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Showing papers on "Deformation (engineering) published in 1993"


Journal ArticleDOI
TL;DR: In this article, an eight-chain representation of the underlying macromolecular network structure of the rubber and the non-Gaussian behavior of the individual chains in the proposed network is proposed.
Abstract: Aconstitutive model is proposed for the deformation of rubber materials which is shown to represent successfully the response of these materials in uniaxial extension, biaxial extension, uniaxial compression, plane strain compression and pure shear. The developed constitutive relation is based on an eight chain representation of the underlying macromolecular network structure of the rubber and the non-Gaussian behavior of the individual chains in the proposed network. The eight chain model accurately captures the cooperative nature of network deformation while requiring only two material parameters, an initial modulus and a limiting chain extensibility. Since these two parameters are mechanistically linked to the physics of molecular chain orientation involved in the deformation of rubber, the proposed model represents a simple and accurate constitutive model of rubber deformation. The chain extension in this network model reduces to a function of the root-mean-square of the principal applied stretches as a result of effectively sampling eight orientations of principal stretch space. The results of the proposed eight chain model as well as those of several prominent models are compared with experimental data of Treloar (1944, Trans. Faraday Soc. 40, 59) illustrating the superiority, simplicity and predictive ability of the proposed model. Additionally, a new set of experiments which captures the state of deformation dependence of rubber is described and conducted on three rubber materials. The eight chain model is found to model and predict accurately the behavior of the three tested materials further confirming its superiority and effectiveness over earlier models.

2,583 citations


Journal ArticleDOI
TL;DR: In this paper, a visco-plastic self-consistent (VPSC) anisotropic approach for modeling the plastic deformation of polycrystals, together with a thorough discussion of the assumptions involved and the range of application of such approach is presented.
Abstract: We present in this work a visco-plastic self-consistent (VPSC) anisotropic approach for modeling the plastic deformation of polycrystals, together with a thorough discussion of the assumptions involved and the range of application of such approach. We use the VPSC model for predicting texture development during rolling and axisymmetric deformation of Zirconium alloys, and to calculate the yield locus and the Lankford coefficient of rolled Zircaloy sheet. We compare our results with experimental data and find that they are in good agreement with the available experimental evidence. We also compare the VPSC predictions with the ones of a Full Constraints approach and observe that they differ both quantitatively and qualitatively: according with the predictions of the VPSC scheme, deformation is accommodated mostly by the soft systems, the twinning activity is much lower, and fewer systems are active, in average, per grain. These results are a consequence of having accounted for the grain interaction with its surroundings, which is a crucial aspect when modeling plastically anisotropic materials.

1,834 citations


Book
01 Jan 1993
TL;DR: A survey of engineering materials can be found in this paper, where a stress-based approach to fatigue of materials is presented. But, the approach is not suitable for all types of materials.
Abstract: (NOTE: Each chapter concludes with a Summary, New Terms and Symbols, References, and a Problems and Questions section.) 1. Introduction. 2. Structure and Deformation in Materials. 3. A Survey of Engineering Materials. 4. Mechanical Testing: Tension Test and Other Basic Tests. 5. Stress-Strain Relationships and Behavior. 6. Review of Complex and Principal States of Stress and Strain. 7. Yielding and Fracture under Combined Stresses. 8. Fracture of Cracked Members. 9. Fatigue of Materials: Introduction and Stress-Based Approach. 10. Stress-Based Approach to Fatigue: Notched Members. 11. Fatigue Crack Growth. 12. Plastic Deformation Behavior and Models for Materials. 13. Stress-Strain Analysis of Plastically Deforming Members. 14. Strain-Based Approach to Fatigue. 15. Time-Dependent Behavior: Creep and Damping. Appendix A: Review of Selected Topics from Mechanics of Materials. Appendix B: Statistical Variation in Materials Properties. Bibliography. Index.

1,236 citations


Journal ArticleDOI
O. H. Yeoh1
TL;DR: In this paper, the elastic properties of a rubber were described in terms of a strain energy function which is an infinite power series in the strain invariants I1, I2 and I3.
Abstract: According to Rivlin's Phenomenological Theory of Rubber Elasticity, the elastic properties of a rubber may be described in terms of a strain energy function which is an infinite power series in the strain invariants I1, I2 and I3. The simplest forms of Rivlin's strain energy function are the neo-Hookean, which is obtained by truncating the infinite series to just the first term in I1, and the Mooney-Rivlin, which retains the first terms in I1 and I2. Recently, we proposed a strain energy function which is a cubic in I1. Conceptually, the proposed function is a material model with a shear modulus that varies with deformation. In this paper, we compare the large strain behavior of rubber as predicted by these forms of the strain energy function. The elastic behavior of swollen rubber is also discussed.

