Papers by Keyword: Stress Measurement

Abstract: Effect of multi-section linear non-uniform heat transfer coefficient on quenching residual stress distribution in 27mm-thick Al-Zn-Mg-Cu aluminum alloy plate was simulation studied by using the finite element method, and the surface quenching residual stress distribution was measured by the X-ray diffraction method and hole-drilling method. The results show that the surface quenching residual stress represents the same distribution with non-uniform heat transfer coefficient in the transverse direction and the stress level maintains initial stress level of the heat transfer coefficient at each location. The distribution of the quenching residual stress in the center of the plate is approximately uniform and the stress level is approximately equal to average of maximum and minimum initial stress level. The measured surface quenching residual stress shows a wavy distribution in the transverse direction, which is similar to the simulated surface stress distribution without considering the stress level. The measurement results can be explained by the multi-section linear non-uniform quenching model.

Abstract: The Magnetic Barkhausen Noise (MBN) technique can evaluate the residual stresses in carbon steel and provide information about the relationship between residual stress level and MBN signal. This research work is based on the analysis of MBN signals obtained from carbon steel samples. ASTM A36 and A516 carbon steel were used to vary the residual stress by heat treatment process with 5 conditions: annealing, normalizing, quenching in oil, quenching in water and quenching in salt water. The microstructure and hardness of samples also were varied by these heat treatment processes. Twelve samples (including base materials) were cut to analyze the microstructure and hardness by the microscope and hardness testing machine. Reference materials from each condition were established to represent the MBN signals. The MBN technique was used to evaluate the residual stresses from heat treatment process on each reference material. Then each sample was prepared to tensile specimen. All specimens were applied static tension load below yield point. The load was increased at 25 N/mm² (MPa) in increment. Each tensile stress level was measurement by MBN technique at 0 and 90 degree of direction of tension axis. The experimental results found that the MBN signal amplitude changed as the condition of heat treatment changed and the relationship between tensile stress and MBN signal showed linear correlation. This research is useful to understand and guide for establishing the reference materials for residual stress measurement by MBN technique.

Abstract: In this paper, the effects of Surface Mechanical Attrition Treatment on the high-temperature oxidation of AISI 316L austenitic stainless steel are investigated. Samples treated with different conditions were oxidized at 650°C in order to study the effect of this type of nanocrystallisation on the oxidation resistance of the alloy concerned. X-ray diffraction and in-situ Raman spectroscopy were used to identify the oxides formed at the surface. The results indicate the presence of hematite and chromium oxides. Experimental results obtained by Raman spectroscopy were also used to study the stress evolution in Cr₂O₃ films during isothermal conditions.

Abstract: The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromium oxide are investigated. An extended model is established to take into account the effects of temperature and thermal cycling for the calculation of oxide stress. Numerical results are given in order to predict the influence of different parameters, especially the dependence of some material parameters with temperature. This enables to make comparison with experimental results.

Abstract: 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.

Abstract: Duplex stainless steel is a material that attracts great interest of different branches of engineering and industry because of its combination of good structural and mechanical characteristics and high corrosion resistance. The microstructure of duplex steel presents an example of composite material with approximately equal amounts of austenite and ferrite phases. Physical and mechanical properties of these components are different so their behaviors under loading are different too. Therefore it is important to analyze the distribution of applied stress between ferrite and austenite phases of duplex steel. The analysis of stress distribution was made by X-ray diffraction technique. X-ray diffraction method allows separate measuring of stresses in each phase and determination of others mechanical characteristics as Young ́s modulus, yield stress of ferrite and austenite both in elastic and plastic region. In presented paper the samples of duplex steel after rolling were loaded by calibrated springs; using of Cr-K_α radiation allows carrying out of stress measurements in ferrite and austenite phases of duplex stainless steel.

Abstract: The rotating-slit system was developed to overcome the measurement of internal stress using 2-dimensional detector. The diffraction spot trace method was proposed and examined to measure the internal stress of the material with coarse grains.

Abstract: This paper describes a newly developed set of Barkhausen noise testing system including magnetizing and pick-up coils and the subsequent data acquisition unit based on the generation mechanism of Barkhausen noise. We studied the intensity of magnetic Barkhausen noise (MBN) of 16MnR steel under different states of stress by tensile test of flat-shaped specimens.

Abstract: A micro-displacement, strain and stress measurement method based on electronic speckle pattern interferometry (ESPI) technique is proposed, and the measuring device is designed. Two symmetric laser beams are illuminated on the optical rough surface of a steel cantilever beam, and then speckle images are photographed by CCD. A series of filtering processing is carried out for subtracted images and FEM analysis is performed. Using the speckle fringe patterns finally achieved, displacement, strain and stress can be calculated. By comparing displacement, strain and stress measured by this method with simulation results, feasibility and engineering application value of this method have been proved.

Abstract: Quantitative residual stress depth profile measurements are common in metallic parts but not in glass or plastic. This paper describes some experimental stress depth profile measurements using hole-drilling with electronic speckle pattern interferometry (ESPI) in two types of glasses and two thermoplastics. Stress depth profiles in laminated and toughened glass specimens show the expected low stresses in the former and significant compressive stresses near the surface in the latter for the as-is condition. The stress curves shift towards tensile stresses during slight bending deformation, as expected. The bending devices initially used for experiments with Bayblend® and Makrolon® were deforming the specimens too severely to allow proper, static, measurements. Significant stress reductions due to creep were measured for extended bending times. Subsequent measurements for less severe bending show similar stress curve characteristics. Residual stresses in the as-is condition apparently account for some of the differences to the predicted bending stress profile.