Failure analysis and optimization design of low niobium compacted graphite cast iron exhaust pipe based on finite elements

LIN Yongchuan; LIU Lusheng; ZHANG Yudong; LAI Debin

doi:10.16579/j.issn.1001.9669.2026.08.004

Abstract：[Objective]Local cracking occurs in compacted graphite cast iron exhaust pipes during service.The failure mechanism was revealed and a collaborative optimization scheme of structure and material was proposed.[Methods]Firstly,a thermal-mechanical coupling finite element model of the exhaust pipe was established,and the distribution characteristics of its temperature field,stress field and strain field were analyzed to support the failure cause location and mechanism analysis.Secondly,structural improvement schemes of increasing the transition fillet radius and eliminating redundant stiffeners were proposed,and modal analysis was carried out to verify the dynamic characteristics of the optimized structure and eliminate the risk of resonance failure.Then,Taguchi test design method was adopted to quantitatively analyze the influence law of structural and material parameters such as wall thickness and elastic modulus on low-cycle fatigue life.Finally,a multi-objective evaluation system based on entropy weight-analytic hierarchy process was constructed to comprehensively balance high-temperature mechanical properties,process feasibility and economic indicators,and realize multi-dimensional optimization of material schemes.[Results]The results show that increasing the transition fillet can reduce the stress in the crack area by 119 MPa,and removing the stiffeners can eliminate local stress concentration.The resonance margin ratio after structural optimization reaches 152％,which meets the requirements of ISO 10816-1 standard.The coefficient of thermal expansion has the most significant influence on fatigue life,with a response range of 680 cycles.After combined weighting optimization,compacted graphite cast iron with niobium addition mass fraction of 0.05％-0.07％is determined as the optimal material scheme,which provides reference for the optimal design of similar high-temperature pressure-bearing components.