1,198 citations


Journal ArticleDOI
TL;DR: In this article, a tensorial internal state variable model of the evolving anisotropic polymer response was developed to predict the response of polycarbonate and polymethylmethacrylate over a range of strain rates and temperatures.

469 citations


Journal ArticleDOI
TL;DR: In this article, a micromechanics constitutive model has been proposed to describe the pseudoelastic and shape memory behavior of polycrystalline shape memory alloys under various temperatures.
Abstract: A MICROMECHANICS constitutive model has been proposed in this paper to describe the pseudoelastic and shape memory behavior of polycrystalline shape memory alloys under various temperatures The derivation of the model is based on the thermodynamics, micromechanics and microstructural physical mechanism analysis of the material during deformation and it is shown that the inelastic deformation of the material in the mechanical and/or thermal loading processes is associated with some temperature, stress state and loading history dependent yielding surfaces which microscopically correspond to the forward and reverse transformation (or reorientation) processes, respectively

414 citations


Journal ArticleDOI
TL;DR: In this paper, the characteristics of metal components proposed as impact energy absorbers are reviewed, focusing on the modes of deformation which stem from the axial compression of metal tubes.

285 citations


Journal ArticleDOI
TL;DR: In this article, the asymptotic stress and deformation fields for a crack tip embedded in a power-law elastic-plastic material are developed for a plane problems, and the most singular term in the series solution is the HRR solution, after Hutchinson and Rice and Rosengren.

277 citations


Book
01 Jan 1993
TL;DR: In this article, Mughrabi et al. discuss the properties of metal, ceramics, and intermetallics, including superplasticity in metal, glass, and polysilicon.
Abstract: Introductory Chapter: Microstructure and Mechanical Properties (H. Mughrabi). Flow Stress and Work Hardening (J. Sevillano). Deformation and Textures of Metals at Large Strain (E. Aernoudt, et al.). Dislocation Patterning (L. Kubin). Solid Solution Strengthening (H. Neuh?user & C. Schwink). Deformation of Intermetallic Compounds (Y. Umakoshi). Particle Strengthening (B. Reppich). High-Temperature Deformation and Creep of Crystalline Solids (W. Blum). Superplasticity in Metals, Ceramics and Intermetallics (A. Mukherjee). Inelastic Deformation and Fracture of Glassy Solids (A. Argon). Cyclic Deformation and Fatigue (S. Suresh). Fracture Mechanisms (H. Riedel). Friction and Wear (K. Kato). Index.

259 citations


Journal ArticleDOI
TL;DR: In this article, energy-based considerations on the inelastic surface deformation of brittle materials are conducted, where the hysteresis loop energy Ur which is dissipated during the indentation loading-unloading cycle is related to the true hardness H, apparent hardness H, and the work-of-indentation Γ 1.
Abstract: Energy-based considerations on the inelastic surface deformation of brittle materials are conducted. The hysteresis loop energy Ur which is dissipated during the indentation loading-unloading cycle is related to the true hardness H, apparent hardness H , and the work-of-indentation Γ1. The true hardness has its energy-derived meaning of the irreversible energy consumption to create a unit volume of the indentation impression of ideally plastic materials. The relationships between Ur and the three-half power of indentation load P 3 2 , and between Ur and the volume of the indentation impression V1 are used to separate the plastic contribution from the complicated plastic/elastic surface deformation processes in indentation hardness tests. The linear relationship of Ur vs P 3 2 provides an important experimental technique for determining the true hardness H of brittle materials. The linear relationship of Ur vs V1 is available to the experimental determination of Γ1. The mechanical and physical meanings of the conventional Vickers indentation hardness of brittle materials are also addressed in relation to H, H and Γ1.

