The Hopkinson tension bar has been widely employed for obtaining the dynamic tensile behavior of materials under high strain rates, and a constant true strain rate is theoretically required for evaluating the potential strain rate effect of materials. However, it actually happens seldom. In this study, a universal incident stress wave equation is theoretically derived based on stress wave theory, which functions to conduct tensional and constant true strain rate loading on various materials. Experiments on different materials are performed to verify its advantages, together with extensive evidence from numerical simulations for true strain rate loading. Experimental achievement is approached by an abnormally shaped striker tube for an ideal incident stress wave, and the quantitative relation between the wave configuration and striker tube shape is also theoretically formulated for actual experimental guidance demonstrated via numerical simulations. The findings facilitate the efficient performance of the Hopkinson tension bar and the evaluation of advanced materials.

Copper alloys exhibit significant fatigue life differences under low-cycle fatigue (LCF) and creep-fatigue interaction (CFI), which poses a significant challenge to the reliability of fatigue life assessments of rocket engine thrust chambers. Consequently, it is imperative to develop an effective methodology for the life assessment of the thrust chambers. A Physics-Informed Neural Network (PINN) based on a modified energy-based method is proposed for the life prediction of copper alloys under both LCF and CFI. The proposed PINN model embeds the modified energy-based model which innovatively separates the plastic strain energy term and the creep strain energy term, and further constrains the network output by establishing a hierarchical penalty mechanism within the loss function. All 88 experimental data samples used were derived from LCF and CFI tests on QCr0.8 copper alloy. Compared to physical models, such as the Plastic Strain Energy Density (PSED) model and the Inelastic Strain Energy Density (ISED) model, the proposed PINN model demonstrates superior prediction accuracy. All its prediction points fall within 2-factor error bands, and approximately 85 % within 1.5-factor error bands. Compared to machine learning models, such as Random Forest (RF), Support Vector Regression (SVR), and Deep Neural Networks (DNN), the proposed PINN model exhibits enhanced prediction stability and generalization capability, as well as superior physical interpretability. This approach offers a novel solution for predicting the fatigue life of copper alloy under LCF and CFI.

To clarify the failure mechanism and improve the life prediction accuracy of the regeneratively cooled rocket thrust chamber inner wall, a temperature-dependent crystal plasticity finite element method (CPFEM) considering grain texture effects is developed for the copper-alloy inner wall. Sequential thermomechanical simulations are performed under representative service loading conditions. The results show that cyclic thermomechanical loading induces pronounced ratcheting deformation, and the comparable scale between grain size and inner wall thickness leads to strong deformation heterogeneity. Localized compressive shear bands form along specific grain paths during heating and remain after cooling, resulting in asymmetric deformation about the inner wall centerline that cannot be captured by conventional homogeneous constitutive models. Simulations of multiple random polycrystalline models reveal significant scatter in strain localization and critical deformation locations, highlighting the dominant role of grain texture and crystallographic orientation in failure evolution. Life evaluation based on ratcheting and low-cycle fatigue damage indicates that ratcheting is the primary damage mechanism. Compared with the traditional homogeneous model, the proposed CPFEM predicts markedly higher local plastic strain and substantially shorter service life, which is in better agreement with experimental observations. This work provides a microscale-based approach for accurate deformation analysis and life prediction of thrust chamber inner walls, supporting the structural design and reliability evaluation of reusable rocket engines.

Unveiling the deformation mechanisms and life prediction of novel nickel-based superalloys fabricated by additive manufacturing (AM) is of paramount importance for their application in liquid rocket engines. In this study, the uniaxial tensile and cyclic stress-strain behaviors of a novel AM nickel-based superalloy were investigated using a crystal plasticity finite element (CPFEM) model. The simulation of uniaxial tensile behavior revealed a certain degree of plastic slip occurring intergranular, with the slip direction aligning with the macroscopic fracture direction. In the low-cycle fatigue behavior simulation, the accumulated plastic slip (APS) was incorporated into the fatigue indicator parameter (FIP) to predict the low-cycle fatigue life under two strain amplitudes. Compared to experimental data at strain amplitudes of 0.75

