It has been estimated that one third of the paper materials in libraries are too brittle to handle. A typical paper sheet is comprised of semi-rigid cellulose fibers that are more than ten times longer than the sheet thickness and can be considered a two dimensional random fiber network. The main pathways of degradation, acid-catalyzed hydrolysis and oxidation, cause depolymerization of the cellulose chains and breaking of the intrafiber bonds. Conventional mechanical measurements of aged paper are destructive and often too severe to understand the true extent of deterioration. By comparing the roll test, folding endurance tests, tensile tests and stiffness tests of naturally aged papers with varying amounts of brittleness, we intend to show the limits of each test and relate the state of the paper degradation to the mechanical test results. We thank the Andrew W. Mellon Foundation for funding this research.

  1. Potential of carnuba wax in ameliorating brittle fracture during tableting.

    PubMed

    Uhumwangho, M U; Okor, R S; Adogah, J T

    2009-01-01

    Carnuba wax (as binder) forms hard tablets even at low compression load attributable to its high plasticity. The aim of the present study is to investigate its potential in ameliorating brittle fracture (i.e., lamination and capping) a problem often encountered during tableting. Granules of paracetamol (test drug) were made by triturating the drug powder with the melted wax or starch mucilage (20%w/v). Resulting granules were separated into different size fractions which were separately compressed into tablets with and without a centre hole (as in- built defect) using different compression loads. The tablets were evaluated for tensile strength and the data used to calculate the brittle fracture index (BFI), using the expression: BFI = 0.5(T/T(0)-1) where T0 and T are the tensile strength of tablets with and without a centre hole respectively. The BFI values were significantly lower (p<0.05) in tablets made with carnuba wax compared with tablets made with maize starch as binders. Increase in particle size of the granules or lowering of the compression load further ameliorated the brittle fracture tendency of the tablets. Using granules with the larger particle size (850microm) and applying the lowest unit of load (6 arbitrary unit on the load scale of the tableting machine) the BFI values were 0.03 (carnuba wax tablets) and 0.11 (maize starch tablets). When the conditions were reversed (i.e., a highest load, 8 units and the smallest particle size, 212microm) the BFI values now became 0.17 (carnuba wax tablets) and 0.26 (maize starch tablets). The indication is that the use of large granules and low compression loads to form tablets can further enhance the potential of carnuba wax in ameliorating brittle fracture tendency of tablets during their manufacture. PMID:19168422

  2. Rate-dependent deformation of rocks in the brittle regime

    NASA Astrophysics Data System (ADS)

    Baud, P.; Brantut, N.; Heap, M. J.; Meredith, P. G.

    2013-12-01

    Rate-dependent brittle deformation of rocks, a phenomenon relevant for long-term interseismic phases of deformation, is poorly understood quantitatively. Rate-dependence can arise from chemically-activated, subcritical crack growth, which is known to occur in the presence of aqueous fluids. Here we attempt to establish quantitative links between this small scale process and its macroscopic manifestations. We performed a series of brittle deformation experiments in porous sandstones, in creep (constant stress) and constant strain rate conditions, in order to investigate the relationship between their short- and long-term mechanical behaviors. Elastic wave velocities measurements indicate that the amount of microcracking follows the amount of inelastic strain in a trend which does not depend upon the timescale involved. The comparison of stress-strain curves between constant strain rate and creep tests allows us to define a stress difference between the two, which can be viewed as a difference in energy release rate. We empirically show that the creep strain rates are proportional to an exponential function of this stress difference. We then establish a general method to estimate empirical micromechanical functions relating the applied stresses to mode I stress intensity factors at microcrack tips, and we determine the relationship between creep strain rates and stress intensity factors in our sandstone creep experiments. We finally provide an estimate of the sub-critical crack growth law parameters, and find that they match -within the experimental errors and approximations of the method- the typical values observed in independent single crack tests. Our approach provides a comprehensive and unifying explanation for the origin and the macroscopic manifestation of time-dependent brittle deformation in brittle rocks.

  3. Statistical characterization of fracture of brittle MEMS materials

    NASA Astrophysics Data System (ADS)

    Jones, Peter T.; Johnson, George C.; Howe, Roger T.

    1999-08-01

    The fracture of brittle MEMS materials is often characterized by ultimate strength measures such as the maximum stress or strain in an element at failure. It has been known for many decades that a better way to characterize the strength of a brittle material on the macro-scale is to make use of statistical measures. This is due to the nature of brittle materials in which failure occurs when a critically sized flaw exists in the region that is under tensile stress. The distribution of flaws is often random, so the strength of a brittle material can only be properly characterized by statistical measures. Working with MEMS devices, where the site scale is small, it becomes even more important to use a statistical approach. Doing so can explain two observed effects. First, there is an apparent size effect on the strength of the material. The larger the structure that is under a given stress, the larger the region where a critically sized flaw may exist, resulting a higher probability of failure. Second, two identical beams with different stress states, loaded to the same maximum stress can have dramatically different average strengths. In this paper, Weibull statistics are used to characterize the strength of one MEMS material-- polycrystalline silicon. The relevant statistical measures are obtained from the fracture of a large number of cantilever beams. It is shown that, for this material, the average failure strength of a beam loaded in uniaxial tension should be on the order of 40% lower than the average strength of identical beams loaded in cantilever bending.

  4. A Weibull characterization for tensile fracture of multicomponent brittle fibers

    NASA Technical Reports Server (NTRS)

    Barrows, R. G.

    1977-01-01

    A statistical characterization for multicomponent brittle fibers in presented. The method, which is an extension of usual Weibull distribution procedures, statistically considers the components making up a fiber (e.g., substrate, sheath, and surface) as separate entities and taken together as in a fiber. Tensile data for silicon carbide fiber and for an experimental carbon-boron alloy fiber are evaluated in terms of the proposed multicomponent Weibull characterization.

  5. Interpreting finite element results for brittle materials in endodontic restorations

    PubMed Central

    2011-01-01

    Background Finite element simulation has been used in last years for analysing the biomechanical performance of post-core restorations in endodontics, but results of these simulations have been interpreted in most of the works using von Mises stress criterion. However, the validity of this failure criterion for brittle materials, which are present in these restorations, is questionable. The objective of the paper is to analyse how finite element results for brittle materials of endodontic restorations should be interpreted to obtain correct conclusions about the possible failure in the restoration. Methods Different failure criteria (Von Mises, Rankine, Coulomb-Mohr, Modified Mohr and Christensen) and material strength data (diametral tensile strength and flexural strength) were considered in the study. Three finite element models (FEM) were developed to simulate an endodontic restoration and two typical material tests: diametral tensile test and flexural test. Results Results showed that the Christensen criterion predicts similar results as the Von Mises criterion for ductile components, while it predicts similar results to all other criteria for brittle components. The different criteria predict different failure points for the diametral tensile test, all of them under multi-axial stress states. All criteria except Von Mises predict failure for flexural test at the same point of the specimen, with this point under uniaxial tensile stress. Conclusions From the results it is concluded that the Christensen criterion is recommended for FEM result interpretation in endodontic restorations and that the flexural test is recommended to estimate tensile strength instead of the diametral tensile test. PMID:21635759

  6. Guidelines for Design and Analysis of Large, Brittle Spacecraft Components

    NASA Technical Reports Server (NTRS)

    Robinson, E. Y.

    1993-01-01

    There were two related parts to this work. The first, conducted at The Aerospace Corporation was to develop and define methods for integrating the statistical theory of brittle strength with conventional finite element stress analysis, and to carry out a limited laboratory test program to illustrate the methods. The second part, separately funded at Aerojet Electronic Systems Division, was to create the finite element postprocessing program for integrating the statistical strength analysis with the structural analysis. The second part was monitored by Capt. Jeff McCann of USAF/SMC, as Special Study No.11, which authorized Aerojet to support Aerospace on this work requested by NASA. This second part is documented in Appendix A. The activity at Aerojet was guided by the Aerospace methods developed in the first part of this work. This joint work of Aerospace and Aerojet stemmed from prior related work for the Defense Support Program (DSP) Program Office, to qualify the DSP sensor main mirror and corrector lens for flight as part of a shuttle payload. These large brittle components of the DSP sensor are provided by Aerojet. This document defines rational methods for addressing the structural integrity and safety of large, brittle, payload components, which have low and variable tensile strength and can suddenly break or shatter. The methods are applicable to the evaluation and validation of such components, which, because of size and configuration restrictions, cannot be validated by direct proof test.

  7. Modeling multiscale evolution of numerous voids in shocked brittle material

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  8. Transcriptome pyrosequencing of the Antarctic brittle star Ophionotus victoriae.

    PubMed

    Burns, Gavin; Thorndyke, Michael C; Peck, Lloyd S; Clark, Melody S

    2013-03-01

    Brittle stars are included within a whole range of species, which contribute to knowledge in the medically important area of tissue regeneration. All brittle stars regenerate lose limbs, but the rate at which this occurs is highly variable and species-specific. One of the slowest rates of arm regeneration reported so far is that of the Antarctic Ophionotus victoriae. Additionally, O. victoriae also has an unusual delay in the onset of regeneration of about 5months. Both processes are of interest for the areas of regeneration biology and adaptation to cold environments. One method of understanding the details of regeneration events in brittle stars is to characterise the genes involved. In the largest transcriptome study of any ophiuroid to date, we describe the results of mRNA pyrosequencing from pooled samples of regenerating arms of O. victoriae. The sequencing reads resulted in 18,000 assembled contiguous sequences of which 19% were putatively annotated by blast sequence similarity searching. We focus on the identification of major gene families and pathways with potential relevance to the regenerative processes including the Wnt/β-catenin pathway, Hox genes, the SOX gene family and the TGF beta signalling pathways. These data significantly increase the amount of ophiuroid sequences publicly available and provide candidate transcripts for the further investigation of the unusual regenerative process in this Antarctic ophiuroid. PMID:23904059

  9. Patterns of brittle deformation under extension on Venus

    NASA Technical Reports Server (NTRS)

    Neumann, G. A.; Zuber, M. T.

    1994-01-01

    The development of fractures at regular length scales is a widespread feature of Venusian tectonics. Models of lithospheric deformation under extension based on non-Newtonian viscous flow and brittle-plastic flow develop localized failure at preferred wavelengths that depend on lithospheric thickness and stratification. The characteristic wavelengths seen in rift zones and tessera can therefore provide constraints on crustal and thermal structure. Analytic solutions were obtained for growth rates in infinitesimal perturbations imposed on a one-dimensional, layered rheology. Brittle layers were approximated by perfectly-plastic, uniform strength, overlying ductile layers exhibiting thermally-activated power-law creep. This study investigates the formation of faults under finite amounts of extension, employing a finite-element approach. Our model incorporates non-linear viscous rheology and a Coulomb failure envelope. An initial perturbation in crustal thickness gives rise to necking instabilities. A small amount of velocity weakening serves to localize deformation into planar regions of high strain rate. Such planes are analogous to normal faults seen in terrestrial rift zones. These 'faults' evolve to low angle under finite extension. Fault spacing, orientation and location, and the depth to the brittle-ductile transition, depend in a complex way on lateral variations in crustal thickness. In general, we find that multiple wavelengths of deformation can arise from the interaction of crustal and mantle lithosphere.

  10. Displacement–length scaling of brittle faults in ductile shear

    PubMed Central

    Grasemann, Bernhard; Exner, Ulrike; Tschegg, Cornelius

    2011-01-01

    Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement–distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow. PMID:26806996

  11. Rice BRITTLE CULM 5 (BRITTLE NODE) is Involved in Secondary Cell Wall Formation in the Sclerenchyma Tissue of Nodes

    PubMed Central

    Aohara, Tsutomu; Kotake, Toshihisa; Kaneko, Yasuko; Takatsuji, Hiroshi; Tsumuraya, Yoichi; Kawasaki, Shinji

    2009-01-01

    Several brittle culm (bc) mutants known in grasses are considered excellent materials to study the process of secondary cell wall formation. The brittle phenotype of the rice bc5 (brittle node) mutant appears exclusively in the developed nodes, which is distinct from other bc mutants (bc1, 2, 3, 4, 6 and 7) that show the brittle phenotype in culms and leaves. To address the defects of the rice bc5 mutant in node-specific cell wall formation, we analyzed tissue morphology and cell wall composition. The bc5 mutation was found to affect the cell wall deposition of node sclerenchyma tissues at 1 week after heading, the stage at which the cell wall sugar content is reduced, in the bc5 nodes, compared with wild-type nodes. Moreover, decreased accumulation of lignin and thickness of cell walls in the sclerenchyma tissues were also observed in the bc5 nodes. The amounts of cellulose and hemicellulose were reduced to 53 and 65% of those in the wild-type plants, respectively. Sugar composition and glycosidic linkage analyses of the hemicellulose showed that the accumulation of glucuronosyl arabinoxylan in bc5 nodes was perturbed by the mutation. The bc5 locus was narrowed to an approximately 3.1 Mb region of chromosome 2, where none of the other bc genes is located. The bc5 mutation appeared to reduce the expression levels of the OsCesA genes in the nodes after heading. The results indicate that the BC5 gene regulates the development of secondary cell walls of node sclerenchyma tissues. PMID:19812064

  12. Selecting Software.

    ERIC Educational Resources Information Center

    Pereus, Steven C.

    2002-01-01

    Describes a comprehensive computer software selection and evaluation process, including documenting district needs, evaluating software packages, weighing the alternatives, and making the purchase. (PKP)

  13. Slip transfer across fault discontinuities within granitic rock at the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Nevitt, J. M.; Pollard, D. D.; Warren, J. M.

    2011-12-01

    Fault mechanics are strongly influenced by discontinuities in fault geometry and constitutive differences between the brittle and ductile regions of the lithosphere. This project uses field observations, laboratory analysis and numerical modeling to investigate deformational processes within a contractional step at the brittle-ductile transition, and in particular, how slip is transferred between faults via ductile deformation across the step. The Bear Creek field area (central Sierra Nevada, CA) is comprised of late Cretaceous biotite-hornblende granodiorite and experienced a period of faulting at the brittle-ductile transition. Abundant echelon faults in Bear Creek, some of which were seismically active, provide many textbook examples of contractional steps, which are characterized by well-developed ductile fabrics. The occurrence of hydrothermal alteration halos and hydrothermal minerals in fracture fill documents the presence of water, which we suggest played a weakening role in the constitutive behavior of the granodiorite. Furthermore, the mechanism that accomplishes slip transfer in contractional steps appears to be related to water-enhanced ductile deformation. We focus our investigation on Outcrop SG10, which features a 10cm thick aplite dike that is offset 0.45m through a contractional step between two sub-parallel left-lateral faults. Within the step, the aplite undergoes dramatic thinning (stretch ~1/10) and the granodiorite is characterized by a well-developed mylonitic foliation, in which quartz and biotite plastically flow around larger grains of feldspars, hornblende and opaque minerals. Electron backscatter diffraction (EBSD) analysis gives a more quantitative depiction of the active micromechanics and reveals how slip is accommodated at the crystal scale throughout the step. We use Abaqus, a commercial finite element software, to test several constitutive laws that may account for the deformation observed both macro- and microscopically throughout

  14. Neogene transtensional brittle tectonics in the Lepontine D

    NASA Astrophysics Data System (ADS)

    Allanic, C.; Sue, C.; Champagnac, J.-D.

    2009-04-01

    The Lepontine Dome is investigated regarding faulting and paleostress, which allows to constrain the late brittle deformation of this gneissic core. Its tectonic evolution under brittle conditions was determined using fault mapping and paleostress inversions. Three brittle phases were reconstructed. The older phase is a NW-SE extension restricted to the eastern parts of the Dome. The second phase (major signal) is an upper Miocene transtension with stable orogen-parallel sigma3 axes (NE-SW), which is found from the Mont-Blanc to the Bergell massifs. The late phase is a N-S extension, expressed north of the Dome, and probably linked to the current collapse of the belt. The stress fields we determine for the Lepontine Dome are very similar to the stress fields determined by Champagnac et al (2006) westward in the South-Valais area, with a major signal in orogen-parallel extension and a minor signal in orogen-perpendicular extension. In the close vicinity of the Simplon fault, Grosjean et al (2004) only reported the orogen-parallel extensional stress field. Eastward, in the Bergell area, Ciancaleoni and Marquer (2008) also found a very regular NE-SW extensional paleostress field, using similar methods. Indeed, the main paleostress field determined in the Lepontine Dome is very homogeneous from a regional viewpoint. It is largely dominated by the NE-SW brittle extension, described in the whole northwestern Alps. The Lepontine Dome also bears witness of two minor extensional signals (N-S and WNW-ESE directions of extension). The absolute dating of this orogen-parallel extensional phase is based on the occurrence of pseudotachylytes locally injected in the related fault system. Pseudotachylyte development is directly linked to frictional heating due to earthquake and faulting. The Ar/Ar dating of three pseudotachylytes samples of the Lepontine Dome provided ages in the range of 9-11 Ma ±1 (Allanic, et al., 2006). Thus, one can attribute a global 10 Ma age for the orogen

  15. Overcoming "the Valley of Death".

    PubMed

    McIntyre, Robin A

    2014-01-01

    On a global level there are major challenges arising from climate change, resource use and changing age demographics. These issues have created a global marketplace for novel innovative products and solutions which can help to combat and overcome these challenges which have created significant commercial opportunities for companies, particularly for small and medium size enterprises or SMEs. Companies most likely to take advantage of these opportunities will be those which can innovate in a timely manner. Innovation significantly contributes to higher productivity and economic growth, and is core to a company's competitiveness within often challenging marketplaces. However, many factors can stifle innovation. Companies can struggle to identify finance for early-stage development, the returns can be difficult to predict, and the innovation 'landscape' is often complex and unclear. This brief review describes some of the main issues with commercialising innovative ideas and provides guidance with respect to the often complicated funding landscape both on a National and European level. PMID:25549408

  16. Overcoming challenges in improvement work.

    PubMed

    Crisp, Helen

    2013-09-01

    The Health Foundation is an independent charity working to improve healthcare in the UK, so that we have a system of the highest possible quality-safe, effective, person-centred, timely, efficient and equitable. We believe that in order to achieve this, health services need to continually improve the way they work. The Foundation conducts research and evaluation, puts ideas into practice through improvement programmes, develops leaders and shares evidence to drive wider change. The work is a focused around two priority areas: patient safety and person-centred care. The Foundation has supported work to improve services for patients with kidney disease and, in common with other quality improvement projects, there have been challenges to overcome. Awareness of these common challenges can help others to be more prepared when planning service improvements. PMID:23941702

  17. Quantitative comparisons of numerical models of brittle deformation

    NASA Astrophysics Data System (ADS)

    Buiter, S.

    2009-04-01

    Numerical modelling of brittle deformation in the uppermost crust can be challenging owing to the requirement of an accurate pressure calculation, the ability to achieve post-yield deformation and localisation, and the choice of rheology (plasticity law). One way to approach these issues is to conduct model comparisons that can evaluate the effects of different implementations of brittle behaviour in crustal deformation models. We present a comparison of three brittle shortening experiments for fourteen different numerical codes, which use finite element, finite difference, boundary element and distinct element techniques. Our aim is to constrain and quantify the variability among models in order to improve our understanding of causes leading to differences between model results. Our first experiment of translation of a stable sand-like wedge serves as a reference that allows for testing against analytical solutions (e.g., taper angle, root-mean-square velocity and gravitational rate of work). The next two experiments investigate an unstable wedge in a sandbox-like setup which deforms by inward translation of a mobile wall. All models accommodate shortening by in-sequence formation of forward shear zones. We analyse the location, dip angle and spacing of thrusts in detail as previous comparisons have shown that these can be highly variable in numerical and analogue models of crustal shortening and extension. We find that an accurate implementation of boundary friction is important for our models. Our results are encouraging in the overall agreement in their dynamic evolution, but show at the same time the effort that is needed to understand shear zone evolution. GeoMod2008 Team: Markus Albertz, Michele Cooke, Susan Ellis, Taras Gerya, Luke Hodkinson, Kristin Hughes, Katrin Huhn, Boris Kaus, Walter Landry, Bertrand Maillot, Christophe Pascal, Anton Popov, Guido Schreurs, Christopher Beaumont, Tony Crook, Mario Del Castello and Yves Leroy

  18. On the brittle nature of rare earth pnictides

    NASA Astrophysics Data System (ADS)

    Shriya, S.; Sapkale, R.; Singh, N.; Varshney, M.; Varshney, Dinesh

    2016-05-01

    The high-pressure structural phase transition and pressure as well temperature induced elastic properties in ReY; (Re = La, Sc, Pr; Y = N, P, As, Sb, Bi) pnictides have been performed using effective interionic interaction potential with emphasis on charge transfer interactions and covalent contribution. Estimated values of phase transition pressure and the volume discontinuity in pressure-volume phase diagram indicate the structural phase transition from NaCl to CsCl structure. From the investigations of elastic constants the pressure (temperature) dependent volume collapse/expansion, second order Cauchy discrepancy, anisotropy, hardness and brittle/ductile nature of rare earth pnictides are computed.

  19. Elastic shear moduli of brittle matrix composites with interfacial debonding

    SciTech Connect

    Yuan, F.G.; Pagano, N.J.

    1994-12-31

    Elastic shear moduli of brittle matrix composites with interfacial debonding are studied. Compatibility displacement boundary conditions between representative volume elements are imposed through finite element analyses. Comparisons of the moduli between the full RVE model and quarter cell model are made. Parametric studies assessing the effect of the debonding, the shear moduli ratios in the constituents and the fiber volume fractions on the composite shear moduli are also presented. Results show that the commonly used quarter cell model overestimate the moduli. The disparity increases as the rigidity of the fibers or fiber volume fraction increases.

  20. Cavitation-Induced Fracture Causes Nanocorrugations in Brittle Metallic Glasses.

    PubMed

    Singh, I; Narasimhan, R; Ramamurty, Upadrasta

    2016-07-22

    Brittle metallic glasses exhibit a unique and intriguing fracture morphology of periodic nanocorrugations whose spacing and amplitude are of the order of tens of nanometers. We show through continuum simulations that they fail by spontaneous and simultaneous cavitation within multiple weak zones arising due to intrinsic atomic density fluctuations ahead of a notch tip. Dynamic crack growth would then occur along curved but narrowly confined shear bands that link the growing cavities. This mechanism involves little dissipation and also explains the formation of nanocorrugations. PMID:27494475

  1. Development of massproductive ultraprecision grinding technology for brittle material devices

    SciTech Connect

    Kanai, A.; Miyashita, M.; Daito, M.

    1996-12-31

    Experimental results from an ultaprecision, centerless grinding system are reported. The system is designed for ductile mode grinding of brittle material devices on a mass production scale. A postprocess work diameter measuring stand was used with the high stiffness grinding machine.Size error correction was shown to be practically applicable as a mass production ultraprecision ferrule grinding technology. The key items were determined to be: (1) force-operated positioning servo system of slide on plain bearing guideways, (2) measurement of relative motion between grinding and regulating wheels with differential linear encoder, (3) application of linear encoder stability, and (4) application of microtruing technology to wheels.

  2. Micromorphic homogenization of a porous medium: elastic behavior and quasi-brittle damage

    NASA Astrophysics Data System (ADS)

    Hütter, Geralf; Mühlich, Uwe; Kuna, Meinhard

    2015-11-01

    Today it is well known that the classical Cauchy continuum theory is insufficient to describe the deformation behavior of solids if gradients occur over distances which are comparable to the microstructure of the material. This becomes crucial e.g., for small specimens or during localization of deformation induced by material degradation (damage). Higher-order continuum approaches like micromorphic theories are established to address such problems. However, such theories require the formulation of respective constitutive laws, which account for the microstructural interactions. Especially in damage mechanics such laws are mostly formulated in a purely heuristic way, which leads to physical and numerical problems. In the present contribution, the fully micromorphic constitutive law for a porous medium is obtained in closed form by homogenization based on the minimal boundary conditions concept. It is shown that this model describes size effects of porous media like foams adequately. The model is extended toward quasi-brittle damage overcoming the physical and numerical limitations of purely heuristic approaches.

  3. Self-repair of cracks in brittle material systems

    NASA Astrophysics Data System (ADS)

    Dry, Carolyn M.

    2016-04-01

    One of the most effective uses for self repair is in material systems that crack because the cracks can allow the repair chemical to flow into the crack damage sites in all three dimensions. In order for the repair chemical to stay in the damage site and flow along to all the crack and repair there must be enough chemical to fill the entire crack. The repair chemical must be designed appropriately for the particular crack size and total volume of cracks. In each of the three examples of self repair in crackable brittle systems, the viscosity and chemical makeup and volume of the repair chemicals used is different for each system. Further the chemical delivery system has to be designed for each application also. Test results from self repair of three brittle systems are discussed. In "Self Repair of Concrete Bridges and Infrastructure" two chemicals were used due to different placements in bridges to repair different types of cracks- surface shrinkage and shear cracks, In "Airplane Wings and Fuselage, in Graphite" the composite has very different properties than the concrete bridges. In the graphite for airplane components the chemical also had to survive the high processing temperatures. In this composite the cracks were so definite and deep and thin that the repair chemical could flow easily and repair in all layers of the composite. In "Ceramic/Composite Demonstrating Self Repair" the self repair system not only repaired the broken ceramic but also rebounded the composite to the ceramic layer

  4. Interfacial sliding in fibrous brittle-matrix composites

    NASA Astrophysics Data System (ADS)

    Miles, Herbert Frederick, II

    Ceramic materials have desirable characteristics for use in high temperature applications, but due to their brittle nature they were avoided until the recent advent of ceramic matrix composites (CMCs) in which ceramic fibers are inserted into a ceramic matrix to toughen the material by retarding crack growth. This work investigates the role of sliding at interfaces in making brittle matrix composites (BMCs) more crack resistant. A two-dimensional study investigates the effects of roughness, toughness, and friction on the fracture behavior of BMCs. This study was then expanded to an axisymmetric study of a fiber engulfed by a crack. The results indicate that there are significant interaction effects between friction and the other parameters. To achieve 'long' sliding lengths, the magnitude of the interfacial critical energy release rate must be significantly less than the magnitude required to ensure crack deflection. The study then investigates the three-dimensional nature of a crack as it flows past a fiber. A computational analysis is performed to determine the crack propagation angle at a frictional interface. The computational results show good agreement with a novel experimental analysis using modified DCDC specimens. The experiments show, in real time, the propagation of a crack which is perpendicular to and intersects a frictional interface.

  5. How plasticizer makes a ductile polymer glass brittle?

    NASA Astrophysics Data System (ADS)

    Zhao, Yue; Li, Xiaoxiao; Wang, Shi-Qing

    During uniaxial extension, a polymer glass of high molecular weight is ductile at high temperatures (still below Tg) and turns brittle when the temperature is sufficiently lowered. Incorporation of small-molecular additives to polymer glasses can speed up segmental relaxation considerably. The effect of such plasticization should be to make the polymers more ductile. We examined the effect of blending a few weight percent of either triphenyl phosphate (TPP) or a mineral oil to a commercial-grade PS and PMMA. Our Instron tests show that the plasticized PS is less ductile. Specifically, at 70 oC, the original PS is ductile at an extensional rate of 0.02 s-1 whereas the PS with 4 wt. % TPP turns brittle. Mechanical spectroscopic measurements show that the alpha relaxation time is shortened by more than two orders of magnitude with 4 wt. % TPP. On the other hand, such anomalous behavior did not occur in PMMA. We need to go beyond the conventional description to rationalize these results This work is supported, in part, by a NSF Grant (DMR-EAGER-1444859).

  6. Quantifying reliability statistics for electrochemical shock of brittle materials

    NASA Astrophysics Data System (ADS)

    Woodford, William H.; Chiang, Yet-Ming; Carter, W. Craig

    2014-10-01

    In brittle polycrystalline materials, anisotropic shape changes-such as those due to thermal expansion, composition changes, and piezoelectricity-can induce stresses severe enough to drive fracture. The stresses developed are microstructurally heterogeneous and develop in proportion to a generalized external stimulus rather than an applied load; as a consequence, traditional Weibull models do not capture the relevant scaling of failure probabilities with respect to applied stimulus or microstructural feature sizes. These limitations are surmounted by a stochastic method, called Finite Element plus Monte Carlo (FE+MC), which enables quantification of reliability statistics in brittle polycrystalline materials subjected to microstructurally heterogeneous stresses which may be driven by non-mechanical stimulii. A finite element analysis computes the stress distributions for a hypothetical defect-free virtual microstructure and a subsequent Monte Carlo analysis distributes flaws throughout the microstructure with sizes chosen from an experimental flaw size distribution. The FE+MC method is validated for uniaxial tensile loading, for which the expected Weibull distribution of failure probability is reproduced. As a demonstration of the utility of this method in a more complex stress state, we consider electrochemical shock of polycrystalline LiXCoO2 electrodes; the computed composition-dependent failure probabilities reproduce key features of experimental acoustic emission measurements not explained by previous modeling approaches.

  7. The maize brittle 1 gene encodes amyloplast membrane polypeptides.

    PubMed

    Sullivan, T D; Kaneko, Y

    1995-01-01

    A chimeric protein, formed of 56 amino acids from the carboxy terminus of the maize (Zea mays L.) wild-type Brittle1 (Bt1) protein fused to the glutathione-S-transferase gene, was synthesized in Escherichia coli, and used to raise antibodies. Following affinity purification, the antibodies recognized a set of 38- to 42-kDa proteins in endosperm from wild-type Bt1 plants, as well as from brittle2, shrunken2 and sugary1 plants, but not in mutant bt1 endosperm. Bt1 proteins were not detected with the preimmune antibodies. A low level of Bt1-specific proteins was detected at 10 d after pollination (DAP) and increased to a plateau at 16 DAP. At the same time, the ratio of slow- to fast-migrating forms of the protein decreased. During endosperm fractionation by differential centrifugation and membrane sedimentation in sucrose gradients, the Bt1 proteins co-purified with the carotenoid-containing plastid membranes. They were localized to amyloplasts by electron-microscopic immunocytochemistry; most of the signal was detected at the plastid periphery. These results are consistent with predictions made from the deduced amino-acid sequence and previous in-vitro experiments that the bt1 locus encodes amyloplast membrane proteins. PMID:7647682

  8. Brittle failure prediction of ceramics using a multiscale approach

    SciTech Connect

    Berdin, C.; Cailletaud, G.; Jeulin, D.

    1996-11-01

    Brittle failure is classically modeled by the Weibull distribution, based on a phenomenological approach. The procedure fails if the distribution of the failure-initiating defects varies within material batches and may lead to a wrong conclusion about the predictive power of the model. The purpose of this paper is to highlight this problem, which can occur with brittle materials such as ceramics. This study, based on the results of tensile and bending tests made on silicon nitride specimens, consists of three steps: (i) micrographic and fractographic studies are performed to determine the defect-size density in each type of specimen and the mechanical behavior of the defects, (ii) the classical modeling with a Weibull distribution is shown to fail to predict the results, and (iii) a new approach for the identification of a fracture model is developed, based on step (i). The fracture prediction is computed from the actual defect-size distribution in each material batch, so that the procedure can be adapted to changes in the defect-size distribution caused by the manufacturing process.

  9. Cyclic fatigue of intrinsically brittle ceramics in contact with spheres

    SciTech Connect

    Kim, D.K.; Jung, Y.G.; Peterson, I.M.; Lawn, B.R.

    1999-12-10

    Contact damage modes in cyclic loading with spheres are investigated in three nominally brittle ceramics, soda-lime glass, porcelain and fine-grain silicon nitride, in moist environments. Initial damage at small numbers of cycles and low loads consists of tensile-driven macroscopic cone cracks (brittle mode). Secondary damage at large numbers of cycles and high loads consists of shear-driven distributed microdamage (quasi-plastic mode), with attendant radial cracks and a new form of deeply penetrating subsidiary cone cracks. Strength tests on indented specimens are used to quantify the degree of damage. Both damage modes degrade the strength: the first, immediately after cone crack initiation, relatively slowly; the second, after development of radial cracks, much more rapidly. A fracture mechanics model describing the first mode, based on time-integration of slow growth of cone cracks, is presented. This model provides simple power-law relations for the remaining strength in terms of number of cycles and contact load for materials design. Extrapolations of these relations into the quasi-plastic region are shown to be non-conservative, highlighting the need for further understanding of the deleterious quasi-plastic mode in tougher ceramics. Comparison with static contact data indicates a strong mechanical (as opposed to chemical) component in the cyclic fatigue in the quasi-plastic region.

  10. The initiation of brittle faults in crystalline rock

    NASA Astrophysics Data System (ADS)

    Crider, Juliet G.

    2015-08-01

    Faults in the upper crust initiate from pre-existing (inherited) or precursory (early-formed) structures and typically grow by the mechanical interaction and linkage of these structures. In crystalline rock, rock architecture, composition, cooling, and exhumation influence the initiation of faults, with contrasting styles observed in plutonic rocks, extrusive igneous rocks, and foliated metamorphic rocks. Brittle fault growth in granitic rock is commonly controlled by the architecture of inherited joints or preexisting dikes. In basalt, abundant joints control the surface expression of faulting, and enhanced compliance due to abundant joints leads to folding and deformation asymmetry in the fault zone. Highly reactive mafic minerals likely become rapidly evolving fault rocks. In foliated metamorphic rocks, fault initiation style is strongly influenced by strength anisotropy relative to the principal stress directions, with fracturing favored when the foliation is aligned with the directions of principal stress. The continuity of micas within the foliation also influences the micromechanics of fault initiation. Brittle kink bands are an example of a strain-hardening precursory structure unique to foliated rock. Each of these fault initiation processes produces different initial fault geometry and spatial heterogeneity that influence such properties as fault permeability and seismogenesis.

  11. A generalized law for brittle deformation of Westerly granite

    USGS Publications Warehouse

    Lockner, D.A.

    1998-01-01

    A semiempirical constitutive law is presented for the brittle deformation of intact Westerly granite. The law can be extended to larger displacements, dominated by localized deformation, by including a displacement-weakening break-down region terminating in a frictional sliding regime often described by a rate- and state-dependent constitutive law. The intact deformation law, based on an Arrhenius type rate equation, relates inelastic strain rate to confining pressure Pc, differential stress ????, inelastic strain ??i, and temperature T. The basic form of the law for deformation prior to fault nucleation is In ????i = c - (E*/RT) + (????/a??o)sin-??(???? i/2??o) where ??o and ??o are normalization constants (dependent on confining pressure), a is rate sensitivity of stress, and ?? is a shape parameter. At room temperature, eight experimentally determined coefficients are needed to fully describe the stress-strain-strain rate response for Westerly granite from initial loading to failure. Temperature dependence requires apparent activation energy (E* ??? 90 kJ/mol) and one additional experimentally determined coefficient. The similarity between the prefailure constitutive law for intact rock and the rate- and state-dependent friction laws for frictional sliding on fracture surfaces suggests a close connection between these brittle phenomena.

  12. Powerplant software

    SciTech Connect

    Elliott, T.C.

    1995-07-01

    Powerplants need software to thrive and compete. Covered here are many programs and applications -- an overview of the functions, tasks, and problem-solving software is used for today. Software or, more accurately, software-driven systems are pervasive. Their presence is felt in every nook and cranny of the powerplant -- from design and construction through operation and maintenance, even dismantling and decommissioning -- embracing whole systems but also focusing on individual pieces of equipment. No one software supplier or two or three dominates -- powerplant software is the purview of scores if not hundreds of suppliers ranging from the largest corporations to individual consultants and application developers.

  13. Overcoming Degeneracies in Exoplanet Spectra

    NASA Astrophysics Data System (ADS)

    Benneke, Björn

    2015-08-01

    Spectroscopic observations of exoplanets can provide invaluable insights into the planets’ compositions, their formation and evolution histories, and even their habitability. Obtaining exoplanet spectra is observationally challenging; however, and we are generally limited to relatively low signal-to-noise, low spectral resolution, disk-integrated observations , often with relatively narrow wavelength coverage. This low data situation results in strong correlations and degeneracies between the different planet and atmospheric parameters of interest. In this talk, I will present a conceptual picture of how vital information about the planet is encoded in its observable spectrum. I will then give an overview about the wide range of correlations and degeneracies relevant to today’s exoplanet observations. Finally, I will demonstrate how some degeneracies can be overcome and improved constraints can be obtained by including prior knowledge of atmospheric chemistry and physics in the retrieval. I present a new atmospheric retrieval framework, SCARLET, that combines observational data and our prior (limited) knowledge of atmospheric processes in a statistical robust Bayesian framework. New results for hot Jupiters will be presented.

  14. Method for preparing surfaces of metal composites having a brittle phase for plating. [Patent application

    DOEpatents

    Coates, C.W.; Wilson, T.J.

    1982-05-19

    The present invention is directed to a method for preparing surfaces of two-phase metal composites having relatively brittle and malleable components for plating with corrosion-resistant material. In practice of the present invention, the surfaces of the composite are etched to remove a major portion or fraction of the brittle component. The etched surface is then peened with particulates for breaking the brittle component from the surfaces and for spreading or smearing the malleable component over the surfaces. The peened surface is then chemically cleaned of residual traces of the brittle component to which the corrosion-resistant material may be plated thereon in an adherent manner.

  15. Hydraulic Fracture and Toughening of a Brittle Layer Bonded to a Hydrogel

    NASA Astrophysics Data System (ADS)

    Lucantonio, Alessandro; Noselli, Giovanni; Trepat, Xavier; DeSimone, Antonio; Arroyo, Marino

    2015-10-01

    Brittle materials propagate opening cracks under tension. When stress increases beyond a critical magnitude, then quasistatic crack propagation becomes unstable. In the presence of several precracks, a brittle material always propagates only the weakest crack, leading to catastrophic failure. Here, we show that all these features of brittle fracture are fundamentally modified when the material susceptible to cracking is bonded to a hydrogel, a common situation in biological tissues. In the presence of the hydrogel, the brittle material can fracture in compression and can hydraulically resist cracking in tension. Furthermore, the poroelastic coupling regularizes the crack dynamics and enhances material toughness by promoting multiple cracking.

  16. Software Program: Software Management Guidebook

    NASA Technical Reports Server (NTRS)

    1996-01-01

    The purpose of this NASA Software Management Guidebook is twofold. First, this document defines the core products and activities required of NASA software projects. It defines life-cycle models and activity-related methods but acknowledges that no single life-cycle model is appropriate for all NASA software projects. It also acknowledges that the appropriate method for accomplishing a required activity depends on characteristics of the software project. Second, this guidebook provides specific guidance to software project managers and team leaders in selecting appropriate life cycles and methods to develop a tailored plan for a software engineering project.

  17. Proprietary software

    NASA Technical Reports Server (NTRS)

    Marnock, M. J.

    1971-01-01

    The protection of intellectual property by a patent, a copyright, or trade secrets is reviewed. The present and future use of computers and software are discussed, along with the governmental uses of software. The popularity of contractual agreements for sale or lease of computer programs and software services is also summarized.

  18. Testing Scientific Software: A Systematic Literature Review

    PubMed Central

    Kanewala, Upulee; Bieman, James M.

    2014-01-01

    Context Scientific software plays an important role in critical decision making, for example making weather predictions based on climate models, and computation of evidence for research publications. Recently, scientists have had to retract publications due to errors caused by software faults. Systematic testing can identify such faults in code. Objective This study aims to identify specific challenges, proposed solutions, and unsolved problems faced when testing scientific software. Method We conducted a systematic literature survey to identify and analyze relevant literature. We identified 62 studies that provided relevant information about testing scientific software. Results We found that challenges faced when testing scientific software fall into two main categories: (1) testing challenges that occur due to characteristics of scientific software such as oracle problems and (2) testing challenges that occur due to cultural differences between scientists and the software engineering community such as viewing the code and the model that it implements as inseparable entities. In addition, we identified methods to potentially overcome these challenges and their limitations. Finally we describe unsolved challenges and how software engineering researchers and practitioners can help to overcome them. Conclusions Scientific software presents special challenges for testing. Specifically, cultural differences between scientist developers and software engineers, along with the characteristics of the scientific software make testing more difficult. Existing techniques such as code clone detection can help to improve the testing process. Software engineers should consider special challenges posed by scientific software such as oracle problems when developing testing techniques. PMID:25125798

  19. Methods for assessing the structural reliability of brittle materials

    NASA Technical Reports Server (NTRS)

    Freiman, S. W. (Editor); Hudson, C. M. (Editor)

    1984-01-01

    Failure from contact-induced surface flaws is considered along with controlled indentation flaws for construction of toughness and fatigue master maps, fatigue properties of ceramics with natural and controlled flaws, and a statistical analysis of size and stress state effects on the strength of an alumina ceramic. Attention is also given to dynamic and static fatigue of a machinable glass ceramic, the effect of multiregion crack growth on proof testing, and a fracture mechanics analysis of defect sizes. Other topics explored are related to the effect of temperature and humidity on delayed failure of optical glass fibers, subthreshold indentation flaws in the study of fatigue properties of ultrahigh-strength glass, the lifetime prediction for hot-pressed silicon nitride at high temperatures, static fatigue in high-performance ceramics, and requirements for flexure testing of brittle materials.

  20. Depinning transition in the failure of inhomogeneous brittle materials.

    PubMed

    Ponson, Laurent

    2009-07-31

    The dynamics of cracks propagating in elastic inhomogeneous materials is investigated experimentally. The variations of the average crack velocity with the external driving force are measured for a brittle rock and shown to display two distinct regimes: an exponential law characteristic of subcritical propagation at a low driving force and a power law above a critical threshold. This behavior can be explained quantitatively by extending linear elastic fracture mechanics to disordered systems. In this description, the motion of a crack is analogous to the one of an elastic line driven in a random medium, and critical failure occurs when the external force is sufficiently large to depin the crack front from the heterogeneities of the material. PMID:19792511

  1. Peripartum anesthetic management of a patient with brittle cornea syndrome.

    PubMed

    Ioscovich, A; Grisaru-Granovsky, S; Halpern, S; Shapiro, Y

    2011-03-01

    Brittle cornea syndrome (BCS) is a rare autosomal recessive disease that affects the connective tissue. The syndrome is caused by genetic changes in the 4.7-Mb interval between the D16S3423 and D16S3425 markers on the 16q24 chromosome and mutations in the Zinc-Finger 469 gene (ZNF469). BCS is characterized by thin and fragile cornea that tends to perforate spontaneously or as a result of minor trauma to the eye. In addition, the patient usually suffers from hearing loss, mental retardation, hyperextensibility of skin and joints, as well as varying degrees of scoliosis. This phenotypical expression presents an interesting challenge to anesthetic care. We briefly present the perioperative management of a patient with BCS who underwent three cesarean sections. PMID:21258811

  2. Brittle onset of monodispersed magmatic suspensions: from spheres to spheroid

    NASA Astrophysics Data System (ADS)

    Cordonnier, B.; Kaus, B.; Manga, M.; Caricchi, L.; Pistone, M.; Castro, J.; Hess, K.-U.; Gottschaller, S.; Dingwell, D. B.; Burlini, L.

    2012-04-01

    This abstract describes one of the last projects engaged by Dr. Luigi Burlini. It highlights his wish to make a close link between experimental and numerical studies, and push even further our understanding of rock mechanics. His students, engaged in this study, wish to credit these results to the legacy left by him owing to his constant involvement in Science and in educating the next generation of rheologists. While he could not see this project to fruition, his constant support and help during the conception of the project made it possible. The brittle-ductile transition remains a central question of modern geology as rock failure is the main parameter in mitigating geological risks, such as, for volcanic eruptions, the transitions from effusive to explosive eruptive style. Although numerical simulations are the only way to fully understanding the physical processes involved, we are in a strong need of an experimental validation of the proposed models. We first recall some experimental results obtained under torsion and uni-axial compression on both pure melts and crystal-bearing magmas. Torsion experiments were performed at high temperature (600 to 900 degC) and high pressure (200 to 300 MPa) using a Paterson-type rock deformation apparatus (ETH Zurich). We characterized the brittle onset of two phases magmas from 0 to 65 vol% crystals. The strain-rates span 5 orders of magnitude, with a change in the behavior of the material from viscous to brittle (10^-5- 100 s^-1). The materials tested are a standard borosilicate glass (NIST717), a natural crystal bearing rhyolitic melt (Mt Unzen volcano) and a suspension of haplogranitic synthetic sample with corundum particles. To characterize the physical processes leading to failure in the experiments, we performed 2D and 3D numerical simulations on monodispersed rigid spheroids with eccentricities ranging from 10^-2 to 10^2. The model is numerically solved with Finite Elements Methods. The pre-processing, processing and

  3. Micromechanical modelling of quasi-brittle materials behavior

    SciTech Connect

    Li, V.C.

    1992-12-01

    This special issues on Micromechanical modelling of quasi-brittle materials behavior represents an outgrowth of presentations given at a symposium of the same title held at the 1991 ASME Applied Mechanics and Biomechanics Summer Conference at the Ohio State University. The symposium was organized to promote communication between researchers in three materials groups: rock, cementitious materials, ceramics and related composites. The enthusiastic response of both speakers and attendants at the ASME symposium convinced the organizer that it would be useful to put together a coherent volume which can reach a larger audience. It was decided that the papers individually and as a volume ought to provide a broader view, so that as much as possible, the work contained in each paper would be accessible to readers working in any of the three materials groups. Applied Mechanics Reviews presents an appropriate platform for achieving these objectives.

  4. Composition effect on intrinsic plasticity or brittleness in metallic glasses.

    PubMed

    Zhao, Yuan-Yun; Inoue, Akihisa; Chang, Chuntao; Liu, Jian; Shen, Baolong; Wang, Xinmin; Li, Run-Wei

    2014-01-01

    The high plasticity of metallic glasses is highly desirable for a wide range of novel engineering applications. However, the physical origin of the ductile/brittle behaviour of metallic glasses with various compositions and thermal histories has not been fully clarified. Here we have found that metallic glasses with compositions at or near intermetallic compounds, in contrast to the ones at or near eutectics, are extremely ductile and also insensitive to annealing-induced embrittlement. We have also proposed a close correlation between the element distribution features and the plasticity of metallic glasses by tracing the evolutions of the element distribution rearrangement and the corresponding potential energy change within the sliding shear band. These novel results provide useful and universal guidelines to search for new ductile metallic glasses at or near the intermetallic compound compositions in a number of glass-forming alloy systems. PMID:25043428

  5. Composition Effect on Intrinsic Plasticity or Brittleness in Metallic Glasses

    PubMed Central

    Zhao, Yuan-Yun; Inoue, Akihisa; Chang, Chuntao; Liu, Jian; Shen, Baolong; Wang, Xinmin; Li, Run-Wei

    2014-01-01

    The high plasticity of metallic glasses is highly desirable for a wide range of novel engineering applications. However, the physical origin of the ductile/brittle behaviour of metallic glasses with various compositions and thermal histories has not been fully clarified. Here we have found that metallic glasses with compositions at or near intermetallic compounds, in contrast to the ones at or near eutectics, are extremely ductile and also insensitive to annealing-induced embrittlement. We have also proposed a close correlation between the element distribution features and the plasticity of metallic glasses by tracing the evolutions of the element distribution rearrangement and the corresponding potential energy change within the sliding shear band. These novel results provide useful and universal guidelines to search for new ductile metallic glasses at or near the intermetallic compound compositions in a number of glass-forming alloy systems. PMID:25043428

  6. Simulations of ductile flow in brittle material processing

    SciTech Connect

    Luh, M.H.; Strenkowski, J.S.

    1988-12-01

    Research is continuing on the effects of thermal properties of the cutting tool and workpiece on the overall temperature distribution. Using an Eulerian finite element model, diamond and steel tools cutting aluminum have been simulated at various, speeds, and depths of cut. The relative magnitude of the thermal conductivity of the tool and the workpiece is believed to be a primary factor in the resulting temperature distribution in the workpiece. This effect is demonstrated in the change of maximum surface temperatures for diamond on aluminum vs. steel on aluminum. As a preliminary step toward the study of ductile flow in brittle materials, the relative thermal conductivities of diamond on polycarbonate is simulated. In this case, the maximum temperature shifts from the rake face of the tool to the surface of the machined workpiece, thus promoting ductile flow in the workpiece surface.

  7. Stability analysis of bridged cracks in brittle matrix composites

    NASA Technical Reports Server (NTRS)

    Ballarini, Roberto; Muju, Sandeep

    1991-01-01

    The bridging of matrix cracks by fibers is an important toughening mechanism in fiber reinforced brittle matrix composites. This paper presents the results of a nonlinear finite element analysis of the Mode-I propagation of a bridged matrix crack in a finite size specimen. The composite is modeled as an orthotropic continuum and the bridging due to the fibers is modeled as a distribution of tractions which resist crack opening. A critical stress intensity factor criterion is employed for matrix crack propagation while a critical crack opening condition is used for fiber failure. The structural response of the specimen (load-deflection curves) as well as the stress intensity factor of the propagating crack are calculated for various constituent properties and specimen configurations for both tensile and bending loading. By controlling the length of the bridged crack results are obtained which highlight the transition from stable to unstable behavior of the propagating crack.

  8. New probability distribution for the strength of brittle fibers

    SciTech Connect

    Black, C.M.; Durham, S.D.; Lynch, J.D.; Padgett, W.J.

