Axial Residual Stress Research Articles

Sustainable Diamond Burnishing of Chromium–Nickel Austenitic Stainless Steels: Effects on Surface Integrity and Fatigue Limit

This study aims to evaluate the influence of lubrication and cooling conditions in the diamond burnishing (DB) process on the surface integrity and fatigue limit of chromium–nickel austenitic stainless steels (CNASSs) and, on this basis, identify a cost-effective and sustainable DB process. Evidence was presented that DB of CNASS performed without lubricating cooling liquid satisfies the requirements for a sustainable process: the three key sustainability dimensions (environmental, economic, and social) are satisfied, and the cost/quality ratio is favorable. DB was implemented with the same values of the main governing factors; however, four different lubrication and cooling conditions were applied: (1) flood lubrication (process F); (2) dry without cooling (process D); (3) dry with air cooling at a temperature of −19 °C (process A); and (4) dry with nitrogen cooling at a temperature of −31 °C (process N). Conditions A and N were realized via a device based on the principle of vortex tubes. All four DB processes provide mirror-finished surfaces with Ra roughness parameter values from 0.041 to 0.049 μm, zones with residual compressive stresses deeper than 0.5 mm, and increases in the specimens’ fatigue limit (as determined by the accelerated Locati’s method) compared to turning and polishing. Processes F and D produce the highest microhardness on the surface and at depth. The process D introduces maximum compressive residual axial and hoop stresses in the surface layer. The dry DB processes (D, A, and N) form a submicrocrystalline structure with high atomic density, which is most strongly developed under process D. When high fatigue strength is required, DB with air cooling should be chosen, as it provides a more favorable cost/quality ratio, whereas dry DB without cooling is the most suitable choice for applications that require increased wear resistance.

Analysis and evaluation of multi-state wear mechanism of elastic-flexible thin-walled bearings

EFTWBs (Elastic-flexible thin-walled bearings) are mainly used in harmonic reducers. Under the condition of large reduction ratio and cyclic rotation, LFW (linear fretting wear), CFW (curve fretting wear) and CRF (complete rolling friction) appear in the bearing raceway. In this study, LFW and CFW experiments were carried out, and the relationship between coefficient of friction and surface hardness was analyzed. Meanwhile, the multi-dimensional analysis (surface hardness, residual stress, surface/subsurface retained austenite) of the raceway surface integrity of EFTWBs after 8000 h of high service was analyzed. Combined with the manufacturing process of EFTWBs and the above conclusions, the multi-state wear mechanism of raceway was comprehensively evaluated. The evaluation conclusions show that the raceway of EFTWBs contained CRF (including pitting and spalling) and sliding fretting wear (including LFW and CFW). The axial and tangential residual stresses of the untested and tested outer and inner ring raceways were compressive stresses. Grain delamination appeared on the tested outer and inner ring raceway subsurface (20 µm from the surface). The wear of the outer ring raceway of EFTWBs was greater than that of the inner ring, and the wear was multiple. A 430 nm nanocrystalline layer was found under FIB-TEM on the surface layer of the outer ring raceway, and the fracture and obvious dislocation appeared. The rolling-sliding wear mechanism of EFTWBs raceway was comprehensively evaluated. The accuracy of this analysis was verified by combining thin-walled ring and Hertz theories. There are many detailed conclusions which provide theoretical support and data analysis for relevant manufacturers of harmonic reducer and robot EFTWBs.