To assess the viability of additively manufactured (AM) alloys in reusable liquid rocket engines, a novel Ni-based superalloy with a complex microstructure was prepared via selective laser melting. The effect of the AM sample microstructure on fatigue crack initiation and propagation was quantitatively elucidated via experimental characterization and crystal plasticity (CP) simulation. The findings indicate that the AM sample exhibited enhanced low cycle fatigue performance compared to traditional wrought (WR) samples. Specifically, in the initiation stage, the < 001 > texture orientation along the build direction promoted intergranular strain compatibility in AM samples. Meanwhile, the high geometric compatibility factor between adjacent grains disperses local slip accumulation. This synergistic effect promotes a more uniform distribution of plastic deformation, resulting in a longer initiation life than WR samples. In contrast, WR samples exhibit early crack initiation due to strong strain localization caused by the large elastic modulus gradient at twin boundaries. During the propagation stage, the similar grain orientations of the AM samples resulted in a small difference in the transgranular crack deflection angle, which accelerated the propagation of fatigue cracks. The large orientation difference between adjacent grains in the WR sample caused a significant deflection of the crack propagation path, which in turn reduced the crack propagation rate. Overall, although the WR sample exhibited stronger resistance to crack propagation, its early severe strain localization accelerated damage accumulation and limited overall fatigue performance. Finally, the Coffin-Manson equation based on accumulated plastic slip correction achieves accurate prediction of cross-scale life in both AM and WR samples.

To clarify the thermomechanical deformation mechanism and improve the life prediction accuracy of the regeneratively cooled rocket thrust chamber inner wall, a temperature-dependent crystal plasticity finite element method (CPFEM) considering grain morphology effects is developed for the copper-alloy inner wall. Sequential thermomechanical simulations are performed under representative service loading conditions. The results show that cyclic thermomechanical loading induces pronounced ratcheting deformation, and the comparable length scale between grain size and inner wall thickness leads to strong deformation heterogeneity. Localized compressive shear bands form along specific grain paths during heating and remain after cooling, resulting in asymmetric deformation about the inner wall centerline that cannot be captured by conventional homogeneous constitutive models. Simulations of multiple random polycrystalline models reveal significant scatter in strain localization and critical deformation locations, highlighting the dominant role of grain morphology and crystallographic orientation in failure evolution. Life evaluation based on ratcheting and low-cycle fatigue damage indicates that ratcheting is the primary damage mechanism. Compared with the traditional homogeneous model, the proposed CPFEM successfully captures the stochastic and asymmetric strain localization of the thrust chamber inner wall and predicts markedly higher localized plastic strains and substantially shorter service life, which is qualitatively aligned with the “doghouse” type failure characteristics reported in the literature. This work provides a microscale-based approach for accurate deformation analysis and life prediction of thrust chamber inner walls, supporting the structural design and reliability evaluation of reusable rocket engines.

Thrust chambers commonly reported in application features straight cooling channels and thin thermal barrier coatings. However, this design suffers from durability limitations due to hightemperature degradation, cyclic fatigue, and coating spalling. In this study, a different design incorporating electrodeposited multilayer metal coatings and spiral cooling channels is investigated. It reveals a progressive coating-to-inner wall cracking mode of the thrust chamber, distinct from the classical "doghouse failure" mechanism. Through multiscale characterization (macro to micro), multi-dimensional observation (3D to 2D), and fluid-thermal-structural coupling simulations, the crack behaviors in a tested thrust chamber segment after repeated hot firing tests are systematically analyzed. The results indicate that radial micro-cracks predominantly initiate near and above the Cr-Ni interface, exhibiting diversity in initiation location, morphology, and formation process. On a larger scale, the macro-cracks formed by micro-cracks growth and interaction are most likely to originate around the throat. Investigations on crack propagation demonstrate that the axial extension of macro-cracks along the thrust chamber is governed by localized influences from mud cracks within the Cr coating and global regulation through circumferential stresses. Nevertheless, their radial propagation is constrained by the thick coatings, leading to sequential fracture initiation across different metallic layers. In addition, distinct crack propagation mechanisms are identified: in the Cr coating, cracks propagate through leading crack formation at the tip; however, in the Ni coating, propagation occurs via nucleation, growth, and coalescence of voids near the crack tip, ultimately connecting with the tip. Based on these insights, several optimization strategies are proposed. This work can provide guidance for improving the reliability and longevity of reusable rocket engines with multilayer metal coatings and spiral cooling channels.

