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Showing papers on "Stress relaxation published in 1991"


Journal ArticleDOI
TL;DR: A growth mode is proposed whereby strain relaxation is initially achieved through the kinetically limited evolution of surface morphology, in contrast to traditional critical-thickness theories, where significant strain relief is accommodated by a coherent island morphology.
Abstract: The early stages of growth of highly strained ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As on GaAs(100) have been investigated as a function of composition. The evolution of the film microstructure as determined by in situ STM and RHEED is from a two-dimensional rippled surface in the beginning stages of growth to a three-dimensional island morphology. A growth mode is proposed whereby strain relaxation is initially achieved through the kinetically limited evolution of surface morphology. In contrast to traditional critical-thickness theories, significant strain relief is accommodated by a coherent island morphology. This study represents a new view for both the growth mode and initial strain relaxation in thin films.

420 citations


Journal ArticleDOI
TL;DR: In this article, a semi-empirical kinetic model is presented which maps out the thermal budget for processing of Si1−xGex/Si heterostructures through epitaxial growth and postgrowth anneals.
Abstract: A semiempirical kinetic model is presented which maps out the thermal budget for processing of strained layer devices through epitaxial growth and postgrowth anneals. Misfit strain relaxation in Si1−xGex/Si heterostructures by the injection and propagation of a/2 〈110〉 60°‐type misfit dislocations has been studied for a range of geometries and dimensions. Strained layer superlattices, Si1−xGex alloy layers, 0

369 citations


Journal ArticleDOI
TL;DR: In this article, the structural, optical, electrical and physical properties of amorphous carbon deposited from the filtered plasma stream of a vacuum arc were investigated, and the tetrahedral coordination of the material was confirmed by measurements of stress and plasmon energy as a function of ion energy.

217 citations


Journal ArticleDOI
TL;DR: In this paper, the authors evaluated mean stress-strain effects under smooth specimen axial strain controlled low cycle fatigue conditions with strain ratios R of −2, −1, 0, 0.5 and 0.75.
Abstract: — ASTM A723 Q & T steel with a yield strength and ultimate strength of 1170 and 1262 MPa respectively was evaluated for mean stress-strain effects under smooth specimen axial strain controlled low cycle fatigue conditions with strain ratios R of −2, −1, 0, 0.5 and 0.75. Cycles to failure ranged from 15 to 105. Cyclic stress-strain response based upon half-life hysteresis loop peaks were similar for all R ratios. Mean stress relaxation occurred for R≠−1 only when plastic strain amplitudes were present and this occurred above total strain amplitudes of 0.005. Thus, mean stress relaxation was completely dependent upon cyclic plasticity. Mean strains did not affect low cycle fatigue life unless accompanied by half-life mean stress. Tensile mean stress was detrimental and compressive mean stress was beneficial and these effects only occurred at strain ampltidues below 0.005. Three different mean stress models were used to evaluate the low cycle fatigue data and the SWT log-log linear model best represented the data. These results can be used with the local notch strain fatigue life prediction methodology.

178 citations


Journal ArticleDOI
TL;DR: In this paper, the deformation of the matrix around the inclusions is found to take the form of (i) rows of prismatic dislocation loops puched into the matrix and/or (ii) a plastic zone containing tangled dislocations surrounding the inclusion.
Abstract: Silver chloride containing alumina fibers or glass microspheres is used as a model material to study matrix plasticity induced by thermal mismatch in metal matrix composites. Resulting matrix dislocations are decorated at room temperature in the bulk material and observed by optical microscopy. Plastic deformation of the matrix around the inclusions is found to take the form of (i) rows of prismatic dislocation loops puched into the matrix and/or (ii) a plastic zone containing tangled dislocations surrounding the inclusions. From the number of loops punched by spheres, the temperature interval over which slip of prismatic loops is operative is calculated to be 100 ± 30 K wide. The stress in the plastic zone around fibers is determined from the radius of curvature of pinned dislocations, leading to the conclusion that the matrix is locally strain-hardened. A simple model taking this fact into account is proposed to predict the radius of the plastic zone around embedded cylinders and spheres and is compared to the experimental data.

