Stress-strain hysteresis and damping in MnCu and NiTi alloys

Abstract

Uniaxial stress-strain hysteresis loops for high damping manganese-copper (MnCu) and nickel-titanium (NiTi) shape memory alloys are experimentally determined. The characterization concerns two MnCu samples, one containing 60 pct Mn, the other 40 pct Mn, and two NiTi samples, one in the martensitic phase and the other in the austenitic phase at room temperature. In the 225 to 360 Hz frequency range, tests are conducted using a vibration exciter; for lower frequencies (2Hz), we use a Material Test System (MTS) servohydraulic apparatus. The ensuing characterization allows us to compute the energy dissipated per unit volume per cycle, the dynamic modulus, and the loss factor as a function of frequency and strain amplitude. The sensitivity of these results to such factors as frequency, temperature increments during the tests, and vibration duration are discussed. The experimental stress-strain characterization is also used to express the tangent stiffness along the stress-strain path as an analytical function of strain (within the vibration cycle) and strain amplitude using kriging interpolation. Behavioral differences both between the alloys and also from equivalent linear viscous models are discussed.