An Improved Approach to Direct Simulation of an Actual Almen Shot Peening Intensity Test with a Large Number of Shots

Abstract

In existing simulations of the Almen intensity test, arc height is indirectly obtained by an equivalent method including a representative cell, a few shots and equivalent loading. Most of these equivalent methods cannot consider the transverse deformation of the strip, the complex stress state of the plastic hardening layer and process parameters, resulting in deviation from the actual test. This paper introduces an improved and experimentally validated discrete element model (DEM)-finite element model (FEM) to predict the actual Almen intensity. The improvement of this model is mainly reflected in the large and real number of shots involved in the actual Almen intensity test, shot–shot interactions, and real-size solid finite element model of the Almen strip. A new method for calculating the shot stream is proposed based on the test and considering test process parameters such as the mass flowrate, nozzle movement speed and nozzle–workpiece distance. The shot stream impacting the strip with a fully restrained underside was first simulated in improved DEM-FEM to bring the forming energy. As a second step, an implicit solver of the Almen strip FEM calculates the spring-back to simulate strip removal from the holder. The results achieved by the present approach are compared with the results obtained by the experimental results and those in the literature. The results show that the arc height and Almen intensity obtained by the present approach match much better with the literature than the traditional method. Some new results obtained by the improved coupling DEM-FEM method are presented. The influences of the transverse deformation and surface plastic layer on the deformation of the Almen strip are discussed. This improved method provides an alternative characterization method for precision peen forming simulation.

Study on the Measurement Method of Shot Velocity and Mechanical Properties Based on Conventional Shot Peening

“…The Almen strip intensity method is the most commonly used standard experimental method to quantitatively evaluate shot peening effects in industrial practice. In the Almen intensity experiments, the test strategy presented by Wang et al 6 was applied to obtain the Almen intensity. The most common Almen strip of type A with a thickness of 1.29 mm was selected as the research object in all experiments, as schematically displayed in Figure 4 a.…”

“…At present, there are two methods to simulate the Almen intensity test: representative elementary volumes 19 , 36 and the direct simulation method of real shot numbers. 6 In this study, the simulation strategy presented by Wang et al 33 was applied to simulate realistic peening data from the Almen intensity test. A specific target mesh, with dimensions of 1.2 × 1.2 × 0.5 mm, was selected as a representative volume to study the induced and residual stress and surface roughness, as shown in Figure 5 a.…”

“… 3 − 5 The effectiveness and repeatability of the shot peening process are verified by using a simple and rapid standard test: the Almen intensity test. 6 It is well known that the Almen intensity is proportional to the shot kinetic energy. 7 Therefore, if one were able to accurately measure the shot velocity, they would also be able to determine the Almen intensity.…”

“… 13 − 17 For example, discrete element models were proposed to simulate a large number of shots. 18 Jebahi et al 19 and Wang et al 6 presented the coupling model of discrete elements and finite elements (DEM–FEM) and used elastic theory to calculate the arc height of the Almen strip with different shot velocities. These analytical models have been proposed to relate the deformation of the strip to shot velocity and other parameters.…”

“…Conventional shot peening refers to the transfer of energy through solid media, such as stainless-steel balls, ceramic balls, and so forth, different from laser shot peening, high-pressure water shot peening, and ultrasonic shot peening. During this mature cold-working process, a large number of small shots are accelerated by high-pressure air to repeatedly impact the metal surface, causing plastic deformation, gradient microstructure changes, , and hardening of the surface layer. − The effectiveness and repeatability of the shot peening process are verified by using a simple and rapid standard test: the Almen intensity test . It is well known that the Almen intensity is proportional to the shot kinetic energy .…”