136 citations


Journal ArticleDOI
R. Seshadri1
TL;DR: The GLOSS analysis is emerging as a useful technique for determining multiaxial stress relaxation, follow-up, creep damage, inelastic strain concentrations and low-cycle fatigue estimates, limit analysis and issues pertaining to stress classification as discussed by the authors.
Abstract: The underlying theory relates redistribution of inelastic stresses at a given location under consideration to the uniaxial stress relaxation process. GLOSS analysis is emerging as a useful technique for determining multiaxial stress relaxation, follow-up, creep damage, inelastic strain concentrations and low-cycle fatigue estimates, limit analysis and issues pertaining to stress-classification

119 citations


Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this paper, the authors investigated the thermal properties of oriented polymer networks obtained by photopolymerization of liquid crystalline acrylates and found that the tensile modulus and the strength of the oriented networks were anisotropic and highly temperature dependent.

108 citations


Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: The facts that t∗ is independent of the magnitude of the strain and that the volume recovery after a quench remains unaltered, in spite of the imposition of mechanical deformations, support the argument that mechanical stimuli neither alter the underlying (non-equilibrium) thermodynamic state of the glass nor erase physical ageing.

97 citations


Journal ArticleDOI
TL;DR: In this paper, the authors analyzed room temperature stress relaxation and associated physical phenomena in passivated and unpassivated aluminum-based metallizations, subsequent to exposure to high temperatures, based both on theoretically estimated and experimentally determined thermal stresses.
Abstract: Thermal stress‐induced voiding in narrow aluminum‐based metallizations used as interconnects in microelectronic circuits has recently become a serious reliability concern. Room‐temperature stress relaxation and associated physical phenomena in passivated and unpassivated aluminum‐based metallizations, subsequent to exposure to high temperatures, are analyzed based both on theoretically estimated and experimentally determined thermal stresses. It is shown that stress relaxation at longer times involves mainly dislocation climb, while short‐term relaxation during cool down from higher temperatures, and immediately thereafter, involves significant dislocation glide. Void growth, frequently observed in passivated metallizations, provides a new source of atoms to feed stress relaxation by the same processes as in the absence of voiding.

97 citations


Journal ArticleDOI
TL;DR: In this paper, the authors report measurements of the plastic relaxation of InGaAs layers grown above critical thickness on GaAs substrates and the relaxation is accurately hyperbolic, proportional to the reciprocal of the layer thickness, in agreement with a recent geometrical theory of critical thickness.
Abstract: We report measurements of the plastic relaxation of InGaAs layers grown above critical thickness on GaAs substrates. The relaxation is accurately hyperbolic, proportional to the reciprocal of the layer thickness, in agreement with a recent geometrical theory of critical thickness [D. J. Dunstan, S. Young, and R. H. Dixon, J. Appl. Phys. 70, 3038 (1991)]. At large thicknesses, work hardening is observed which leads to a residual strain dependent on the original misfit.

97 citations


Journal ArticleDOI
TL;DR: In this article, the authors used both continuous indentation and x-ray diffraction techniques to characterize stress relaxation in aluminum films of several thicknesses and found that the results of the indentation data from thicker films do not compare well to the x-rays data due to the presence of a residual stress distribution.
Abstract: Stress relaxation in aluminum films of several thicknesses was characterized by using both continuous indentation and x-ray diffraction techniques. Results of the indentation and x-ray stress measurements compare closely for films of small thicknesses. Indentation data from thicker films do not compare well to the x-ray data due to the presence of a residual stress distribution.

Journal ArticleDOI
TL;DR: It is found that the model produces realistic values for the dissipated energy during cyclic loading only when relaxation parameter values are chosen which result in an overestimation of the stress relaxation data by more than 100%.

Journal ArticleDOI
TL;DR: In this paper, constant stress creep tests were combined with detailed transmission electron microscopy in order to characterize and explain the intermediate temperature creep properties of Ni 3 Al, and it was observed that octahedral glide, the mechanism associated with the anomalous yielding behavior of this alloy, is exhausted during primary creep.
Abstract: In this study, constant stress creep tests were combined with detailed transmission electron microscopy in order to characterize and explain the intermediate temperature creep properties of Ni 3 Al. It was observed that octahedral glide, the mechanism associated with the anomalous yielding behavior of this alloy, is exhausted during primary creep. Primary creep does not lead to steady state creep but is instead followed by inverse creep. TEM observations indicate that the Kear-Wilsdorf locks that are formed during primary creep do lead to the exhaustion of octahedral glide, but that given sufficient time and temperature these cross-slipped segments are able to bow out and glide on the cube cross-slip plane. This dislocation generation, and subsequent glide, on the (010) plane is the basis for the observation of inverse creep in this alloy. Dislocation motion on the cube plane is a thermally activated process and as such is able to explain the strong temperature dependence that was observed for the intermediate temperature creep strength of Ni 3 Al.

