Study On Micro Damage Evolution Mechanism Of Aluminum Alloy Based On Acoustic Emission

Aluminum alloy is widely used in aerospace, transportation, building decoration and other important occasions because of its advantages such as low density, strengthening,easy processing,corrosion resistance and so on. Studies show that the damage evolution mechanism of aluminum alloy components in engineering practice is very complicated and different stress states can also assume different damage mechanisms and different micro damage evolution process,which has brought a lot of difficulties on the assessment and prevention of fracture failure of engineering service materials. As a kind of passivity,dynamic nondestructive testing technology, acoustic emission detection has the characteristics of high sensitivity and real-time monitoring, which make it extremely suitable for solid materials such as aluminum alloy in the research of micro damage evolution process. The micro damage evolution mechanism of aluminum alloy 1060 and 6063 is studied in this paper by acoustic emission, the main work and results are as follows:(1) For the standard specimen of two materials,acoustic emission signal generated from micro damage of material internal is acquired based on test and then a multivariate random damage variable D is defined, based on which, an entropy curves is derived and to realize the quantitative analysis of the micro damage evolution process,and the similarities and differences between the two kinds of entropy curves are compared and analyzed for both materials,the micro damage evolution is a change process which is tensile stress as the dominant role, mixing tensile and shear stress, to the shear stress as the dominant role;while the same kind of load condition between different materials, there are some differences in the micro damage evolution process because of the difference of physical property. Then the Andrews plot method is employed to exploratory cluster analyze the micro damage evolution process of two materials which shows that the same stress state damage has a high degree of similarity, namely damage mechanism and micro damage similarity depends mainly on the type of stress state within the material rather than the size of stress value. Finally the observation results based on scanning electron microscopy(SEM) also verify the above conclusions,namely two kinds of aluminum alloy materials with different physical properties show the types of micro damage is almost same under the same kind of load condition and the same kind of stress state, the size of stress value will only affect the appearance of micro damage such as the size and depth, which will not affect the existence type of micro damage.(2) For the shear and tensile specimen of two materials, comparatively analyze the entropy curve trend shows that the shear specimen compares to the tensile specimen, the entropy curve form is single,the trend is clearer and more regular,also reflects the shear stress of the dominant role of the damage the mechanism is relatively simple. By using Andrews plot method, the damage data of two specimens of the same kind of material can be clearly separated, it shows that the micro damage information contained in the damage data generated by shear and tensile specimen is completely different, corresponding to the stress state of specimen internal and the damage mechanism also have the radical difference,proving once again that the similarity of material damage mechanism and micro damage type is a large extent depends on the stress state type of the material internal. SEM observation results also show that the shear fracture is formed by shear specimens, the micro damage types are mainly long or parabolic shaped elongated tough nest, and the same specimen two fracture toughness nest in the opposite direction; the tensile fracture is formed by tensile specimens, the micro damage types are mainly circular or elliptical shaped equiaxed tough nest.The damage and destruction of solid materials, for example aluminum alloys, are the result of the evolution of micro damage in materials. The micro damage evolution of materials is also a key problem which is concerned by both the mechanical and engineering fields. This paper proposes an acoustic emission technology based approach to explore materials of micro damage evolution mechanism, realizes the detection and evaluation of the micro damage evolution process for the two kinds of aluminum alloy materials, and provides the reference value for engineering materials damage evaluation and prevention in the process of serving.