A custom punch-die fixture allowing full field three-dimensional Digital Image Correlation (DIC) measurements on the rear surface of the specimen is introduced for dynamic and quasi-static punch experiments. The punch fixture design methodology is described. Results from punch experiments on 5.08 mm Ti-6Al-4V disk specimens using three different punch geometries in both dynamic and quasi-static conditions are presented and discussed. These experiments can be used to generate material failure data under complex stress states. Such data is essential in developing and calibrating complex material models, like those developed for precipitate hardened Inconel 718.
The plastic behavior of precipitate hardened Inconel 718 under various strain rates, orientations, and temperatures is examined; and a punch experiment that uses 3D-DIC measurements of the punch specimen is presented. The research presented herein is part of an ongoing project to develop and calibrate a material model in a finite element code, LS-DYNA. Such models are valuable for the simulation of dynamic events, such as blade off failure in aircraft engines.
The equipment, theory, and methodologies used to complete experiments in tension and compression at different strain rates and temperatures are presented. Quasi-static experiments are conducted using a biaxial servo-hydraulic load frame and dynamic experiments using two split Hopkinson bars. A specially designed furnace and adapters are used to complete experiments at elevated temperatures. DIC is an optical method for measuring full field deformations and strains on the specimen surface that is utilized extensively in this work.
Experimental results for precipitate hardened Inconel 718 are presented and discussed. The material shows significant strain hardening and some strain rate sensitivity in tension. Data from experiments at elevated temperature show complex temperature dependence. The material shows decreasing flow stress with increasing temperature and decreasing ductility between 21°C and 600°C. Between 600° and 800°C the ductility increases significantly. Compression experiments at various strain rates show similar strain hardening and less rate sensitivity than in tension. The material is anisotropic in the ±45° from rolling directions and shows anisotropy between tension and compression loadings in the transverse direction. These data are used to determine parameters for a Johnson-Cook plasticity model, and yield criteria are discussed.
Additional work is presented for the design of plane stress, plane strain, and axisymmetric fracture specimens. These specimens will be used in future work in the generation of a failure surface based on stress triaxiality and lode parameter – two stress-state parameters which govern material failure.