No abstract

A unique X-ray diffraction instrument for residual stress measurement has been developed that provides for speed, ease of measurement, accuracy, and economy of surface stress measurement. Application of this instrument with a material removal technique, e.g., electropolishing, has facilitated detailed, high resolution studies of three-dimensional stress fields. This paper describes the instrumentation and techniques applied to conduct the residual stress measurement and presents maps of the residual stress data obtained for the surfaces of a heavy 2 1/4 Cr 1 Mo steel plate weldment.

This paper presents initial results in the development and testing of SiC-based Continuous Fiber Ceramic Composites (CFCC) materials for combustor and stage 1 shroud components of large utility-class gas turbines. Use of CFCC’s for these components has the potential for increasing output power and thermal efficiency and reducing emissions. First stage turbine shroud components were fabricated using five material systems including three SiC/SiC-Si systems made by silicon melt infiltration (MI), chemical vapor infiltrated (CVI) enhanced SiC-SiC and directed metal oxidation (DIMOX) Al2O3-SiC composite. A combustor liner was made of MI CFCC. Before and after testing the components were inspected by several NDE techniques including IR thermography, resonance testing and visual examination. A novel, high pressure test rig was used to test four shroud components and a combustor liner simultaneously. Components were exposed to hot gas temperature of 1200°C at 12.5 bar in cyclic and steady-state tests. Cyclic testing simulated engine trip conditions with 200 flame-on, flame-off cycles. Steady state testing involved 100 hours of exposure at high temperature and pressure with hot combustion gases. At the conclusion of the first phase of testing there was visible damage to two pieces of one of the material systems. Destructive testing of the components following rig exposure showed little degradation to the MI composite materials. In summary, high pressure combustion rig testing of these components demonstrated excellent performance with little degradation among the material systems.

The Pennsylvania State University has developed and tested a miniature x-ray instrument for the measurement of residual stress (strains). The stress head including x-ray source and detection surface is approximately four and one-half inches long and can be inserted into an orifice less than two and one-half inches in diameter. This head is on the end of a several-foot long cable and is extremely manipulatable.The instrumentation design is based upon a unique position sensitive scintillation detector which ie capable of applying the single-exposure x-ray stress measurement technique. Total lapse time data collection periods for aluminum alloys are less than ten seconds with x-ray tube powers of 120 watts. Results from a four-point bend test on an aluminum alloy specimen showed excellent precision. The configuration of the instrument and the procedures for its application are described.

A typical TBC system consists of a ceramic top coat material, such as 7–8% yttria stabilized zirconia, applied over a metallic bond coat material, such as diffusion aluminide or MCrAIY. The bond coat serves as an oxidation protection layer for the substrate, as well as providing an adherent surface for the ceramic top coat layer. Estimation of coating durability is critical for design of highly reliable TBC coated parts. Laboratory testing and historical engine experience have revealed that TBC can degrade by various mechanisms; such as fatigue, oxidation, erosion, and impact. Mechanism-based life prediction techniques are needed to assess the durability of TBC in a simulated gas turbine service cycle consisting of: start-up to full speed, steady state operation at full load, and shut-down to zero speed. New testing protocols have been developed in order to simulate the TBC loading under these conditions. The lifing methodology has been calibrated using GE Power Systems gas turbine experience. A nondestructive technique was also used for evaluation of pre- and post-tested TBC specimens.