    1989-11-01

    Brittle fibers, used in modern fibrous composite materials, are found in many structures such as ships, airplanes, swimming pools, etc.These fibers are commonly made from materials such as boron, glass, and carbon. There can be substantial benefits in using fiber composites rather than the traditional materials such as metal and wood, including lighter weight and added stiffness. For example, seventy-five to eighty percent of a projected Grumman aircraft will be constructed from carbon fiber composites. This will reduce the weight of the structure by an estimated 26 percent (Gordon, 1988). However, the intrinsic tensile strength per unit volume of most fibers is less than that of most metals. Their strength is a function of their microstructure, the fiber length, and the number and types of flaws in the fiber. (JS)

  9. Fracture toughness of brittle materials determined with chevron notch specimens

    NASA Technical Reports Server (NTRS)

    Shannon, J. L., Jr.; Bubsey, R. T.; Pierce, W. S.; Munz, D.

    1981-01-01

    Short bar, short rod, and four-point-bend chevron-notch specimens were used to determine the plane strain fracture toughness of hot-pressed silicon nitride and sintered aluminum oxide brittle ceramics. The unique advantages of this specimen type are: (1) the production of a sharp natural crack during the early stage of test loading, so that no precracking is required, and (2) the load passes through a maximum at a constant, material-independent crack length-to-width ratio for a specific geometry, so that no post-test crack measurement is required. The plane strain fracture toughness is proportional to the maximum test load and functions of the specimen geometry and elastic compliance. Although results obtained for silicon nitride are in good mutual agreement and relatively free of geometry and size effects, aluminum oxide results were affected in both these respects by the rising crack growth resistance curve of the material.

  10. High Speed Strain Measurements Surrounding Hydraulic Fracture in Brittle Hydrogel

    NASA Astrophysics Data System (ADS)

    Steinhardt, Will; Rubinstein, Shmuel

    2015-11-01

    Hydraulic fractures of oil and gas shales occur miles underground, below complex, layered rocks, making measurements of their dynamics, extent, or structure difficult to impossible. Rocks are heterogeneous at a wide range of length scales, and investigating how these non-uniformities affect the propagation and extent of fractures is vital to improving both the safety and efficiency of hydraulic fracturing operations. To study these effects we have developed a model system using brittle, heavily cross-linked hydrogels that we can fracture with fluids and observe with a fast camera. By embedding tracer particles within the gel and using laser sheet microscopy, we obtain three dimensional stress and strain maps of the zone surrounding a hydraulic fracture tip. Gels can also be set in layers or interfaces with tunable strengths or with designed heterogeneities, allowing us to understand the fundamental science of hydraulic fractures and investigate the dynamics of controllably complex materials.

  11. Dynamic brittle material response based on a continuum damage model

    SciTech Connect

    Chen, E.P.

    1994-12-31

    The response of brittle materials to dynamic loads was studied in this investigation based on a continuum damage model. Damage mechanism was selected to be interaction and growth of subscale cracks. Briefly, the cracks are activated by bulk tension and the density of activated cracks are described by a Weibull statistical distribution. The moduli of a cracked solid derived by Budiansky and O`Connell are then used to represent the global material degradation due to subscale cracking. This continuum damage model was originally developed to study rock fragmentation and was modified in the present study to improve on the post-limit structural response. The model was implemented into a transient dynamic explicit finite element code PRONTO 2D and then used for a numerical study involving the sudden stretching of a plate with a centrally located hole. Numerical results characterizing the dynamic responses of the material were presented. The effect of damage on dynamic material behavior was discussed.

  12. Quantitative comparisons of numerical models of brittle wedge dynamics

    NASA Astrophysics Data System (ADS)

    Buiter, Susanne

    2010-05-01

    Numerical and laboratory models are often used to investigate the evolution of deformation processes at various scales in crust and lithosphere. In both approaches, the freedom in choice of simulation method, materials and their properties, and deformation laws could affect model outcomes. To assess the role of modelling method and to quantify the variability among models, we have performed a comparison of laboratory and numerical experiments. Here, we present results of 11 numerical codes, which use finite element, finite difference and distinct element techniques. We present three experiments that describe shortening of a sand-like, brittle wedge. The material properties of the numerical ‘sand', the model set-up and the boundary conditions are strictly prescribed and follow the analogue setup as closely as possible. Our first experiment translates a non-accreting wedge with a stable surface slope of 20 degrees. In agreement with critical wedge theory, all models maintain the same surface slope and do not deform. This experiment serves as a reference that allows for testing against analytical solutions for taper angle, root-mean-square velocity and gravitational rate of work. The next two experiments investigate an unstable wedge in a sandbox-like setup, which deforms by inward translation of a mobile wall. The models accommodate shortening by formation of forward and backward shear zones. We compare surface slope, rate of dissipation of energy, root-mean-square velocity, and the location, dip angle and spacing of shear zones. We show that we successfully simulate sandbox-style brittle behaviour using different numerical modelling techniques and that we obtain the same styles of deformation behaviour in numerical and laboratory experiments at similar levels of variability. The GeoMod2008 Numerical Team: Markus Albertz, Michelle Cooke, Tony Crook, David Egholm, Susan Ellis, Taras Gerya, Luke Hodkinson, Boris Kaus, Walter Landry, Bertrand Maillot, Yury Mishin

  13. Rate- and strain-dependent brittle deformation of rocks

    NASA Astrophysics Data System (ADS)

    Brantut, N.; Heap, M. J.; Baud, P.; Meredith, P. G.

    2014-03-01

    We develop a unifying framework to quantify rate-dependent deformation in the brittle field and establish links between the microscale time-dependent crack growth processes and the macroscopically observed rate dependency. Triaxial deformation experiments have been performed under both constant strain rate and constant stress (creep) conditions on three types of sandstone. The measured relative evolution of P wave speeds as a function of inelastic axial strain is similar for both types of test, despite differences in strain rate of up to 3 orders of magnitude. This similarity indicates that there exists a direct, time-independent link between the microstructural state (as reflected by the variations in P wave speed) and the inelastic axial strain. Comparison of applied stresses between constant strain rate and creep experiments as a function of inelastic strain indicates that creep deformation requires less mechanical work to bring the sample to failure. This energy deficit corresponds to a stress deficit, which can be related to a deficit in energy release rate of the microcracks. We establish empirically that the creep strain rate is given by ɛ˙∝exp(ΔQ/σ∗), where ΔQ is the stress deficit (negative) and σ∗ is an activation stress. This empirical exponential relation between creep strain rate and stress deficit is analogous to rate-and-state friction law. We develop a micromechanical approach based on fracture mechanics to determine the evolution of an effective stress intensity factor at crack tips during creep deformation and estimate the activation volume of the stress corrosion reaction responsible for brittle creep.

  14. Using Brittle Fragmentation Theory to represent Aerosol Mineral Composition

    NASA Astrophysics Data System (ADS)

    Pérez García-Pando, C.; Miller, R. L.; Perlwitz, J. P.

    2014-12-01

    Improved estimates of dust aerosol effects upon climate require the characterization of dust mineral and chemical composition. Regional variations in soil mineral composition lead to variations in dust aerosol composition. Yet, deriving aerosol mineral content also requires knowledge of the parent soil size distribution along with the fragmentation of soil particles and aggregates during the emission process. These processes modify the size distribution and mineral abundance of the emitted aerosols compared to the parent soil. An additional challenge for modeling is that global atlases of soil texture and composition are based on wet sieving, a technique that breaks the aggregates, particularly phyllosilicates, that are encountered in natural soils, drastically altering the original size distribution of the soil that is subject to wind erosion. We propose both a semi-empirical and theoretical method to constrain the size-resolved mineral composition of emitted dust aerosols based on global atlases of soil texture and composition. Our semi-empirical method re-aggregates clay phyllosilicate minerals into larger soil particle sizes and constrains the size distribution of each emitted mineral based on observed mineral distributions at the source. Our theoretical method extends Kok's brittle fragmentation theory to individual minerals. To this end we reconstruct the undisturbed size distribution for each mineral as a function of soil texture and soil type and calculate the emitted size distribution applying brittle fragmentation and assuming homogeneous fragmentation properties among the mineral aggregates. These approaches were tested within the NASA GISS Earth System ModelE. We discuss the improvements achieved and suggest future developments.

  15. Computer software.

    PubMed

    Rosenthal, L E

    1986-10-01

    Software is the component in a computer system that permits the hardware to perform the various functions that a computer system is capable of doing. The history of software and its development can be traced to the early nineteenth century. All computer systems are designed to utilize the "stored program concept" as first developed by Charles Babbage in the 1850s. The concept was lost until the mid-1940s, when modern computers made their appearance. Today, because of the complex and myriad tasks that a computer system can perform, there has been a differentiation of types of software. There is software designed to perform specific business applications. There is software that controls the overall operation of a computer system. And there is software that is designed to carry out specialized tasks. Regardless of types, software is the most critical component of any computer system. Without it, all one has is a collection of circuits, transistors, and silicone chips. PMID:3536223

  16. A combined analytical-experimental tensile test technique for brittle materials

    NASA Technical Reports Server (NTRS)

    Chu, M. L.; Scavuzzo, R. J.; Srivatsan, T. S.

    1992-01-01

    A semiconventional tensile test technique is developed for impact ices and other brittle materials. Accurate results have been obtained on ultimate strength and modulus of elasticity in a refrigerated ice test. It is noted that the technique can be used to determine the physical properties of impact ices accreted inside icing wind tunnels or other brittle materials.

  17. Brittle-ductile shear zone formation in the McKim Limestone: eastern Monument Upwarp, Utah

    NASA Astrophysics Data System (ADS)

    Seyum, S.; Pollard, D. D.

    2011-12-01

    The McKim Limestone is part of a regressive, marine sedimentary sequence of strata that was deposited in the Pennsylvanian to Permian periods. It is well-exposed across large portions of Raplee anticline and Comb monocline; a pair of kilometer-scale folds that mark the Monument Upwarp of the Colorado Plateau in southeastern Utah. Two conjugate sets of echelon vein arrays, with complementary echelon pressure solution seam arrays, occur as bed-perpendicular, systematic deformation features in the 1-3 m thick McKim Limestone unit. Based on large vein to vein array angles, large vein aperture to length ratios, and the presence of vein-perpendicular pressure solution seams, these structures are interpreted to have developed within localized, brittle-ductile shear zones. Topics of debate among structural geologists regarding the formation mechanism of echelon veins include the initiation mode of vein segments (tensile or shear), the relative age between shear zone initiation and vein formation, the interpretation of strain within a shear zone, and the development of sigmoidal veins as being indicative of rotation. These concepts often are founded on geometric observations and kinematic models of deformation (e.g. simple shear) that are independent of the constitutive properties of the rock, are not constrained by the equations of motion, and do not honor the boundary conditions on the vein surfaces. Here we show a more realistic representation of brittle-ductile shear zone formation by introducing numerical models that consider the mechanical properties of limestone, are constrained by the equations of motion, and explicitly define the vein surfaces and their boundary conditions. The commercial finite element software, Abaqus FEA, is used to investigate the deformed geometry of model echelon vein arrays as a function of the remotely applied stress, the initial geometry of the vein arrays, and the constitutive properties of the solid. These geometric patterns are compared

  18. Software safety

    NASA Technical Reports Server (NTRS)

    Leveson, Nancy

    1987-01-01

    Software safety and its relationship to other qualities are discussed. It is shown that standard reliability and fault tolerance techniques will not solve the safety problem for the present. A new attitude requires: looking at what you do NOT want software to do along with what you want it to do; and assuming things will go wrong. New procedures and changes to entire software development process are necessary: special software safety analysis techniques are needed; and design techniques, especially eliminating complexity, can be very helpful.

  19. Modeling Shear Instabilities With Block Sliders: Brittle and Ductile

    NASA Astrophysics Data System (ADS)

    Riedel, M. R.

    2003-12-01

    Block slider-type models have been succesfully used for almost 35 years to describe the spatio-temporal development of shear instabilities in the brittle crust (Burridge & Knopoff, 1967; Olami et al., 1992). More recently, increasing attention is paid on the extension of the classical Burridge-Knopoff model (based on a pure Mohr-Coulomb rheology) with a viscous component, either to include depth-dependent properties into the model or aiming at a more accurate description of fore- and aftershock sequences of a main earthquake event (e.g. Hainzl et al., 1999). On the other hand, viscous feedback mechanisms of various types have become an increasingly attractive mechanism for the generation of intermediate-depth and deep-focus earthquakes in the ductile mantle lithosphere (e.g. Wiens & Snider, 2001). Heat generated during viscous deformation provides a positive feedback to creep and eventually faulting under high pressure (Karato et al., 2001, Bercovici & Karato, 2003). The present paper discusses the specific properties of block slider-type models that are extended with a viscous component and compare their behaviour with the pure brittle ("classical") case. Block slider-type models for ductile instabilities are numerically much less demanding than solutions based on the corresponding, thermal-mechanically coupled, continuum equations. They allow for the inclusion of possible non-equilibrium effects associated with mineral phase transformations in a subducting slab (kinetic overshoot, grainsize reduction, latent heat release) in a straightforward manner. They may therefore serve as an effective tool to study the coupling of viscous heating, temperature-dependent viscosity and brittle stress transfer that are thought to cause the specific spatial-temporal clustering of intermediate-depth and deep-focus eartquakes. References D. Bercovici and S. Karato "Theoretical Analysis of Shear Localization in the Lithosphere", in: Reviews in Mineralogy and Geochemistry 51, eds. S

  20. SAFOD Brittle Microstructure and Mechanics Knowledge Base (BM2KB)

    NASA Astrophysics Data System (ADS)

    Babaie, Hassan A.; Broda Cindi, M.; Hadizadeh, Jafar; Kumar, Anuj

    2013-07-01

    Scientific drilling near Parkfield, California has established the San Andreas Fault Observatory at Depth (SAFOD), which provides the solid earth community with short range geophysical and fault zone material data. The BM2KB ontology was developed in order to formalize the knowledge about brittle microstructures in the fault rocks sampled from the SAFOD cores. A knowledge base, instantiated from this domain ontology, stores and presents the observed microstructural and analytical data with respect to implications for brittle deformation and mechanics of faulting. These data can be searched on the knowledge base‧s Web interface by selecting a set of terms (classes, properties) from different drop-down lists that are dynamically populated from the ontology. In addition to this general search, a query can also be conducted to view data contributed by a specific investigator. A search by sample is done using the EarthScope SAFOD Core Viewer that allows a user to locate samples on high resolution images of core sections belonging to different runs and holes. The class hierarchy of the BM2KB ontology was initially designed using the Unified Modeling Language (UML), which was used as a visual guide to develop the ontology in OWL applying the Protégé ontology editor. Various Semantic Web technologies such as the RDF, RDFS, and OWL ontology languages, SPARQL query language, and Pellet reasoning engine, were used to develop the ontology. An interactive Web application interface was developed through Jena, a java based framework, with AJAX technology, jsp pages, and java servlets, and deployed via an Apache tomcat server. The interface allows the registered user to submit data related to their research on a sample of the SAFOD core. The submitted data, after initial review by the knowledge base administrator, are added to the extensible knowledge base and become available in subsequent queries to all types of users. The interface facilitates inference capabilities in the

  1. Semi-brittle flow of granitoid fault rocks in experiments

    NASA Astrophysics Data System (ADS)

    Pec, Matej; Stünitz, Holger; Heilbronner, Renée.; Drury, Martyn

    2016-03-01

    Field studies and seismic data show that semi-brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so-called frictional-viscous transition. To understand the physical and chemical processes accommodating semi-brittle flow, we have performed an experimental study on synthetic granitoid fault rocks exploring a broad parameter space (temperature, T = 300, 400, 500, and 600°C, confining pressure, Pc ≈ 300, 500, 1000, and 1500 MPa, shear strain rate, γṡ ≈ 10-3, 10-4, 10-5, and 10-6 s-1, to finite shear strains, γ = 0-5). The experiments have been carried out using a granular material with grain size smaller than 200 µm with a little H2O added (0.2 wt %). Only two experiments (performed at the fastest strain rates and lowest temperatures) have failed abruptly right after reaching peak strength (τ ~ 1400 MPa). All other samples reach high shear stresses (τ ~ 570-1600 MPa) then weaken slightly (by Δτ ~ 10-190 MPa) and continue to deform at a more or less steady state stress level. Clear temperature dependence and a weak strain rate dependence of the peak as well as steady state stress levels are observed. In order to express this relationship, the strain rate-stress sensitivity has been fit with a stress exponent, assuming γ˙ ∝ τn and yields high stress exponents (n ≈ 10-140), which decrease with increasing temperature. The microstructures show widespread comminution, strain partitioning, and localization into slip zones. The slip zones contain at first nanocrystalline and partly amorphous material. Later, during continued deformation, fully amorphous material develops in some of the slip zones. Despite the mechanical steady state conditions, the fabrics in the slip zones and outside continue to evolve and do not reach a steady state microstructure below γ = 5. Within the slip zones, the fault rock material progressively transforms from a crystalline solid to an amorphous material. We

  2. Brittle-tough transitions during crack growth in toughened adhesives

    NASA Astrophysics Data System (ADS)

    Thoules, Michael

    2008-03-01

    The use of structural adhesives in automotive applications relies on an effective understanding of their performance under crash conditions. In particular, there is considerable potential for mechanics-based modeling of the interaction between an adhesive layer and the adherends, to replace current empirical approaches to design. Since energy dissipation during a crash, mediated by plastic deformation of the structure, is a primary consideration for automotive applications, traditional approaches of fracture mechanics are not appropriate. Cohesive-zone models that use two fracture parameters - cohesive strength and toughness - have been shown to provide a method for quantitative mechanics analysis. Combined numerical and experimental techniques have been developed to deduce the toughness and strength parameters of adhesive layers, allowing qualitative modeling of the performance of adhesive joints. These techniques have been used to study the failure of joints, formed from a toughened adhesive and sheet metal, over a wide range of loading rates. Two fracture modes are observed: quasi-static crack growth and dynamic crack growth. The quasi-static crack growth is associated with a toughened mode of failure; the dynamic crack growth is associated with a more brittle mode of failure. The results of the experiments and analyses indicate that the fracture parameters for quasi-static crack growth in this toughened system are essentially rate independent, and that quasi-static crack growth can occur even at the highest crack velocities. Effects of rate appear to be limited to the ease with which a transition to dynamic fracture could be triggered. This transition appears to be stochastic in nature, and it does not appear to be associated with the attainment of any critical value for crack velocity or loading rate. Fracture-mechanics models exist in the literature for brittle-ductile transitions in rate-dependent polymers, which rely on rate dependent values of toughness

  3. Failure processes in soft and quasi-brittle materials with nonhomogeneous microstructures

    NASA Astrophysics Data System (ADS)

    Spring, Daniel W.

    , coupled cohesive-friction relation and detail its formulation and implementation. In the process of this investigation, we developed a small library of cohesive elements for use with a commercially available finite element analysis software package. Additionally, in this thesis, we present a series of methods for reducing mesh dependency in two-dimensional dynamic cohesive fracture simulations of quasi-brittle materials. In this setting, cracks are only permitted to propagate along element facets, thus a poorly designed discretization of the problem domain can introduce artifacts into the fracture behavior. To reduce mesh induced artifacts, we consider unstructured polygonal finite elements. A randomly-seeded polygonal mesh leads to an isotropic discretization of the problem domain, which does not bias the direction of crack propagation. However, polygonal meshes tend to limit the possible directions a crack may travel at each node, making this discretization a poor candidate for dynamic cohesive fracture simulations. To alleviate this problem, we propose two new topological operators. The first operator we propose is adaptive element-splitting, and the second is adaptive mesh refinement. Both operators are designed to improve the ability of unstructured polygonal meshes to capture crack patterns in dynamic cohesive fracture simulations. However, we demonstrate that element-splitting is more suited to pervasive fracture problems, whereas, adaptive refinement is more suited to problems exhibiting a dominant crack. Finally, we investigate the use of geometric and constitutive design features to regularize pervasive fragmentation behavior in three-dimensions. Throughout pervasive fracture simulations, many cracks initiate, propagate, branch and coalesce simultaneously. Because of the cohesive element method's unique framework, this behavior can be captured in a regularized manner. In this investigation, unstructuring techniques are used to introduce randomness into a

  4. Software Reviews.

    ERIC Educational Resources Information Center

    Bitter, Gary G., Ed.

    1990-01-01

    Reviews three computer software: (1) "Elastic Lines: The Electronic Geoboard" on elementary geometry; (2) "Wildlife Adventures: Whales" on environmental science; and (3) "What Do You Do with a Broken Calculator?" on computation and problem solving. Summarizes the descriptions, strengths and weaknesses, and applications of each software. (YP)

  5. Software Repository

    NASA Technical Reports Server (NTRS)

    Merwarth, P., D.

    1983-01-01

    The Common Software Module Repository (CSMR) is computerized library system with high product and service visibility to potential users. Online capabilities of system allow both librarian and user to interact with library. Librarian is responsible for maintaining information in CSMR library. User searches library to locate software modules that meet his or her current needs.

  6. Software Reviews.

    ERIC Educational Resources Information Center

    Miller, Anne, Ed.; Radziemski, Cathy, Ed.

    1988-01-01

    Reviews two software packages for the Macintosh series. "Course Builder 2.0," a courseware authoring system, allows the user to create programs which stand alone and may be used independently in the classroom. "World Builder," an artificial intelligence software package, allows creative thinking, problem-solving, and decision-making. (YP)

  7. Software Bridge

    NASA Technical Reports Server (NTRS)

    1995-01-01

    I-Bridge is a commercial version of software developed by I-Kinetics under a NASA Small Business Innovation Research (SBIR) contract. The software allows users of Windows applications to gain quick, easy access to databases, programs and files on UNIX services. Information goes directly onto spreadsheets and other applications; users need not manually locate, transfer and convert data.

  8. Software Reviews.

    ERIC Educational Resources Information Center

    Wulfson, Stephen

    1988-01-01

    Presents reviews of six computer software programs for teaching science. Provides the publisher, grade level, cost, and descriptions of software, including: (1) "Recycling Logic"; (2) "Introduction to Biochemistry"; (3) "Food for Thought"; (4) "Watts in a Home"; (5) "Geology in Action"; and (6) "Biomes." All are for Apple series microcomputers.…

  9. Brittle fracture in a periodic structure with internal potential energy

    PubMed Central

    Mishuris, Gennady S.; Slepyan, Leonid I.

    2014-01-01

    We consider a brittle fracture taking account of self-equilibrated distributed stresses existing at microlevel in the absence of external forces. To determine how the latter can affect the crack equilibrium and growth, a model of a structured linearly elastic body is introduced, consisting of two equal symmetrically arranged layers (or half-planes) connected by an interface as a prospective crack path. The interface comprises a discrete set of elastic bonds. In the initial state, the bonds are assumed to be stressed in such a way that tensile and compressive forces of the same value alternate. In the general considerations, the layers are assumed to be of an unspecified periodic structure, where such self-equilibrated stresses may also exist. A two-line chain and a lattice are examined as the specified structure. We consider the states of the body-with-a-crack under such microlevel stresses (MS) and under a combined action of the remote forces and MS. Analytical solutions to the considered problems are presented based on the introduction of a selective discrete transform. We demonstrate that MS can increase as well as decrease the crack resistance depending on the internal energy level. We also discuss different scenarios of the crack growth. PMID:24808756

  10. Brittle thermoelectric semiconductors extrusion under high hydrostatic pressure

    SciTech Connect

    Sidorenko, N.A.

    1994-08-10

    Origins of strength increase of brittle materials like thermoelectric (TE) semiconductors during plastic deformation under high external pressure are analyzed. TE material stressed state in the process of extrusion is reviewed. Plastic deformation of monocrystalline TE material billet produced by extrusion under sufficiently high external hydrostatic pressure is more uniform than under ordinary ambient pressure and can lead to crack free extruded TE material structure, crystallographic symmetry of which coincides with original billet one. Experimental device realized the scheme of extrusion under high hydrostatic pressure is described. Here extrusion are carrying out in compressed liquid medium. The developed device ensures the value of hydrostatic pressure up to 2 GPa and extrusion temperature interval 300--600 K. Properties of extruded Bi-Sb and Bi-Sb-Te single crystals are also reviewed. Possible application of presented method of extrusion under high hydrostatic pressure to form TE branches with highly accurate cross section for miniature TE coolers or generators is discussed. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  11. Thermal stress fracture in elastic-brittle materials

    NASA Technical Reports Server (NTRS)

    Emery, A. F.

    1980-01-01

    The reported investigation shows that the assessment of the possibility of the thermal fracture of brittle materials depends upon an accurate evaluation of the thermal stresses and the determination of the resulting stress intensity factors. The stress intensity factors can be calculated in a variety of ways ranging from the very precise to approximate, but only for a limited number of geometries. The main difficulty is related to the determination of the thermal stress field because of its unusual character and its dependence upon boundary conditions at points far from the region of thermal activity. Examination of a number of examples suggests that the best visualization of the thermal stresses and any associated fracture can be made by considering the problem to be the combination of thermal and isothermal problems or by considering that the prime effect of the temperature is in the generation of thermal strains and that the thermal stresses are simply the result of the region trying to accommodate these strains.

  12. Experimental formation of brittle structural assemblages in oblique divergence

    NASA Astrophysics Data System (ADS)

    Smith, J. V.; Durney, D. W.

    1992-12-01

    A series of experiments is reported in which brittle minor structures are initiated in narrow deformation zones in clay under conditions of kinematically controlled oblique divergent displacement. Nineteen settings of boundary displacement angle were used from pure wrench to pure divergence under conditions favouring either faults (dry experiments) or extension fractures (wet experiments). Pure wrench produced the well known assemblage of Riedel strike-slip faults whereas experiments in pure divergence produced conjugate arrays of normal faults and extension fractures with a dihedral angle of 30° bisected by the direction of the zone, as has been described in rift zones. Experiments with boundary displacements at intermediate settings show a continuum of structural orientations and dihedral angles between these two extremes. A boundary between assemblages dominated by strike-slip faults and extensional faults was found at a displacement angle of 45° from the deformation zone. These results are interpreted kinematically in terms of: (1) principal axes of infinitesimal incremental strain; (2) material dilatancy control on shear structure dihedral angles; and (3) whether the vertical strain in divergent wrench settings is a thickening (strike-slip assemblage) or a thinning (normal fault assemblage).

  13. A Maxwell elasto-brittle rheology for sea ice modelling

    NASA Astrophysics Data System (ADS)

    Dansereau, Véronique; Weiss, Jérôme; Saramito, Pierre; Lattes, Philippe

    2016-07-01

    A new rheological model is developed that builds on an elasto-brittle (EB) framework used for sea ice and rock mechanics, with the intent of representing both the small elastic deformations associated with fracturing processes and the larger deformations occurring along the faults/leads once the material is highly damaged and fragmented. A viscous-like relaxation term is added to the linear-elastic constitutive law together with an effective viscosity that evolves according to the local level of damage of the material, like its elastic modulus. The coupling between the level of damage and both mechanical parameters is such that within an undamaged ice cover the viscosity is infinitely large and deformations are strictly elastic, while along highly damaged zones the elastic modulus vanishes and most of the stress is dissipated through permanent deformations. A healing mechanism is also introduced, counterbalancing the effects of damaging over large timescales. In this new model, named Maxwell-EB after the Maxwell rheology, the irreversible and reversible deformations are solved for simultaneously; hence drift velocities are defined naturally. First idealized simulations without advection show that the model reproduces the main characteristics of sea ice mechanics and deformation: strain localization, anisotropy, intermittency and associated scaling laws.

  14. Brittle cornea syndrome: recognition, molecular diagnosis and management

    PubMed Central

    2013-01-01

    Brittle cornea syndrome (BCS) is an autosomal recessive disorder characterised by extreme corneal thinning and fragility. Corneal rupture can therefore occur either spontaneously or following minimal trauma in affected patients. Two genes, ZNF469 and PRDM5, have now been identified, in which causative pathogenic mutations collectively account for the condition in nearly all patients with BCS ascertained to date. Therefore, effective molecular diagnosis is now available for affected patients, and those at risk of being heterozygous carriers for BCS. We have previously identified mutations in ZNF469 in 14 families (in addition to 6 reported by others in the literature), and in PRDM5 in 8 families (with 1 further family now published by others). Clinical features include extreme corneal thinning with rupture, high myopia, blue sclerae, deafness of mixed aetiology with hypercompliant tympanic membranes, and variable skeletal manifestations. Corneal rupture may be the presenting feature of BCS, and it is possible that this may be incorrectly attributed to non-accidental injury. Mainstays of management include the prevention of ocular rupture by provision of protective polycarbonate spectacles, careful monitoring of visual and auditory function, and assessment for skeletal complications such as developmental dysplasia of the hip. Effective management depends upon appropriate identification of affected individuals, which may be challenging given the phenotypic overlap of BCS with other connective tissue disorders. PMID:23642083

  15. Fracture toughness of brittle materials determined with chevron notch specimens

    NASA Technical Reports Server (NTRS)

    Shannon, J. L., Jr.; Bursey, R. T.; Munz, D.; Pierce, W. S.

    1980-01-01

    The use of chevron-notch specimens for determining the plane strain fracture toughness (K sub Ic) of brittle materials is discussed. Three chevron-notch specimens were investigated: short bar, short rod, and four-point-bend. The dimensionless stress intensity coefficient used in computing K sub Ic is derived for the short bar specimen from the superposition of ligament-dependent and ligament-independent solutions for the straight through crack, and also from experimental compliance calibrations. Coefficients for the four-point-bend specimen were developed by the same superposition procedure, and with additional refinement using the slice model of Bluhm. Short rod specimen stress intensity coefficients were determined only by experimental compliance calibration. Performance of the three chevron-notch specimens and their stress intensity factor relations were evaluated by tests on hot-pressed silicon nitride and sintered aluminum oxide. Results obtained with the short bar and the four-point-bend specimens on silicon nitride are in good agreement and relatively free of specimen geometry and size effects within the range investigated. Results on aluminum oxide were affected by specimen size and chevron-notch geometry, believed due to a rising crack growth resistance curve for the material. Only the results for the short bar specimen are presented in detail.

  16. Coupling between anisotropic damage and permeability variation in brittle rocks

    NASA Astrophysics Data System (ADS)

    Shao, J. F.; Zhou, H.; Chau, K. T.

    2005-10-01

    In this paper, a coupled constitutive model is proposed for anisotropic damage and permeability variation in brittle rocks under deviatoric compressive stresses. The formulation of the model is based on experimental evidences and main physical mechanisms involved in the scale of microcracks are taken into account. The proposed model is expressed in the macroscopic framework and can be easily implemented for engineering application. The macroscopic free enthalpy of cracked solid is first determined by approximating crack distribution by a second-order damage tensor. The effective elastic properties of damaged material are then derived from the free enthalpy function. The damage evolution is related to the crack growth in multiple orientations. A pragmatic approach inspired from fracture mechanics is used for the formulation of the crack propagation criterion. Compressive stress induced crack opening is taken into account and leads to macroscopic volumetric dilatancy and permeability variation. The overall permeability tensor of cracked material is determined using a micro-macro averaging procedure. Darcy's law is used for fluid flow at the macroscopic scale whereas laminar flow is assumed at the microcrack scale. Hydraulic connectivity of cracks increases with crack growth. The proposed model is applied to the Lac du Bonnet granite. Generally, good agreement is observed between numerical simulations and experimental data. Copyright

  17. Simulating Brittle Fracture of Rocks using Smoothed Particle Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Das, Rajarshi; Cleary, Paul W.

    2009-05-01

    Numerical modelling can assist in understanding and predicting complex fracture processes. Smoothed Particle Hydrodynamics (SPH) is a particle-based Lagrangian method that is particularly suited to the analysis of fracture due to its capacity to model large deformation and to track free surfaces generated. A damage model is used to predict the fracture of elastic solids. The damage parameter represents the volume-averaged micro-fracture of the volume of material represented by an SPH particle. Evolution of damage is predicted using the strain history of each particle. Damage inhibits the transmission of tensile stress between particles, and once it reaches unity, the interface becomes unable to transmit tensile stress, resulting in a macro-crack. Connected macro-cracks lead to complete fragmentation. In this paper, we explore the ability of an SPH-based damage model to predict brittle fracture of rocks during impact. Rock shape is found to have considerable influence on the fracture process, the fragment sizes, the energy dissipation during impact, and the post-fracture motion of the fragments.

  18. Culture shock: Improving software quality

    SciTech Connect

    de Jong, K.; Trauth, S.L.

    1988-01-01

    The concept of software quality can represent a significant shock to an individual who has been developing software for many years and who believes he or she has been doing a high quality job. The very idea that software includes lines of code and associated documentation is foreign and difficult to grasp, at best. Implementation of a software quality program hinges on the concept that software is a product whose quality needs improving. When this idea is introduced into a technical community that is largely ''self-taught'' and has been producing ''good'' software for some time, a fundamental understanding of the concepts associated with software is often weak. Software developers can react as if to say, ''What are you talking about. What do you mean I'm not doing a good job. I haven't gotten any complaints about my code yetexclamation'' Coupling such surprise and resentment with the shock that software really is a product and software quality concepts do exist, can fuel the volatility of these emotions. In this paper, we demonstrate that the concept of software quality can indeed pose a culture shock to developers. We also show that a ''typical'' quality assurance approach, that of imposing a standard and providing inspectors and auditors to assure its adherence, contributes to this shock and detracts from the very goal the approach should achieve. We offer an alternative, adopted through experience, to implement a software quality program: cooperative assistance. We show how cooperation, education, consultation and friendly assistance can overcome this culture shock. 3 refs.

  19. Delayed brittle-like fragmentation of vesicular magma analogue by decompression

    NASA Astrophysics Data System (ADS)

    Kameda, Masaharu; Ichihara, Mie; Shimanuki, Susumu; Okabe, Wataru; Shida, Tsukasa

    2013-05-01

    A rapid decompression experiment using syrup containing gas bubbles was conducted in order to clarify the fragmentation of vesicular magma, which is a key phenomenon in volcanic eruptions. We focus on brittle-like fragmentation, which occurs with a longer time scale than brittle fragmentation. The response of the bubbly syrup to the decompression for various viscosities and porosities was tested under various initial pressures, pressure differences, and decompression times. The response observed by high-speed photography was classified using the Deborah number DeDT, which is defined as the ratio of the viscoelastic relaxation time of the syrup to the decompression time, the maximum differential stress at the bubble surface Δσmax, and a measure of instantaneous brittleness at the bubble surface βc at the time when the differential stress at the surface reaches the critical fracture stress Δσc. In a number of the experimental runs in which both DeDT and βc indicated ductile response of the material, brittle-like fragmentation occurred when Δσmax substantially exceeded Δσc. For all of the runs in which brittle-like fragmentation was observed, the onset of fragmentation was delayed substantially from the relaxation time, whereas the onset occurred within the characteristic time for viscous expansion of the bubbles. In many cases of brittle-like fragmentation, fragmentation continued after the onset triggered by a single decompression event. Detailed analysis indicates that brittle-like fragmentation started with a sudden release of the gas in the bubbly syrup through a surface crack, which might lead to an increase in local brittleness. Magma fragmentation may be viewed as sequential brittle-like fragmentation. This view may provide an explanation for the observed time delay for the onset of an explosive eruption after a triggering decompression event.

  20. Software Smarts

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Under an SBIR (Small Business Innovative Research) contract with Johnson Space Center, Knowledge Based Systems Inc. (KBSI) developed an intelligent software environment for modeling and analyzing mission planning activities, simulating behavior, and, using a unique constraint propagation mechanism, updating plans with each change in mission planning activities. KBSI developed this technology into a commercial product, PROJECTLINK, a two-way bridge between PROSIm, KBSI's process modeling and simulation software and leading project management software like Microsoft Project and Primavera's SureTrak Project Manager.

  1. Software testing

    NASA Astrophysics Data System (ADS)

    Price-Whelan, Adrian M.

    2016-01-01

    Now more than ever, scientific results are dependent on sophisticated software and analysis. Why should we trust code written by others? How do you ensure your own code produces sensible results? How do you make sure it continues to do so as you update, modify, and add functionality? Software testing is an integral part of code validation and writing tests should be a requirement for any software project. I will talk about Python-based tools that make managing and running tests much easier and explore some statistics for projects hosted on GitHub that contain tests.

  2. Software Reviews.

    ERIC Educational Resources Information Center

    Wulfson, Stephen, Ed.

    1990-01-01

    Reviewed are six computer software packages including "Lunar Greenhouse,""Dyno-Quest,""How Weather Works,""Animal Trackers,""Personal Science Laboratory," and "The Skeletal and Muscular Systems." Availability, functional, and hardware requirements are discussed. (CW)

  3. Software Reviews.

    ERIC Educational Resources Information Center

    McGrath, Diane

    1990-01-01

    Reviews two programs: (1) "The Weather Machine" on understanding weather and weather forecasting and (2) "The Mystery of the Hotel Victoria" on problem solving in mathematics. Presents the descriptions, advantages, and weaknesses of the software. (YP)

  4. Software Reviews.

    ERIC Educational Resources Information Center

    Davis, Shelly J., Ed.; Knaupp, Jon, Ed.

    1984-01-01

    Reviewed is computer software on: (1) classification of living things, a tutorial program for grades 5-10; and (2) polynomial practice using tiles, a drill-and-practice program for algebra students. (MNS)

  5. Software Reviews.

    ERIC Educational Resources Information Center

    Wulfson, Stephen, Ed.

    1987-01-01

    Provides a review of four science software programs. Includes topics such as plate tectonics, laboratory experiment simulations, the human body, and light and temperature. Contains information on ordering and reviewers' comments. (ML)

  6. Software Reviews.

    ERIC Educational Resources Information Center

    Dwyer, Donna; And Others

    1989-01-01

    Reviewed are seven software packages for Apple and IBM computers. Included are: "Toxicology"; "Science Corner: Space Probe"; "Alcohol and Pregnancy"; "Science Tool Kit Plus"; Computer Investigations: Plant Growth"; "Climatrolls"; and "Animal Watch: Whales." (CW)

  7. Software Reviews.

    ERIC Educational Resources Information Center

    Kimball, Jeffrey P.; And Others

    1987-01-01

    Describes a variety of computer software. The packages reviewed include a variety of simulations, a spread sheet, a printer driver and an alternative operating system for DBM.PCs and compatible programs. (BSR)

  8. Software Reviews.

    ERIC Educational Resources Information Center

    Wulfson, Eugene T., Ed.

    1988-01-01

    Presents reviews by classroom teachers of software for teaching science. Includes material on the work of geologists, genetics, earth science, classification of living things, astronomy, endangered species, skeleton, drugs, and heartbeat. Provides information on availability and equipment needed. (RT)

  9. Software Reviews.

    ERIC Educational Resources Information Center

    Classroom Computer Learning, 1990

    1990-01-01

    Reviewed are three computer software packages including "Martin Luther King, Jr.: Instant Replay of History,""Weeds to Trees," and "The New Print Shop, School Edition." Discussed are hardware requirements, costs, grade levels, availability, emphasis, strengths, and weaknesses. (CW)

  10. Software Reviews.

    ERIC Educational Resources Information Center

    Mathematics and Computer Education, 1988

    1988-01-01

    Presents reviews of six software packages. Includes (1) "Plain Vanilla Statistics"; (2) "MathCAD 2.0"; (3) "GrFx"; (4) "Trigonometry"; (5) "Algebra II"; (6) "Algebra Drill and Practice I, II, and III." (PK)

  11. Micromechanics of brittle faulting and cataclastic flow in Berea sandstone

    NASA Astrophysics Data System (ADS)

    Menéndez, Beatriz; Zhu, Wenlu; Wong, Teng-Fong

    1996-01-01

    The micromechanics of failure in Berea sandstone were investigated by characterizing quantitatively the evolution of damage under the optical and scanning electron microscopes. Three series of triaxial compression experiments were conducted at the fixed pore pressure of 10 MPa and confining pressures of 20, 50 and 260 MPa, respectively, corresponding to three different failure modes: shear localization with positive dilatancy, shear localization with relatively little dilatancy and distributed cataclastic flow. To distinguish the effect of non-hydrostatic stress from that of hydrostatic pressure, a fourth suite of hydrostatically loaded samples was also studied. Using stereological procedures, we characterized quantitatively the following damage parameters: microcrack density and its anisotropy, pore-size distribution, comminuted volume fraction and mineral damage index. In the brittle regime, shear localization did not develop until the post-failure stage, after the peak stress had been attained. The microcrack density data show that very little intragranular cracking occurred before the peak stress was attained. We infer that dilatancy and acoustic emission activity in the prefailure stage are primarily due to intergranular cracking, probably related to the shear rupture of lithified and cemented grain contacts. Near the peak stress, intragranular cracking initiates from grain contacts and this type of Hertzian fracture first develops in isolated clusters, and their subsequent coalescence results in shear localization in the post-failure stage. The very high density of intragranular microcracking and pronounced stress-induced anisotropy in the post-failure samples are the consequence of shear localization and compactive processes operative inside the shear band. In contrast, Hertzian fracture was a primary cause for shear-enhanced compaction and strain hardening throughout the cataclastic flow regime. Grain crushing and pore collapse seem to be most intense in

  12. Astronomy Software

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Software Bisque's TheSky, SkyPro and Remote Astronomy Software incorporate technology developed for the Hubble Space Telescope. TheSky and SkyPro work together to orchestrate locating, identifying and acquiring images of deep sky objects. With all three systems, the user can directly control computer-driven telescopes and charge coupled device (CCD) cameras through serial ports. Through the systems, astronomers and students can remotely operate a telescope at the Mount Wilson Observatory Institute.

  13. Method for preparing surfaces of metal composites having a brittle phase for plating

    DOEpatents

    Coates, Cameron W.; Wilson, Thomas J.

    1984-01-01

    The present invention is directed to a method for preparing surfaces of two-phase metal composites having relatively brittle and malleable components for plating with corrosion-resistant material. In practice of the present invention, the surfaces of the composites are etched to remove a major portion or fraction of the brittle component. The etched surface is then peened with particulates for breaking the brittle component from the surfaces and for spreading or smearing the malleable component over the surfaces. The peened surface is then chemically cleaned of residual traces of the brittle component so as to provide a surface of essentially the malleable component to which the corrosion-resistant material may be plated thereon in an adherent manner.

  14. Preventing and Treating Brittle Bones and Osteoporosis | NIH MedlinePlus the Magazine

    MedlinePlus

    ... Javascript on. Feature: Osteoporosis Preventing and Treating Brittle Bones and Osteoporosis Past Issues / Winter 2011 Table of ... at high risk due to low bone mass. Bone and Bone Loss Bone is living, growing tissue. ...

  15. The ceramic brittleness of the pressed and sintered yttria zirconia-mullite-magnesia system

    NASA Astrophysics Data System (ADS)

    Hakim, Budi L.; Soepriyanto, Syoni; Korda, Akhmad A.; Sunendar, Bambang

    2015-09-01

    The brittleness behaviour of the pressed and sintered Yttria Zirconia-Mullite-Magnesia system has been studied. Specifically, the brittleness index represents a correlation of material properties for predicting mechanical properties such as for the characterization of machinability, wear or erosion resistance. The brittleness index as well as fracture toughness were obtained from indentation testing of the Vickers hardness. In this study, the fracture toughness considered the crack extension mechanism to accommodate Palmqvist crack criteria for the measured data. The additional of Mullite at amount of 15% into 3Y-TZP system significantly reduces the brittleness index while compared to pure Mullite system up to 69%. In the other hand, the additional Mullite 15% by weight into 3Y-TZP system proved an increase of fracture toughness value up to 138% than pure 3Y-TZP system

  16. Dissecting the distribution of brittle stars along a sewage pollution gradient indicated by organic markers.

    PubMed

    Barboza, Carlos Alberto de Moura; Martins, César C; Lana, Paulo da Cunha

    2015-11-15

    We have assessed variation in brittle star distribution patterns along a contamination gradient identified by fecal steroids and aliphatic hydrocarbons in Paranaguá Bay, southern Brazil. A hierarchical design using multiple spatial scales (centimeters-kilometers) was applied. Generalized linear mixed models (GLMMs) were used to investigate the spatial and temporal variability of brittle stars. Main principal components from the contamination and environmental matrices were used to investigate the best explanatory dataset. The abundance of brittle stars was significantly lower in sites with high concentrations of fecal steroids and aliphatic hydrocarbons. The best model fitting always included components from the contamination gradients, which precludes a purely environmental driving of brittle star abundance. Variability in spatial scales lower than kilometers was probably driven by sediment characteristics. We highlighted the importance of a robust multi-scale sampling design for a better biological indication of coastal contamination. PMID:26323862

  17. Hydraulic fracture and toughening of a brittle layer bonded to a hydrogel

    NASA Astrophysics Data System (ADS)

    Lucantonio, Alessandro; Noselli, Giovanni; Trepat, Xavier; Desimone, Antonio; Arroyo, Marino

    Brittle materials fracture under tensile or shear stress. When stress attains a critical threshold, crack propagation becomes unstable and proceeds dynamically. In the presence of several precracks, a brittle material always propagates only the weakest crack, leading to catastrophic failure. Here, we show that all these features of brittle fracture are radically modified when the material susceptible to cracking is bonded to a poroelastic medium, such as a hydrogel, a common situation in biological tissues. In particular, we show that the brittle material can fracture in compression and can resist cracking in tension, thanks to the hydraulic coupling with the hydrogel. In the case of multiple cracks, we find that localized fracture occurs when the permeability of the hydrogel is high, whereas decreased permeability leads to toughening by promoting multiple cracking. Our results may contribute to the understanding of fracture in biological tissues and provide inspiration for the design of tough, biomimetic materials.

  18. Brittle cornea syndrome: a case report and comparison with Ehlers Danlos syndrome.

    PubMed

    Ramappa, Muralidhar; Wilson, M Edward; Rogers, R Curtis; Trivedi, Rupal H

    2014-10-01

    We report a 6-week-old white boy of nonconsanguineous parents who presented with bluish scleral discoloration, thin corneas, and progressive high myopia. A diagnosis of brittle cornea syndrome was confirmed by molecular analysis and prompt measures were taken to manage the condition. Long-term follow-up of children diagnosed with brittle cornea syndrome is important to minimize the risks of corneal rupture and for detecting late-onset systemic conditions. PMID:25266838

  19. Atomistic Simulation of Brittle to Ductile Transition in GaN Nanotubes

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao; Gao, Fei; Weber, William J.

    2006-12-11

    Molecular dynamics methods with a Stillinger-Weber potential have been used to investigate the mechanical properties of wurtzite-type single crystalline GaN nanotubes under applied tensile stresses. At lower temperatures, the nanotubes show brittle properties; whereas at higher temperatures, they behave as ductile materials. The brittle to ductile transition (BDT) is systemically investigated, and the corresponding transition temperatures have been determined in GaN. The BDT temperature generally increases with increasing thickness of nanotubes and strain rate.

  20. Synthesis and single crystal structure refinement of the one-layer hydrate of sodium brittle mica

    SciTech Connect

    Kalo, Hussein; Milius, Wolfgang; Braeu, Michael; Breu, Josef

    2013-02-15

    A sodium brittle mica with the ideal composition [Na{sub 4}]{sup inter}[Mg{sub 6}]{sup oct}[Si{sub 4}Al{sub 4}]{sup tet}O{sub 20}F{sub 4} was synthesized via melt synthesis in a gas tight crucible. This mica is unusual inasmuch as the known mica structure holds only room for two interlayer cations per unit cell and inasmuch as it readily hydrates despite the high layer charge while ordinary micas and brittle micas are non-swelling. The crystal structure of one-layer hydrate sodium brittle mica was determined and refined from single crystal X-ray data. Interlayer cations reside at the center of the distorted hexagonal cavities and are coordinated by the three inner basal oxygen atoms. The coordination of the interlayer cation is completed by three interlayer water molecules residing at the center of the interlayer region. The relative position of adjacent 2:1-layers thus is fixed by these octahedrally coordinated interlayer cations. Pseudo-symmetry leads to extensive twinning. In total five twin operations generate the same environment for the interlayer species and are energetically degenerate. - Graphical abstract: The sodium brittle mica has been successfully synthesized by melt synthesis and the crystal structure of the one-layer hydrate of sodium brittle mica was determined from single crystal X-ray diffraction data. Highlights: Black-Right-Pointing-Pointer Melt synthesis yielded coarse grained sodium brittle mica which showed little disorder. Black-Right-Pointing-Pointer Sodium brittle mica hydrated completely to the state of one-layer hydrate. Black-Right-Pointing-Pointer Structure of one-layer hydrate of sodium brittle mica could therefore be determined and refined. Black-Right-Pointing-Pointer Arrangement of upper and lower tetrahedral sheet encompassing interlayer cation were clarified.

  1. A new approach to rock brittleness and its usability at prediction of drillability

    NASA Astrophysics Data System (ADS)

    Özfırat, M. Kemal; Yenice, Hayati; Şimşir, Ferhan; Yaralı, Olgay

    2016-07-01

    Rock brittleness is one of the most important issues in rock drilling and cutting. The relations between drillability and brittleness will assist engineers in excavation works. The demand for representative rock parameters related to planning of underground excavations is increasing, as these parameters constitute fundamental input for obtaining the most reliable cost and time estimates. In rock cutting mechanics, the effects of the rock and brittleness on the efficiency of drilling and excavation are examined by many researchers. In this study, 41 different rock types were tested in laboratory to investigate the relations between the drilling rate index and different brittleness values. Firstly, the relations defined in literature are tested. Strength tests are made according to International Society for Rock Mechanics standards. In addition Norwegian University of Science and Technology standards are used to determine drilling rate index. Then, a new brittleness index is proposed which is the arithmetic average of uniaxial compressive strength and tensile strength. Considering the regression analysis carried out, it was seen that the proposed formula showed good correlation for these samples handled in this study. As a result of this study, a high correlation is obtained between the proposed index and drilling rate index values (R:0.84). The results are found to be at least reliable as well as other brittleness equations given in literature.