Journal ArticleDOI
TL;DR: In this article, the authors show that the strain at the interface between Cu films and a Ru(0001) substrate is reduced by a structural transformation from a more tightly bound, strained pseudomorphic first Cu layer to a unidirectionally contracted second Cu layer with periodic partial misfit dislocations.
Abstract: We show, from scanning tunneling microscopy measurements, that the strain at the interface between Cu films and a Ru(0001) substrate is reduced by a structural transformation from a more tightly bound, strained pseudomorphic first Cu layer to a unidirectionally contracted second Cu layer with periodic partial misfit dislocations. These results for a two-dimensional structure confirm the mechanism of stress accommodation in strained layers predicted in the one-dimensional dislocation model of Frank and ven der Merwe.

Journal ArticleDOI
TL;DR: Comparisons of theoretical and published experimental results show that extracellular fluid flow can account for several observed biomechanical features of passive myocardium, including the insensitivity of stress-strain curves to loading rate and ofstress-relaxation curves to the amount of stretch.

Journal ArticleDOI
TL;DR: In this article, the authors reviewed the creep mechanisms in ceramics and compared experimental data, showing that there are three major types of creep behavior: a stress exponent close to 5 due to control by dislocation climb and fully ductile behaviour; a stress expander close to 3 due to controlling by climb from Bardeen-Herring sources and less than jive interpenetrating independent slip systems; and a stress extraction close to 1 due to diffusion creep.
Abstract: The creep mechanisms in ceramics are reviewed briefly and then compared with experimental data. It is shown that there are three major types of creep behaviour: a stress exponent close to 5 due to control by dislocation climb and fully ductile behaviour; a stress exponent close to 3 due to control by climb from Bardeen–Herring sources and less than jive interpenetrating independent slip systems; and a stress exponent close to 1 due to diffusion creep. The role of interface reaction control and the transitions from diffusion to power law creep are also examined.MST/1389

Journal ArticleDOI
TL;DR: In this paper, the Eshelby theory of inclusions is applied to model the stresses arising after heat treatment at 400°C in aluminum line metallizations, embedded in silicon/passivation matrix.
Abstract: In the present study, the Eshelby theory of inclusions is applied to model the stresses arising after heat treatment at 400 °C in aluminum line metallizations, embedded in silicon/passivation matrix. The stresses obtained are about 200 MPa higher than the ones previously reported. Moreover, the stresses in the axial and width directions of the lines are shown to be on the same order, while the normal stress is smaller, especially in the lines of low thickness‐to‐width ratio. A modification of the familiar sin2 ψ method of x‐ray stress measurement is presented to deal more accurately with the [111]‐fiber texture present in the aluminum lines studied. The lateral and normal stresses in the aluminum metallizations after a heat treatment at 400 °C are measured in room temperature by x‐ray diffraction from 4 h after the heat treatment at 400 °C up to 3 months. The experimental results are well in accord with predictions obtained from the Eshelby model. Particularly, the lateral stresses are found to be about equal, while the initial normal stress is smaller, but eventually becomes the largest stress component. Dislocation mechanisms to rationalize the present observations are discussed: at longer times, diffusion‐controlled dislocation climb and void growth connected to it appear to be the most important mechanisms to relieve the stress, while during cooling dislocation glide is also significant.

Journal ArticleDOI
TL;DR: In this paper, the creep and fracture behavior of two hot-pressed aluminas are presented, for both flexural and tensile testing, and three distinct fracture regimes are found.
Abstract: The creep and creep fracture behavior of two hot-pressed aluminas are presented, for both flexural and tensile testing. Steady-state power-law creep is observed with a stress exponent of about 2 for each material. Three distinct fracture regimes are found. At high stress in flexure, fracture occurs by slow crack growth with a high stress dependence of the failure time. At intermediate stresses, in both flexure and tension, creep fracture occurs by multiple microcracking after modest strains. Failure times exhibit a modest stress dependence (stress exponent of 2.5 in tension and 3 in flexure), with a constant failure strain equal to 0.09. The failure times are considerably longer in flexure than in tension, because of the constraint imposed on crack growth by the bending geometry. We conclude that flexure cannot be used for creep lifetime assessment, even in simple, single-phase materials such as Al2O3. At low stresses, in tension, failure also exhibits a modest stress dependence but with a much higher failure strain. The material shows the onset of super-plastic behavior.

