Stress relaxation

About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.

The viscoelastic compression behavior of liquid composite molding preforms

Abstract: The compressive deformation of reinforcements is an important consideration for many composites manufacturing processes. The apparent viscoelastic behavior of three common Liquid Composite Molding reinforcements has been studied, and the implications for modeling mold filling processes discussed. Though no resin was present, these fibrous structures have displayed complex time-dependent response, including loading hysteresis, stress relaxation, and strain rate dependent loading behavior. Stress relaxations have been observed to be as high as 64% of the peak stress, with the magnitude of relaxation being dependent on the preform fiber volume fraction. Increasing peak stresses are generated with faster strain rates, and two of the materials studied displayed stress relaxation sensitive to the initial strain rate. Two mold filling experiments are also presented, demonstrating the significant influence of preform viscoelasticity, and providing motivation for further study of these effects.

Long-term creep deformation property of modified 9Cr-1Mo steel

Abstract: The first volume of “Atlas of Creep Deformation Properties” was published on modified 9Cr–1Mo steels in March 2007, as a part of the NIMS (National Institute for Materials Science) Creep Data Sheet series Creep deformation properties up to about 70,000 h have been investigated No clear steady-state creep stage has been observed, and creep deformation of the steel consists of transient and accelerating creep stages Good linear relationships between creep strain vs time and creep rate vs time were observed within a transient stage in a log–log plot It was appropriately expressed by a power law rather than an exponential law, logarithmic law and Blackburn's equation With decrease in stress, the magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the long-term region Life fraction of the time to specific strain of 1% creep strain and 1% total strain, to time to rupture tended to increase with decrease in stress The time to 1% total strain, that is an important parameter for design of high temperature components, was observed to lie in the transient creep stage in the short-term regime, however, it shifted to the accelerating creep stage in the long-term regime For evaluation of long-term creep strength properties, an experimental creep test data should be extrapolated in consideration of the stress dependence of creep deformation properties

Precipitation and relaxation in strained Si1−yCy/Si heterostructures

Abstract: We have studied the thermal stability of Si1−yCy/Si (y=0.007 and 0.014) heterostructures formed by solid phase epitaxial regrowth of C implanted layers. The loss of substitutional C was monitored over a temperature range of 810–925 °C using Fourier transform infrared absorbance spectroscopy. Concurrent strain measurements were performed using rocking curve x‐ray diffraction to correlate strain relaxation with the loss of substitutional C from the lattice. Loss of C from the lattice was initiated immediately without an incubation period, indicative of a low barrier to C clustering. The activation energy as calculated from a time to 50% completion analysis (3.3±5 eV) is near the activation energy for the diffusion of C in Si. Over the entire temperature range studied, annealing to complete loss of substitutional C resulted in the precipitation of C into β‐SiC. The precipitates are nearly spherical with diameters of 2–4 nm. These precipitates have the same crystallographic orientation as the Si matrix but th...

Mechanical properties of Cu–Cr system alloys with and without Zr and Ag

Abstract: The effects of addition of Zr and Ag on the mechanical properties of a Cu–0.5 wt%Cr alloy have been investigated. The addition of 0.15 wt%Zr enhances the strength and resistance to stress relaxation of the Cu–Cr alloy. The increase in strength is caused by both the decrease in inter-precipitate spacing of Cr precipitates and the precipitation of Cu5Zr phase. The stress relaxation resistance is improved by the preferentially forming Cu5Zr precipitates on dislocations, in addition to Cr precipitates on dislocations. The addition of 0.1 wt%Ag to the Cu–Cr and Cu–Cr–Zr alloys improves the strength, stress relaxation resistance and bend formability of these alloys. The increase in strength and stress relaxation resistance is ascribed to the decrease in inter-precipitate spacing of Cr precipitates and the suppression of recovery during aging, and to the Ag-atom-drag effect on dislocation motion. The better bend formability of the Ag-added alloys is explained in terms of the larger post-uniform elongation of the alloys.

Strain relaxation and defect formation in heteroepitaxial Si1−xGex films via surface roughening induced by controlled annealing experiments

Abstract: Mechanisms of strain relaxation and defect formation during surface roughening in Si1−xGex films grown epitaxially on (100)Si substrates have been investigated by controlled annealing experiments. Epitaxial films 10 nm in thickness and containing 18% Ge, which are subcritical with respect to the formation of misfit dislocations, show strain relaxation through surface roughening on annealing at 850 °C, where surface grooves are aligned along 〈100〉 directions. Other films with 22% Ge and supercritical thicknesses have also been studied, where surface grooves are aligned along 〈110〉 directions.