| At present, the deep diving structure has achieved its technical limit both in structure form and material. It cannot further improve submergence depth and achieve the technical index of long cruising endurance and high volume-weight ratio at the same time, which is the key technical bottleneck that constrains the exploration scale of ocean engineering and developm ent of deep sea. “Hoop residual stress with the characteristics of inner tensile and external compressive” can improve the ultimate bearing capacity, increase volume-weight ratio and reconcile the irreconcilable of exploration depth and work capacity, whic h is expected to make a breakthrough of pressure hull in the present technical condition. Based on the status, the aluminum alloy cylindrical structure is taken as the research object in this paper and a way is put forward to improve the comprehensive properties of cylindrical structure by residual stress formed by quenching.Quenching is a complex and highly non-linear question coupling among temperature, phase transformation and stress. There are some limitations and deficiency in the traditional methods for measuring the quenching residual stress distribution, and it also hardly tracks the evolution law of stress field accurately. According to the instance that the initial temperature of most quenching simulation of aluminum alloy is solution temperature, the finite element models which could reveal the effect of heating process on the quenching simulation of aluminum alloy are established by finite element analysis software ABAQUS. The quenching process of aluminum alloy cylindrical structure is analyzed by finite element simulation with coupled thermal-mechanical approach.Through the simulation and calculation, this paper researches the distribution and variation of temperature field and stress field through quenching process,the course and mechanism of formation of quenching residual stress,the effects of key parameters on quenching residual stress,and the effect of the quenching residual stress on the geometry of cylinder. Based on the machining distortion characteristics resulted from the releasing of residual stresses, it tests the distribution feature of quenching residua l stress field. In addition, the quenching distortion of cylinder resulted from quenching residual stress is verified by testing.The results are as follows:(1)The heating process has little effect on temperature field and stress field of the quenching simulation of aluminum alloy cylinder, while it has significant effect on the quenching distortion.(2)At the initial stage of quenching, the temperature of the outer layer of cylinder d rops sharply, and temperature difference between interior and exterior increases rapidly; as the cooling processed cooling rate reduces significantly with temperature difference between interior and exterior becoming smaller, and the temperature of cylinder is approaching gradually to the temperature of quenching medium.(3)At the initial stage of quenching, the outer layer of cylinder shrinks rapidly, which is impeded by inner layer and engenders tensile stress, while the inner layer engenders compressive stress because of the effect the shrink of outer layer; the stress field changes reversely at the later stage of quenching, and then hoop residual stress with the characteristics of inner tensile and external compressive is formed.(4)The hoop residual stress will increase with decreasing the diameter-thickness, yield limit, plastic modulus, water temperature and increasing the elastic modulus, solution temperature, cooling rate, while the length of cylinder has negligible impact on it.(5)The test results and measured results are in good agreement, the cylinder can form hoop residual stress with the characteristics of inner tensile and external compressive by spray quenching on outside surface, and it appears an overall trend of tiny deformation like a double-trumpet, which has little effect on bearing behavior. |
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