Journal ArticleDOI
TL;DR: In this paper, the elastic displacement and strain fields and the elastic energy of a system composed of a misfitting layer of finite thickness coherently deposited on a bulk semi-infinite substrate and covered by a capping layer, when the intrinsic stress-free strain in the intermediate layer is a sinusoidal modulation of dilatation along a direction parallel to the substrate surface.
Abstract: We first calculate analytically the elastic displacement and strain fields and the elastic energy of the system composed of a misfitting layer of finite thickness coherently deposited on a bulk semi‐infinite substrate and covered by a capping layer, when the intrinsic stress‐free strain in the intermediate layer is a sinusoidal modulation of dilatation along a direction parallel to the substrate surface. This is achieved by the direct application of Eshelby’s method and the determination of the appropriate stress function. We show that, combined with Fourier analysis, this basic calculation provides a new general analytical solution to the problem of the coherent relaxation of any misfitting dilatational inhomogeneity in a half space. More specifically, this method is here applied to the full analytical solution of the cases of a coherent misfitting parallelepipedic inclusion buried under a planar free surface, and of a coherent step at the interface between a substrate and a misfitting overlayer. Applications are briefly discussed.

Journal ArticleDOI
TL;DR: In this paper, a simple linearly viscoelastic model is used to characterize the stiffness and viscosity of the interface separating the libers and the matrix, and an approximate representation of the time-dependent macroscopic behavior of the composite is derived analytically and compared with the numerical results.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the means by which complete stress relaxation can occur through dislocation reactions during annealing of very thick as-deposited lattice mismatch systems.
Abstract: Defect characterization by high-resolution electron microscopy is presented for (001) epitaxy of the CdTe/GaAs and ZnTe/GaAs heterojunctions, before and after a long vacuum anneal. The annealed interface structure consists of a periodic array of perfect edge Lomer misfit dislocations, with spacing corresponding to a strain-free thin film. Since this is the most efficient manner to obtain complete relaxation, it represents the equilibrium microstructure. The as-deposited films are very thick, three to four orders of magnitude greater than the critical thicknesses, which are both less than a monolayer for these large lattice mismatch systems. Their microstructure corresponds to a metastable distribution of defects in that the thin film residual strain is nearly zero and neighboring defects can react to form Lomer misfits. A variety of defects exist both in the form of perfect misfit dislocations at the interface and extended defects into the thin film. The extended defects result from formation of stacking faults bounded by either Shockley or Frank partials, and more complicated defect structures due to interacting perfect and partial dislocations on intersecting slip planes. The purpose of this paper is to investigate the means by which complete stress relaxation can occur through dislocation reactions during annealing of very thick as-deposited films.

Journal ArticleDOI
TL;DR: In this paper, a model for the stress change in a thin film on a thick substrate during annealing was given, taking into account temperature changes, volume changes, viscous flow, and anelastic relaxation occurring in the film.
Abstract: A model is given for the stress change in a thin film on a thick substrate during annealing. It takes into account temperature changes, volume changes, viscous flow, and anelastic relaxation occurring in the film. The stress change in amorphous Mo/Si multilayer films deposited on Si single-crystal substrates was obtained from in situ wafer-curvature measurements during annealing at temperatures below the glass temperature. The thickness change and the interdiffusion coefficient were obtained from the position and the intensity of the first-order multilayer x-ray reflection. The unconstrained volume change was derived from the measured stress and thickness changes. The free-volume model for amorphous solids has been used to interpret the interdiffusion in and the volume change of the amorphous Mo/Si multilayers. The stress change as it occurred during isothermal annealing was explained by free-volume annihilation, viscous flow, and anelastic relaxation. If anisotropy of the volume change is accepted, the stress change could also be described with free-volume annihilation and viscous flow alone. The product of the experimentally observed viscosity and diffusion coefficient for amorphous Mo/Si multilayers was compared to the value expected from the free-volume-model-based equivalent of the Stokes-Einstein relation.

