This study presents an enhanced cumulative damage model derived from the classical Manson–Halford (M–H) model. Through theoretical analysis, this study examines the advantages of the enhanced model regarding load sequence and interaction effects, validating its practical effectiveness through case studies. The findings reveal that the enhanced model characterizes the cumulative damage process under complex loading conditions more accurately. It also improves computational precision, especially when considering load sequence and interaction effects. Compared to the conventional M–H model and other improved models proposed in the literature, the enhanced model developed in this study demonstrates superior reliability in predicting fatigue life and damage accumulation, thereby providing a more robust theoretical basis for fatigue life assessment in engineering applications. The findings of this study provide novel insights into cumulative damage theory and present significant potential for engineering applications.

In this work, refill friction stir spot welding (RFSSW) was used to join dissimilar 6063/2060 Al alloys for skin-stringer applications. The effect of tool plunging speed on the microstructure and mechanical properties of the joints was studied. Results show that all the hooks in the joints show flat morphologies, but they are still the failure crack initiation points of the joints. A large plunging speed of 115 mm/min causes incomplete refilling in the joint. Compared with the 6063 Al alloy, the 2060 Al alloy has coarser grains in the base material but finer grains in the stir zone. The stir zone has higher hardness when using higher plunging speed due to slight softness. Increasing the plunging speed slightly decreased the joint lap shear failure load. The maximum failure load of 8.53 kN is obtained when the tool plunging speed of 40 mm/min is used.

How to obtain a high-strength and corrosion resistance of Al/Sn/Al joint has been a longstanding goal for electronics industry. In this work, 6063Al was joined in the air by ultrasonic-assisted liquid phase diffusion bonding using a Sn filler metal. It was performed by applying an uninterrupted ultrasonic vibration at a heating temperature of 360 ℃, final obtaining a 6063Al joint without enriched-Sn. Under the action of ultrasonic vibrating, the breaking of oxide film, the diffusing of Sn and dissolving of Al alloy occurred in sequence. It resulted in a transition of bonding interface from Sn/Al to an α-Al/α-Al bonding interface embedded a few Mg2Sn partials, after depleting Sn by grain boundary diffusion. The joints possessed a high strength coefficient of 89.9% of 6063Al base metal and 161.8% of soldering joint. The joint had a better corrosion resistance that the tensile strength only reduced 35.3% after a corroding of 72h in 3.5wt% NaCl solution in comparison with the soldering joints. Finally, the evolution of the interface structure and mechanism of improving corrosion resistance were discussed in detail. It is a promising technology for manufacturing high-reliable Al/Sn heterogeneous joints.

Experimental and numerical investigations on the small-size butt-welded plates subjected to air blast loads were conducted to highlight the effect of welded joints on the blast proof structures. The inherent characteristics of welded joints, including geometry, mechanical properties and welding residual stress were evaluated and discussed in the computation of blast loading. The geometry shape was assessed through macrographic of the welded joints. The distribution of mechanical and thermal physics property was determined through basic experiments using the specimens extracted from different zones of a welded joint. Welding residual stress was calculated in a thermo-mechanical coupled model. Conventional Weapons Effects Program (CONWEP) is more economic but limited compared with Arbitrary-Lagrangian-Eulerian (ALE) method. ALE and CONWEP methods were applied to simulate the air blast load applied on the plates. Effectiveness and efficiency of the methods were discussed. The results of the two programs could both coincide well with the experiment measurements. The models under six conditions were calculated to uncouple and discuss the effect of material property distribution and welding residual stress on the dynamic response of the welded structure. Permanent deflections were considered to assess the capacity of welded structures. Welding residual stress fields and the local weak materials are advantageous to the bending deformation. The phenomenological expressions of permanent deflection across thickness under different welding conditions were established based on simulation results. The effect of aspect ratio of the welded structures was also be discussed.

High corrosion-resistance aluminum alloy joint obtained by filler metal containing Sn at relatively low temperatures is a longstanding goal for electronic products. In this research, 6063Al alloys was joined by a novel ultrasonic-assisted diffusion bonding via liquid phase and solid phase synergistic diffusion. It was performed via a hypereutectic interlayer of Zn-30Sn at 360 ℃ to joining 6063Al, obtaining a Zn-Al eutectoid structures joint. By the ultrasonic vibrating, the breaking of oxide film, the diffusing of liquid and solid state had been occurring in sequence during the joining process. It resulted in a series of diffusing phase transitions from “η-Zn phases + Sn-Zn eutectic structures” to “Zn-Al eutectoid structures + η-Zn phases”, and finally to “full Zn-Al eutectoid structures”, which were driven by the grain boundary penetration and chemical potential, respectively. The joints possessed a higher strength than the base metal. The joints with Zn-Al eutectoids have a better corrosion resistance that the tensile strength reduced 37.3% after a corroding of 72h in 3.5wt% NaCl solution in comparison with the soldered joints. Finally, the mechanism of ultrasonic accelerated diffusion, joint formation process and mechanism of improving corrosion resistance were discussed in detail.

