Showing papers on "Stress relaxation published in 1983"
Book•
01 Jan 1983
TL;DR: Phenomenological treatment of Viscoelasticity Time--Temperature Correspondence Transitions and Relaxation in Amorphous Polymers Statistics of a Polymer Chain Rubber Elasticity Viscoelsastic Models Dielectric Relaxation Chemical Stress Relaxation Appendix References Answers to Problems List of Major Symbols Index
Abstract: Phenomenological Treatment of Viscoelasticity Time--Temperature Correspondence Transitions and Relaxation in Amorphous Polymers Statistics of a Polymer Chain Rubber Elasticity Viscoelastic Models Dielectric Relaxation Chemical Stress Relaxation Appendix References Answers to Problems List of Major Symbols Index
1,033 citations
TL;DR: In uniaxial tensile experiments in vitro mechanical properties of the different parts of porcine aortic valves, the leaflets, the sinus wall and the aorts, have been dealt with and predictions based upon the model indicate that on cyclic loading the larger viscous losses have to be expected in the leaflets.
144 citations
TL;DR: In this article, a general expression for the free energy of deformation was derived, as well as the specific form which applies to an instantaneous shear deformation, and the latter was used to analyze the possibility that instabilities, or deformational phase separations, arise in the course of stress relaxation experiments.
Abstract: The molecular model used by Doi and Edwards in developing their rheological theory admits a simple form for the free energy of deformation, at least when the independent alignment approximation is used. A general expression is derived, as well as the specific form which applies to an instantaneous shear deformation. The latter is used to analyze the possibility that instabilities, or “deformational phase separations,” arise in the course of stress relaxation experiments. The results of the analysis are compared with recent experimental results by Osaki and Kurata and by Vrentas and Graessley which show an anomalous relaxation behavior.
103 citations
TL;DR: In this paper, an integrodifferential equation giving the inverse growth rate dt/deox vs eox is established, valid in any case of thickness growth rate dependence, it allows us to fit dry silicon oxidation data on a wide range of oxidation temperature (780 −980°C).
Abstract: This paper deals with a model of silicon oxidation including stress relaxation by viscous flow during growth. Based on a Deal–Grove process and a Maxwellian stress relaxation approach, an integrodifferential equation giving the inverse growth rate dt/deox vs eox is established. Valid in any case of thickness growth rate dependence, it allows us to fit dry silicon oxidation data on a wide range of oxidation temperature (780–980 °C).
101 citations
TL;DR: In this paper, a fine, unligated clot of human or bovine fibrin prepared from purified Fibrinogen is subjected to a large torsional deformation (maximum shear strain γ up to 1.37) with superposed small oscillating deformations (Δγ ca. 0.03) at frequencies from 0.2 to 1 Hz.
Abstract: A fine, unligated clot of human or bovine fibrin prepared from purified fibrinogen is subjected to a large torsional deformation (maximum shear strain γ up to 1.37) with superposed small oscillating deformations (Δγ ca. 0.03) at frequencies from 0.2 to 1 Hz. The “secant modulus” is defined as Gi(γ)=σi/γ, where σ is stress and the subscript i refers to an initial measurement about 25 s after imposition of strain. The storage modulus G′(ω,γ) refers to a differential oscillating measurement at frequency ω superposed on a static strain γ. For γ up to about 0.1, Gi(γ) was independent of γ and equal to G′(ω,0) measured at about 1 Hz and zero static strain. At large static deformations, the differential storage modulus G′(ω,γ) could be used to monitor changes in structure. Since there is very little time dependence of the relaxation modulus in the range from 1 to 60 s, and the loss tangent is very small, Gi′(ω,γ) could be considered simply as the differential modulus Gi(γ)+γdGi/dγ, and agreed with the latter exp...
100 citations
TL;DR: In this paper, the residual stresses after die-attachment have been studied experimentally using a test chip with diffused resistor strain gauges, and extensive measurements were reported for the following dieattachment/leadframe combinations: Au-Si/Alloy 42, epoxy adhesive/ Copper 194, and polyimide adhesive/Copper 194.
Abstract: The residual stresses after die-attachment have been studied experimentally using a test chip with diffused resistor strain gauges. Extensive measurements are reported for the following dieattachment/leadframe combinations: Au-Si/Alloy 42, epoxy adhesive/ Copper 194, and polyimide adhesive/Copper 194. Two-dimensional distributions of the stresses in the device surface are shown, and additional thickness measurements of the adhesive layer are used to assess the amount of stress relaxation occuring in adhesive die-attachment. Large variations in the measured stresses were found for die-attachment with polyimide adhesive. Thickness measurements and radiography showed that the stress variations are caused by large voids formed during the drying cycle of the adhesive. The effect of voids on die-attachment stresses is analyzed, and its potential as a cause of vertical die-cracking is discussed.