  2. Software engineering

    NASA Technical Reports Server (NTRS)

    Fridge, Ernest M., III; Hiott, Jim; Golej, Jim; Plumb, Allan

    1993-01-01

    Today's software systems generally use obsolete technology, are not integrated properly with other software systems, and are difficult and costly to maintain. The discipline of reverse engineering is becoming prominent as organizations try to move their systems up to more modern and maintainable technology in a cost effective manner. The Johnson Space Center (JSC) created a significant set of tools to develop and maintain FORTRAN and C code during development of the space shuttle. This tool set forms the basis for an integrated environment to reengineer existing code into modern software engineering structures which are then easier and less costly to maintain and which allow a fairly straightforward translation into other target languages. The environment will support these structures and practices even in areas where the language definition and compilers do not enforce good software engineering. The knowledge and data captured using the reverse engineering tools is passed to standard forward engineering tools to redesign or perform major upgrades to software systems in a much more cost effective manner than using older technologies. The latest release of the environment was in Feb. 1992.

  3. Software reengineering

    NASA Technical Reports Server (NTRS)

    Fridge, Ernest M., III

    1991-01-01

    Today's software systems generally use obsolete technology, are not integrated properly with other software systems, and are difficult and costly to maintain. The discipline of reverse engineering is becoming prominent as organizations try to move their systems up to more modern and maintainable technology in a cost effective manner. JSC created a significant set of tools to develop and maintain FORTRAN and C code during development of the Space Shuttle. This tool set forms the basis for an integrated environment to re-engineer existing code into modern software engineering structures which are then easier and less costly to maintain and which allow a fairly straightforward translation into other target languages. The environment will support these structures and practices even in areas where the language definition and compilers do not enforce good software engineering. The knowledge and data captured using the reverse engineering tools is passed to standard forward engineering tools to redesign or perform major upgrades to software systems in a much more cost effective manner than using older technologies. A beta vision of the environment was released in Mar. 1991. The commercial potential for such re-engineering tools is very great. CASE TRENDS magazine reported it to be the primary concern of over four hundred of the top MIS executives.

  4. The brittle deformation regime of water-saturated siliceous sandstones

    NASA Astrophysics Data System (ADS)

    Reviron, N.; Reuschlé, T.; Bernard, J.-D.

    2009-09-01

    We present here new experimental data on the mechanical behaviour of water-saturated Bentheim and Fontainebleau sandstones deformed in the brittle failure regime. Bentheim sandstone samples were stressed at room temperature and subjected to confining pressures PC ranging from 12 to 120 MPa and pore pressures PP ranging from 1 to 70 MPa. For all samples the evolution of the volumetric strain first shows compaction eventually reversing to dilation of the pore volume when approaching the peak stress. All samples failed localized on a single shear zone. Critical stresses that is onset of dilatancy and peak stress, can be uniquely defined as a function of the effective pressure Peff = PC - PP. The failure curve parameters, when fitted with the Hoek-Brown criterion or a parabolic envelope, are consistent with previous values obtained on similar material. When compared to data obtained on dry samples of the same rock, the present data show no notable effect of the presence of water on the critical stress levels. The same conclusion holds for the stress-strain curves when dry and water-saturated experiments under equivalent effective confining pressures are compared. When compared to previously published data obtained on various quartzose rocks, which show a quite variable water-weakening effect, our results lead to the conclusion that the quasi-exclusive presence of quartz grains bonded together by a quartzose cement combined with the absence of clayey minerals may explain the absence of this effect in Bentheim sandstone. Moreover, this conclusion is supported by complementary results obtained by Fontainebleau sandstone with similar microstructural and compositional characteristics. A previously developed micromechanical model based on the interaction of pore cracks has been used and modified to take into account the presence of water. When compared to the experimental data, the results of the model show good agreement for low to intermediate effective confining pressures

  5. Forecasting volcanic eruptions: the control of elastic-brittle deformation

    NASA Astrophysics Data System (ADS)

    Kilburn, Christopher; Robertson, Robert; Wall, Richard; Steele, Alexander

    2016-04-01

    At volcanoes reawakening after long repose, patterns of unrest normally reflect the elastic-brittle deformation of crust above a magma reservoir. Local fault movements, detected as volcano-tectonic (VT) earthquakes, increase in number with surface deformation, at first approximately exponentially and then linearly. The trends describe how crustal behaviour evolves from quasi-elastic deformation under an increasing stress to inelastic deformation under a constant stress. They have been quantified and verified against experiments for deformation in compression [1]. We have extended the analysis to extensional deformation. The results agree well with field data for crust being stretched by a pressurizing magmatic system [2]. They also provide new criteria for enhancing the definitions of alert levels and preferred times to eruption. The VT-deformation sequence is a field proxy for changes in deformation with applied stress. The transition from quasi-elastic to inelastic behaviour is characterised in extension by the ratio of differential failure stress SF to tensile strength σT. Unrest data from at least basaltic to andesitic stratovolcanoes, as well as large calderas, yield preferred values for SF/σT ≤ 4, coinciding with the range for tensile failure expected from established theoretical constraints (from Mohr-Coulomb-Griffiths failure). We thus associate the transition with the approach to tensile rupture at the wall of a pressurized magma reservoir. In particular, values of about 2 are consistent with the rupture of a cylindrical reservoir, such as a closed conduit within a volcanic edifice, whereas values of about 3 suggest an approximately spherical reservoir, such as may exist at deeper levels. The onset of inelastic behaviour reflects the emergence of self-accelerating crack growth under a constant stress. Applied to forecasting eruptions, it provides a new and objective criterion for raising alert levels during an emergency; it yields the classic linear

  6. Analysis of the progressive failure of brittle matrix composites

    NASA Technical Reports Server (NTRS)

    Thomas, David J.

    1995-01-01

    This report investigates two of the most common modes of localized failures, namely, periodic fiber-bridged matrix cracks and transverse matrix cracks. A modification of Daniels' bundle theory is combined with Weibull's weakest link theory to model the statistical distribution of the periodic matrix cracking strength for an individual layer. Results of the model predictions are compared with experimental data from the open literature. Extensions to the model are made to account for possible imperfections within the layer (i.e., nonuniform fiber lengths, irregular crack spacing, and degraded in-situ fiber properties), and the results of these studies are presented. A generalized shear-lag analysis is derived which is capable of modeling the development of transverse matrix cracks in material systems having a general multilayer configuration and under states of full in-plane load. A method for computing the effective elastic properties for the damaged layer at the global level is detailed based upon the solution for the effects of the damage at the local level. This methodology is general in nature and is therefore also applicable to (0(sub m)/90(sub n))(sub s) systems. The characteristic stress-strain response for more general cases is shown to be qualitatively correct (experimental data is not available for a quantitative evaluation), and the damage evolution is recorded in terms of the matrix crack density as a function of the applied strain. Probabilistic effects are introduced to account for the statistical nature of the material strengths, thus allowing cumulative distribution curves for the probability of failure to be generated for each of the example laminates. Additionally, Oh and Finney's classic work on fracture location in brittle materials is extended and combined with the shear-lag analysis. The result is an analytical form for predicting the probability density function for the location of the next transverse crack occurrence within a crack bounded

  7. Control Software

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Real-Time Innovations, Inc. (RTI) collaborated with Ames Research Center, the Jet Propulsion Laboratory and Stanford University to leverage NASA research to produce ControlShell software. RTI is the first "graduate" of Ames Research Center's Technology Commercialization Center. The ControlShell system was used extensively on a cooperative project to enhance the capabilities of a Russian-built Marsokhod rover being evaluated for eventual flight to Mars. RTI's ControlShell is complex, real-time command and control software, capable of processing information and controlling mechanical devices. One ControlShell tool is StethoScope. As a real-time data collection and display tool, StethoScope allows a user to see how a program is running without changing its execution. RTI has successfully applied its software savvy in other arenas, such as telecommunications, networking, video editing, semiconductor manufacturing, automobile systems, and medical imaging.

  8. Antiterrorist Software

    NASA Technical Reports Server (NTRS)

    Clark, David A.

    1998-01-01

    In light of the escalation of terrorism, the Department of Defense spearheaded the development of new antiterrorist software for all Government agencies by issuing a Broad Agency Announcement to solicit proposals. This Government-wide competition resulted in a team that includes NASA Lewis Research Center's Computer Services Division, who will develop the graphical user interface (GUI) and test it in their usability lab. The team launched a program entitled Joint Sphere of Security (JSOS), crafted a design architecture (see the following figure), and is testing the interface. This software system has a state-ofthe- art, object-oriented architecture, with a main kernel composed of the Dynamic Information Architecture System (DIAS) developed by Argonne National Laboratory. DIAS will be used as the software "breadboard" for assembling the components of explosions, such as blast and collapse simulations.

  9. Software Reviews.

    ERIC Educational Resources Information Center

    Classroom Computer Learning, 1990

    1990-01-01

    Reviewed are two computer software packages: "Super Solvers Midnight Rescue!" a problem-solving program for IBM PCs; and "Interactive Physics," a simulation program for the Macintosh computer. The functions of the package are discussed including strengths and weaknesses and teaching suggestions. (CW)

  10. Reviews, Software.

    ERIC Educational Resources Information Center

    Science Teacher, 1988

    1988-01-01

    Reviews two software programs for Apple series computers. Includes "Orbital Mech," a basic planetary orbital simulation for the Macintosh, and "START: Stimulus and Response Tools for Experiments in Memory, Learning, Cognition, and Perception," a program that demonstrates basic psychological principles and experiments. (CW)

  11. Software Reviews.

    ERIC Educational Resources Information Center

    Wulfson, Stephen, Ed.

    1989-01-01

    Six software packages are described in this review. Included are "Molecules and Atoms: Exploring the Essence of Matter"; "Heart Probe"; "GM Sunraycer"; "Six Puzzles"; "Information Laboratory--Life Science"; and "Science Test Builder." Hardware requirements, prices, and a summary of the abilities of each program are presented. (CW)

  12. Educational Software.

    ERIC Educational Resources Information Center

    Northwest Regional Educational Lab., Portland, OR.

    The third session of IT@EDU98 consisted of five papers on educational software and was chaired by Tran Van Hao (University of Education, Ho Chi Minh City, Vietnam). "Courseware Engineering" (Nguyen Thanh Son, Ngo Ngoc Bao Tran, Quan Thanh Tho, Nguyen Hong Lam) briefly describes the use of courseware. "Machine Discovery Theorems in Geometry: A…

  13. Software Reviews.

    ERIC Educational Resources Information Center

    Computing Teacher, 1985

    1985-01-01

    Reprinted from "The Computing Teacher," this document contains software reviews for 23 computer programs that educators could use in the classroom or for administrative purposes. Each review describes the program by listing the program title, subject, producer, grade level (if applicable), hardware required, cost, and reviewer's name and…

  14. Software Reviews.

    ERIC Educational Resources Information Center

    Bitter, Gary G., Ed.

    1989-01-01

    Reviews three software packages: (1) "The Weather Machine Courseware Kit" for grades 7-12; (2) "Exploring Measurement, Time, and Money--Level I," for primary level mathematics; and (3) "Professor DOS with SmartGuide for DOS" providing an extensive tutorial covering DOS 2.1 to 4.0. Discusses the strengths and weaknesses of each package. (YP)

  15. Software Reviews.

    ERIC Educational Resources Information Center

    Smith, Richard L., Ed.

    1987-01-01

    Reviewed are three computer software programs: the Astronomer (astronomy program for middle school students and older); Hands-on-Statistics: Explorations with a Microcomputer (statistics program for secondary school students and older); and CATGEN (a genetics program for secondary school students and older). Each review provides information on:…

  16. Software Reviews.

    ERIC Educational Resources Information Center

    Science and Children, 1990

    1990-01-01

    Reviewed are seven computer software packages for IBM and/or Apple Computers. Included are "Windows on Science: Volume 1--Physical Science"; "Science Probe--Physical Science"; "Wildlife Adventures--Grizzly Bears"; "Science Skills--Development Programs"; "The Clean Machine"; "Rock Doctor"; and "Geology Search." Cost, quality, hardware, and…

  17. Software Review.

    ERIC Educational Resources Information Center

    McGrath, Diane, Ed.

    1989-01-01

    Reviewed is a computer software package entitled "Audubon Wildlife Adventures: Grizzly Bears" for Apple II and IBM microcomputers. Included are availability, hardware requirements, cost, and a description of the program. The murder-mystery flavor of the program is stressed in this program that focuses on illegal hunting and game management. (CW)

  18. Software Reviews.

    ERIC Educational Resources Information Center

    Wulfson, Stephen, Ed.

    1989-01-01

    Presents comments by classroom teachers on software for science teaching including topics on: the size of a molecule, matter, leaves, vitamins and minerals, dinosaurs, and collecting and measuring data. Each is an Apple computer series. Availability and costs are included. (RT)

  19. Software Comparison

    NASA Technical Reports Server (NTRS)

    Blanchard, D. C.

    1986-01-01

    Software Comparison Package (SCP) compares similar files. Normally, these are 90-character files produced by CDC UPDATE utility from program libraries that contain FORTRAN source code plus identifier. SCP also used to compare load maps, cross-reference outputs, and UPDATE corrections sets. Helps wherever line-by-line comparison of similarly structured files required.

  20. Software Patents.

    ERIC Educational Resources Information Center

    Burke, Edmund B.

    1994-01-01

    Outlines basic patent law information that pertains to computer software programs. Topics addressed include protection in other countries; how to obtain patents; kinds of patents; duration; classes of patentable subject matter, including machines and processes; patentability searches; experimental use prior to obtaining a patent; and patent…

  1. Software reengineering

    NASA Technical Reports Server (NTRS)

    Fridge, Ernest M., III

    1991-01-01

    Programs in use today generally have all of the function and information processing capabilities required to do their specified job. However, older programs usually use obsolete technology, are not integrated properly with other programs, and are difficult to maintain. Reengineering is becoming a prominent discipline as organizations try to move their systems to more modern and maintainable technologies. The Johnson Space Center (JSC) Software Technology Branch (STB) is researching and developing a system to support reengineering older FORTRAN programs into more maintainable forms that can also be more readily translated to a modern languages such as FORTRAN 8x, Ada, or C. This activity has led to the development of maintenance strategies for design recovery and reengineering. These strategies include a set of standards, methodologies, and the concepts for a software environment to support design recovery and reengineering. A brief description of the problem being addressed and the approach that is being taken by the STB toward providing an economic solution to the problem is provided. A statement of the maintenance problems, the benefits and drawbacks of three alternative solutions, and a brief history of the STB experience in software reengineering are followed by the STB new FORTRAN standards, methodology, and the concepts for a software environment.

  2. Software Reviews.

    ERIC Educational Resources Information Center

    Smith, Richard L., Ed.

    1988-01-01

    Reviews two software packages, "Solutions Unlimited" and "BASIC Data Base System." Provides a description, summary, strengths and weaknesses, availability and costs. Includes reviews of three structured BASIC packages: "True BASIC (2.0)"; "Turbo BASIC (1.0)"; and "QuickBASIC (3.0)." Explains significant features such as graphics, costs,…

  3. Design Software

    NASA Technical Reports Server (NTRS)

    1991-01-01

    A NASA contractor and Small Business Innovation Research (SBIR) participant has converted its research into commercial software products for auto design, structural analysis and other applications. ViGYAN, Inc., utilizing the aeronautical research principle of computational fluid dynamics, has created - with VGRID3D and VPLOT3D - an easier alternative to conventional structured grids for fluid dynamic calculations.

  4. Software Reviews.

    ERIC Educational Resources Information Center

    Science and Children, 1988

    1988-01-01

    Reviews six software packages for use with school age children ranging from grade 3 to grade 12. Includes "The Microcomputer Based Lab Project: Motion, Sound"; "Genetics"; "Geologic History"; "The Microscope Simulator"; and "Wiz Works" all for Apple II and "Reading for Information: Level II" for IBM. (CW)

  5. Software Reviews.

    ERIC Educational Resources Information Center

    Science and Children, 1989

    1989-01-01

    Reviews of seven software packages are presented including "The Environment I: Habitats and EcoSystems; II Cycles and Interactions"; "Super Sign Maker"; "The Great Knowledge Race: Substance Abuse"; "Exploring Science: Temperature"; "Fast Food Calculator and RD Aide"; "The Human Body: Circulation and Respiration" and "Forces in Liquids and Gases."…

  6. Software Reviews.

    ERIC Educational Resources Information Center

    Wulfson, Stephen, Ed.

    1990-01-01

    Reviewed are seven computer software packages including "Frog Dissection Lab Report,""Backyard Birds,""LEGO TC Logo,""Alcohol--Four Interactive Programs,""Windows on Science--Life Science,""Climate and Weather/Our Town Database," and "Weeds to Trees." Discussed are availability, features, strengths, and weaknesses. (CW)

  7. Star Software.

    ERIC Educational Resources Information Center

    Kloza, Brad

    2000-01-01

    Presents a collection of computer software programs designed to spark learning enthusiasm at every grade level and across the curriculum. They include Reader Rabbit's Learn to Read, Spelling Power, Mind Twister Math, Community Construction Kit, Breaking the Code, Encarta Africana 2000, Virtual Serengeti, Operation: Frog (Deluxe), and My First…

  8. Software Reviews.

    ERIC Educational Resources Information Center

    McGrath, Diane, Ed.

    1989-01-01

    Reviewed are two computer software programs for Apple II computers on weather for upper elementary and middle school grades. "Weather" introduces the major factors (temperature, humidity, wind, and air pressure) affecting weather. "How Weather Works" uses simulation and auto-tutorial formats on sun, wind, fronts, clouds, and storms. (YP)

  9. Statistical Software.

    ERIC Educational Resources Information Center

    Callamaras, Peter

    1983-01-01

    This buyer's guide to seven major types of statistics software packages for microcomputers reviews Edu-Ware Statistics 3.0; Financial Planning; Speed Stat; Statistics with DAISY; Human Systems Dynamics package of Stats Plus, ANOVA II, and REGRESS II; Maxistat; and Moore-Barnes' MBC Test Construction and MBC Correlation. (MBR)

  10. Software Reviews.

    ERIC Educational Resources Information Center

    Teles, Elizabeth, Ed.; And Others

    1990-01-01

    Reviewed are two computer software packages for Macintosh microcomputers including "Phase Portraits," an exploratory graphics tool for studying first-order planar systems; and "MacMath," a set of programs for exploring differential equations, linear algebra, and other mathematical topics. Features, ease of use, cost, availability, and hardware…

  11. Reviews: Software.

    ERIC Educational Resources Information Center

    Mackenzie, Norma N.; And Others

    1988-01-01

    Reviews four computer software packages including: "The Physical Science Series: Sound" which demonstrates making waves, speed of sound, doppler effect, and human hearing; "Andromeda" depicting celestial motions in any direction; "Biology Quiz: Humans" covering chemistry, cells, viruses, and human biology; and "MacStronomy" covering information on…

  12. Software Reviews.

    ERIC Educational Resources Information Center

    Mackenzie, Norma N.; And Others

    1988-01-01

    Describes computer software for use with various age groups. Topics include activities involving temperature, simulations, earth science, the circulatory system, human body, reading in science, and ecology. Provides information on equipment needed, availability, package contents, and price. Comments of reviews are presented by classroom teachers.…

  13. Software interoperability for energy simulation

    SciTech Connect

    Hitchcock, Robert J.

    2002-07-31

    This paper provides an overview of software interoperability as it relates to the energy simulation of buildings. The paper begins with a discussion of the difficulties in using sophisticated analysis tools like energy simulation at various stages in the building life cycle, and the potential for interoperability to help overcome these difficulties. An overview of the Industry Foundation Classes (IFC), a common data model for supporting interoperability under continuing development by the International Alliance for Interoperability (IAI) is then given. The process of creating interoperable software is described next, followed by specific details for energy simulation tools. The paper closes with the current status of, and future plans for, the ongoing efforts to achieve software interoperability.

  14. Overcoming Anarchy in the Advanced Language Class.

    ERIC Educational Resources Information Center

    Gutierrez, John R.

    1990-01-01

    The coordination, articulation, and implementation of informed teaching techniques and objectives will help to overcome the anarchy and confusion that characterize higher education advanced-level foreign language classes, and will begin to produce a pool of highly competent foreign language speakers and writers. (33 references) (CB)

  15. Overcoming the Limitations of Learning Objects

    ERIC Educational Resources Information Center

    Wiley, David; Waters, Sandie; Dawson, Deonne; Lambert, Brent; Barclay, Matthew; Wade, David; Nelson, Laurie

    2004-01-01

    There are a number of issues that face individuals who would use learning objects for instructional purposes. These issues include problems with decontextualization, enabling meaningful reusability, and overcoming biases toward didactic approaches in the use of learning objects. We discuss these problems in some detail, and present a project-based…

  16. Understanding and Overcoming "Bottlenecks" in Student Learning

    ERIC Educational Resources Information Center

    Sturts, Jill R.; Mowatt, Rasul A.

    2012-01-01

    Pedagogically, the term "bottleneck" refers to a moment when students may face barriers to understanding content in the process of learning. As instructors identify "bottlenecks" within their courses, they are faced with the challenge of how to best assist students in overcoming them. Further, most instructors want to know what selected teaching…

  17. Overcoming Xenophobia: Learning to Accept Differences.

    ERIC Educational Resources Information Center

    Baker, Judith A.

    1990-01-01

    Quality health education requires that health educators engage in the professional and personal development necessary to overcome xenophobia when working with special populations (obese, elderly, indigent, minorities, etc.). This article describes strategies employed in a university community health education class to help students overcome…

  18. Learn to Avoid or Overcome Leadership Obstacles

    ERIC Educational Resources Information Center

    D'Auria, John

    2015-01-01

    Leadership is increasingly recognized as an important factor in moving schools forward, yet we have been relatively random in how we prepare and support them. Four obstacles often block or diminish their effectiveness. Avoiding or overcoming each of these requires an underlying set of skills and knowledge that we believe can be learned and…

  19. Successful Writing: Five Roadblocks to Overcome

    ERIC Educational Resources Information Center

    King, Kathleen P.

    2013-01-01

    This article provides essential strategies to be more successful in one of the major roles in academia: writing. Most academics struggle with roadblocks in their writing process. We are forever battling to complete research articles, manuscripts, grant proposals or other documents. The strategies and perspective shared here help overcome several…

  20. Students Write to Overcome Learning Blocks.

    ERIC Educational Resources Information Center

    Lavoie, Dan; Backus, Ann

    1990-01-01

    Discussed is the use of writing as a tool to monitor student growth and development. The value of writing to help overcome obstacles such as misconceptions and preconceptions is stressed. A concept map of a hierarchy of writing strategies is provided. Stressed is the value of writing in the development of process skills. (CW)

  1. Overcoming Barriers in Working with Families

    ERIC Educational Resources Information Center

    Heru, Alison M.; Drury, Laura

    2006-01-01

    Objective: The Accreditation Council for Graduate Medical Education and the Residency Review Committee for psychiatry outline the expected competencies for residents. These competencies include working with families. This article describes barriers that residents face when working with families, and offers ways to overcome these barriers. Method:…

  2. Overcoming Barriers in the Media Center

    ERIC Educational Resources Information Center

    Winter, Clint

    2011-01-01

    Web 2.0 has revolutionized one's ability to teach students in new and exciting ways. Students with disabilities can now overcome many barriers that once kept them from being successful in the regular education classroom. Media specialists can effectively advocate for students with disabilities. School library media specialists have the ability to…

  3. First Davis Strait discovery overcomes offshore hazards

    SciTech Connect

    Munro, R.G.

    1982-04-01

    In spite of icebergs umpredictable currents and brief drilling seasons, the first discovery well was completed recently in the Davis Strait. The success of this well, known as Hekja 0-71, has opened the waters off the northeastern coast of Canada to more exploration. A discussion is presented of how the well was drilled, the problems encountered and how they were overcome.

  4. Overcoming Barriers to Engaging in College Academics

    ERIC Educational Resources Information Center

    Hensley, Lauren; Shaulskiy, Stephanie; Zircher, Andrew; Sanders, Megan

    2015-01-01

    Underprepared college students face transition issues that prevent full academic engagement. The written responses of 176 students in a learning-strategies course were used to develop a grounded model of overcoming barriers to academic engagement. Findings revealed contexts in which academic engagement involved high costs (i.e., effort, trade-off,…

  5. Two brittle ductile transitions in subduction wedges, as revealed by topography

    NASA Astrophysics Data System (ADS)

    Thissen, C.; Brandon, M. T.

    2013-12-01

    Subduction wedges contain two brittle ductile transitions. One transition occurs within the wedge interior, and a second transition occurs along the decollement. The decollement typically has faster strain rates, which suggests that the brittle ductile transition along the decollement will be more rearward (deeper) than the transition within the interior. However, the presence of distinct rheologies or other factors such as pore fluid pressure along the decollement may reverse the order of the brittle-ductile transitions. We adopt a solution by Williams et al., (1994) to invert for these brittle ductile transitions using the wedge surface topography. At present, this model does not include an s point or sediment loading atop the wedge. The Hellenic wedge, however, as exposed in Crete presents an ideal setting to test these ideas. We find that the broad high of the Mediterranean ridge represents the coulomb frictional part of the Hellenic wedge. The rollover in topography north of the ridge results from curvature of the down going plate, creating a negative alpha depression in the vicinity of the Strabo, Pliny, and Ionian 'troughs' south of Crete. A steep topographic rise out of these troughs and subsequent flattening reflects the brittle ductile transition at depth in both the decollement and the wedge interior. Crete exposes the high-pressure viscous core of the wedge, and pressure solution textures provide additional evidence for viscous deformation in the rearward part of the wedge. The location of the decollement brittle ductile transition has been previously poorly constrained, and Crete has never experienced a subduction zone earthquake in recorded history. Williams, C. A., et al., (1994). Effect of the brittle ductile transition on the topography of compressive mountain belts on Earth and Venus. Journal of Geophysical Research Solid Earth

  6. Benchmarking the Sandbox: Quantitative Comparisons of Numerical and Analogue Models of Brittle Wedge Dynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Buiter, S.; Schreurs, G.; Geomod2008 Team

    2010-12-01

    When numerical and analogue models are used to investigate the evolution of deformation processes in crust and lithosphere, they face specific challenges related to, among others, large contrasts in material properties, the heterogeneous character of continental lithosphere, the presence of a free surface, the occurrence of large deformations including viscous flow and offset on shear zones, and the observation that several deformation mechanisms may be active simultaneously. These pose specific demands on numerical software and laboratory models. By combining the two techniques, we can utilize the strengths of each individual method and test the model-independence of our results. We can perhaps even consider our findings to be more robust if we find similar-to-same results irrespective of the modeling method that was used. To assess the role of modeling method and to quantify the variability among models with identical setups, we have performed a direct comparison of results of 11 numerical codes and 15 analogue experiments. We present three experiments that describe shortening of brittle wedges and that resemble setups frequently used by especially analogue modelers. Our first experiment translates a non-accreting wedge with a stable surface slope. In agreement with critical wedge theory, all models maintain their surface slope and do not show internal deformation. This experiment serves as a reference that allows for testing against analytical solutions for taper angle, root-mean-square velocity and gravitational rate of work. The next two experiments investigate an unstable wedge, which deforms by inward translation of a mobile wall. The models accommodate shortening by formation of forward and backward shear zones. We compare surface slope, rate of dissipation of energy, root-mean-square velocity, and the location, dip angle and spacing of shear zones. All models show similar cross-sectional evolutions that demonstrate reproducibility to first order. However

  7. The evolution of fabric with displacement in natural brittle faults

    NASA Astrophysics Data System (ADS)

    Mittempergher, S.; Di Toro, G.; Gratier, J.; Aretusini, S.; Boullier-Bertrand, A.

    2011-12-01

    and titanite in the foliation planes. The cataclasites are cemented by pervasive precipitation of K-feldspar plagues and idiomorphic, randomly oriented, epidote and chlorite. We conclude that the textures of these small displacement (< 500 mm) faults are controlled by brittle processes (fracture propagation and cataclastic comminution) similar to those reproduced in friction experiments performed on granite gouge (e.g., Beeler et al., 1996; Logan, 2007). Then progressively, stress driven fluid-rock reactions develop as fracturing and grain size reduction allows the kinetics of these reactions to be more efficient and fracture interconnection allows fluid infiltration. Healing of microfractures and fault rock cementation caused a rapid posteismic recovery of fault strength. References Beeler, N.M., Tullis, T.E., Blanpied, L., Weeks, J.D., 1996. Frictional behaviour of large displacement experimental faults. Journal of Geophysical Research 101, B4, 8697-8715. Logan, J.M., 2007. The progression from damage to localization of displacement observed in laboratory testing of porous rocks, in Lewis, H., and Couples, G.D. (eds.) The relationship between damage and localization. Geological Society of London Special Publication 289, 75-87.

  8. Quantitative comparisons of analogue models of brittle wedge dynamics

    NASA Astrophysics Data System (ADS)

    Schreurs, Guido

    2010-05-01

    Analogue model experiments are widely used to gain insights into the evolution of geological structures. In this study, we present a direct comparison of experimental results of 14 analogue modelling laboratories using prescribed set-ups. A quantitative analysis of the results will document the variability among models and will allow an appraisal of reproducibility and limits of interpretation. This has direct implications for comparisons between structures in analogue models and natural field examples. All laboratories used the same frictional analogue materials (quartz and corundum sand) and prescribed model-building techniques (sieving and levelling). Although each laboratory used its own experimental apparatus, the same type of self-adhesive foil was used to cover the base and all the walls of the experimental apparatus in order to guarantee identical boundary conditions (i.e. identical shear stresses at the base and walls). Three experimental set-ups using only brittle frictional materials were examined. In each of the three set-ups the model was shortened by a vertical wall, which moved with respect to the fixed base and the three remaining sidewalls. The minimum width of the model (dimension parallel to mobile wall) was also prescribed. In the first experimental set-up, a quartz sand wedge with a surface slope of ˜20° was pushed by a mobile wall. All models conformed to the critical taper theory, maintained a stable surface slope and did not show internal deformation. In the next two experimental set-ups, a horizontal sand pack consisting of alternating quartz sand and corundum sand layers was shortened from one side by the mobile wall. In one of the set-ups a thin rigid sheet covered part of the model base and was attached to the mobile wall (i.e. a basal velocity discontinuity distant from the mobile wall). In the other set-up a basal rigid sheet was absent and the basal velocity discontinuity was located at the mobile wall. In both types of experiments

  9. Software Innovation in a Mission Critical Environment

    NASA Technical Reports Server (NTRS)

    Fredrickson, Steven

    2015-01-01

    Operating in mission-critical environments requires trusted solutions, and the preference for "tried and true" approaches presents a potential barrier to infusing innovation into mission-critical systems. This presentation explores opportunities to overcome this barrier in the software domain. It outlines specific areas of innovation in software development achieved by the Johnson Space Center (JSC) Engineering Directorate in support of NASA's major human spaceflight programs, including International Space Station, Multi-Purpose Crew Vehicle (Orion), and Commercial Crew Programs. Software engineering teams at JSC work with hardware developers, mission planners, and system operators to integrate flight vehicles, habitats, robotics, and other spacecraft elements for genuinely mission critical applications. The innovations described, including the use of NASA Core Flight Software and its associated software tool chain, can lead to software that is more affordable, more reliable, better modelled, more flexible, more easily maintained, better tested, and enabling of automation.

  10. Space Station Software Issues

    NASA Technical Reports Server (NTRS)

    Voigt, S. (Editor); Beskenis, S. (Editor)

    1985-01-01

    Issues in the development of software for the Space Station are discussed. Software acquisition and management, software development environment, standards, information system support for software developers, and a future software advisory board are addressed.

  11. Brittle Rock Modeling Approach and its Validation Using Excavation-Induced Micro-Seismicity

    NASA Astrophysics Data System (ADS)

    Ma, Chun-Chi; Li, Tian-Bin; Xing, Hui-Lin; Zhang, Hang; Wang, Min-Jie; Liu, Tian-Yi; Chen, Guo-Qing; Chen, Zi-Quan

    2016-08-01

    With improvements to the bonded-particle model, a custom indicator of crack intensity is introduced to grade rock fractures accurately. Brittle fracturing of rock mass is studied using the bonded-particle model; here, "brittle" refers to the process where more energy is released towards making particles collide and disperse, and hence results in the quick emergence of "chain cracks". Certain principles concerning how to construct brittle rock are then proposed. Furthermore, a modeling approach for brittle rocks based on the adaptive continuum/discontinuum (AC/DC) method is proposed to aid the construction of large-scale models of tunnel excavations. To connect with actual tunneling conditions, fundamental mechanical properties, the mechanism for brittle fracturing, the joint distribution, and the initial stress field are considered in the modeling approach. Results from micro-seismic monitoring of a tunnel excavation confirmed the suitability of this modeling approach to simulate crack behavior, and results show that simulated cracking exhibit similar trends (evolution, location, and intensity) with micro-seismic cracking.

  12. Ultraprecision machining of micro-structured functional surfaces on brittle materials

    NASA Astrophysics Data System (ADS)

    Yu, D. P.; Wong, Y. S.; Hong, G. S.

    2011-09-01

    Ultraprecision micro-structured functional surfaces on hard and brittle materials, e.g. ceramic and glass, are gaining increasing application in a range of areas such as engineering optics and semiconductor and biomedical products. However, due to their tendency of being damaged in brittle fracture in machining, it is challenging to achieve both a high surface finish and complex surface shapes. In this paper, ultraprecision machining of micro-structured functional surfaces on brittle materials by fast tool servo diamond turning is studied. A machining model has been developed to ensure ductile regime machining of the brittle material, in which the material is removed by both plastic deformation and brittle fracture, but the cracks produced are prevented from being extended into the finished surface. Based on the model, an iterative numerical method has been proposed to predict the maximum feed rate for producing crack-free micro-structured surfaces. Machining experiments on typical micro-structured functional surfaces have been carried out to validate the effectiveness of the proposed method for producing ultraprecision micro-structured functional surfaces.

  13. Insensitivity of compaction properties of brittle granules to size enlargement by roller compaction.

    PubMed

    Wu, Sy-Juen; Sun, Changquan 'Calvin'

    2007-05-01

    Pharmaceutical granules prepared by roller compaction often exhibit significant loss of tabletability, that is, reduction in tensile strength, when compared to virgin powder. This may be attributed to granule size enlargement for highly plastic materials, for example, microcrystalline cellulose. The sensitivity of powder compaction properties on granule size variations impacts the robustness of the dry granulation process. We hypothesize that such sensitivity of compaction properties on granule size is minimum for brittle materials because extensive fracture of brittle granules during compaction minimizes differences in initial granule size. We tested the hypothesis using three common brittle excipients. Results show that the fine (44-106 microm), medium (106-250 microm), and coarse (250-500 microm) granules exhibit essentially identical tabletability below a certain critical compaction pressure, 100, 140, and 100 MPa for spray-dried lactose monohydrate, anhydrous dibasic calcium phosphate, and mannitol, respectively. Above respective critical pressure, tabletability lines diverge with smaller granules exhibiting slightly higher tablet tensile strength at identical compaction conditions. Overall, tabletability of brittle granules is insensitive to granule size enlargement. The results provide a scientific basis to the common practice of incorporating brittle filler to a typical tablet formulation processed by roller compaction granulation. PMID:17455348

  14. Rationally designed nanovehicles to overcome cancer chemoresistance.

    PubMed

    Livney, Yoav D; Assaraf, Yehuda G

    2013-11-01

    Drug resistance is a primary hindrance towards curative cancer chemotherapy. Nanotechnology holds great promise in establishing efficacious and innovative strategies to overcome chemoresistance, and markedly facilitate complementary treatments and cancer diagnostics. Various nanomedical devices are being introduced and evaluated, demonstrating encouraging results. While stealth liposomes serve as a benchmark, astonishing progress is witnessed in polymeric nanovehicles, sometimes combined with low molecular weight surfactants, some of which inhibit drug resistance in addition to solubilizing drugs. Cutting edge multifunctional or quadrugnostic nanoparticles currently developed offer simultaneous targeted delivery of chemotherapeutics and chemosensitizers or drug-resistance gene silencing cargo, along with diagnostic imaging agents, like metallic NPs. Viral and cellular components offer exciting new routes for cancer targeting and treatment. Targeting intracellular compartments is another challenging frontier spawning pioneering approaches and results. To further enhance rational design of nanomedicine for overcoming drug resistance, we review the latest thoughts and accomplishments in recent literature. PMID:23954781

  15. [Cancer immunotherapy. Importance of overcoming immune suppression].

    PubMed

    Malvicini, Mariana; Puchulo, Guillermo; Matar, Pablo; Mazzolini, Guillermo

    2010-01-01

    Increasing evidence indicates that the immune system is involved in the control of tumor progression. Effective antitumor immune response depends on the interaction between several components of the immune system, including antigen-presenting cells and different T cell subsets. However, tumor cells develop a number of mechanisms to escape recognition and elimination by the immune system. In this review we discuss these mechanisms and address possible therapeutic approaches to overcome the immune suppression generated by tumors. PMID:21163748

  16. Software management tools: Lessons learned from use

    NASA Technical Reports Server (NTRS)

    Reifer, D. J.; Valett, J.; Knight, J.; Wenneson, G.

    1985-01-01

    Experience in inserting software project planning tools into more than 100 projects producing mission critical software are discussed. The problems the software project manager faces are listed along with methods and tools available to handle them. Experience is reported with the Project Manager's Workstation (PMW) and the SoftCost-R cost estimating package. Finally, the results of a survey, which looked at what could be done in the future to overcome the problems experienced and build a set of truly useful tools, are presented.

  17. Software Engineering Approaches to Ontology Development

    NASA Astrophysics Data System (ADS)

    Gaševic, Dragan; Djuric, Dragan; Devedžic, Vladan

    Ontologies, as formal representations of domain knowledge, enable knowledge sharing between different knowledge-based applications. Diverse techniques originating from the field of artificial intelligence are aimed at facilitating ontology development. However, these techniques, although well known to AI experts, are typically unknown to a large population of software engineers. In order to overcome the gap between the knowledge of software engineering practitioners and AI techniques, a few proposals have been made suggesting the use of well-known software engineering techniques, such as UML, for ontology development (Cranefield 2001a).

  18. Sometimes two arms are enough--an unusual life-stage in brittle stars (Echinodermata: Ophiuroidea).

    PubMed

    Stöhr, Sabine; Alme, Øydis

    2015-01-01

    Off West Africa (Angola-Morocco), benthos samples were collected in the years 2005-2012. These contained 124 specimens of brittle stars with two long arms and three extremely short or absent arms and an elongated, narrow disc. These unusual brittle stars, as well as 33 specimens with five fully developed arms, were identified as Amphiura ungulata. The specimens with unequal arms were juvenile stages, whereas adults had five equal arms. The large number of specimens with unequal arms suggests that this condition is not the result of damage and regeneration, but a normal growth pattern in this species. This study documents the morphology by SEM, amends the species description, and discusses possible explanations for the evolution of this condition. Although brittle star species with unequal arm growth have been reported, this is an extreme case that was unknown before this study. PMID:26250282

  19. ADOLESCENT ROMANCE AND DELINQUENCY: A FURTHER EXPLORATION OF HIRSCHI'S "COLD AND BRITTLE" RELATIONSHIPS HYPOTHESIS.

    PubMed

    Giordano, Peggy C; Lonardo, Robert A; Manning, Wendy D; Longmore, Monica A

    2010-11-28

    Hirschi argued that delinquent youth tend to form relatively "cold and brittle" relationships with peers, depicting these youths as deficient in their attachments to others. The current analysis explores connections between delinquency and the character of adolescent romantic ties, drawing primarily on the first wave of the Toledo Adolescent Relationships Study, and focusing on 957 teens with dating experience. We examine multiple relationship qualities/dynamics in order to explore both the "cold" and "brittle" dimensions of Hirschi's hypothesis. Regarding the "cold" assumption, results suggest that delinquency is not related to perceived importance of the romantic relationship, level of intimate self-disclosure or feelings of romantic love, and more delinquent youth actually report more frequent contact with their romantic partners. Analyses focused on two dimensions tapping the "brittle" description indicate that while durations of a focal relationship do not differ according to level of respondent delinquency, more delinquent youths report higher levels of verbal conflict. PMID:21423845

  20. Analytical model of brittle destruction based on hypothesis of scale similarity

    SciTech Connect

    Arakcheev, A. S. Lotov, K. V.

    2012-08-15

    The size distribution of dust particles in thermonuclear (fusion) devices is closely described by a power law, which may be related to the brittle destruction of materials. The hypothesis of scale similarity leads to the conclusion that the size distribution of particles formed as a result of a brittle destruction is described by a power law with the exponent -{alpha} that can range from -4 to -1. The model of brittle destruction is described in terms of the fractal geometry, and the distribution exponent is expressed via the fractal dimension of packing. Under additional assumptions, it is possible to refine the {alpha} value and, vice versa, to determine the type of destruction using the measured size distribution of particles.

  1. Simulation study on the avalanche process of the mixed brittle-plastic fiber bundle model

    NASA Astrophysics Data System (ADS)

    Hao, Da-Peng; Tang, Gang; Xun, Zhi-Peng; Xia, Hui; Han, Kui

    2016-01-01

    The mixed brittle-plastic fiber bundle model is an extension model based on the classical fiber bundle model to describe the nonbrittle failure process of some hierarchical structure materials such as spider silk. In order to explore the breaking dynamic properties of the hierarchical structure materials in short-range correlation, the mixed brittle-plastic fiber bundle model in local load sharing condition is detailed and numerically studied. The impacts of the proportion of plastic fibers and the plastic strength of a single plastic fiber on the macroscopic constitutive behavior, the avalanche size distribution and the step number of the external load increasing are investigated, respectively. The numerical results show that the insert of plastic fibers will hinder the brittle fracture process; as a result, both the macroscopic mechanical natures and the statistical properties of fracture are significantly influenced.

  2. Possible transient creep events in a brittle-ductile continental crust: observations, experiments and potential models.

    NASA Astrophysics Data System (ADS)

    Lavier, Luc

    2016-04-01

    In a given tectonic province and over thousands to millions of years, slip on faults is believed to be constant and approximately equal to the local tectonic rate in agreement with rigid plate tectonic theory. In this model the ductile lower crust flows in response to this steady plate motion. Moreover brittle and ductile behaviors interact only at a sharp boundary defined as the brittle ductile transition (BDT). However in the continental lithosphere brittle and ductile behavior may coexist over a large range of pressure and temperature conditions for different mineral compositions. This generates heterogeneities in the brittle and ductile crust that are often ignored in models of shear zones. We hypothesize that the interaction between brittle (elastic) and ductile (viscous) behavior may cause deviations from steady-state slip and generates transient creep events on shear zones that release many meters of creep over years to thousands of years marked by a single period of tectonic activity followed by quiescence. We present a set of numerical and analytical models, analogue experiments as well as some observations in nature that may support this hypothesis. In this presentation we extend an analytic formulation to model creep events within shear zones at the transition between brittle and ductile behavior in the crust. We assume that creep events are triggered by a set of interconnected fractures modeled as propagating dislocations. The amount of connectivity controls the nature and the intensity of the transient creep events. The shear zone behaves as a forced damped oscillator that can release strain accumulated during jammed/locked periods. The creep can be over-, critically-, or under-damped. The time scale of the events may vary between seconds to thousands of years depending on the viscous, elastic and plastic (fractures) properties of the shear zone.

  3. Influence of Composition and Deformation Conditions on the Strength and Brittleness of Shale Rock

    NASA Astrophysics Data System (ADS)

    Rybacki, E.; Reinicke, A.; Meier, T.; Makasi, M.; Dresen, G. H.

    2015-12-01

    Stimulation of shale gas reservoirs by hydraulic fracturing operations aims to increase the production rate by increasing the rock surface connected to the borehole. Prospective shales are often believed to display high strength and brittleness to decrease the breakdown pressure required to (re-) initiate a fracture as well as slow healing of natural and hydraulically induced fractures to increase the lifetime of the fracture network. Laboratory deformation tests were performed on several, mainly European black shales with different mineralogical composition, porosity and maturity at ambient and elevated pressures and temperatures. Mechanical properties such as compressive strength and elastic moduli strongly depend on shale composition, porosity, water content, structural anisotropy, and on pressure (P) and temperature (T) conditions, but less on strain rate. We observed a transition from brittle to semibrittle deformation at high P-T conditions, in particular for high porosity shales. At given P-T conditions, the variation of compressive strength and Young's modulus with composition can be roughly estimated from the volumetric proportion of all components including organic matter and pores. We determined also brittleness index values based on pre-failure deformation behavior, Young's modulus and bulk composition. At low P-T conditions, where samples showed pronounced post-failure weakening, brittleness may be empirically estimated from bulk composition or Young's modulus. Similar to strength, at given P-T conditions, brittleness depends on the fraction of all components and not the amount of a specific component, e.g. clays, alone. Beside strength and brittleness, knowledge of the long term creep properties of shales is required to estimate in-situ stress anisotropy and the healing of (propped) hydraulic fractures.

  4. The Potential of Brittle Star Extracted Polysaccharide in Promoting Apoptosis via Intrinsic Signaling Pathway

    PubMed Central

    Baharara, Javad; Amini, Elaheh

    2015-01-01

    Background: Anti-cancer potential of marine natural products such as polysaccharides represented therapeutic potential in oncological researches. In this study, total polysaccharide from brittle star [Ophiocoma erinaceus (O. erinaceus)] was extracted and chemopreventive efficacy of Persian Gulf brittle star polysaccharide was investigated in HeLa human cervical cancer cells. Methods: To extract polysaccharide, dried brittle stars were ground and extracted mechanically. Then, detection of polysaccharide was performed by phenol sulfuric acid, Ultra Violet (UV)-sulfuric acid method and FTIR. The anti proliferative activity of isolated polysaccharide was examined by MTT assay and evaluation of cell death was done through morphological cell changes; Propodium Iodide staining, fluorescence microscopy and caspase-3, -9 enzymatic measurements. To assess its underlying mechanism, expression of Bax, Bcl-2 was evaluated. Results: The polysaccharide detection methods demonstrated isolation of crude polysaccharide from Persian Gulf brittle star. The results revealed that O. erinaceus polysaccharide suppressed the proliferation of HeLa cells in a dose and time dependent manner. Morphological observation of DAPI and Acridine Orange/Propodium Iodide staining was documented by typical characteristics of apoptotic cell death. Flow cytometry analyses exhibited the accumulation of treated cells in sub-G1 region. Additionally, polysaccharide extracted induced intrinsic apoptosis via up-regulation of caspase-3, caspase-9 and Bax along with down-regulation of Bcl-2 in HeLa cells. Conclusion: Taken together, the apoptosis inducing effect of brittle star polysaccharide via intrinsic pathway confirmed the anti tumor potential of marine polysaccharide. Therefore, these findings proposed new insight into anti cancer properties of brittle star polysaccharide as a promising agent in cervical cancer treatment. PMID:26605009

  5. Prediction of Brittle Failure for TBM Tunnels in Anisotropic Rock: A Case Study from Northern Norway

    NASA Astrophysics Data System (ADS)

    Dammyr, Øyvind

    2016-06-01

    Prediction of spalling and rock burst is especially important for hard rock TBM tunneling, because failure can have larger impact than in a drill and blast tunnel and ultimately threaten excavation feasibility. The majority of research on brittle failure has focused on rock types with isotropic behavior. This paper gives a review of existing theory and its application before a 3.5-m-diameter TBM tunnel in foliated granitic gneiss is used as a case to study brittle failure characteristics of anisotropic rock. Important aspects that should be considered in order to predict brittle failure in anisotropic rock are highlighted. Foliation is responsible for considerable strength anisotropy and is believed to influence the preferred side of v-shaped notch development in the investigated tunnel. Prediction methods such as the semi- empirical criterion, the Hoek- Brown brittle parameters, and the non-linear damage initiation and spalling limit method give reliable results; but only as long as the angle between compression axis and foliation in uniaxial compressive tests is relevant, dependent on the relation between tunnel trend/plunge, strike/dip of foliation, and tunnel boundary stresses. It is further demonstrated that local in situ stress variations, for example, due to the presence of discontinuities, can have profound impact on failure predictions. Other carefully documented case studies into the brittle failure nature of rock, in particular anisotropic rock, are encouraged in order to expand the existing and relatively small database. This will be valuable for future TBM planning and construction stages in highly stressed brittle anisotropic rock.

  6. How melt stretching affect the brittle-ductile transition temperature of polymer glasses

    NASA Astrophysics Data System (ADS)

    Cheng, Shiwang; Wang, Shi-Qing

    2013-03-01

    Upon increasing temperature a brittle polymer glass can turn ductile. PMMA is a good example. For a while this brittle-ductile transition (BDT) was thought to be determined by the emergence of a secondary relaxation....1-3 On the other hand, it has been known for a long time...4-6 that predeformation in the melt state (e.g., melt stretching) can also make brittle glasses behave in a ductile manner. This transformation has recently received a satisfactory explanation based on a picture of structural hybrid for polymer glasses....7 It appears that BDT is dictated by the relative mechanical characteristics of the primary structure (due to the van der Waals bonds) and the chain network. The present work, based on conventional Instron tensile extension tests and DMA tests, shows that melt stretching does not alter the secondary relaxation behavior of PMMA and PC yet can turn them the brittle PMMA ductile and the ductile PC brittle. Moreover, sufficient melt stretching makes the brittle PS ductile although it does not produce any secondary relaxation process..1. Monnerie, L.; Laupretre, F.; Halary, J. L. Adv. Polym. Sci2005, 187, 35-213. 2. Monnerie, L.; Halary, J. L.; Kausch, H. Adv. Polym. Sci2005, 187, 215-364. 3. Wu, S. J. Appl. Polym. Sci.1992, 46, (4), 619-624. 4. Vincent, P. I. Polymer1960, 1, (0), 425-444. 5. Harris, J. S.; Ward, I. M. J. Mater. Sci.1970, 5, (7), 573-579. 6. Ender, D. H.; Andrews, R. D. J. Appl. Phys.1965, 36, (10), 3057-3062. 7. Zartman, G. D.; Cheng, S.; Li, X.; Lin, F.; Becker, M. L.; Wang, S.-Q. Macromolecules2012, 45, (16), 6719-6732.

