As we know, an accident or impact is a sudden occurrence, causing irreparable physical and financial damage to the occupants. In order to reduce the damage to components affected by dynamic and quasi-static loading, energy absorption and determining the response of these components to applied impact are important topics that are being studied in this area. In mechanics of impact, Bumpers play a vital role in case of preventing shock in the aircraft, automotive, railway, aerospace industries and etc. Components absorb the kinetic energy of the impact through the Elasto-plastic deformation. The amount of energy absorption, the maximum force of crushing and crushing force efficiency are among the important parameters in energy absorption structures. In many studies, there is effort to optimize these parameters by using prediction and analysis. Investigation, analysis and design of energy absorption systems are also significant importance in the automotive industry.
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Bridget Driscoll was the first person to die in a petrol-engine car accident, and the first pedestrian victim of an automobile collision (Impact speed was about 4 miles per hour (6.4 km/h)) in the United Kingdom. As population increase, traffic jams are on the rise day-by-day, and when the roads hosts more than their capacity, the rates of accidents and subsequent road fatalities are also rising. According to statistics, 1.2 million people die every year due to road accidents. According to global research, the ten countries with the highest number of deaths from road accidents are Namibia, Thailand, Iran, Sudan, Swaziland, Venezuela, Congo, Malawi, Dominican Republic and Iraq, respectively.
Suppose a car moves at a speed of 75 Km/h and suddenly hits a brick wall. The speed of vehicle takes about 0.1 seconds to reaches zero. The mass of the car is 1,000 kilograms. As a result of the collision, a force from the brick wall is pushed into the car in the opposite direction of the car. As a result, we will have a sharp drop in acceleration. For example, the negative acceleration value is 200 m/s^2 . The applied force will be 200,000 N. This force is very large due to its short apply duration. Assuming that the crash time doubles (0.2 seconds), the force will be half (100,000 N). Therefore, every millisecond leads to save the occupants from injuries and death. Since the final speed of the collision is zero, the total kinetic energy of the vehicle is wasted by the work done on the vehicle (deformation) and the environment by crumpling, bending, heat, lighting, etc.
From the above mentioned points, we conclude that, in order to save the occupants, we must increase the impact or collision time so that the occupant is not injured. These factors include deformation of various components of car, seat belts, airbags, and more. Engine, frames, bumper, chassis and trunk are major energy absorption areas that increase the distance and stop time. By bending and crushing, these components wipe out the crash energy before entering the passenger cabin and provide security for the occupants. Therefore, the dynamic collision of the car is hampered by an extremely complex process. Because at a short period, a large number of elastic and plastic deformations take place and affect the elastic connections of certain masses. The characteristic of the positive effect of deformation today and certainly in the future is a very important issue that manufacturer of car have to face. The maintenance cost of car is significantly affected by the cost of repairs and premiums. Success in vehicle safety is seen in the premium category. In addition, the damage that needs the limited repair, reduces the repair time and improves the economic efficiency of the car.
The study of the characteristics of deformed body is one of the most important issues that automakers face. In the study of Vehicle body ductility, two controversial issues are debatable. One is the low ductility of the vehicle’s body and the second one is the high ductility of that. In the low ductility case, it is obvious that the body of the car will be less damaged. Therefore, the cost of repairs will be lower; instead, due to low energy absorption (low ductility), passenger safety will be reduced. On the contrary, in the case of a high ductility, it is obvious that the body of the car will be more damaged. Therefore, the cost of repairs will be high; instead, due to high energy absorption (high ductility), passenger safety is rising. The car body is designed to not cause so much deformation in low-velocity crashes (to reduce the cost of repairs) and in high-velocity crashes, the body composition should work in such a way as to ensure passenger safety (In this case, the cost of repairing the car against survival of the occupant is ignored). To achieve this sophisticated design, the components of the car body should be designed to meet these demands.
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