1 Analysis method
First of all, the cracked brake automobile fuel line for microanalysis, and then use the line cutting machine in the fracture adjacent to the cut samples. With X2650 type scanning electron microscope and EDAX29100 type X-ray energy dispersive spectrometer investigation and analysis of brake fluid pipe fracture on the corrosion products, with Jiajia brand detergent and ultrasonic washing to remove the fracture of oil with acetone and ultrasonic cleaning of the fracture, and then X2650 type scanning electron microscope investigation and analysis of the clean fracture.
2 Analysis results
2.1 Microanalysis
Sedan brake fluid pipe assembly is composed of a brake fluid pipe and two hollow fixed nut. Brake fluid pipe is steel, steel parts outside the copper-plated layer. The flare part of the brake fluid pipe is outstanding, and no defects are found. No cracks were found in the flare portion. The cracked position of the brake pipe is below the nut, about 15mm from the flare, and there is a copper plating layer falling off on the outer wall of the cracked brake pipe. In the 5 times the enlargement of the mirror investigation, can see the shell-shaped trick, but also can see the fracture on the many brightly polished small sections, by the fracture of the microanalysis can begin to speculate that the cracking of the brake fluid pipe for the exhaustion of cracking [1].
2.2 Analysis of corrosion products on the fracture
In the scanning electron microscope to investigate the fracture before cleaning, found that there are corrosion products in many places on the fracture. After X-ray spectroscopy analysis, the corrosion products include Na, Al, Si, S, Cl, K, Ca.
2.3 Microanalysis of the fracture
The brake fluid pipe fracture cleaning in the scanning electron microscope investigation. Figure 1 for the brake fluid pipe fracture of the whole tracing, visible from the figure on the fracture shell-shaped trick. Further careful investigation of the fracture, can be seen on the fracture of the brake fluid pipe there are several sources of fatigue (Figure 1, a, b, c), for multiple sources of fatigue cracking [2]. The cracking phenomenon caused by cyclic load or alternating stress effect is fatigue cracking.
Fatigue cracking consists of three stages: (1) fatigue crack initiation, i.e., the nucleation stage of fatigue cracks; (2) fatigue crack expansion stage, i.e., the substable expansion of fatigue cracks; (3) final crack or instantaneous breakage stage, i.e., the destabilizing expansion of fatigue cracks. The fracture can be further expanded to investigate the second stage of large-area fatigue cracking the most outstanding microscopic features - a lot of parallel to each other, that is, the fatigue stripe (see Figure 2). Under the scanning electron microscope investigation to the third stage of fatigue cracking transient fracture region depicted as tough nest trick.
3 Anatomical comments
Comprehensive above microanalysis and microanalysis results can be obtained:.
(1) The raw material of brake fluid pipe meets the requirements of the technical conditions, without serious adulteration. Brake fluid pipe production process is normal, no serious shortcomings. Brake fluid pipe cracking is not due to material adulteration and production process shortcomings caused by.
(2) brake fluid pipe fracture, nut appearance is outstanding, the whole brake fluid pipe can not see the impact of external forces or twisting traces, can sweep away the elements of man-made damage.
(3) brake fluid pipe fracture some corrosion traces, but the brake fluid pipe cracking is not caused by corrosion fatigue. Because in the brake fluid pipe fracture is not found on the corrosion pit, mud-like trick of microscopic tracing, that is, no corrosion fatigue characteristics.
(4) brake fluid pipe cracking is caused by fatigue. In the process of van operation, because of the boom, brake fluid pipe inner wall, outer wall of the many places on the occurrence of stress concentration, and because of the boom so that the brake fluid pipe accepts the stress is larger, so more than one source of fatigue. In the van's operation process road surface unevenness caused by bumps and booms make the brake fluid pipe constantly accept the alternating stress, which makes the top of the crack constantly accept the tensile, tightening cyclic load. Under the effect of this cyclic load, the crack repeats the process of opening, passivation, expansion, sharpening [3], leaving a trace on the fracture crack surface, the occurrence of fatigue glow. Because of the expansion of multiple cracks, so that the practical bearing area of the brake fluid pipe is very small, under the effect of a small load may be destabilized expansion, instantaneous cracking.
4 Conclusion
(1) The cracking of the brake fluid pipe is not caused by the shortcomings of the raw materials or production process.
(2) The cracking of brake fluid pipe is not caused by man-made damage.
(3) The fracture of the brake fluid pipe is partially corroded, but it is not the main reason for cracking.
(4) The cracking of the brake pipe is caused by fatigue, which is categorized as extensive fatigue cracking.