Effect of single/multi-particle grinding parameters on surface properties of bearing steel GCr15

Grinding surface residual stress (RS) has an important influence on the service life of parts. In this study, the mathematical model of grinding force (GF) and grinding temperature (GT) of single particle was established. The relationship between grinding parameters, grinding force-thermal coupling and residual stress of single particle was analyzed by numerical simulation. Meanwhile, aiming at the multi-grain grinding of aviation precision high-speed bearing rings, the experimental analysis of crystal fragmentation, element content and residual stress of service and non-service bearing rings were carried out. Based on the above, the following results were obtained: in the simulation, the residual stress in the Y direction > the residual stress in the X direction > the residual stress in the Z direction at the same grinding force and grinding temperature. In the experiment, (1) The grain size of bearing raceway before service was about 24 μm, and the grain size of bearing raceway after service was about 3 times smaller than that before service. (2) C, Si, Cr and Fe decreased by 0.83 %, 0.07 %, 1.09 % and 32.75 % respectively after crushing (after service). On the contrary, it increased 0.66 % O and 34.08 % Pr. The Pr element was mainly distributed in the broken grain boundaries. (3) After service, the tangential residual compressive stress decreased by 169.3 MPa, while the axial residual stress increased by 172.6 MPa.

Pipeline Circumferential Cracking in Near-Neutral pH Environment Under the Influence of Residual Stress: Dormancy and Crack Initiation

The purpose of this study is to identify the integrity challenges encountered by buried pipeline steels, specifically to address Circumferential Near-Neutral pH Corrosion Fatigue (C-NNpH-CF). Damage to the pipeline’s protective coating and corrosion conditions increase the risk of service failures caused by C-NNpH-CF. (Note that this mechanism has previously been termed near-neutral pH stress corrosion cracking.) Unlike axial cracking, circumferential cracking is primarily influenced by residual stress from pipeline bending, geohazards, and girth welds. External corrosion pits often lead to dormant cracks, with growth ceasing around 1 mm depth due to reduced dissolution rates. Investigating the impact of bending residual stress (an appropriate source of axial residual stress) and cyclic loading (simulated pipeline pressure fluctuation), the study employs the digital image correlation (DIC) method for stress distribution analysis. Factors like applied loading, initial notch depth, and bending conditions influence crack initiation and recovery from the dormancy stage by affecting stress distribution, stress cells, and stress concentration. Cross-sectional and fractographic images reveal time/stress-dependent mechanisms governing crack initiation, including dissolution rate and hydrogen-enhanced corrosion fatigue. The study emphasizes the role of various residual stress types and their interactions with axial cyclic loading in determining the threshold conditions for crack initiation.

Semi-destructive methods for evaluating the micro-scale residual stresses of carbon fiber reinforced polymers

Micro-scale residual stress in carbon fiber reinforced polymers have a significant impact on their mechanical performance. The residual stresses in the carbon fibers were released by micro-slotting and micro-ring-core methods using focused ion beam (FIB). The released deformation fields were captured by cross-gratings and mapped by geometric phase analysis (GPA) and digital image correlation (DIC) methods. The in-plane residual stresses in the carbon fibers were experimentally determined to be −40.5 MPa using elastic constitutive relations, which is consistent with the composites cylinder model. The axial compressive residual stresses in the fibers were found to be greater than −100 MPa. Moreover, the maximum value of residual stress in the polymer matrix was observed at the interface, potentially serving as a crack initiation site.

Stress engineering of SiCf/SiC composites: Interfacial stress adjustment and its effects on tensile behaviors of UD SiCf/SiC composites fabricated by hybrid CVI and PIP methods

Internal stress is usually generated during the preparation of the SiCf/SiC composites and is generally considered to be uncontrollable and detrimental to SiCf/SiC composite's mechanical properties. However, in this study, internal stress is proposed for the first time as a tool to regulate the interfacial bonding properties of the SiCf/SiC composites. And the interfacial compressive stress was successfully controlled by hybrid CVI and PIP methods. The results of Raman analysis show that the interfacial compressive stress increases with the increase of the PIP SiC content. The interfacial shear strength (τi) and interfacial dynamic friction strength (τf) was determined by micro-shear tests. Both τi and τf increase with the increase of interfacial compressive stress. With different interfacial bonding strength, the SiCf/SiC composites show different tensile behaviors. A high τi can lead to a high tensile modulus and proportional limit stress (PLS) and a high τf can lead to the disappearance of the second linear stage and low fracture strain. The axial residual stress of matrix also was tested, and the results indicate that it does not have a dominant influence on the mechanical properties. Finally, the SiCf/SiC composites achieve the superhigh PLS of 729.8 ± 9.2 MPa and modulus of 288.0 ± 7.9 GPa when the BN thickness is 100 nm and the interfacial compressive stress is 1127.7 MPa. This strategy of interfacial stress engineering may provide a new and valuable design idea for improving the mechanical properties of the SiCf/SiC composite and other composites. This strategy is also of great significance for broadening the design criteria and enriching the preparation methods and internal stress regulation methods of high-performance composites.

