Papers by Author: Winfried Petry

Abstract: Composite castings exhibit high residual stresses, mainly because of different thermal expansion of the used materials. Similar to the in-cast cylinder liners in a motor block, a composite specimen, consisting of a steel insert and an aluminum cast surrounding, was analyzed by neutron diffraction. The temperature- and time-dependent change of lattice spacing and thus the strain evolution was investigated by in-situ experiments directly after casting and during the cooling of the part. Different cooling conditions were investigated using two different molds, namely a sand and a permanent (steel) mold, optimized for in-situ neutron diffraction.

Abstract: The materials science diffractometer STRESS-SPEC located at Forschungsneutronen¬quelle Heinz Maier-Leibnitz (FRM-II) in Garching/Germany is a dedicated instrument for residual strain, texture and microstrain analysis. Comparably low gauge volumes of 1x1x1mm³ for gradient investigations in many types of materials can be investigated. A robot system consisting of a robot type Stäubli RX160, a laser tracker and a heavy vibration free basement was installed to overcome limitations in gradient investigations of residual stresses and crystallographic textures in semi-finished and finished products. The robot can carry up to 30kg with precise positioning. Al7020, an Al-alloy for airspace application, was used to perform a first global texture measurement using the robot.

Abstract: Mechanical and thermal treatments during the manufacturing process inevitably cause the accumulation of residual stresses in parts consisting of materials with complex microstructures. Neutron diffraction is particularly well suited to determine residual stress distributions within the bulk of the component. Due to the nature of a diffraction experiment an inextricable mixture of type I and II residual stresses is measured. The accumulation of type II stresses (microstresses) is strongly related to the microstructure. The impact of changes in the microstructure on neutron diffraction experiments has been investigated on Inconel 718 (IN718) samples.