239 citations


Journal ArticleDOI
TL;DR: In this article, a method for simulating the dynamic behavior of rigid and flexible fibers in a flow field is proposed, where each pair of bonded spheres can stretch, bend, and twist, by changing bond distance, bond angle, and torsion angle between spheres, respectively.
Abstract: A method is proposed for simulating the dynamic behavior of rigid and flexible fibers in a flow field. The fiber is regarded as made up of spheres that are lined up and bonded to each neighbor. Each pair of bonded spheres can stretch, bend, and twist, by changing bond distance, bond angle, and torsion angle between spheres, respectively. The strength of bonding, or flexibility of the fiber model, is defined by three parameters of stretching, bending, and twisting constants. By altering these parameters, the property of the fiber model can be changed to be rigid to flexible. The motion of the fiber model in a flow field is determined by solving the translational and rotational equations for individual spheres under the hydrodynamic force and torque exerting on. This method was applied to simulate rotational motions with and without bending deformation of the fiber in a simple shear flow under the conditions of infinitely dilute system, no hydrodynamic interaction and low Reynolds number of a particle. For the rigid fiber, the computed period of rotation and the computed distribution of orientation angle agree with those calculated by Jeffery’s equation with an equivalent ellipsoidal aspect ratio. For the flexible fiber, the period of rotation decreases rapidly with the growth of bending deformation of the fiber and rotation orbits deviate from a circular one of the rigid fiber. These tendencies are similar to experimental ones described by Forgacs and Mason. These results show that the proposed method using bonded spheres’ model can reproduce the dynamic behavior of rigid and flexible fibers in a flow field successfully.

Journal ArticleDOI
01 Dec 1993-Polymer
TL;DR: In this article, the microstructural state of glassy polymers that evolve during physical ageing and inelastic deformation was studied, showing that ageing is accompanied by enthalpy relaxation.

Journal ArticleDOI
TL;DR: It was found that upon deformation the dislocation density increases by about 2 orders of magnitude, providing the first direct evidence for quasicrystal deformation by a dislocation mechanism.
Abstract: Single quasicrystals of Al 7 0Pd 21 Mn 9 were plastically deformed by 25% under compression at 750 o C. Both these samples as well as control samples of as-grown and heat-treated material were investigated by transmission electron microscopy. It was found that upon deformation the dislocation density increases by about 2 orders of magnitude. This provides the first direct evidence for quasicrystal deformation by a dislocation mechanism. The dislocation were found to have twofold and fivefold Burgers vector directions in physical space

Journal ArticleDOI
TL;DR: In this paper, the analysis of carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument.
Abstract: The application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.

Journal ArticleDOI
TL;DR: In this article, a micromechanically-based composite model is proposed to study large plastic deformation and texture evolution in semi-crystalline polymers, which consists of co-existing crystalline and amorphous phases locally associated with each other in a fine plate-like morphological structure.
Abstract: A micromechanically-based composite model is proposed to study large plastic deformation and texture evolution in semi-crystalline polymers. The microstructure of many semi-crystalline polymers consists of co-existing crystalline and amorphous phases locally associated with each other in a fine plate-like morphological structure. An aggregate of two-phase composite inclusions is used to model these materials. Special consideration is given to molecular chain inextensibility within the crystalline phase. The introduction of a back stress tensor in the constitutive model of the amorphous phase accounts for hardening due to deformation-induced molecular alignment. Interface compatibility and traction equilibrium are enforced within each composite inclusion. A Sachs-like model and two newly-developed self-consistent-like hybrid models are proposed to relate volume-average deformation and stress within the two-phase composite inclusion to the remote (macroscopic) fields. Applications of these composite models arc made to predict stress strain behavior and texture evolution in initially isolropic high density polyethylene (HOPE) under different modes of straining.

Journal ArticleDOI
TL;DR: In this paper, a submicrometer-grained (SMG) Al−3% Mg solid solution alloy, with an initial grain size of ∼0.2 μm, was produced by intense plastic straining.
Abstract: A submicrometer-grained (SMG) Al−3% Mg solid solution alloy, with an initial grain size of ∼0.2 μm, was produced by intense plastic straining. Experiments show that tensile specimens of the SMG alloy exhibit high elongations to failure at low testing strain rates at the relatively low temperature of 403 K. The stress exponent is high (∼7–8) and calculations show deformation is within the region of power-law breakdown. The initial microstructure of the alloy consists of diffuse boundaries between highly deformed grains. At strain rates of ∼10−4 s−1 and lower, plastic deformation leads to dynamic recrystallization and the formation of highly nonequilibrium grain boundaries that gradually evolve into a more equilibrated configuration.