Evolution and formation mechanism of residual stress in Al-Cu alloy rings during ring rolling and quenching

The large-scale ring components, as thin-walled structures, are prone to unpredictable machining deformation due to the initial residual stresses introduced by rolling and quenching, which seriously affect the dimensional accuracy and service life of the ring components. Therefore, the relief and homogenization of residual stress inside large-scale ring components is crucial. However, the existing studies rarely involve the essential causes and the evolution laws of residual stresses during the manufacturing of ring components, which are indispensable for understanding the failure mechanisms of components caused by residual stresses and specifying relevant protective measures. Therefore, the evolution and distribution laws of stress-microstructure-property non-uniformity during the hot forming (ring rolling) and heat treatment (quenching) of 2219 Al-Cu alloy rings were precisely and deeply explored using scaled experiments in this paper. The relationship between non-uniform deformation and residual stresses was analyzed, and the basic equation that residual stresses must satisfy was established. Furthermore, the concept of the “non-coordination coefficient” was proposed, revealing the physical mechanism of residual stresses induced by non-uniform deformation. In addition, the influencing factors and formation mechanisms of residual stresses in the rolled and quenched state of rings were studied, and the essential reasons for the differences in residual stresses between the rolling and quenching processes were obtained. The experimental results indicate that the circumferential and axial residual stresses increased from 1.48 and 0.51 MPa to −142.68 and −122.31 MPa, respectively. The standard deviation changed from 13.47 and 33.52 MPa to 63.42 and 61.61 MPa, respectively. The maximum range of tensile strength, yield strength and elongation rates of the rolling and quenched state is 12.82 and 20.16 MPa, 17.49 and 22.14 MPa, and 8.62 % and 7.56 %, respectively. All fractures are microporous aggregation ductile, including dimple transgranular fracture and intergranular fracture. The quenched state exhibits a significantly larger grain size compared to the rolled state. The appearance of residual stress is essentially to force the inconsistent deformation of various parts inside the object to maintain its integrity and continuity, which leads to a local mismatch of micro-elements inside the ring and further induces non-uniform strain and stress. The difference in the severity of “penetrability” induced by different temperature gradients determines the difference in residual stress between rolled and quenched rings, larger rings have higher and more non-uniform residual stress than smaller rings under the same process conditions. The above results deepen the theoretical understanding of residual stress formation mechanisms and lay a theoretical foundation for the comprehensive evaluation of performance degradation and service failure analysis of large ring components.

Cryogenics performance enhancement of epoxy resin composites through negative expansion nanomaterials: Mechanism and predictive modeling

AbstractThe matrix cracking of carbon fiber reinforced epoxy resin based composites (CFRPs) at cryogenics (such as liquid nitrogen temperature) is a major issue affecting the normal operation of deep space and deep‐sea detectors, as microcracks caused by the thermal residual stress of both can reduce the structural integrity of the devices. In this work, we report an epoxy (EP) nanofiller CuO nanorods (CuO NRs) with negative thermal expansion properties at cryogenics. Experiments showed that CuO NRs can effectively inhibit the shrinkage of EP at cryogenics and improve the mechanical properties of EP at cryogenics. A temperature dependent prediction model for the tensile strength of EP/CuO NRs was proposed, and the predicted results were in good agreement with experimental results. Finally, through a combination of experiments and theory, it was demonstrated that the tensile strength of EP/CuO NRs at cryogenics is jointly enhanced by the enhancement effect of the nanomaterials and the axial compressive thermal residual stress between EP and CuO NRs.Highlights Successfully prepared CuO nanorods with negative expansion properties at low temperatures, and found that they can effectively inhibit the shrinkage of epoxy resin at cryogenics. At cryogenics, the expansion of CuO nanorods enhances their interface effect with epoxy resin and improves the tensile strength of epoxy resin composites. The theory of tensile strength of epoxy resin at cryogenics was proposed for the first time. Theoretical analysis shows that the low temperature residual thermal stress between CuO nanorods and epoxy resin is the main factor to improve its tensile strength.

