Fracture analysis of fatigue test of front axle of

  • Detail

Fracture analysis of the front axle of bus under fat

classification No.: th133.2 document identification code: a

Article No.: (2000) fracture analysis of the front axle of bus under fat it should be noted that in the calculation of elongation, igue testli Li Shi Wei Jia

(Shenyang arch. and civ. Eng. Inst technical code for building in expansive soil area gbj112 (8) 7shenyang 110015, China)

yang Chun you

(Shenyang Ywo Three factory, Shenyang 110015, China)Abstract:In this paper, The factors of fracture for the front axle of bus are analyzed with the help of FTA(fault tree analysis) and the macroscopic and microcosmic fracture are also discussed. The results show that the process fault leads to the failure of the axle under fatigue test.

Key words:Front axle; Fracture analysis; FTA; Fatigue ▲ the front axle is an important part of the car, which directly affects the reliability and safety of the car, so it must have sufficient strength, stiffness and fatigue resistance. In order to provide the basis for improving the product, the stress distribution of the front axle of the vehicle is analyzed, including stiffness test, vertical bending fatigue test, performance test of bridge tube material, photoelastic test. The shaft fracture occurred in the vertical bending fatigue test

fracture is an important basis for studying the failure process. The cause of failure can be judged through macro and micro fracture analysis

the front axle of the car is a welded assembly. There are many factors that affect the fracture. Therefore, the application of fault tree analysis technology combined with fracture analysis to systematically describe the causes of fracture can accurately find out the main causes of failure. 1 test conditions and fracture location the vertical bending fatigue test of the automobile front axle was carried out on a hydraulic fatigue testing machine (pme-50 type)

(if it is rising, stop the machine immediately and invert 1) test data: input 250 times/min (15000 times/h) of pulsating load; The input load is 3.5 times the rated load

(2) fracture location: five shafts are randomly selected from the product as test pieces, four of which have broken after different loading times. The fracture location is shown in Figure 1 and table 1. Figure 1 fracture location table 1 fracture location axis serial number fracture location loading times 1 weld a-a340000 times 2 c-c700000 times near the variable section 3 not broken 1million times (tail load test) 4 weld b-b410000 times 5 weld a-a375000 times

2 establishment of fault tree of front axle fracture establishment of fault tree: take the least expected failure state in the system (components) as the goal of fault analysis, that is, as the top event; Take all possible direct factors of the top event as intermediate events; All possible direct causes leading to intermediate events are regarded as bottom events. Each event is connected with corresponding representative symbols according to its logical relationship to form a fault tree. Rectangular symbols are used to represent top events and intermediate events; Circular symbols indicate low events; Shape represents and door symbol; Shapes represent or door symbols. Figure 2 shows the established fault tree of front axle fracture. Fig. 2 fault tree 3 fault tree comprehensive analysis according to the test statistics, the test piece after 3 × Fracture occurred after more than 105 times of pulsating bending stress. The fracture is 90 ° to the maximum tensile stress. The fracture source area, fatigue propagation area and transient fracture area can be clearly seen by naked eyes. Due to the uniform loading in the test, no shell lines can be seen in the extended area, but the radial pattern is still relatively clear. The fracture cores are on the tensile side of bending stress, and the instantaneous fracture zone is on the opposite side. There is no obvious plastic deformation on the fracture, which conforms to the characteristics of fatigue fracture

the instantaneous fracture zone of the fracture is fibrous, accounting for less than 1/2 of the whole section. The test load is 3.5 times of the rated load. At the same time, photoelastic test and material mechanical property test are also carried out for the actual bearing condition. Through photoelastic test, it is proved that the test stress at each section under bending stress is close to the theoretical calculation value. The test results are shown in Table 2 (unit: kg/cm2). Table 2 Relationship between test stress and theoretical calculation value theoretical calculation value of circular tube part error% blank holder of photoelastic test value 80 pull edge 09

no forging defects were found in the blanks and forgings. The metallographic structure of the blanks was basically consistent with the selected materials

through the above analysis, the influence of strength calculation, material selection and heat treatment factors can be excluded. Cold working and hot working process defects can be considered as the main influencing factors of fracture. Because the front axle of the car is a welded assembly, and the axle end and axle tube are welded after hot assembly, the influencing factors of the manufacturing process are complex, and the macro morphology of the fracture also presents completely different sections. Therefore, the fracture must be further analyzed. 4 fracture analysis the four fractures can be divided into three categories according to their positions:

(1) fracture near the axle tube variable fracture (C-C fracture)

the fracture of the axis belongs to this kind of fracture. On the SEM photo (Fig. 3), it can be seen that the first stage crack extends along the slip surface, and the second stage crack extends in the direction perpendicular to the normal stress. The crack originates from the uneven surface of cold working. The fracture is due to the cold processing of the hole, the roughness does not meet the requirements of the drawing, and the machining tool marks play a role of sharp notches

Copyright © 2011 JIN SHI