Kristina Langer

Material model validation for laser shock peening process simulation

Advanced mechanical surface enhancement techniques have been used successfully to increase the fatigue life of metallic components. These techniques impart deep compressive residual stresses into the component to counter potentially damage-inducing tensile stresses generated under service loading. Laser shock peening (LSP) is an advanced mechanical surface enhancement technique used predominantly in the aircraft industry. To reduce costs and make the technique available on a large-scale basis for industrial applications, simulation of the LSP process is required. Accurate simulation of the LSP process is a challenging task, because the process has many parameters such as laser spot size, pressure profile and material model that must be precisely determined. This work focuses on investigating the appropriate material model that could be used in simulation and design. In the LSP process material is subjected to strain rates of 106 s−1, which is very high compared with conventional strain rates. The importance of an accurate material model increases because the material behaves significantly different at such high strain rates. This work investigates the effect of multiple nonlinear material models for representing the elastic–plastic behavior of materials. Elastic perfectly plastic, Johnson–Cook and Zerilli–Armstrong models are used, and the performance of each model is compared with available experimental results.

Experimental validation of simulated fatigue life estimates in laser‐peened aluminum

Purpose – The purpose of this paper is to develop and implement a structural fatigue life estimation framework that includes laser‐peened (LP) residual stresses and then experimentally validates these fatigue life estimations.Design/methodology/approach – A three‐dimensional finite element analysis of an Al 7075‐O three‐point bending coupon being LP was created and used to estimate the fatigue life when loaded. Fatigue tests were conducted to validate these estimations.Findings – The framework developed for fatigue life estimation of LP‐processed coupons yielded estimates with goodness‐of‐fit between the log‐transformed experimental and analytical data of R2=0.97 for the baseline coupons and R2=0.94 for the LP‐processed coupons.Research limitations/implications – Approximated e‐life fatigue parameters were used to calculate the fatigue life resulting from the complex residual stress fields due to the simulated LP process.Originality/value – A fatigue life estimation framework that considers LP residual st...

Modeling and Optimization of a Laser Shock Peening Process

In the laser shock peening (LSP) process, favorable residual stresses are induced on a surface to improve fatigue and fretting properties of that part of the metal surface. In the literature, experimental-based advances have been attempted to understand and derive the maximum benefits from the process and to demonstrate the benefits of the technology. However, time consuming and expensive experiments, and limited simulations on simple geometries are not sufficient for optimal LSP process design. A comprehensive simulation procedure is required that can be employed in process optimization for pressure pulse and laser spot properties, multiple treatments of LSP at the same location, sequential LSP at multiple locations, and different overlapping configurations. In this research, a simulation framework is developed and validated using available experimental results. For process optimization, the combination of continuous (pressure magnitude, duration and amount of overlap) and discrete (number of treatments and sequence of treatment) variables is creating a challenging mixed-variable task in which a representative simulation can take up to 4 days. The particle swarm optimization with a strategy to handle discrete variables are employed to solve the problem. With the target of applying LSP on an aircraft component, a representative plate structure is considered for case studies.

Fatigue Response of Aluminum Aircraft Structure under Engineered Residual Stress Processing

Advanced surface treatment methods for imparting beneficial residual compressive stresses into fatigue-prone metallic components such as laser shock processing (LSP) and low plasticity burnishing (LPB) have proven highly effective in prolonging the life of titanium turbine engine blades. The objective of the current effort was to experimentally evaluate whether similar life enhancement benefits are possible for metallic aircraft structures. Under this initiative, aluminum test specimens were processed using three engineered residual stress techniques, referred to as LSP 1, LSP 2, and LPB, and subsequently fatigue tested under uniaxial, constant amplitude loading conditions. Evaluation of the test results indicated that both the LSP and LPB processes, if carefully designed and applied, have the potential to increase the fatigue life of aircraft structural components.