Variable Damping Profiles Using Modal Analysis for Laser Shock Peening Simulation

The single explicit analysis using time-dependent damping (SEATD) technique for laser shock peening (LSP) simulation employs variable damping to relax the excited model between laser shots, thus distinguishing it from conventional optimum constant damping methods. Dynamic relaxation (DR) is the well-established conventional technique that mathematically identifies the optimum constant damping coefficient and incremental time-step that guarantees stability and convergence while damping all mode shapes uniformly when bringing a model to quasi-static equilibrium. Examined in this research is a new systematic procedure to strive for a more effective, time-dependent variable damping profile for general LSP configurations and boundary conditions, based on excited modal parameters of a given laser-shocked system. The effects of increasing the number of mode shapes and selecting modes by contributed effective masses are studied, and a procedure to identify the most efficient variable damping profile is designed. Two different simulation cases are studied. It is found that the computational time is reduced by up to 25% (62.5 min) for just five laser shots using the presented variable damping method versus conventional optimum constant damping. Since LSP typically involved hundreds of shots, the accumulated savings in computation time during prediction of desired process parameters is significant.

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Variable Damping Profiles for Laser Shock Peening Simulation Using Modal Analysis and the SEATD Method

Volume 1: Processes ◽

10.1115/msec2017-2891 ◽

2017 ◽

Cited By ~ 1

Author(s):

Mohammad I. Hatamleh ◽

Jagannathan Shankar Mahadevan ◽

Arif S. Malik ◽

Dong Qian

Keyword(s):

Boundary Conditions ◽

Modal Analysis ◽

Surface Engineering ◽

Spot Size ◽

Laser Shock Peening ◽

Laser Shock ◽

Dynamic Relaxation ◽

Alloy Plate ◽

Variable Damping ◽

Shock Peening

Laser shock peening (LSP) is a surface engineering technique, which aims to increase the fatigue life of various metallic components by inducing compressive residual stress at or near their surface. The finite element method (FEM) is used to identify the most suitable parameters in LSP. Various explicit analyses with artificial material damping are used to attain quasistatic equilibrium between laser shots. Dynamic relaxation (DR) is a well-known conventional technique that uses constant artificial damping to settle an excited model to quasi-static equilibrium. In contrast, the recently developed “Single Explicit Analysis using Time-Dependent Damping” (SEATD) method employs variable damping and performs better in terms of simulation time and accuracy. While recent study has shown that a variable damping profile used in the SEATD technique is beneficial for an LSP set up, identifying the most suitable variable damping profile in general is still ambiguous, given the variety of possible set-ups and boundary conditions. In this paper, a systematic procedure to strive for the best variable damping profile is developed, based on the excited modal parameters of the model. The simulation results are compared with those of an optimum constant damping profile developed using the conventional dynamic relaxation technique, as well as for the best variable damping profile based on exhaustive trial-and-error. The simulation case studies involve circular LSP shot(s) of 5.5 mm diameter spot size applied to Al 2024-T351 aluminum alloy plate under different boundary conditions. Dissipation rates of stain energy, kinetic energy, and total energy and the accuracy of surface residual stresses are investigated to compare the performance of different damping profiles. The results indicate that the proposed method involving modal analysis to systematically identify a variable damping profile, to promote simulation efficiency, appears to work well.

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Explicit analysis using time-dependent damping simulation of one-sided laser shock peening on martensitic steel turbine blades

SIMULATION ◽

10.1177/0037549720954272 ◽

2020 ◽

Vol 96 (12) ◽

pp. 927-938

Author(s):

Festus Fameso ◽

Dawood Desai

Keyword(s):

Martensitic Steel ◽

Service Failure ◽

Turbine Blades ◽

Experimental Studies ◽

Laser Shock Peening ◽

Time Dependent ◽

Laser Shock ◽

Implicit Methods ◽

Finite Element Software ◽

Shock Peening

Down-times from the in-service failure of power plant components, such as turbine blades, portend dire impacts and consequences in the form of huge financial losses. The susceptibility of steam turbine blades to failure is now being reduced by a novel technique, laser shock peening (LSP), which induces compressive layers through the surface of the blades. Current simulation studies of LSP employing conventional methods are indeed computationally expensive and time-consuming. Hence, this paper explores an alternative numerical modeling technique to investigate the economic parameters of residual stresses induced in martensitic steel turbine blades when subjected to LSP treatment. An explicit simulation method of analysis, using commercial finite-element software, which employs time-dependent damping, is presented. The study shows that this technique is time-efficient compared with the conventional explicit-implicit methods commonly used for such simulations. It is interesting to note that the results indicate that up to 500 MPa of induced compressive stress of layers reaching 1 mm in depth can be obtained. Encouragingly, these results correlate well with previous experimental studies, lending credence to the method’s validity. The technique employed hence offers solutions for timely, non-destructive, methodical maintenance and improvement of the mechanical properties of turbine blades, in the quest to reduce the risks of their in-service failure, as well as lengthening of their service life.

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