Aircraft engine turbine disks experience high-temperature cyclic loading, making precise low-cycle fatigue (LCF) life prediction critical for ensuring reliability. This study proposes a macro-mesoscopic life prediction framework by coupling crystal plasticity theory with the extended finite element method (CP-XFEM). The framework employs submodeling techniques, localized mesh refinement, and macro-mesoscopic constitutive modeling to address the scale mismatch between real engineering structures and microlevel models. Life predictions are conducted for turbine disks under ideal surface conditions, surfaces with tool marks, and surfaces containing inclusions, considering varying grain orientations. Results show that, for turbine disks without inclusions, fatigue life has a substantial safety margin, with an average life reaching 502,757 cycles even in the presence of tool marks. In contrast, the presence of inclusions significantly reduces fatigue life, with the minimum life in the throat region dropping to 5523 cycles. Moreover, under the most adverse inclusion conditions, the calculated safe life is 3894 cycles, highlighting the need for stringent inclusion standards in turbine disk design to optimize fatigue life. The proposed macro-mesoscopic method provides a basis for structural optimization of turbine disks with respect to short crack fatigue life in engineering contexts.

The oxygen pump constitutes a crucial and intricate component within liquid rocket engines, serving as a primary source of engine vibration. This study delves into the unsteady fluid-induced excitation loading, considering the interplay between gap flow and main flow. The findings are validated through testing on a liquid rocket engine. Modal characteristics of the oxygen pump under varying liquid mediums are examined. The Rayleigh damping parameter is determined, accounting for the frequency characteristics of fluid-induced excitation, thereby establishing a comprehensive transient dynamic model. Subsequently, the transient dynamic response of the volute in an oxygen pump to unsteady fluid-induced excitation is analyzed, unveiling both time-domain and frequency-domain vibration response characteristics. The analysis methodology is corroborated through comparison with the statistical distribution of test results. Notably, the vibration response of the oxygen pump volute predominantly exhibits frequency doubling of rotational speed, with prominent occurrences observed at the 12X and 18X frequencies.

PurposeReinforced S-shape bellows are novel metal bellows with high pressure resistance. Displacement compensation ability is a key index in the design of metal bellows. Axial-tension-compression deformation and bending deformation are two typical displacement compensation forms. Thus, analysis of axial and bending stiffness is important in structure design.Design/methodology/approachIn this study, theory analytics of axial tension and compression stiffness of reinforced S-shaped bellows structure is derived, and the load-displacement relationship during axial deformation is obtained by correcting the geometric parameters of waveform during axial tension and compression deformations. On the basis of them, the relationships of bending stiffness with axial tensile and compression stiffness under the action of bending loading are constructed, and thus, the theory analytics of bending stiffness is realized for S-shaped bellows.FindingsThis theory analytics is verified by comparing the results of theory analytics with those of numerical simulation for a few typical examples. An investigation on the axial and bending non-linear mechanical behaviors of multi-layer-reinforced S-shaped bellows was also carried out by numerical simulation and experiment, and the experimental results verified the reliability of the analysis method.Originality/valueIt is found that non-linearity behavior occurs greatly during the first loading course of reinforced S-shaped bellows, and the structure is strain-strengthened due to plastic deformation; however, stable stiffness characteristic is exhibited during the succeeding cyclic-loading course.

Traditional unidirectional cold expansion technology usually generates non-uniform distribution of residual stress in the thickness direction of holes, which is harmful to the improvement of fatigue life of holes. The present work proposed a bi-directional cold expansion procedure to realize the homogenization of residual stress in the thickness direction of the cold expanded hole, thereby further improved antifatigue performance of cold expanded hole. For this aim, a series of finite element (FE) simulations were carried out to investigate the effectiveness of the bi-directional cold expansion procedure and optimize the process parameters. The results showed that the optimized bi-directional cold expansion process generated a more uniform distribution of residual circumferential compressive stress in the thickness direction comparing to the simplified bidirectional cold expansion process using a single mandrel. For the Aluminum alloy 7050-T7451, when the first interference level I-1 = 1.8%, the largest and the most uniform residual circumferential compressive stress was achieved, which suggested the best anti-fatigue performance.

