Fatigue Characterization of Ultrasonic Additive Manufactured Aluminum 3003

An aluminum 3003 H-18 block was built using ultrasonic additive manufacturing with process parameters which optimize mechanical strength. Transverse tensile fatigue tests were conducted on samples cut from the block and a stress vs. number of cycles curve was generated. Results show the curve is relatively flat and a stress threshold of 50% of the ultimate transverse tensile strength exists below which failure does not occur within 3.75 × 107 cycles. Optical and scanning electron microscopy conducted on failure surfaces shows no signs of crack initiation or growth typical of fatigue loading, but exhibits areas of no bonding between foil layers. To explain the failure, a model was developed based on the probabilistic failure of bonded areas in tension. The model uses a Frechet distribution to describe the probability of failure at each individual bonded area. Discrete bond failure and subsequent redistribution of stress to the surviving areas eventually leads to failure for the entire sample. Predictions from the model show good correlation with the experimental results.