جستجوی مقالات مرتبط با کلیدواژه "بستار" در نشریات گروه "مکانیک"

In the present paper، a new low cycle fatigue lifetime prediction model for magnesium alloy is presented and low cycle fatigue experimental results of magnesium specimens were used to achieve this target. In such this case، an energy approach was applied to consider both stress and strain effects. This model had less material constants in comparison to other classical theories and had higher accuracy، since in the energy method، a plastic energy-lifetime relation was used، in which the plastic strain energy was equal to a multiple of plastic strain and stress numbers. In addition، the effect of the mean stress was considered in the fatigue lifetime prediction model by using a correction factor. Results of mentioned model demonstrated a proper agreement to experiments. At last، an applicable example was presented including a low cycle fatigue analysis of a diesel engine cylinder head، made of magnesium alloy، by using presented lifetime prediction model.

This paper investigates the high cycle fatigue behavior of the AZ91 magnesium alloy. The feasibility study of replacing this alloy with the A356 aluminum alloy for a diesel engine cylinder head is discussed. For this purpose، the AZ91 alloy was casted in a permanent mold and the microscopic examination with optical and scanning electron microscopes (SEM) and mechanical tests include tensile، hardness and high cycle fatigue tests were performed on samples which were prepared based on standards. Results are compared to the A356 aluminum alloy. High cycle fatigue tests were carried out at a stress ratio (R) of -1 and a frequency of 50 Hz at room temperature in the air. The microscopic investigation demonstrates that the microstructure composed of alpha and beta (Mg17Al12) phases. Fatigue test results show that the fatigue strength of the AZ91 alloy is lower than the A356 alloy، but still in the range of required values for the application in cylinder heads.

Multi-layer steel (MLS) cylinder head gaskets (CHG) are widely used to seal the engine cylinder head. Therefore, The interaction between the engine cylinder head, cylinder block and the cylinder head gasket is very important from technical point of view. To avoid the escaping gas from the engine affecting the overall performance of the engine during operation, both the pre-stressing force of the bolts as well as the gasket designare critical factors in enhancing the efficiency of the sealing of the gasket.In this paper the finite element method (FEM) is used to investigate the interaction between the cylinder head and the cylinder block. Further more the distribution of the contact pressure on the gasket and the cylinder head and the cylinder block stresses at different condition, such as cold assembly, hot assembly, cold start, firing, engine cooling down to 20°(c) and -25°(c) are calculated. The validation are performed using Fuji papertest and thermal survey test. The results revealed that the sealing pressure on the gasket strongly depends on the pre-stressing force of the bolts. However, the location of minimum contact pressure on the gasket is changed by considering the thermal loading.