Journal ArticleDOI
TL;DR: In this paper, the combined effects of thermal residual stresses anmd fiber spatial distribution on the deformation of a 6061 aluminum alloy containing a fixed concentration unidirectional boron fibers have been analyzed using detailed finite element models.
Abstract: The combined effects of thermal residual stresses anmd fiber spatial distribution on the deformation of a 6061 aluminum alloy containing a fixed concentration unidirectional boron fibers have been analyzed using detailed finite element models. The geometrical structure includes perfectly periodic, uniformly spaced fiber arrangements in square and hexagonal cells, as well as different cells in which either 30 or 60 fibers are randomly placed in the ductile matrix. The model involves an elastic-plastic matrix, elastic fibers, and mechanically bonded interfaces. The results indicate that both fiber packing and thermal residual stresses can have a significant effect on the stress-strain characteristics of the composite. The thermal residual stresses cause pronounced matrix yielding which also influences the apparent overall stiffness of the composite during the initial stages of subsequent far-field loading along the axial and transverse direction. Furthermore, the thermal residual stresses apparently elevate the flow stress of the composite during transverse tension. Such effects can be traced back to the level of constraint imposed on the matrix by local fiber spacing. The implications of the present results to the processing of the composites are also briefly addressed.

Journal ArticleDOI
TL;DR: In this paper, a complete theory and reliable mathematical models for plane-strain sheet bending have been established to predict springback, bendability or the minimum bending ratio (R/t ), strain and stress distributions, and the maximum loads on the punch and the die.

Journal ArticleDOI
TL;DR: In this article, the potential and gravity changes caused by dislocations in spherically symmetric earth models were studied, and the results for a homogeneous earth model agree very well with those predicted from flat-earth theory.
Abstract: SUMMARY This paper studies the potential and gravity changes caused by dislocations in spherically symmetric earth models. We define dislocation Love numbers to describe the elastic deformation of the earth raised by point sources. We discuss the shear and tensile dislocations, which can be expressed by four independent components: a vertical strike-slip, a vertical dip-slip, a tensile opening on a horizontal plane, and a tensile opening on a vertical plane. The results for a homogeneous earth model agree very well, at least within lo, with those predicted from flat-earth theory. The far-field results indicate no larger than 10per cent difference within 10". It makes little difference whether we use the theory on a sphere or that for a flat earth in the near field, while it is reasonable to use the spherical theory for global calculation. We proceed to calculations with a radially heterogeneous earth model (Model 1066A). The results are as a whole similar to those for a homogeneous sphere. In some cases, however, the difference between the two becomes significant. For example, the locations of the nodal lines of the gravity change differ significantly between the two models. This indicates that the vertical layering can cause considerable effects on the deformation fields.

Journal ArticleDOI
TL;DR: In this article, the formation of microstructure with grain size up to 0.06 μm may occur during the course of plastic deformation of the Ti-6Al-3.2Mo (α+β)-alloy with the initial coarse-grained lamellar structure.
Abstract: It is shown that the formation of microstructure with grain size up to 0.06 μm may occur during the course of plastic deformation of the Ti-6Al-3.2Mo (α+β)-alloy with the initial coarse-grained lamellar structure. The formation of submicrocrystalline structure results from the development of dynamic recrystallization concurrent with the process of spheroidization. The temperature of superplastic deformation significantly decreases while strength characteristics at room temperature sharply increase in the alloy with such a microstructure.

Journal ArticleDOI
Thak Sang Byun1, In Sup Kim1
TL;DR: In this paper, the tensile properties and inhomogeneous deformation of coarse ferrite-martensite dual-phase steels containing 17-50% martensite were analyzed.
Abstract: The tensile properties and inhomogeneous deformation of coarse ferrite-martensite dual-phase steels containing 17–50% martensite were analysed. The stress of dual-phase steels at equal strain increased with increasing volume fraction of martensite, f, but the rate of increase was reduced after f=0.3. The strain hardening rate was dependent on f at small strains (ɛ ⩽ 0.03), however, it became independent of f at larger strains. It was found that the deformation of the dual-phase steels divided into three different stages when f was less than about 0.3. The concurrent in situ stress-strain states of ferrite, martensite and their composite, and the stress ratios and strain ratios between ferrite and martensite were evaluated by means of a new stress and strain partition theory. The martensite phase deformed plastically after the uniform strain for f 0.25. The theoretical analyses for inhomogeneous deformation implied that the volume-fraction dependence of the stress and the characteristics of the strain-hardening rate were influenced by the plastic deformation of martensite. Further, the in situ stress-strain curves of ferrite and martensite and the internal stresses at respective phases were calculated from the partitioned stresses and strains.

