Cyclic creep process in AISI 316L stainless steel in terms of dislocation patterns and internal stresses

Ratchetting process in the stainless steel AISI 316L at 300 K: an experimental investigation

Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

Finite element analysis of the thermal residual stresses of SiC particle reinforced aluminum composite

Residual stress fields are now widely accepted to have significant influence on fatigue crack growth. Tensile stresses have detrimental effects on fatigue lives, whereas compressive residual stresses can be beneficial. Control of fatigue lives via residual stress is now established in many industrial applications, using techniques such as shot peening or cold expansion. However, knowledge of the processes that occur when a fatigue crack grows through a pre-existing stress field is far from complete. Although the residual stress field will clearly have an effect on crack growth, the crack will equally have an effect on the residual stress field. The determination of this effect is not trivial, and direct measurement may be the designer’s best safeguard. This article outlines the complementary effects that a growing fatigue crack and a residual stress field have on each other. Two types of residual stress field are considered: mechanically induced and thermally induced. The results are discussed in terms of the implications that residual stress interactions have for damage-tolerant-based design.

Fatigue Crack/Residual Stress Field Interactions and Their Implications for Damage-Tolerant Design

In metal matrix composites (MMCs) residual stresses are unavoidable during cooling from high temperature in fabrication or heat treatment because of the difference in the thermal expansion coefficients between the matrix and the reinforcement. In particle reinforced MMC the residual stresses have been proved to be hydrostatic in this study by both experiments and mathematical analysis. A very slight surface effect on the measured stresses was predicted in the case Cu Kα radiation was used. The residual stresses were determined to be tensile in the Al matrix and compressive in the reinforcement. A reduction in residual stress magnitudes of both the matrix and reinforcement was observed after the sample was cooled into liquid nitrogen and heated back to room temperature, which is believed to be caused by plastic deformation of the matrix in low temperature treatment.

Residual stresses in silicon carbide particulate reinforced aluminum composites

The effect of cyclic stress on high temperature creep and also the dislocation structures developed during cyclic creep for three Al Mg solid solutions have been studied. When the steady state creep rate is in the range of 10[sup [minus]8]-10[sup [minus]3]s[sup [minus]1], cyclic creep with complete unloading (R = 0) exhibited only the transition from class M to class A creep instead of the two transitions from class M to class A and then to class M again in the corresponding static creep. The threshold stress for the transition in cyclic creep was found to be close to or larger than that for the class A to class M transition in the static creep. With increase in magnesium content, cyclic creep retardation became stronger at lower stresses. However the transition from retardation to acceleration in the cyclic creep has been observed at higher stress levels only in the high magnesium alloys. Also found were two types of relationships between the unloading amount and steady state creep rate. The micromechanisms of cyclic creep, especially the interaction of dislocations with solute atoms, have also been discussed.

Effect of cyclic stress on the high-temperature creep-behavior of al-mg alloys

hu, xb (reprint author), acad sinica,inst met res,fatigue & fracture mat lab,shenyang 110015,peoples r china

Periodicity of strain bursts in Al0.87%Mg alloy during cyclic creep at intermediate temperatures

Intermediate-temperature cyclic creep of Al0.87% Mg alloy under different cyclic peak stresses was studied. In the secondary creep stage, periodic strain bursts occurred only in a certain region of both stress and temperature. The threshold stress of strain burst appearance was found to be almost independent of temperature, but its temperature range for a constant stress decreased with increasing applied stress. The period of strain bursts decreased with increase in both stress and temperature, whereas their amplitude changed with stress only. The average creep rate during strain bursts was observed to be more sensitive to both stress and temperature than that during conventional creep. A new model on strain bursts is proposed based upon the strain equation in terms of mobile dislocation density and also the collective motion of pile-up dislocations in front of forest dislocations under concentrated stress. Relationships of strain burst period and amplitude with (i) temperature, (ii) cyclic peak stress, (iii) average creep rate and finally (iv) cyclic stress frequency have been deduced and also verified by the experimental results.

Zhongguang Wang

Papers

Residual stresses in silicon carbide particulate reinforced aluminum composites

Effect of cyclic stress on the high-temperature creep-behavior of al-mg alloys

Periodicity of strain bursts in Al0.87%Mg alloy during cyclic creep at intermediate temperatures

Periodic strain burst behaviour of Al0.87 Mg alloy in cyclic creep at intermediate temperatures