The stress distribution close to the tip of a crack which has a finite tip radius and which is being opened either by means of a remotely applied tension field σ y , 0 or by means of a concentrated force (e. g. a wedge driven into the crack) has been computed. It is shown that there exist tensile stresses (σ x ) parallel to the plane of the crack and ahead of the crack tip. The maximum value of the tension σ x is an approximately constant fraction (~ 1/5) of the peak stress concentration σ y , max . which usually causes crack propagation. Inside a brittle solid, if a plane of weakness or potential cleavage is present and is roughly normal to the plane of the original crack, this interface may break and produce a secondary crack in such a manner as to interfere with the progress of the primary crack. If the ratio of the adhesive strength of the interface to the general cohesive strength of the solid is in the right range large increases in the strength and toughness of otherwise brittle solids may result.

This paper describes analyses of a railroad tank car impacted at its side by a ram car with a rigid punch. This generalized collision, referred to as a shell impact, is examined using nonlinear (i.e., elastic-plastic) finite element analysis (FEA) and three-dimensional (3-D) collision dynamics modeling. Moreover, the analysis results are compared to full-scale test data to validate the models. Commercial software packages are used to carry out the nonlinear FEA (ABAQUS and LS-DYNA) and the 3-D collision dynamics analysis (ADAMS). Model results from the two finite element codes are compared to verify the analysis methodology. Results from static, nonlinear FEA are compared to closed-form solutions based on rigid-plastic collapse for additional verification of the analysis. Results from dynamic, nonlinear FEA are compared to data obtained from full-scale tests to validate the analysis. The collision dynamics model is calibrated using test data. While the nonlinear FEA requires high computational times, the collision dynamics model calculates gross behavior of the colliding cars in times that are several orders of magnitude less than the FEA models.

This paper describes a nonlinear finite element analysis (FEA) framework that examines the impact energy to fracture unnotched Charpy specimens by an oversized, nonstandard pendulum impactor called the Bulk Fracture Charpy Machine (BFCM). The specimens are made from railroad tank car steel, have different thicknesses and interact with impact tups with different sharpness. The FEA employs a Ramberg-Osgood equation for plastic deformations. Progressive damage and failure modeling is applied to predict initiation and evolution of fracture and ultimate material failure. Two types of fracture initiation criterion, i.e., the constant equivalent strain criterion and the stress triaxiality dependent equivalent strain criterion, are compared in material modeling. The impact energy needed to fracture a BFCM specimen is calculated from the FEA. Comparisons with the test data show that the FEA results obtained using the stress triaxiality dependent fracture criterion are in excellent agreement with the BFCM test data.

This paper investigates the influence of physical track conditions in the vicinity of a rail joint on the fatigue life of the joint bars. Recent derailments due to broken joint bars, such as the Minot, ND accident in January 2002, have highlighted the need for better understanding of the effects of joint conditions on premature joint bar failure. Fatigue life estimates can be used to guide the selection of inspection intervals for joint bars in service. Engineering approximations are used to infer the dynamic load factor at a rail joint due to joint characteristics including: • rail end gap; • joint efficiency (looseness); • track stiffness (vertical foundation modulus). A three-dimensional finite element analysis of a rail joint is conducted and the dynamic load is applied to develop an estimate of the live (bending) stresses at the joint due to passing wheels. These stresses are then used to estimate the fatigue life of the joint bars. The methodology is demonstrated for 132RE rail with companion joint bars. The effect of thermal expansion (or the temperature difference below the rail neutral temperature) is investigated. Typical wheel loads and railcar speeds are considered and results are presented for a baseline a joint condition.

Several industries now use risk analysis to develop inspection programs to ensure acceptable mechanical integrity and reliability. These industries include nuclear and electric power generation, oil refining, gas processing, onshore and offshore exploration and production, chemical processing, and pipelines. Risk analysis may also be used as a decision-making tool in the railroad industry to develop systematic improvements in track maintenance and inspection strategies. In the course of conducting research in support of the Federal Railroad Administration, a Monte Carlo risk assessment model has been developed to simulate certain aspects of rail inspection (also referred to as rail testing) to find and remove defects that may grow to sufficient size to cause rail failures. In this paper, the model is used to examine the relationship between the occurrence of rail failures and various operational factors. These operational factors include rail size, average axle loading, and inspection frequency. In addition, the risk assessment model is used to evaluate an alternative rail testing concept in which detector cars would conduct inspections at speeds higher than those used in current practice.