Journal ArticleDOI
TL;DR: In this paper, the role of intragranular dislocation movement in superplastic region II was investigated by taking careful measurements within individual grains of a specimen tested at 423 K at a strain rate near the center of region II, and it was concluded that grain boundary sliding and relative translation of individual grains represents the dominant flow mechanism.
Abstract: Experiments were conducted on the Pb-62% Sn eutectic alloy to determine the role of intragranular dislocation movement in the superplastic region II. By taking careful measurements within individual grains of a specimen tested at 423 K at a strain rate near the center of region II, it is demonstrated that there is evidence for the movement of some intragranular dislocations, but the strain is non-uniform and oscillatory in nature with changes from positive to negative contributions to the total strain as the deformation continues. The results show that the Sn and Pb phases behave similarly and the net contribution to the total strain is close to zero. It is concluded that grain boundary sliding and the relative translation of individual grains represents the dominant flow mechanism, and intragranular dislocation movement occurs as an accommodation process which, nevertheless, has an important influence on the flow mechanism because it represents a source of mobile extrinsic grain boundary dislocations.

Journal ArticleDOI
TL;DR: In this article, the authors studied the elastic properties of elastic cellular solids via experiments upon foam and upon single-cell models, and found that foam exhibits a monotonic stress-strain relation with a plateau region; deformation is localized in transverse bands.
Abstract: Compressive properties of elastic cellular solids are studied via experiments upon foam and upon single-cell models. Open-cell foam exhibits a monotonic stress-strain relation with a plateau region; deformation is localized in transverse bands. Single-cell models exhibit a force-deformation relation which is not monotonic. In view of recent concepts of the continuum theory of elasticity, the banding instability of the foam in compression is considered to be a consequence of the non-monotonic relation between force and deformation of the single cell.

Journal ArticleDOI
TL;DR: In this article, a finite element method is used to solve for the three-dimensional deformation of a plastic workpiece, where the elemental constitutive response is derived from the microstructural response of a polycrystal aggregate situated in the element.

Journal ArticleDOI
TL;DR: In this paper, the mechanisms of deformation and failure in a 2618 Al alloy reinforced with 15 vol pct SiC particilates were studied and compared with those of the unreinforced alloy, processed by spray forming as well.
Abstract: The mechanisms of deformation and failure in a 2618 Al alloy reinforced with 15 vol pct SiC particilates were studied and compared with those of the unreinforced alloy, processed by spray forming as well. Tensile and fracture toughness tests were carried out on naturally aged and peak-aged specimens. The broken specimens were sliced through the middle, and the geometric features of fractured and intact particulates were measured. The experimental observations led to the conclusion that failure took place by the progressive fracture of the particulates until a critical volume fraction was reached. An influence of the particulate size and aspect ratio on the probability of fracture was found, the large and elongated particulates being more prone to fail, and the fracture stress in the particulates seemed to obey the Weibull statistics. The dif- ferences in ductility found between the naturally aged and peak-aged composites were explained in terms of the number of broken particulates as a function of the applied strain. Numerical simulations of the deformation process indicated that the stresses acting on the particulates are higher in the peak-aged material, precipitating the specimen failure. Moreover, the compressive residual stresses induced on the SiC during water quenching delayed the onset of particulate breakage in the naturally aged material.

Journal ArticleDOI
TL;DR: In this paper, the authors provide an overview of superplastic deformation and failure in ceramics, with specific emphasis on a 3 mol.% yttria stabilized zirconia and a 20wt.% alumina composite.
Abstract: Superplasticity in ceramics has now been reported in a wide range of materials with elongations to failure of more than 100%. Although the experimental observations of large deformation are in some ways similar to those reported in numerous metallic alloys, there are significant differences in the mechanical properties and cavitation failure characteristics of superplastic ceramics. This paper provides an overview of superplastic deformation and failure in ceramics, with specific emphasis on a 3 mol.% yttria stabilized zirconia and a zirconia-20wt.%alumina composite. It is demonstrated that there is a transition in the deformation behavior of zirconia which is dependent on the grain size and the impurity content of the material. Many of these materials fail by the nucleation, growth and interlinkage of cavities, so that the ductility is governed by the imposed stress and the grain size. Potential areas for additional research on superplastic ceramics are highlighted.

