FEA Structural Stress of Modalohr System for Semi-trailer Rail Transportation: Weld Root Fatigue Focus

Abstract

In order to fulfill green requirement (reduction of CO2 emissions given by French “Grenelle”), a great need appears concerning roll-on roll-off efficient technology. Heavy seam welded structures manufacturer has to present an optimized product to fulfill this requirement. In this purpose, the Modalohr system overcomes several challenges: transport 4m height and 38 tons semi- trailer in UIC kinematic gauging with a low floor rail vehicle, use of conventional large wheel bogie with maximum axle load, 9 million kilometers running over 30 years service life. For cost effectiveness, the compact vehicle design uses welded assembly and avoids systematic full penetration welds which may require costly preparation machining. The idea is to develop a one shot FEA which provides both global structural bending and torsional vehicle behaviors and also the fatigue focus on each joint for both weld toe and weld root. The local stress analysis requires too much effort and the structural stress using appropriate inclined shell element in a global system model complies such requirement. A home made tool implements these techniques. LOHR “Seam Sim” development deals with the partial automation of the FEA model generation based on the following key points: solid weld feature are generated in CAD, FEA model automation idealization is achieved without additional manual operation. Postal2 post processing tool has been developed to allows standard FEA code results processing for both static and fatigue assessment. The final display is a scalar stress safety margin map associated for each element to the appropriate criterion over the system depending on the area type; plain metal, sheet metal edges, weld toe, weld root, bolt connection … “Seam Sim” theory [2,3] and Verification & Validation (V&V) has been presented during last fatigue Design conference in 2011 [4], today's aim is to present a highly fatigue demanding industrial application. Loads are applied at a system level to fulfill EN12663-2 standard and additional manufacturer load cases (including longitudinal dynamic fatigue load for 1050m long train and lifting, boarding kinematic load cases). The fatigue results are focused on each detail.