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。

TC4钛合金比强度高,抗腐蚀性好,同时具有较好的蠕变强度、持久强度以及疲劳强度而被作为汽轮机叶片的首选结构材料。然而,在大型汽轮机的中高压级往往具有较高的温度,TC4钛合金不可避免的会发生蠕变变形。材料的蠕变性能不仅与服役环境有关,还与相关的成形工艺紧密相关。在工业领域中,装备中承载的核心零部件大多采用锻造塑性成形,考虑效率和成本的问题,目前TC4钛合金的锻造塑性成形更多采用的是非等温锻造。已有的研究大多数集中在锻造工艺参数对TC4钛合金微观组织及力学性能的影响,考虑锻造工艺参数对其高温服役性能的影响很少,尤其是其蠕变行为。因此,本文分析研究锻造工艺参数对TC4钛合金锻件蠕变行为的影响规律,以寻求合理的锻造工艺与蠕变行为的最优匹配。主要的研究内容如下:（1）根据工程实际并结合TC4钛合金材料特性选取了关键锻造工艺参数（锻造温度和锻造变形量）,制定了合适的非等温锻造工艺实验;对所获得的TC4钛合金锻件分别进行了高温单轴拉伸试验,获取了相应的力学性能参数,为蠕变试验的实施奠定了一定的基础;（2）对已有的蠕变模型进行了分析和研究,并在此基础上结合相关工程应用设计了 TC4钛合金在不同锻造温度及变形量下所得锻件的蠕变试验,绘制了蠕变应变-时间曲线;通过分析不同锻造温度及变形量对TC4钛合金锻件蠕变行为的影响规律,建立了能相对应的描述TC4钛合金锻件蠕变行为的数学方程;明确了不同锻造工艺参数对蠕变方程中关键参数的影响,探讨了非等温锻造下TC4钛合金锻件的蠕变变形机制;（3）在明确锻造工艺参数对TC4钛合金锻件蠕变行为影响的基础上,获得并确定了 TC4钛合金锻件蠕变性能较好的最佳工艺参数组,并结合相关蠕变数学方程,建立了仿真模型,进行了相关工艺参数组下的TC4钛合金锻件的蠕变数值模拟分析,获得了其蠕变极限行为特征参数。本文的研究明确了锻造工艺参数对于TC4钛合金在高温服役环境下的蠕变行为有重要的影响,这对于依据TC4钛合金锻件的实际服役性能的要求不同,进行相对应的锻造工艺参数的合理选择和优化具有重要的工程指导意义。

TC4钛合金由于其优秀的综合性能而被广泛应用于航空航天、海洋船舶以及大型核电领域,并作为装备中核心零部件的重要结构材料,其成形方法多采用锻造塑性成形。严苛的服役环境和高标准的服役需求,使得TC4钛合金的疲劳寿命愈显重要。TC4钛合金热导率低、应变速率敏感以及锻造温度范围窄,极大的增加了 TC4钛合金的锻造加工难度,容易导致锻件质量不稳定,进而威胁零部件服役的安全性和可靠性。因此,深入研究不同锻造工艺参数对TC4钛合金疲劳行为的影响,进而建立锻造工艺参数与疲劳寿命之间的复杂映射关联,显得至关重要。本文通过物理实验和仿真模拟及回归分析等方法,揭示TC4钛合金在锻造加工效应下工艺参数与锻件试样疲劳寿命的关系,主要研究内容如下:（1）依据工程实践调研确定出关键的锻造工艺参数,并制定了合理的锻造实验方案以及相关力学性能检测实验方案;在得到了物理实验数据的基础上利用ABAQUS结合Fe-safe软件建立并修正了 TC4钛合金锻件试样的疲劳寿命仿真模型;（2）对当前已有的疲劳寿命预测理论及数学模型进行了甄别验证,结合研究内容1中的相关工程应用背景下的疲劳实验数据,确定合适的寿命预测方法并对其进行了进一步修正,为后续搭建锻造工艺参数对疲劳寿命影响的关系模型奠定了基础,同时明确了影响TC4钛合金锻件寿命的关键力学特征参量;（3）基于锻件的常温拉伸实验数据,分析了锻造工艺对上述特征参量的影响规律,并通过多元非线性回归确定了锻造工艺参数与特征参量的映射关系;结合之前所选取的寿命预测方法建立了基于锻造工艺参数的疲劳寿命预测模型,并由此确定针对TC4钛合金锻件疲劳寿命的要求是可以由相对应的最优锻造工艺参数组来实现的。本文所建立的基于锻造工艺参数的疲劳寿命预测模型对于指导锻造工艺的优化及锻件疲劳性能的提升有着积极的作用,并对于进一步完善锻造塑性成形制备技术有着重要的指导意义。