Effect of Process Parameters on Welding Residual Stress of 316L Stainless Steel Pipe.

316L stainless steel pipes are widely used in the storage and transportation of low-temperature media due to their excellent low-temperature mechanical properties and corrosion resistance. However, due to their low thermal conductivity and large coefficient of linear expansion, they often lead to significant welding residual tensile stress and thermal cracks in the weld seam. This also poses many challenges for their secure and reliable applications. In order to effectively control the crack defects caused by stress concentration near the heat-affected zone of the weld, this paper establishes a thermal elastoplastic three-dimensional finite element (FE) model, constructs a welding heat source, and simulates and studies the influence of process parameters on the residual stress around the pipeline circumference and axial direction in the heat-affected zone. Comparison and verification were conducted using simulation and experimental methods, respectively, proving the rationality of the finite element model establishment. The axial and circumferential residual stress distribution obtained by the simulation method did not have an average deviation of more than 30 MPa from the numerical values obtained by the experimental method. This study also considers the effects of welding energy, welding speed, and welding start position on the pipe's circumferential and axial residual stress laws. The results indicate that changes in welding energy and welding speed have almost no effect on the longitudinal residual stress but have a more significant effect on the transverse residual stress. The maximum transverse residual stress is reached at a welding energy of 1007.4~859.3 J/mm and a welding speed of 6.6 mm/s. Various interlayer arc-striking deflection angles can impact the cyclic phase angle of the transverse residual stress distribution in the seam center, but they do not alter its cyclic pattern. They do influence the amplitude and distribution of the longitudinal residual stress along the circumference. The residual stress distribution on the surface of the pipe fitting is homogenized and improved at 120°.

Comparison of the effects of induction heating composite shot peening and conventional shot peening on residual stress, microhardness, and microstructure of 20CrMnTi gear steel

As a commonly used surface strengthening technology, shot peening, which can significantly improve the fatigue strength of mechanical parts, is widely used in the fields of vehicles and aviation. To obtain a larger residual compressive stress and further refine the grain size under normal shot peening intensity and coverage, this study proposes an induction heating composite shot peening (IHCSP) surface strengthening method, aiming to utilize the coupling effect of temperature and stress fields to promote the shot peening strengthening effect. An IHCSP test plan was designed and an IHCSP test bench was created to achieve simultaneous induction heating and shot peening. This study compares the surface integrity parameters and microstructures under three processes: un-peened, conventional shot peening, and IHCSP. The results show that the maximum axial and radial compressive residual stresses increase by 72.41 and 75.4 MPa respectively; the depth of the hardened layer increases by 0.3 mm, the martensitic transformation more complete, the grain size decreases by 483 nm, the dislocation density increases significantly, and nanocrystals are obtained on the surface of the material. These results verify the superiority of IHCSP surface strengthening.