介绍了船体结构中含缺陷的焊接接头完整性评估以及疲劳寿命预测方法,对结构完整性评估的K准则、COD准则、J积分准则、SINTAP/FITNET安全性评定方法以及评定流程、国内外标准进行介绍.并对焊接接头的疲劳强度影响因素,如平均应力、残余应力以及接头几何形状应力集中等进行了分析;介绍了焊接接头疲劳寿命预测的常用方法,如基于名义应力的评估方法、基于断裂力学的评估方法、基于损伤力学的评估方法以及其它疲劳评估方法等.此外,还对基于断裂力学法建立的焊接残余应力与疲劳裂纹扩展寿命之间的函数关系进行了介绍,该方法实现了对含残余应力的焊接结构疲劳寿命的精确预测.

Hook is a typical defect of lap joint. It can induce stress concentration and is detrimental to joint strength. Thus, hook should be eliminated. In this work, by using the vertical squeezing force of the plastic material near the lap interface, we have successfully eliminated the hook by a double-size friction stir welding process. The results show that the double-side welding method can eliminate the hook in a wide parameter range. The rotating speeds ranging from 800 to 2000 rpm can effectively depress the bending of the lap interface, thereby eliminating the hook. The joint shows high strengths after the hook is eliminated. The maximum failure load of 15.195 kN is obtained when using the rotating speed of 1200 rpm. The joints show shear fracture mode when using rotating speed lower than 1200 rpm, and tensile fracture when the rotating speed is higher than 1600 rpm.

In this work, ultrasonic-assisted transient liquid bonding (UATLP) was used to rapidly join dissimilar Al/Mg alloys in the air. The pure Zn interlayer was chosen to prevent Al-Mg intermetallic compounds (IMCs). The effects of the bonding time on the microstructure and mechanical properties of the joints were studied. The joint formation mechanism was analyzed. Results show that the Al-Mg IMCs can be avoided when the ultrasonic time was shorter than 3 s. The oxide layer on the Al substrate was incompletely removed when the ultrasonic time was shorter than 2 s, and the joint was characterized by Mg-Zn eutectic, MgZn, and MgZn2 from the Mg side to the Al side. The joint had a shear strength of 16 MPa and failed through the MgZn2/Al interface under such condition. The oxide layer on the Al substrate was removed when the ultrasonic time was increased to 3 s. The joint had a shear strength of 24 MPa, and it failed through the MgZn2 layer and the Mg-Zn eutectic. The entire Zn foil interacted with the Mg and Al substrate at a prolonged ultrasonic time of 6 s. Al-Mg IMCs of Al3Mg2 and Al12Mg17 appeared because a large amount of Al and Mg atoms diffused into the joint. The joint strength decreased to 11 MPa and failed through the Al3Mg2 layer.

The aim of this paper is to clarify how and to what extent varied welding residual stresses (WRSes) affect the plane stress plasticity induced crack closure (PICC) simulation. A well-characterized, representative WRS field with tensile and compressive reversals was imported and the predicted PICC results were evaluated against the relevant WRS-free ones. It turned out that instead of WRS typically reported in the literature, there is actually a Kres (stress intensity factor resulting from residual stresses) controlled crack closure mechanism when investigating the PICC behavior in the presence of a WRS field, i.e., WRS influences PICC in the form of Kres. Four major categories where the crack tip was located in different Kres zones were defined using MT (middle tension) and SENT (single edge notch tension) specimens to investigate the mechanism in detail. In summary, the Kres value determined the general steady-state PICC level in the WRS field, i.e., a diminished steady-state opening stress level was predicted in the WRS field with a positive Kres regardless of whether the crack is located in a tensile or a compressive WRS zone, and an elevated value was estimated when the Kres was negative. Besides, the initial transient period was scrutinized that occurred in some WRS scenarios and the concept of primary and secondary plastic wake evolution was proposed to explain its formation. It was found that the transient behavior could be eradicated by tailoring the secondary plastic wake employing appropriate constitutive models and mesh refinement levels. The results attained in the present work provide some guidelines for the WRS-PICC modeling and simulation in the fracture mechanics community.

