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The series of work introduced in this paper is originated from a structural failure of the vehicle A/C (Air-Conditioner) pipe, and when many possible factors having been excluded, the main investigating endeavor is focused on RLD acquisition and analysis, which eventually leads to the successful design improvement. During this process, many important signal collectives, such as micro-strains, accelerations, and engine speed are provided by RLD acquisition in some predefined conditions. Subsequently, these signals are analyzed both in time and frequency domain. Furthermore, order analysis by correlation of acceleration and engine speed is also performed to find a definite reason. As a conclusion, the root cause to the crack is not excitation from the road, but mainly from the engine. Based on this conclusion, structure design is improved and is theoretically proved to be effective by the RLD comparison analysis.

An accelerated specification introduced in this paper is developed during the process of solving the crack problem of a powertrain rear mounting structure. By sufficient analysis, the reason for such cracking is believed to be failure of fatigue under random loads in the proving ground. Meanwhile, due to special structuring of the rear mounting bracket, it is sensible to convert loads of various conditions to a one-simple-direction load case. Thus, acceleration of the test becomes possible. The accelerated test specification is resulted from the need of fast risk confirmation, as well as design verification, and is theoretically based on the damage equivalence principle [1]. To realize it, RLD (Road Load Data) acquisition also plays an important role by providing the quantities of different test methods to be compared. With the problem solved, good correlation is also achieved between proving ground and the accelerated test.

In this paper, a good example on integration of CAE (Computer Aided Engineering) and RLD (Road Load Data) analysis is introduced. It works well in the process of investigating the hinge crack problem of a vehicle hood and leads to schemes which are suitable to the root cause found. As the byproducts, a design target is confirmed and a procedure of problem investigating is proposed, as shown in Flowchart 1. Flowchart 1 Problem Investigating Procedure In order to ascertain the reason of the crack, multiple methods have been used, such as material verification, manufacturing examination, typical load case evaluation by CAE, and RLD analysis etc. Eventually, the reason is proved to be structural resonance by the common thread of both CAE and RLD. During the progress of problem solving, four main steps are involved and mentioned in the following sections.

A design procedure is developed to simulate the durability behavior of an electric wiper linkage mechanism subjected to operation cycles. The first stage determines the stress and strain levels that the linkage components are subjected to during the operation cycles. This requires the reaction loads at the joints of the wiper linkage. It is achieved by performing the mechanism dynamic analysis using multi-body dynamics software (MSC.ADMAS) together with a three dimensional transient finite element analysis (MSC.NASTRAN). Once the stress and strain of the wiper linkages are obtained during the operation cycle, the low cycle fatigue analysis is applied in the time domain. This analysis is based on strain-life curve, the Palmgreen-Miner’s rule, to compute the cumulative damage, the rain flow method for cycles counting, and the mean stress effect. Using the methodology presented in this paper, good correlation with laboratory test can be achieved.