Thermal fatigue evaluation of cast iron discs for railway vehicles

AbstractThermal fatigue of brake discs for railway vehicles has been a troublesome problem since the advent of disc brake. To develop cast-iron brake discs with high heat resistance to thermal shock loading, three candidate materials with different components were developed. Main components of the cast irons are Fe, C, Si, Mn, Ni, Cr, Mo, Cu and Al. Mechanical and thermal properties were measured. Then thermal fatigue tests were carried out by a thermal fatigue test equipment developed by the authors. The possible temperature range of the equipment is 20∼1500 °C. Cylindrical solid specimens ϕ20×80 mm were heated by an induction coil and cooled in water. At an interval of 20∼30 thermal cycles, the surfaces of the specimens were examined with an optical microscope to check thermal cracks. To quantify the total length of cracks an image analyzing program that can measure the length of cracks from micrographs was developed. It was found the fatigue lifetime of cast iron can be elongated by regulating composition and metallurgical structures

Stress Rate Effect on the Pseudoelastic Behaviour of CuZnAl Single Crystals

Tensile pseudoelastic tests performed on elaborated single crystals show that the width of hysteresis loops and the slope of the stress-strain curves during phase transformation increase as the applied stress rate increases. In the first elementary model without mechanical dissipation, the integration of heat equation permits the qualitative description of hysteresis loop. The second model with a non-convex free energy and mechanical dissipation allows us a quantitatively good modeling of loading rate effects

Characterization, Thermomechanical Behavior and Micromechanics Constitutive Model of Shape Memory Cu-Zn-Al Single Crystal

Cu-Zn-Al shape memory alloys are grown as single crystals by the Bridgman technique with a final shape directly suitable for thermomechanical tests (cylinders with tapered heads: 25 mm gauge length, 4 mm in diameter). The four classical transformation temperatures are checked by Differential Scanning Calorimetry and resistivity. The orientation of crystal structure is investigated by X-ray diffraction. Isothermal pseudoelastic tensile tests show that the width of the hysteresis loops and the slope of the stress-strain curves during phase transformation increase as the applied stress rate increases. A micromechanical-based constitutive model allows us to describe this single crystal behaviour. Copyright (C) 1996 Acta Metallurgica Inc

Growth and Characterization of Shape Memory Cu-Zn-Al Single Crystals

To provide a better insight of shape memory alloys (SMA) behavior, Cu- Zn-Al single crystals were grown by the Bridgman technique. Melting was performed under pure argon in a graphite crucible allowing to obtain samples (total length 40 mm) with the final shape directly suitable for mechanical tests (cylinders with taper heads : 25 mm useful length, 4 mm in diameter). The chemical composition was checked by Differential Scanning Calorimetry and resistivity. It was found that a small zinc concentration gradient exists along the samples : it induces a difference less than 5 K for transformation temperatures in the useful length. The morphology, the shape deformation, crystal structure, sub-structure and orientation have been investigated by optical, transmission and scanning electron microscopy and by X-Ray diffraction. Pseudoelastic isothermal tensile tests and training under constant applied stress and variable temperatures were carried out. The training efficiency for these elaborated alloys is very large (about 80-90%)