Ch. Grossmann

Bio: Ch. Grossmann is an academic researcher from Ruhr University Bochum. The author has contributed to research in topics: Deformation (engineering) & Nickel titanium. The author has an hindex of 1, co-authored 1 publications receiving 87 citations.

Elementary Transformation and Deformation Processes and the Cyclic Stability of NiTi and NiTiCu Shape Memory Spring Actuators

Abstract: The present work addresses functional fatigue of binary NiTi and ternary NiTiCu (with 5, 75, and 10 at pct Cu) shape memory (SM) spring actuators We study how the alloy composition and processing affect the actuator stability during thermomechanical cycling Spring lengths and temperatures were monitored and it was found that functional fatigue results in an accumulation of irreversible strain (in austenite and martensite) and in increasing martensite start temperatures We present phenomenological equations that quantify both phenomena We show that cyclic actuator stability can be improved by using precycling, subjecting the material to cold work, and adding copper Adding copper is more attractive than cold work, because it improves cyclic stability without sacrificing the exploitable actuator stroke Copper reduces the width of the thermal hysteresis and improves geometrical and thermal actuator stability, because it results in a better crystallographic compatibility between the parent and the product phase There is a good correlation between the width of the thermal hysteresis and the intensity of irrecoverable deformation associated with thermomechanical cycling We interpret this finding on the basis of a scenario in which dislocations are created during the phase transformations that remain in the microstructure during subsequent cycling These dislocations facilitate the formation of martensite (increasing martensite start (M S ) temperatures) and account for the accumulation of irreversible strain in martensite and austenite

Identification of Quaternary Shape Memory Alloys with Near‐Zero Thermal Hysteresis and Unprecedented Functional Stability

Abstract: Improving the functional stability of shape memory alloys (SMAs), which undergo a reversible martensitic transformation, is critical for their applications and remains a central research theme driving advances in shape memory technology. By using a thin-film composition-spread technique and high-throughput characterization methods, the lattice parameters of quaternary Ti-Ni-Cu-Pd SMAs and the thermal hysteresis are tailored. Novel alloys with near-zero thermal hysteresis, as predicted by the geometric nonlinear theory of martensite, are identified. The thin-film results are successfully transferred to bulk materials and near-zero thermal hysteresis is observed for the phase transformation in bulk alloys using the temperature-dependent alternating current potential drop method. A universal behavior of hysteresis versus the middle eigenvalue of the transformation stretch matrix is observed for different alloy systems. Furthermore, significantly improved functional stability, investigated by thermal cycling using differential scanning calorimetry, is found for the quaternary bulk alloy Ti 50.2 Ni 34.4 Cu 12.3 Pd 3.1 .