  7. Apparatus for measuring internal friction Q factors in brittle materials. [applied to lunar samples

    NASA Technical Reports Server (NTRS)

    Tittmann, B. R.; Curnow, J. M.

    1976-01-01

    A flexural analog of the torsion pendulum for measuring the Young's modulus and the internal friction Q factor of brittle materials has been developed for Q greater than 10 to the 3rd measurements at a zero static stress and at 10 to the -7th strains of brittle materials in the Hz frequency range. The present design was motivated by the desire to measure Q in fragile lunar return samples at zero static stress to shed light on the anomalously low attenuation of seismic waves on the moon. The use of the apparatus is demonstrated with data on fused silica and on a terrestrial analog of lunar basalt.

  8. Micromechanics-Based Permeability Evolution in Brittle Materials at High Strain Rates

    NASA Astrophysics Data System (ADS)

    Perol, Thibaut; Bhat, Harsha S.

    2016-08-01

    We develop a micromechanics-based permeability evolution model for brittle materials at high strain rates (≥ 100 s^{-1}). Extending for undrained deformation the mechanical constitutive description of brittle solids, whose constitutive response is governed by micro-cracks, we now relate the damage-induced strains to micro-crack aperture. We then use an existing permeability model to evaluate the permeability evolution. This model predicts both the percolative and connected regime of permeability evolution of Westerly Granite during triaxial loading at high strain rate. This model can simulate pore pressure history during earthquake coseismic dynamic ruptures under undrained conditions.

  9. Analysis Software

    NASA Technical Reports Server (NTRS)

    1994-01-01

    General Purpose Boundary Element Solution Technology (GPBEST) software employs the boundary element method of mechanical engineering analysis, as opposed to finite element. It is, according to one of its developers, 10 times faster in data preparation and more accurate than other methods. Its use results in less expensive products because the time between design and manufacturing is shortened. A commercial derivative of a NASA-developed computer code, it is marketed by Best Corporation to solve problems in stress analysis, heat transfer, fluid analysis and yielding and cracking of solids. Other applications include designing tractor and auto parts, household appliances and acoustic analysis.

  10. Seminar Software

    NASA Technical Reports Server (NTRS)

    1993-01-01

    The Society for Computer Simulation International is a professional technical society that distributes information on methodology techniques and uses of computer simulation. The society uses NETS, a NASA-developed program, to assist seminar participants in learning to use neural networks for computer simulation. NETS is a software system modeled after the human brain; it is designed to help scientists exploring artificial intelligence to solve pattern matching problems. Examples from NETS are presented to seminar participants, who can then manipulate, alter or enhance them for their own applications.

  11. Simulation Software

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Various NASA Small Business Innovation Research grants from Marshall Space Flight Center, Langley Research Center and Ames Research Center were used to develop the 'kernel' of COMCO's modeling and simulation software, the PHLEX finite element code. NASA needed it to model designs of flight vehicles; one of many customized commercial applications is UNISIM, a PHLEX-based code for analyzing underground flows in oil reservoirs for Texaco, Inc. COMCO's products simulate a computational mechanics problem, estimate the solution's error and produce the optimal hp-adapted mesh for the accuracy the user chooses. The system is also used as a research or training tool in universities and in mechanical design in industrial corporations.

  12. Software Surrogate

    NASA Technical Reports Server (NTRS)

    1999-01-01

    In 1994, Blackboard Technology received a NASA Phase I SBIR award entitled "A Blackboard-Based Framework for Mixed-Initiative, Crewed- Space-System Applications." This research continued in Phase II at JSC, where a generic architecture was developed in which a software surrogate serves as the operator's representative in the fast-paced realm of nearly autonomous, intelligent systems. This SBIR research effort addressed the need to support human-operator monitoring and intervention with intelligent systems such as those being developed for NASA's crewed space program.

  13. Software system safety

    NASA Technical Reports Server (NTRS)

    Uber, James G.

    1988-01-01

    Software itself is not hazardous, but since software and hardware share common interfaces there is an opportunity for software to create hazards. Further, these software systems are complex, and proven methods for the design, analysis, and measurement of software safety are not yet available. Some past software failures, future NASA software trends, software engineering methods, and tools and techniques for various software safety analyses are reviewed. Recommendations to NASA are made based on this review.

  14. Complex brittle deformation pattern along the Southern Patagonian Andes (Argentina)

    NASA Astrophysics Data System (ADS)

    Barberón, Vanesa; Sue, Christian; Ronda, Gonzalo; Ghiglione, Matías

    2016-04-01

    The Southern Patagonian Andes is located in the southern extreme of the Pacific subduction zone, where the Antartic oceanic plate sinks underneath South America. The history of the area begins with compression during Paleozoic, Jurassic extension associated to the rift and opening of the South Atlantic Ocean, then a sag stage in the Lower Cretaceous followed by a foreland phase as a result of plate tectonics (Ghiglione et al., 2016). The kinematic study is concentrated in the Argentinean foothills, between 46°40' and 48° SL. We measured around 800 fault planes and their striaes with the sense of movement in order to characterize the stress field. The software used to make the stress inversion were Tensor (Delvaux, 2011) and Multiple Inverse Method MIM (Yamaji et al., 2011). The stress field map was built with the results of the MIM. We present new data from 48 sites located in the northern sector of the Southern Patagonian Andes. The measurements were made in several rocks from Paleozoic to Lower Cretaceous, even though most were taken in pyroclastic jurassic rocks from El Quemado Complex. Paleostress tensors obtained are mostly strike-slip, although a 25% is normal and there are a few compresional. The pattern of faults found is complex. In some sites the tensor can be locally linked to satellite images and observations from the field or be related to a major thrust front. There is no clear correlation between the age and/or lithology with the tensor since the youngest rocks measured are Lower Cretaceous. Probably there are several generations of family faults connected to different and recent tectonic phases then the paleostress tensors might correspond to the latest tectonic events.

  15. Overcoming Challenges in Engineering the Genetic Code.

    PubMed

    Lajoie, M J; Söll, D; Church, G M

    2016-02-27

    Withstanding 3.5 billion years of genetic drift, the canonical genetic code remains such a fundamental foundation for the complexity of life that it is highly conserved across all three phylogenetic domains. Genome engineering technologies are now making it possible to rationally change the genetic code, offering resistance to viruses, genetic isolation from horizontal gene transfer, and prevention of environmental escape by genetically modified organisms. We discuss the biochemical, genetic, and technological challenges that must be overcome in order to engineer the genetic code. PMID:26348789

  16. Overcoming Scalability Challenges for Tool Daemon Launching

    SciTech Connect

    Ahn, D H; Arnold, D C; de Supinski, B R; Lee, G L; Miller, B P; Schulz, M

    2008-02-15

    Many tools that target parallel and distributed environments must co-locate a set of daemons with the distributed processes of the target application. However, efficient and portable deployment of these daemons on large scale systems is an unsolved problem. We overcome this gap with LaunchMON, a scalable, robust, portable, secure, and general purpose infrastructure for launching tool daemons. Its API allows tool builders to identify all processes of a target job, launch daemons on the relevant nodes and control daemon interaction. Our results show that Launch-MON scales to very large daemon counts and substantially enhances performance over existing ad hoc mechanisms.

  17. Bacterial strategies to overcome insect defences.

    PubMed

    Vallet-Gely, Isabelle; Lemaitre, Bruno; Boccard, Frédéric

    2008-04-01

    Recent genetic and molecular analyses have revealed how several strategies enable bacteria to persist and overcome insect immune defences. Genetic and genomic tools that can be used with Drosophila melanogaster have enabled the characterization of the pathways that are used by insects to detect bacterial invaders and combat infection. Conservation of bacterial virulence factors and insect immune repertoires indicates that there are common strategies of host invasion and pathogen eradication. Long-term interactions of bacteria with insects might ensure efficient dissemination of pathogens to other hosts, including humans. PMID:18327270

  18. Machine Condition Monitoring Software Agent Using JADE and Data Mining

    NASA Astrophysics Data System (ADS)

    Anandan, R.

    2015-03-01

    In recent days there is a huge demand to increase the production of any mechanical components without any disturbance or mechanical faults in the machine. Therefore, to increase the productivity, it is necessary to monitor the running machine at regular intervals. To overcome such difficulties, a new machine condition monitoring software is designed using the multi agent software. This software is designed using the JADE framework and the data are analyzed using free open source Weka explorer for statistical calculations.

  19. CARES/Life Software for Designing More Reliable Ceramic Parts

    NASA Technical Reports Server (NTRS)

    Nemeth, Noel N.; Powers, Lynn M.; Baker, Eric H.

    1997-01-01

    Products made from advanced ceramics show great promise for revolutionizing aerospace and terrestrial propulsion, and power generation. However, ceramic components are difficult to design because brittle materials in general have widely varying strength values. The CAPES/Life software eases this task by providing a tool to optimize the design and manufacture of brittle material components using probabilistic reliability analysis techniques. Probabilistic component design involves predicting the probability of failure for a thermomechanically loaded component from specimen rupture data. Typically, these experiments are performed using many simple geometry flexural or tensile test specimens. A static, dynamic, or cyclic load is applied to each specimen until fracture. Statistical strength and SCG (fatigue) parameters are then determined from these data. Using these parameters and the results obtained from a finite element analysis, the time-dependent reliability for a complex component geometry and loading is then predicted. Appropriate design changes are made until an acceptable probability of failure has been reached.

  20. Balanced-activity improved inverse emulsion to inhibit brittle lutite hydration in oil fields

    SciTech Connect

    Olmedo, E. P.; de J. Hernandez Alvarez, R.; Barrera, C. D.; Ramos, J. D. G.

    1984-10-02

    An improved inverse emulsion for use as a drilling fluid that inhibits brittle lutite hydration. The emulsion includes a heavy oil; brine; a viscosity agent with thermostabilizing properties; an emulsifying agent; a thickening agent; a gelatinizing additive; and an alkaline earth metal hydroxide. The emulsion avoids hole collapsing and improves well gage stability.

  1. The effect of crack instability/stability on fracture toughness of brittle materials

    SciTech Connect

    Baratta, F.I.

    1997-12-31

    This paper summarizes three recent experimental works coauthored by the present author regarding the effect of crack instability/stability on fracture toughness, and also includes the necessary formulae for predicting stability. Two recent works have shown that unstable crack extension resulted in apparent increases in fracture toughness compared to that determined during stable crack growth. In the first investigation a quasi-brittle polymer, polymethylmethacrylate, was examined. In the second, a more brittle metallic material, tungsten, was tested. In both cases the transition from unstable to stable behavior was predicted based on stability analyses. The third investigation was conducted on a truly brittle ceramic material, hot pressed silicon nitride. These three papers showed that fracture toughness test results conducted on brittle materials vary according to whether the material fractures in an unstable or stable manner. Suggestions for achieving this important yet difficult phenomenon of stable crack growth, which is necessary when determining the fracture toughness variation occurring during unstable/stable crack advance, are presented, as well as recommendations for further research.

  2. Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

    NASA Astrophysics Data System (ADS)

    Wang, Minghai; Wang, Hujun; Liu, Zhonghai

    2010-12-01

    Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

  3. Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

    NASA Astrophysics Data System (ADS)

    Wang, Minghai; Wang, Hujun; Liu, Zhonghai

    2011-05-01

    Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

  4. A hybrid QM-MD method to study brittle fracture in vitreous silica

    NASA Astrophysics Data System (ADS)

    Muralidharan, Krishna; Deymier, Pierre; Simmons, Joseph; Taylor, Carlos; Runge, Keith; Rozyczko, Piotr

    2003-03-01

    Fracture in brittle materials under a macroscopic load, results from the propagation of atomic-scale defects/cracks under the influence of a local stress field. Specifically, the bulk fracture characteristics of a brittle material are controlled by breaking of bonds at the atomic level. Thus in order to study brittle fracture, one has to model the physics' of bond breaking very accurately. Vitreous silica is an ideal' brittle fracture material and previous MD simulations using classical potentials have indicated that failure of the glass was a result of a gradual growth and coalescence of large voids (a virtual crack) during the strain application due to the thermal vibrations of atoms. In our work, we improve on previous work by using ab-initio methods (MNDO) to model the interatomic interactions in critical regions (corresponding to regions of void coalescence) and the classical BKS' potential to model interactions in the other regions. The method of wavelets is used to identify and characterize these regions in the preliminary stages of fracture.

  5. Unsteady Crack Motion and Branching in a Phase-Field Model of Brittle Fracture

    NASA Astrophysics Data System (ADS)

    Karma, Alain; Lobkovsky, Alexander E.

    2004-06-01

    Crack propagation is studied numerically using a continuum phase-field approach to modeIII brittle fracture. The results shed light on the physics that controls the speed of accelerating cracks and the characteristic branching instability at a fraction of the wave speed.

  6. A statistical, micromechanical theory of the compressive strength of brittle materials

    NASA Technical Reports Server (NTRS)

    Adams, M.; Sines, G.

    1978-01-01

    A general theory of the compressive strength of brittle materials is presented. This theory proposes that failure is brought about by structural weakening from accumulated crack damage which increases with the stress level. The statistics of the flaw distribution and the mechanism of crack initiation and extension are important. A sample calculation using the theory is given to demonstrate its application

  7. Seismic Rheological Model and Reflection Coefficients of the Brittle-Ductile Transition

    NASA Astrophysics Data System (ADS)

    Carcione, José M.; Poletto, Flavio

    2013-12-01

    It is well established that the upper—cooler—part of the crust is brittle, while deeper zones present ductile behaviour. In some cases, this brittle-ductile transition is a single seismic reflector with an associated reflection coefficient. We first develop a stress-strain relation including the effects of crust anisotropy, seismic attenuation and ductility in which deformation takes place by shear plastic flow. Viscoelastic anisotropy is based on the eigenstrain model and the Zener and Burgers mechanical models are used to model the effects of seismic attenuation, velocity dispersion, and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the reflection and transmission coefficients of a single brittle-ductile interface and of a ductile thin layer. The PP scattering coefficient has a Brewster angle (a sign change) in both cases, and there is substantial PS conversion at intermediate angles. The PP coefficient is sensitive to the layer thickness, unlike the SS coefficient. Thick layers have a well-defined Brewster angle and show higher reflection amplitudes. Finally, we compute synthetic seismograms in a homogeneous medium as a function of temperature.

  8. Brittle fracture phase-field modeling of a short-rod specimen

    SciTech Connect

    Escobar, Ivana; Tupek, Michael R.; Bishop, Joseph E.

    2015-09-01

    Predictive simulation capabilities for modeling fracture evolution provide further insight into quantities of interest in comparison to experimental testing. Based on the variational approach to fracture, the advent of phase-field modeling achieves the goal to robustly model fracture for brittle materials and captures complex crack topologies in three dimensions.

  9. Award-Winning CARES/Life Ceramics Durability Evaluation Software Is Making Advanced Technology Accessible

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Products made from advanced ceramics show great promise for revolutionizing aerospace and terrestrial propulsion and power generation. However, ceramic components are difficult to design because brittle materials in general have widely varying strength values. The CARES/Life software developed at the NASA Lewis Research Center eases this by providing a tool that uses probabilistic reliability analysis techniques to optimize the design and manufacture of brittle material components. CARES/Life is an integrated package that predicts the probability of a monolithic ceramic component's failure as a function of its time in service. It couples commercial finite element programs--which resolve a component's temperature and stress distribution - with reliability evaluation and fracture mechanics routines for modeling strength - limiting defects. These routines are based on calculations of the probabilistic nature of the brittle material's strength.

  10. Sandia software guidelines: Software quality planning

    SciTech Connect

    Not Available

    1987-08-01

    This volume is one in a series of Sandia Software Guidelines intended for use in producing quality software within Sandia National Laboratories. In consonance with the IEEE Standard for Software Quality Assurance Plans, this volume identifies procedures to follow in producing a Software Quality Assurance Plan for an organization or a project, and provides an example project SQA plan. 2 figs., 4 tabs.

  11. Brittle creep and subcritical crack propagation in glass submitted to triaxial conditions

    NASA Astrophysics Data System (ADS)

    Mallet, Céline; Fortin, Jérôme; Guéguen, Yves; Bouyer, Frédéric

    2015-02-01

    An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle creep conditions. Brittle creep may be an important slow deformation process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle creep due to slow crack-propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. Creep tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential-stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during creep. The effect of temperature on creep was investigated from ambient temperature to 70°C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary creep, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emission activity associated with crack growth. As a consequence, slow crack growth has been evidenced in glass. Beyond secondary creep, failure in tertiary creep was found to be a progressive process. The data are interpreted through a previously developed micromechanical damage model that describes crack propagation. This model allows one to predict the secondary brittle creep phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle creep behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.

  12. How does tooth cusp radius of curvature affect brittle food item processing?

    PubMed Central

    Berthaume, Michael A.; Dumont, Elizabeth R.; Godfrey, Laurie R.; Grosse, Ian R.

    2013-01-01

    Tooth cusp sharpness, measured by radius of curvature (RoC), has been predicted to play a significant role in brittle/hard food item fracture. Here, we set out to test three existing hypotheses about this relationship: namely, the Blunt and Strong Cusp hypotheses, which predict that dull cusps will be most efficient at brittle food item fracture, and the Pointed Cusp hypothesis, which predicts that sharp cusps will be most efficient at brittle food item fracture using a four cusp bunodont molar. We also put forth and test the newly constructed Complex Cusp hypothesis, which predicts that a mixture of dull and sharp cusps will be most efficient at brittle food item fracture. We tested the four hypotheses using finite-element models of four cusped, bunodont molars. When testing the three existing hypotheses, we assumed all cusps had the same level of sharpness (RoC), and gained partial support for the Blunt Cusp hypotheses. We found no support for the Pointed Cusp or Strong Cusp hypotheses. We used the Taguchi sampling method to test the Complex Cusps hypothesis with a morphospace created by independently varying the radii of curvature of the four cusps in the buccolingual and mesiodistal directions. The optimal occlusal morphology for fracturing brittle food items consists of a combination of sharp and dull cusps, which creates high stress concentrations in the food item while stabilizing the food item and keeping the stress concentrations in the enamel low. This model performed better than the Blunt Cusp hypothesis, suggesting a role for optimality in the evolution of cusp form. PMID:23635495

  13. Role of fluid overpressures in crustal strength and the form of the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Suppe, J.

    2014-12-01

    The classic crustal strength-depth model of Brace and Kolhstedt (1980) (see figure) based on experimental rock mechanics depends in the brittle regime on the critical assumption of linearly increasing hydrostatic pore-fluid pressures. This leads to a predicted linearly increasing brittle strength that is well established based on deep borehole stress measurements in crystalline crust. In contrast, fluid overpressures are widely documented in orogenic belts based on borehole data, seismic velocity analysis and analysis of veins, in some cases showing complex fault-valve pressure fluctuations between lithostatic and hydrostatic. Typical observed overpressure-depth relationships predict a brittle crustal strength that is approximately constant with depth in contrast with the classic model. This constant-strength behavior below the fluid-retention depth (ZFRD in figure) has been confirmed using deep borehole stress and fluid-pressure measurements (Suppe, 2014). Recent ductile-plastic modeling of disequilibrium compaction suggests that pressure solution promotes further increases in overpressure and weakening, promoting a very prolonged low-strength brittle-ductile transition. Overpressured conditions can be inferred to exist over a substantial fraction of crustal thickness, spanning the brittle-ductile transition, in several tectonic environments, most straightforwardly in shale-rich clastic sedimentary basins built to sea level on oceanic or highly thinned continental crust such as the US Gulf Coast and Niger Delta. These thick accumulations commonly deform into shale-rich plate boundary mountain belts (e.g. Bangladesh/Miyanmar, Makran, Trinidad/Barbados, Gulf of Alaska, southern Taiwan and New Zealand). There is deep geophysical evidence for near lithostatic pore-fluid pressures existing to depths of 20-30km based on Vp, Vs, Vp/Vs and Q observations. We present active examples from Taiwan and New Zealand, combining borehole data and seismic tomography.

  14. Rock Physics Model and Brittleness Index Calculation for Shale Gas Study in Jambi Basin, Indonesia

    NASA Astrophysics Data System (ADS)

    Fatkhan, Fatkhan; Fauzi, Inusa P.; Sule, Rachmat; Usman, Alfian

    2014-05-01

    Research about shale gas is often conducted in oil and gas industries since the demand of energy supply has increased recently. Indonesia is newly interested on researching, exploring and even producing shale gas. To seek prospects of shale gas play in an area, one needs to look into some of characteristics. This paper describes about rock physics model that is used to investigate a prospect zone of shale gas play by looking into percentage of TOC and brittleness index. Method used to modeling rock physics are as follows, first Hashin-Shtrikman bound is employed to estimate percentage of minerals, then inclusions are modeled by Kuster-Toksoz method and finally kerogens are calculated by Ciz and Shapiro's model. In addition, we compared between inclusion saturated by kerogen and water and inclusion filled up by only kerogen. Modulus Young is used to estimate brittleness index. Then in order to map and delineate brittle area, simultaneous seismic inversion method using pre stack data is employed to generate volume of P-wave, S-wave and density. Finally, these volumes are used to calculate Modulus Young value. Since the area of study has a very thick shale then the area is divided into four zones based on modulus shear and bulk values. The rock physics model shows that there are two zones having quartz-rich mineral and the inclusion saturated by water and kerogen. More over Modulus Young calculations show there are two zones having high values or more than 50%. The rock physics model can be used for predicting mineralogy leading into zones of prospect brittle shale. These zones are then correlated with brittleness index calculations. In addition, results show that the study area has a shale gas prospect for further exploration.

  15. Office Computer Software: A Comprehensive Review of Software Programs.

    ERIC Educational Resources Information Center

    Secretary, 1992

    1992-01-01

    Describes types of software including system software, application software, spreadsheets, accounting software, graphics packages, desktop publishing software, database, desktop and personal information management software, project and records management software, groupware, and shareware. (JOW)

  16. T7 replisome directly overcomes DNA damage

    PubMed Central

    Sun, Bo; Pandey, Manjula; Inman, James T.; Yang, Yi; Kashlev, Mikhail; Patel, Smita S.; Wang, Michelle D.

    2015-01-01

    Cells and viruses possess several known ‘restart' pathways to overcome lesions during DNA replication. However, these ‘bypass' pathways leave a gap in replicated DNA or require recruitment of accessory proteins, resulting in significant delays to fork movement or even cell division arrest. Using single-molecule and ensemble methods, we demonstrate that the bacteriophage T7 replisome is able to directly replicate through a leading-strand cyclobutane pyrimidine dimer (CPD) lesion. We show that when a replisome encounters the lesion, a substantial fraction of DNA polymerase (DNAP) and helicase stay together at the lesion, the replisome does not dissociate and the helicase does not move forward on its own. The DNAP is able to directly replicate through the lesion by working in conjunction with helicase through specific helicase–DNAP interactions. These observations suggest that the T7 replisome is fundamentally permissive of DNA lesions via pathways that do not require fork adjustment or replisome reassembly. PMID:26675048

  17. T7 replisome directly overcomes DNA damage

    NASA Astrophysics Data System (ADS)

    Sun, Bo; Pandey, Manjula; Inman, James T.; Yang, Yi; Kashlev, Mikhail; Patel, Smita S.; Wang, Michelle D.

    2015-12-01

    Cells and viruses possess several known `restart' pathways to overcome lesions during DNA replication. However, these `bypass' pathways leave a gap in replicated DNA or require recruitment of accessory proteins, resulting in significant delays to fork movement or even cell division arrest. Using single-molecule and ensemble methods, we demonstrate that the bacteriophage T7 replisome is able to directly replicate through a leading-strand cyclobutane pyrimidine dimer (CPD) lesion. We show that when a replisome encounters the lesion, a substantial fraction of DNA polymerase (DNAP) and helicase stay together at the lesion, the replisome does not dissociate and the helicase does not move forward on its own. The DNAP is able to directly replicate through the lesion by working in conjunction with helicase through specific helicase-DNAP interactions. These observations suggest that the T7 replisome is fundamentally permissive of DNA lesions via pathways that do not require fork adjustment or replisome reassembly.

  18. Overcoming the effects of intentional forgetting.

    PubMed

    Lehman, Melissa; Malmberg, Kenneth J

    2011-02-01

    The long-term effects of the compartmentalization of task-irrelevant memories were investigated using a directed forgetting procedure. Many models tacitly assume the persistence of the costs and benefits of directed forgetting or otherwise fail to predict what factors might reduce or eliminate them. In contrast, a retrieving effectively from memory model (REM; Lehman & Malmberg, 2009) predicts that intentional forgetting should only be observed for free recall when temporal context is used to probe memory. By manipulating whether study lists were constructed from category exemplars or from a random set of words, and by either providing temporal or category cues at test, we tested the prediction. The effects of directed forgetting were eliminated when categorized lists were studied and category cues were provided. When categorized lists were used but category cues were not provided, the usual costs and benefits of directed forgetting were observed. These results specify the conditions under which the consequences of intentional forgetting can be overcome. PMID:21264615

  19. Innovative Strategies to Overcome Biofilm Resistance

    PubMed Central

    Taraszkiewicz, Aleksandra; Fila, Grzegorz; Grinholc, Mariusz; Nakonieczna, Joanna

    2013-01-01

    We review the recent literature concerning the efficiency of antimicrobial photodynamic inactivation toward various microbial species in planktonic and biofilm cultures. The review is mainly focused on biofilm-growing microrganisms because this form of growth poses a threat to chronically infected or immunocompromised patients and is difficult to eradicate from medical devices. We discuss the biofilm formation process and mechanisms of its increased resistance to various antimicrobials. We present, based on data in the literature, strategies for overcoming the problem of biofilm resistance. Factors that have potential for use in increasing the efficiency of the killing of biofilm-forming bacteria include plant extracts, enzymes that disturb the biofilm structure, and other nonenzymatic molecules. We propose combining antimicrobial photodynamic therapy with various antimicrobial and antibiofilm approaches to obtain a synergistic effect to permit efficient microbial growth control at low photosensitizer doses. PMID:23509680

  20. How to overcome difficulties with reserves replacement

    SciTech Connect

    Brashear, J.P.; Becker, A.B.; Godec, M.L.; Crawford, P.M.

    1997-03-10

    The first part of this article discussed the challenge of replacing reserves while maintaining high levels of profitability. An examination of the 82 largest US-based, publicly traded exploration and production (E and P) companies, grouped by size, suggested a potential conflict between reserves replacement and profitability--a ``devil`s dilemma`` between long term viability and financial performance. The 10 largest companies failed to replace their production in the US or worldwide (although they did in non-US operations). They were, however, the most profitable on a per-barrel-equivalent basis. In general, the smaller the company, the higher its reserves-replacement ratio, reflecting greater relative effort but lower unit profitability. This article examines the difficulties that companies face in reserves replacement planning, the accommodations they make to these difficulties, and the problems caused by these accommodations. It then suggests an analytical structure for reserves replacement planning that contributes to overcoming the difficulties.

  1. Overcoming Multidrug Resistance in Cancer Stem Cells

    PubMed Central

    Moitra, Karobi

    2015-01-01

    The principle mechanism of protection of stem cells is through the expression of ATP-binding cassette (ABC) transporters. These transporters serve as the guardians of the stem cell population in the body. Unfortunately these very same ABC efflux pumps afford protection to cancer stem cells in tumors, shielding them from the adverse effects of chemotherapy. A number of strategies to circumvent the function of these transporters in cancer stem cells are currently under investigation. These strategies include the development of competitive and allosteric modulators, nanoparticle mediated delivery of inhibitors, targeted transcriptional regulation of ABC transporters, miRNA mediated inhibition, and targeting of signaling pathways that modulate ABC transporters. The role of ABC transporters in cancer stem cells will be explored in this paper and strategies aimed at overcoming drug resistance caused by these particular transporters will also be discussed. PMID:26649310

  2. Photonic ADC: overcoming the bottleneck of electronic jitter.

    PubMed

    Khilo, Anatol; Spector, Steven J; Grein, Matthew E; Nejadmalayeri, Amir H; Holzwarth, Charles W; Sander, Michelle Y; Dahlem, Marcus S; Peng, Michael Y; Geis, Michael W; DiLello, Nicole A; Yoon, Jung U; Motamedi, Ali; Orcutt, Jason S; Wang, Jade P; Sorace-Agaskar, Cheryl M; Popović, Miloš A; Sun, Jie; Zhou, Gui-Rong; Byun, Hyunil; Chen, Jian; Hoyt, Judy L; Smith, Henry I; Ram, Rajeev J; Perrott, Michael; Lyszczarz, Theodore M; Ippen, Erich P; Kärtner, Franz X

    2012-02-13

    Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated. PMID:22418205

  3. Software Model Of Software-Development Process

    NASA Technical Reports Server (NTRS)

    Lin, Chi Y.; Synott, Debra J.; Levary, Reuven R.

    1990-01-01

    Collection of computer programs constitutes software tool for simulation of medium- to large-scale software-development projects. Necessary to include easily identifiable and more-readily quantifiable characteristics like costs, times, and numbers of errors. Mathematical model incorporating these and other factors of dynamics of software-development process implemented in the Software Life Cycle Simulator (SLICS) computer program. Simulates dynamics of software-development process. In combination with input and output expert software systems and knowledge-based management software system, develops information for use in managing large software-development project. Intended to aid managers in planning, managing, and controlling software-development processes by reducing uncertainties in budgets, required personnel, and schedules.

  4. Predicting brittle zones in the Bakken Formation using well logs and seismic data

    NASA Astrophysics Data System (ADS)

    Beecher, Michael E.

    The oil-in-place estimate for the Bakken Formation has varied from 10 billion barrels in 1974 to 503 billion barrels in 1999. However, only a small fraction of this estimate is recoverable due to the formation having very low porosity and permeability. Implementation of hydraulic fracture stages along horizontal wells in the Bakken has been productive. Recently, identification of zones where the formation is brittle has been used to improve hydraulic fracture stimulation efficiency in an effort to improve production. The first goal for this thesis is to identify a correlation between brittleness and production data by using elastic moduli and normalized production values. The hypothesis for this study is that rock with a low Poisson's ratio and high Young's modulus will be more brittle and will ultimately produce a higher amount of oil than more ductile rock. The next goal was to create and test a method to identify brittle zones with high normalized production in a 3D seismic data set without well control using producing wells from outside the survey with dipole sonic logs from the Bakken Formation. Correlations between normalized production values and elastic moduli were subsequently identified. Cumulative first-four-months' production was found to have the best correlation to the elastic moduli. Correlations of normalized production values and Poisson's ratio showed that sections of the middle Bakken with low Poisson's ratio yield higher normalized production values. Correlations of Young's modulus and normalized production showed that middle Bakken zones with low Young's modulus have higher normalized production values. However, when using additional wells that were not used for well-to-3D seismic correlations, the correlation shows that higher Young's modulus yield higher normalized production. The correlation with additional wells best represented the data and agrees with the initial hypothesis. Brittle zones were mapped in a 3D seismic data set by

  5. Forward-thinking practices can overcome technophobia, enjoy benefits of new software.

    PubMed

    2001-05-01

    The Medical Group Management Association set out to answer the question with a survey of almost 500 physician practices. It offers some explanations and an update on the state of computer use among physicians. PMID:11430225

  6. Discrete element modeling on the crack evolution behavior of brittle sandstone containing three fissures under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Huang, Yan-Hua; Ranjith, P. G.; Jiao, Yu-Yong; Ji, Jian

    2015-12-01

    Based on experimental results of brittle, intact sandstone under uniaxial compression, the micro-parameters were firstly confirmed by adopting particle flow code (PFC^{2D}). Then, the validation of the simulated models were cross checked with the experimental results of brittle sandstone containing three parallel fissures under uniaxial compression. The simulated results agreed very well with the experimental results, including the peak strength, peak axial strain, and ultimate failure mode. Using the same micro-parameters, the numerical models containing a new geometry of three fissures are constructed to investigate the fissure angle on the fracture mechanical behavior of brittle sandstone under uniaxial compression. The strength and deformation parameters of brittle sandstone containing new three fissures are dependent to the fissure angle. With the increase of the fissure angle, the elastic modulus, the crack damage threshold, and the peak strength of brittle sandstone containing three fissures firstly increase and secondly decrease. But the peak axial strain is nonlinearly related to the fissure angle. In the entire process of deformation, the crack initiation and propagation behavior of brittle sandstone containing three fissures under uniaxial compression are investigated with respect to the fissure angle. Six different crack coalescence modes are identified for brittle sandstone containing three fissures under uniaxial compression. The influence of the fissure angle on the length of crack propagation and crack coalescence stress is evaluated. These investigated conclusions are very important for ensuring the stability and safety of rock engineering with intermittent structures.

  7. Modeling brittle material failure under high velocity impact conditions: From experiments to simulations

    NASA Astrophysics Data System (ADS)

    Tonge, Andrew; Ramesh, K. T.

    2013-03-01

    Brittle materials have a deviatoric strength that is highly dependent on the applied pressure. To successfully model impact events involving brittle materials it is important to capture both the hydrostatic response, which is dominated by the equation of state, and the deviatoric response witch is dominated by the activation of microcracks within the material. The behavior of microcracks within the material is strongly affected by the applied pressure and gives rise to a material strength that is rate, size, and pressure dependent. In this work we present a material model that is based on an experimentally motivated micromechanics damage growth model coupled with a Mie-Gruneisen equation of state. We use this material model to simulate quarter inch glass spheres impacting a basalt cube at 2.2 km/s.

  8. Study on subsurface-inclined crack propagation during machining of brittle crystal materials

    NASA Astrophysics Data System (ADS)

    Guo, Jiawen; Chen, Jianbin; Li, Jia; Fang, Qihong; Liu, Youwen

    2016-05-01

    There is an immense need to obtain high-quality surface and subsurface on brittle material owing to the advantage of its improved performance. Thus, in this paper, we proposed a mechanical and numerical study of fracture mechanics from the perspective of external loading and indentation geometry in brittle machining. Stress intensity factors are computed to analyze various impacts of external loading and indentation configuration on subsurface crack propagation. Results indicate that the main fracture mode for inclined crack is shear rather than opening and the apex angle of the indentation plays an important role in fracture behavior. As a certain external loading is exerted to the surface of the silicon, a large apex angle of indentation may lead to strong shielding effect on mode II crack propagation. A relationship between critical value of external loading to the crack propagation and the apex angle of the indentation is given in this paper that shows quantitative indication for suppression of crack growth.

  9. Amish brittle hair syndrome gene maps to 7p14.1.

    PubMed

    Seboun, Eric; Lemainque, Arnaud; Jackson, Charles E

    2005-04-30

    The brittle hair syndrome (BHS) is characterized by short stature, intellectual impairment, brittle hair, and decreased fertility in 20 members from a large Amish consanguineous kindred previously reported affected with this syndrome. We mapped the BHS gene by genome scan to chromosome 7p14.1. Evidence of linkage was supported by a maximum multipoint LOD score of 6 obtained with GENEHUNTER for the linkage interval defined by markers D7S484-D7S2422 distant by 17.2 cM. Two-point linkage analysis performed with SUPERLINK yielded a LOD score of 9.02 at theta = 0 for marker D7S2497 located within that interval. Analysis of haplotypes homozygous-by-descent allowed fine mapping of the BHS gene within a 4.81 cM interval delimited by markers D7S2497 and D7S691, a region that spreads over 3.42 Mb. PMID:15723315

  10. Linking Nanoscales and Dislocation Shielding to the Ductile-Brittle Transition of Silicon

    NASA Astrophysics Data System (ADS)

    Hintsala, Eric; Teresi, Claire; Gerberich, William W.

    2016-06-01

    The ductile-brittle transition of nano/microscale silicon is explored at low-temperature, high stress conditions. A pathway to eventual mechanism maps describing this ductile-brittle transition behavior using sample size, strain rate, and temperature is outlined. First, a discussion of variables controlling the BDT in silicon is given and discussed in the context of development of eventual modeling that could simultaneously incorporate all their effects. For description of energy dissipation by dislocation nucleation from a crack tip, three critical input parameters are identified: the effective stress, activation volume, and activation energy for dislocation motion. These are discussed individually relating to the controlling variables for the BDT. Lastly, possibilities for measuring these parameters experimentally are also described.

  11. Core/shell structural transformation and brittle-to-ductile transition in nanowires

    NASA Astrophysics Data System (ADS)

    Yuan, Zaoshi; Nomura, Ken-ichi; Nakano, Aiichiro

    2012-04-01

    Nanowires (NWs) exhibit thermo-mechanical properties that are distinct from their bulk properties, and their understanding is critical for the reliability, manufacturability, and optimization of a wide range of devices consisting of NWs. Here, molecular-dynamics simulation reveals a rich size-temperature "phase diagram" for the mechanical response of a zinc-oxide NW under tension. For smaller diameters and higher temperatures, transitions are found from brittle cleavage to structural transformation-mediated brittle cleavage to ductile failure. Atomistic mechanisms of the unique nano-thermo-mechanical behavior are elucidated as a consequence of surface-structural relaxation, which in particular predicts spontaneous formation of a core/shell structure under tension. The nano-thermo-mechanical phase diagram resolves controversies between previous experiments and theory, and the predicted "intrinsic" core/shell structure may find device applications.

  12. On the brittle-ductile behavior of iron meteorites - New experimental constraints

    NASA Technical Reports Server (NTRS)

    Matsui, T.; Schultz, P. H.

    1984-01-01

    Impact trials were performed at the NASA vertical gun range to study low-temperature brittle-ductile transitions in meteoritic, steel and iron targets. The trials were performed to enhance the data base underlying the concept of formation of planetesimals in collisional coagulation. Impact velocities of 1.6-5.5 km/sec were used, as were temperatures from 100-300 K. Spallation was observed in the tests with meteorite samples, even at room temperature, and brittleness was enhanced at temperature below 200 C. Net mass losses were induced at the higher impact velocities. It is suggested that iron meteorite agglomerations could form in the inner solar region during nebular condensation, but would not form in farther-out regions such as the asteroid belt. The protoplanets could have an iron core, with metallicity decreasing with radius from the core, which may have happened with the earth.

  13. Brittleness estimation from seismic measurements in unconventional reservoirs: Application to the Barnett shale

    NASA Astrophysics Data System (ADS)

    Perez Altimar, Roderick

    Brittleness is a key characteristic for effective reservoir stimulation and is mainly controlled by mineralogy in unconventional reservoirs. Unfortunately, there is no universally accepted means of predicting brittleness from measures made in wells or from surface seismic data. Brittleness indices (BI) are based on mineralogy, while brittleness average estimations are based on Young's modulus and Poisson's ratio. I evaluate two of the more popular brittleness estimation techniques and apply them to a Barnett Shale seismic survey in order to estimate its geomechanical properties. Using specialized logging tools such as elemental capture tool, density, and P- and S wave sonic logs calibrated to previous core descriptions and laboratory measurements, I create a survey-specific BI template in Young's modulus versus Poisson's ratio or alternatively lambdarho versus murho space. I use this template to predict BI from elastic parameters computed from surface seismic data, providing a continuous estimate of BI estimate in the Barnett Shale survey. Extracting lambdarho-murho values from microseismic event locations, I compute brittleness index from the template and find that most microsemic events occur in the more brittle part of the reservoir. My template is validated through a suite of microseismic experiments that shows most events occurring in brittle zones, fewer events in the ductile shale, and fewer events still in the limestone fracture barriers. Estimated ultimate recovery (EUR) is an estimate of the expected total production of oil and/or gas for the economic life of a well and is widely used in the evaluation of resource play reserves. In the literature it is possible to find several approaches for forecasting purposes and economic analyses. However, the extension to newer infill wells is somewhat challenging because production forecasts in unconventional reservoirs are a function of both completion effectiveness and reservoir quality. For shale gas reservoirs

  14. Prediction of material strength and fracture of brittle materials using the SPHINX smooth particle hydrodynamics code

    SciTech Connect

    Mandell, D.A.; Wingate, C.A.; Stellingwwerf, R.F.

    1995-12-31

    The design of many devices involves numerical predictions of the material strength and fracture of brittle materials. The materials of interest include ceramics that are used in armor packages; glass that is used in windshields; and rock and concrete that are used in oil wells. As part of a program to develop advanced hydrocode design tools, the authors have implemented a brittle fracture model for glass into the SPHINX smooth particle hydrodynamics code. The authors have evaluated this model and the code by predicting data from tungsten rods impacting glass. Since fractured glass properties, which are needed in the model, are not available, they did sensitivity studies of these properties, as well as sensitivity studies to determine the number of particles needed in the calculations. The numerical results are in good agreement with the data.

  15. Plasticity and an Inverse Brittle-to-Ductile Transition in Strontium Titanate

    SciTech Connect

    Gumbsch, P.; Taeri-Baghbadrani, S.; Brunner, D.; Sigle, W.; Ruehle, M.

    2001-08-20

    The use of ceramic materials is often restricted by a transition from ductile behavior to brittle fracture with decreasing temperature. For example, strontium titanate (SrTiO{sub 3} ) is known to be extremely fragile and brittle below 1300 K. It is therefore surprising to find that SrTiO{sub 3} single crystals can be deformed in compression below 1050 K again. Extensive plastic deformation up to 7% strain at low yield stresses of the order of only 120 MPa is possible at room temperature. Low temperature plasticity is carried by the same <110>{l_brace}1{bar 1} 0{r_brace} dislocations as the high temperature deformation along the <001> axis. From this we conclude that these dislocations must exist in two different core configurations.

  16. Neutron irradiation effects on the ductile-brittle transition of ferritic/martensitic steels

    SciTech Connect

    Klueh, R.L.; Alexander, D.J.

    1997-08-01

    Ferritic/martensitic steels such as the conventional 9Cr-1MoVNb (Fe-9Cr-1Mo-0.25V-0.06Nb-0.1C) and 12Cr-1MoVW (Fe-12Cr-1Mo-0.25V-0.5W-0.5Ni-0.2C) steels have been considered potential structural materials for future fusion power plants. The major obstacle to their use is embrittlement caused by neutron irradiation. Observations on this irradiation embrittlement is reviewed. Below 425-450{degrees}C, neutron irradiation hardens the steels. Hardening reduces ductility, but the major effect is an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy, as measured by a Charpy impact test. After irradiation, DBTT values can increase to well above room temperature, thus increasing the chances of brittle rather than ductile fracture.

  17. Forming of Brittle Materials—A New and Valuable Application of Diode Lasers

    NASA Astrophysics Data System (ADS)

    Schuöcker, D.; Bammer, F.; Schumi, T.; Holzinger, B.

    2010-10-01

    Laser assisted bending is a new and versatile method to allow simple bending of brittle materials. Laser technology is used to illuminate and heat the forming zone. Only a laser allows directing the power on a narrow area. Further there is no unnecessary heating of other parts of the bending equipment, no wear of the tool and, if properly done, no damage of the surface of the metal. We describe now the integration of 200 W-diode-laser-bars on micro-channel coolers that where installed into the lower tool of the bending press. The solution allows any required bending length by a combination of several bending tools with integrated lasers. The optical power of 16 kW per meter bending length allows achieving the temperature necessary to bend brittle sheet metals within seconds.

  18. Brittle-to-ductile transition of lithiated silicon electrodes: Crazing to stable nanopore growth

    SciTech Connect

    Wang, Haoran; Chew, Huck Beng; Wang, Xueju; Xia, Shuman

    2015-09-14

    Using first principle calculations, we uncover the underlying mechanisms explaining the brittle-to-ductile transition of Li{sub x}Si electrodes in lithium ion batteries with increasing Li content. We show that plasticity initiates at x = ∼ 0.5 with the formation of a craze-like network of nanopores separated by Si–Si bonds, while subsequent failure is still brittle-like with the breaking of Si–Si bonds. Transition to ductile behavior occurs at x ⩾ 1 due to the increased density of highly stretchable Li–Li bonds, which delays nanopore formation and stabilizes nanopore growth. Collapse of the nanopores during unloading of the Li{sub x}Si alloys leads to significant strain recovery.

  19. Effect of prestraining on the brittle-to-ductile transition of NiAl single crystals

    SciTech Connect

    Shrivastava, S.; Ebrahimi, F.

    1997-12-31

    The brittle-to-ductile transition (BDT) has been established for NiAl single crystals as evaluated by fracture toughness testing and also the effects of prestraining on the brittle-to-ductile transition temperature (BDTT) have been investigated. Specimens were prestrained to a 10% plastic strain level at 200 C under tension prior to toughness testing. The BDT of the prestrained specimens was compared to that of the as homogenized specimens. The results have revealed the occurrence of two competing effects upon prestraining: (1) an increase in dislocation sources causing a difficulty in micro-crack initiation and resulting in an increase in toughness at low temperatures, and (2) an increase in the flow stress resulting in an increase in BDT temperature. The crack initiation and propagation mechanisms were also analyzed and have been discussed.

  20. Interim report of brittle-fracture impact studies: development of methodology

    SciTech Connect

    Mecham, W.J.; Jardine, L.J.; Pelto, R.H.; Reedy, G.T.; Steindler, M.J.

    1981-10-01

    A comprehensive methodology for characterizing the results of impact fracture of brittle waste forms is presented, and its use illustrated by application to available particle-size data obtained in impact tests of various materials. The respirable-size fraction and the total surface area of the fracture particulates are the major criteria for characterization. Particle-size distributions were all found to be characterized approximately by the two parameters of the lognormal probability function (the geometric mean diameter D/sub g/ and the geometric standard deviation sigma/sub g/). These results are explained in terms of the brittle-fracture process as it is described in the technical literature. The methodology appears promising both for standardized evaluation of the impact strength of various solid-waste compositions, either vitreous or crystalline, and for studying the deformation of canistered waste forms in scale-model tests.

  1. Ductile-brittle transition behavior of tungsten under shock loading conditions

    SciTech Connect

    Lassila, D.H.; Gray, G.T. III

    1993-02-01

    In an effort to characterize the ductile-brittle transition behavior of warm forged tungsten under shock loading conditions, we have performed shock/soft-recovery experiments at 22 and 4000 C. Results at 22 C indicate that shock (19 GPa) induced strains appear to be accommodated by fracture processes, i.e. there were no indications of shock induced plastic deformation and the test sample was reduced to rubble. At 400 C, the test sample was recovered intact and the shock induced plasticity caused deformation banding and an increase in the dislocation density of the material. For reasons unclear, almost no change in the post shock mechanical behavior was observed, despite the significant changes in the microstructure. The results of these experiments demonstrate the principal of a ductile-brittle transition behavior of tungsten under uniaxial shock loading conditions and indicate that explosively driven deformation of tungsten of this material will result in pulverization due to shock loading.

  2. Brittle-to-ductile transition of lithiated silicon electrodes: Crazing to stable nanopore growth.

    PubMed

    Wang, Haoran; Wang, Xueju; Xia, Shuman; Chew, Huck Beng

    2015-09-14

    Using first principle calculations, we uncover the underlying mechanisms explaining the brittle-to-ductile transition of LixSi electrodes in lithium ion batteries with increasing Li content. We show that plasticity initiates at x = ∼ 0.5 with the formation of a craze-like network of nanopores separated by Si-Si bonds, while subsequent failure is still brittle-like with the breaking of Si-Si bonds. Transition to ductile behavior occurs at x ⩾ 1 due to the increased density of highly stretchable Li-Li bonds, which delays nanopore formation and stabilizes nanopore growth. Collapse of the nanopores during unloading of the LixSi alloys leads to significant strain recovery. PMID:26374052

  3. Brittle-to-ductile transition of lithiated silicon electrodes: Crazing to stable nanopore growth

    NASA Astrophysics Data System (ADS)

    Wang, Haoran; Wang, Xueju; Xia, Shuman; Chew, Huck Beng

    2015-09-01

    Using first principle calculations, we uncover the underlying mechanisms explaining the brittle-to-ductile transition of LixSi electrodes in lithium ion batteries with increasing Li content. We show that plasticity initiates at x = ˜ 0.5 with the formation of a craze-like network of nanopores separated by Si-Si bonds, while subsequent failure is still brittle-like with the breaking of Si-Si bonds. Transition to ductile behavior occurs at x ⩾ 1 due to the increased density of highly stretchable Li-Li bonds, which delays nanopore formation and stabilizes nanopore growth. Collapse of the nanopores during unloading of the LixSi alloys leads to significant strain recovery.

  4. Ductile-to-brittle transition of oxidised Zircaloy-4 and E110 claddings

    NASA Astrophysics Data System (ADS)

    Hózer, Zoltán; Győri, Csaba; Matus, Lajos; Horváth, Márta

    2008-02-01

    The ductile-to-brittle transition of the claddings of PWR and VVER nuclear fuel rods has been investigated in ring compression tests performed at room temperature with Zircaloy-4 and E110 samples oxidised in high temperature steam. These experiments were evaluated on the basis of the form of load-displacement curves. The ductile samples were characterised by a horizontal ductile plateau after the elastic deformation, while in the case of the brittle samples the ductile plateau was missing. The ductility limits of both alloys were expressed in terms of oxidation time and cladding temperature. From this, a numerical procedure was derived for the simulation of Zr cladding embrittlement during loss-of-coolant accidents. The results indicated a faster embrittlement of the E110 alloy than that of the Zircaloy-4 under identical conditions. The new approach is proposed as an alternative of the 17% ECR criterion to evaluate cladding embrittlement in design basis accident (DBA) scenarios.

