HyperWorks在基于频域的振动疲劳分析中的应用

关键词：HyperWorks 振动 疲劳 频域方法 累加损伤 Abstract: Shaker-based vibration durability tests have been drawing increasing attention. This
paper studies the fatigue problem associated with a common vibration durability test called ‘sine sweep test’, and further introduces the procedure of performing a fatigue-life analysis in the HyperWorks environment by using frequency-domain method. In essence, the frequency-domain method for fatigue-life analysis is based on an assumption which assumes that the cumulative damage ratio is the accumulation of individual damage ratios. In this paper, we first obtain the frequency response function of Von Mises stress of a structure in OptiStruct, then convert the Von Mises stress spectrum into damage ratio by invoking a user defined HyperMath function according to a given S-N curve, and finally determine the cumulative damage by adopting the utility ‘Linear Superposition’ in HyperView. We also investigate the effect of the frequency interval on the accuracy of the result and find that performing a numerical integration in HyperGraph is more efficient than the method ‘Linear Superposition’ for determining the maximum cumulative damage ratio of a structure.
Altair 2013 技术大会论文集
HyperWorks 在基于频域的振动疲劳分析中的应用 Vibration-fatigue-life Analysis Using Frequencydomain Method in the HyperWorks Environment
吴振 刘强 马叶红 （奥托立夫（上海）汽车安全系统研发有限公司 上海 201807）
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ቤተ መጻሕፍቲ ባይዱ
Altair 2013 技术大会论文集
vibrational environment that a structure is exposed to in the real world, and then to verify whether the structure has failed or not after the test. For today’s automobile industry, there exists a large number of test specifications (including both ISO standards and customer test specifications) dictating in detail the test setup along with the acceptance criteria for vibration durability tests on various auto parts. This means that surviving a specified vibration test is one of the necessary requirements for designing an auto part. Vibration will induce fluctuating stress which will in turn result in a type of failure displayed in the form of crack or rupture. This type of failure is referred to as fatigue[1]. In view of this, when an auto part is at the stage of design, engineers may ask: ‘Can this part survive the vibration durability test? How long will this part perform until fatigue occurs?’ These two questions yield the main goal of this paper - vibration-fatigue-life analysis. This paper first introduces some basic knowledge about the theoretical backgrounds that we employed for fatigue-life analysis. Different from other existing fatigue analysis methods which mainly focus on time-domain data, this paper views the problem from a different perspective, that is, from the view of frequency domain. We call this method ‘frequency-domain method’. Subsequently, the paper shows how to employ this method to perform a fatigue-life analysis in the HyperWorks environment. In particular, this paper illustrates the method by studying a common vibration durability test, known as sine-sweep vibration durability test (or sine sweep in abbreviate). The procedure can be described as follows: (1) Develop the finite element model, setup the load step, and calculate the frequency response function (FRF) of stress in OptiStruct; (2) Code a user defined HyperMath function prescribing the material law of fatigue according to a given S-N curve; (3) View the result in HyperView, and, by employing the HyperMath program, convert (Von Mises) stress which is expressed in the frequency domain to material damage ratio which is also expressed in the frequency domain; (4) By using the utility “Linear Superposition” in HyperView, the damage ratio in the frequency domain can be cumulated together, and then the overall damage ratio called ‘cumulative damage ratio’ is derived. This damage ratio represents the cumulated damage in the structure after one sweep of sine-swept vibration test; (5) Point out the weak point of the structure and estimate the fatigue-life.
2 THEORETICAL BACKGROUNDS FOR VIBRATION-FATIGUE-LIFE ANALYSIS
Generally speaking, there exist two methods for vibration-fatigue-life analysis. One method focuses on real time-domain data, while the other concentrates on frequency-domain data. Though the time-domain method is beyond the scope of this paper, a better understanding of it will help us to appreciate the merits of its frequency-domain counterpart. For the fatigue-life analysis based on the time-domain method, it follows the following procedure: (1) Obtain the time history of the applied load or the enforced displacement; (2) Perform a transient or quasi-static calculation, and derive the time history of stress; (3) By the use of Rainflow counting method, determine the peak stress and count the corresponding number of stress cycles; (4) Using the above data along with the material S-N curve, the cumulative damage ratio is finally obtained. It must be noted that, since the time-2-