Journal ArticleDOI
TL;DR: In this paper, the deformation microstructures and texture at five strain levels were observed and characterized using transmission electron microscopy (TEM) and neutron diffraction, and the microstructural evolution was discussed with special emphasis on factors that contribute to the transition from structures characteristic of small and medium strain micro-structures to those characteristic of large strain micro structures.
Abstract: High-purity nickel (99. 99 pct) with a grain size of 80 to 100 µm was deformed by cold-rolling from 37 to 98 pct reductions (von Mises effective strains ofevm = 0. 5 to 4. 5). The deformation microstructures and texture at five strain levels were observed and characterized using transmission electron microscopy (TEM) and neutron diffraction. The microstructures evolved within a framework common to medium and high stacking fault energy fee polycrystals. This framework consists of structural subdivision by higher angle boundaries (geometrically necessary boundaries) at one volume scale and at a smaller volume scale by lower angle cell boundaries (incidental boundaries) for all strain levels. We have characterized the dislocation boundaries, including dense dislocation walls (DDWs), microbands (MBs), and lamellar boundaries (LBs) in terms of crystallographic and macroscopic orientations, morphology, and frequency of occurrence. The microstructural evolution is discussed with special emphasis on factors that contribute to the transition from structures characteristic of small and medium strain microstructures to those characteristic of large strain microstructures.

Journal ArticleDOI
TL;DR: The shape memory effect as discussed by the authors is a phenomenon that occurs when a shape memory alloy is deformed in the martensitic condition (martensite), and the shape recovery occurs during heating when the specimen undergoes a reverse transformation of the Martensite to its parent phase.
Abstract: Numerous metallic alloys are now known to exhibit a shape memory effect through which an article deformed at a lower temperature will regain its original undeformed shape when heated to a higher temperature. This behavior is basically a consequence of a martensitic phase transformation. When compared, the various shape memory materials are found to have common characteristics such as atomic ordering, a thermoelastic martensitic transformation that is crystallographically reversible, and a martensite phase that forms in a self-accommodating manner. The explanation of the shape memory phenomenon is now universal and well in hand. In addition to the familiar “one-way” memory, shape memory alloys also exhibit a “two-way” memory as well and a “mechanical” shape memory resulting from the formation and reversal of stressinduced martensite.Fundamental to the shape memory effect (SME) is the occurrence of a martensitic phase transformation and its subsequent reversal Basically, a shape memory alloy (SMA) is deformed in the martensitic condition (martensite), and the shape recovery occurs during heating when the specimen undergoes a reverse transformation of the martensite to its parent phase. This is the essence of the shape memory effect. Materials that exhibit shape memory behavior also show a two-way shape memory, as well as a phenomenon called superelasticity. These are also discussed.The shape memory response after deformation and thermal stimulation constitutes “smart” behavior, i.e., Stimulated Martensite-Austenite Reverse Transformation.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the strength and work hardening properties of high nitrogen austenitic steel and concluded that the high yield strength of cold worked nitrogen-bearing steel is essentially due to tight stackings of twins and stacking faults.
Abstract: The strengthening and work hardening characteristics of high nitrogen austenitic steel have been investigated by TEM in order to explain the outstanding mechanical properties, which are very high yield strength and good toughness. It is shown that plastic deformation of those steels always occurs by a combination of planar glide and mechanical twinning. However, the critical stress/strain conditions for the onset of mechanical twinning depend strongly on the actual nitrogen content. Specifically, as the nitrogen content is increased, the onset of deformation twinning is shifted to lower strains and higher stresses, i.e. the more important becomes the contribution of deformation twinning to the total strain. The observed behaviour is explained by the influence of nitrogen on internal friction and stacking fault energy. It is concluded that the high yield strength of cold worked nitrogen-bearing steel is essentially due to tight stackings of twins and stacking faults. Apart from regular structure evolution, inhomogeneous structures are observed, which can be explained in terms of texture formation and the dynamic properties of stacking faults under stress.

Journal ArticleDOI
TL;DR: In this paper, the relationship between a composite and its constituents with respect to high-temperature deformation behavior was investigated using the Al2O3-Y3Al5O12 (YAG) eutectic system.
Abstract: The relationship between a composite and its constituents with respect to high-temperature deformation behavior was investigated using the Al2O3-Y3Al5O12 (YAG) eutectic system. The eutectic is essentially a composite with sapphire and YAG as the two phases with a volume fraction of YAG of 0.45. The deformation behavior of the eutectic and those of single-crystal sapphire and YAG were studied under identical conditions, using constant-strain-rate compression tests in air at 1530°C. The composite was also studied at 1650°C and compared with existing data on sapphire and YAG. The stronger YAG phase was found to reinforce the sapphire matrix at higher strain rates, but the composite crept faster than sapphire at lower strain rates. It is suggested using a simple semiempirical analysis that diffusional relaxation at the YAG-sapphire interface boundaries may cause the inferior creep behavior at lower strain rates.