搅拌摩擦焊焊后残留的匙孔会极大地降低焊缝力学性能,对其进行修复具有重要的工程意义.以AZ31B镁合金为对象,对比研究了超声加入对被动填充搅拌摩擦修复工艺的影响.结果表明:与未加入超声相比,超声可以减小飞边、促进材料流动、增加原子扩散能力,进而获得无缺陷的修复接头;采用超声辅助被动填充搅拌摩擦修复工艺的修复接头抗拉强度达到182.9MPa;与未加入超声的工艺相比,修复接头拉伸强度提高38％.同时,超声辅助被动填充搅拌摩擦修复接头的断口形貌有大量韧窝,为典型的韧性断裂.

In this study, TC4 alloys were brazed with ultrasonic assistance in air using pure Zn filler. The effect of ultrasonic power on the microstructure and mechanical properties of brazed joints was studied. The results show that the wetting of pure Zn filler on TC4 alloy is characterized by the formation of a TiZn3 intermetallic compound (IMC). The low ultrasonic powder of Mode I results in incomplete wetting of the substrate. Increasing the ultrasonic power changes spot wetting to surface wetting. A continuous TiZn3 IMC layer with cracks is observed when the ultrasonic powder is increased to Mode III. The grains of the filler inside the joint are refined from 5.54 µm to 4.00 µm when the ultrasonic power increases from Mode I to III. The shear strength of the brazed joint first increases and then decreases with an increase in the ultrasonic power. A maximum shear strength of 73.07 MPa is achieved when the ultrasonic power is in Mode II. The low joint strength at a high ultrasonic power is attributed to the cracks inside the TiZn3 IMC layer.

在铝/钢异种材料的搅拌摩擦搭接焊中,存在着连续分布的界面金属间化合物层,阻碍了元素的扩散与界面冶金结合,严重制约了接头力学性能的进一步提升.以6061铝合金和301L钢为研究对象,在搅拌摩擦搭接过程中施加下置式的超声振动以提高界面铝侧材料的强塑性流变,从而抑制金属间化合物的过度生长,提升接头强度.研究表明,施加超声激励后,铝/钢FSLW接头搭接界面连续金属间化合物层平均厚度由10 μm减薄到6 μm.同时,搭接接头的抗拉载荷提升27.9％.

The paper investigates the Welding Residual Stresses (WRS) of 10CrNi3MoV high strength steel multipass butt welded joints by experimental measurement and numerical calculation considering the effects of weld metal strength mismatch and back-chipping processing. Firstly, a thermo-metallurgical-mechanical simulation model was developed incorporating the Effect of Solid-State Phase Transformation (SSPT) to obtain multipass welding residual stress distributions after the back-chipping processing for evenmatched filler material. Phase trans-formation modeling of diffusionless transformation kinetics based on the Koistinen-Marburger formula was performed by a user subroutine implemented in ABAQUS. Additionally, strain transformation calculation due to volumetric and heating change during the SSPT was completed by the user-defined subroutine. Then, the effects of weldment mismatch and back-chipping processing on WRS for the multipass welds were analyzed. Comparing the calculated residual stress results (with and without consideration of SSPT) with experimental data shows that more accurate WRS predictions are obtained when the SSPT effect is incorporated in the simulation procedure. For evenmatched welded joints, the compressive WRS were distributed in the top and back weld layer due to the involvement of SSPT behavior. While the considerable tensile WRS in undermatched weldments was obtained without considering the SSPT, the magnitudes were lower than those in Heat Affected Zone (HAZ). The proposed finite element model can predict the WRS of high-strength steel multipass welded joints and provide a theoretical basis for conducting the structural integrity assessment.

To avoid substrate softness, AA7075 were rapidly soldered using a Sn-9Zn solder at 200 degrees C under ultrasonication. The effect of acoustic intensity on the microstructure and mechanical properties of the soldered joint was studied. The acoustic intensity inside the solder was improved by decreasing the lap width without increasing the input ultrasonic power. Results showed that the softness of the substrate was almost avoided with minimal hardness decrease. The acoustic intensity increased by four times when the width of the lap clearance was reduced from 0.8 mm to 0.2 mm. Pronounced erosion of the substrate occurred under high acoustic intensity. Thus, the content of Al in the joint seam increased from 3.35% to 10.84% after reducing the lap width from 0.8 mm to 0.2 mm. The joint seam was characterized by interlaced fine/coarse Sn-Zn eutectic. The Sn and Zn grains had average sizes of 2.31 and 0.31 mu m in the fine eutectic and 3.03 and 0.41 mu m in the coarse eutectic. Increasing the acoustic intensity during soldering can effectively increase joint strength. The maximum shear strength of 65.4 MPa and hardness of 29.5 HV were obtained in the joint soldered at 0.2 mm. The cavitation bubble with a nucleation diameter of 10 mu m had a large liquid velocity of 7653 m/s, a temperature over 1800 K, and a pressure of 4 x 10(12) Pa during its collapse.