Journal ArticleDOI
Haavard T. Gjestland1, G. Nussbaum, G. Regazzoni, O. Lohne, Ø. Bauger 
TL;DR: In this article, the authors focus on the optimal microstructure for good mechanical properties and creep resistance of planar flow cast magnesium alloys and evaluate the tensile creep properties at temperatures from RT to 150 °C.
Abstract: Application of rapid solidification to magnesium alloys generally increases the mechanical properties by a factor of 2–2.5 compared with conventional wrought magnesium alloys. This is mainly due to a smaller grain size. What is the creep behaviour of these high strength magnesium alloys? Planar flow cast magnesium alloys have been cast and extruded. The mechanical properties in tension and compression, the stress-relaxation in compression and the tensile creep properties have been tested at temperatures from RT to 150 °C. Traditionally one would expect poor creep resistance in a small grained material. In some rapidly solidified aluminium alloys, however, the creep resistance is good, due to fine particles pinning grain boundaries and impeding dislocation movements. In the magnesium alloys tested there is a big difference in the creep resistance depending on the microstructure of the alloys. The on-going study focuses on the optimal microstructure for good mechanical properties and creep resistance.

Journal ArticleDOI
TL;DR: In this paper, the strain gradient through the thickness of 0.5, 1.0, and 2.0mm-thick Al-2% Cu films on oxidized (001) Si wafers has been examined by using glancing-angle x-ray diffraction to measure the d spacing as a function of penetration depth of the incident x•ray beam.
Abstract: The strain gradient through the thickness of 0.5‐, 1.0‐, and 2.0‐mm‐thick Al‐2% Cu films on oxidized (001) Si wafers has been examined by using glancing‐angle x‐ray diffraction to measure the d spacing as a function of penetration depth of the incident x‐ray beam. Samples with and without a 1‐μm sputtered quartz passivation layer were examined. The only gradient observed in these samples corresponded to surface relaxation in the unpassivated samples at depths of less than 50 A. This result was verified by examining the shape of the diffraction peaks. The dislocation densities of the films were also determined from the peak shape.

Journal ArticleDOI
TL;DR: In this paper, an infrared dichroism and birefringence measurement was used to study component relaxation in bimodal molecular weight distribution melts. And the results for the step-strain relaxation of each component and of the total sample are presented and discussed for binary blends of 10, 20, 30, 50, and 75% by volume of the higher molecular weight species for three seta of blends: 53K/125K, 53k/370K, and 125K/370k.
Abstract: Simultaneous measurement of infrared dichroism and birefringence is used to study component relaxation in bimodal molecular weight distribution melts. Nearly monodisperse poly(ethylenepropylene) samples of molecular weights 53K, 125K, and 370K, all above the critical molecular weight for entanglement, were used. Results for the step-strain relaxation of each component and of the total sample are presented and discussed for binary blends of 10, 20, 30, 50, and 75% by volume of the higher molecular weight species for three seta of blends: 53K/125K, 53K/370K, and 125K/370K. For each sample, the relaxation dynamics of the blend and of each component depend upon the two polymer relaxation times and the blend composition. Effects of intermolecular orientational coupling interactions were observed, and a coupling strength of 0.45 was measured. The results of these experiments are compared to a reptation-based constraint release model, and a qualitative agreement is found.

Journal ArticleDOI
TL;DR: In this article, a thermal bending analysis of a laminated composite rectangular plate due to a partially distributed heat supply is presented, where the authors have introduced the methods of finite cosine transformation and Laplace transformation to the temperature field and adapted the classical plate theory based on Kirchhoff-love's hypothesis to the thermoeiastic field.
Abstract: This article is concerned with a thermal bending analysis of a laminated composite rectangular plate due to a partially distributed heat supply. For the theoretical development, we have introduced the methods of finite cosine transformation and Laplace transformation to the temperature field and adapted the classical plate theory based on Kirchhoff-Love's hypothesis to the thermoeiastic field. Thereafter, we have applied the theoretical development proposed in the present article to the analysis of a nonhomogeneous rectangular plate of the thermal stress relaxation type such as functionally gradient material. Then we have evaluated temperature change, thermal stress, and thermal deflection of simply supported plates and clamped ones. And we have examined the effect of relaxation on distributions of the thermal stress and thermal deflection for the nonhomogeneous rectangular plate.

