Determination of residual stresses in thermal barrier coating due to the amount of CMAS infiltration

In this work, we present the effect of the amount of CMAS infiltration into YSZ of Thermal barrier coatings (TBC) on the magnitude of residual stresses. The (TBC) were deposited by thermal spraying of CoNiCrAlY (Bond Coat-BC) and YSZ (Top Coat-TC) powders. The deposition of the BC was through the high velocity oxygen fuel (HVOF) system. The TC was deposited via an atmospheric plasma-spraying gun (APS). The TBCs were heat treated at 1250 °C, with a CMAS attack at a concentration of 10 mg/cm².The attack exposure was for 2 and 4 hours respectively. In this evaluation, the measured parameter was the magnitude of the residual stress state in Yttria Stabilized Zirconia (YSZ). The residual stress profiles were obtained using the Modified Layer Removal Method for Duplex Coatings (MRCMRB) and the Noda equations. An increase of 26.446 MPa was determined for 2 hours of thermal treatment and 30.743 MPa for 4 hours.

Neutron Through-Thickness Stress Measurements in Coatings with High Spatial Resolution

A great variety of techniques are nowadays used to spray coatings with different functionality and properties for the purpose of surface enhancement. Depending on application and design, these can be thermal (plasma or high-velocity oxy-fuel are the most widely used) and warm or cold spraying, which are known to generate considerable residual stresses. This stress is a function of the spaying process as well as the material and thickness of the coating-substrate system. The mechanical integrity of coatings is critical for certain applications, e.g. wear resistant and thermal-barrier coatings, hence residual stress control and mitigation are essential in preventing the coating’s mechanical failure, improving the coating’s performance and the its operational lifetime. Although hole drilling technique or x-ray diffraction combined with layer removal method can be applicable for stress measurements in coatings, the neutron diffraction stress analysis also provides an effective and efficient tool for non-destructive through-thickness stress measurements with a commensurately high resolution, down to 0.1-0.2 mm. The most recent results of neutron diffraction stress measurements in coating systems are presented herein.

Study on the machining distortion of aluminum alloy parts induced by forging residual stresses

A weak-rigid monolithic component is subjected to significant distortion after the removal of material. This condition is principally due to flexibility of the part and the release of initial residual stresses resulting from fabrication. This article reports a systematic study on the measurement of initial residual stresses and the distortion of a windshield frame part induced by material removal from the forged blanks of aluminum alloy 7085-T7452. A layer-removal method was employed to measure the stress profiles of the blank. The stresses after analytical correction were found to be closer to actual condition. The effect of material removal on distortion from stressed blank was investigated using the finite element analysis software ANSYS. The simulated results indicate that after the proportion of removed material exceeds 60%, part distortion becomes stable. The comparisons of the simulation with experimental data suggest sufficient agreement with conclusion that the use of finite element analysis proves to be an attractive and reliable method for predicting stress-induced distortion.

Sensitivity Analysis of the Crack Compliance and Layer Removal Methods for Residual Stress Measurement in GFRP Pipes

A comparison is presented between the sensitivity to measurement error of the crack compliance and layer removal methods of residual stress measurement when applied to glass fiber reinforced plastic (GFRP) pipes. This is done by adding random scatter to the exact strain distribution associated with a known stress distribution. This defines strain data that simulate experimental measurements. These data are used to determine the corresponding residual stress distributions. The error in the residual stress distribution when scatter is included can thereby be determined. It is shown that the layer removal and crack compliance methods are equally suitable for the measurement of axial and circumferential stresses in a pipe wound at only ±55 deg. The layer removal method, however, is shown to have significantly lower sensitivity to measurement error when the axial residual stresses in layered GFRP pipes are considered.

Improvement to Stress Calculation Model of LRM in Thick Plate

Layer removal method is an experiment method which is used to calculate the average stress indirectly by deformation of the specimen. However, in the experiment, some certain predeformation can be caused after each clamping, which can affect the accuracy of the test data, and make the deformation data larger. Based on the comparison of the simulation calculation, this paper builds an amended function by fitting the deformation error, which solves the deviation caused by larger deformation on stress calculation while the specimen is milled by layer, that is to say, the stress calculation model can be compensated by this function. This method can make the experimental calculation model more accurate.