| Aluminum alloy is one of the most popular materials in modern industrial manufacturing,which is very important in aerospace,automobile,high-speed rail,shipbuilding and other industries.Aluminum alloy is also the most popular alloy material in industry today.Aluminum alloy can be divided into deformed aluminum alloy and cast aluminum alloy according to the processing method.6061-T6 aluminum alloy is one of the deformed aluminum alloys.It has been widely used in aerospace,shipping and high-speed iron plate fields.At present,the research on crack growth law and fatigue fracture mechanism of 6061-T6,which has important application significance,is mainly focused on type I crack.However,it is very rare to study the fracture(composite fracture)mechanism and fatigue(compound fatigue)characteristics of the composite crack.In the process of actual engineering construction and application,the load bearing condition of the member is complex and changeable,which leads to a lot of complexity of the actual load borne by the crack.The crack is not a simple type?,type?or type?crack,but exists as a complex compound crack.The study of composite fracture and compound fatigue mechanism can predict the composite fracture mechanism,fatigue propagation rule,and composite fatigue crack growth rate of composite crack in materials.It has important theoretical and engineering significance in anti-fracture,anti-fatigue design,structural failure evaluation and structural residual life estimation.In this paper,the fracture mechanism and fatigue characteristics of?-?composite cracks of6061-T6 aluminum alloy under different loading angles are studied by means of experimental research and based on fracture mechanics,the main research work is as follows:1.A complete and comprehensive test system is established,which consists of a real-time image shooting system,a MTS 809 material testing machine and a special fixture.The experiments of composite fracture(5 loading angles)and composite fatigue(6 loading angles)were completed by this system.2.The experimental process and experimental data of the composite fatigue of aluminum alloy 6061-T6 were observed and recorded to obtain the fatigue crack propagation data of the material(crack length?a,number of cycles N and cracking angle,etc.).The stress intensity factor of I-type crack is calculated,and the da/dN-(35)K_I curve and lg da/dN-lg(35)K_I curve of type I crack are obtained.The extension rate curve of composite fatigue crack is analyzed,and the extension rule of composite fatigue crack is analyzed.3.The experimental process and experimental data of composite fracture of aluminum alloy6061-T6 were observed and recorded.The P-?a curve of bearing capacity and the length of stable crack propagation,as well as the fracture morphology and fracture angle were obtained,and the law of composite fracture was analyzed and summarized.4.The stress and strain fields near the crack tip are calculated by finite element software when the fatigue crack extends to 1 mm and 10 mm,respectively,and the propagation mechanism is analyzed in combination with the experimental results.5.The propagation path and fracture morphology of the composite crack under two kinds of failure mechanisms of the composite fracture and the composite fatigue are compared and observed and analyzed,and the different destruction mechanisms and rules are sought. |
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