When talking about a motor vehicle accident, I will tell you about the key role of the leaf spring break in the accident process, and it also casts a shadow over the analysis of the entire accident. The qualitative point of the leaf spring break time is related to the final qualitative determination of the entire accident, and also relates to the identification of accident liability. The article explains the process of the accident and gives some pictures of key evidence. There may be inaccurate vocabulary in the text, and readers are expected to correct it themselves.
The fault analysis described in this paper utilizes fracture surface contamination, abnormal fracture morphology, stress analysis, and fracture mechanics to determine the time point at which a motor vehicle leaf spring fails in the accident sequence. The predecessor of this work was a large number of out-of-control accident investigations in which the leaf springs and rear axles were found to be damaged after the accident.
The obvious question is "Is it one of these components that caused the accident, or is its fracture the result of an accident?" After the accident, people always have problems or conjectures of one kind or another. A brief description of the accident is as follows.
Write reports, statements, and on-site mappings to indicate road signs and target locations, revealing that the motor vehicle is driving on a dirt road at a speed of 60-70 km/h. After hearing the squeaking sound, it enters a soft downhill section. The motor vehicle drifted to the left side of the road, then jerked to the right side of the road, and then sharply turned to the left side of the circuit.The motor vehicle then travels along the left edge of the middle until it hits a boulder. The left side of the vehicle collided with the rock, and according to the same report, the vehicle broke out of the pit at this position. The right rear wheel is fully inflated, in the middle of the road, near the start of the accident sequence. Subsequent inspection revealed that the left rear leaf spring broke at the position of the forward eye, and the position of the last end of the first piece of auxiliary spring was sharply rolled up.
In the following days, the investigators found a mark on the scene of the accident at the center of the dirt road. This mark was preserved quite well and became the basis for drawing the route of the vehicle. They also found traces of contact between the right rear brake floor and the dirt road in the early stage of the accident sequence. Geological analysis of the dirt found that they were embedded in the back floor, and it was determined that the dirt or dust embedded in the back floor was consistent with the soil composition on the road, and it was mainly limestone and sand.
This is different from the composition of the soil outside the roadbed, mainly red sand and a small amount of limestone. A large number of analyses of dust adhering to the backplane found that it is very similar to the roadbed material and different from the surrounding soil. No indentations or tire bounces were found on the road pointing away from the road.
Inspection of the motor vehicle revealed that the rotating tire scratches pointed to the rear end of the left rear wheelwell and that traces of tire rotation were found at the front end of the right rear wheel well. A left rear spring break occurs at the front joint, which will cause the left side support of the shaft to be rearward approximately at the right rear spring-shaft joint. Therefore, the left wheel will rub the rear side of the wheel well and the right wheel will rub the front wheel well.
The pivoting shaft will produce a steering effect that is independent of the front wheels and will pick up the right rear wheel into the frame rail. Because the tire trace indicates that the right rear wheel is still rotating and not broken, the left rear spring is first destroyed. Therefore, the remaining investigation focused on the failure of the left rear spring.
Figure 1 The broken parts of the spring have been put together, taking a picture of the relative position before the break using a magnifying reed.
Figure 2 The half-fracture of the spring has been cracked along the mid-surface.
Figure 3 There is a rust on the outside half of the fracture. The crack pointed by the arrow is an old crack, and most of it is rusted along the outside.
Figure 4 The clear inner rust is visible in the inner half of the fracture.
Figure 5 The crack in the half-eye section of the reed area shows a clear secondary crack on the middle surface and an old crack on the outer surface, as indicated by the arrow.
Figure 6 The more details of the old crack indicated by the arrow indicate that rust has occurred here compared to its adjacent position.
Figure 7 X-ray analysis of old crack fractures produces high levels of carbon and oxygen. Other elements, such as calcium, aluminum and silicon, are consistent with the composition of the roadbed material and also found to adhere to chlorine during shipping.
Figure 8 The pattern of the chevron extends from the edge of the ID indicated by the arrow.
Figure 9 This section is at the position between the inner and middle faces of the spring. It consists of a transgranular section and micropores.
Figure 10 After tilting the section, you can see the wood grain fracture indicated by the arrow and the secondary crack.
Figure 11 The grainy secondary fracture image shows that intergranular cracking is related to it.
Figure 12 The wood grain fracture in the middle is also observed on sample B.
Figure 13 shows the outer edge of the spring sample B fracture. This is the same position as the old crack of the accident spring.
Figure 14 shows very fine equiaxed pores on the outer diameter of the fracture, while the formation of micropores indicates a plastic deformation mechanism, and the microscopic pores of macroscopic or ductile fracture are fine and low.
Figure 15 On the accident spring, a scratch was found in the damaged area of ​​the wood-like fracture on the spring B sample.
Easy to tighten small editor tips: View the follow-up analysis of the accident, please pay attention to "a motor vehicle accident: the scientific problem behind the metal leaf spring break (the next part) report"!
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