The effect of laser shock peening on selective laser melted aluminum SLM A357 and structural response of 3D printed rubber lattice structures

Residual stress (RS) is a major processing issue for selective laser melting (SLM) of metal alloys. Postprocessing is usually required for acceptable mechanical properties. In this present research, laser shock peening (LSP) treatment on both SLM and cast aluminum A357 alloys are compared with regard to the development of beneficial near-surface compressive RS. Experiments are conducted using high-energy nanosecond pulsed laser, together with a fast photodetector connected to a high-resolution oscilloscope and high-speed camera to identify detailed temporal and spatial laser pulse profiles to improve numerical predictions. Constitutive modeling for SLM A357 alloy is performed using finite element simulation and data obtained from X-ray diffraction (XRD) measurements. Since XRD-RS measurements are accompanied with significant machine-reported error, an effective method is introduced to quantify the material constitutive model uncertainty in terms of a joint probability mass function. Conventionally, most constitutive behavior research for LSP involves deterministic material modeling. Predicted RS using deterministic approaches fail to reflect real-world variations in the materials, laser treatment, or RS measurements. A discretized Bayesian inference is used to quantify the rate-dependent plasticity material model parameters as a joint probability function. RS are then characterized as random fields, which provides far greater insight into the practical ability to attain desired residual stresses.

In addition, a new direct UV curing, polyurethane-like, highly stretchable rubber, Elastic ToughRubber90 (ETR 90), will be demonstrated for 3D printing via photocuring with Texas Instruments (DLP) optical systems. An array of test specimens, comprising a sandwich structure with a body-centered cubic lattice core, are 3D printed from ETR 90. The compressive behavior of these specimens is characterized up to 10 k and up to 100 k fatigue-loading cycles. The internal, visually obstructed, structures under loads are visualized using in situ X-ray tomography. All lattice structures remain intact and full recovery is observed, indicating the cyclic durability of the 3D-printed rubber.