Durability Assessment Of A New Free Piston Spark Ignition Linear Engine: A Computational Approach
Authors: Rahman M. M. , Ariffin A. K. , Jamaludin N. , Haron C. H. C. 
Published: January 2013

Pendekatan pengkomputeran moden yang berasaskan analisis unsur terhingga untuk penilaian ketahanan dalam komponen enjin linear palam pencucuh piston bebas dua lejang dibentangkan. Maklumat pembebanan adalah sukar ditentukan tanpa sebarang prototaip. Sejarah pembebanan boleh ditentukan menggunakan dinamik multi–jasad. Dengan menggabungkan dinamik multi–jasad, analisis unsur terhingga dan analisis hayat lesu, hayat lesu bagi enjin linear boleh diramal awal semasa reka bentuk. Kertas kerja ini membentangkan ramalan hayat lesu bagi komponen enjin linear piston bebas dengan pembebanan amplitud berubah. Permodelan dan analisis unsur terhingga dijalankan menggunakan reka bentuk terbantu komputer dan perisian analisis unsur terhingga serta ramalan hayat lesu adalah menggunakan kod lesu komersial. Pendekatan permulaan retak digunakan bagi meramal hayat lesu komponen bagi enjin linear piston bebas. Keputusan yang diharapkan adalah plot kontur hayat lesu dan histogram kerosakan pada kes yang paling rosak. Keputusan yang diperolehi menunjukkan bila menggunakan rangkaian beban tegangan yang lebih banyak (beban SAETRN), SWT dan Morrow memberikan hayat lebih singkat daripada model Coffin Manson Walau bagaimanapun, kaedah Coffin–Manson memberikan ramalan yang konservertif bila sejarah masa beban mampatan lebih banyak dan tegasan min sifar. Keputusan juga menunjukkan julat tegasan yang besar juga menyumbang lebih besar kerosakan.

Kata kunci: ketahanan, hayat lesu, unsur terhingga, dinamik multi–jasad, enjin linear piston bebas.

A modern computational approach based on finite element analysis for integrated durability assessment in a two–stroke free piston spark ignition linear engine components is presented. The loading information is difficult to determine without a prototype. The loading histories can be determined using multi–body dynamics. By combining the multi–body dynamics, finite element analysis and fatigue life analysis, the fatigue life of the linear engine components can be predicted early in the design cycle. This paper presents the prediction of fatigue life for free piston linear engine components with complex variable amplitude loadings. The finite element modeling and analysis has been performed using a computer–aided design and finite element analysis software packages, and the fatigue life prediction was carried out using commercial fatigue codes. Crack initiation approach is applied to predict the fatigue life of the component of a free piston linear engine. The results are expected to show contour plots of fatigue life, and damage histogram at the worst or most damaging case. The obtained results indicate that when using the loading sequences is predominantly tensile in nature (SAETRN loading), the SWT and the Morrow models give shorter life than that results obtained using the Coffin–Manson model. However, the Coffin–Manson method gives conservative prediction when the time histories are predominantly compressive, and zero mean stress loadings. It was also observed that the damage to be generated from the cycles is in the higher stress range.

Key words: Durability, fatigue life, finite element, multi–body dynamics, free piston linear engine.