Amount Of Compressive Residual Stress Research Articles

Inner surface peening for long and narrow helical pipe using acoustic cavitation

The inner surface peening of helical pipes is highly challenging due to the inaccessibility of the inner surface. To the end, we propose to peen the inner surface by introducing acoustic cavitation inside the pipe. We also provide a theory to account for how the inner surface peening can be achieved by the acoustic cavitation for a long helical pipe. We evaluate the validity of theory with experiments conducted on helical pipe specimens. The experimental results well agree with the theorical predictions. Also, it was found that a significant amount of compressive residual stress was achieved by the acoustic cavitation on the inner surface. The experimental results imply that the acoustic-cavitation-generation of compressive residual stress is effective regardless of pipe length, which promises that the present peening method will be applicable for a wide range of helical pipe length.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Compressive residual stress generation at crack tip in bulk metal using acoustic cavitation

We propose to generate compressive residual stress at the crack tip in the bulk metal by introducing acoustic cavitation to the crack tip. We conducted experiments using pre-cracked specimens to measure compressive residual stress at the crack tip achieved by the acoustic cavitation. In the experiments, the pre-cracked metal specimens were subject to an acoustic load with a frequency of 20 kHz to introduce acoustic cavitation to the crack tip. We found that the acoustic cavitation generates a significant amount of compressive residual stress at the crack tip and the generated compressive residual stress effectively retarded the crack growth.

Effect of laser shock peening on microstructural, mechanical and corrosion properties of laser beam welded commercially pure titanium

In the present study, laser beam welding of commercially pure titanium has been carried out at different scan speeds in the range from 2.4 m/min to 4 m/min at 2.15 kW laser power and its influence on molten pool thermal history, microstructure, residual stress, mechanical and corrosion properties has been studied. Weld thermals cycles were monitored using a single wavelength infrared pyrometer. Effect of laser shock peening on laser welded specimens was also studied. Laser shock peening inducted significant amount of compressive residual stress through plastic deformation. Strain hardening and changes in microstructure such as formation of twining lead to significant improvement in tensile and fatigue properties. Micro-hardness in the fusion zone at sub-surface region got improved by ~26% and fatigue strength increased by ~24%. Corrosion resistance also got increased due to high compressive residual stress and grain refinement after LSP.

An analysis of thermal autofrettage process with heat treatment

In this work, a finite element method (FEM) analysis of a thermal autofrettage process coupled with heat treatment is carried out. The objective is to strengthen a cylindrical pressure vessel with compressive stresses on the outer as well as inner walls. In the proposed method, after thermal autofrettage, the outer wall of the cylinder is heated above the lower critical temperature to cause austenization of the cylinder in its vicinity. When the cylinder is quenched to room temperature, it retains beneficial compressive residual stresses at both the inner and outer walls. The analysis considers temperature and microstructure dependent material properties of AISI 1080 steel. Phase transformation kinetics is incorporated through user defined subroutine UMATHT in commercial FEM package ABAQUS®. The simulation results indicate that heat treatment after thermal autofrettage converts tensile residual stresses at the outer wall to compressive residual stresses. On the other hand, it does cause a slight relaxation of compressive residual stresses at the inner wall. Nevertheless, with the ability to retain significant amount of compressive residual stresses at both the walls, the process can mitigate the problems of stress-corrosion cracking and fatigue failure due to tensile residual stresses at the surface.

Effect of Residual Stress on the Mechanical Properties of FSW Joints with SUS409L

This study was performed to investigate both the residual stress distribution and the effect of the residual stress formed at the welding region on the mechanical properties of the friction stir welded joints with 409L stainless steel sheets. Residual stress measurement with hole-drilling method; mechanical property evaluation including tensile test, Charpy impact test, and fatigue test; and microstructure observation were conducted. It has got no residual stresses to speak of at the center region of the stir zone because the stored stresses are released in the process of the dynamic recrystallization, while a small quantity of compressive residual stresses is formed at the surface region of the stir zone because of strong compression reaction by the tool shoulder. A considerable amount of compressive residual stresses is formed at the thermomechanical affected zone because of the synergy between the thermal expansion due to the heat conduction from the stir zone and mechanical compression by the tool. The formation of residual stresses shows a similar tendency between the advancing side and the retreating side. Both the mitigation of residual stress in the stir zone and the formation of compressive residual stress in the thermomechanical affected zone contribute to the improvement of the mechanical properties of the friction stir welded joints.