Distribution and Characteristics of Residual Stresses in Super Duplex Stainless Steel Pipe Weld

This paper explores the distribution and features of residual stresses formed by super duplex stainless steel pipe welding. Experimental investigations, which encompass an elevated temperature tensile test and metallographic observation along with a hardness test and residual stress measurement, were first conducted to obtain the mechanical properties at high base metal temperatures and to confirm whether or not the duplex stainless steel undergoes martensitic phase development during the welding process. Finally, experiments were performed to scrutinize the residual stress evolution through the metallurgical phase transformation in the weld region and its vicinity. A sequentially coupled 3D thermal, mechanical and metallurgical finite element (FE) model capable of incorporating the experimental consequences was established next. A 3D FE simulation of the girth welding process was conducted, and the axial and hoop residual stress profiles along the girth were evaluated. The results substantiate that martensitic phase evolution occurs in the process of cooling during the welding of super duplex stainless steel, and they also highlight the significance of taking the metallurgical phase transformation into account in the numerical reproduction of the girth welding process for the accurate expression of weld-induced residual stresses, which is especially important for precisely predicting hoop residual stresses.

Influence of surface integrity on the fatigue performance of TiB2/Al composite treated by ultrasonic deep rolling: Experiments and simulations

The influences of surface integrity on the fatigue performance of in-situ 6 wt% TiB2/2024Al composite treated by ultrasonic deep rolling (UDR) were comprehensively investigated with both experiments and simulations. Results reveal that only a single pass of UDR treatment can impressively reduce the surface roughness of the fine-turned specimens by 94 %. Moreover, axial compressive residual stress (RSc) larger than −400 MPa and strain hardening (SH) higher than 50 % were obtained on the surface. The comprehensive effect of these surface integrity improvements has enhanced the fatigue limit by 22 %, extended the fatigue life by 10∼20 times, and expanded the safe region in the Goodman-Haigh graph by 14.6 %. More importantly, UDR significantly dispersed the TiB2-particle aggregates in the composite surface, which provided the possibility of improving the surface comprehensive mechanical properties of particles reinforced metal matrix composites (PRMMCs) through a simple and convenient mechanical way.

Research on analyzing and valuing residual stress for micro wire busbar

The electroplated diamond wire saw made from high-carbon steel wire busbar (busbar), which directly affects the quality of cutting monocrystalline silicon, polysilicon, sapphire and SiC. When the wire diameter is on the micro-scale, there is no equipment to precisely measure the distribution of residual stress at present. The free circle diameter (FC-diameter) is used as the quality index to measure the distribution of axial residual stress of the busbar post-drawing. The existing finite element simulation of residual stress of steel wire post-drawing is mainly aimed at steel wire diameter of millimeter, and most of it is two-dimensional finite element simulation. The effect of actual factors on residual stress of the busbar is not considered in the simulation. In this paper, finite element simulation is carried out for steel wire with diameter in micron scale. The influences of die deflection, die friction coefficient, die sizing band ellipse and steel wire ellipse on axial residual stress is considered. The relationship between residual stress distribution and FC-diameter is established, and the correctness of simulation results is verified by experiments.

Effect of fiber roughness on interfacial friction of fiber reinforced ceramic matrix composites

Interfacial friction plays a crucial role on mechanical behaviors of fiber reinforced ceramic matrix composites (FRCMCs), such as matrix cracking, damage evolution, and fracture, and the fiber surface roughness has been shown to enhance the interface friction. However, the influence of interphase thickness and residual stress on the friction enhancement of fiber roughness was neglected in previous works. Therefore, in this paper a thoroughly theoretical model is established and the additional radial stress is derived to intuitively reflect the contribution of fiber roughness to the interfacial friction. The results indicate that the interfacial friction can usually be enhanced by increasing the fiber roughness and reducing the interphase thickness, which however is severely overestimated by more than 5 times by the previous models. Moreover, the residual stress and fiber axial stress have a nonnegligible effect on the contribution of fiber roughness. For a given fiber axial stress, the residual stress that is too large or too small will weaken or even eliminate the contribution of fiber roughness, and only when the residual stress is within a proper range, can the fiber roughness play an effective role. On the other hand, for a given target load and ambient temperature, a critical fiber roughness that can enhance the interfacial friction is analytically derived. This work can provide valuable insights into the design of fiber roughness and interphase thickness for FRCMCs.