Welding of steel is a technique frequently used in practical engineering applications; however, their mechanical performance is strongly dependent on the physical metallurgical status of the weldments. In the present study, fully reversed, strain-controlled low-cycle fatigue (LCF) tests were conducted on 10CrNi3MoV steel and its undermatched weldments with strain amplitudes varying from Δ ε = ±0.5 to ±1.2%. Both base metal and weldments exhibited softening behavior at the beginning of the cyclic stage. Numerical investigations of cyclic stress–strain evolutions of the materials have been studied by the cyclic plastic model considering nonlinear hardening. The continuous damage mechanics (CDM) theory based on the experimental hysteresis stress–strain energy concept was employed to illustrate LCF failure, including damage initiation and deterioration. The damage mechanics approach calibrates the material parameters from the measured fatigue life for initiation and growth stages. Afterward, the combination of material cyclic plastic parameters and damage parameters was implemented to predict the LCF life. Good agreement can be observed between the experimental results and the FE results based on the CDM approach. Finally, the damage evolution of the materials under different strain amplitudes by this approach was assessed.

This study examines the Low and High Cycle Fatigue failure (LCF and HCF) of Load-carrying Cruciform Welded Joints (LCWJ) made of 10CrNi3MoV steel through a combined investigation of experimental, simulation, and analytical methods. LCF and HCF tests were conducted on LCWJ specimens with various weldment strength matching conditions and geometric configurations. Different fatigue failure modes can be observed from potential fracture points due to the discrepancy of strength and geometry in weldments, which exhibits the discrepancy of fatigue life. New uniform energy analytical formulations for Weld Toe (WT) and Weld Root (WR) are established to predict the LCF and HCF indicator of LCWJ considering the plasticity and mechanical heterogeneity effects of the weldments based on the generalized Neuber concept of Fictitious Notch Rounding (FNR). Furthermore, an effective notch energy indicator is introduced and implemented to evaluate fatigue behaviors of welded components in both LCF and HCF regimes. According to the proposed analytical solutions, experimental data from WT and WR failure under force and displacement-controlled cyclic loadings are evaluated and verified. The results show that the notch-energy indicator can express the unique relationship with fatigue life regardless of the strength mismatch ratios and geometry discrepancy.

AZ31B magnesium alloy is the experimental material in this study. Considering its anisotropy, fatigue assessment based on self-heating is carried out for both the extrusion direction and the transverse direction. The self-heating behavior in the two orientations is compared. Similar to steels, an obvious inflection point that corresponds to the fatigue limit can be found in the self-heating vs. load curve for AZ31B. A new fatigue limit assessment method is proposed based on a statistical analysis of self-heating data. This method can provide a satisfactory assessment of the fatigue limit for AZ31B in the both orientations.

The slope method is a popular energy dissipation estimation method, which ignores the influence of heat exchange. Within the framework of the zero-dimensional thermal diffusion model, this paper presents a calculation method for evaluating the energy dissipation of materials in the initial stage of fatigue, which can be called the optimization method. Different from the slope method, this method takes the influence of thermal boundary conditions into consideration. Numerical simulation showed that the optimization method has the ability to accurately estimate energy dissipation in different experimental environments and is not sensitive to measurement noise. Compared with the popular slope method, the newly proposed optimization method has certain advantages in adaptability to different environments and flexibility in parameter selection. A case study was also carried out to study a high-cycle fatigue life of an aluminum alloy which demonstrated that results predicted by the proposed method matched the experimental data in the range of short fatigue life.

This study mainly investigates the Fatigue Crack Growth Rate (FCGR) of 10CrNi3MoV high strength steel and its welded joints used in modern marine environment considering the stress ratio and strength mismatch. To reflect the strength mismatch of weldment, two kinds of weld filler material are selected to obtain Even-Matched (EM) and Under-Matched (UM) marine Ni-Cr-Mo-V steel welded joints. The Fatigue Crack Growth (FCG) rates of base metal and related welded joints are investigated considering load ratio (0.1, 0.4, 0.7) and post-welding heat treatment. The experimental FCG trends for base metal and weldments have been compared with the trends available in standards. The FCG rate (da/dN) results show fatigue crack propagation resistance under post welded heat treatment (PWHT) is lower than the as-welded state for both EM and UM welded joints.