Journal ArticleDOI
William K Miller1
TL;DR: In this paper, the primary and secondary creep rates of die cast AZ91 magnesium were investigated at room temperature while at stresses at least as low as 60 MPa and showed that the dominant creep mechanism may change at stresses below 120 MPa.
Abstract: Die cast AZ91 magnesium is shown to undergo both primary and secondary creep at room temperature while at stresses at least as low as 60 MPa. Empirical primary and secondary creep equations are also presented that allow creep strain to be calculated as a function of stress and time. The measured stress dependency of the secondary creep rate suggests that diffusion-driven dislocation climb may be the rate-controlling creep mechanism, as has been reported for magnesium and other metals at higher temperatures. Changes in the stress dependency of other constants in the creep equations, and in the time and strain at which secondary creep begins, suggest that the dominant creep mechanism may change at stresses below 120 MPa.

Journal ArticleDOI
TL;DR: In this paper, it is shown that the excluded volume stress seems to be much larger in entangled solutions of arbitrarily thin chains, and it suffices that entanglements provide elasticity on the distance scale of the radius of gyration.
Abstract: It is a widespread assumption that the backbone stress is dominant in polymer melts and concentrated solutions. This work suggests on the basis of Brownian simulations that the assumption is incorrect. The excluded volume stress seems to be much larger in entangled solutions of arbitrarily thin chains. A restriction to backbone stresses in the popular reptation model leads to the necessity for a rigid primitive path. To explain the persistence and eventual relaxation of the excluded volume stress, it suffices that entanglements provide elasticity on the distance scale of the radius of gyration.

Journal ArticleDOI
TL;DR: In this article, a systematic study of local stress relaxation effects in thin Alfilms,deposited on silicon substrates by sputtering or electron beam evaporation, was performed in the vacuum chamber of a scanning electron microscope.
Abstract: This article reports a systematic study of local stress relaxationeffects in thin Alfilms,deposited on silicon substrates by sputtering or electron beam evaporation. The stresses were induced thermally during an annealing cycle, as well as thermomechanically by micromechanical technique. The latter experiments were performed i n s i t u in the vacuum chamber of a scanning electron microscope(SEM), which made it possible to monitor the reconstruction of the film surface as it happened, and simultaneously register applied forces, strains, and temperatures. Three fundamental, local stress relaxation phenomena were observed. Compressive film stresses were, at elevated temperature, relaxed by hillock formation. The i n s i t u experiments in the SEM, combined with cross‐sectional transmission electron microscopy of hillock structures, provided important information on the growth mechanism of hillocks. Tensional film stresses at elevated temperature were relaxed by two modes of local stress relief. One mode of tensional stress relief occurred in films of thickness 1 μm or more. Singular Al grains were observed to ‘‘collapse’’ and become wider and thinner than neighboring grains. Such grain collapses are scarcely reported by previous workers, and were in the present investigation seen to occur very suddenly, in a second or less, as the strain and the temperature reached critical levels. A collapse mechanism, based on local plastic yield and interfacial slip, is suggested. Films of submicron thickness relaxed by a second mode: hole formation. Essentially two types of holes were observed: small, circular holes and large branched‐out holes. A hole formation mechanism, based on creep cavitation and interfacial slip, is suggested. The observed holes resemble the ‘‘voids’’ many other workers have reported in narrow, passivated Al lines. The present results show that passivation coatings and narrow geometries are not necessary prerequisites for holes in Alfilms; a high tensional film stress is enough.

Journal ArticleDOI
TL;DR: In this article, the shape of the anisotropic scattering lines has been visualized on a bidimensional detector: the isointensity lines have a shape similar to lozenges, which has a main axis orthogonal to the main axis of the ellipses.
Abstract: We discuss the neutron scattering features of melts containing a fraction of labeled chains, and of rubbers containing a fraction of deuterated paths along several successive elementary chains. Both types of material are studied during relaxation after a fast deformation in very similar conditions. An unusual feature is the shape of the anisotropic scattering as visualized on a bidimensional detector: the isointensity lines have the shape of lozenges. A detailed review of various cases makes this appear as a general feature in SANS scattering from melts and rubbers in a state of partially relaxed deformation. We then describe results for mixtures of small labeled chains inside matrices of large entangled chains or crosslinked matrices: we find another unusual shape of the isointensity levels, called “butterfly”. We propose the lozenges to be a combination of the classical elliptical scattering with a butterfly scattering, which has a main axis orthogonal to the main axis of the ellipses. We discuss in more details the origin of the butterfly effect, by following two tracks: the first is several theories about demixing under strain, including influence of the strain on the enthalpic, elastic, and conformational terms of the free energy of mixing. The second track is the influence of heterogeneities in crosslinked materials. An explanation which would be common to the case of crosslinked and uncrosslinked material remains to be established.