The differences in damage values, residual stresses, microstructure and mechanical properties of Ti-6Al-4V alloy under hammer forging and press forging were explored through physical experiments and numerical simulations. The results showed that the temperature field and equivalent strain field of forgings under the hammer forging process were more uniformly distributed, resulting in smaller surface cracks and better residual stress distribution. The impact dynamic loading of hammer forging leads to forgings with higher dislocation densities, while the stabilized strain rate of press forging results in forgings exhibiting finer grain sizes. In this context, the yield strength enhancement of forgings by both processes was nearly identical, while the forgings demonstrated more excellent elongation under the hammer forging process. Additionally, increasing the number of blows in the hammer forging process or enhancing the loading rate in the press forging process can optimize the residual stress distribution of the forgings while simultaneously promoting dislocation multiplication and grain refinement.

为改善固溶时效后TC4钛合金锻件残余应力的大小及分布，从而进一步提高锻件后续加工质量及其服役性能，首先建立了锻后固溶时效数值模型，并进行了实验验证，然后通过数值模拟分析了固溶温度、固溶时间、时效温度和时效时间对锻件残余应力的影响规律，最后采用正交实验设计与极差分析法，确定了各工艺参数对锻件残余应力的影响程度，并得出最优工艺参数组。结果表明，随着固溶温度、时效温度以及时效时间的增加，可显著降低锻件中心部位的残余应力。此外，固溶温度对锻件残余应力的影响最为显著，其次是时效时间、时效温度、固溶时间，在固溶温度900℃、固溶时间80 min、时效温度500℃、时效时间8 h时锻件的残余应力最小，为生产实践提供合理依据。

In this paper, a novel hybrid forging process is proposed for block materials with high specific strength based on the traditional forging process. A prestressing system is established first by clamping the forging using a hydraulic press process in the hybrid process, then rapidly impacting the system using hammer impact process in order to activate and amplify the prestressing force. To achieve the novel hybrid process, integrated equipment is designed based on the structure characteristics of both the press and the hammer, its dynamic characterization is analyzed through simulations to obtain the results of multi-objective optimization. In this study, effectiveness of the novel hybrid forging process by forging Ti-6Al-4V alloy is first reported. Experimental results show that the plastic deformation of the forgings can increase by up to about 3 % and energy loss of equipment elastic deformation can reduce about 25.8 % in the hybrid process, compared to the single hydraulic press process. In particular, microstructure of forgings occurs finer grain size and higher and more uniformly distributed dislocation density. This study reveals the potential of the novel hybrid forging process technology, which lays a solid foundation for expanding its application in forging industrial production about high specific strength material.

This paper proposes an improved nonprobabilistic Monte Carlo simulation method for structural reliability analysis based on convex models. The novelty of the proposed method is to use a unit hyper-sphere sampling technique to ensure the validity of all samples, and to restrict the sampling domain to the evaluated domain which is geometrically the intersection of a hyper-spherical shell and a hyper-spherical sector and generally has a smaller volume than the whole ellipsoid. The nonprobabilistic characteristics and application to the interval model of the proposed method are also discussed. Seven numerical examples are provided to demonstrate the efficacy of the proposed methodology.

Due to the difficulty of accurately predicting system reliability for many engineering structures, bounds on system reliability have received increasing attention. By dealing with structural uncertain parameters with an ellipsoid model, a linear programming-based non-probabilistic reliability bounds method is proposed in this paper for series systems. In this research, a linear programming model is first established, and then several strategies are proposed to simplify the model by removing zero design variables. Three numerical examples are presented to demonstrate the feasibility and validity of the proposed method.

非概率凸集合模型仅需获知结构不确定性的范围或界限来度量结构可靠性，因而适用于小样本不确定性结构工程问题。针对广义超椭球模型，对其非概率可靠性度量问题进行了研究。首先，提出基于广义超椭球模型的简单非概率可靠性指标，定义为结构功能函数的均值与离差之比，并讨论了该可靠性指标的不一致性问题。其次，为克服上述不一致性问题，提出一种比例因子非概率可靠性指标，定义为不确定域向外扩大或向内收缩时，失效面与不确定域接触的最小比例因子。通过三个工程算例分析验证了所提非概率可靠性指标的有效性和可行性。

多维平行六面体模型是一种能够同时考虑相关变量和独立变量的非概率凸集模型，更适用于工程结构中常见的多源不确定性问题。为更加有效合理地度量结构不确定性，提出一种改进多维平行六面体模型。通过定义区间变量的相关角和边缘区间，给出模型不确定域的显式表达式，进而给出依据实验样本点构建多维平行六面体模型的方法。三个算例分析结果表明，改进多维平行六面体模型能够较好地反映区间变量之间的相关性，是一种比传统多维平行六面体模型更为紧凑合理的模型。

It is a novel promising technology that the advantages of vibration are applied to the plastic forming process. This study is prompted by the effect of the number of blows and dwell time on the forming properties of forgings when hammer forging impact is considered as vibration excitation. Taking Ti-6Al-4V alloy as the research object, this study investigates the forging quality and strength-toughness through hammer forging experiments. Then, a numerical model is established and verified by experiments. The results show that increasing the number of blows at constant total dwell time can obviously decrease the cumulative damage, stress concentration and residual stress in forgings, while improving the uniformity of forging deformation, average grain size and residual stress distribution. In addition, the proportion of fine grains in the forging is also increased. The adjustment of hammer forging impact parameters from the perspective of vibration excitation is effective in improving the performance of forgings, which can provide a theoretical basis for the future development of advanced hammer forging technology.

为了减小模拟结果与实际锻造的误差,需要建立更准确的有限元分析模型。本文以X射线衍射法测量锻件残余应力为依据,利用Deform-3D有限元软件对TC4钛合金锻造变形以及锻件卸载空冷过程进行模拟,分析试验结果与模拟结果的误差,得到更加准