Fatigue Strength Verification of Additively Manufactured Structures Considering the Local Loading Conditions and Microstructure (LBM-Fatigue)

考虑局部载荷条件和微观结构的增材制造结构的疲劳强度验证（LBM-疲劳）

• 批准号: 505646807
• 负责人: Professor Dr.-Ing. Tilmann Beck
• 金额: --
• 依托单位: Lehrstuhl für Werkstoffkunde (WKK)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/505646807?language=en
• 关键词: Fatigue; Strength; Verification; Additively; Manufactured

Additive Manufacturing (AM), especially the powder-based Laser Beam Melting (LBM) process, enables a high potential to manufacture structural components in a lightweight design. Therefore, a valid fatigue strength verification concept is indispensable. Although established design concepts allow to consider AM specific influencing factors (e.g. anisotropy, “as-built” (AB) surface, etc.), this often results in a high deviation to the actual lifetime of parts. However, the current state of research shows that microstructure, defect characteristic, which comprises the size, number, position and type of process-induced defects, as well as mechanical properties can vary within an additively manufactured component. Thereby, relevant research works further demonstrate that the defect tolerance of an AM material highly influences the fatigue lifetime. These aspects must be considered, but cannot be integrated readily in existing verification concepts yet. Moreover, the influence of the loading condition and its interrelation with the influencing factors described above, must be included into an extended design concept. Consequently, the main goal of this research project is the elaboration of a valid fatigue strength verification concept, which is based on local concepts and/or fracture mechanics, and which considers the AM specific influencing factors described above. This concept will be elaborated over 3 stages, which are represented by 3 working packages (AP), by using specimens made of AISI 316L and manufactured via LBM.In AP1, the influence of the AB surface, building direction and their interrelation will be analyzed and quantified based on uniaxial push-pull fatigue tests. Additionally, the defect tolerance will be determined for the different building directions by using the √area-approach and instrumented cyclic indentation tests (CIT), complemented by an analysis of the local defect characteristic and microstructure. Subsequently, these relations will be quantified and integrated in a first fatigue strength verification concept.Based on this, the effect of loading gradients, achieved by rotational bending and torsion, as well as their interrelations with the influencing factors analyzed in AP1 will be elaborated in AP2. In this context, a special focus will be on the defect tolerance. These findings will be integrated in the verification concept, which will be prevalidated in biaxial fatigue tests.Finally, the concept developed will be validated in AP3 by means of fatigue tests at a demonstrator, which has to be developed and exhibits multiaxial graduated loadings caused by a complex geometry. To enable the transferability of the approaches elaborated in AP1 and AP2, the defect characteristics, the microstructure, the surface topography as well as the mechanical properties of the critical areas will be analyzed. Moreover, advises for a durable design of additively manufactured components will be drawn based on the verification concept.

增材制造（AM），特别是基于粉末的激光束熔化（LBM）工艺，使制造轻量化设计的结构部件具有很高的潜力。因此，有效的疲劳强度验证概念是必不可少的。尽管已建立的设计概念允许考虑AM特定的影响因素（例如，各向异性、“竣工”（AB）表面等），这通常导致与部件的实际寿命的高度偏差。然而，目前的研究状况表明，微观结构，缺陷特征，包括工艺引起的缺陷的大小，数量，位置和类型，以及机械性能在增材制造的部件中可能会有所不同。因此，相关研究工作进一步表明，AM材料的缺陷容限对疲劳寿命有很大影响。这些方面必须加以考虑，但尚不能轻易纳入现有的核查概念。此外，荷载条件的影响及其与上述影响因素的相互关系必须包括在扩展的设计概念中。因此，本研究项目的主要目标是制定有效的疲劳强度验证概念，该概念基于局部概念和/或断裂力学，并考虑了上述AM特定影响因素。这一概念将在3个阶段进行阐述，这3个阶段由3个工作包（AP）代表，使用AISI 316L制成的试样，通过LBM制造。在AP 1中，AB表面的影响，建设方向及其相互关系将基于单轴推拉疲劳试验进行分析和量化。此外，缺陷容限将被确定为不同的建设方向，通过使用面积的方法和仪器循环压痕试验（CIT），辅之以局部缺陷特性和微观结构的分析。随后，这些关系将被量化并整合到第一个疲劳强度验证概念中。在此基础上，通过旋转弯曲和扭转实现的载荷梯度效应，以及它们与AP 1中分析的影响因素的相互关系，将在AP 2中详细说明。在这种情况下，将特别关注缺陷容限。这些发现将被整合到验证概念中，并将在双轴疲劳试验中进行预验证。最后，开发的概念将在AP 3中通过在演示器上进行疲劳试验进行验证，该演示器必须开发并显示由复杂几何形状引起的多轴分级载荷。为了实现AP 1和AP 2中阐述的方法的可移植性，将分析关键区域的缺陷特征、微观结构、表面形貌以及机械性能。此外，将根据验证概念提出增材制造组件的耐用设计建议。