  5. Hypervelocity impact on brittle materials of semi-infinite thickness: fracture morphology related to projectile diameter

    NASA Astrophysics Data System (ADS)

    Taylor, Emma A.; Kay, Laurie; Shrine, Nick R. G.

    Hypervelocity impact on brittle materials produces features not observed on ductile targets. Low fracture toughness and high yield strength produce a range of fracture morphologies including cracking, spallation and shatter. For sub-mm diameter projectiles, impact features are characterised by petaloid spallation separated by radial cracks. The conchoidal or spallation diameter is a parameter in current cratering equations. An alternative method for interpreting hypervelocity impacts on glass targets of semi-infinite thickness is tested against impact data produced using the Light Gas Gun (LGG) facility at the University of Kent at Canterbury (UKC), U.K. Spherical projectiles of glass and other materials with diameters 30-300 μm were fired at ~5 km s^-1 at a glass target of semi-infinite thickness. The data is used to test a power law relationship between projectile diameter and crack length. The results of this work are compared with published cratering/spallation equations for brittle materials.

  6. Alternating brittle and ductile response of coherent twin boundaries in nanotwinned metals

    SciTech Connect

    Sinha, Tanushree; Kulkarni, Yashashree

    2014-11-14

    Nanotwinned metals have opened exciting avenues for the design of high strength and high ductility materials. In this work, we investigate crack propagation along coherent twin boundaries in nanotwinned metals using molecular dynamics. Our simulations reveal that alternating twin boundaries exhibit intrinsic brittleness and ductility owing to the opposite crystallographic orientations of the adjoining twins. This is a startling consequence of the directional anisotropy of an atomically sharp crack along a twin boundary that favors cleavage in one direction and dislocation emission from the crack tip in the opposite direction. We further find that a blunt crack exhibits ductility in all cases albeit with very distinct deformation mechanisms and yield strength associated with intrinsically brittle and ductile coherent twin boundaries.

  7. On the role of microcracks in the dynamic fracture of brittle materials

    NASA Astrophysics Data System (ADS)

    Ravi-Chandar, K.; Yang, B.

    1997-04-01

    The dynamic fracture behavior of brittle materials is investigated. The morphology of the fracture surface is examined in detail in four polymers: polymethylmethacrylate, Solithane-113, Homalite-100 and poly-carbonate. The fracture surface markings are examined to determine the micromechanisms of fracture. This examination reveals clearly that the operative micromechanism that governs dynamic fracture in brittle materials is the nucleation, growth and coalescence of microcracks. Following a quantitative characterization of the microcracking patterns, a very simple nucleation and growth model is then put forward. Imposing nucleation and growth criteria based on the experimental observations, the simulation recreates the experimental observations, not only of the microscope surface features, but also of the macroscopic behavior such as the constancy of the crack speed.

  8. The pale brittle stem mushroom, Psathyrella candolleana (higher Basidiomycetes): an indigenous medicinal mushroom new to Iraq.

    PubMed

    Al-Habib, Mouthana N; Holliday, John C; Tura, Daniel

    2014-01-01

    The pale brittle stem mushroom, Psathyrella candolleana, a species new to Iraq, is described from the sub-arid region of Aljazira (Iraq). Both classical taxonomy and DNA analyses confirm the identification of the fungus strain (RM-0861) as P. candolleana, a species that belongs to the family Psatherellaceae known to possess medicinal properties. Being a saprophyte, this fungus is cultivatable in laboratory conditions and therefore shows potential for production and use as a medicinal mushroom in human and veterinary health. PMID:25404226

  9. Pinch and swell structures: evidence for brittle-viscous behaviour in the middle crust

    NASA Astrophysics Data System (ADS)

    Gardner, R.; Piazolo, S.; Daczko, N.

    2015-04-01

    The flow properties of middle to lower crustal rocks are commonly represented by viscous flow. However, examples of pinch and swell structures found in a mid-crustal high strain zone at St. Anne Point (Fiordland, New Zealand) suggest pinch and swell structures are initiated by brittle failure of the more competent layer in conjunction with material softening. On this basis we develop a flexible numerical model using brittle-viscous flow where Mohr-Coulomb failure is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow provided the competent layer has enough viscosity contrast and initially fails brittlely. The degree of material softening after initial failure is shown to impact pinch and swell characteristics with high rates of material softening causing the formation of thick necks between swells by limiting the successful localisation of strain. The flow regime and yielding characteristics of the matrix do not impact pinch and swell structure formation itself, so long as the matrix is less competent. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr-Coulomb behaviour combined with viscous flow is an appropriate way to represent the heterogeneous rocks of the middle to lower crust. This type of mid-crustal rheological behaviour has significant influence on the localization of strain at all scales. For example, inclusion of Mohr-Coulomb brittle failure with viscous flow in just some mid-crustal layers within a crustal scale model will result in strain localisation throughout the whole crustal section allowing the development of through-going high strain structures from the upper crust into the middle and lower crust. This localization then has a significant

  10. Micromechanisms of brittle fracture: STM, TEM and electron channeling analysis. Final report

    SciTech Connect

    Gerberich, W.W.

    1997-01-01

    The original thrust of this grant was to apply newly developed techniques in scanning tunneling and transmission electron microscopy to elucidate the mechanism of brittle fracture. This grant spun-off several new directions in that some of the findings on bulk structural materials could be utilized on thin films or intermetallic single crystals. Modeling and material evaluation efforts in this grant are represented in a figure. Out of this grant evolved the field the author has designated as Contact Fracture Mechanics. By appropriate modeling of stress and strain distribution fields around normal indentations or scratch tracks, various measures of thin film fracture or decohesion and brittle fracture of low ductility intermetallics is possible. These measures of fracture resistance in small volumes are still evolving and as such no standard technique or analysis has been uniformly accepted. For brittle ceramics and ceramic films, there are a number of acceptable analyses such as those published by Lawn, Evans and Hutchinson. For more dissipative systems involving metallic or polymeric films and/or substrates, there is still much to be accomplished as can be surmised from some of the findings in the present grant. In Section 2 the author reviews the funding history and accomplishments associated mostly with bulk brittle fracture. This is followed by Section 3 which covers more recent work on using novel techniques to evaluate fracture in low ductility single crystals or thin films using micromechanical probes. Basically Section 3 outlines how the recent work fits in with the goals of defining contact fracture mechanics and gives an overview of how the several examples in Section 4 (the Appendices) fit into this framework.

  11. Permeability and mechanical behavior of carbonates during semi-brittle flow

    NASA Astrophysics Data System (ADS)

    Slim, Mirna; Evans, Brian

    2010-05-01

    Permeability and mechanical behavior of carbonates during semi-brittle flow Mirna Slim and Brian Evans, Department of Earth, Atmospheric, and Planetary Sciences, Mass. Inst. Tech., Cambridge, MA 02139, USA In both natural and engineering conditions, carbonate rocks exhibit deformation modes ranging from localized brittle fracture to non-localized plastic flow, depending on overburden pressure, deviatoric stress, temperature, strain-rate, pore geometry, and the pressure and chemistry of the pore-fluid. At relatively low temperatures and confinement, the strength of low porosity carbonates is relatively rate-insensitive, even the deformation mechanism include a mixture of twinning, slip, and local cataclasis, and brittle fracture is generally accompanied by dilatancy and permeability enhancement. But, in rocks with even modest porosity, non-localized flow can induce transitions from brittle fracture to compactive flow, and thus, permeability may either decrease with further straining. As temperature is elevated, variations in temperature, strain rate, and pore fluid chemistry also affect the yield stress, the strain to failure, and the ultimate failure strength. For example in Solnhofen limestone, the stress required for the inception of dilatancy and localization decreases considerably when samples are saturated with water. Even when temperature, pressure and strain rate are such that deformation is accommodated by an increasingly large proportion of crystal plastic processes, carbonates with small amounts of porosity still exhibit a double-surface yield cap. When subjected to triaxial deformation at elevated temperatures, calcite-quartz aggregates with porosity of 20% or less exhibit shear-enhanced compaction. Interestingly and somewhat counter to intuition, the permeability of these rocks deforming under triaxial loads was not as sensitive to porosity changes as that for the same material during isostatic compaction. In addition, the percolation threshold for the

  12. A model for multiple-drop-impact erosion of brittle solids

    NASA Technical Reports Server (NTRS)

    Engel, O. G.

    1971-01-01

    A statistical model for the multiple-drop-impact erosion of brittle solids was developed. An equation for calculating the rate of erosion is given. The development is not complete since two quantities that are needed to calculate the rate of erosion with use of the equation must be assessed from experimental data. A partial test of the equation shows that it gives results that are in good agreement with experimental observation.

  13. A Weibull brittle material failure model for the ABAQUS computer program

    SciTech Connect

    Bennett, J.

    1991-08-01

    A statistical failure theory for brittle materials that traces its origins to the Weibull distribution function is developed for use in the general purpose ABAQUS finite element computer program. One of the fundamental assumptions for this development is that Mode 1 microfractures perpendicular to the direction of the principal stress contribute independently to the fast fracture. The theory is implemented by a user subroutine for ABAQUS. Example problems illustrating the capability and accuracy of the model are given. 24 refs., 12 figs.

  14. NANOPREPARATIONS TO OVERCOME MULTIDRUG RESISTANCE IN CANCER

    PubMed Central

    Patel, Niravkumar R.; Pattni, Bhushan S.; Abouzeid, Abraham H.; Torchilin, Vladimir P.

    2013-01-01

    Multidrug resistance is the most widely exploited phenomenon by which cancer eludes chemotherapy. Broad variety of factors, ranging from the cellular ones, such as over-expression of efflux transporters, defective apoptotic machineries, and altered molecular targets, to the physiological factors such as higher interstitial fluid pressure, low extracellular pH, and formation of irregular tumor vasculature are responsible for multidrug resistance. A combination of various undesirable factors associated with biological surroundings together with poor solubility and instability of many potential therapeutic small & large molecules within the biological systems and systemic toxicity of chemotherapeutic agents has necessitated the need for nano-preparations to optimize drug delivery. The physiology of solid tumors presents numerous challenges for successful therapy. However, it also offers unique opportunities for the use of nanotechnology. Nanoparticles, up to 400 nm in size, have shown great promise for carrying, protecting and delivering potential therapeutic molecules with diverse physiological properties. In this review, various factors responsible for the MDR and the use of nanotechnology to overcome the MDR, the use of spheroid culture as well as the current technique of producing micro tumor tissues in vitro are discussed in detail. PMID:23973912

  15. Overcoming Old in Age-Friendliness

    PubMed Central

    Lindenberg, J.; Westendorp, R.G.J.

    2015-01-01

    In this article, we explore views on an age-friendly space in the Netherlands by analysing the responses of older individuals (N = 54) in focus groups and by examining the perspectives around an age-friendly zone in the Netherlands, Parkstad Limburg. We found that a central issue in the wishes for living at a later age are adjustments to envisioned physical limitations that come with the ageing process; this includes adjustments to ensure safety, accessibility and mobility, in order to facilitate older individuals' efforts to stay engaged with the world around them. In their wishes, the older participants constructed ideal dwelling places that closely resembled a senior home, but at the same time they rejected wishing to live in a place that was identified as a senior home. We explain this paradox by the representation of such a space as being for old people, i.e. needy older individuals, which was not how the older participants wished to be identified. We conclude that the conception of age-friendly environments will have to face the difficult challenge of overcoming the association with old age, while simultaneously taking into account adjustments that signify and relate to the ageing process and that seem inescapably tied to oldness. PMID:26028795

  16. Evaluative pressure overcomes perceptual load effects.

    PubMed

    Normand, Alice; Autin, Frédérique; Croizet, Jean-Claude

    2015-06-01

    Perceptual load has been found to be a powerful bottom-up determinant of distractibility, with high perceptual load preventing distraction by any irrelevant information. However, when under evaluative pressure, individuals exert top-down attentional control by giving greater weight to task-relevant features, making them more distractible from task-relevant distractors. One study tested whether the top-down modulation of attention under evaluative pressure overcomes the beneficial bottom-up effect of high perceptual load on distraction. Using a response-competition task, we replicated previous findings that high levels of perceptual load suppress task-relevant distractor response interference, but only for participants in a control condition. Participants under evaluative pressure (i.e., who believed their intelligence was assessed) showed interference from task-relevant distractor at all levels of perceptual load. This research challenges the assumptions of the perceptual load theory and sheds light on a neglected determinant of distractibility: the self-relevance of the performance situation in which attentional control is solicited. PMID:25233881

  17. Overcoming Current Limitations in Humanized Mouse Research

    PubMed Central

    Brehm, Michael A.; Shultz, Leonard D.; Luban, Jeremy; Greiner, Dale L.

    2013-01-01

    Immunodeficient mice engrafted with human cells and tissues have provided an exciting alternative to in vitro studies with human tissues and nonhuman primates for the study of human immunobiology. A major breakthrough in the early 2000s was the introduction of a targeted mutation in the interleukin 2 (IL-2) receptor common gamma chain (IL2rgnull) into mice that were already deficient in T and B cells. Among other immune defects, natural killer (NK) cells are disrupted in these mice, permitting efficient engraftment with human hematopoietic cells that generate a functional human immune system. These humanized mouse models are becoming increasingly important for preclinical studies of human immunity, hematopoiesis, tissue regeneration, cancer, and infectious diseases. In particular, humanized mice have enabled studies of the pathogenesis of human-specific pathogens, including human immunodeficiency virus type 1, Epstein Barr virus, and Salmonella typhi. However, there are a number of limitations in the currently available humanized mouse models. Investigators are continuing to identify molecular mechanisms underlying the remaining defects in the engrafted human immune system and are generating “next generation” models to overcome these final deficiencies. This article provides an overview of some of the emerging models of humanized mice, their use in the study of infectious diseases, and some of the remaining limitations that are currently being addressed. PMID:24151318

  18. Overcoming the grand challenges in Quantum Simulations

    NASA Astrophysics Data System (ADS)

    Zhou, Qi

    2010-03-01

    The highly ambitious goal of the ``Quantum Simulation'' program is to simulate the behavior of strongly correlated solid-state systems using cold atoms in optical lattices. It promises to provide insight into a range of long-standing problems in many-body physics. There are, however, significant challenges which need to be overcome in order for these efforts to succeed. The first challenge is that the required temperatures for studying strongly correlated physics in optical lattices are far below those achievable in laboratories today. The second problem concerns the fact that many important thermodynamic qualities, which distribute non-uniformly in the confining trap, are inaccessible by standard imaging methods. In this talk, I will discuss ways to solve these grand challenges. First, I will present schemes which allow for strongly correlated regimes of atoms in optical lattices to be reached. These schemes are based on transferring the entropy out of the region of interest. Examples will be given to demonstrate that these schemes can reach temperature regions down to a few tens of pico-Kelvin. Secondly, I will discuss algorithms to map out the phase diagrams of quantum models and deduce the thermodynamic properties of homogeneous systems, such as the superfluid density and entropy density, which have eluded cold atom experiments for years. Using only the density profile of trapped atoms as input, these algorithms can fulfill the lofty goal of quantum simulation.

  19. Cooperative networks overcoming defectors by social influence

    NASA Astrophysics Data System (ADS)

    Gomez Portillo, Ignacio

    2014-01-01

    We address the cooperation problem in structured populations by considering the prisoner’s dilemma game as a metaphor of the social interactions between individuals with imitation capacity. We present a new strategy update rule called democratic weighted update where the individual’s behavior is socially influenced by each one of their neighbors. In particular, the capacity of an individual to socially influence other ones is proportional to its accumulated payoff. When in a neighborhood there are cooperators and defectors, the focal player is contradictorily influenced by them and, therefore, the effective social influence is given by the difference of the accumulated payoff of each strategy in its neighborhood. First, by considering the growing process of the network and neglecting mutations, we show the evolution of highly cooperative systems. Then, we broadly show that the social influence allows to overcome the emergence of defectors into highly cooperative systems. In this way, we conclude that in a structured system formed by a growing process, the cooperation evolves if the individuals have an imitation capacity socially influenced by each one of their neighbors. Therefore, here we present a theoretical solution of the cooperation problem among genetically unrelated individuals.

  20. Software attribute visualization for high integrity software

    SciTech Connect

    Pollock, G.M.

    1998-03-01

    This report documents a prototype tool developed to investigate the use of visualization and virtual reality technologies for improving software surety confidence. The tool is utilized within the execution phase of the software life cycle. It provides a capability to monitor an executing program against prespecified requirements constraints provided in a program written in the requirements specification language SAGE. The resulting Software Attribute Visual Analysis Tool (SAVAnT) also provides a technique to assess the completeness of a software specification.

  1. Fracture-mode map of brittle coatings: Theoretical development and experimental verification

    NASA Astrophysics Data System (ADS)

    He, Chong; Xie, Zhaoqian; Guo, Zhenbin; Yao, Haimin

    2015-10-01

    Brittle coatings, upon sufficiently high indentation load, tend to fracture through either ring cracking or radial cracking. In this paper, we systematically study the factors determining the fracture modes of bilayer material under indentation. By analyzing the stress field developed in a coating/substrate bilayer under indentation in combination with the application of the maximum-tensile-stress fracture criterion, we show that the fracture mode of brittle coatings due to indentation is determined synergistically by two dimensionless parameters being functions of the mechanical properties of coating and substrate, coating thickness and indenter tip radius. Such dependence can be graphically depicted by a diagram called 'fracture-mode map', whereby the fracture modes can be directly predicated based on these two dimensionless parameters. Experimental verification of the fracture-mode map is carried out by examining the fracture modes of fused quartz/cement bilayer materials under indentation. The experimental observation exhibits good agreement with the prediction by the fracture-mode map. Our finding in this paper may not only shed light on the mechanics accounting for the fracture modes of brittle coatings in bilayer structures but also pave a new avenue to combating catastrophic damage through fracture mode control.

  2. 3D modelling of salt tectonics with a brittle overburden in an extensional regime

    NASA Astrophysics Data System (ADS)

    Eichheimer, Philipp; Reuber, Georg; Kaus, Boris

    2016-04-01

    Most previous numerical models of salt tectonics only considered 2D cases or did not taken a brittle sedimentary overburden into account, both of which are likely to be important in nature. To get insights into the dynamics of diapiric rise of salt we here present time-dependent high resolution 3D models of salt tectonics in the presence of a brittle overburden and sedimentation. We focus on the internal deformation of an embedded anhydrite layer within a nonlinear viscous salt layer. As salt in nature tends to rise upwards to the surface along fault zones, the salt layer is overlain by a brittle overburden to simulate faulting. The resulting complex folding of the anhydrite layer obtained in our models is consistent with natural observations, e.g. Gorleben [1]. Regarding field examples we vary the shape of the anhydrite layer to understand different modes of deformation [2]. We test the effect of overburden rheology, extension and sedimentation rates on the 3D salt dome patterns and on its internal deformation. [1] O. Bornemann. Zur Geologie des Salzstocks Gorleben nach den Bohrergebnissen. Bundesamt für Strahlenschutz (1991). [2] Z. Chemia, H. Koyi, and H. Schmeling. Numerical modelling of rise and fall of a dense layer in salt diapirs. Geophysical Journal International 172.2 (2008): 798-816.

  3. Final report of experimental laboratory-scale brittle fracture studies of glasses and ceramics

    SciTech Connect

    Jardine, L.J.; Mecham, W.J.; Reedy, G.T.; Steindler, M.J.

    1982-10-01

    An experimental program was conducted to characterize the fragments generated when brittle glasses and ceramics are impacted. The direct application of the results is to radioactive waste forms for which the effects of accidental impacts must be known or predictable. Two major measurable experimental responses used for characterization of these effects are (1) the size distribution of the fragments, including the sizes that are respirable, and (2) the increase in surface area of the brittle test specimen. This report describes the glass and ceramic materials characterized, the procedures and techniques used for the characterization of size distributions and surface areas, and the results of the two key responses of the impact tests. Five alternative methods of determining size distributions were compared. Also examined were the effects of diametral and axial specimen impact configurations and the use of mechanical stops to eliminate secondary crushing during testing. Microscopic characterizations of Pyrex and SRL 131 simulated waste glass and SYNROC fragments were also performed. Preliminary correlations of impact energy with key size-distribution parameters, fragment surface areas, and respirable fines were proposed as useful for future verification and for use with modeling and scale-up studies of brittle fracture of larger realistic waste forms. The impact fragments of all specimens could be described by lognormal size distributions.

  4. Reliable Support Design for Excavations in Brittle Rock Using a Global Response Surface Method

    NASA Astrophysics Data System (ADS)

    Langford, J. Connor; Diederichs, Mark S.

    2015-03-01

    Spalling damage can pose significant risks during the construction of underground excavations in brittle rock. While deterministic analyses have traditionally been used in the design of these structures, reliability-based design (RBD) methods provide a more rational approach to quantify spalling risk by directly incorporating input uncertainty into the design process and quantifying variable ground response. This paper presents a new RBD approach to evaluate the excavation response and support performance for a tunnel in brittle ground. Guidance for the selection of appropriate parameters for variable brittle materials is provided using a combination of the damage initiation and spalling limit method and theories of microcrack initiation. System performance is then evaluated using a proposed global response surface method (GRSM) coupled with the first-order reliability method, random sampling and finite element analysis. The proposed GRSM provides a computationally efficient way to evaluate the probability of failure for various limit states, allowing for the selection of appropriate design parameters such as minimum bolt length and required bolt capacity during early stages of design. To demonstrate the usefulness of this approach, a preliminary design option for a proposed deep geologic repository located in Canada was assessed. Numerical analyses were completed using finite element modeling to determine the depth of spalling around the excavation and support loads over the range of possible rock mass and in situ stress conditions. The results of these analyses were then used to assess support performance and make support recommendations.

  5. Formulation and computational aspects of plasticity and damage models with application to quasi-brittle materials

    SciTech Connect

    Chen, Z.; Schreyer, H.L.

    1995-09-01

    The response of underground structures and transportation facilities under various external loadings and environments is critical for human safety as well as environmental protection. Since quasi-brittle materials such as concrete and rock are commonly used for underground construction, the constitutive modeling of these engineering materials, including post-limit behaviors, is one of the most important aspects in safety assessment. From experimental, theoretical, and computational points of view, this report considers the constitutive modeling of quasi-brittle materials in general and concentrates on concrete in particular. Based on the internal variable theory of thermodynamics, the general formulations of plasticity and damage models are given to simulate two distinct modes of microstructural changes, inelastic flow and degradation of material strength and stiffness, that identify the phenomenological nonlinear behaviors of quasi-brittle materials. The computational aspects of plasticity and damage models are explored with respect to their effects on structural analyses. Specific constitutive models are then developed in a systematic manner according to the degree of completeness. A comprehensive literature survey is made to provide the up-to-date information on prediction of structural failures, which can serve as a reference for future research.

  6. "Ductile to brittle" transition in thermally stable antigorite gouge at mantle pressures

    NASA Astrophysics Data System (ADS)

    Proctor, Brooks; Hirth, Greg

    2016-03-01

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

  7. Rock Drilling Performance Evaluation by an Energy Dissipation Based Rock Brittleness Index

    NASA Astrophysics Data System (ADS)

    Munoz, H.; Taheri, A.; Chanda, E. K.

    2016-08-01

    To reliably estimate drilling performance both tool-rock interaction laws along with a proper rock brittleness index are required to be implemented. In this study, the performance of a single polycrystalline diamond compact (PDC) cutter cutting and different drilling methods including PDC rotary drilling, roller-cone rotary drilling and percussive drilling were investigated. To investigate drilling performance by rock strength properties, laboratory PDC cutting tests were performed on different rocks to obtain cutting parameters. In addition, results of laboratory and field drilling on different rocks found elsewhere in literature were used. Laboratory and field cutting and drilling test results were coupled with values of a new rock brittleness index proposed herein and developed based on energy dissipation withdrawn from the complete stress-strain curve in uniaxial compression. To quantify cutting and drilling performance, the intrinsic specific energy in rotary-cutting action, i.e. the energy consumed in pure cutting action, and drilling penetration rate values in percussive action were used. The results show that the new energy-based brittleness index successfully describes the performance of different cutting and drilling methods and therefore is relevant to assess drilling performance for engineering applications.

  8. Space Flight Software Development Software for Intelligent System Health Management

    NASA Technical Reports Server (NTRS)

    Trevino, Luis C.; Crumbley, Tim

    2004-01-01

    The slide presentation examines the Marshall Space Flight Center Flight Software Branch, including software development projects, mission critical space flight software development, software technical insight, advanced software development technologies, and continuous improvement in the software development processes and methods.

  9. Report: Scientific Software.

    ERIC Educational Resources Information Center

    Borman, Stuart A.

    1985-01-01

    Discusses various aspects of scientific software, including evaluation and selection of commercial software products; program exchanges, catalogs, and other information sources; major data analysis packages; statistics and chemometrics software; and artificial intelligence. (JN)

  10. Controlling Software Piracy.

    ERIC Educational Resources Information Center

    King, Albert S.

    1992-01-01

    Explains what software manufacturers are doing to combat software piracy, recommends how managers should deal with this problem, and provides a role-playing exercise to help students understand the issues in software piracy. (SR)

  11. Software Engineering Guidebook

    NASA Technical Reports Server (NTRS)

    Connell, John; Wenneson, Greg

    1993-01-01

    The Software Engineering Guidebook describes SEPG (Software Engineering Process Group) supported processes and techniques for engineering quality software in NASA environments. Three process models are supported: structured, object-oriented, and evolutionary rapid-prototyping. The guidebook covers software life-cycles, engineering, assurance, and configuration management. The guidebook is written for managers and engineers who manage, develop, enhance, and/or maintain software under the Computer Software Services Contract.

  12. The role of fluids on the brittle-ductile transition in the crust

    NASA Astrophysics Data System (ADS)

    Hirth, Greg; Beeler, Nick

    2015-04-01

    To characterize stress and deformation style at the base of the seismogenic zone we investigate how the mechanical properties of fluid-rock systems respond to variations in temperature and strain rate. The role of fluids on the processes responsible for the brittle-ductile transition in quartz-rich rocks has not been explored at experimental conditions where the kinetic competition between microcracking and viscous flow is similar to that expected in the Earth. Our initial analysis of this competition suggests that the effective pressure law for sliding friction should not work as effectively near the brittle-ductile transition (BDT) as it does at shallow conditions. Our motivation comes from three observations. First, extrapolation of quartzite flow laws indicates the brittle-ductile transition (BDT) occurs at ~300 °C at geologic strain rates for conditions where fault strength is controlled by a coefficient of friction of ~0.6 with a hydrostatic pore-fluid pressure gradient. Second, we suggest that the preservation of relatively high stress microstructures indicates that the effective stress law must sometimes evolve rapidly near the BDT. There is abundant evidence for the presence of fluids during viscous deformation of mylonites (e.g., recrystallization and redistribution of micas, dissolution and reprecipitation of quartz). The relatively high viscous stresses inferred from these microstructures are incompatible with the standard effective stress relationship. A similar "paradox" is evident at experimental conditions where viscous creep is studied in the laboratory. In this case, the presence of fluid (which should produce low effective stress) does not promote localized brittle failure, even though these experiments are conducted under undrained conditions. Third, experiments on partially molten rocks illustrate viscous creep behavior during both drained compaction and undrained triaxial deformation tests, even though the melt pressure approaches or equals

  13. Transition from cataclastic flow to aseismic brittle failure in Carrarra marble

    NASA Astrophysics Data System (ADS)

    Walker, E.; Schubnel, A.; Thompson, B.; Fortin, J.; Nasseri, M.; Young, R.

    2004-12-01

    Interest in the brittle-ductile transition has increased considerably in recent years, in large part due to the fact that the maximum depth of seismicity corresponds to a transition in the crust and in the upper mantle from seismogenic brittle failure to aseismic cataclastic flow, i.e. from localized to homogeneous deformation. The mechanics of the transition depends both on some extrinsic variable (state of solid stress, pore pressure, temperature, fluid chemistry and strain rate) and intrinsic parameters (crack and dislocation density, modal composition of the rock or porosity for example). In the present study, two triaxial experiments were performed on Carrara marble at room temperature. The rock samples were first deformed in the cataclastic domain (up to ˜5% axial strain) until they exhibited severe damage accumulation, i.e. wavespeed attenuation. Damaged samples were then brought back at constant differential stress into the the brittle field by solely reducing the effective mean stress. Throughout both experiments, compressional wave velocities were measured along several raypaths. Acoustic Emissions, when any, were monitored and localized after testing. A complete 2 minutes failure recordings of failure (12 channels at 10MHz sampling frequency) was also obtained using ESG's Hyperion gigarecorder during one of the experiment. Our new set of data shows that during cataclastic deformation, elastic wave velocities show large variations, but only a small degree of elastic anisotropy when compared to what is generally observed in typical brittle materials such as granite or sandstones. After sufficient damage accumulation and when reducing the mean stress, both samples exhibited a fast acceleration in axial strain. Tertiary creep was followed by the nucleation of a brittle failure. Observed differential stress drops during rupture propagation were of the order of 150 MPa. Although failure occurred with large slip and stress drop, only very few AEs could be

  14. Rheology of Pure Glasses and Crystal Bearing Melts: from the Newtonian Field to the Brittle Onset

    NASA Astrophysics Data System (ADS)

    Cordonnier, B.; Caricchi, L.; Pistone, M.; Castro, J. M.; Hess, K.; Dingwell, D. B.

    2010-12-01

    The brittle-ductile transition remains a central question of modern geology. If rocks can be perceived as a granular flow on geological time-scale, their behavior is brittle in dynamic areas. Understanding rock failure conditions is the main parameter in mitigating geological risks, more specifically the eruptive style transitions from effusive to explosive. If numerical simulations are the only way to fully understanding the physical processes involved, we are in a strong need of an experimental validation of the proposed models. here we present results obtained under torsion and uni-axial compression on both pure glasses and crystal bearing melts. We characterized the brittle onset of two phases magmas from 0 to 65% crystals. The strain-rates span a 5 orders magnitude range, from the Newtonian flow to the Brittle field (10-5 - 100 s-1). We particularly emphasize the time dependency of the measured rheology. The materials tested are a borosilicate glass from the National Bureau of Standards, a natural sample from Mt Unzen volcano and a synthetic sample. The lattest is an HPG8 melt with 7% sodium mole excess. The particles are quasi-isometric corundum crystalschosen for their shape and integrity under the stress range investigated. The crystal fraction ranges from 0 to 0.65. Concerning pure magmas, we recently demonstrated that the material passes from a Newtonian to a non-Nemtonian behavior with increasing strain-rate. This onset can mostly be explained by viscous-heating effects. However, for even greater strain-rates, the material cracks and finally fail. The brittle onset is here explained with the visco-elastic theory and corresponds to a Deborah number greater than 10-2. Concerning crystal bearing melts the departure from the Newtonian state is characterized by two effects: a shear-thinning and a time weakening effect. The first one is instantaneous and loading-unloading cyclic tests suggest an elastic contribution of the crystal network. The second one

  15. Deciphering the brittle evolution of SW Norway through a combined structural, mineralogical and geochronological approach

    NASA Astrophysics Data System (ADS)

    Scheiber, Thomas; Viola, Giulio; Fredin, Ola; Zwingmann, Horst; Wilkinson, Camilla Maya; Ganerød, Morgan

    2016-04-01

    SW Norway has experienced a complex brittle history after cessation of the Caledonian orogeny, and the recent discoveries of major hydrocarbon reserves in heavily fractured and weathered basement offshore SW Norway has triggered a renewed interest in understanding this complex tectonic evolution. In this contribution we present results from a multidisciplinary study combining lineament analysis, field work, paleo-stress inversion, mineralogical characterization and radiometric dating in the Bømlo area of SW Norway in order to develop a tectonic model for the brittle evolution of this important region. The study area mainly consists of the Rolvsnes granodiorite (U-Pb zircon age of ca. 466 Ma), which is devoid of penetrative ductile deformation features. The first identified brittle faults are muscovite-bearing top-to-the-NNW thrusts and E-W striking dextral strike-slip faults decorated with stretched biotite. These are mechanically compatible and are assigned to the same NNW-SSE transpressional regime. Ar-Ar muscovite and biotite dates of ca. 450 Ma (Late Ordovician) indicate fault activity in the course of a Taconian-equivalent orogenic event. During the subsequent Silurian Laurentia-Baltica collision variably oriented, lower-grade chlorite and epidote-coated faults formed in response to a ENE-WSW compressional stress regime. A large number of mainly N-S striking normal faults consist of variably thick fault gouge cores with illite, quartz, kaolinite, calcite and epidote mineralizations, accommodating mainly E-W extension. K-Ar dating of illites separated from representative fault gouges and zones of altered granodiorite constrain deformation ranging from the Permian to the Late Jurassic, indicating a long history of crustal extension where faults were repeatedly activated. In addition, a set of ca. SW-NE striking faults associated with alteration zones give Cretaceous dates, either representing a young phase of NW-SE extension or reactivation of previously formed

  16. Mid-Atlantic Wind - Overcoming the Challenges

    SciTech Connect

    Daniel F. Ancona III; Kathryn E. George; Lynn Sparling; Bruce C. Buckheit; Daniel LoBue; and Richard P. Bowers

    2012-06-29

    This study, supported by the US Department of Energy, Wind Powering America Program, Maryland Department of Natural Resources and Chesapeake Bay Foundation, analyzed barriers to wind energy development in the Mid-Atlantic region along with options for overcoming or mitigating them. The Mid-Atlantic States including Delaware, Maryland, North Carolina and Virginia, have excellent wind energy potential and growing demand for electricity, but only two utility-scale projects have been installed to date. Reasons for this apathetic development of wind resources were analyzed and quantified for four markets. Specific applications are: 1) Appalachian mountain ridgeline sites, 2) on coastal plains and peninsulas, 3) at shallow water sites in Delaware and Chesapeake Bays, Albemarle and Pamlico Sounds, and 4) at deeper water sites off the Atlantic coast. Each market has distinctly different opportunities and barriers. The primary barriers to wind development described in this report can be grouped into four categories; state policy and regulatory issues, wind resource technical uncertainty, economic viability, and public interest in environmental issues. The properties of these typologies are not mutually independent and do interact. The report concluded that there are no insurmountable barriers to land-based wind energy projects and they could be economically viable today. Likewise potential sites in sheltered shallow waters in regional bay and sounds have been largely overlooked but could be viable currently. Offshore ocean-based applications face higher costs and technical and wind resource uncertainties. The ongoing research and development program, revision of state incentive policies, additional wind measurement efforts, transmission system expansion, environmental baseline studies and outreach to private developers and stakeholders are needed to reduce barriers to wind energy development.

  17. Mid-Atlantic Wind - Overcoming the Challenges

    SciTech Connect

    Daniel F. Ancona III; Kathryn E. George; Richard P. Bowers; Dr. Lynn Sparling; Bruce Buckheit; Daniel LoBue

    2012-05-31

    This study, supported by the US Department of Energy, Wind Powering America Program, Maryland Department of Natural Resources and Chesapeake Bay Foundation, analyzed barriers to wind energy development in the Mid-Atlantic region along with options for overcoming or mitigating them. The Mid-Atlantic States including Delaware, Maryland, North Carolina and Virginia, have excellent wind energy potential and growing demand for electricity, but only two utility-scale projects have been installed to date. Reasons for this apathetic development of wind resources were analyzed and quantified for four markets. Specific applications are: 1) Appalachian mountain ridgeline sites, 2) on coastal plains and peninsulas, 3) at shallow water sites in Delaware and Chesapeake Bays, Albemarle and Pamlico Sounds, and 4) at deeper water sites off the Atlantic coast. Each market has distinctly different opportunities and barriers. The primary barriers to wind development described in this report can be grouped into four categories; state policy and regulatory issues, wind resource technical uncertainty, economic viability, and public interest in environmental issues. The properties of these typologies are not mutually independent and do interact. The report concluded that there are no insurmountable barriers to land-based wind energy projects and they could be economically viable today. Likewise potential sites in sheltered shallow waters in regional bay and sounds have been largely overlooked but could be viable currently. Offshore ocean-based applications face higher costs and technical and wind resource uncertainties. The ongoing research and development program, revision of state incentive policies, additional wind measurement efforts, transmission system expansion, environmental baseline studies and outreach to private developers and stakeholders are needed to reduce barriers to wind energy development.

  18. SG2PS (structural geology to postscript converter) - A graphical solution for brittle structural data evaluation and paleostress calculation

    NASA Astrophysics Data System (ADS)

    Sasvári, Ágoston; Baharev, Ali

    2014-05-01

    The aim of this work was to create an open source cross platform application to process brittle structural geological data with seven paleostress inversion algorithms published by different authors and formerly not available within a single desktop application. The tool facilitates separate processing and plotting of different localities, data types and user made groups, using the same single input file. Simplified data input is supported, requiring as small amount of data as possible. Data rotation to correct for bedding tilting, rotation with paleomagnetic declination and k-means clustering are available. RUP and ANG stress estimators calculation and visualization, resolved shear direction display and Mohr circle stress visualization are available. RGB-colored vector graphical outputs are automatically generated in Encapsulated PostScript and Portable Document Format. Stereographical displays on great circle or pole point plot, equal area or equal angle net and upper or lower hemisphere projections are implemented. Rose plots displaying dip direction or strike, with dip angle distribution of the input data set are available. This tool is ideal for preliminary data interpretation on the field (quick processing and visualization in seconds); the implemented methods can be regularly used in the daily academic and industrial work as well. The authors' goal was to create an open source and self-contained desktop application that does not require any additional third party framework (such as .NET) or the Java Virtual Machine. The software has a clear and highly modular structure enabling good code portability, easy maintainability, reusability and extensibility. A Windows installer is publicly available and the program is also fully functional on Linux. The Mac OS X port should be feasible with minimal effort. The install file with test and demo data sets, detailed manual, and links to the GitHub repositories are available on the regularly updated website www.sg2ps.eu.

  19. Software Configuration Management Guidebook

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The growth in cost and importance of software to NASA has caused NASA to address the improvement of software development across the agency. One of the products of this program is a series of guidebooks that define a NASA concept of the assurance processes which are used in software development. The Software Assurance Guidebook, SMAP-GB-A201, issued in September, 1989, provides an overall picture of the concepts and practices of NASA in software assurance. Lower level guidebooks focus on specific activities that fall within the software assurance discipline, and provide more detailed information for the manager and/or practitioner. This is the Software Configuration Management Guidebook which describes software configuration management in a way that is compatible with practices in industry and at NASA Centers. Software configuration management is a key software development process, and is essential for doing software assurance.

  20. Overcoming the Challenges of 21cm Cosmology

    NASA Astrophysics Data System (ADS)

    Pober, Jonathan

    The highly-redshifted 21cm line of neutral hydrogen is one of the most promising and unique probes of cosmology for the next decade and beyond. The past few years have seen a number of dedicated experiments targeting the 21cm signal from the Epoch of Reionization (EoR) begin operation, including the LOw-Frequency ARray (LOFAR), the Murchison Widefield Array (MWA), and the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER). For these experiments to yield cosmological results, they require new calibration and analysis algorithms which will need to achieve unprecedented levels of separation between the 21cm signal and contaminating foreground emission. Although much work has been spent developing these algorithms over the past decade, their success or failure will ultimately depend on their ability to overcome the complications associated with real-world systems and their inherent complications. The work in this dissertation is closely tied to the late-stage commissioning and early observations with PAPER. The first two chapters focus on developing calibration algorithms to overcome unique problems arising in the PAPER system. To test these algorithms, I rely on not only simulations, but on commissioning observations, ultimately tying the success of the algorithm to its performance on actual, celestial data. The first algorithm works to correct gain-drifts in the PAPER system caused by the heating and cooling of various components (the amplifiers and above ground co-axial cables, in particular). It is shown that a simple measurement of the ambient temperature can remove ˜ 10% gain fluctuations in the observed brightness of calibrator sources. This result is highly encouraging for the ability of PAPER to remove a potentially dominant systematic in its power spectrum and cataloging measurements without resorting to a complicated system overhaul. The second new algorithm developed in this dissertation solves a major calibration challenge not

  1. Software distribution using xnetlib

    SciTech Connect

    Dongarra, J.J. |; Rowan, T.H.; Wade, R.C.

    1993-06-01

    Xnetlib is a new tool for software distribution. Whereas its predecessor netlib uses e-mail as the user interface to its large collection of public-domain mathematical software, xnetlib uses an X Window interface and socket-based communication. Xnetlib makes it easy to search through a large distributed collection of software and to retrieve requested software in seconds.

  2. Agile Software Development

    ERIC Educational Resources Information Center

    Biju, Soly Mathew

    2008-01-01

    Many software development firms are now adopting the agile software development method. This method involves the customer at every level of software development, thus reducing the impact of change in the requirement at a later stage. In this article, the principles of the agile method for software development are explored and there is a focus on…

  3. Software productivity improvement through software engineering technology

    NASA Technical Reports Server (NTRS)

    Mcgarry, F. E.

    1985-01-01

    It has been estimated that NASA expends anywhere from 6 to 10 percent of its annual budget on the acquisition, implementation and maintenance of computer software. Although researchers have produced numerous software engineering approaches over the past 5-10 years; each claiming to be more effective than the other, there is very limited quantitative information verifying the measurable impact htat any of these technologies may have in a production environment. At NASA/GSFC, an extended research effort aimed at identifying and measuring software techniques that favorably impact productivity of software development, has been active over the past 8 years. Specific, measurable, software development technologies have been applied and measured in a production environment. Resulting software development approaches have been shown to be effective in both improving quality as well as productivity in this one environment.

  4. Software Formal Inspections Standard

    NASA Technical Reports Server (NTRS)

    1993-01-01

    This Software Formal Inspections Standard (hereinafter referred to as Standard) is applicable to NASA software. This Standard defines the requirements that shall be fulfilled by the software formal inspections process whenever this process is specified for NASA software. The objective of this Standard is to define the requirements for a process that inspects software products to detect and eliminate defects as early as possible in the software life cycle. The process also provides for the collection and analysis of inspection data to improve the inspection process as well as the quality of the software.

  5. VOUS Software Facilitates Development Of Other Software

    NASA Technical Reports Server (NTRS)

    Oliger, Joseph; Pichumani, Ramini; Ponceleon, Dulce

    1992-01-01

    Visual Object Oriented Unification System (VOUS) computer program provides facility for development of other, high-level software. Does not replace, but rather extends, preexisting software tools for development of other software. Provides comprehensive, graphical, interactive medium for all phases in development of computer code from early exploration of concepts, through detailed coding-and-error-checking process, to final reporting of finished code and compilation of instruction manual for its use. Simplifies and partly automates programmer's task.

  6. Brittle deformation and exhumation mechanisms in the core of the Eastern Alps, The Tauern Window

    NASA Astrophysics Data System (ADS)

    Bertrand, Audrey; Garcia, Sebastian; Rosenberg, Claudio

    2010-05-01

    The Tauern Window (TW) is a Tertiary structural and thermal dome located in the core of the Eastern Alpine orogen and in front of the Dolomite indenter. The Penninic basement and cover units within the TW attained their thermal peak about 30 Myr ago (e.g., Selverstone et al., 1992) followed by cooling and exhumation from Early Oligocene to late Miocene time (e.g., Grundmann and Morteani, 1985). Most exhumation was partly accommodated by two normal faults at the western and eastern ends of the TW (Brenner and Katschberg faults, respectively). Although these normal faults are well described in the literature, their roles in the exhumation of the TW are still under debate: Exhumation accommodated primarily by folding and erosion (e.g., Rosenberg et al., 2004) versus exhumation mainly accommodated by Brenner and Katschberg normal faulting (e.g., Selverstone, 1988; Ratschbacher et al., 1989). New fault-slip data from the TW allow us to reconstruct paleostress axes by inversion and to constrain the relative roles of the folding and orogen-parallel extension during the late deformation history of the TW, in the brittle-field. Our results show little evidence of compression and a clear zoning of the paleostress field in the TW. In the central part of the TW, the σ1 direction is sub-horizontal N-S to NE-SW (strike-slip), whereas it is steep in the footwall of the Brenner and the Katschberg normal faults. Local variability of the σ3 direction are observed; indeed, the σ3 direction varies from E-W to WNW-ESE along the Brenner fault, to NW-SE along the Jaufen fault, the inferred southern continuation of the Brenner fault (Schneider et al., this session). Along the Katschberg fault, the σ3 direction is mainly NNW-SSE oriented, which is consistent with extension in front of a triangular dead zone shape induced by the WSW-striking Dolomites indenter. Nearly no evidence of a stress field compatible with upright folding (D2 phase of deformation) was found in the brittle domain

  7. Software For Computing Reliability Of Other Software

    NASA Technical Reports Server (NTRS)

    Nikora, Allen; Antczak, Thomas M.; Lyu, Michael

    1995-01-01

    Computer Aided Software Reliability Estimation (CASRE) computer program developed for use in measuring reliability of other software. Easier for non-specialists in reliability to use than many other currently available programs developed for same purpose. CASRE incorporates mathematical modeling capabilities of public-domain Statistical Modeling and Estimation of Reliability Functions for Software (SMERFS) computer program and runs in Windows software environment. Provides menu-driven command interface; enabling and disabling of menu options guides user through (1) selection of set of failure data, (2) execution of mathematical model, and (3) analysis of results from model. Written in C language.

  8. Starlink Software Submission

    NASA Astrophysics Data System (ADS)

    Lawden, M. D.

    The definition, structure and management of the Starlink Software Collection is described in SGP/20 which should be read by everyone involved in the production of software for the Starlink project. The Collection is managed by the Starlink Software Librarian (username STAR) who decides where new software should be stored in the existing structure and who has editorial control of Starlink documentation. This paper describes the principles governing the preparation and submission of software for inclusion in the Collection.

  9. Responsbility for unreliable software

    SciTech Connect

    Wahl, N.J.

    1994-12-31

    Unreliable software exposes software developers and distributors to legal risks. Under certain circumstances, the developer and distributor of unreliable software can be sued. To avoid lawsuits, software developers should do the following: determine what the risks am, understand the extent of the risks, and identify ways of avoiding the risks and lessening the consequences of the risks. Liability issues associated with unreliable software are explored in this article.

  10. Software component quality evaluation

    NASA Technical Reports Server (NTRS)

    Clough, A. J.

    1991-01-01

    The paper describes a software inspection process that can be used to evaluate the quality of software components. Quality criteria, process application, independent testing of the process and proposed associated tool support are covered. Early results indicate that this technique is well suited for assessing software component quality in a standardized fashion. With automated machine assistance to facilitate both the evaluation and selection of software components, such a technique should promote effective reuse of software components.

  11. DOCLIB: a software library for document processing

    NASA Astrophysics Data System (ADS)

    Jaeger, Stefan; Zhu, Guangyu; Doermann, David; Chen, Kevin; Sampat, Summit

    2006-01-01

    Most researchers would agree that research in the field of document processing can benefit tremendously from a common software library through which institutions are able to develop and share research-related software and applications across academic, business, and government domains. However, despite several attempts in the past, the research community still lacks a widely-accepted standard software library for document processing. This paper describes a new library called DOCLIB, which tries to overcome the drawbacks of earlier approaches. Many of DOCLIB's features are unique either in themselves or in their combination with others, e.g. the factory concept for support of different image types, the juxtaposition of image data and metadata, or the add-on mechanism. We cherish the hope that DOCLIB serves the needs of researchers better than previous approaches and will readily be accepted by a larger group of scientists.

  12. Experiments on buoyancy-driven crack around the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Sumita, Ikuro; Ota, Yukari

    2011-04-01

    We report the results of laboratory experiments exploring how a buoyancy-driven liquid-filled crack migrates within a viscoelastic medium whose rheology is around the brittle-ductile transition. To model such medium, we use a low concentration agar, which has a small yield stress and a large yield strain (deformation) when it fractures. We find that around the transition, the fluid migrates as a hybrid of a diapir (head) and a dyke (tail). Here the diapir is a bulged crack in which fracturing occurs at its tip and closes at its tail to form a dyke. A small amount of fluid is left along its trail and the fluid decelerates with time. We study how the shape and velocity of a constant volume fluid change as two control parameters are varied; the agar concentration ( C) and the density difference Δρ between the fluid and the agar. Under a fixed Δρ, as C decreases the medium becomes ductile, and the trajectory and shape of the fluid changes from a linearly migrating dyke to a meandering or a bifurcating dyke, and finally to a diapir-dyke hybrid. In this transition, the shape of the crack tip viewed from above, changes from blade-like to a cusped-ellipse. A similar transition is also observed when Δρ increases under a fixed C, which can be interpreted using a force balance between the buoyancy and the yield stress. Our experiments indicate that cracks around the brittle-ductile transition deviates from those in an elastic medium by several ways, such as the relaxation of the crack bulge, slower deceleration rate, and velocity becoming insensitive to medium rheology. Our experiments suggest that the fluid migrates as a diapir-dyke hybrid around the brittle-ductile transition and that fluid migration of various styles can coexist at the same depth, if they have different buoyancy.

