저자명 박주형 
년도 2013 

The shock absorber of a helicopter cockpit is indispensable to protect a pilot in case of crash, which requires weight lightening and small size to save fuel. Researchers developed a lot of small and light shock absorbers for long time and a variety of them are used. A shock absorber using a bending strap and adhesive is excellent when they are evaluated on complexity, weight and adjusting capacity for shock absorption bases. However, it has three problems. First, the adhesive is sensitive to environment like temperature or humidity. Secondly, the cost is expensive. Lastly, the adhesive may fracture when it is exposed at high or low temperature because of difference in thermal expansion coefficient of stainless steel and adhesive.  

The object of the present work is to suggest a new type of a shock absorber available for a helicopter cockpit. In order to maintain advantage of a bending strap and compensate the defect, a new type of a bending strap using fracture is proposed. Stainless steel 304 and Twinning Induced Plasticity (TWIP) 980 are selected for materials of a bending strap after considering high elongation, high strength and corrosion resistant. Shock absorption capacity of proposed bending strap is predicted by finite element analysis using ABAQUS/EXPLICIT. To carry out accuracy analysis, characteristics of material considering the strain rate effect are used. Uniaxial tension tests are carried out using INSTRON 5583 and High Speed Material Testing Machine for dog-bone specimens. Ductile fracture criterion suggested by Ko and Huh is used to describe accuracy fracture of bending strap. This ductile fracture criterion is considered about maximum principal stress and stress triaxiality. It was verified by applying hub-hole expanding process. Many parametric studies are carried out to know characteristic of a new bending strap. It is noticed that the shape of tearing part in a bending strap hardly influences shock absorption capacity when analysis carried out considering round, trapezoid and rectangle shape. It is also known that the element size of tearing part in a bending strap barely effects shock absorption capacity. When the bending diameter of a bending strap decreases and the thickness increases, shock absorption capacity increases. Shock absorption capacity of TWIP 980 is about 40 percent higher than that of stainless steel 304. Based on the parametric study result, a new model of a shock absorber is suggested to substitute existing models.

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