Shot dynamics

This paper presents a fast and interesting chaining method for ultrasonic shot peening that allows a quick prediction of the deformed shot peened part from the ultrasonic shot peening process parameters. A simulation of the shot dynamics is done using the exact process parameters, in order to obtain the impact velocity field on the peened surface. This field is then used as an input data for an analytical residual stresses model to predict the induced residual stress field in the sample. The latter is then fed to a Finite Element Method model as an initial condition for an elastic equilibrium calculation to predict the deformation of the part. This allows a complete and fast chaining from the process parameters to the deformed shot peened component. This approach has been applied to an Almen strip. Experimental and numerical data of the strip curvature have been compared and show very promising results.

This paper presents a fast and interesting chaining method for ultrasonic shot peening that allows a quick prediction of the deformed shot peened part from the ultrasonic shot peening process parameters. A simulation of the shot dynamics is done using the exact process parameters, in order to obtain the impact velocity field on the peened surface. This field is then used as an input data for an analytical residual stresses model to predict the induced residual stress field in the sample. The latter is then fed to a Finite Element Method model as an initial condition for an elastic equilibrium calculation to predict the deformation of the part. This allows a complete and fast chaining from the process parameters to the deformed shot peened component. This approach has been applied to an Almen strip. Experimental and numerical data of the strip curvature have been compared and show very promising results.

"A 3D model of the shot dynamics has been created based on models usually used in granular gases. A triangular mesh, representing the geometry of the entire setup (sonotrode, peening chamber and peened sample), is used in the calculations and define the space in which the spheres are able to move. In doing so, we are able to simulate thousands of impacts on the peened surface, from which statistical studies can be made to obtain direct information on the physical parameters. An experimental setup has been developed to access the shot trajectories and velocities during a peening operation, the surface coverage, as well as material related data used in the model. Preliminary studies show a good correlation with the numerical results.
An important contribution of the model to the various residual stresses prediction models (finite element models, analytical models, etc.) is that it allows them to benefit from more realistic data regarding the impact frequency and distribution on the sample, the energy dissipation, the impact velocities, etc. Such data is not available or very difficult to access experimentally at the present time.
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Ultrasonic shot peening is a mechanical surface treatment which consists of projecting spherical shots with a vibrating system called sonotrode on to a metallic surface to introduce compressive residual stresses. These residual stresses have the benefit of increasing significantly the life span of the component. Nevertheless, the choice of the peening parameters – such as the diameter and number of shots, the sonotrode amplitude and frequency of vibration – is difficult to make and requires a lot of hard and costly experimentation. Modeling the dynamics of the shots during this process gives a better understanding and control of these physical parameters. The models developed - based on the theory of granular gases – allow the deduction of quantitative information such as impact, velocity and angle distributions, as well as surface impact density and frequency for the treated surface. This information can then be used to correlate experimental with numerical data and result in a better understanding and choice of the physical parameters listed above.