100 citations
Journal Article•
TL;DR: In this article, a constitutive law for a bituminous mixture subjected to repeated loading is presented, where elastic, plastic, viscoelastic, and viscoplastic strain components are incorporated into the model as they are simultaneously present in the loading process.
Abstract: A constitutive law for a bituminous mixture subjected to repeated loading is presented. The elastic, plastic, viscoelastic, and viscoplastic strain components are incorporated into the model as they are simultaneously present in the loading process. The model parameters are extracted from a series of repeated uniaxial creep and creep recovery experiments conducted under constant compression stress. The experiments were performed at constant temperature for various stress levels, time periods, and numbers of cycles. The elastic strain is found to depend solely and linearly on the stress. The plastic strain is linearly proportional to stress and exhibits a power-law dependence on the number of loading cycles. The viscoelastic strain is nonlinear with respect to stress and is governed by a power law of time. The viscoplastic strain component is nonlinear with respect to stress and thus can be represented by the product of a second-order polynomial of stress and two power laws of time and number of cycles, respectively. The reliability of this constitutive equation was evaluated by means of two verification tests. Good agreement was found between the predicted and measured strains. (Author)
87 citations
TL;DR: In this article, it was pointed out that the stress relaxation time that determines viscosity is partly controlled by the viscoity itself via diffusional structural relaxation, and that the feedback is mediated by atomic-scale-wavelength density fluctuations, being coupled to viscous flow on the one hand, with their relaxation being visco-ity-controlled on the other hand.
Abstract: It is pointed out that the stress relaxation time that determines viscosity is partly controlled by the viscosity itself via diffusional structural relaxation. This feedback may make the viscosity of a simple liquid without localised defects diverge at some finite temperature. The feedback is mediated by atomic-scale-wavelength density fluctuations, being coupled to viscous flow on the one hand, with their relaxation being viscosity-controlled on the other hand.
79 citations
TL;DR: In this article, the shape of the gamma-prime phase in the single-crystal nickel base alloy NASAIR 100 during tensile and compressive creep was investigated experimentally by Laue X-ray diffractometry.
63 citations
TL;DR: In this paper, the authors extend earlier molecular dynamic calculations to a study of the rheological properties and failure of sodium silicate glass, and show that the simulated glass "breaks" by forming cavities when subjected to a sudden large biaxial expansion.
Abstract: We extend earlier molecular dynamic calculations to a study of the rheological properties and failure of sodium silicate glass. Under biaxial compressions glass flow and stress relaxation are observed. The simulated glass ‘‘breaks’’ by forming cavities when subjected to a sudden large biaxial expansion. A microscopic model of a fiber behaves elastically up to stresses of near one million psi and then breaks with significant plastic deformation. The strength of the fiber is related to the ultimate strength of the glass. Under severe uniaxial compression the microscopic fiber undergoes a change in its atomic structure to a layered structure.
55 citations
TL;DR: In this paper, the magnetic anistropy induced by constant tensile stress and constant torsional strain annealing has been studied for liquid quenched alloys of the compositions (FexCo1−x)75Si15B10 (x = 0.1−1.0) and (Fe0.11Co0.89)72Mo3Si 15B10.
TL;DR: In this paper, an attempt was made to model these data in terms of a total flow stress composed of three components including an internal stress, an effective stress and a stress resulting from dynamic strain aging.
TL;DR: In this article, a numerical integration method of predicting the strain path corresponding to a given stress history, and hence the stress-strain relation, has been developed for polycrystalline materials like ice at high homologous temperatures.
TL;DR: General solutions sigma (t) of the Maxwell-type equation are discussed in the case of stress relaxation (after the cessation of steady flow) and stress formation (under constant shear rate) and the latter exhibits the well-known "overshoot" behavior.
TL;DR: In this article, the effect of cracks formed during the deformation of polycrystalline ceramics on the rate of creep deformation is discussed and four distinct regions of the creep curve are identified.
