Yunfeng Cao

Laser shock peening on Zr-based bulk metallic glass and its effect on plasticity: Experiment and modeling

The Zr-based bulk metallic glasses (BMGs) are a new family of attractive materials with good glass-forming ability and excellent mechanical properties, such as high strength and good wear resistance, which make them candidates for structural and biomedical materials. Although the mechanical behavior of BMGs has been widely investigated, their deformation mechanisms are still poorly understood. In particular, their poor ductility significantly impedes their industrial application. In the present work, we show that the ductility of Zr-based BMGs with nearly zero plasticity is improved by a laser shock peening technique. Moreover, we map the distribution of laser-induced residual stresses via the micro-slot cutting method, and then predict them using a three-dimensional finite-element method coupled with a confined plasma model. Reasonable agreement is achieved between the experimental and modeling results. The analyses of serrated flows reveal plentiful and useful information of the underlying deformation process. Our work provides an easy and effective way to extend the ductility of intrinsically-brittle BMGs, opening up wider applications of these materials.

Analysis of nanosecond laser ablation of aluminum with and without phase explosion in air and water

Despite extensive research work, accurate prediction of the ablation behavior in the high energy nanosecond laser ablation process is still lacking, which may differ significantly depending on laser parameters, surrounding medium, and target material characteristics. In this paper, nanosecond laser ablation of aluminum in air and water is investigated through a self-contained hydrodynamic model under different laser fluences involving no phase explosion and phase explosion. The ablation depths and profiles are predicted and validated against the literature data and experiments. In case of nanosecond laser ablation of aluminum in water, deeper crater depths are found in all the conditions studied in this work, which may be attributed to the combination effects of laser ablation and shock compression. The analysis of the shock compression in air and water indicates that the shock compression is mainly responsible for this enhancement of ablation in water.

Parametric Study on Single Shot and Overlapping Laser Shock Peening on Various Metals via Modeling and Experiments

Laser shock peening (LSP) under water confinement regime involves several complicated physical phenomena. Among these phenomena, the interaction between laser and coating material during LSP is very important to the laser-induced residual stress, which has an important effect on the fatigue and corrosion properties of the substrate material. To gain a better understanding of this interaction, a series of experiments, including single shot, single-track overlapping, and multitrack overlapping LSP, has been carried out on various metals with different coatings. A 3D finite element model has also been developed to simulate the LSP process. Combining this with a previously developed confined plasma model, which has been verified by the experimental data from literature, the 3D finite element model is used to predict the residual stresses induced in the substrate material as well as the indentation profile on the substrate surface. The model prediction of indentation profiles is compared with the experimental data. The residual stresses in the depth direction are also validated against the X-ray diffraction measurement data for 4140 steel and Ti-6Al-4V, and good agreements are obtained for both predictions. The effect of process parameters on the residual stress is also investigated both experimentally and theoretically. [DOI: 10.1115/1.4002850]

Shock Wave Propagation and Spallation Study in Laser Shock Peening

This paper deals with the spallation induced by shock wave propagation in targets during the laser shock peening process. Physical aspects concerning laser-matter interaction, shock wave propagation, and spallation are considered. A continuous kinetic model for the spallation process is included in a one-dimensional finite difference hydrodynamic code using Lagrangian coordinates in order to calculate the laser-induced spallation phenomena. Shock wave propagation in solids is calculated and validated by experimental data. The spallation zone location is then calculated for various materials with different thickness of foils and various laser shock peening parameters. The numerical simulations are compared with previously reported experimental results, and good agreement is obtained for the spallation threshold and damage zone location.Copyright