Numerical Simulation of the Effect of Fusion Welding Processes on Residual Stress in Stainless Steel Pipe Weld Joints Used in Fast Reactors

The main structural material used in the building of Fast Breeder Reactors (FBR) is stainless steel of type 316L(N). Finite Element Model (FEM)-based simulations were carried out to understand the effect of various welding processes on the residual stresses induced in 316L(N) stainless steel primary sodium-carrying pipes with an inner diameter of 208 mm and a wall thickness of 5.6 mm. The welding processes considered include multi-pass Tungsten Inert Gas (TIG) welding, A-TIG, laser, hybrid laser-TIG, and Hybrid laser-Metal Inert Gas (MIG). First, single or hybrid heat sources are chosen based on the welding process, and then weld bead profiles obtained during simulation are made to match with that of the actual weld bead profiles obtained during experiments. Then, the optimised heat source is employed for the thermal analysis. The thermal analysis output is then successively linked and provided as input to the mechanical analysis, which uses an isotropic hardening model to predict hoop and axial residual stresses in pipe weld joints. The results show that the A-TIG weld joint exhibited lower hoop stress (165 MPa at inner diameter and -2 MPa at outer diameter) in comparison with that of the other weld joints. The lower residual stress is attributed due to the straight-sided weld bead, lower peak temperature, and slower cooling rate of the A-TIG welding. Therefore, A-TIG welding is recommended among the chosen fusion welding processes for welding of 316L(N) stainless steel primary sodium carrying pipes to minimise the residual stresses and mitigate the premature failure of the pipe weld joints.

Preparation of ZnO Piezoelectric Thin-Film Material for Ultrasonic Transducers Applied in Bolt Stress Measurement

The measurement of bolt preload by using ultrasound can be accurate, convenient, and can realize the real-time monitoring of the change in the residual axial stress of a bolt during use. In order to realize the ultrasonic measurement of bolt preload, the use of zinc oxide (ZnO) piezoelectric thin-film material as an ultrasonic transducer material to stimulate an ultrasonic signal on the bolt is a feasible solution. In this paper, we choose to use RF magnetron sputtering technology to prepare ZnO piezoelectric thin-film materials and study the effects of sputtering power and target substrate distance on the structure and ultrasonic properties of ZnO piezoelectric thin films during the preparation process, in order to lay the foundation for realizing the application of ZnO piezoelectric thin films in the field of bolt preload measurement. The experimental results show that too-large sputtering power or too-small target substrate distance will result in the particles having too much kinetic energy during sputtering and exhibiting a structure of multiorientation growth, which excites ultrasonic longitudinal–transverse waves. A sputtering power of 600 W, sputtering time of 4 h, and target substrate distance of 100 mm are ideal experimental parameters for a ZnO piezoelectric thin-film material to be excited by an ultrasonic longitudinal wave signal, and its ideal operating frequency is 41 MHZ. These research results of bolt stress detection demonstrate good application prospects.

Modeling and Optimization of Surface Integrity and Sliding Wear Resistance of Diamond-Burnished Holes in Austenitic Stainless Steel Cylinder Lines

This article outlines a technology for hole-finishing in short-length cylinder lines to improve wear resistance. The technology is based on an optimized diamond-burnishing (DB) process. The latter was implemented on conventional and CNC lathes, milling machines, and machining centers using a simple burnishing device with an elastic beam. The material used in this study was AISI 321 austenitic stainless steel. The governing factors used were the radius of the diamond insert, burnishing force and feed rate. The objective functions relating to surface integrity characteristics were selected on the basis of their functional importance relative to the wear resistance of the processed hole surface: height and shape roughness parameters, surface microhardness, and surface residual axial and hoop stresses. The one-factor-at-a-time method (used to reduce the factor space), a planned experiment, and regression analyses were used. The multi-objective optimization tasks, which were defined for three diamond insert radius values of 2, 3, and 4 mm, were solved via the Pareto-optimal solutions approach available for a non-dominated sorting genetic algorithm (NSGA-II). Using the optimal values of the governing factors selected from the Pareto fronts, cylinder lines were processed. Samples were then cut from these cylinder lines for reciprocating sliding wear tests under two modes: dry friction and boundary lubrication friction. Additionally, wear test samples were cut from the cylinder line, which was finished with traditional grinding. A finite element simulation was then used to select an appropriate pressing force. The results obtained from the reciprocating sliding wear tests under both the dry and boundary lubrication friction regimes show that to minimize the wear on cylinder lines made of AISI 321 steel, DB with a diamond insert of radius 2 mm is the optimal finishing process.

