Effect Of Compressive Residual Stress Research Articles

Prediction of notch fatigue limits in a compressive residual stress field

Analyses are made for predicting fatigue limit of notches with and without the effect of compressive residual stresses. The residual stresses are introduced by shot peening or surface rolling, and detected by X-ray diffraction technique. The theoretical work is based on the local stress method and focused on an asymmetrical stress condition at the notch root. Fatigue tests are carried out, and an agreement is reached between predicted and tested data.

Examination of the effect of Shot-Peening Conditions on the Improvement of Fatigue Reliability of Meatl-Molded Austempered Ductile Iron.

An examination of the effect of shot-peening (SP) conditions on the improvement of fatigue reliability of metal-molded ADI was performed with a mesoscopic observation of fracture morphology. The main results obtained were as follows: (1) The 106 endurance limit could be improved with an increase of SP strength, but the endurance limit of 1.0mmA-Sp material was as high as that of 0.8-SP material. On the other hand, the 2×107 endurance limit as not improved with SP treatment. (2) The origin of fatigue cracks of metal-molded ADI as not the pores, since the cooling rate of metal-molded ADI was slower than that of sand-molded ADI. (3) The origin of fatigue cracks was transferred from the surface to the inside with an increase of SP strength, due to the effect of compressive residual stress induced by SP treatment. (4) Although the depth affected by SP treatment of 1.0-SP material was greater than that of 0.8-SP material. The influence of SP strength on the endurance limit of metal-molded ADI was only effective up to 0.8-SP strength because of the existence of a stress gradient.

Residual Stress Effects on the Fracture of Tantalum Nitride Films

ABSTRACTIn this study, continuous microscratch testing was used to determine the effects of compressive residual stresses on the fracture of thin tantalum nitride films. The films were sputter deposited at room temperature onto single crystal sapphire substrates to a thickness of 600 nm. Some films were left in the as-deposited condition while the remaining films were vacuum annealed at 300°C. The only discernible change in structure was a surface rearrangement of atoms into parallel arrays of striations on the vacuum annealed samples revealing a high compressive residual stress in the films. These stresses had a strong effect on fracture as shown by the as-deposited films which buckled readily during scratch tests forming uniform-width and circular blisters while the vacuum annealed films exhibited a much lower susceptibility to fracture. Application of mechanics-based models for film buckling defined the levels of compressive residual stress and their effect on interfacial fracture.

Phase and composition depth distribution analyses of low energy, high flux N implanted stainless steel

The phase and composition depth distributions of a low-energy (0.7 keV), high-flux (2.5 mA/cm2) N implanted fcc AISI 304 stainless steel held at 400 °C have been investigated by step-wise Ar+ beam sputter removal in conjunction with conversion electron Mössbauer spectroscopy and x-ray diffraction (XRD). A metastable, fcc, high-N phase (γN), with both magnetic and paramagnetic characteristics, was found to be distributed in the N implanted layer generated by the low-energy, elevated temperature, implantation conditions. The magnetic γN was found to be ferromagnetic and was distributed in the highest N concentration region of the implanted layer (the top 0.5 μm) while the paramagnetic γN becomes predominant below 0.5 μm, where the N content is only slightly lower. The ferromagnetic state is linked to large lattice expansions due to high N contents (∼30 at.%) as determined by XRD and electron microprobe. The relatively uniform XRD N distribution to a depth of ∼1 μm suggests a sensitive dependence of the magnetic γN phase stability on N concentration and degree of lattice expansion. The XRD results also show that the N contents and depths depend on the polycrystalline grain orientation relative to the ion beam direction. The N was found to diffuse deeper in the (200) oriented polycrystalline grains compared to the (111) oriented grains and the N contents were significantly higher in the (200) planes relative to the (111) planes. The effect of compressive residual stresses (∼2 GPa) is considered. The scanning electron microscopy (SEM) analysis reveals quite clearly the uniform nature of the γN layers with a reasonably well defined interface between the γN layer and the substrate, suggesting uniform N contents with uniform layer thicknesses within a given grain. However, they also show significant variations in the γN layer thickness from one grain to the next along the N implanted layer, clearly supporting the XRD findings of the variation in N diffusivity with grain orientation.

On the strength of fiber reinforced ceramic composites containing an elliptic hole

Abstract This paper studies the tensile strength of a fiber reinforced ceramic composite containing a hole. The strength is determined on the basis of a full analysis of matrix cracking in the presence of the hole and the failure of crack bridging fibers. The crack bridging fibers are assumed to undergo large amounts of slipping relative to the matrix and are modeled as an array of springs. The dependence of the composite tensile strength on fiber tensile strength, orthotropic parameters, hole size and shape parameters, and frictional shear stress at the fiber-matrix interface is determined and described in terms of a universal set of nondimensional parameters. The effects of compressive residual stress in the fibers upon the strength are also discussed.

Effect of residual stress on fatigue behaviour of notches

The effects of surface-rolling-induced residual stresses on the endurance limit and the growth behaviour of short cracks were investigated for notched steel parts. Unlike the case of smooth specimens tested in laboratory conditions, the endurance limit of notches under axial loading was enhanced by surface rolling, but the improvement was limited owing to the detrimental effect of tensile residual stresses at a distance from the surface. The second fatigue origin, which was just ahead of the crack tip and destroyed the condition of slowed propagation rate of the short crack in the compressive residual stress field, would be produced at the position where the maximum tensile residual stress was acting. This effect could be effectively eliminated by tensile preloading in such a way that the tensile residual stresses were greatly released by plastic deformation and the short fatigue crack in the compressive residual stress field became non-propagating at the loading of endurance limit. The effect of compressive residual stress on growth behaviour of short fatigue cracks lies in two aspects: (a) increasing the crack closure effect; and (b) decreasing the maximum stress intensity factor. A predicted d a/dN versus ΔK eff curve based on this assumption agreed with the experimental results.