  13. An investigation of the mineral in ductile and brittle cortical mouse bone.

    PubMed

    Rodriguez-Florez, Naiara; Garcia-Tunon, Esther; Mukadam, Quresh; Saiz, Eduardo; Oldknow, Karla J; Farquharson, Colin; Millán, José Luis; Boyde, Alan; Shefelbine, Sandra J

    2015-05-01

    Bone is a strong and tough material composed of apatite mineral, organic matter, and water. Changes in composition and organization of these building blocks affect bone's mechanical integrity. Skeletal disorders often affect bone's mineral phase, either by variations in the collagen or directly altering mineralization. The aim of the current study was to explore the differences in the mineral of brittle and ductile cortical bone at the mineral (nm) and tissue (µm) levels using two mouse phenotypes. Osteogenesis imperfecta model, oim(-/-) , mice have a defect in the collagen, which leads to brittle bone; PHOSPHO1 mutants, Phospho1(-/-) , have ductile bone resulting from altered mineralization. Oim(-/-) and Phospho1(-/-) were compared with their respective wild-type controls. Femora were defatted and ground to powder to measure average mineral crystal size using X-ray diffraction (XRD) and to monitor the bulk mineral to matrix ratio via thermogravimetric analysis (TGA). XRD scans were run after TGA for phase identification to assess the fractions of hydroxyapatite and β-tricalcium phosphate. Tibiae were embedded to measure elastic properties with nanoindentation and the extent of mineralization with backscattered electron microscopy (BSE SEM). Results revealed that although both pathology models had extremely different whole-bone mechanics, they both had smaller apatite crystals, lower bulk mineral to matrix ratio, and showed more thermal conversion to β-tricalcium phosphate than their wild types, indicating deviations from stoichiometric hydroxyapatite in the original mineral. In contrast, the degree of mineralization of bone matrix was different for each strain: brittle oim(-/-) were hypermineralized, whereas ductile Phospho1(-/-) were hypomineralized. Despite differences in the mineralization, nanoscale alterations in the mineral were associated with reduced tissue elastic moduli in both pathologies. Results indicated that alterations from normal crystal size

  14. What do we know about the initiation and early stages of brittle faulting in crystalline rocks?

    NASA Astrophysics Data System (ADS)

    Crider, J. G.

    2011-12-01

    The styles of initiation and subsequent growth of faults control fault length-slip scaling, the internal structure of fault zones, and fault-rock properties, influencing seismogenic behavior and fluid flow along the faults. Observations by many researchers over the last several decades have illustrated that faults in the upper crust initiate on pre-existing (inherited) or precursory (early-formed) structures and grow by the mechanical interaction and linkage of these structures. These pre-existing and precursory structures are typically mode I fractures (joints, veins, dikes) but may also be semi-brittle shear zones (such as deformation bands in porous sandstone). Research in the granitic outcrops of the central Sierra Nevada (California) has provided significant insight into the geometry and fundamental mechanics of the early stages of fault development. This work has shown that faults in plutonic rocks initiate on pre-existing or precursory joints or dikes and that the discontinuous nature of early mode I fractures has a strong influence on the subsequent development of the fault zone. In basalt, we have similarly observed the important influence of preexisting joints, and, at a broader scale, precursory, semi-brittle shear zones in the form of fault-tip monoclines. In metamorphic rocks, foliation appears to control the initial development of faults, influencing fault orientation, or enabling precursory structures such as kink bands. Kink bands, like deformation bands in porous sandstone, accommodate only small strains before locking, but then become strong inclusions in the material, serving to localize brittle fractures. The quasi-static mechanics of isotropic, isothermal linear-elastic materials in two and three dimensions provides first order understanding of controls on interaction and linkage of early structures, including the concentration of stresses and local stress reorientation. Fruitful research directions important to faulting in crystalline rock

  15. New perspectives on the transition between discrete fracture, fragmentation, and pulverization during brittle failure of rocks

    NASA Astrophysics Data System (ADS)

    Griffith, W. A.; Ghaffari, H.; Barber, T. J.; Borjas, C.

    2015-12-01

    The motions of Earth's tectonic plates are typically measured in millimeters to tens of centimeters per year, seemingly confirming the generally-held view that tectonic processes are slow, and have been throughout Earth's history. In line with this perspective, the vast majority of laboratory rock mechanics research focused on failure in the brittle regime has been limited to experiments utilizing slow loading rates. On the other hand, many natural processes that pose significant risk for humans (e.g., earthquakes and extraterrestrial impacts), as well as risks associated with human activities (blow-outs, explosions, mining and mine failures, projectile penetration), occur at rates that are hundreds to thousands of times faster than those typically simulated in the laboratory. Little experimental data exists to confirm or calibrate theoretical models explaining the connection between these dramatic events and the pulverized rocks found in fault zones, impacts, or explosions; however the experimental data that does exist is thought-provoking: At the earth's surface, the process of brittle fracture passes through a critical transition in rocks at high strain rates (101-103s-1) between regimes of discrete fracture and distributed fragmentation, accompanied by a dramatic increase in strength. Previous experimental works on this topic have focused on key thresholds (e.g., peak stress, peak strain, average strain rate) that define this transition, but more recent work suggests that this transition is more fundamentally dependent on characteristics (e.g., shape) of the loading pulse and related microcrack dynamics, perhaps explaining why for different lithologies different thresholds more effectively define the pulverization transition. In this presentation we summarize some of our work focused on this transition, including the evolution of individual defects at the microscopic, microsecond scale and the energy budget associated with the brittle fragmentation process as a

  16. Dykes, cups, saucers and sills: Analogue experiments on magma intrusion into brittle rocks

    NASA Astrophysics Data System (ADS)

    Mathieu, L.; van Wyk de Vries, B.; Holohan, Eoghan P.; Troll, Valentin R.

    2008-07-01

    Magma is transported in the crust by blade-like intrusions such as dykes, sills, saucers, and also collects in thicker laccoliths, lopoliths and plutons. Recently, the importance and great number of shallow (< 5 km) saucer-shaped intrusions has been recognized. Lopoliths and cup-shaped intrusions have also been reported in many geological contexts. Our field observations indicate that many intrusions, especially those emplaced into breccias or fractured rocks, have bulging, lobate margins and have shear faults at their bulbous terminations. Such features suggest that magma can propagate along a self-induced shear fault rather than a hydraulic tension-fracture. To investigate this we use analogue models to explore intrusion propagation in a brittle country rock. The models consist of the injection of analogue magma (honey or Golden syrup) in a granular material (sand or sieved ignimbrite) that is a good analogue for brittle or brecciated rocks. These models have the advantage (over other models that use gelatin) to well represent the properties of brittle materials by allowing both shear-faults and tension fractures to be produced at suitable stresses. In our experiments we mainly obtain vertical dykes and inverted-cone like structures that we call cup-shaped intrusions. Dykes bifurcate into cup-shaped intrusions at depths depending on their viscosity. All cup-shaped intrusions uplift a central block. By injecting against a vertical glass plate we obtain detailed observations of the intrusion propagation style. We observe that dykes commonly split and produce cup-shaped intrusions near the surface and that shear zone-related intrusions develop at the dyke tip. We conclude that many dykes propagate as a viscous indenter resulting from shear failure of host rock rather than tensional hydraulic fracturing of host rocks. The shear propagation model provides an explanation for the shape and formation of cup-shaped intrusions, saucer-sills and lopoliths.

  17. Crack arrest toughness of a heat-affected zone containing local brittle zones

    SciTech Connect

    Malik, L.; Pussegoda, L.N.; Graville, B.A.; Tyson, W.R.

    1996-11-01

    The awareness of the presence of local brittle zones (LBZs) in the heat-affected zone (HAZ) of welds has led to the requirements for minimum initiation toughness for the HAZ for critical applications. A fracture control philosophy that is proposed to be an attractive alternative for heat-affected zones containing LBZs is the prevention of crack propagation rather than of crack initiation. Such an approach would be viable if it could be demonstrated that cracks initiated in the LBZs will be arrested without causing catastrophic failure, notwithstanding the low initiation (CTOD) toughness resulting from the presence of LBZs. Unstable propagation of a crack initiating from an LBZ requires the rupture of tougher microstructural regions surrounding the LBZ in HAZ, and therefore the CTOD value reflecting the presence of LBZ is unlikely to provide a true indication of the potential for fast fracture along the heat-affected zone. Base metal specifications usually ensure that small unstable cracks propagating from the weld zone into the base metal would be arrested. To investigate the likelihood of fast fracture within the HAZ, a test program has been carried out that involved performing compact plane strain and plane stress crack arrest tests on a heat-affected zone that contained LBZs, and thus exhibited unacceptable low CTOD toughness for resistance to brittle fracture initiation. The results indicated that the crack arrest toughness was little influenced by the presence of local brittle zones. Instead, the superior toughness of the larger proportion of finer-grain HAZ surrounding the LBZ present along the crack path has a greater influence on the crack arrest toughness.

  18. Brittle versus ductile deformation as the main control of the deep fluid circulation in continental crust

    NASA Astrophysics Data System (ADS)

    Violay, Marie; Madonna, Claudio; Burg, Jean-Pierre

    2016-04-01

    The Japan Beyond-Brittle Project (JBBP) and the Taupo Volcanic Zone-Deep geothermal drilling project in New Zealand (TVZ-DGDP) proposed a new concept of engineered geothermal development where reservoirs are created in ductile rocks. This system has several advantages including (1) a simpler design and control of the reservoir due to homogeneous rock properties and stress states in the ductile domain ,(2) possible extraction of supercritical fluids (3) less probability for induced earthquakes. However, it is at present unknwon what and how porosity and permeability can be engineered in such environments. It has been proposed that the magmatic chamber is surrounded by a hot and ductile carapace through which heat transfer is conductive because the plastic behaviour of the rock will close possible fluid pathways. Further outward, as temperature declines, the rock will encounter the brittle-ductile transition with a concomitant increase in porosity and permeability. The thickness of the conduction-dominated, ductile boundary zone between the magmatic chamber and the convecting geothermal fluid directly determines the rate of heat transfer. To examine the brittle to ductile transition in the context of the Japanese crust, we conducted deformation experiments on very-fine-grain granite in conventional servocontrolled, gas-medium triaxial apparatus (from Paterson instrument). Temperature ranged from 600° C to 1100° C and effective confining pressure from 100 to 150 MPa. Dilatancy was measured during deformation. The method consisted in monitoring the volume of pore fluid that flows into or out of the sample at constant pore pressure. Permeability was measured under static conditions by transient pressure pulse method. Mechanical and micro-structural observations at experimental constant strain rate of 10‑5 s‑1 indicated that the granite was brittle and dilatant up to 900 ° C. At higher temperatures the deformation mode becomes macroscopically ductile, i

  19. Estimating the tensile strength of super hard brittle materials using truncated spheroidal specimens

    NASA Astrophysics Data System (ADS)

    Serati, Mehdi; Alehossein, Habib; Williams, David J.

    2015-05-01

    New approaches need to be introduced to measure the tensile capacity of super hard materials since the standard methods are not effective. To pursue this objective, a series of laboratory tests were constructed to replicate the fracture mechanism of diamond-based materials. Experiments indicate that under a certain compressive test condition, stresses normal to the axisymmetric line in truncated spheroidal specimens (bullet-shaped specimens) are in tension contributing to the tensile fracture of the material. From experimental and numerical studies, it is concluded that semi-prolate spheroidal specimens can be used to determine precisely the tensile strength of brittle stiff diamond-like composites.

  20. Deformation and Fracture of Porous Brittle Materials Under Different Loading Schemes

    NASA Astrophysics Data System (ADS)

    Savchenko, N. L.; Sablina, T. Yu.; Sevostyanova, I. N.; Buyakova, S. P.; Kulkov, S. N.

    2016-03-01

    The behavior of alumina and zirconia compression- and shear-test specimens with porosity ranging from 10 to 70% is investigated. Analysis of the stress-strain curves for the materials under study has revealed a transition from a characteristically brittle fracture of fairly dense Al2O3 and ZrO2 specimens to pseudo-plastic fracture for a high porosity level. The ultimate compression strength, effective elastic and shear moduli, and Poisson's ratio are found to decrease with increase in the pore space volume of the ceramic specimens, which is shown to correlate with development of strain-induced multiple cracking of the materials.

  1. From Brittle to Pliant Viscoelastic Materials with Solid State Linear Polyphosphonium - Carboxylate Assemblies

    PubMed Central

    Godeau, Guilhem; Navailles, Laurence; Nallet, Frédéric; Lin, Xinrong; McIntosh, Thomas J.; Grinstaff, Mark W.

    2013-01-01

    A polystyrenylphosphonium polymer was synthesized and complexed with various carboxylic acid derivatives to form new solid-state polyelectrolyte-surfactant assemblies. The properties of these ionic materials were highly dependent on the nature of the anion and included a brittle material, a rubbery ball that bounces, or a sticky fiber. The values for the equilibrium modulus, storage modulus, and loss modulus were dependent on the composition of the carboxylic acid and the number of electrostatic interactions. Small-angle X-ray scattering studies on the supramolecular assemblies confirmed a bilayer structure for two of the assemblies. PMID:24511156

  2. A multiscale coupling method for the modeling of dynamics of solids with application to brittle cracks

    SciTech Connect

    Li Xiantao Yang, Jerry Z. E, Weinan

    2010-05-20

    We present a multiscale model for numerical simulations of dynamics of crystalline solids. The method combines the continuum nonlinear elasto-dynamics model, which models the stress waves and physical loading conditions, and molecular dynamics model, which provides the nonlinear constitutive relation and resolves the atomic structures near local defects. The coupling of the two models is achieved based on a general framework for multiscale modeling - the heterogeneous multiscale method (HMM). We derive an explicit coupling condition at the atomistic/continuum interface. Application to the dynamics of brittle cracks under various loading conditions is presented as test examples.

  3. Process diagnostics for precision grinding brittle materials in a production environment

    SciTech Connect

    Blaedel, K L; Davis, P J; Piscotty, M A

    1999-04-01

    Precision grinding processes are steadily migrating from research laboratory environments into manufacturing production lines as precision machines and processes become increasingly more commonplace throughout industry. Low-roughness, low-damage precision grinding is gaining widespread commercial acceptance for a host of brittle materials including advanced structural ceramics. The development of these processes is often problematic and requires diagnostic information and analysis to harden the processes for manufacturing. This paper presents a series of practical precision grinding tests developed and practiced at Lawrence Livermore National Laboratory that yield important information to help move a new process idea into production.

  4. Mechanical Behavior of Low Porosity Carbonate Rock: From Brittle Creep to Ductile Creep.

    NASA Astrophysics Data System (ADS)

    Nicolas, A.; Fortin, J.; Gueguen, Y.

    2014-12-01

    Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this study, we focus on the mechanical behavior of a 14.7% porosity white Tavel (France) carbonate rock (>98% calcite). The samples were deformed in a triaxial cell at effective confining pressures ranging from 0 MPa to 85 MPa at room temperature and 70°C. Experiments were carried under dry and water saturated conditions in order to explore the role played by the pore fluids. Two types of experiments have been carried out: (1) a first series in order to investigate the rupture envelopes, and (2) a second series with creep experiments. During the experiments, elastic wave velocities (P and S) were measured to infer crack density evolution. Permeability was also measured during creep experiments. Our results show two different mechanical behaviors: (1) brittle behavior is observed at low confining pressures, whereas (2) ductile behavior is observed at higher confining pressures. During creep experiments, these two behaviors have a different signature in term of elastic wave velocities and permeability changes, due to two different mechanisms: development of micro-cracks at low confining pressures and competition between cracks and microplasticity at high confining pressure. The attached figure is a summary of 20 triaxial experiments performed on Tavel limestone under different conditions. Stress states C',C* and C*' and brittle strength are shown in the P-Q space: (a) 20°C and dry

  5. Brittle-viscous deformation cycles in the dry lower continental crust

    NASA Astrophysics Data System (ADS)

    Menegon, Luca; Pennacchioni, Giorgio

    2015-04-01

    Many rheological models of the lithosphere (based on "strength envelopes") predict a weak aseismic lower crust below the strong brittle upper crust. An alternative view, based on the distribution of crustal seismicity, is that the lower crust could also be strong and seismic. It has been suggested that a strong, seismogenic lower crust results from the dry conditions of granulite facies rocks, which inhibit crystal plastic flow. This study investigates exhumed networks of shear zones from Nusfjord (Lofoten, northern Norway) to understand initiation and localization of viscous shearing in the dry lower crust. In the study area, different sets of ultramylonitic shear zones are hosted in the massive coarse-grained anorthosite. Metamorphic conditions of 720 °C, 0.9 GPa have been estimated for ductile deformation using amphibole-plagioclase geothermobarometry. Field evidence indicates that ductile shearing exploited pseudotachylyte veins and the associated damage zone of extensive fracturing. Undeformed pseudotachylyte veins locally overprint mylonitic pseudotachylytes suggesting that frictional melting occurred at the same metamorphic conditions of mylonitization. The deep crustal origin of the pseudotachylytes is also indicated by (1) the presence of microlites of labradoritic plagioclase and clinopyroxene, and of dendritic garnet, and (2) the recrystallization of clinopyroxene in the damage zone flanking the pseudotachylyte veins. Therefore the association of pseudotachylytes and mylonites records brittle-viscous deformation cycles under lower crustal conditions. The ultramylonites show phase mixing, fine grain size (5-20 μm) and equant shape of all minerals. Nucleation of amphibole in triple junctions and dilatant sites is common. EBSD analysis indicates that the minerals in the matrix are internally strain free and do not show a crystallographic preferred orientation. Taken together, these observations suggest that diffusion creep and grain boundary sliding were

  6. Nietzschean Images of Self-Overcoming: Response to Rosenow.

    ERIC Educational Resources Information Center

    Hillesheim, James W.

    1990-01-01

    Discusses interpretations of a key Nietzschean concept, "Selbstuberwindung," translated as "self-overcoming," which challenges the concept of "self-mastery" or "self-control" found in traditional educational thought. Also discussed is Nietzsche's construction of images of self-overcoming individuals, examples designed to stimulate the process of…

  7. Software Quality Assurance Metrics

    NASA Technical Reports Server (NTRS)

    McRae, Kalindra A.

    2004-01-01

    Software Quality Assurance (SQA) is a planned and systematic set of activities that ensures conformance of software life cycle processes and products conform to requirements, standards and procedures. In software development, software quality means meeting requirements and a degree of excellence and refinement of a project or product. Software Quality is a set of attributes of a software product by which its quality is described and evaluated. The set of attributes includes functionality, reliability, usability, efficiency, maintainability, and portability. Software Metrics help us understand the technical process that is used to develop a product. The process is measured to improve it and the product is measured to increase quality throughout the life cycle of software. Software Metrics are measurements of the quality of software. Software is measured to indicate the quality of the product, to assess the productivity of the people who produce the product, to assess the benefits derived from new software engineering methods and tools, to form a baseline for estimation, and to help justify requests for new tools or additional training. Any part of the software development can be measured. If Software Metrics are implemented in software development, it can save time, money, and allow the organization to identify the caused of defects which have the greatest effect on software development. The summer of 2004, I worked with Cynthia Calhoun and Frank Robinson in the Software Assurance/Risk Management department. My task was to research and collect, compile, and analyze SQA Metrics that have been used in other projects that are not currently being used by the SA team and report them to the Software Assurance team to see if any metrics can be implemented in their software assurance life cycle process.

  8. Space Station Software Recommendations

    NASA Technical Reports Server (NTRS)

    Voigt, S. (Editor)

    1985-01-01

    Four panels of invited experts and NASA representatives focused on the following topics: software management, software development environment, languages, and software standards. Each panel deliberated in private, held two open sessions with audience participation, and developed recommendations for the NASA Space Station Program. The major thrusts of the recommendations were as follows: (1) The software management plan should establish policies, responsibilities, and decision points for software acquisition; (2) NASA should furnish a uniform modular software support environment and require its use for all space station software acquired (or developed); (3) The language Ada should be selected for space station software, and NASA should begin to address issues related to the effective use of Ada; and (4) The space station software standards should be selected (based upon existing standards where possible), and an organization should be identified to promulgate and enforce them. These and related recommendations are described in detail in the conference proceedings.

  9. Payload software technology: Software technology development plan

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Programmatic requirements for the advancement of software technology are identified for meeting the space flight requirements in the 1980 to 1990 time period. The development items are described, and software technology item derivation worksheets are presented along with the cost/time/priority assessments.

  10. Software For Simulation Of Development Of Software

    NASA Technical Reports Server (NTRS)

    Tausworthe, Robert C.

    1991-01-01

    SOFTREL is prototype software package simulating creation, detection, and repair of defects and faults during software-development project. Personnel, resources, errors, and other realistic factors represented in simulation. Available in executable form only for IBM PC. SOFTREL is copyrighted work with all copyright vested in NASA.

  11. Software Engineering Program: Software Process Improvement Guidebook

    NASA Technical Reports Server (NTRS)

    1996-01-01

    The purpose of this document is to provide experience-based guidance in implementing a software process improvement program in any NASA software development or maintenance community. This guidebook details how to define, operate, and implement a working software process improvement program. It describes the concept of the software process improvement program and its basic organizational components. It then describes the structure, organization, and operation of the software process improvement program, illustrating all these concepts with specific NASA examples. The information presented in the document is derived from the experiences of several NASA software organizations, including the SEL, the SEAL, and the SORCE. Their experiences reflect many of the elements of software process improvement within NASA. This guidebook presents lessons learned in a form usable by anyone considering establishing a software process improvement program within his or her own environment. This guidebook attempts to balance general and detailed information. It provides material general enough to be usable by NASA organizations whose characteristics do not directly match those of the sources of the information and models presented herein. It also keeps the ideas sufficiently close to the sources of the practical experiences that have generated the models and information.

  12. Software Defined Radio with Parallelized Software Architecture

    NASA Technical Reports Server (NTRS)

    Heckler, Greg

    2013-01-01

    This software implements software-defined radio procession over multicore, multi-CPU systems in a way that maximizes the use of CPU resources in the system. The software treats each processing step in either a communications or navigation modulator or demodulator system as an independent, threaded block. Each threaded block is defined with a programmable number of input or output buffers; these buffers are implemented using POSIX pipes. In addition, each threaded block is assigned a unique thread upon block installation. A modulator or demodulator system is built by assembly of the threaded blocks into a flow graph, which assembles the processing blocks to accomplish the desired signal processing. This software architecture allows the software to scale effortlessly between single CPU/single-core computers or multi-CPU/multi-core computers without recompilation. NASA spaceflight and ground communications systems currently rely exclusively on ASICs or FPGAs. This software allows low- and medium-bandwidth (100 bps to approx.50 Mbps) software defined radios to be designed and implemented solely in C/C++ software, while lowering development costs and facilitating reuse and extensibility.

  13. Software Defined Radio with Parallelized Software Architecture

    NASA Technical Reports Server (NTRS)

    Heckler, Greg

    2013-01-01

    This software implements software-defined radio procession over multi-core, multi-CPU systems in a way that maximizes the use of CPU resources in the system. The software treats each processing step in either a communications or navigation modulator or demodulator system as an independent, threaded block. Each threaded block is defined with a programmable number of input or output buffers; these buffers are implemented using POSIX pipes. In addition, each threaded block is assigned a unique thread upon block installation. A modulator or demodulator system is built by assembly of the threaded blocks into a flow graph, which assembles the processing blocks to accomplish the desired signal processing. This software architecture allows the software to scale effortlessly between single CPU/single-core computers or multi-CPU/multi-core computers without recompilation. NASA spaceflight and ground communications systems currently rely exclusively on ASICs or FPGAs. This software allows low- and medium-bandwidth (100 bps to .50 Mbps) software defined radios to be designed and implemented solely in C/C++ software, while lowering development costs and facilitating reuse and extensibility.

  14. Structural hierarchies define toughness and defect-tolerance despite simple and mechanically inferior brittle building blocks

    PubMed Central

    Sen, Dipanjan; Buehler, Markus J.

    2011-01-01

    Mineralized biological materials such as bone, sea sponges or diatoms provide load-bearing and armor functions and universally feature structural hierarchies from nano to macro. Here we report a systematic investigation of the effect of hierarchical structures on toughness and defect-tolerance based on a single and mechanically inferior brittle base material, silica, using a bottom-up approach rooted in atomistic modeling. Our analysis reveals drastic changes in the material crack-propagation resistance (R-curve) solely due to the introduction of hierarchical structures that also result in a vastly increased toughness and defect-tolerance, enabling stable crack propagation over an extensive range of crack sizes. Over a range of up to four hierarchy levels, we find an exponential increase in the defect-tolerance approaching hundred micrometers without introducing additional mechanisms or materials. This presents a significant departure from the defect-tolerance of the base material, silica, which is brittle and highly sensitive even to extremely small nanometer-scale defects. PMID:22355554

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

    PubMed Central

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

    2016-01-01

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

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

    PubMed

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

    2016-01-01

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

  17. PREDICTION OF CHARACTERISTIC LENGTH AND FRACTURE TOUGHNESS IN DUCTILE-BRITTLE TRANSITION

    SciTech Connect

    Lam, P

    2008-04-15

    Finite element method was used to analyze the three-point bend experimental data of A533B-1 pressure vessel steel obtained by Sherry, Lidbury, and Beardsmore [1] from -160 to -45 C within the ductile-brittle transition regime. As many researchers have shown, the failure stress ({sigma}{sub f}) of the material could be approximated as a constant. The characteristic length, or the critical distance (r{sub c}) from the crack tip, at which {sigma}{sub f} is reached, is shown to be temperature dependent based on the crack tip stress field calculated by the finite element method. With the J-A{sub 2} two-parameter constraint theory in fracture mechanics, the fracture toughness (J{sub C} or K{sub JC}) can be expressed as a function of the constraint level (A{sub 2}) and the critical distance r{sub c}. This relationship is used to predict the fracture toughness of A533B-1 in the ductile-brittle transition regime with a constant {sigma}{sub f} and a set of temperature-dependent r{sub c}. It can be shown that the prediction agrees well with the test data for wide range of constraint levels from shallow cracks (a/W= 0.075) to deep cracks (a/W= 0.5), where a is the crack length and W is the specimen width.

  18. Observation of microscopic damage accumulation in brittle solids subjected to dynamic compressive loading

    NASA Astrophysics Data System (ADS)

    Huang, S.; Xia, K.; Zheng, H.

    2013-09-01

    Dynamic failure of brittle materials is a fundamental physical problem that has significantly impacts to many science and engineering disciplines. As the first and the most important step towards the full understanding of this problem, one has to observe dynamic damage accumulation in brittle solids. In this work, we proposed a methodology to do that and demonstrated it by studying the dynamic compressive damage evolution of a granitic rock loaded with a modified split Hopkinson pressure bar system. To ensure consistency of the experimental results, we used cylindrical rock samples fabricated from the same rock core and subjected them to identical incident loading pulse. Using a special soft recovery technique, we stopped the dynamic loading on the samples at different strain levels, ranging from 0.3% to 1.4%. Therefore, we were able to recover intact samples loaded all the way to the post-peak deformation stage. The recovered samples were subsequently examined with X-ray micro-CT scanning machine. Three dimensional microcrack network induced by the dynamic loading was observed and the evolution of microcracks as a function of the dynamic loading strain was obtained.

  19. KrF excimer laser precision machining of hard and brittle ceramic biomaterials.

    PubMed

    Huang, Yao-Xiong; Lu, Jian-Yi; Huang, Jin-Xia

    2014-06-01

    KrF excimer laser precision machining of porous hard-brittle ceramic biomaterials was studied to find a suitable way of machining the materials into various desired shapes and sizes without distorting their intrinsic structure and porosity. Calcium phosphate glass ceramics (CPGs) and hydroxyapatite (HA) were chosen for the study. It was found that KrF excimer laser can cut both CPGs and HA with high efficiency and precision. The ablation rates of CPGs and HA are respectively 0.081 µm/(pulse J cm(-2)) and 0.048 µm/(pulse  J cm(-2)), while their threshold fluences are individually 0.72 and 1.5 J cm(-2). The cutting quality (smoothness of the cut surface) is a function of laser repetition rate and cutting speed. The higher the repetition rate and lower the cutting speed, the better the cutting quality. A comparison between the cross sections of CPGs and HA cut using the excimer laser and using a conventional diamond cutting blade indicates that those cut by the excimer laser could retain their intrinsic porosity and geometry without distortion. In contrast, those cut by conventional machining had distorted geometry and most of their surface porosities were lost. Therefore, when cutting hard-brittle ceramic biomaterials to prepare scaffold and implant or when sectioning them for porosity evaluation, it is better to choose KrF excimer laser machining. PMID:24784833

  20. A micromechanical constitutive model for the dynamic response of brittle materials "Dynamic response of marble"

    NASA Astrophysics Data System (ADS)

    Haberman, Keith

    2001-07-01

    A micromechanically based constitutive model for the dynamic inelastic behavior of brittle materials, specifically "Dionysus-Pentelicon marble" with distributed microcracking is presented. Dionysus-Pentelicon marble was used in the construction of the Parthenon, in Athens, Greece. The constitutive model is a key component in the ability to simulate this historic explosion and the preceding bombardment form cannon fire that occurred at the Parthenon in 1678. Experiments were performed by Rosakis (1999) that characterized the static and dynamic response of this unique material. A micromechanical constitutive model that was previously successfully used to model the dynamic response of granular brittle materials is presented. The constitutive model was fitted to the experimental data for marble and reproduced the experimentally observed basic uniaxial dynamic behavior quite well. This micromechanical constitutive model was then implemented into the three dimensional nonlinear lagrangain finite element code Dyna3d(1998). Implementing this methodology into the three dimensional nonlinear dynamic finite element code allowed the model to be exercised on several preliminary impact experiments. During future simulations, the model is to be used in conjunction with other numerical techniques to simulate projectile impact and blast loading on the Dionysus-Pentelicon marble and on the structure of the Parthenon.

  1. Visco-poroelastic damage model for brittle-ductile failure of porous rocks

    NASA Astrophysics Data System (ADS)

    Lyakhovsky, Vladimir; Zhu, Wenlu; Shalev, Eyal

    2015-04-01

    The coupling between damage accumulation, dilation, and compaction during loading of sandstones is responsible for different structural features such as localized deformation bands and homogeneous inelastic deformation. We distinguish and quantify the role of each deformation mechanism using new mathematical model and its numerical implementation. Formulation includes three different deformation regimes: (I) quasi-elastic deformation characterized by material strengthening and compaction; (II) cataclastic flow characterized by damage increase and compaction; and (III) brittle failure characterized by damage increase, dilation, and shear localization. Using a three-dimensional numerical model, we simulate the deformation behavior of cylindrical porous Berea sandstone samples under different confining pressures. The obtained stress, strain, porosity changes and macroscopic deformation features well reproduce the laboratory results. The model predicts different rock behavior as a function of confining pressures. The quasi-elastic and brittle regimes associated with formation of shear and/or dilatant bands occur at low effective pressures. The model also successfully reproduces cataclastic flow and homogeneous compaction under high pressures. Complex behavior with overlap of common features of all regimes is simulated under intermediate pressures, resulting with localized compaction or shear enhanced compaction bands. Numerical results elucidate three steps in the formation of compaction bands: (1) dilation and subsequent shear localization, (2) formation of shear enhanced compaction band, and (3) formation of pure compaction band.

  2. Migrating swarms of brittle-failure earthquakes in the lower crust beneath Mammoth Mountain, California

    USGS Publications Warehouse

    Shelly, D.R.; Hill, D.P.

    2011-01-01

    Brittle-failure earthquakes in the lower crust, where high pressures and temperatures would typically promote ductile deformation, are relatively rare but occasionally observed beneath active volcanic centers. Where they occur, these earthquakes provide a rare opportunity to observe volcanic processes in the lower crust, such as fluid injection and migration, which may induce brittle faulting under these conditions. Here, we examine recent short-duration earthquake swarms deep beneath the southwestern margin of Long Valley Caldera, near Mammoth Mountain. We focus in particular on a swarm that occurred September 29-30, 2009. To maximally illuminate the spatial-temporal progression, we supplement catalog events by detecting additional small events with similar waveforms in the continuous data, achieving up to a 10-fold increase in the number of locatable events. We then relocate all events, using cross-correlation and a double-difference algorithm. We find that the 2009 swarm exhibits systematically decelerating upward migration, with hypocenters shallowing from 21 to 19 km depth over approximately 12 hours. This relatively high migration rate, combined with a modest maximum magnitude of 1.4 in this swarm, suggests the trigger might be ascending CO2 released from underlying magma.

  3. Micromechanics of brittle faulting and cataclastic flow in Mount Etna basalt

    NASA Astrophysics Data System (ADS)

    Zhu, Wei; Baud, Patrick; Vinciguerra, Sergio; Wong, Teng-fong

    2016-06-01

    Understanding how the strength of volcanic rocks varies with stress state, pressure, and microstructural attributes is fundamental to understanding the dynamics and tectonics of a volcanic system and also very important in applications such as geothermics or reservoir management in volcanic environments. In this study we investigated the micromechanics of deformation and failure in basalt, focusing on samples from Mount Etna. We performed 65 uniaxial and triaxial compression experiments on nominally dry and water-saturated samples covering a porosity range between 5 and 16%, at effective pressures up to 200 MPa. Dilatancy and brittle faulting were observed in all samples with porosity of 5%. Water-saturated samples were found to be significantly weaker than comparable dry samples. Shear-enhanced compaction was observed at effective pressures as low as 80 MPa in samples of 8% porosity. Microstructural data revealed the complex interplay of microcracks, pores, and phenocrysts on dilatant failure and inelastic compaction in basalt. The micromechanics of brittle failure is controlled by wing crack propagation under triaxial compression and by pore-emanated cracking under uniaxial compression especially in the more porous samples. The mechanism of inelastic compaction in basalt is cataclastic pore-collapse in agreement with a recent dual-porosity model.

  4. Brittle and semibrittle behaviours of a carbonate rock: Influence of water and temperature

    NASA Astrophysics Data System (ADS)

    Nicolas, A.; Fortin, J.; Regnet, J. B.; Dimanov, A.; Guéguen, Y.

    2016-04-01

    Inelastic deformation can either occur with dilatancy or compaction, implying differences in porosity changes, failure and petrophysical properties. In this study, the roles of water as a pore fluid, and of temperature, on the deformation and failure of a micritic limestone (white Tavel limestone, porosity 14.7%) were investigated under triaxial stresses. For each sample, a hydrostatic load was applied up to the desired confining pressure (from 0 MPa up to 85 MPa) at either room temperature or at 70°C. Two pore fluid conditions were investigated at room temperature: dry and water saturated. The samples were deformed up to failure at a constant strain rate of ˜10-5s-1. The experiments were coupled with ultrasonic wave velocity surveys to monitor crack densities. The linear trend between the axial crack density and the relative volumetric strain beyond the onset of dilatancy suggests that cracks propagate at constant aspect ratio. The decrease of ultrasonic wave velocities beyond the onset of inelastic compaction in the semibrittle regime indicate the ongoing interplay of shear-enhanced compaction and crack development. Water has a weakening effect on the onset of dilatancy in the brittle regime, but no measurable influence on the peak strength. Temperature lowers the confining pressure at which the brittle-semibrittle transition is observed but does not change the stress states at the onset of inelastic compaction and at the post-yield onset of dilatancy.

  5. An Experimental Study of the Fracture Coalescence Behaviour of Brittle Sandstone Specimens Containing Three Fissures

    NASA Astrophysics Data System (ADS)

    Yang, S. Q.; Yang, D. S.; Jing, H. W.; Li, Y. H.; Wang, S. Y.

    2012-07-01

    To analyse the fracture coalescence behaviour of rock, rectangular prismatic sandstone specimens (80 × 160 × 30 mm in size) containing three fissures were tested under uniaxial compression. The strength and deformation behaviours of the specimens are first analysed by investigating the effects of the ligament angle β2 on the peak strength, peak strain and crack initiation stress of the specimens. To confirm the sequence of crack coalescence, a photographic monitoring technique is used throughout the entire period of deformation. Based on the results, the relationship between the real-time crack coalescence process and the axial stress-strain curve of brittle sandstone specimens is also developed, and this relationship can be used to evaluate the macroscopic deformation characteristics of pre-cracked rock. The equivalent strain evolution fields of the specimen, with α = β1 = 45° and β2 = 90°, are obtained using the digital image correlation technique and show good agreement with the experimental results of pre-cracked brittle sandstone. These experimental results are expected to improve the understanding of fracture mechanisms and be used in rock engineering with intermittent structures, such as deep underground excavated tunnels.

  6. Brittle and Ductile Behavior in Deep-Seated Landslides: Learning from the Vajont Experience

    NASA Astrophysics Data System (ADS)

    Paronuzzi, Paolo; Bolla, Alberto; Rigo, Elia

    2016-06-01

    This paper analyzes the mechanical behavior of the unstable Mt. Toc slope before the 1963 catastrophic collapse, considering both the measured data (surface displacements and microseismicity) and the updated geological model of the prehistoric rockslide. From February 1960 up to 9 October 1963, the unstable mass behaved as a brittle-ductile `mechanical system,' characterized by remarkable microseismicity as well as by considerable surface displacements (up to 4-5 m). Recorded microshocks were the result of progressive rock fracturing of distinct resisting stiff parts made up of intact rock (indentations, undulations, and rock bridges). The main resisting stiff part was a large rock indentation located at the NE extremity of the unstable mass that acted as a mechanical constraint during the whole 1960-1963 period, inducing a progressive rototranslation toward the NE. This large constraint failed in autumn 1960, when an overall slope failure took place, as emphasized by the occurrence of the large perimetrical crack in the upper slope. In this circumstance, the collapse was inhibited by a reblocking phenomenon of the unstable mass that had been previously destabilized by the first reservoir filling. Progressive failure of localized intact rock parts progressively propagated westwards as a consequence of the two further filling-drawdown cycles of the reservoir (1962 and 1963). The characteristic brittle-ductile behavior of the Vajont landslide was made possible by the presence of a very thick (40-50 m) and highly deformable shear zone underlying the upper rigid rock mass (100-120 m thick).

  7. The effective stress law at a brittle-plastic transition with a halite gouge layer

    NASA Astrophysics Data System (ADS)

    Noda, H.; Takahashi, M.

    2016-03-01

    We investigated the effect of pore pressure Pf near the brittle-plastic transition (BPT) for a halite (NaCl) shear zone. Our series of precut friction experiments with a gas-medium apparatus with temperature T ≤ 200°C, confining gas pressure Pc ≤ 150 MPa and Pf ≤ 140 MPa, revealed that a tanh connection between the brittle and plastic regimes works well even at elevated Pf, with a coefficient for Pf in an effective stress law α being unity. Plastic deformation around the real contacts independent of the mean stress results in α = 1 regardless of the ratio of the real contact area Ar/A. The functional dependency of the shear strength on the effective normal stress may deviate from a linear dependency with increasing Ar/A. The present findings support a smooth transition in a hypothetical steady state strength profile around a BPT, providing new insights in geologically obtained paleostress data in exhumed mylonitic shear zones.

  8. Analytical and numerical analysis of frictional damage in quasi brittle materials

    NASA Astrophysics Data System (ADS)

    Zhu, Q. Z.; Zhao, L. Y.; Shao, J. F.

    2016-07-01

    Frictional sliding and crack growth are two main dissipation processes in quasi brittle materials. The frictional sliding along closed cracks is the origin of macroscopic plastic deformation while the crack growth induces a material damage. The main difficulty of modeling is to consider the inherent coupling between these two processes. Various models and associated numerical algorithms have been proposed. But there are so far no analytical solutions even for simple loading paths for the validation of such algorithms. In this paper, we first present a micro-mechanical model taking into account the damage-friction coupling for a large class of quasi brittle materials. The model is formulated by combining a linear homogenization procedure with the Mori-Tanaka scheme and the irreversible thermodynamics framework. As an original contribution, a series of analytical solutions of stress-strain relations are developed for various loading paths. Based on the micro-mechanical model, two numerical integration algorithms are exploited. The first one involves a coupled friction/damage correction scheme, which is consistent with the coupling nature of the constitutive model. The second one contains a friction/damage decoupling scheme with two consecutive steps: the friction correction followed by the damage correction. With the analytical solutions as reference results, the two algorithms are assessed through a series of numerical tests. It is found that the decoupling correction scheme is efficient to guarantee a systematic numerical convergence.

  9. Pressure induced stiffening, thermal softening of bulk modulus and brittle nature of mercury chalcogenides

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Shriya, Swarna; Sapkale, Raju; Varshney, Meenu; Ameri, M.

    2015-07-01

    The pressure and temperature dependent elastic properties of mercury chalcogenides (HgX; X = S, Se and Te) with pressure induced structural transition from ZnS-type (B3) to NaCl-type (B1) structure have been analyzed within the framework of a model interionic interaction potential with long-range Coulomb and charge transfer interactions, short-range overlap repulsion and van der Waals (vdW) interactions as well as zero point energy effects. Emphasis is on the evaluation of the Bulk modulus with pressure and temperature dependency to yield the Poisson's ratio ν, the Pugh ratio ϕ, anisotropy parameter, Shear and Young's modulus, Lamé's constant, Klein man parameter, elastic wave velocity and Debye temperature. The Poisson's ratio behavior infers that HgX are brittle in nature. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of elastic and thermodynamical properties explicitly the ductile (brittle) nature of HgX and still awaits experimental confirmations.

  10. An approach to scaling size effect on strength of quasi-brittle biomedical materials.

    PubMed

    Lei, Wei-Sheng; Su, Peng

    2016-09-01

    Two-parameter Weibull statistics is commonly used for characterizing and modeling strength distribution of biomedical materials and its size dependence. The calibrated scale parameter and shape factor are usually sensitive to specimen size. Since Weibull statistics is subject to the weakest link postulate, this work proposed to directly resort to the weakest-link formulation for the cumulative failure probability to characterize size effect on strength distribution of quasi-brittle biomedical materials. As a preliminary examination, the approach was assessed by two sets of published strength data. It shows that the resultant expression for the cumulative probability follows either Weibull distribution or other type of distributions. The calibrated model parameters are independent of specimen size, so they can be used to transfer strength distribution from one set of specimens to another set of specimens with geometrical similarity under same loading mode. These initial results motivate a more comprehensive validation of the proposed approach to proceed via a larger set of case studies covering different quasi-brittle biomedical materials over a wider range of size variation. PMID:27266476

  11. Life Predicted in a Probabilistic Design Space for Brittle Materials With Transient Loads

    NASA Technical Reports Server (NTRS)

    Nemeth, Noel N.; Palfi, Tamas; Reh, Stefan

    2005-01-01

    Analytical techniques have progressively become more sophisticated, and now we can consider the probabilistic nature of the entire space of random input variables on the lifetime reliability of brittle structures. This was demonstrated with NASA s CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code combined with the commercially available ANSYS/Probabilistic Design System (ANSYS/PDS), a probabilistic analysis tool that is an integral part of the ANSYS finite-element analysis program. ANSYS/PDS allows probabilistic loads, component geometry, and material properties to be considered in the finite-element analysis. CARES/Life predicts the time dependent probability of failure of brittle material structures under generalized thermomechanical loading--such as that found in a turbine engine hot-section. Glenn researchers coupled ANSYS/PDS with CARES/Life to assess the effects of the stochastic variables of component geometry, loading, and material properties on the predicted life of the component for fully transient thermomechanical loading and cyclic loading.

  12. Influence of surface cracks on laser-induced damage resistance of brittle KH₂PO₄ crystal.

    PubMed

    Cheng, Jian; Chen, Mingjun; Liao, Wei; Wang, Haijun; Wang, Jinghe; Xiao, Yong; Li, Mingquan

    2014-11-17

    Single point diamond turning (SPDT) currently is the leading finishing method for achieving ultra-smooth surface on brittle KH(2)PO(4) crystal. In this work, the light intensification modulated by surface cracks introduced by SPDT cutting is numerically simulated using finite-difference time-domain algorithm. The results indicate that the light intensification caused by surface cracks is wavelength, crack geometry and position dependent. Under the irradiation of 355 nm laser, lateral cracks on front surfaces and conical cracks on both front and rear surfaces can produce light intensification as high as hundreds of times, which is sufficient to trigger avalanche ionization and finally lower the laser damage resistance of crystal components. Furthermore, we experimentally tested the laser-induced damage thresholds (LIDTs) on both crack-free and flawed crystal surfaces. The results imply that brittle fracture with a series of surface cracks is the dominant source of laser damage initiation in crystal components. Due to the negative effect of surface cracks, the LIDT on KDP crystal surface could be sharply reduced from 7.85J/cm(2) to 2.33J/cm(2) (355 nm, 6.4 ns). In addition, the experiment of laser-induced damage growth is performed and the damage growth behavior agrees well with the simulation results of light intensification caused by surface cracks with increasing crack depths. PMID:25402114

  13. Generalized Reliability Methodology Applied to Brittle Anisotropic Single Crystals. Degree awarded by Washington Univ., 1999

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.

    2002-01-01

    A generalized reliability model was developed for use in the design of structural components made from brittle, homogeneous anisotropic materials such as single crystals. The model is based on the Weibull distribution and incorporates a variable strength distribution and any equivalent stress failure criteria. In addition to the reliability model, an energy based failure criterion for elastically anisotropic materials was formulated. The model is different from typical Weibull-based models in that it accounts for strength anisotropy arising from fracture toughness anisotropy and thereby allows for strength and reliability predictions of brittle, anisotropic single crystals subjected to multiaxial stresses. The model is also applicable to elastically isotropic materials exhibiting strength anisotropy due to an anisotropic distribution of flaws. In order to develop and experimentally verify the model, the uniaxial and biaxial strengths of a single crystal nickel aluminide were measured. The uniaxial strengths of the <100> and <110> crystal directions were measured in three and four-point flexure. The biaxial strength was measured by subjecting <100> plates to a uniform pressure in a test apparatus that was developed and experimentally verified. The biaxial strengths of the single crystal plates were estimated by extending and verifying the displacement solution for a circular, anisotropic plate to the case of a variable radius and thickness. The best correlation between the experimental strength data and the model predictions occurred when an anisotropic stress analysis was combined with the normal stress criterion and the strength parameters associated with the <110> crystal direction.

  14. Dominant time scale for brittle fragmentation of vesicular magma by decompression

    NASA Astrophysics Data System (ADS)

    Kameda, Masaharu; Kuribara, Hideaki; Ichihara, Mie

    2008-07-01

    Brittle fragmentation was examined in a vesicular material analogous to magma, in this case, maltose syrup with bubbles. All the key time scales for magma fragmentation are controlled in the experiment using a rapid decompression facility. It was found that the onset of fragmentation can be well characterized using the Maxwell relaxation time τ r and the decompression time Δt dec, in the case where sufficiently large stress is generated in the material. As the ratio Δt dec/τ r increases from less than unity to over fifty, the response of the specimen changes from brittle fragmentation to ductile expansion without fragmentation. During the transition, the specimen exhibits small ductile deformation before the onset of fragmentation. The transition occurs even though the stress at the bubble wall is the same. The results suggest that Δt dec/τ r is the controlling parameter not only for the onset of, but also for the variation of magma fragmentation by decompression.

  15. Predicting the Reliability of Brittle Material Structures Subjected to Transient Proof Test and Service Loading

    NASA Astrophysics Data System (ADS)

    Nemeth, Noel N.; Jadaan, Osama M.; Palfi, Tamas; Baker, Eric H.

    Brittle materials today are being used, or considered, for a wide variety of high tech applications that operate in harsh environments, including static and rotating turbine parts, thermal protection systems, dental prosthetics, fuel cells, oxygen transport membranes, radomes, and MEMS. Designing brittle material components to sustain repeated load without fracturing while using the minimum amount of material requires the use of a probabilistic design methodology. The NASA CARES/Life 1 (Ceramic Analysis and Reliability Evaluation of Structure/Life) code provides a general-purpose analysis tool that predicts the probability of failure of a ceramic component as a function of its time in service. This capability includes predicting the time-dependent failure probability of ceramic components against catastrophic rupture when subjected to transient thermomechanical loads (including cyclic loads). The developed methodology allows for changes in material response that can occur with temperature or time (i.e. changing fatigue and Weibull parameters with temperature or time). For this article an overview of the transient reliability methodology and how this methodology is extended to account for proof testing is described. The CARES/Life code has been modified to have the ability to interface with commercially available finite element analysis (FEA) codes executed for transient load histories. Examples are provided to demonstrate the features of the methodology as implemented in the CARES/Life program.

  16. Fracture initiation by local brittle zones in weldments of quenched and tempered structural alloy steel plate

    SciTech Connect

    Kenney, K.L.; Reuter, W.G.; Reemsnyder, H.S.; Matlock, D.K.

    1997-12-31

    The heat-affected zone (HAZ) embrittlement of an API 2Y Grade 50T quenched and tempered offshore structural steel plate, welded by the submerged-arc process at a heat input of 4.5 kJ/mm, was investigated from the viewpoint of identifying the local brittle zone (LBZ) microstructure and the metallurgical factors associated with its formation. Microstructural and fractographic analysis showed the LBZ microstructure to be dual phase martensite-austenite (M-A) constituent. The formation of M-A constituent was found to be related to microstructural banding of the hot-rolled base plate. When the banded base plate was welded, M-A constituent formed only within the band microstructure which penetrated the intercritically-reheated coarse-grain HAZ (IRCGHAZ). The chemistry of the band microstructure in conjunction with the thermal cycle of the IRCGHAZ provided the critical conditions for the formation of M-A constituent in the API 2Y Grade 50T steel investigated. The influence of local brittle zones (i.e., M-A constituent) on the HAZ fracture toughness was evaluated by means of Crack-Tip Opening Displacement (CTOD) tests. These tests showed the steel to suffer embrittlement when the fatigue precrack sampled an intercritically-reheated coarse-grain HAZ which contained M-A constituent, confirming that M-A constituent is the major microstructural factor controlling the HAZ toughness of this particular steel.