Effect of multiple passes treatment in waterjet peening on fatigue performance

The influence of waterjet peening on the residual stresses and fatigue performance of AISI 304 is investigated. The specimen surfaces were treated with multiple jet passes. The fatigue strength was evaluated using an alternating bending fatigue tester. The results of XRD measurements showed that a higher amount of compressive residual stresses is induced in the treated specimens. This strengthening layer is limited within the first 100μm below the surface, which had been confirmed by micro hardness measurements. Even though the treated specimens showed compressive residual stresses the fatigue limit is lower than that of the untreated specimens. The roughness of the surface and the resulting notch effect seems to be stronger than the positive effect of the hardened layer.

Modeling and Measurement of Residual Stresses along the Process Chain of Autofrettaged Components by Using FEA and Hole-Drilling Method with ESPI

The incremental hole-drilling method is a well-known mechanical measurement procedure for the analysis of residual stresses. The newly developed PRISM® technology by Stresstech Group measures stress relaxation optically using electronic speckle pattern interferometry (ESPI). In case of autofrettaged components, the large amount of compressive residual stresses and the radius of the pressurized bores can be challenging for the measurement system. This research discusses the applicability of the measurement principle for autofrettaged cylinders made of steel AISI 4140. The residual stresses are measured after AF and after subsequent boring and reaming. The experimental residual stress depth profiles are compared to numerically acquired results from a finite element analysis (FEA) with the software code ABAQUS. Sample preparation will be considered as the parts have to be sectioned in half in order to access the measurement position. Following this, the influence of the boring and reaming operation on the final residual stress distribution as well as the accuracy of the presented measurement setup will be discussed. Finally, the usability of the FEA method in early design stages is discussed in order to predict the final residual stress distribution after AF and a following post-machining operation.

Surface nanocrystallization of aluminium alloy by controlled ball impact technique

A novel surface modification process namely controlled ball impact peening was developed for synthesizing a nanostructured surface layer and to impart compressive residual stresses on metallic materials in order to enhance the overall surface properties. This article demonstrates the microstructural evolution, surface hardening and introduction of the residual stresses in the ball impact peened aluminium alloy surfaces, AA6063-T6. Hardened steel balls were impinged in controlled manner inducing high strain rates on the aluminium samples which are precisely moved using independent programmable logic controlled linear actuators in the controlled ball impact peening process. Mechanical properties of the nanocrystalline surface layer were investigated using dynamic ultra micro-hardness tester. The hardness of the nanocrystalline surface layer is (~1.3GPa) improved compared to the matrix (~0.58GPa) and the depth of the hardened layer is about ~350μm depending upon the peening conditions. The amount of compressive residual stress developed by the treatment is also studied using depth sensing indentation method. The surface compressive residual stresses induced in the ball impact peened samples is about 70–127% of yield strength of the target material depending upon the peening conditions. X-ray diffraction analysis and transmission electron microscope analysis revealed the formation of nanograin crystalline structure on the ball impact peened surface layer. The mean grain size of the peened sample determined by transmission electron microscope is about 8±2nm in the top surface layer. High strain rate and repeated directional loading imparted in the contact zone generates the various dislocation activities and microstructural features which were responsible for the formation of the randomly oriented nanostructured grains on the metallic materials. With increasing strain, the various microstructural features produced in the ball impact peened aluminium samples are deformation twins, multiple shear bands, high density dislocation and dislocation pile-up at the grain boundaries as investigated by transmission electron microscope. Grain refinement on the ball impact peened aluminium surfaces resulted in the formation of high density dislocation associated with the subdivision of original grains into subgrains. The peening coverage and number of overlapping impacts depend upon the sample travelling velocity, which in turn affects the hardness, compressive residual stresses induced and grain size formed for a given ball diameter and impact velocity.