Analysis of Toughening Mechanism of Ceramic-Matrix Composites in Consideration of Interface Debonding. 1st Report. Energy Release Rate for Interface Debonding Crack and Evaluation of Critical Debonding Length.

In this study, the energy release rate is derived for interface debonding cracks in ceramic-matrix composites, using approximate solutions of an axisymmetric cylindrical fiber-matrix model. The energy release rate expression includes the important effects of compressive residual stresses and frictional sliding stress on the debonded interface in a closed-form equation. A parametric study of the energy release rate is carried out and the effects of various parameters on the energy release rate are clarified and compared with results of other studies. The method to determine the critical debonding length is proposed based on the energy release rate and the fracture criterion of the interface and fiber. The predicted debonding length gives good agreement with published experimental results.

Experimental evaluation of environmentally assisted cracking: the effect of compressive residual stresses at the crack tip

Experimental evaluation of environmentally assisted cracking: the effect of compressive residual stresses at the crack tip

Load Bearing Capacity of Plasma Nitrided Steelunder Rolling–Sliding Contact

The wear behaviour of plasma nitrided low alloy steel has been investigated under dry rolling contact with sliding traction. Particular attention was paid to subsurface shear behaviour during the wear process, and to prediction of the load bearing capacity of the nitrided specimens. A simple model has been developed to describe the influence of hardened depth, strength and residual stresses of the nitrided case, and coefficient of friction on the initiation of shear deformation in the contact bodies during the wear process. Experimental results and the model show that a relatively thick and strong nitrided case is required for the specimens to bear high loads without severe wear. The model also indicates the complex effect of compressive residual stresses on the maximum shear stress distribution in the subsurface induced by the applied forces.

The Effects of Welded Residual Stress and Corrosion Deposits on Corrosion Fatigue Crack Propagation Rate of Butt Welded Joints in Natural Seawater

The corrosion fatigue crack growth behavior in the butt welded joints of low carbon steel has been studied and discussed in relation to the welding residual stress and corrosion deposits.In air, the fatigue crack growth rate was scarcely influenced by the tensile residual stress, but the compressive residual stress reduced the fatigue crack growth rate. In seawater, the effect of compressive residual stress on the corrosion fatigue crack growth rate was less than that in air. When the stress ratio was increased, this effect was scarcely observed. However the occurrence of the wedging effect due to corrosion deposits was confirmed in seawater except the case of compressive residual stress at low stress ratio. When the crack closure occurred by the compressive residual stress in seawater, the corrosion deposits formed within fatigue cracks were fractured by contact with the closing crack planes, but they were formed again. Such an mechanism seemed to occur particularly in the compressive residual stress field. Thus, the corrosion fatigue crack growth rate in the compressive residual stress field was remarkably accelerated by the aggressive attack of seawater.

Fracture analysis of thick-wall cylinder pressure vessels

Fracture mechanics analysis of cylindrical pressure vessels is described in a brief fracture case study. Also included are additional examples of crack growth in pressure vessels and cannons. The case study is of an early brittle failure and subsequent redesign of a cannon tube. Fracture mechanics test methods are described which were developed specifically for testing of cylindrical geometries. Three examples of current fracture analysis of cylindrical pressure vessels are presented. Fast fracture of a vessel is described, including effects of tension residual stress and crack shape. Evidence of environmentally assisted fracture of a cannon tube is presented. Fatigue crack growth and life calculation methods for cylindrical pressure vessels are discussed including effects of compressive residual stress due to overstrain.

The significance of residual stresses in relation to the integrity of LWR pressure vessels

This review is concerned with assessing the significance of residual stresses in relation to the integrity of nuclear reactor pressure vessels. The discussion is largely centred on light water reactors (LWRs), with particular emphasis on pressurised water reactors (PWRs); moreover, residual stresses are only explicitly considered in connection with PWR primary pressure vessels. However, much that is discussed is of general relevance to other reactor systems and pressure boundary components. The level and distribution of residual stresses in heavy section weldments and the factors affecting their relaxation with post-weld heat treatment (PWHT) are discussed; residual stresses are also considered in relation to the deposition of austenitic strip cladding and repair welding. A brief survey is made of currently available methods of measuring surface and sub-surface residual stresses in heavy section weldments; the effects of compressive residual stresses on the detection and sizing of planar defects are similarly considered. Available fracture mechanics methodologies with the capability of evaluating defect significance in the presence of residual and other secondary stresses are reviewed in some detail. On-going experimental investigations of the effects of residual stresses on structural integrity are also described. Following a general discussion, the desirability of internationally agreed Codes and Methods for assessing defects in the presence of residual and other self-limiting stresses is pointed out. It is argued that before such agreement could be achieved, however, further work is necessary in order to: (i) establish the level and distribution of surface and sub-surface residual stresses due to fabrication and repair welding: (ii) relate material properties, especially those influencing relaxation behaviour, to the level and distribution of residual stresses following PWHT; (iii) develop (or improve), and suitably validate, numerical and analytical methods for quantifying residual stresses and their effects on fracture behaviour. Within this context, a number of recommendations are given in Appendix 1 concerning areas requiring further research or engineering investigation.