A fatigue damage model to assess the development of subsurface fatigue cracks in railway wheels is presented in this paper. A 3‐dimensional finite element model (FEM) is constructed to simulate repeated cycles of contact loading between a railway wheel and a rail. The computational approach includes a hard‐contact over‐closure relationship and an elastoplastic material model with isotropic and kinematic hardening.
Results from the simulation are used in a multiaxial critical‐plane fatigue damage analysis. The employed strain‐based critical‐plane fatigue damage approach is based on Fatemi‐Socie fatigue index that takes into account the non‐proportional and out‐of‐phase nature of the multiaxial state of stress occurs when a railway wheel rolls on a rail. It predicts fatigue‐induced micro‐crack nucleation at a depth of about 3.7 mm beneath the wheel tread, as well as the crack plane growth orientation which indicates the possible failure pattern. Additionally, the influence of various factors such as contribution of normal stresses, higher wheel load, and material model have been investigated.
The Federal Highway Administration (FHWA) clarifies appropriate height measures for W-beam guardrails. Identification of existing locations where rail height is lower than recommended by FHWA is common. A research study was conducted to investigate the crashworthiness of raising blockouts on posts to restore barrier height and provide clarification on implementation of such methodology. The researchers evaluated the crashworthiness of raising blockouts by conducting a full-scale Manual for Assessing Safety Hardware (MASH) Crash Test 3-11 of a 28-in. W-beam guardrail system with composite blockouts raised 4 in. on posts. The 28-in. W-beam guardrail system with raised composite blockouts contained and redirected the 2270P vehicle, and it performed acceptably for MASH Test 3-11. The results of this study include guidance on the procedure for raising blockout mounting height on steel posts to achieve recommended rail height for a W-beam guardrail.
Buried-in-backslope (BIB) terminal designs for beam guardrails were developed under the National Cooperative Highway Research Program (NCHRP) Report 350 criteria for 27¾-in. high guardrail systems. The design terminates a W-beam guardrail installation by burying the end terminal in the backslope. When properly designed and located, this type of anchor eliminates the possibility of an end-on impact with the barrier terminal and minimizes the likelihood of vehicular intrusion behind the barrier. Considering the increase in guardrail height to 31 in. in recent years, there is a need to modify the BIB terminal design for a 27¾-in. high guardrail to satisfy current crashworthiness standard criteria for a 31-in. high guardrail. The crash tests reported in this paper were performed in accordance with the Manual for Assessing Safety Hardware (MASH) Tests 3-34 and 3-35 for non-gating terminals, which represent the tests considered necessary to demonstrate MASH compliance of the device. The TL-3 BIB terminal system met MASH requirements and is considered MASH compliant. It is considered suitable for implementation at V-ditch locations with a 4H:1V or flatter foreslope where a MASH TL-3 BIB terminal system is needed and/or desired.
The design of longitudinal barriers using reinforced concrete is typical in roadside safety design. Roadside safety hardware such as bridge rails, median barriers, and transitions are designed to safely contain and redirect impacting vehicles without imposing any significant risks to the occupants. As full-scale crash tests of new designs are expensive and time-consuming, finite element modeling and simulation of the impact event is often involved. In LS-DYNA, one of the most popular software in roadside design, there are multiple material models for concrete modeling and there is no specific guideline on the selection of the concrete material model. This paper evaluates the behavior of material models MAT_CSCM_CONCRETE and MAT_RHT during the study of truck platoon implications. The concrete erosion, deflection, and failure mechanism of two consecutive tractor-van trailer impacts into the barrier FEA models were analyzed to select a representative material model for further study.
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