Abstract: A discussion is presented of the effect of cracks formed during the creep deformation of polycrystalline ceramics on the rate of creep deformation. Four distinct regions of the creep curve are identified. In region I, creep is controlled by the basic creep mechanism without cracks. Creep in region II is the combined effect of elastic creep by crack growth due to time-dependent changes in elastic properties and crack-enhanced creep described by Weertman. I n region III, in which the cracks have reached their final size, the rate of creep is governed by the sole effect of crack-enhanced creep. Region IV, not discussed in detail, is represented by accelerated creep due to crack coalescence prior to failure. The apparent stress exponent of crack-enhanced creep is shown to be governed by the value of the stress exponent of the basic creep mechanism as well as the stress dependence of the number of cracks formed per unit area or volume. The dependence of crack density on grain size also modifies the grain-size dependence of Nabarro-Herring and Coble creep. Depending on the specific mechanism of crack growth, region II creep can exhibit an apparent activation energy which can differ from the corresponding values for region I and III creep. Detailed microstructural information on crack size, crack density and other relevant variables is required for the quantitative analysis of the creep kinetics of polycrystalline ceramics subject to crack formation.
TL;DR: In this article, the workhardening rates during the creep of polycrystalline aluminium were determined from instantaneous plastic strains in stress change tests in the temperature range 455-650 K under stresses for which the steady state creep rates lie within the range 5 × 10 −7 − 2 × 10−5 s −1.
TL;DR: In this article, an internal friction method was used to study the stress relaxation caused by diffusion around second phase particles in a copper single crystal containing iron particles, and it was found that the relaxation time is proportional to the third power of the particle size.
TL;DR: In this article, a method for estimating the threshold stress intensity for crack growth is presented, which requires prior knowledge of the flaw population of a material and uses applied static loads followed by fast fracture to assess the effect of initial applied stress intensity on flaw behavior.
Abstract: A method for estimating the threshold stress intensity for crack growth is presented. The technique requires prior knowledge of the flaw population of a material and uses applied static loads followed by fast fracture to assess the effect of initial applied stress intensity on flaw behavior. The technique was applied to a hot-pressed Sic at 1200° and 1400°C in a nonoxidizing atmosphere. At 1400°C with a static load time of 4 h, the threshold stress intensity was determined to be ∼ 1.75 MPa·m1/2 with a slight tendency toward higher fracture stress with increasing initial stress intensity below the threshold. At 1200°C for a static load time of 4 h, apparent strengthening was observed below a threshold stress intensity of ∼2.25 MPa·m1/2. This strengthening effect appears to result from stress relaxation in the crack-tip region, probably by plastic deformation which involves the oxide grain-boundary phase.
TL;DR: In this article, the activation energy values of the shift factors aT were determined and the master curves were obtained for the various structures for isotactic polypropylene having different morphologies and crystallinities.
Abstract: Samples of isotactic polypropylene having different morphologies and crystallinities were prepared and subjected to stress-relaxation experiments at different levels of strain. The relaxation moduli were determined in the range of temperature between – 20 and 40°C over a period of time from 1 to 1000 seconds. Using the time-temperature superposition principle, the activation energy values of the shift factors aT were determined and the master curves were obtained for the various structures. Increasing crystallinity and/or crystalline aggregate size increases the relaxation modulus of the material and changes both shape and location of the spectrum of relaxation times so that no simple method can be found to correlate the various master curves.
TL;DR: In this article, the authors measured the dichroic ratio of atactic polystyrene absorption bands for determination of orientation as well as relaxation of chains during stretching and obtained a master curve at a reference temperature T 0 = 115°C.
TL;DR: In this paper, the influence of structural relaxation on the anelasticity was studied by continuous measurements of apparent viscosity, and it was found that, while viscoplastic deformation drastically decreases with annealing, theanelastic behavior is only weakly affected.
TL;DR: In this article, a theory for the relaxation of large strains in polymer melts is outlined based on the Doi-Edwards slip-link model and the new concept of tube relaxation.
Abstract: A theory for the relaxation of large strains in polymer melts is outlined. It is based on the Doi–Edwards slip-link model and the new concept of tube relaxation. Self-consistency makes this concept necessary when polymer melts are concerned. The discrepancy with previous non-self-consistent theories is not negligible and should be easy to observe experimentally. Special attention is given to the overall size and to the mean orientation of a labeled N-chain in a step-strained melt of P-chains. Using semiquantitative arguments, we predict different regimes depending on the respective values of N and P, and propose approximate evolution equations for each case. These equations may be used to design and interpret a variety of fluorescence, infrared, or NMR polarization measurements, as well as small-angle neutron scattering experiments.
