Interfacial Fracture Behaviors of Single Particle Impacts During Aluminum Cold Spray Additive Manufacturing and Repair Process

Abstract

The current research represents a preliminary investigation of the cold spray metal deposition process which is a form of additive manufacturing and coating repair. It relates the deformations produced from a single particle impact with a substrate surface to the post-impact interfacial fracture behaviors resulting from separate globally applied mode-I and mode-II loadings. The particle and substrate materials were Al 5056 and Al 6061-T6, respectively. A description of the modeling process is presented and its inherent difficulties are discussed. A two-step numerical modeling process was pursued. First, the particle and substrate impact deformations were obtained using the strain rate-dependent Johnson-Cook Flow Stress Material Model for three particle velocities of interest. Second, the modes-I, II and III strain energy release rates (GI, GII, and GIII, respectively) were characterized along the curvilinear impact surfaces using linear-elastic fracture mechanics (LEFM). Crack initiation, crack growth and ultimate fracture loads of the particle-to-substrate interfaces were determined using the Virtual Crack Closure Technique (VCCT). The predicted results were compared for each particle velocity. The influence of mesh discretization, element distortions, interfacial contact surfaces, etc. are elaborated on for consideration in future modeling efforts. This research, in conjunction with future validation tests, is a fundamental step towards the numerical modeling of cold spray fracture behaviors across multiple material length scales; beginning with a single particle/substrate interface, extending to multiple particles and progressing towards the bulk material scale. Results of such models and experiments will identify specific cold spray processing parameters that may be optimized to improve the interface strengths and fracture resistance levels.