Purpose The fracture mechanism of S-07 steel was investigated by observing the fracture surface of the specimens with scanning electron microscope (SEM). Furthermore, the overall elastic–plastic behaviors and the stress state evolution during the loading procedure of all specimens were simulated by FE analysis to obtain the local strain at crack nucleated location and the average triaxiality of each type of specimen. Design/methodology/approach Three types of tests under various stress states were performed to study the ductile fracture characteristics of S-07 high strength steel in quasi-static condition. Findings Under tensile and torsion loading conditions, S-07 steel exhibits two distinctive rupture mechanisms: the growth and internal necking of voids governs the rupture mechanism in tension dominated loading mode, while the change of void shape and internal shearing in the ligaments between voids dominants for shear conditions. Originality/value The failure criterion for S-07 steel considering the influence of the triaxial stress state was established.

Purpose Regeneratively cooled thrust chamber is a key component of reusable liquid rocket engines. Subjected to cyclic thermal-mechanical loadings, its failure can seriously affect the service life of engines. QCr0.8 copper alloy is widely used in thrust chamber walls due to its excellent thermal conductivity, and its mechanical and fatigue properties are essential for the evaluation of thrust chamber life. This paper contributes to the understanding of the damage mechanism and material selection of regeneratively cooled thrust chambers for reusable liquid rocket engines. Design/methodology/approach In this paper, tensile and low-cycle fatigue (LCF) tests were conducted for QCr0.8 alloy, and a Chaboche combined hardening model was established to describe the elastic-plastic behavior of QCr0.8 at different temperatures and strain levels. In addition, an LCF life prediction model was established based on the Manson–Coffin formula. The reliability and accuracy of models were then verified by simulations in ABAQUS. Finally, the service life was evaluated for a regenerative cooling thrust chamber, under the condition of cyclic startup and shutdown. Findings In this paper, a Chaboche combined hardening model was established to describe the elastoplastic behavior of QCr0.8 alloy at different temperatures and strain levels through LCF experiments. The parameters of the fitted Chaboche model were simulated in ABAQUS, and the simulation results were compared with the experimental results. The results show that the model has high reliability and accuracy in characterizing the viscoplastic behavior of QCr0.8 alloy. Originality/value (1)The parameters of a Chaboche combined hardening constitutive model and LCF life equation were optimized by tensile and strain-controlled fatigue tests of QCr0.8 copper alloy. (2) Based on the Manson–Coffin formula, the reliability and accuracy of constitutive model were then verified by simulations in ABAQUS. (3)Thermal-mechanical analysis was carried out for regeneratively cooled thrust chamber wall of a reusable liquid rocket engine, and the service life considering LCF, creep and ratcheting damage was analyzed.

液体火箭发动机涡轮泵内非定常流体力主要通过流体-壳体以及流体-转子-支承-壳体两条传递途径激励壳体发生振动,对发动机的安全可靠性造成威胁.为获得流体激励下涡轮泵壳体振动特性,建立了两条流体力传递途径下涡轮泵壳体振动响应定量预测方法,利用发动机热试车结果对预测方法的精度及可靠性进行了验证.在此基础上获得了不同途径下涡轮泵壳体的振动特性.结果表明:所建立的涡轮泵流体激励壳体振动预测方法能够较好地预测壳体振动响应主导频率及幅值,主频幅值误差小于13.85％;壳体的最大振动能量源自于泵内动静干涉非定常流动与壳体结构之间的相互作用;流体-壳体途径是涡轮泵流体激励壳体振动的主要来源,其引起的壳体振动响应幅值相比流体-转子-支承-壳体传递途径大2个量级以上.

The load-carrying capacities of welded joints need to be paid attention to in the design of the frame, which transfers the thrust generated by the rocket engine to the rocket body. A load-carrying capacity evaluation method of welded joints based on the structural stress method is proposed in this study. Both the ultimate load-carrying capacity and fracture section angle are precisely obtained by the evaluation method. At the same time, a definition of weld-failure stress is given based on the evaluation method and tests. The load-carrying capacity of welded joints in the rocket engine frame is analyzed through the finite element model, including the overall structure and local weld details. The weld-failure stress of welded joints is obtained based on the analysis of three types of welded structures-standard shear specimen, U-shaped fillet welded specimen and pipe-plate fillet welded specimen. The safety factors of the transverse rod and longitudinal bearing rod welded joints of the frame are 8.6 and 13.4, respectively.