TL;DR: In this article, the authors analyse slow chain diffusional process effects on n.m.r. properties of nuclei linked to long linear polymer molecules in melts or in concentrated solutions, and show how stress-relaxation processes induced on a macroscopic scale can be monitored on a semi-local space scale.
TL;DR: In this article, a computer model has been described for the prediction of stress relaxation and stress relief cracking (in coarse grained, heat affected zone microstructure) during the heating period of a simulated post-weld heat treatment in four-point bend single edge notched (SEN) testpieces.
Abstract: A computer model has been described for the prediction of stress relaxation and stress relief cracking (in coarse grained, heat affected zone microstructure) during the heating period of a simulated post-weld heat treatment in four-point bend single edge notched (SEN) testpieces. Stress relaxation by plastic deformation was calculated from isothermal creep strain rate data. The two main mechanisms of stress relief cracking were considered, i.e. higher temperature, intergranular microvoid coalescence and lower temperature, low ductility intergranular fracture. Existing theoretical models for ‘creep cavitation’ were used to estimate crack growth by the intergranular microvoid coalescence mechanism. An experimental relationship between crack propagation rate, stress intensity, and temperature was derived for the estimation of crack growth by the low ductility intergranular fracture mechanism. A comparison was made between the model predictions and experimental results from a recently developed, rehea...
TL;DR: In this paper, it is shown that uniaxial anisotropy parallel to pattern boundaries, which is due to stress relaxation normal to pattern edges, is necessary for the formation of charged walls.
Abstract: This paper reviews present understanding and presents new data on the effects of ion implantation on garnet materials and on the mechanisms giving rise to charged walls at boundaries between implanted and unimplanted regions. It is shown that uniaxial anisotropy parallel to pattern boundaries, which is due to stress relaxation normal to pattern edges, is necessary for the formation of charged walls. Furthermore. it is shown that, whereas early reseachers ascribed the three-fold symmetric behavior of charged walls in the ion implanted layers of
TL;DR: In this article, the history effects of prior creep on subsequent plasticity were studied for type 316 stainless steel at 600°C under combined torsion and tension following each of three different amounts of prior torsional creep, plastic deformation tests were performed under torsions in the same and opposite directions of the prior creep.
Abstract: History effects of prior creep on subsequent plasticity were studied for type 316 stainless steel at 600°C under combined torsion and tension Following each of three different amounts of prior torsional creep, plastic deformation tests were performed under torsions in the same and opposite directions of the prior creep and axial tension, respectively The experimental results showed the marked influence of prior creep on subsequent plasticity That is, the flow stress in the subsequent plastic deformation after creep became larger than the one in the corresponding pure plastic test where the prior creep strain in the combined creep-plasticity test was replaced by a plastic strain of the same amount Finally, predictions by means of existing separated and unified constitutive equations were discussed on the basis of the experimental results
TL;DR: In this article, a uniaxial constitutive equation describing the deviations from the linear principle of superposition of aging concrete at constant moisture content and temperature is presented, where both the creep increase (flow) at high stress and the stiffening (adaptation) due to low sustained compressive stress are modeled.
Abstract: A uniaxial constitutive equation describing the deviations from the linear principle of superposition of aging concrete at constant moisture content and temperature is presented. Both the creep increase (flow) at high stress and the stiffening (adaptation) due to low sustained compressive stress are modeled, the latter being of principal interest. The constitutive equation expresses the creep rate as a history integral with a singular kernel involving the time lag of creep strain. The integral has the property that the strain response is proportional to the stress history but depends nonlinearly on the stress history when nonproportional stress histories are superposed. The double power law for aging creep is a special limiting case. The constitutive relation is also explained in terms of the rate-process (activation energy) theory for the rate of bond ruptures causing creep. For structural creep problems, a corresponding step-by-step integration algorithm which correctly captures the asymptotic properties of the integral is also developed. A good agreement with test data from the literature is achieved.
TL;DR: Transient creep of high purity iron was investigated at low stresses and homologous temperatures 0.40-0.54 using the technique of helicoid specimens as discussed by the authors, showing that the transient creep strain is caused primarily by bowing out of links of the three-dimensional dislocation network accompanied by releasing and moving of some of these links.
TL;DR: In this paper, the lattice parameters of an Fe-32Ni alloy prepared by different cooling rates from the austenitization temperature have been measured in the states before and after the martensitic transformation.
TL;DR: In this article, the steady state creep and stress relaxation behaviors of oriented Al-CuAl 2 single eutectic grains are analyzed in a synthetic manner, including the role of the phase boundary sliding and the heterogeneity of the deformation.