Strengthening of Ceramics by Shot Peening

Non-transformation toughened ceramics show the typical brittle material behavior of failure before deformation at room temperature. Thus, strengthening of ceramics due to deformation induced compressive residual stresses has been thought to be not possible. Nevertheless, preliminary investigations had shown that, using ceramic-specific parameters, shot peening can introduce high compressive residual stresses into the near-surface region of silicon nitride which improve the load capacity. The aim of the presented investigation was to improve the shot peening conditions in order to increase the amount of compressive residual stresses while maintaining the surface integrity. The materials investigated where alumina and silicon nitride, the properties determined where residual stresses, load capacity and topography. The results show that high compressive residual stresses in the GPa-range can be introduced in silicon nitride and alumina which may boost the load capacity of the near surface layers by a factor of up to 9. Only little effect on the surface integrity could be obtained.

Fatigue properties of cold worked holes

The introduction of holes in a body would inevitably raise the stress locally around the holes. This stress concentration would in turn affect the performance of the body under static and fatigue loading conditions. The aim of the present paper is to investigate how three cold working processes, namely, shot peening, wet blasting and ballising would affect the fatigue lives of holes. Fatigue tests on 3mm thick tensile specimens of Assab 760 steel showed that ballising with interference between 1 and 3.3% enhanced the fatigue lives of the holes by about 60 to 220%. For shot peening with pressure from 138 to 414 kPa, the enhancement was about 30 to 100%, while for wet blasting at pressure between 69 and 690 kPa, 10 to 50%. The residual stresses around the holes as a result of the cold working processes were evaluated using a fracture mechanics approach. It was found that all the three processes studied induced compressive residual stress field at the surfaces of the holes. The compressive stress decreased and became tensile as the distance from the surface of the hole increased. The compressive stress was observed to increase with pressure in the shot peened and wet blasted holes and with interference in the ballised holes. Within the range of pressure and interference investigated, residual stress measurements revealed that ballising induced the greatest amount of compressive residual stress while wet blasting, the lowest. This is well manifested in the fatigue lives of the holes.

浸炭鋼の疲れ強さにおよぼすショットピーニングの影響

Shot peening is one of the cold working processes performed by projecting hard particles onto the surface of works. In spite of old technology, it has been reconsidered in automotive industries as the means to improve fatigue durability in terms of “Hard shot peening”. Hard shot peening is a high intensity peening technology resulting in larger amount of compressive residual stress and higher fatigue resistance than conventional intensity peening. In hard shot peening process, however, the peak value of the stress is located at the depth of 0.05mm below the surface and the surface value is not so high. To compensate this stress depression at sub-surface, additional beads peening was studied. By applying the additional beads peening further improvement of fatigue resistance has been confirmed. The beads peening process is effective to give residual compressive stress at the surface without surface degradation.

急冷残留応力によるセラミックスの強化

Pressureless sintered alumina with 92% purity was quenched from 1500°C into silicon oil with the kinematic viscosity of 1, 100 and 10000cs. The residual stress distribution in the quenched ceramics was measured by the X-ray diffraction method. The increase of the bending strength of quenched ceramics was discussed on the basis of the measured residual stress. The results obtained were summarized as follows:The compressive residual stress was formed near the surface of quenched ceramics, and its magnitude increased with decreasing viscosity of silicon oil. The bending fracture of quenched ceramics started from the material defect embedded in the surface layer with large compressive residual stresses. The bending strength increased in proportion to the amount of compressive residual stress measured on the surface. The maximum strength was obtained for the case of quenching into 1cs silicon oil. It was 531MPa which is about 1.4 times the strength of annealed specimens. The microscopic residual stress, estimated from the broadening of the X-ray diffraction profile, could reduce the stress for fracture from a small (microscopic) defect.