Papers by Keyword: Residual Stress Measurement

Abstract: This research is aimed to compare the influence of backing materials on characteristics of ultrasonic probe for residual stress measurement. A disk-shaped piezoelectric ceramic (PZT) acts as the active element to generate the ultrasonic wave. An optimization composition of backing material was investigated in order to produce suitable acoustic impedance which matches to the active element. In this study, the backing material has been successfully fabricated from tungsten powder combined with epoxy resin (T-ER) and bronze powder associated with epoxy resin (B-ER). The influences of metal powder content on sound velocity and acoustic impedance of the backing materials were measured by using Pulser/Receiver and displayed by an oscilloscope. Each ultrasonic probe was then implemented to measure residual stress obtained from static tension load below yield point. The results shown that the highest acoustic impedance of T-ER and B-ER was 14.7 10⁶ and 7.2 10⁶ kg/m²s, respectively. The fabricated ultrasonic probe using B-ER as a backing material exhibited lower noise and higher amplitude than ultrasonic probe using T-ER backing material.

Abstract: In this study, residual stresses in polyamide (PA) materials were measured by the x-ray stress measurement technique. X-ray stress measurement is widely used to measure residual stresses, however, this measurement is not many used in polymeric materials. There are two problems for measuring residual stresses in polymer. Firstly, the diffraction peak from the polymer appears at the low 2θ angle region. Thus the measurement accuracy for strains reduces. Secondly, the low 2θ angle region is very difficult to use the sin2ψ method. In this study, Ω-diffractometer with transmission method was used to resolve these problems. The measured data was plotted in the d-sin2ψ diagram, and it was coincident with the linear regression line clearly. X-ray elastic constant (XEC) of PA was estimated from these results.

Abstract: Technological residual stresses have great importance in the manufacturing processes and the lifetime of components. The residual stresses formed by quenching can be very diverse because of its multiple sources. Alternative quenching processes such as laser hardening have a great potential for different applications. The direction of heat transfer during laser hardening is the opposite compared to conventional quenching. This further increases the complexity of the developed stress state. The residual stress profile and the microstructure formed by laser hardening treatment are investigated in the present manuscript.

Abstract: Shot-Peening is used to generate surface-near compressive residual stresses in final shape parts, usually to improve their fatigue properties. The success of the process can be checked in different ways. XRD and Hole-Drilling determine quantitative stress depth profiles in specific locations. Barkhausen noise measurements evaluate a near-surface zone in real-time and can cover large areas quickly. It is a fully nondestructive method. This study compares ESPI Hole-Drilling, which is a very fast technique, and XRD, which is very precise but slower, to Barkhausen Noise results for the case of three steel rings shot-peened with different intensities.

Abstract: Ultra-sonic measure of residual stress has been along for a while. One main drawback of this technique is the need for a measuring head adapted to each new surface shape. We introduce a new measurement head designed to adapt to changing curves. This device will open the possibility of curved surfaces residual stress cartography. We focus on the device geometric design, its possibilities and limitations.

Abstract: Heat transfer during laser hardening occurs from the surface towards the bulk in contrast to conventional quenching, where it occurs from the bulk towards the surrounding. The residual stress distributions due to laser hardening and conventional quenching of plain carbon steel samples were measured using X-ray diffraction. The effect of changing the treatment parameters, that is laser power and feed rate, was examined on the resulting stress distribution. The relationship between the measured stress distribution and the evolved microstructure is established.

Abstract: The hole drilling technique is probably the most widely used residual stress measurement technique. The ASTM E837 standard covers hole drilling measurements for thin and thick specimens. VEQTER have encountered several cases when the specimen was between the thick and thin specification. In order to gain a greater understanding of the sensitivity of the analyses and accurately measure the residual stresses using the hole drilling technique within intermediate thickness specimens and within thin specimens containing non-uniform residual stresses a study was performed.

Abstract: Measuring theory of two types of X-ray stress analysis method was compared with each other. One is the conventional method, in which zero-or one-dimensional detector is used for obtaining diffracted beam and stress is determined using the standard sin²ψ method. Another is the new type of X-ray stress analysis method, in which two-dimensional detector is used to obtain whole Debye ring and stress is determined using the cosα method. An experiment was conducted to investigate the validity.

Abstract: Nickel based alloys are widely used in steam generator tubes for nuclear power plants. 1-D X-ray stress measurements have been used for these alloys. But 1-D method requires large equipment and it is practically impossible to measure stress in power plants. In order to overcome this problem, we adopted 2-D X-ray method which requires significantly smaller equipment. In this paper we report preliminary results of 2-D X-ray stress measurements of nickel based alloys.

Abstract: It is understood that residual stresses in aluminothermic rail welds play an important role in the fatigue behaviour of the welds. Measuring the residual stresses in the critical areas and finding the correlation between these stresses and welding parameters can be useful in order to alter the welding procedure and improve the fatigue performance of these welds. In this paper, residual stresses in the foot of the rail weld were measured using neutron diffraction and the preliminary results are presented.