The purpose of this study was to investigate the wetting behavior and interfacial reactions of Sn-Ti alloys, which has been widely applied to join ceramics with metals, on Si3N4 substrates. The isothermal wetting process of Sn-xTi alloys (x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) on Si3N4 was systematically studied from 1223 K to 1273 K through sessile drop methods. The microstructures of the interface were characterized by X-ray diffraction (XRD) and microscope (SEM). The active Ti element remarkably enhanced the wettability of Sn-xTi melts on Si3N4 substrates because of the formation of metallic reaction layers (Ti5Si3 and TiN). With the Ti content rising, thicker Ti5Si3 layer formed on the TiN phase inducing a lower equilibrium contact angle. The value of the lowest contact angle was 6°, which was obtained in the Sn-2.0Ti/Si3N4 system at 1273 K. Larger Ti5Si3 grains were found in Sn-2.5Ti melt and a higher final contact angle was obtained. Lower temperature increased the final contact angle and slowed down the spreading rate. The formation of reaction products was calculated thematically, and the spreading kinetics was calculated according to the reaction-driven theory. The spreading behavior of Sn-Ti alloy on Si3N4 ceramic was composed of rapid-spreading stage and sluggish-spreading stage. The calculated activity energy of spreading was 395 kJ/mol. Eventually, the wetting process of Sn-2.0Ti/Si3N4 system was successfully elucidated. These results provide significant guidance information for the brazing between metals and Si3N4 ceramic.

针对增强S形波纹管,结合理论分析与数值仿真分析方法,给出内压稳定性的分析方法.首先基于数值分析方法获得波纹管轴向刚度,由最小轴向刚度确定结构弯曲刚度.然后,基于内压作用下薄壁圆柱壳轴线控制方程和弯曲过程波纹管结构几何关系,获得摇摆过程边界影响系数的选取方法.最后,基于Euler公式并参考EJMA规范,给出增强S形波纹管稳定性临界内压分析方法,方法综合考虑材料弹塑性、内压和边界影响系数等因素,较真实反映波纹管实际情况,能够较好地应用于增强S形波纹管结构稳定性分析.

气-气同轴直流式喷注器广泛应用于全流量补燃循环发动机,喷注器的结构设计在很大程度上影响发动机主推力室的性能.为了探究气-气同轴直流式喷注器的结构参数对燃烧性能的影响,通过数值计算,分析了氧喷嘴直径、燃料喷嘴宽度、燃料喷嘴与氧喷嘴之间的壁厚以及中心氧喷嘴的缩进距离这4方面的结构参数对燃烧效率以及火焰长度的影响.结果表明:氧喷嘴直径以及燃料喷嘴与氧喷嘴之间的壁厚对火焰长度影响较大,燃料喷嘴宽度以及缩进距离对火焰长度影响较小.随着氧喷嘴直径以及氧喷嘴与燃料喷嘴之间的壁厚增加,火焰长度增加,燃烧效率降低.另外,燃料喷嘴的宽度与缩进距离对推进剂组元的混合影响较大,一定的缩进距离可以加快组元的混合,并且提高火焰稳定性.

The effect of loading rate of force in repetitive high stress loading/unloading (RHSL) treatment on the formation of deformation twins in a martensite stainless steel was studied by SEM-EBSD and TEM. It is found that RHSL successfully generates a large number of twins at room temperature with low strain rate and small plastic deformation. The number fraction and area fraction of twin grains are monotonously increased with the loading rate. RHSL provide a continuously driving force that promotes the abundant generation of twins. Higher loading rate favors the more nucleation of stacking faults and twins and their intersections of multi-orientation.

The effects of post-weld heat treatment (PWHT) parameters on residual stress release and mechanical properties of SMA490BW steel were investigated by mechanical experiments and finite element analysis. The creep behavior of the SMA490BW steel at high temperatures (500-600 degrees C) has been described numerically by implementing the Norton-Bailey model. The mechanical performance of two distinct PWHT schemes was studied as well as the residual stress relief mechanism. The simulation results reveal that the evolution of the equivalent creep strain contributes to the residual stress relief in the welded joint, and the longitudinal and transverse residual stresses are reduced by about 65%. In the case of the PWHT holding temperature equal to 600 degrees C, the hardness of the weld metal decrease from 200 H V for 1 h to 190 H V for 2 h. The PWHT holding time has no remarkable effect on the ultimate tensile strength of the joint, which is reported to be 495 MPa for 1 h and 502 MPa for 2 h.