  17. Experimental Study of the Brittle Behavior of Clay shale in Rapid Unconfined Compression

    NASA Astrophysics Data System (ADS)

    Amann, Florian; Button, Edward Alan; Evans, Keith Frederick; Gischig, Valentin Samuel; Blümel, Manfred

    2011-07-01

    The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal, underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France) in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovered from the Mont Terri Underground Research Laboratory, a series of 19 unconfined uniaxial compression tests were performed utilizing servo-controlled testing procedures. All specimens were tested at their natural water content with loading approximately normal to the bedding. Acoustic emission (AE) measurements were utilized to help quantify stress levels associated with crack initiation and propagation. The unconfined compression strength of the tested specimens averaged 6.9 MPa. The crack initiation threshold occurred at approximately 30% of the rupture stress based on analyzing both the acoustic emission measurements and the stress-strain behavior. The crack damage threshold showed large variability and occurred at approximately 70% of the rupture stress.

  18. Sensory and physical properties of peanut brittle prepared in different types of cookware and with different levels of sodium bicarbonate.

    PubMed

    McKee, L H; Christopher, J; Remmenga, M

    2003-01-01

    Two studies to evaluate peanut brittle containing either raw or roasted peanuts were conducted. In the first study, brittles were prepared in iron, aluminum, stainless steel and nonstick stainless steel pans. In the second study, brittles containing 0, 2 or 4 g of sodium bicarbonate prepared in either stainless steel or nonstick stainless steel pans were evaluated. All brittles were evaluated for color, shear strength and sensory properties at 0, 30 and 60 days. Products prepared in a nonstick stainless steel pan and those with added sodium bicarbonate were lighter, more yellow and slightly greener than other products. Pan type did not affect shear force but increasing sodium bicarbonate was associated with decreasing force needed to shear brittles. Peanut and caramel aromas were not affected by pan type or sodium bicarbonate level but were greater (p < 0.05) in products containing roasted peanuts. Burned flavors were more prevalent in products prepared in iron or stainless steel pans with roasted peanuts. More intense sweet and buttery flavors were detected as level of sodium bicarbonate increased. PMID:12906354

  19. Breaking new ground in the mind: an initial study of mental brittle transformation and mental rigid rotation in science experts.

    PubMed

    Resnick, Ilyse; Shipley, Thomas F

    2013-05-01

    The current study examines the spatial skills employed in different spatial reasoning tasks, by asking how science experts who are practiced in different types of visualizations perform on different spatial tasks. Specifically, the current study examines the varieties of mental transformations. We hypothesize that there may be two broad classes of mental transformations: rigid body mental transformations and non-rigid mental transformations. We focus on the disciplines of geology and organic chemistry because different types of transformations are central to the two disciplines: While geologists and organic chemists may both confront rotation in the practice of their profession, only geologists confront brittle transformations. A new instrument was developed to measure mental brittle transformation (visualizing breaking). Geologists and organic chemists performed similarly on a measure of mental rotation, while geologists outperformed organic chemists on the mental brittle transformation test. The differential pattern of skill on the two tests for the two groups of experts suggests that mental brittle transformation and mental rotation are different spatial skills. The roles of domain general cognitive resources (attentional control, spatial working memory, and perceptual filling in) and strategy in completing mental brittle transformation are discussed. The current study illustrates how ecological and interdisciplinary approaches complement traditional cognitive science to offer a comprehensive approach to understanding the nature of spatial thinking. PMID:23440527

  20. An Improved Approach to Fracture Toughness Assessment of Brittle Coating on Ductile Substrate Systems under Indentation

    NASA Astrophysics Data System (ADS)

    Demidova, Natalia V.

    Fracture toughness is an important material property that determines the structural integrity of a component with pre-existing or service-generated flaws. In the present research, an indentation-based method and the associated fracture mechanics model are proposed for fracture toughness assessment of brittle coating/ductile substrate systems. The proposed models consider well-developed radial/median cracks generated under sharp indentation, despite that the crack formation process may have gone through crack initiation and propagation phases. For generality, the geometry of a well-developed crack is assumed to be semi-elliptical in shape. The driving force of the crack is considered to stem from the residual plastic zone expansion under the indenter, as well as the far-field Boussinesq (elastic) stress. Three well-defined configurations are studied. For the first configuration, a crack with a depth of less than 7% of the coating thickness is considered. In this case, the problem is treated as the one for the monolithic material with the coating material properties. For the second configuration, a crack that runs deeper than 7% of the coating thickness but is still within the coating layer is analyzed. In this case, the composite hardness is introduced into the analysis to account for the influence of the substrate material properties; and furthermore, an interface correction factor is proposed to take into account the presence of the coating/substrate interface and its influence on the stress intensity factor of the well-developed elliptical cracks. For the third configuration, a crack penetrating into the substrate is considered. In this case, based on the condition of deformation compatibility across the coating/substrate interface, the bulk modulus for the coating/substrate system is introduced into the analysis. A series of indentation tests are conducted on a WC/10Co/4Cr coating/1080 low carbon steel substrate specimen, which is a brittle coating on a ductile

  1. Simulation of seismic waves in the brittle-ductile transition (BDT) using a Burgers model

    NASA Astrophysics Data System (ADS)

    Poletto, Flavio; Farina, Biancamaria; Carcione, José Maria

    2014-05-01

    The seismic characterization of the brittle-ductile transition (BDT) in the Earth's crust is of great importance for the study of high-enthalpy geothermal fields in the proximity of magmatic zones. It is well known that the BDT can be viewed as the transition between zones with viscoelastic and plastic behavior, i.e., the transition between the upper, cooler, brittle crustal zone, and the deeper ductile zone. Depending on stress and temperature conditions, the BDT behavior is basically determined by the viscosity of the crustal rocks, which acts as a key factor. In situ shear stress and temperature are related to shear viscosity and steady-state creep flow through the Arrhenius equation, and deviatory stress by octahedral stress criterion. We present a numerical approach to simulate the propagation of P-S and SH seismic waves in a 2D model of the heterogeneous Earth's crust. The full-waveform simulation code is based on a Burgers mechanical model (Carcione, 2007), which enables us to describe both the seismic attenuation effects and the steady-state creep flow (Carcione and Poletto, 2013; Carcione et al. 2013). The differential equations of motion are calculated for the Burgers model, and recast in the velocity-stress formulation. Equations are solved in the time domain using memory variables. The approach uses a direct method based on the Runge-Kutta technique, and the Fourier pseudo-spectral methods, for time integration and for spatial derivation, respectively. In this simulation we assume isotropic models. To test the code, the signals generated by the full-waveform simulation algorithm are compared with success to analytic solutions obtained with different shear viscosities. Moreover, synthetic results are calculated to simulate surface and VSP seismograms in a realistic rheological model with a dramatic temperature change, to study the observability of BDT by seismic reflection methods. The medium corresponds to a selected rheology of the Iceland scenario

  2. Design software for reuse

    NASA Technical Reports Server (NTRS)

    Tracz, Will

    1990-01-01

    Viewgraphs are presented on the designing of software for reuse. Topics include terminology, software reuse maxims, the science of programming, an interface design example, a modularization example, and reuse and implementation guidelines.

  3. Software assurance standard

    NASA Technical Reports Server (NTRS)

    1992-01-01

    This standard specifies the software assurance program for the provider of software. It also delineates the assurance activities for the provider and the assurance data that are to be furnished by the provider to the acquirer. In any software development effort, the provider is the entity or individual that actually designs, develops, and implements the software product, while the acquirer is the entity or individual who specifies the requirements and accepts the resulting products. This standard specifies at a high level an overall software assurance program for software developed for and by NASA. Assurance includes the disciplines of quality assurance, quality engineering, verification and validation, nonconformance reporting and corrective action, safety assurance, and security assurance. The application of these disciplines during a software development life cycle is called software assurance. Subsequent lower-level standards will specify the specific processes within these disciplines.

  4. Guidelines for software inspections

    NASA Technical Reports Server (NTRS)

    1983-01-01

    Quality control inspections are software problem finding procedures which provide defect removal as well as improvements in software functionality, maintenance, quality, and development and testing methodology is discussed. The many side benefits include education, documentation, training, and scheduling.

  5. Commercial Data Mining Software

    NASA Astrophysics Data System (ADS)

    Zhang, Qingyu; Segall, Richard S.

    This chapter discusses selected commercial software for data mining, supercomputing data mining, text mining, and web mining. The selected software are compared with their features and also applied to available data sets. The software for data mining are SAS Enterprise Miner, Megaputer PolyAnalyst 5.0, PASW (formerly SPSS Clementine), IBM Intelligent Miner, and BioDiscovery GeneSight. The software for supercomputing are Avizo by Visualization Science Group and JMP Genomics from SAS Institute. The software for text mining are SAS Text Miner and Megaputer PolyAnalyst 5.0. The software for web mining are Megaputer PolyAnalyst and SPSS Clementine . Background on related literature and software are presented. Screen shots of each of the selected software are presented, as are conclusions and future directions.

  6. Software Engineering Improvement Plan

    NASA Technical Reports Server (NTRS)

    2006-01-01

    In performance of this task order, bd Systems personnel provided support to the Flight Software Branch and the Software Working Group through multiple tasks related to software engineering improvement and to activities of the independent Technical Authority (iTA) Discipline Technical Warrant Holder (DTWH) for software engineering. To ensure that the products, comments, and recommendations complied with customer requirements and the statement of work, bd Systems personnel maintained close coordination with the customer. These personnel performed work in areas such as update of agency requirements and directives database, software effort estimation, software problem reports, a web-based process asset library, miscellaneous documentation review, software system requirements, issue tracking software survey, systems engineering NPR, and project-related reviews. This report contains a summary of the work performed and the accomplishments in each of these areas.

  7. Software verification and testing

    NASA Technical Reports Server (NTRS)

    1985-01-01

    General procedures for software verification and validation are provided as a guide for managers, programmers, and analysts involved in software development. The verification and validation procedures described are based primarily on testing techniques. Testing refers to the execution of all or part of a software system for the purpose of detecting errors. Planning, execution, and analysis of tests are outlined in this document. Code reading and static analysis techniques for software verification are also described.

  8. Agent Building Software

    NASA Technical Reports Server (NTRS)

    2000-01-01

    AgentBuilder is a software component developed under an SBIR contract between Reticular Systems, Inc., and Goddard Space Flight Center. AgentBuilder allows software developers without experience in intelligent agent technologies to easily build software applications using intelligent agents. Agents are components of software that will perform tasks automatically, with no intervention or command from a user. AgentBuilder reduces the time and cost of developing agent systems and provides a simple mechanism for implementing high-performance agent systems.

  9. Experimentation in software engineering

    NASA Technical Reports Server (NTRS)

    Basili, V. R.; Selby, R. W.; Hutchens, D. H.

    1986-01-01

    Experimentation in software engineering supports the advancement of the field through an iterative learning process. In this paper, a framework for analyzing most of the experimental work performed in software engineering over the past several years is presented. A variety of experiments in the framework is described and their contribution to the software engineering discipline is discussed. Some useful recommendations for the application of the experimental process in software engineering are included.

  10. Standard Annuciator Software overview

    SciTech Connect

    Anspach, D.A. ); Fox, E.T.; Kissock, P.S. )

    1990-01-01

    The Standard Annunciator Software is responsible for maintaining a current display of system status conditions. The software interfaces with other systems -- IACS, CCTV, UPS, and portable PC -- to determine their status and then displays this information at the operator's console. This manual describes the software organization, operation, and generation mechanisms for development and target environments. 6 figs.

  11. Java for flight software

    NASA Technical Reports Server (NTRS)

    Benowitz, E.; Niessner, A.

    2003-01-01

    This work involves developing representative mission-critical spacecraft software using the Real-Time Specification for Java (RTSJ). This work currently leverages actual flight software used in the design of actual flight software in the NASA's Deep Space 1 (DSI), which flew in 1998.

  12. Software Architecture Evolution

    ERIC Educational Resources Information Center

    Barnes, Jeffrey M.

    2013-01-01

    Many software systems eventually undergo changes to their basic architectural structure. Such changes may be prompted by new feature requests, new quality attribute requirements, changing technology, or other reasons. Whatever the causes, architecture evolution is commonplace in real-world software projects. Today's software architects, however,…

  13. CALIPSO Data Read Software

    Atmospheric Science Data Center

    2015-11-02

      CALIPSO Data Read Software Callable routines in Interactive Data Language ... Solutions . CALIPSO_READERS_3.5v1 Software (IDL) tar (611.5 KB) zip (261 KB) ... CALIPSO_READERS_3.4v1 Software (IDL) tar  (612.9 KB) zip  (261.4 KB) ...

  14. Evaluation Software in Counseling.

    ERIC Educational Resources Information Center

    Sabella, Russell A.

    Counselors today are presented with a number of differing applications software. This article intends to advance the counselor's knowledge and considerations of the various aspects of application software. Included is a discussion of the software applications typically of help to counselors in (a) managing their work (computer managed counseling);…

  15. SPEAR 3 Commissioning Software

    SciTech Connect

    Corbett, W.J.; Portmann, G.J.; Safranek, J.A.; Terebilo, A.; /SLAC, SSRL

    2005-05-09

    The short SPEAR 3 startup time required precommissioned software for machine setup, beam measurements and data analysis. To accomplish this goal, we used Matlab with the Accelerator Toolbox (AT), the Channel Access Toolbox (MCA) and Middle Layer software to integrate code and streamline production. This paper outlines the software architecture, describes the Middle Layer component and provides examples from SPEAR 3 commissioning.

  16. Astronomical Software Directory Service

    NASA Technical Reports Server (NTRS)

    Hanisch, R. J.; Payne, H.; Hayes, J.

    1998-01-01

    This is the final report on the development of the Astronomical Software Directory Service (ASDS), a distributable, searchable, WWW-based database of software packages and their related documentation. ASDS provides integrated access to 56 astronomical software packages, with more than 16,000 URL's indexed for full-text searching.

  17. Software Shopper. Revised.

    ERIC Educational Resources Information Center

    Davis, Sandra Hart, Comp.

    This annotated index describes and illustrates a wide selection of public domain instructional software that may be useful in the education of deaf students and provides educators with a way to order the listed programs. The software programs are designed for use on Apple computers and their compatibles. The software descriptions are presented in…

  18. Transient creep, aseismic damage and slow failure in Carrara marble deformed across the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Schubnel, A.; Walker, E.; Thompson, B. D.; Fortin, J.; Guéguen, Y.; Young, R. P.

    2006-09-01

    Two triaxial compression experiments were performed on Carrara marble at high confining pressure, in creep conditions across the brittle-ductile transition. During cataclastic deformation, elastic wave velocity decrease demonstrated damage accumulation (microcracks). Keeping differential stress constant and reducing normal stress induced transient creep events (i.e., fast accelerations in strain) due to the sudden increase of microcrack growth. Tertiary creep and brittle failure followed as damage came close to criticality. Coalescence and rupture propagation were slow (60-200 seconds with ~150 MPa stress drops and millimetric slips) and radiated little energy in the experimental frequency range (0.1-1 MHz). Microstructural analysis pointed out strong interactions between intra-crystalline plastic deformation (twinning and dislocation glide) and brittle deformation (microcracking) at the macroscopic level. Our observations highlight the dependence of acoustic efficiency on the material's rheology, at least in the ultrasonic frequency range, and the role played by pore fluid diffusion as an incubation process for delayed failure triggering.

  19. Brittle Cornea Syndrome: Case Report with Novel Mutation in the PRDM5 Gene and Review of the Literature

    PubMed Central

    Avgitidou, Georgia; Siebelmann, Sebastian; Bachmann, Bjoern; Kohlhase, Juergen; Heindl, Ludwig M.; Cursiefen, Claus

    2015-01-01

    A 3-year-old boy presented with acute corneal hydrops on the left eye and spontaneous corneal rupture on the right eye. A diagnosis of brittle cornea syndrome was confirmed by molecular analysis. A novel mutation, the homozygous variant c.17T>G, p.V6G, was found in the gene for PR-domain-containing protein 5 (PRDM5) in exon 1. Brittle cornea syndrome is a rare connective tissue disease with typical ocular, auditory, musculoskeletal, and cutaneous disorders. Almost all patients suffer from declined vision due to corneal scarring, thinning, and rupture. The most common ophthalmologic findings include keratoconus, progressive central corneal thinning, high myopia, irregular astigmatism, retinal detachment, and high risk for spontaneous corneal or scleral rupture. In addition to describing the case with a novel mutation here we review the current literature on brittle cornea syndrome pathogenesis, clinical findings, and therapy. PMID:26221552

  20. Mixed brittle-plastic deformation behaviour in a slate belt. Examples from the High-Ardenne slate belt (Belgium, Germany)

    NASA Astrophysics Data System (ADS)

    Sintubin, Manuel; van Baelen, Hervé; van Noten, Koen; Muchez, Philippe

    2010-05-01

    In the High-Ardenne slate belt, part of the Rhenohercynian external fold-and-thrust belt at the northern extremity of the Late Palaeozoic Variscan orogen (Belgium, Germany, France), particular quartz vein occurrences can be observed in predominantly fine-grained siliciclastic metasediments. Detailed structural, petrographical and geochemical studies has revealed that these vein occurrences can be related to a mixed brittle-plastic deformation behaviour in a low-grade metamorphic mid-crustal environment. The first type of quartz veins are bedding-perpendicular, lens-shaped extension veins that are confined to the sandstone layers within the multilayer sequence. Fluid inclusion studies demonstrate high fluid pressures suggesting that the individual sandstone bodies acted as isolated high-pressure compartments in an overpressured basin. Hydraulic fracturing occurred during the tectonic inversion (from extension to compression) in the earliest stages of the Variscan orogeny. The vein fill shows a blocky character indicating crystal growth in open cavities. Both the typical lens shape of the veins and the subsequent cuspate-lobate folding of the bed interfaces in between the quartz veins suggest plastic deformation of cohesionless fluid-filled fissures. Metamorphic grade of the host rock and fluid temperature and pressure clearly indicates mid-crustal conditions below the brittle-plastic transition. This first type of quartz veins exemplifies mixed brittle-plastic deformation behaviour, possibly related to a transient deepening of the brittle-plastic transition. This is in contrast with contemporaneous bedding-perpendicular crack-seal veins observed in higher - upper-crustal - structural levels in the slate belt, reflecting pure brittle deformation behaviour. The second type are discordant quartz veins confined to extensional low-angle detachment shear zones. These very irregular veins transect a pre-existing pervasive cleavage fabric. They show no matching walls and

  1. Open Source Software (OSS) Adoption Framework for Local Environment and its Comparison

    NASA Astrophysics Data System (ADS)

    Laila, U.; Bukhari, S. F. A.

    According to Business Software Alliance (BSA) Pakistan is ranked in the top 10 countries having highest piracy rate [1]. To overcome the problem of piracy local Information Technology (IT) companies are willing to migrate towards Open Source Software (OSS). Due to this reason need for framework/model for OSS adoption has become more pronounced.

  2. Origin and evolution of extensional faults within the ductile-to-brittle transition, Badwater Turtleback, Death Valley, CA

    SciTech Connect

    Miller, M.G. . Geological Sciences)

    1992-01-01

    Field relations in the footwall of the Badwater Turtleback suggest a model for two geometrically distinct sets of brittle faults. The model shows how extensional brittle faults may (1) initiate within mylonite zones as a result of strain incompatibilities, and (2) become inactive as a function of decreased dip angles. Cross-cutting relations indicate that, as the footwall cooled, late stages of ductile strain concentrated in calcite marble shear zones while brittle faults formed within the other rocks. These faults fall into two groups: decollement-style faults (DSF) and high angle faults (HAF). They must have formed concurrently with calcite mylonitization because they locally terminate at the calcite shear zones. DSF are subparallel to mylonitic foliation and locally re-occupy calcite shear zones. They are moderately nonplanar, discontinuous at scales of 10--100m, and show limited evidence for transport parallel to stretching lineations in adjacent mylonites. HAF cut foliation at high angles. These faults either (1) end downwards into unfractured calcite mylonite, (2) cut calcite mylonite and join underlying DSF, or (3) cut calcite mylonite and DSF. Where they join DSF, HAF are strongly listric and maintain integrity as distinct slip surfaces within the DSF zone (see inset). DSF formed at rheological boundaries and at places where actively deforming calcite marble pinched out into brittle rocks. HAF formed in brittle upper plates of calcite marble shear zones to accommodate differences in strain between brittle and nonbrittle rock. With continued strain and consequent cooling and eastward tilting of the footwall, calcite shear zones stopped deforming ductility, became occupied by DSF, and gradually rotated to lower angles.

  3. Beliefs about Overcoming Psychological Problems among British and Japanese Students.

    ERIC Educational Resources Information Center

    Furnham, Adrian; Ota, Hiromi; Tatsuro, Hosoe; Koyasu, Masuo

    2000-01-01

    Examines the cultural differences among Japanese students, British students, and Japanese students studying in Britain, concerning their beliefs on overcoming five psychological problems: depression, obesity, smoking cessation, agoraphobia, and lack of confidence. (CMK)

  4. De Novo Adult Transcriptomes of Two European Brittle Stars: Spotlight on Opsin-Based Photoreception

    PubMed Central

    Mallefet, Jérôme; Flammang, Patrick

    2016-01-01

    Next generation sequencing (NGS) technology allows to obtain a deeper and more complete view of transcriptomes. For non-model or emerging model marine organisms, NGS technologies offer a great opportunity for rapid access to genetic information. In this study, paired-end Illumina HiSeqTM technology has been employed to analyse transcriptomes from the arm tissues of two European brittle star species, Amphiura filiformis and Ophiopsila aranea. About 48 million Illumina reads were generated and 136,387 total unigenes were predicted from A. filiformis arm tissues. For O. aranea arm tissues, about 47 million reads were generated and 123,324 total unigenes were obtained. Twenty-four percent of the total unigenes from A. filiformis show significant matches with sequences present in reference online databases, whereas, for O. aranea, this percentage amounts to 23%. In both species, around 50% of the predicted annotated unigenes were significantly similar to transcripts from the purple sea urchin, the closest species to date that has undergone complete genome sequencing and annotation. GO, COG and KEGG analyses were performed on predicted brittle star unigenes. We focused our analyses on the phototransduction actors involved in light perception. Firstly, two new echinoderm opsins were identified in O. aranea: one rhabdomeric opsin (homologous to vertebrate melanopsin) and one RGR opsin. The RGR-opsin is supposed to be involved in retinal regeneration while the r-opsin is suspected to play a role in visual-like behaviour. Secondly, potential phototransduction actors were identified in both transcriptomes using the fly (rhabdomeric) and mammal (ciliary) classical phototransduction pathways as references. Finally, the sensitivity of O.aranea to monochromatic light was investigated to complement data available for A. filiformis. The presence of microlens-like structures at the surface of dorsal arm plate of O. aranea could potentially explain phototactic behaviour differences

  5. AN INVESTIGATION OF THE MINERAL IN DUCTILE AND BRITTLE CORTICAL MOUSE BONE

    PubMed Central

    Rodriguez-Florez, Naiara; Garcia-Tunon, Esther; Mukadam, Quresh; Saiz, Eduardo; Oldknow, Karla J.; Farquharson, Colin; Millán, José Luis; Boyde, Alan; Shefelbine, Sandra J.

    2015-01-01

    Bone is a strong and tough material composed of apatite mineral, organic matter and water. Changes in composition and organization of these building blocks affect bone’s mechanical integrity. Skeletal disorders often affect bone’s mineral phase, either by variations in the collagen or directly altering mineralization. The aim of the current study was to explore the differences in the mineral of brittle and ductile cortical bone at the mineral (nm) and tissue (µm) levels using two mouse phenotypes. Osteogenesis imperfecta murine (oim−/−) mice were used to model brittle bone; PHOSPHO1 mutants (Phospho1−/−) had ductile bone. They were compared to their respective wild-type controls. Femora were defatted and ground to powder to measure average mineral crystal size using X-ray diffraction (XRD), and to monitor the bulk mineral to matrix ratio via thermogravimetric analysis (TGA). XRD scans were run after TGA for phase identification, to assess the fractions of hydroxyapatite and β-tricalcium phosphate. Tibiae were embedded to measure elastic properties with nanoindentation and the extent of mineralization with backscattered electron microscopy (qbSEM). Interestingly, the mineral of brittle oim−/− and ductile Phospho1−/− bones had many similar characteristics. Both pathology models had smaller apatite crystals, lower mineral to matrix ratio, and showed more thermal conversion to β-tricalcium phosphate than their wild-types, indicating deviations from stoichiometric hydroxyapatite in the original mineral. The degree of mineralization of the bone matrix was different for each strain: oim−/− were hypermineralized, while Phospho1−/− were hypomineralized. However, alterations in the mineral were associated with reduced tissue elastic moduli in both pathologies. Results revealed that despite having extremely different whole bone mechanics, the mineral of oim−/− and Phospho1−/− has several similar trends at smaller length scales. This

  6. Mechanical behavior of low porosity carbonate rock: from brittle creep to ductile creep

    NASA Astrophysics Data System (ADS)

    Nicolas, A.; Fortin, J.; Gueguen, Y.

    2013-12-01

    Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this experimental study, we focus on the mechanical behavior of a low porosity (9%) white Tavel (France) carbonate rock (>98% calcite) at P-Q conditions beyond the elastic domain. It has been shown that in sandstones composed of quartz, cracks are developing under these conditions. However, in carbonates, calcite minerals can meanwhile also exhibit microplasticity. The samples were deformed in the triaxial cell of the Ecole Normale Superieure de Paris at effective confining pressures ranging from 35 MPa to 85 MPa and room temperature. Experiments were carried on dry and water saturated samples to explore the role played by the pore fluids. Time dependency was investigated by a creep steps methodology: at each step, differential stress was increased rapidly and kept constant for at least 24h. During these steps elastic wave velocities (P and S) and permeability were measured continuously. Our results show two different creep behaviors: (1) brittle creep is observed at low confining pressures, whereas (2) ductile creep is observed at higher confining pressures. These two creep behaviors have a different signature in term of elastic wave velocities and permeability changes. Indeed, in the brittle domain, the primary creep is associated with a decrease of elastic wave velocities and an increase of permeability, and no secondary creep is observed. In the ductile domain, the primary creep

  7. The influence of porosity and vesicle size on the brittle strength of volcanic rocks and magma

    NASA Astrophysics Data System (ADS)

    Heap, Michael J.; Xu, Tao; Chen, Chong-feng

    2014-09-01

    Volcanic rocks and magma display a wide range of porosity and vesicle size, a result of their complex genesis. While the role of porosity is known to exert a fundamental control on strength in the brittle field, less is known as to the influence of vesicle size. To help resolve this issue, here, we lean on a combination of micromechanical (Sammis and Ashby's pore-emanating crack model) and stochastic (rock failure and process analysis code) modelling. The models show, for a homogenous vesicle size, that an increase in porosity (in the form of circular vesicles, from 0 to 40 %) and/or vesicle diameter (from 0.1 to 2.0 mm) results in a dramatic reduction in strength. For example, uniaxial compressive strength can be reduced by about a factor of 5 as porosity is increased from 0 to 40 %. The presence of vesicles locally amplifies the stress within the groundmass and promotes the nucleation of vesicle-emanating microcracks that grow in the direction of the applied macroscopic stress. As strain increases, these microcracks continue to grow and eventually coalesce leading to macroscopic failure. Vesicle clustering, which promotes the overlap and interaction of the tensile stress lobes at the north and south poles of neighbouring vesicles, and the increased ease of microcrack interaction, is encouraged at higher porosity and reduces sample strength. Once a microcrack nucleates at the vesicle wall, larger vesicles impart higher stress intensities at the crack tips, allowing microcracks to propagate at a lower applied macroscopic stress. Larger vesicles also permit a shorter route through the groundmass for the macroscopic shear fracture. This explains the reduction in strength at higher vesicle diameters (at a constant porosity). The modelling highlights that the reduction in strength as porosity or vesicle size increases is nonlinear; the largest reductions are observed at low porosity and small vesicle diameters. In detail, we find that vesicle diameter can play an

  8. Analytical and Experimental Nanomechanical Approaches to Understanding the Ductile-to-Brittle Transition

    NASA Astrophysics Data System (ADS)

    Hintsala, Eric Daniel

    This dissertation presents progress towards understanding the ductile-to-brittle transition (DBT) using a mixture of nanomechanical experiments and an analytical model. The key concept is dislocation shielding of crack tips, which is occurs due to a dislocation back stress. In order to properly evaluate the role of these interactions, in-situ experiments are ideal by reducing the number of interacting dislocations and allowing direct observation of cracking behavior and the dislocations themselves. First, in-situ transmission electron microscope (TEM) compression experiments of plasma-synthesized silicon nanocubes (NCs) are presented which shows plastic strains greater than 50% in a semi-brittle material. The mechanical properties are discussed and plasticity mechanisms are identified using post-mortem imaging with a combination of dark field and high-resolution imaging. This observations help to develop a back stress model which is used to fit the hardening regime. This represents the first study of its kind where back stresses are used in a discrete manner to match hardening rates. However, the important measurable quantities for evaluating the DBT include fracture toughness values and energetic activation parameters for cracking and plasticity. In order to do this, a new method for doing in-situ fracture experiments is explored. This method is pre-notched three point bending experiments, which were fabricated by focused ion beam (FIB) milling. Two different materials are evaluated: a model ductile material, Nitronic 50, an austenitic steel alloy, and a model brittle material, silicon. These experiments are performed in-situ scanning electron microscope (SEM) and TEM and explore different aspects including electron backscatter diffraction (EBSD) to track deformation in SEM scale experiments, pre-notching using a converged TEM beam to produce sharper notches better replicating natural cracks, etching procedures to reduce residual FIB damage and elevated

  9. Friction experiments of halite in brittle-ductile transition with high pore pressure

    NASA Astrophysics Data System (ADS)

    Noda, H.; Takahashi, M.; Katayama, I.

    2015-12-01

    Flow stress of rock (τ) approximately linearly depends on normal stress on a shear zone (σn) minus pore pressure (p) in a brittle regime, and insensitive to σn in a fully plastic regime where pores are isolated and filled with fluid of high pressure comparable to the mean stress, like oil drops in water. How p affects τ in the transitional regime is not fully understood, although it is a key to understanding many important geological problems such as role of fluids in deformation mechanism, stress and strength profile of the crust, seismogenic depth range, and so on. The effective normal stress σe is often given by σe = σn - α p (α: a constant around 1 in the brittle regime), and frictional resistance, by τ = f σe (f: friction coefficient). Recently, Hirth and Beeler [2015] proposed a model of the effective stress law in the transitional regime. Because of increasing ratio of real area of contact to nominal area of frictional interface, α may decrease to zero towards fully plastic regime, causing a sharper peak in the strength profile than a conventional Brace-Goetze strength profile which is sometimes referred to as "Christmas tree". We investigated this idea by means of friction experiments at high temperature and pore pressure. We used halite as an analogue material which undergoes a transition from brittle to fully plastic regime under convenient conditions [Shimamoto, 1986]. We conducted friction experiments of a pre-cut sliding interface filled with halite gouge with gas-medium triaxial apparatus in Hiroshima University, at 150 MPa confining pressure, from room temperature to 210 °C, and from atmospheric pressure to more than 100 MPa fluid (argon gas) pressure in a reservoir. Our preliminary result shows that the sharp peak in the flow stress is probably absent. A phenomenological smooth connection proposed by Shimamoto and Noda [2014] based on friction experiments without a jacket (i.e. atmospheric pore pressure) may work in explaining the

  10. Are magma chamber boundaries brittle or ductile? Rheological insights from thermal stressing experiments

    NASA Astrophysics Data System (ADS)

    Browning, John; Meredith, Philip G.; Gudmundsson, Agust; Lavallée, Yan; Drymoni, Kyriaki

    2015-04-01

    Rheological conditions at magma chamber boundaries remain poorly understood. Many field observations of deeply-eroded and well-exposed plutons, for example Slaufrudalur and Geitafell in SE Iceland, exhibit a sharp transition between what may have been a partially or fully molten magma chamber and its surrounding brittle host rock. Some studies have suggested a more gradual change in the rheological properties of chamber boundaries, marked by a ductile halo, which is likely to exert a significant impact on their rheological response. Understanding the state and rheological conditions of magma-rock interface and interaction is essential for constraining chamber-boundary failure conditions leading to dyke propagation, onset of volcanic eruption as well as caldera fault formation. We present results from a series of thermal stressing experiments in which we attempt to recreate the likely conditions at magma-chamber boundaries. Cores of volcanic material (25 mm diameter x 65 mm long) were heated to magmatic temperatures under controlled conditions in a horizontal tube furnace (at atmospheric pressure) and then held at those temperatures over variable dwell times. At the maximum temperatures reached, the inner part of the samples undergoes partial melting whilst the outer part remains solid. After cooling the brittle shells commonly exhibit axial, fissure-like fractures with protruded blobs of solidified melt. This phenomenon is interpreted as being the result of volume expansion during partial melting. The internal melt overpressure generates fluid-driven fractures analogous to filter-pressing textures or on a large scale, dykes. We complement our observations with acoustic emission and seismic velocity data obtained from measurements throughout the experiments. These complementary data are used to infer the style and timescale of fracture formation. Our results pinpoint the temperature ranges over which brittle fractures form as a result of internal melt overpressure

  11. De Novo Adult Transcriptomes of Two European Brittle Stars: Spotlight on Opsin-Based Photoreception.

    PubMed

    Delroisse, Jérôme; Mallefet, Jérôme; Flammang, Patrick

    2016-01-01

    Next generation sequencing (NGS) technology allows to obtain a deeper and more complete view of transcriptomes. For non-model or emerging model marine organisms, NGS technologies offer a great opportunity for rapid access to genetic information. In this study, paired-end Illumina HiSeqTM technology has been employed to analyse transcriptomes from the arm tissues of two European brittle star species, Amphiura filiformis and Ophiopsila aranea. About 48 million Illumina reads were generated and 136,387 total unigenes were predicted from A. filiformis arm tissues. For O. aranea arm tissues, about 47 million reads were generated and 123,324 total unigenes were obtained. Twenty-four percent of the total unigenes from A. filiformis show significant matches with sequences present in reference online databases, whereas, for O. aranea, this percentage amounts to 23%. In both species, around 50% of the predicted annotated unigenes were significantly similar to transcripts from the purple sea urchin, the closest species to date that has undergone complete genome sequencing and annotation. GO, COG and KEGG analyses were performed on predicted brittle star unigenes. We focused our analyses on the phototransduction actors involved in light perception. Firstly, two new echinoderm opsins were identified in O. aranea: one rhabdomeric opsin (homologous to vertebrate melanopsin) and one RGR opsin. The RGR-opsin is supposed to be involved in retinal regeneration while the r-opsin is suspected to play a role in visual-like behaviour. Secondly, potential phototransduction actors were identified in both transcriptomes using the fly (rhabdomeric) and mammal (ciliary) classical phototransduction pathways as references. Finally, the sensitivity of O.aranea to monochromatic light was investigated to complement data available for A. filiformis. The presence of microlens-like structures at the surface of dorsal arm plate of O. aranea could potentially explain phototactic behaviour differences

  12. Ultraprecision, high stiffness CNC grinding machines for ductile mode grinding of brittle materials

    NASA Astrophysics Data System (ADS)

    McKeown, Patrick A.; Carlisle, Keith; Shore, Paul; Read, R. F.

    1990-10-01

    Under certain controlled conditions it is now possible to machine brittle materials such as glasses and ceramics using single or multi-point diamond tools (grinding), so that material is removed by plastic flow, leaving crack-free surfaces. This process is called 'shear' or 'ductile' mode grinding. It represents a major breakthrough in modern manufacturing engineering since it promises to enable: - complex optical components, both transmission and reflecting to be generated by advanced CNC machines with very little (or even zero) subsequent polishing. - complex shaped components such as turbine blades, nozzle guide vanes, etc. to be finish machined after near net shape forming, to high precision in advanced ceramics such as silicon nitride, without inducing micro-cracking and thus lowering ultimate rupture strength and fatigue life. Ductile mode "damage free" grinding occurs when the volume of materials stressed by each grit of the grinding wheel is small enough to yield rather than exhibit brittle fracture, i.e. cracking. In practice, this means maintaining the undeformed chip thickness to below the ductile-brittle transition value; this varies from material to material but is generally in the order of 0.1 pm or 100 nm, (hence the term "nanogrinding" is sometimes used) . Thus the critical factors for operating successfully in the ductile regime are machine system accuracy and dynamic stiffness between each grit and the workpiece. In detail this means: (i) High precision 'truing' of the diamond grits, together with dressing of the wheel bond to ensure adequate ' openness'; (ii) Design and build of the grinding wheel spindle with very high dynamic stiffness; error motions, radial and axial, must be considerably less than 100 nfl. (iii) Design and build of the workpiece carriage motion system with very high dynamic stiffness; error motions, linear or rotary, must be well within 100 nm. (iv) Smooth, rumble-free, high-stiffness servo-drives controlling the motions

  13. Software for computerised analysis of cardiotocographic traces.

    PubMed

    Romano, M; Bifulco, P; Ruffo, M; Improta, G; Clemente, F; Cesarelli, M

    2016-02-01

    Despite the widespread use of cardiotocography in foetal monitoring, the evaluation of foetal status suffers from a considerable inter and intra-observer variability. In order to overcome the main limitations of visual cardiotocographic assessment, computerised methods to analyse cardiotocographic recordings have been recently developed. In this study, a new software for automated analysis of foetal heart rate is presented. It allows an automatic procedure for measuring the most relevant parameters derivable from cardiotocographic traces. Simulated and real cardiotocographic traces were analysed to test software reliability. In artificial traces, we simulated a set number of events (accelerations, decelerations and contractions) to be recognised. In the case of real signals, instead, results of the computerised analysis were compared with the visual assessment performed by 18 expert clinicians and three performance indexes were computed to gain information about performances of the proposed software. The software showed preliminary performance we judged satisfactory in that the results matched completely the requirements, as proved by tests on artificial signals in which all simulated events were detected from the software. Performance indexes computed in comparison with obstetricians' evaluations are, on the contrary, not so satisfactory; in fact they led to obtain the following values of the statistical parameters: sensitivity equal to 93%, positive predictive value equal to 82% and accuracy equal to 77%. Very probably this arises from the high variability of trace annotation carried out by clinicians. PMID:26638805

  14. Problem-Solving Software

    NASA Technical Reports Server (NTRS)

    1992-01-01

    CBR Express software solves problems by adapting sorted solutions to new problems specified by a user. It is applicable to a wide range of situations. The technology was originally developed by Inference Corporation for Johnson Space Center's Advanced Software Development Workstation. The project focused on the reuse of software designs, and Inference used CBR as part of the ACCESS prototype software. The commercial CBR Express is used as a "help desk" for customer support, enabling reuse of existing information when necessary. It has been adopted by several companies, among them American Airlines, which uses it to solve reservation system software problems.

  15. Tracker 300 Software

    SciTech Connect

    Wysor, R. Wes

    2006-01-12

    The Tracker300 software is downloaded to an off-the-shelf product called RCM3400/RCM3410 made by Rabbit Semiconductor. The software is a closed loop control which computes the sun's position and provides stability compensation. Using the RCM3400/RCM3410 module, the software stores and retrieves parameters from the onboard flash. The software also allows for communication with a host. It will allow the parameters to be downloaded or uploaded, it will show the status of the controller, it will provide real-time feedback, and it will send command acknowledgements. The software will capture the GPS response and ensure the internal clock is set correctly.

  16. Payload software technology

    NASA Technical Reports Server (NTRS)

    1976-01-01

    A software analysis was performed of known STS sortie payload elements and their associated experiments. This provided basic data for STS payload software characteristics and sizes. A set of technology drivers was identified based on a survey of future technology needs and an assessment of current software technology. The results will be used to evolve a planned approach to software technology development. The purpose of this plan is to ensure that software technology is advanced at a pace and a depth sufficient to fulfill the identified future needs.

  17. Thermal treatment-induced ductile-to-brittle transition of submicron-sized Si pillars fabricated by focused ion beam

    SciTech Connect

    Wang, Yue-cun; Xie, De-gang; Ning, Xiao-hui; Shan, Zhi-wei

    2015-02-23

    Si pillars fabricated by focused ion beam (FIB) had been reported to have a critical size of 310–400 nm, below which their deformation behavior would experience a brittle-to-ductile transition at room temperature. Here, we demonstrated that the size-dependent transition was actually stemmed from the amorphous Si (a-Si) shell introduced during the FIB fabrication process. Once the a-Si shell was crystallized, Si pillars would behave brittle again with their modulus comparable to their bulk counterpart. The analytical model we developed has been proved to be valid in deriving the moduli of crystalline Si core and a-Si shell.

  18. Amorphous layer coating induced brittle to ductile transition in single crystalline SiC nanowires: an atomistic simulation

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao T.; Li, Zhijie; Gao, Fei

    2008-08-07

    Molecular dynamics simulations with Tersoff potentials were used to study the response of SiC nanowires with and without amorphous coating to a tensile strain along the axial direction. The uncoated nanowires show brittle properties and fail through bond breaking. Although the amorphous coating leads to the decrease of Young’s modulus of nanowires, yet it also leads the appearance of plastic deformation under axial strain. These results provide an effective way to modify the brittle properties of some other semiconductor nanowires.

  19. Multi-scale modeling of microstructure dependent intergranular brittle fracture using a quantitative phase-field based method

    SciTech Connect

    Chakraborty, Pritam; Zhang, Yongfeng; Tonks, Michael R.

    2015-12-07

    In this study, the fracture behavior of brittle materials is strongly influenced by their underlying microstructure that needs explicit consideration for accurate prediction of fracture properties and the associated scatter. In this work, a hierarchical multi-scale approach is pursued to model microstructure sensitive brittle fracture. A quantitative phase-field based fracture model is utilized to capture the complex crack growth behavior in the microstructure and the related parameters are calibrated from lower length scale atomistic simulations instead of engineering scale experimental data. The workability of this approach is demonstrated by performing porosity dependent intergranular fracture simulations in UO2 and comparing the predictions with experiments.

  20. HAZARD ANALYSIS SOFTWARE

    SciTech Connect

    Sommer, S; Tinh Tran, T

    2008-04-08

    Washington Safety Management Solutions, LLC developed web-based software to improve the efficiency and consistency of hazard identification and analysis, control selection and classification, and to standardize analysis reporting at Savannah River Site. In the new nuclear age, information technology provides methods to improve the efficiency of the documented safety analysis development process which includes hazard analysis activities. This software provides a web interface that interacts with a relational database to support analysis, record data, and to ensure reporting consistency. A team of subject matter experts participated in a series of meetings to review the associated processes and procedures for requirements and standard practices. Through these meetings, a set of software requirements were developed and compiled into a requirements traceability matrix from which software could be developed. The software was tested to ensure compliance with the requirements. Training was provided to the hazard analysis leads. Hazard analysis teams using the software have verified its operability. The software has been classified as NQA-1, Level D, as it supports the analysis team but does not perform the analysis. The software can be transported to other sites with alternate risk schemes. The software is being used to support the development of 14 hazard analyses. User responses have been positive with a number of suggestions for improvement which are being incorporated as time permits. The software has enforced a uniform implementation of the site procedures. The software has significantly improved the efficiency and standardization of the hazard analysis process.

  1. Healthcare Software Assurance

    PubMed Central

    Cooper, Jason G.; Pauley, Keith A.

    2006-01-01

    Software assurance is a rigorous, lifecycle phase-independent set of activities which ensure completeness, safety, and reliability of software processes and products. This is accomplished by guaranteeing conformance to all requirements, standards, procedures, and regulations. These assurance processes are even more important when coupled with healthcare software systems, embedded software in medical instrumentation, and other healthcare-oriented life-critical systems. The current Food and Drug Administration (FDA) regulatory requirements and guidance documentation do not address certain aspects of complete software assurance activities. In addition, the FDA’s software oversight processes require enhancement to include increasingly complex healthcare systems such as Hospital Information Systems (HIS). The importance of complete software assurance is introduced, current regulatory requirements and guidance discussed, and the necessity for enhancements to the current processes shall be highlighted. PMID:17238324

  2. Healthcare software assurance.

    PubMed

    Cooper, Jason G; Pauley, Keith A

    2006-01-01

    Software assurance is a rigorous, lifecycle phase-independent set of activities which ensure completeness, safety, and reliability of software processes and products. This is accomplished by guaranteeing conformance to all requirements, standards, procedures, and regulations. These assurance processes are even more important when coupled with healthcare software systems, embedded software in medical instrumentation, and other healthcare-oriented life-critical systems. The current Food and Drug Administration (FDA) regulatory requirements and guidance documentation do not address certain aspects of complete software assurance activities. In addition, the FDA's software oversight processes require enhancement to include increasingly complex healthcare systems such as Hospital Information Systems (HIS). The importance of complete software assurance is introduced, current regulatory requirements and guidance discussed, and the necessity for enhancements to the current processes shall be highlighted. PMID:17238324

  3. A graphene meta-interface for enhancing the stretchability of brittle oxide layers.

    PubMed

    Won, Sejeong; Jang, Jae-Won; Choi, Hyung-Jin; Kim, Chang-Hyun; Lee, Sang Bong; Hwangbo, Yun; Kim, Kwang-Seop; Yoon, Soon-Gil; Lee, Hak-Joo; Kim, Jae-Hyun; Lee, Soon-Bok

    2016-03-01

    Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers. PMID:26540317

  4. Origin of compression-induced failure in brittle solids under shock loading

    NASA Astrophysics Data System (ADS)

    Huang, J. Y.; Li, Y.; Liu, Q. C.; Zhou, X. M.; Liu, L. W.; Liu, C. L.; Zhu, M. H.; Luo, S. N.

    2015-10-01

    The origin of compression-induced failure in brittle solids has been a subject of debate. Using in situ, high-speed, strain field mapping of a representative material, polymethylmethacrylate, we reveal that shock loading leads to heterogeneity in a compressive strain field, which in turn gives rise to localized lateral tension and shear through Poisson's effects, and, subsequently, localized microdamage. A failure wave nucleates from the impact surface and its propagation into the microdamage zone is self-sustained, triggering interior failure. Its velocity increases with increasing shock strength and eventually approaches the shock velocity. The seemingly puzzling phenomena observed in previous experiments, including incubation time, failure wave velocity variations, and surface roughness effects, can all be explained consistently with the nucleation and growth of the microdamage, and the effects of loading strength and preexisting defects.

  5. Experimental and continuum plasticity aspects of the brittleness and ductility of bicrystal interfacial fracture

    NASA Astrophysics Data System (ADS)

    Kysar, Jeffrey William

    1998-12-01

    The philosophical basis of this work is to gain a better understanding of the issues which determine the brittleness and ductility of materials. One approach to the question, pioneered by Rice and Thomson, has been to characterize a material in terms of its intrinsic brittleness and ductility based on a competition between dislocation emission and cleavage failure at a crack tip. To test this hypothesis, Beltz and Wang constructed a copper/sapphire bicrystal which exhibits a directional dependence of fracture when loaded in four-point bending and reported that the observed directional dependence can be rationalized on the basis of dislocation nucleation at the crack tips. In the present work we independently repeat the Beltz and Wang experiments in an effort to quantify them and to compare the results to finite element simulation. In the process we show that the observed directional dependence of fracture is opposite to that predicted on the basis of dislocation nucleation at the crack tip. One goal of the present work is to experimentally characterize the directional dependence of fracture. A specially designed crack opening interferometer and an Atomic Force Microscope are used to measure the crack opening displacement profile. General features of crack growth are also observed directly through the transparent sapphire. Another main thrust of this work is to use continuum plasticity in an attempt to explain the directional dependence of fracture. To that end we model the copper/sapphire specimen with the finite element technique while accounting for the full elastic-plastic anisotropy of the single copper crystal. The experimental results show that both cracks propagate in a quasistatic manner at a fixed crack tip angle opening, at least away from the crack tip. The experimentally observed brittle crack has an opening approximately one-half that of the ductile crack. Further, atomic force microscopy measurements show that the near tip crack opening displacement

  6. Externally applied stress sign and film elastic properties effects on brittle film fracture

    NASA Astrophysics Data System (ADS)

    Guo, Tao; Pang, Xiaolu; Xi, Yeting; Volinsky, Alex A.; Qiao, Lijie

    2016-02-01

    Rectangular stainless steel samples with TiN film deposited on the front lateral surface were loaded in three-point bending to the maximum normal strain of 6%. Scanning electron microscopy showed that vertical cracks appeared in the tension zone when the tensile strain exceeded 1.5%, while horizontal cracks appeared in the compression zone when the compressive strain exceeded -2.9%. Film cracks in the compressive zone originate from the tensile stress imposed by the plastically deformed substrate due to the Poisson's expansion. Taking plastic deformation and Poisson's expansion of the substrate in compression into account, theoretical analysis of normal stress distribution along the cracked film segment in compression is presented. Substrate strain and film elastic properties affect film cracking in the compressive zone. At larger compressive strain, some transverse cracks along with buckling cause the film spallation. The presented method is useful for studying brittle film fracture with variable strain levels in a single sample.

  7. Metamorphic core complexes: Expression of crustal extension by ductile-brittle shearing of the geologic column

    NASA Technical Reports Server (NTRS)

    Davis, G. H.

    1985-01-01

    Metamorphic core complexes and detachment fault terranes in the American Southwest are products of stretching of continental crust in the Tertiary. The physical and geometric properties of the structures, fault rocks, and contact relationships that developed as a consequence of the extension are especially well displayed in southeastern Arizona. The structures and fault rocks, as a system, reflect a ductile-through-brittle continuum of deformation, with individual structures and faults rocks showing remarkably coordinated strain and displacement patterns. Careful mapping and analysis of the structural system has led to the realization that strain and displacement were partitioned across a host of structures, through a spectrum of scales, in rocks of progressively changing rheology. By integrating observations made in different parts of the extensional system, especially at different inferred depth levels, it has been possible to construct a descriptive/kinematic model of the progressive deformation that achieved continental crustal extension in general, and the development of metamorphic core complexes in particular.