In-plane thermal expansion behavior of M55J carbon fiber reinforced SiC matrix composite

With the rapid development of high-precision ultra-stable spacecraft, the absolute values of coefficients of thermal expansion (CTE) of carbon fiber reinforced SiC matrix composite (C/SiC) are required to be closer to 10−7 K−1 or even lower. In this work, high-modulus and low-expansion M55J carbon fiber was selected to replace T300 carbon fiber as the reinforcement to decrease the CTE of C/SiC. The interfacial region, pore distribution and microstructure evolution during the densification process were investigated. With the replacement of T300 carbon fiber by M55J carbon fiber as the reinforcement, axial thermal residual stress in SiC matrix can increase to 378 ± 26 MPa, resulting in the generation of matrix microcracks. This can reduce the constraint of matrix to carbon fiber and provide expansion space for M55J-C/SiC. Therefore, the average in-plane technical CTE of C/SiC in the range of −20 to 50 °C can be reduced from 1.09 × 10−6 to 0.34 × 10−6 K−1.

Thermally Assisted Rotational Autofrettage of Long Cylinders With Free Ends

Abstract Autofrettage is a widely employed process for strengthening cylindrical or spherical pressure vessels. The process involves applying a uniform load to the inner wall of a vessel to cause a controlled plastic deformation, where the vessel yields starting from the inner wall up to an intermediate radius. When the load is removed, elastic recovery takes place and compressive residual stresses are induced in the vicinity of the inner wall, which strengthen the vessel against high static and pulsating loads during service. Based on the load employed, autofrettage can be of five types—hydraulic, swage, explosive, thermal, and rotational. This work analyzes a rotational autofrettage augmented by a thermal load where the load is applied by rotating the cylinder about its axis while maintaining a temperature gradient across the wall. The combined centrifugal and thermally induced stresses cause plastic deformation in the cylinder. When the cylinder is unloaded by bringing it to rest and cooling down to room temperature, compressive hoop residual stresses are introduced in the vicinity of the inner wall. A finite element method model of the proposed thermally assisted rotational autofrettage is developed for a cylinder made of AH36 mild steel in a commercial package ABAQUS®. The results indicate that the thermal load reduces the rotational speed required for autofrettage, when compared to a conventional pure rotational autofrettage. The thermal load also mitigates the tensile axial residual stresses, which are typical in a purely rotational autofrettage. A conceptual design of the experimental setup is also presented.

The Residual Stress Control of Thin-walled Sleeve Parts with Weak Rigidity

Photoelectric products in the military industry tend to be lightweight in design, requiring the part to be lightweight and have high specific strength. As one of the structural parts of photoelectric products, the thin-walled sleeve part has the peculiarity of lightweight and thin wall thickness. Nevertheless, the residual stress during machining processing poses an adverse effect on the accuracy of the parts. In this paper, the influence of residual stress on the accuracy of the parts during the processing was studied. Before fine machining, the residual stress was reduced by artificial aging techniques and ultrasonic beam control methods. Finally, the effect of the two stress relief methods was evaluated according to the qualified rate of the processing accuracy of the parts. The research results show that the axial residual stress of the part is larger than the circumferential residual stress. Both artificial aging techniques and ultrasonic beam control can eliminate residual stress, and the ultrasonic beam control method is more targeted and uniform.