Hans-Joachim Kühn

High-temperature behaviour of IN 738 LC under isothermal and thermo-mechanical cyclic loading

Abstract The temperature dependence of the cyclic behavior of IN 738 LC was studied. Cyclic iso- and non-isothermal tests were performed with proportional and non-proportional tension/torsion strain paths. It was shown that maximum and minimum stress values measured in isothermal strain controlled tests correspond quite well with results of non-isothermal tests. Thermal-mechanical constitutive equations based on the viscoplastic Chaboche model were used to describe the non-isothermal stress-strain behavior.

The Stress-Strain Behaviour of IN738LC under Thermomechanical Uni- and Multiaxial Fatigue Loading

High temperature components such as cooled or uncooled first stage turbine blades are subjected to triaxial stress fields, mainly induced by constrained thermal strain fields during service. The steepest temperature gradients and consequently the largest thermoinduced stresses are generated during start-up and shut-down phases of turbine operation.

High Temperature Inelastic Deformation of in 738 LC Under Uniaxial and Multiaxial Loading

The uniaxial and multiaxial inelastic deformation behaviour of IN 738 LC has been investigated by performing isothermal tensile, creep, cyclic, stress relaxation, and cyclic proportional and nonproportional tension/torsion tests with the ultimate aim to obtain an understanding of the hardening/softening and failure behaviour of this alloy. The range of strain rates examined was 10-6s-1 to 10-2s-1 while the test temperatures ranged from 25 °C to 950 °C. The cyclic hardening and softening behaviour of the alloy was found to depend on temperature, strain rate and strain/stress amplitude. It was shown that there is no extra hardening as the result of nonproportional loading. The comparisons of proportional and 90 deg. out-of-phase stress loci at given effective strain, given effective strain rate and temperature revealed that the J2-theory was approximately applicable for describing the multiaxial behaviour of IN 738 LC.

Multiaxial Thermo-mechanical Deformation Behavior of IN 738 LC and SC 16

A study was undertaken to develop an understanding of the fatigue life on IN 738 LC under simple and simulated in-service operating thermomechanical cycling (TMF) in air. The experiments were conducted in the temperature ranges 450 - 950 °C, 450 - 760 °C and 600 - 850 °C. Results indicate that the lives differ with strain-temperature phasing. Diamond cycles gave the longest lives. A life prediction assessment is proposed based on the inelastic work Σ MF σ i j Δe l n i j at Nf. It is, shown that the J 2 theory is applicable to TMF loadings. Initial experiments on single crystal superalloy SC 16 prove that there is a non-uniform strain distribution in the plastic region along the circumference of [001] oriented specimens. These findings must be weighed when performing TMF tests.

THERMOMECHANICAL DEFORMATION BEHAVIOUR OF IN 738 LC AND SC 16

ABSTRACT This article describes the study of uniaxial and biaxial thermo-mechanical fatigue (TMF) response of IN 738 LC and the initial experiments of single crystal superalloy SC 16. A life prediction assessment is proposed based on the inelastic work Σσ ij Δe ij in at N f /2. It is shown that the J 2 -theory is applicable to TMF-loadings. Initial experiments on single crystal superalloy SC 16 prove that there is a non-uniform strain distribution in the plastic region along the circumference of [001] orientated specimens. These findings must be weighed when performing TMF-tests.

LCF-Experiments on Single- and Poly-Crystalline Metals — SRR99 and In 738 LC — Under Uniaxial And Multiaxial Strain Controlled Loading Conditions

This poster summarizes the well defined experimental procedures for elevated temperature testing technologies in BAM. Especially, this paper aims to consider the aspects of alignment of gripping device, temperature measurement and definition of fatigue life. Results obtained from uniaxial and multiaxial experiments on SRR 99 and IN 738 LC are presented.