  8. Investigating the Brittle Ductile Transition Zone Using Southern California Seismicity and the SCEC Community Fault Model

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Shearer, P.; Lin, G.

    2008-12-01

    The depth to the brittle-ductile transition zone depends on crustal parameters such as rock type, temperature, fluid pressure, and strain rate. We analyze the relocated background seismicity (1981-2005) in southern California to identify features that may be associated with rupture patterns near the brittle-ductile transition zone in past major earthquakes. The bulk of this seismicity is aftershocks that decay with time since the occurrence of the mainshock. We focus our analysis on the seismicity associated with the 1987 Mw6.6 Superstition Hills, 1992 Mw6.1 Joshua Tree, 1992 Mw7.3 Landers, 1994 Mw6.7 Northridge, and 1999 Mw7.1 Hector Mine earthquakes. Both observational and modeling studies suggest that the coseismic stress changes from major earthquakes should cause a sudden increase in the strain rate in the vicinity of the brittle-ductile transition zone at the time of the mainshock. For instance, the average depth of seismicity after the 1992 Mw7.3 Landers earthquake became ~2 km deeper as compared to before the mainshock. Apparently, the stress redistribution due to the mainshock faulting caused a strain-rate dependent downward displacement of the brittle-ductile transition. We have also determined the changes in the mean and maximum depths of seismicity for these southern California mainshocks. At the time of the mainshocks, the mean depth of seismicity exhibits a transient change of about 1 to 2 km by decaying to a new deeper depth, except for the Superstition Hills earthquake, where the seismicity depth remained unchanged. Similarly, the D95% (the depth above which 95% of the earthquakes occur) and D5% (the average depth of the deepest 5% of the earthquakes) behave like the mean depth, with a rapid transient and subsequent returning to the same depth or a slightly shallower depth. Only the thrust-faulting Northridge sequence exhibits a deep cluster that is separate from the main aftershock zone, which is predicted by geodynamic the thrust-fault models. We

  9. Nominally brittle cracks in inhomogeneous solids: From microstructural disorder to continuum-level scale

    NASA Astrophysics Data System (ADS)

    Barés, Jonathan; Barlet, Marina; Rountree, Cindy; Barbier, Luc; Bonamy, Daniel

    2014-11-01

    We analyze the intermittent dynamics of cracks in heterogeneous brittle materials and the roughness of the resulting fracture surfaces by investigating theoretically and numerically crack propagation in an elastic solid of spatially-distributed toughness. The crack motion split up into discrete jumps, avalanches, displaying scale-free statistical features characterized by universal exponents. Conversely, the ranges of scales are non-universal and the mean avalanche size and duration depend on the loading microstructure and specimen parameters according to scaling laws which are uncovered. The crack surfaces are found to be logarithmically rough. Their selection by the fracture parameters is formulated in term of scaling laws on the structure functions measured on one-dimensional roughness profiles taken parallel and perpendicular to the direction of crack growth.

  10. A Unified Cohesive Zone Approach to Model Ductile Brittle Transition in Reactor Pressure Vessel Steels

    SciTech Connect

    Pritam Chakraborty; S. Bulent Biner

    2014-08-01

    In this study, a unified cohesive zone model has been proposed to predict, Ductile to Brittle Transition, DBT, in Reactor Pressure Vessel, RPV, steels. A general procedure is described to obtain the Cohesive Zone Model, CZM, parameters for the different temperatures and fracture probabilities. In order to establish the full master-curve, the procedure requires three calibration points with one at the upper-shelf for ductile fracture and two for the fracture probabilities, Pf, of 5% and 95% at the lower-shelf. In the current study, these calibrations were carried out by utilizing the experimental fracture toughness values and flow curves. After the calibration procedure, the simulations of fracture behavior (ranging from completely unstable to stable crack extension behavior) in one inch thick compact tension specimens at different temperatures yielded values that were comparable to the experimental fracture toughness values, indicating the viability of such unified modeling approach.

  11. Model of brittle matrix composite toughening based on discrete fiber reinforcement

    NASA Technical Reports Server (NTRS)

    Rubinstein, Asher A.

    1992-01-01

    An analytical approach for the analysis of the effectiveness of fiber reinforcement in brittle matrix composites is presented. The analytical method allows consideration of discrete fiber distribution and examination of the development of crack growth parameters on microscale. The problem associated with the bridging zone development is addressed here; therefore, the bridging zone is considered to be smaller than the main preexisting crack, and the small scale approach is used. The mechanics of the reinforcement is accurately accounted for in the process zone of a growing crack. Closed form solutions characterizing the initial failure process are presented for linear and nonlinear force - fiber pullout displacement relationships. The implicit exact solution for the extended bridging zone is presented as well.

  12. Crack extension from flaws in a brittle material subjected to compression

    NASA Technical Reports Server (NTRS)

    Adams, M.; Sines, G.

    1978-01-01

    The mechanisms by which cracks extend from flaws in brittle materials subjected to compressive loads are presented. Although it is recognized that most geological materials are neither dense nor single-phase, this experimental study and analysis are restricted to single-phase, dense materials in order to provide a model amenable to analysis and experimental confirmation. The flaws which occur in dense, single-phase materials are divided into three types, each type having different characteristics of crack extension. Experimental studies of crack extension from flaws introduced into blocks of polymethylmethacrylate plastic are described. The studies show that crack extension from three dimensional flaws is more complex than two-dimensional theories predict. The extension of secondary cracks may result in more damage than that which would be predicted by considering only the primary crack extension treated by current theories. The importance of the dynamic behavior of flaws which stick and then suddenly slip is shown.

  13. Perception of brittle nails in dermatologic patients: a cross-sectional study*

    PubMed Central

    Gequelim, Giulio Cesar; Kubota, Cynthia Yone; Sanches, Sarah; Dranka, Daniela; Mejia, Marcelo Murilo; Sumiya, Fernando Mitsuo; Schmitt, Juliano Vilaverde

    2013-01-01

    Brittle Nails Syndrome is characterized by fragility of the nail plate, affecting 27% of women. We evaluated dermatology patients in a cross-sectional study about perception of nail fragility. One hundred and thirtyeight women were included, with median age of 36.5 years. Nail examination showed changes in 57% and 49% reported nail fragility. The first three fingernails were the most affected. Onychoschizia was related to onychophagia (OR = 3.29), housework (OR = 2.95) and water contact (OR = 2.44). Onychorrhexis had the strongest association with nail fragility perception (OR = 17.89). The fragility was more perceived by those who were black, of mixed race and atopic, and was associated with depressed mood. PMID:24474124

  14. Linking megathrust earthquakes to brittle deformation in a fossil accretionary complex.

    PubMed

    Dielforder, Armin; Vollstaedt, Hauke; Vennemann, Torsten; Berger, Alfons; Herwegh, Marco

    2015-01-01

    Seismological data from recent subduction earthquakes suggest that megathrust earthquakes induce transient stress changes in the upper plate that shift accretionary wedges into an unstable state. These stress changes have, however, never been linked to geological structures preserved in fossil accretionary complexes. The importance of coseismically induced wedge failure has therefore remained largely elusive. Here we show that brittle faulting and vein formation in the palaeo-accretionary complex of the European Alps record stress changes generated by subduction-related earthquakes. Early veins formed at shallow levels by bedding-parallel shear during coseismic compression of the outer wedge. In contrast, subsequent vein formation occurred by normal faulting and extensional fracturing at deeper levels in response to coseismic extension of the inner wedge. Our study demonstrates how mineral veins can be used to reveal the dynamics of outer and inner wedges, which respond in opposite ways to megathrust earthquakes by compressional and extensional faulting, respectively. PMID:26105966

  15. Tensile cracking of a brittle conformal coating on a rough substrate

    DOE PAGESBeta

    Reedy, Jr., E. D.

    2016-04-07

    This note examines the effect of interfacial roughness on the initiation and growth of channel cracks in a brittle film. A conformal film with cusp-like surface flaws that replicate the substrate roughness is investigated. This type of surface flaw is relatively severe in the sense that stress diverges as the cusp-tip is approached (i.e., there is a power-law stress singularity). For the geometry and range of film properties considered, the analysis suggests that smoothing the substrate could substantially increase the film’s resistance to the formation of the through-the-thickness cracks that precede channel cracking. Furthermore, smoothing the substrate’s surface has amore » relatively modest effect on the film stress needed to propagate a channel crack.« less

  16. Linking megathrust earthquakes to brittle deformation in a fossil accretionary complex

    PubMed Central

    Dielforder, Armin; Vollstaedt, Hauke; Vennemann, Torsten; Berger, Alfons; Herwegh, Marco

    2015-01-01

    Seismological data from recent subduction earthquakes suggest that megathrust earthquakes induce transient stress changes in the upper plate that shift accretionary wedges into an unstable state. These stress changes have, however, never been linked to geological structures preserved in fossil accretionary complexes. The importance of coseismically induced wedge failure has therefore remained largely elusive. Here we show that brittle faulting and vein formation in the palaeo-accretionary complex of the European Alps record stress changes generated by subduction-related earthquakes. Early veins formed at shallow levels by bedding-parallel shear during coseismic compression of the outer wedge. In contrast, subsequent vein formation occurred by normal faulting and extensional fracturing at deeper levels in response to coseismic extension of the inner wedge. Our study demonstrates how mineral veins can be used to reveal the dynamics of outer and inner wedges, which respond in opposite ways to megathrust earthquakes by compressional and extensional faulting, respectively. PMID:26105966

  17. Coeval brittle and ductile structures associated with extreme deformation partitioning in a multilayer sequence

    NASA Astrophysics Data System (ADS)

    Druguet, Elena; Alsop, G. Ian; Carreras, Jordi

    2009-05-01

    An investigation on the effects of a strong rheological contrast in the deformation of layered anisotropic rocks is presented. The study focuses on the geometric and kinematic analysis of complex structures developed within and adjacent to a thin marble-metapsammite multilayer unit from the Cap de Creus tectonometamorphic belt (NE Spain). Zones of high ductile strain localise in the marble layers, which exhibit complex folds, whereas metapsammites show mostly brittle (boudinage) structures. These structures strongly contrast with coeval retrogressive discrete shear zones developed in the surrounding migmatitic schists. The extreme strain partitioning is due to the rheological contrast between different lithological layers. In addition, the specific orientation of this multilayer unit induces a reversal of local kinematics with regard to bulk kinematics. Consequently, caution should be exercised when interpreting regional tectonics in highly partitioned domains associated with rheological heterogeneities.

  18. Morphological study of elastic-plastic-brittle transitions in disordered media.

    PubMed

    Kale, Sohan; Ostoja-Starzewski, Martin

    2014-10-01

    We use a spring lattice model with springs following a bilinear elastoplastic-brittle constitutive behavior with spatial disorder in the yield and failure thresholds to study patterns of plasticity and damage evolution. The elastic-perfectly plastic transition is observed to follow percolation scaling with the correlation length critical exponent ν≈1.59, implying the universality class corresponding to the long-range correlated percolation. A quantitative analysis of the plastic strain accumulation reveals a dipolar anisotropy (for antiplane loading) which vanishes with increasing hardening modulus. A parametric study with hardening modulus and ductility controlled through the spring level constitutive response demonstrates a wide spectrum of behaviors with varying degree of coupling between plasticity and damage evolution. PMID:25375508

  19. Mafic rocks at the brittle-viscous transition - interplay between fracturing, reaction and viscous deformation

    NASA Astrophysics Data System (ADS)

    Marti, Sina; Stünitz, Holger; Heilbronner, Renée

    2015-04-01

    Deformation experiments have been performed on crushed Maryland Dibase (~ 55% Plg(An60-70), 42% Px, 3% accessories, 0.2 w.t.-% H2O added) in a Griggs-type deformation apparatus in order to explore the brittle-viscous transition and the interplay between deformation and mineral reactions. Shear experiments at constant displacement rate of 1e-8 m/s (resulting shear strain rate ~ 1e-5 /s) are conducted at T=600 to 800°C and confining pressures of Pc = 1.0 and 1.5 GPa. Below 700°C, the microstructure is dominated by brittle deformation processes. At 700°C, the steady state strength approaches the Goetze criterion. The microstructure shows less evidence of brittle deformation and the onset of mineral reactions and diffusive mass transport are observed. Samples deformed at 800°C sustain significantly lower stresses than the Goetze criterion and reaction products are far more abundant. For both, 700°C and 800°C experiments, the main reaction products are Amph, Plg(An45-50) and zoisite (Zo, at Pc=1.5). Deformation localizes in all experiments. At 700°C, displacement takes place either along shear fractures or in shear bands formed by fine grained Plg and fibrous Amph. Reaction products such as Amph and Plg occur almost restricted along such zones of localized deformation. Strain energy introduced by early fracturing seems to be an important factor enhancing reaction kinetics. At 800°C, strain localizes into broader shear bands formed by a mixture of Plg + Amph (+ Zo). Phases in shear bands are extremely fine grained with equivalent diameters between 0.1 - 0.4 µm for Plg. Px grains rarely show signs of deformation and mostly form porphyroclasts overgrown by Amph. Fracturing is largely absent. The spatial distribution of Amph within the shear bands indicates material transport and precipitation of Amph between Plg-Plg boundaries. Thermodynamic modeling suggests that phases such as Grt + Cpx should grow abundantly but grow only in minor amounts (< 1 vol.-%). Amph and

  20. Modeling the viscoelastic and brittle fracture response of a high explosive in an Eulerian hydrocode

    SciTech Connect

    Clancy, S.P.; Johnson, J.N.; Burkett, M.W.

    1998-12-31

    A constitutive model that incorporates brittle-fracture-mechanics and viscoelastic material response for PBX-9501 has been developed and implemented in the two-dimensional hydrocode MESA. The hydrocode with the visco-cracking model has been applied to numerous low-rate deformation and low-speed impact events. Several low-speed impact experiments that have quantified the deformation to the explosive have been used to assess the hydrocode and model for this type of material response problem. Comparisons between MESA w/visco-cracking model calculations and experimentally measured mechanical deformation to the explosive showed that reasonable agreement was achieved for the measured magnitude of deformation but the deformation profiles/shapes were found to be different.

  1. From Bridges and Rockets, Lessons for Software Systems

    NASA Technical Reports Server (NTRS)

    Holloway, C. Michael

    2004-01-01

    Although differences exist between building software systems and building physical structures such as bridges and rockets, enough similarities exist that software engineers can learn lessons from failures in traditional engineering disciplines. This paper draws lessons from two well-known failures the collapse of the Tacoma Narrows Bridge in 1940 and the destruction of the space shuttle Challenger in 1986 and applies these lessons to software system development. The following specific applications are made: (1) the verification and validation of a software system should not be based on a single method, or a single style of methods; (2) the tendency to embrace the latest fad should be overcome; and (3) the introduction of software control into safety-critical systems should be done cautiously.

  2. Development and Application of New Quality Model for Software Projects

    PubMed Central

    Karnavel, K.; Dillibabu, R.

    2014-01-01

    The IT industry tries to employ a number of models to identify the defects in the construction of software projects. In this paper, we present COQUALMO and its limitations and aim to increase the quality without increasing the cost and time. The computation time, cost, and effort to predict the residual defects are very high; this was overcome by developing an appropriate new quality model named the software testing defect corrective model (STDCM). The STDCM was used to estimate the number of remaining residual defects in the software product; a few assumptions and the detailed steps of the STDCM are highlighted. The application of the STDCM is explored in software projects. The implementation of the model is validated using statistical inference, which shows there is a significant improvement in the quality of the software projects. PMID:25478594

  3. Organizational management practices for achieving software process improvement

    NASA Technical Reports Server (NTRS)

    Kandt, Ronald Kirk

    2004-01-01

    The crisis in developing software has been known for over thirty years. Problems that existed in developing software in the early days of computing still exist today. These problems include the delivery of low-quality products, actual development costs that exceed expected development costs, and actual development time that exceeds expected development time. Several solutions have been offered to overcome out inability to deliver high-quality software, on-time and within budget. One of these solutions involves software process improvement. However, such efforts often fail because of organizational management issues. This paper discusses business practices that organizations should follow to improve their chances of initiating and sustaining successful software process improvement efforts.

  4. Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite

    NASA Astrophysics Data System (ADS)

    Hanna, Romy D.; Ketcham, Richard A.; Zolensky, Mike; Behr, Whitney M.

    2015-12-01

    X-ray computed tomographic scanning of a 44 g Murchison stone (USNM 5487) reveals a preferred alignment of deformed, partially altered chondrules, which define a prominent foliation and weak lineation in 3D. The presence of a lineation and evidence for a component of rotational, noncoaxial shear suggest that the deformation was caused by impact. Olivine optical extinction indicates that the sample can be classified as shock stage S1, and electron backscatter diffraction (EBSD) and electron microscopy reveal that plastic deformation within the chondrules was minimal and that brittle deformation in the form of fracturing, cataclasis, and grain boundary sliding was the dominant microstructural strain-accommodating mechanism. Textural evidence such as serpentine veins parallel to the foliation fabric and crosscutting alteration veins strongly suggest that some aqueous alteration post-dated or was contemporaneous with the deformation and that multiple episodes of fracturing and mineralization occurred. Finally, using the deformed shape of the chondrules we estimate that the strain experienced by Murchison was 17-43%. This combined with the current measured porosity of Murchison suggests that the original bulk porosity of Murchison prior to its deformation was 32.2-53.4% and likely at the upper end of this range due to chondrule compressibility, providing a unique estimate of pre-deformation porosity for a carbonaceous chondrite. Our findings suggest that significant porosity loss, deformation, and compaction from impact can occur on chondrite parent bodies whose samples may record only a low level of shock, and that significant chondrule deformation resulting in a chondrite foliation fabric can occur primarily through brittle processes and does not require plastic deformation of grains.

  5. A graphene meta-interface for enhancing the stretchability of brittle oxide layers

    NASA Astrophysics Data System (ADS)

    Won, Sejeong; Jang, Jae-Won; Choi, Hyung-Jin; Kim, Chang-Hyun; Lee, Sang Bong; Hwangbo, Yun; Kim, Kwang-Seop; Yoon, Soon-Gil; Lee, Hak-Joo; Kim, Jae-Hyun; Lee, Soon-Bok

    2016-02-01

    Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers.Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05412e

  6. Mechanical behavior and brittle-ductile transition of high-chromium martensitic steel

    NASA Astrophysics Data System (ADS)

    Odnobokova, M. V.; Kipelova, A. Yu.; Belyakov, A. N.; Kaibyshev, R. O.

    2016-04-01

    The article presents data on the static tensile tests and dynamic impact-toughness tests of a highchromium martensitic 10Kh9V1M1FBR steel (0.12 wt % C, 9.8 wt % Cr, 0.93 wt % W, 1.01 wt % Mo, 0.2 wt % V, 0.05 wt % Nb, 0.05 wt % N, 0.003 wt % B, 0.36 wt % Mn, 0.2 wt % Ni, 0.06 wt % Si, 0.01 wt % P, 0.008 wt % S, 0.02 wt % Cu, 0.1 wt % Co, 0.015 wt % Al, and the remainder is Fe) in the temperature range from 20 to-196°C. In the case of static loading, a reduction in the temperature leads to an increase in the strength characteristics; upon a drop in the temperature from 20 to-100°C, the plasticity also increases. This is connected with the fact that the ductile fracture remains the basic mechanism down to cryogenic temperatures. The brittle-ductile transition related to the transition from ductile intragranular fracture to quasibrittle one is observed at-45°C. The steel exhibits high impact toughness to the temperature of-60°C ( KCV -60 = 95 J/cm2), at which the fraction of the ductile component in fracture is equal to 20%. At 80°C, the impact toughness decreases down to critical values (30 J/cm2), which correlates with the decrease in the fraction of the ductile component on the fracture surface down to 1%. The further decrease in the impact toughness down to 10 J/cm2 at-196°C is related to the transition from intragranular to intergranular brittle fracture.

  7. Brittle-viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions

    NASA Astrophysics Data System (ADS)

    Kjøll, H. J.; Viola, G.; Menegon, L.; Sørensen, B. E.

    2015-06-01

    We studied by Electron BackScatter Diffraction (EBSD) and optical microscopy a coarse-grained (ca. 0.5-6 mm) quartz vein embedded in a phyllonitic matrix to gain insights into the recrystallization mechanisms and the processes of strain localization in quartz deformed under lower greenschist facies conditions, broadly coincident with the brittle-viscous transition. The vein deformed during faulting along a phyllonitic thrust of Caledonian age within the Porsa Imbricate Stack in the Paleoproterozoic Repparfjord Tectonic Window in northern Norway. The phyllonite hosting the vein formed at the expense of a metabasaltic protolith through feldspar breakdown to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the quartz vein acted as a relatively rigid body. Viscous deformation in the vein was initially accommodated by quartz basal slip. Under the prevailing deformation conditions, however, dislocation glide- and possibly creep-accommodated deformation of quartz was inefficient, and this resulted in localized strain hardening. In response to the (1) hardening, (2) progressive and cyclic increase of the fluid pressure, and (3) increasing competence contrast between the vein and the weakly foliated host phyllonite, vein quartz crystals began to deform by brittle processes along specific, suitably oriented lattice planes, creating microgouges along microfractures. Nucleated new grains rapidly sealed these fractures as fluids penetrated the actively deforming system. The grains grew initially by solution precipitation and later by grain boundary migration. We suggest that the different initial orientation of the vein crystals led to strain accommodation by different mechanisms in the individual crystals, generating remarkably different microstructures. Crystals suitably oriented for basal slip, for example, accommodated strain mainly viscously and experienced only minor fracturing. Instead, crystals

  8. Japan Beyond-Brittle Project (JBBP) for Development of EGS Reservoirs in Ductile Zones

    NASA Astrophysics Data System (ADS)

    Asanuma, H.; Muraoka, H.; Tsuchiya, N.; Ito, H.

    2012-12-01

    EGS (Enhanced Geothermal System) geothermal has been identified as a most promising method of geothermal development because of its potential applicability to a much wider range of sites, many of which have previously been considered to be unsuitable for geothermal development. Meanwhile, some critical problems with EGS technologies have been experimentally identified, such as low recovery of injected water, difficulties in establishing universal design/development methodologies, and the occurrence of induced seismicity, suggesting that there may be limitations in realizing EGS in earthquake-prone compression tectonic zones. We propose a new concept of engineered geothermal development where reservoirs are created in ductile basement. This potentially has a number of advantages including: (a) simpler design and control of the reservoir, (b) nearly full recovery of injected water, (c) sustainable production, (d) lower cost when developed in relatively shallower ductile zones in compression tectonic settings, (e) large potential quantities of energy extraction from widely distributed ductile zones, (f) the establishment of a universal design/development methodology, and (g) suppression of felt earthquakes from/around the reservoirs. To further assess the potential of EGS reservoir development in ductile zones we have initiated the "Japan Beyond-Brittle Project (JBBP)". It is intended that the first few years of the JBBP will be spent in basic scientific investigation and necessary technology development, including studies on rock mechanics in the brittle/ductile regime, characterization of ductile rock masses, development of modeling methodologies/technologies, and investigations of induced/triggered earthquakes. We expect to drill a deep experimental borehole that will penetrate the ductile zone in northeast Japan after basic studies are completed. The feasibility of EGS reservoir development in the ductile zone will then be assessed through observations and

  9. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility.

    PubMed

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others. PMID:25652998

  10. A damage mechanics approach for quantifying stress changes due to brittle failure of porous rocks

    NASA Astrophysics Data System (ADS)

    Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena

    2016-04-01

    Natural fault zones or man-made injection or production of fluid impact the regional stress distribution in Earth's crust and can be responsible for localized stress discontinuities. Understanding the processes controlling fracturing of the porous rocks and mechanical behaviour of fault zones is therefore of interest for several applications including geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes controlling the deformation of porous rocks during and after brittle failure. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To illustrate the model, simulation of a compaction experiment of a sandstone leading to shear failure will be presented which allows to quantify the stress drop accompanying the failure. Finally, we will demonstrate that this approach can also be used at the field scale to simulate hydraulic fracturing and assess the resulting changes in the stress field.

  11. Time-resolved study of femtosecond laser induced micro-modifications inside transparent brittle materials

    NASA Astrophysics Data System (ADS)

    Hendricks, F.; Matylitsky, V. V.; Domke, M.; Huber, Heinz P.

    2016-03-01

    Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient, fast and localized energy deposition in nearly all types of solid materials. When an ultra-short laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Thus ultra-short pulse lasers allow cutting of the chemically strengthened glasses such as Corning Gorilla glass without cracking. Non-ablative cutting of transparent, brittle materials, using the newly developed femtosecond process ClearShapeTM from Spectra-Physics, is based on producing a micron-sized material modification track with well-defined geometry inside. The key point for development of the process is to understand the induced modification by a single femtosecond laser shot. In this paper, pump-probe microscopy techniques have been applied to study the defect formation inside of transparent materials, namely soda-lime glass samples, on a time scale between one nanosecond to several tens of microseconds. The observed effects include acoustic wave propagation as well as mechanical stress formation in the bulk of the glass. Besides better understanding of underlying physical mechanisms, our experimental observations have enabled us to find optimal process parameters for the glass cutting application and lead to better quality and speed for the ClearShapeTM process.

  12. Bottom-up modeling of damage in heterogeneous quasi-brittle solids

    NASA Astrophysics Data System (ADS)

    Rinaldi, Antonio

    2013-03-01

    The theoretical modeling of multisite cracking in quasi-brittle materials is a complex damage problem, hard to model with traditional methods of fracture mechanics due to its multiscale nature and to strain localization induced by microcracks interaction. Macroscale "effective" elastic models can be conveniently applied if a suitable Helmholtz free energy function is identified for a given material scenario. Del Piero and Truskinovsky (Continuum Mech Thermodyn 21:141-171, 2009), among other authors, investigated macroscale continuum solutions capable of matching—in a top-down view—the phenomenology of the damage process for quasi-brittle materials regardless of the microstructure. On the contrary, this paper features a physically based solution method that starts from the direct consideration of the microscale properties and, in a bottom-up view, recovers a continuum elastic description. This procedure is illustrated for a simple one-dimensional problem of this type, a bar modeled stretched by an axial displacement, where the bar is modeled as a 2D random lattice of decohesive spring elements of finite strength. The (microscale) data from simulations are used to identify the "exact" (macro-) damage parameter and to build up the (macro-) Helmholtz function for the equivalent elastic model, bridging the macroscale approach by Del Piero and Truskinovsky. The elastic approach, coupled with microstructural knowledge, becomes a more powerful tool to reproduce a broad class of macroscopic material responses by changing the convexity-concavity of the Helmholtz energy. The analysis points out that mean-field statistics are appropriate prior to damage localization but max-field statistics are better suited in the softening regime up to failure, where microstrain fluctuation needs to be incorporated in the continuum model. This observation is of consequence to revise mean-field damage models from literature and to calibrate Nth gradient continuum models.

  13. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility

    NASA Astrophysics Data System (ADS)

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J.

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

  14. Fabric controls on the brittle failure of folded gneiss and schist

    NASA Astrophysics Data System (ADS)

    Agliardi, Federico; Zanchetta, Stefano; Crosta, Giovanni B.

    2014-12-01

    We experimentally studied the brittle failure behaviour of folded gneiss and schist. Rock fabric and petrography were characterised by meso-structural analyses, optical microscopy, X-ray diffraction, and SEM imaging. Uniaxial compression, triaxial compression and indirect tension laboratory tests were performed to characterise their strength and stress-strain behaviour. Fracture patterns generated in compression were resolved in 3D through X-ray computed tomography at different resolutions (30 to 625 μm). Uniaxial compression tests revealed relatively low and scattered values of unconfined compressive strength (UCS) and Young's modulus, with no obvious relationships with the orientation of foliation. Samples systematically failed in four brittle modes, involving different combinations of shear fractures along foliation or parallel to fold axial planes, or the development of cm-scale shear zones. Fracture quantification and microstructural analysis show that different failure modes occur depending on the mutual geometrical arrangement and degree of involvement of two distinct physical anisotropies, i.e. the foliation and the fold axial planes. The Axial Plane Anisotropy (APA) is related to micro-scale grain size reduction and shape preferred orientation within quartz-rich domains, and to mechanical rotation or initial crenulation cleavage within phyllosilicate-rich domains at fold hinge zones. In quartz-rich rocks (gneiss), fracture propagation through quartz aggregates forming the APA corresponds to higher fracture energy and strength than found for fracture through phyllosilicate-rich domains. This results in a strong dependence of strength on the failure mode. Conversely, in phyllosilicate-rich rocks (schist), all the failure modes are dominated by the strength of phyllosilicates, resulting in a sharp reduction of strength anisotropy.

  15. NASA software documentation standard software engineering program

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The NASA Software Documentation Standard (hereinafter referred to as Standard) can be applied to the documentation of all NASA software. This Standard is limited to documentation format and content requirements. It does not mandate specific management, engineering, or assurance standards or techniques. This Standard defines the format and content of documentation for software acquisition, development, and sustaining engineering. Format requirements address where information shall be recorded and content requirements address what information shall be recorded. This Standard provides a framework to allow consistency of documentation across NASA and visibility into the completeness of project documentation. This basic framework consists of four major sections (or volumes). The Management Plan contains all planning and business aspects of a software project, including engineering and assurance planning. The Product Specification contains all technical engineering information, including software requirements and design. The Assurance and Test Procedures contains all technical assurance information, including Test, Quality Assurance (QA), and Verification and Validation (V&V). The Management, Engineering, and Assurance Reports is the library and/or listing of all project reports.

  16. Scientific Software for the Macintosh.

    ERIC Educational Resources Information Center

    Watkins, Douglas; Gabaldon, Diana J.

    1985-01-01

    Lists and describes representative software for Macintosh microcomputers. Included are Apple University Consortium software, word processing software, statistics packages, integrated packages, database management systems, and others. Source of software and costs (when available) are included. (JN)

  17. Brittle deformation and slope failure at the North Menan Butte tuff cone, Eastern Snake River Plain, Idaho

    USGS Publications Warehouse

    Okubo, Chris H.

    2014-01-01

    The manifestation of brittle deformation within inactive slumps along the North Menan Butte, a basaltic tuff cone in the Eastern Snake River Plain, is investigated through field and laboratory studies. Microstructural observations indicate that brittle strain is localized along deformation bands, a class of structural discontinuity that is predominant within moderate to high-porosity, clastic sedimentary rocks. Various subtypes of deformation bands are recognized in the study area based on the sense of strain they accommodate. These include dilation bands (no shear displacement), dilational shear bands, compactional shear bands and simple shear bands (no volume change). Measurements of the host rock permeability between the deformation bands indicate that the amount of brittle strain distributed throughout this part of the rock is negligible, and thus deformation bands are the primary means by which brittle strain is manifest within this tuff. Structural discontinuities that are similar in appearance to deformation bands are observed in other basaltic tuffs. Therefore deformation bands may represent a common structural feature of basaltic tuffs that have been widely misclassified as fractures. Slumping and collapse along the flanks of active volcanoes strongly influence their eruptive behavior and structural evolution. Therefore characterizing the process of deformation band and fault growth within basaltic tuff is key to achieving a more complete understanding of the evolution of basaltic volcanoes and their associated hazards.

  18. Micromechanics of failure in brittle geomaterials. Final technical report (for 7/1/1994 - 8/31/2000)

    SciTech Connect

    Wong, Teng-fong

    2000-12-01

    The overall objective was to provide a fundamental understanding of brittle failure processes in porous and compact geomaterials. This information is central to energy-related programs such as oil and gas exploration/production, reservoir engineering, drilling technology, geothermal energy recovery, nuclear waste isolation, and environmental remediation. The effects of key parameters such as grain boundary structure and cementation, damage state, and load path on the deformation and failure model of brittle geomaterials are still largely unknown. The research methodology emphasized the integration of experimental rock mechanical testing, quantitative microscopy, and detailed analysis using fracture mechanics, continuum plasticity theory, and numerical methods. Significant progress was made in elucidating the micromechanics of brittle failure in compact crystalline rocks, as well as high-porosity siliciclastic and carbonate rocks. Substantial effort was expended toward applying a new quantitative three-dimensional imaging technique to geomaterials and for developing enhanced image analysis capabilities. The research is presented under the following topics: technique for imaging the 3-D pore structure of geomaterials; mechanics of compressive failure in sandstone; effect of water on compressive failure of sandstone; micromechanics of compressive failure: observation and model; and the brittle-ductile transition in porous carbonate rocks.

  19. Recommendations for ductile and brittle failure design criteria for ductile cast iron spent-fuel shipping containers

    SciTech Connect

    Schwartz, M.W.

    1984-04-01

    This report presents recommendations for establishing design and acceptance criteria for the ductile cast iron to be used for fabricating spent-fuel shipping casks. These recommendations address design criteria for preventing ductile failure, and acceptance criteria for preventing brittle fracture, based upon drop testing a flawed prototype cask.

  20. Ductile, Brittle Failure Characteristics as Determined by the State of the Material and the Imposed State of Stress

    SciTech Connect

    Christensen, R M

    2004-02-05

    A method is developed for determining whether a particular mode of failure is expected to be of ductile type or brittle type depending upon both the state of the material and the particular state of stressing the isotropic material to failure. The state of the material is determined by two specific failure properties and a newly formulated failure theory. The ductile versus brittle criterion then involves the state of the material specification and the mean normal stress part of the imposed stress state. Several examples are given for different stress states and a spectrum of materials types. Closely related to the failure mode types are the orientations of the associated failure surfaces. The resulting failure surface angle predictions are compared with those from the Coulomb-Mohr failure criterion. In uniaxial tension, only the present method correctly predicts the octahedral failure angle at the ductile limit, and also shows a distinct failure mode transition from ductile type to brittle type as the state of the material changes. The explicit D-B criterion and the related failure surface orientation methodology are intended to provide a refinement and generalization of the ductile-brittle transition viewed only as a state property to also include a dependence upon the type of stress state taken to failure.

  1. Ductile-brittle transition behavior of V-4Cr-4Ti irradiated in the dynamic helium charging experiment

    SciTech Connect

    Chung, H.M.; Nowicki, L.J.; Busch, D.E.

    1995-04-01

    The objective of this work is to determine the effect of simultaneous displacement damage and dynamically charged helium on the ductile-brittle transition behavior of V-4Cr-4Ti specimens irradiated to 18-31 dpa at 425-600{degrees}C in the Dynamic Helium Charging Experiment (DHCE).

  2. COTS software selection process.

    SciTech Connect

    Watkins, William M. (Strike Wire Technologies, Louisville, CO); Lin, Han Wei; McClelland, Kelly (U.S. Security Associates, Livermore, CA); Ullrich, Rebecca Ann; Khanjenoori, Soheil; Dalton, Karen; Lai, Anh Tri; Kuca, Michal; Pacheco, Sandra; Shaffer-Gant, Jessica

    2006-05-01

    Today's need for rapid software development has generated a great interest in employing Commercial-Off-The-Shelf (COTS) software products as a way of managing cost, developing time, and effort. With an abundance of COTS software packages to choose from, the problem now is how to systematically evaluate, rank, and select a COTS product that best meets the software project requirements and at the same time can leverage off the current corporate information technology architectural environment. This paper describes a systematic process for decision support in evaluating and ranking COTS software. Performed right after the requirements analysis, this process provides the evaluators with more concise, structural, and step-by-step activities for determining the best COTS software product with manageable risk. In addition, the process is presented in phases that are flexible to allow for customization or tailoring to meet various projects' requirements.

  3. Standard Annunciator software overview

    SciTech Connect

    Anspach, D.A. ); Fox, E.T.; Kissock, P.S. )

    1992-10-01

    The Standard Annunciator Software is responsible for controlling the AN/GSS-41 and AN/GSS-44 Annunciator Systems. The software interfaces with other systems-ACS, ECS, CCTV, UPS-to determine current alarm, tamper, and hardware status. Current system status conditions are displayed at the operator's console and on display maps. This manual describes the organization and functionality of the software as well as the generation mechanisms for development and target environments.

  4. Standard Annunciator software overview

    SciTech Connect

    Anspach, D.A.; Fox, E.T.; Kissock, P.S.

    1992-10-01

    The Standard Annunciator Software is responsible for controlling the AN/GSS-41 and AN/GSS-44 Annunciator Systems. The software interfaces with other systems-ACS, ECS, CCTV, UPS-to determine current alarm, tamper, and hardware status. Current system status conditions are displayed at the operator`s console and on display maps. This manual describes the organization and functionality of the software as well as the generation mechanisms for development and target environments.

  5. Gammasphere software development

    SciTech Connect

    Piercey, R.B.

    1993-01-01

    Activities of the nuclear physics group are described. Progress was made in organizing the Gammasphere Software Working Group, establishing a nuclear computing facility, participating in software development at Lawrence Berkeley, developing a common data file format, and adapting the ORNL UPAK software to run at Gammasphere. A universal histogram object was developed that defines a file format and provides for an objective-oriented programming model. An automated liquid nitrogen fill system was developed for Gammasphere (110 Ge detectors comprise the sphere).

  6. IRAS software analysis library

    NASA Technical Reports Server (NTRS)

    Domik, Gitta; Merkle, C. Scott

    1991-01-01

    The goal of this project was to collect 'research software' written in Interactive Data Language (IDL) to support analysis of data from the Infrared Astronomical Satellite (IRAS) and make it available to the larger community. 'Research Software' describes software created by researchers and staff for a specific research goal, but lacks sufficient documentation, easy to use interfaces, and rigorous debugging. Additionally, most of the IDL/IRAS code available needed to be ported to a (largely) hardware independent new version of IDL.

  7. Statistical modelling of software reliability

    NASA Technical Reports Server (NTRS)

    Miller, Douglas R.

    1991-01-01

    During the six-month period from 1 April 1991 to 30 September 1991 the following research papers in statistical modeling of software reliability appeared: (1) A Nonparametric Software Reliability Growth Model; (2) On the Use and the Performance of Software Reliability Growth Models; (3) Research and Development Issues in Software Reliability Engineering; (4) Special Issues on Software; and (5) Software Reliability and Safety.

  8. Rapid Software Evolution

    NASA Astrophysics Data System (ADS)

    Iordanov, Borislav

    The high complexity of modern software systems, described more than twenty years ago in the well-know paper by Fred Brooks [Brooks 1986] has become proverbial amongst practitioners. While the software engineering community has accepted and learned to cope, albeit in a limited way, with what Brooks termed essential difficulties, i.e. intractable obstacles due to the nature of software itself, there is a consensus that the ultra large-scale systems of the future call for a fundamental change in our understanding and practice of software construction [Northrop 2006].

  9. Classification software technique assessment

    NASA Technical Reports Server (NTRS)

    Jayroe, R. R., Jr.; Atkinson, R.; Dasarathy, B. V.; Lybanon, M.; Ramapryian, H. K.

    1976-01-01

    A catalog of software options is presented for the use of local user communities to obtain software for analyzing remotely sensed multispectral imagery. The resources required to utilize a particular software program are described. Descriptions of how a particular program analyzes data and the performance of that program for an application and data set provided by the user are shown. An effort is made to establish a statistical performance base for various software programs with regard to different data sets and analysis applications, to determine the status of the state-of-the-art.

  10. Software Reuse Issues

    NASA Technical Reports Server (NTRS)

    Voigt, Susan J. (Editor); Smith, Kathryn A. (Editor)

    1989-01-01

    NASA Langley Research Center sponsored a Workshop on NASA Research in Software Reuse on November 17-18, 1988 in Melbourne, Florida, hosted by Software Productivity Solutions, Inc. Participants came from four NASA centers and headquarters, eight NASA contractor companies, and three research institutes. Presentations were made on software reuse research at the four NASA centers; on Eli, the reusable software synthesis system designed and currently under development by SPS; on Space Station Freedom plans for reuse; and on other reuse research projects. This publication summarizes the presentations made and the issues discussed during the workshop.

  11. Architecture for Verifiable Software

    NASA Technical Reports Server (NTRS)

    Reinholtz, William; Dvorak, Daniel

    2005-01-01

    Verifiable MDS Architecture (VMA) is a software architecture that facilitates the construction of highly verifiable flight software for NASA s Mission Data System (MDS), especially for smaller missions subject to cost constraints. More specifically, the purpose served by VMA is to facilitate aggressive verification and validation of flight software while imposing a minimum of constraints on overall functionality. VMA exploits the state-based architecture of the MDS and partitions verification issues into elements susceptible to independent verification and validation, in such a manner that scaling issues are minimized, so that relatively large software systems can be aggressively verified in a cost-effective manner.

  12. On Software Compatibility.

    ERIC Educational Resources Information Center

    Ershov, Andrei P.

    The problem of compatibility of software hampers the development of computer application. One solution lies in standardization of languages, terms, peripherais, operating systems and computer characteristics. (AB)

  13. Dtest Testing Software

    NASA Technical Reports Server (NTRS)

    Jain, Abhinandan; Cameron, Jonathan M.; Myint, Steven

    2013-01-01

    This software runs a suite of arbitrary software tests spanning various software languages and types of tests (unit level, system level, or file comparison tests). The dtest utility can be set to automate periodic testing of large suites of software, as well as running individual tests. It supports distributing multiple tests over multiple CPU cores, if available. The dtest tool is a utility program (written in Python) that scans through a directory (and its subdirectories) and finds all directories that match a certain pattern and then executes any tests in that directory as described in simple configuration files.

  14. NASA's Software Safety Standard

    NASA Technical Reports Server (NTRS)

    Ramsay, Christopher M.

    2005-01-01

    NASA (National Aeronautics and Space Administration) relies more and more on software to control, monitor, and verify its safety critical systems, facilities and operations. Since the 1960's there has hardly been a spacecraft (manned or unmanned) launched that did not have a computer on board that provided vital command and control services. Despite this growing dependence on software control and monitoring, there has been no consistent application of software safety practices and methodology to NASA's projects with safety critical software. Led by the NASA Headquarters Office of Safety and Mission Assurance, the NASA Software Safety Standard (STD-18l9.13B) has recently undergone a significant update in an attempt to provide that consistency. This paper will discuss the key features of the new NASA Software Safety Standard. It will start with a brief history of the use and development of software in safety critical applications at NASA. It will then give a brief overview of the NASA Software Working Group and the approach it took to revise the software engineering process across the Agency.

  15. Software Use Control

    SciTech Connect

    Trussell, F.G.

    1994-03-01

    The topic of this technical presentation is Use Control Software. The nuclear weapon software design community is being subjected to many surety forces that are stretching the envelope of their designs. Given that software is a critical part of the use control system design, we must work to limit the errors of the software development process. The objective of this paper is to discuss a methodology that the author, as a member of the Security and Use Control Assessment Department, is working on. This is the first introduction of the proposed methodology. Software that is a part of any use control system, subsystem, device, or component is critical to the operation of that apparatus. The software is expected to meet the criteria of modern software quality. In a use control application, meeting the normal quality standards is short of the expectations in meeting the use control obligations. The NWC community expects the use control features of a nuclear weapon to provide assurance that the weapon is protected from unauthorized nuclear detonation. The methodology that the author is proposing will provide a focused scrutiny to software that is used in the hardware of use control systems, subsystems, devices, and components. The methodology proposes further scrutiny of the structure of the software, memory, variables, storage, and control features.

  16. Professional Ethics of Software Engineers: An Ethical Framework.

    PubMed

    Lurie, Yotam; Mark, Shlomo

    2016-04-01

    The purpose of this article is to propose an ethical framework for software engineers that connects software developers' ethical responsibilities directly to their professional standards. The implementation of such an ethical framework can overcome the traditional dichotomy between professional skills and ethical skills, which plagues the engineering professions, by proposing an approach to the fundamental tasks of the practitioner, i.e., software development, in which the professional standards are intrinsically connected to the ethical responsibilities. In so doing, the ethical framework improves the practitioner's professionalism and ethics. We call this approach Ethical-Driven Software Development (EDSD), as an approach to software development. EDSD manifests the advantages of an ethical framework as an alternative to the all too familiar approach in professional ethics that advocates "stand-alone codes of ethics". We believe that one outcome of this synergy between professional and ethical skills is simply better engineers. Moreover, since there are often different software solutions, which the engineer can provide to an issue at stake, the ethical framework provides a guiding principle, within the process of software development, that helps the engineer evaluate the advantages and disadvantages of different software solutions. It does not and cannot affect the end-product in and of-itself. However, it can and should, make the software engineer more conscious and aware of the ethical ramifications of certain engineering decisions within the process. PMID:26047575

  17. The ASSIST: Bringing Information and Software Together for Scientists

    NASA Technical Reports Server (NTRS)

    Mandel, Eric

    1997-01-01

    The ASSIST was developed as a step toward overcoming the problems faced by researchers when trying to utilize complex and often conflicting astronomical data analysis systems. It implements a uniform graphical interface to analysis systems, documentation, data, and organizational memory. It is layered on top of the Answer Garden Substrate (AGS), a system specially designed to facilitate the collection and dissemination of organizational memory. Under the AISRP program, we further developed the ASSIST to make it even easier for researchers to overcome the difficulties of accessing software and information in a complex computer environment.

  18. Probing the Statistical Validity of the Ductile-to-Brittle Transition in Metallic Nanowires Using GPU Computing.

    PubMed

    French, William R; Pervaje, Amulya K; Santos, Andrew P; Iacovella, Christopher R; Cummings, Peter T

    2013-12-10

    We perform a large-scale statistical analysis (>2000 independent simulations) of the elongation and rupture of gold nanowires, probing the validity and scope of the recently proposed ductile-to-brittle transition that occurs with increasing nanowire length [Wu et al. Nano Lett. 2012, 12, 910-914]. To facilitate a high-throughput simulation approach, we implement the second-moment approximation to the tight-binding (TB-SMA) potential within HOOMD-Blue, a molecular dynamics package which runs on massively parallel graphics processing units (GPUs). In a statistical sense, we find that the nanowires obey the ductile-to-brittle model quite well; however, we observe several unexpected features from the simulations that build on our understanding of the ductile-to-brittle transition. First, occasional failure behavior is observed that qualitatively differs from that predicted by the model prediction; this is attributed to stochastic thermal motion of the Au atoms and occurs at temperatures as low as 10 K. In addition, we also find that the ductile-to-brittle model, which was developed using classical dislocation theory, holds for nanowires as small as 3 nm in diameter. Finally, we demonstrate that the nanowire critical length is higher at 298 K relative to 10 K, a result that is not predicted by the ductile-to-brittle model. These results offer practical design strategies for adjusting nanowire failure and structure and also demonstrate that GPU computing is an excellent tool for studies requiring a large number of independent trajectories in order to fully characterize a system's behavior. PMID:26592289

  19. The Border Ranges shear zone, Glacier Bay National Park, Alaska: An example of an ancient brittle-ductile transition zone

    SciTech Connect

    Smart, K.J. . Dept. of Geological Sciences)

    1992-01-01

    The Border Ranges fault system in southern Alaska forms the tectonic boundary between the Peninsular-Alexander-Wrangellia (PAW) composite terrane and the Chugach terrane. In Glacier Bay National Park, the Border Ranges fault system is a north-northwest trending, 10 kilometer wide zone of ductile shear zones and brittle faults hereafter referred to as the Border Ranges shear zone. Three-dimensional strain analyses of plagioclase lathes in the foliated calc-alkaline plutons reveals a strong flattening fabric with the plane of maximum flattening (XY-plane) oriented northwest-southeast and dipping steeply to the southwest. The distribution and shapes of sub-elliptical mafic enclaves in the calc-alkaline plutons show a similarly oriented flattening fabric. Coeval brittle and ductile deformational processes are indicated by: (1) ductile shear zones narrowing to brittle faults at the outcrop scale; and (2) undulose quartz with subgrain development, kinked biotite, twinned and undulose feldspar, and fractured and twinned hornblende often within a single thin-section. Amphibole geobarometry indicates that two of the calc-alkaline plutons deformed by the shear zone crystallized at pressures of approximately 3 kilobars equivalent to 10 to 12 kilometers depth. Metamorphic mineral assemblages within the mylonites indicate deformation under lower greenschist facies conditions (300--400 C). The shear zone may represent a snapshot of the brittle-ductile transition of an ancient convergent-transform plate boundary. As such, this unique exposure may be an ancient analogue for the brittle-ductile transition of the present day San Andreas fault system.

  20. Nanomedicine therapeutic approaches to overcome cancer drug resistance.

    PubMed

    Markman, Janet L; Rekechenetskiy, Arthur; Holler, Eggehard; Ljubimova, Julia Y

    2013-11-01

    Nanomedicine is an emerging form of therapy that focuses on alternative drug delivery and improvement of the treatment efficacy while reducing detrimental side effects to normal tissues. Cancer drug resistance is a complicated process that involves multiple mechanisms. Here we discuss the major forms of drug resistance and the new possibilities that nanomedicines offer to overcome these treatment obstacles. Novel nanomedicines that have a high ability for flexible, fast drug design and production based on tumor genetic profiles can be created making drug selection for personal patient treatment much more intensive and effective. This review aims to demonstrate the advantage of the young medical science field, nanomedicine, for overcoming cancer drug resistance. With the advanced design and alternative mechanisms of drug delivery known for different nanodrugs including liposomes, polymer conjugates, micelles, dendrimers, carbon-based, and metallic nanoparticles, overcoming various forms of multi-drug resistance looks promising and opens new horizons for cancer treatment. PMID:24120656