Visualization of dynamic stress conditions in elastic solids utilizing high frequency stroboscopic LED arrays

Ultrasonic mechanical vibrations in solids are widely used in non-destructive testing, and high-power applications such as ultrasonic welding or soldering. The visualization of ultrasonic wave propagation in transparent solids is helpful for understanding the ultrasonic behaviours. The classical method of photoelasticity allows the visualization of the static stress distribution in birefringent materials. Utilizing recent high-power LEDs in the photoelasticity allows to capture dynamic stresses by high frequency stroboscopic light. High frequency stationary and transient oscillation processes in elastic solids can be visualized with this method. The designed LED array in this paper has a dimension of 210 mm 300 mm, and every LED has distance of 38mm to each other, and the light intensity has a homogeneity value. The temporal and spatial resolution of stress-optic systems depends mainly on the dynamic properties of the lighting technology used. The high speed synchronization of the stroboscopic light sources results in a high temporal resolution of the photoelasticity analyses. This enables the photoelastic investigation of highly dynamic load conditions, such as longitudinal waves and transverse waves

Surface Integrity of Laser Beam Welded Steel–Aluminium Alloy Hybrid Shafts after Turning

The demands for high-performance solid components are constantly increasing. The reason for this development are the steadily growing requirements such as weight reduction, higher resistance to load stresses, and more functional integration. By using material compounds, for example high-strength steel and aluminium alloy, hybrid massive components, whose properties are specially adapted to the specific application, can be manufactured. The first challenge is the joining of two dissimilar materials like steel and aluminium alloy by laser beam welding. In particular, the formation of hard and brittle intermetallic phases (IMP) has a high influence on the mechanical properties of the joining zone. The second challenge is to examine the machinability of such dissimilar compounds. The machining process is mandatory in order to reach an adequate level of accuracy of shape and dimensions. Furthermore, the functionalization of the hybrid compounds will be realized with the machining process where required surface roughness and lifetime-determining residual stresses are adjusted. Connections between induced residual stresses and material properties have been investigated. A significant influence of machining parameters on the surface and subsurface properties is evident. In particular, the cutting edge rounding has a deep impact on the residual stresses as well as on surface roughness