Research On Residual Stress Measurement Of 6061-T6 Aluminum Alloy By Ultrasonic Method

Composite material has a series of advantages,such as high specific strength and modulus,good damping property and excellent corrosion resistance,so it is widely used in aerospace,ship and automotive industries.However,due to the existence of defects such as pores,delamination and cracks,residual stress will be introduced in the process of preparation,processing,assembly and service.It will not only affect the performance of components,but also has an impact on the structural failure strength and dimensional stability of composite material.Therefore,in order to detect the stress state and accurate evaluation of materials lifetime,it is of great significance to study the measurement of residual stress of composite material.Composite laminates are usually designed to be quasi-isotropic laminates,for avoiding the warping deformation caused by tension-shear and tension-bending coupling.Besides,it is often considered as isotropic treatment in the analysis of quasi-isotropic composites.X-ray diffraction residual stress technique is a method of non-destructive,efficient,accurate measuring data and good repeatability,which is widely accepted in the world.But it is only applicable to the residual stress measurement of crystal materials,and stress detection in amorphous materials like composite material.So,the acoustic elastic expression suitable for quasi-isotropic composite material is derived theoretically,in order to detect its stress state accurately.To verifying the correctness of the theoretical deduction,the 6061-T6 aluminum alloy was selected as the experimental object,and then using X ray diffraction method and the ultrasonic method derived in this paper to measure its stress.The paper has carried out from the following aspects:(1)Based on the theory of acoustoelasticity,the expression for quasi-isotropic composite materials is derived,which shows the relationship between acoustic time difference and internal stress.And the ultrasonic stress detection system is set up,which has one receiving and one transmitting probe distribution mode.In addition,Wedge block used in ultrasonic stress measurement and the optimal algorithm of acoustic time difference are designed.(2)Research on influencing factors of ultrasonicUsing different frequency probes to detect the aluminum alloy plates with different groove depths during the ultrasonic testing,for the determination of the range of propagation depth under different probe frequencies;The relationship between temperature and acoustic time difference is explored,and then the temperature compensation algorithm is put forward;The connection between the applied stress and the acoustic time difference is also studied.Research suggests that the acoustic time difference in the direction of parallel loading increases with the increase of the applied stress,while the sound wave time difference in the vertical loading direction decreases along with the rise in the applied stress.(3)Study on the optimization of the residual stress testing parameters for 6061-T6 aluminum alloy detected by X ray diffractionResearch shows that the most accurate residual stress results are obtained when the Cr target is used to excite X ray and irradiate the surface of aluminum alloy plate through aperture with 0.5×3mm and the Mid chord peak location method is adopt.(4)Experimental verification of ultrasonic stress detection theory by X ray diffraction methodResidual stress measurement of 6061-T6 aluminum alloy using X-ray diffractometer and the ultrasonic stress detection system set up in the paper,respectively.And the correctness of the theoretical derivation is proved through comparative analyzing test results obtained by these two methods.