Search

[Display omitted] • A dislocation-based model with a robust convergence is developed to investigate the contact problems. • A deterministic method is proposed to progressively evaluate the stick and slip contact conditions of crack faces. • The slip accumulation of crack faces during the loading process is accounted for the description of friction evolution. • The effects of friction coefficient, crack alignment and location on the shear behaviors of crack faces are analyzed. Mechanical transmission components are generally under the risk of contact fatigue, resulting in cracks initiated from the subsurface. When subject to compressive stress, these cracks might be forced to be closed, thus their faces are in partial slip contact. Under such conditions, the interactions of stick and slip zones cannot be directly determined, which is one of the greatest challenges of contact fatigue problems. In this study, the distributed dislocation technique is adopted to investigate the stick–slip friction along the alignment of shear cracks in arbitrary orientations in a half-plane under contact loading. The unknown dislocation density describing the crack face displacement is iteratively calculated based on the stress conditions and then introduced to update the surface gap between contacting bodies. The complex expressions of the influence coefficients used to determine the stress and displacement induced by the dislocations are derived and the FORTRAN codes are provided in the Supplementary Materials. A step-by-step loading method is proposed to progressively capture the slip history of crack faces. The model is also capable of simulating rolling contact problems. The results are comparable to those predicted using the finite element method with more robust convergence properties. The effects of friction coefficient, crack alignment, and locations of crack faces are discussed in detail. The model paves the foundation for further studies on competing mechanisms of crack propagation and crack face wear, and provides insights into the frictional fracture of materials under contact loading. [ABSTRACT FROM AUTHOR]

Mode I crack opening effects in compression-loaded cracked cylinders were examined using finite element analysis. The situation ahead of the crack tip was characterized using linear elastic fracture mechanics in the form of the stress intensity factor (K) concept. Different cylinder dimensions in combination with different loads and crack radii (circular crack shapes were used) were investigated. By using the line load as normalization parameter for the K values, load independent K-curves (K as a function of the normalized crack length a/W) were obtained. The K-curves were compared for different cylinder dimensions to examine the scaling behavior. [ABSTRACT FROM AUTHOR]

In this study, fatigue life predictions were made for silicon nitride components undergoing hybrid ceramic-steel rolling contact. Three-dimensional stress fields were extracted using a bespoke finite element model and subsequently used to calculate stress intensity factors by means of the weight function method. Crack-growth rates were estimated by assuming crack growth to follow a Paris power-law expression whose material parameters were obtained from four-point bending fatigue experiments under fluctuating tensile load (R = 0.1) and fully-reversed alternating load (R = −1). The crack-growth behavior obtained from the calculations was compared with experimental results obtained from twin-disk-type RCF experiments. The calculated lifetime predictions were in accordance with the experimental results. Crack formation and propagation was found more likely to occur in locations undergoing alternating load rather than those undergoing pure fluctuating tensile load. [ABSTRACT FROM AUTHOR]

The paper deals with finite element computations of crack driving forces for a surface crack in a rail under cyclic elastic–plastic conditions during wheel/rail contact. A straight crack normal to the surface is investigated. Examinated are influences of wheel load, slip, residual stresses, crack lengths and mesh around the crack tip on the crack driving forces. The specific role of the plastic deformation during one rolling cycle and the resulting development of the crack driving force is discussed. The numerical verification of the configurational force concept is done by comparison with classical J -integral investigations using linear-elastic and elastic–plastic material properties. [ABSTRACT FROM AUTHOR]

• A unique pin-loaded SENT specimen was fabricated using electron-beam welding for fracture testing of thin-walled pipe. • The η CMOD -factor, or crack mouth Eta-factor, significantly differed from literature solutions for pin-loaded SENT specimens. • The experimental J-error was estimated to be < 5% for the present analysis η CMOD and 10–30% for literature values of η CMOD. • The crack growth correction is best derived using the Eta-factor computed at the pin, even when J is calculated using η CMOD. • Friction at the pin-specimen contact reduces the stress intensity geometry factor, F , and η CMOD and increases experimental J-error. There is considerable interest in the fracture community for representative measurements of the resistance of pipe structures to fatigue crack propagation and fracture. However, to date there has been a lack of standard test methods available for the accurate fracture testing of radially propagating longitudinal flaws in thin-walled piping. A pin-loaded single edge-notched tensile (SENT) specimen was developed, denoted the CSR SENT specimen. This test geometry has been shown to reproduce the plastic constraint for longitudinal cracks in thin-walled piping, resulting in transferable fracture test data to that application beyond the conventional limits of single-parameter J-dominated fracture mechanics. The CSR SENT was simulated with finite element analysis (FEA) to yield the parameters necessary for the experimental determination of the J-integral using standard fracture test methods. The FEA results showed that the stress intensity geometry factor, F , for the CSR SENT matched literature solutions for most crack lengths, but that the CMOD-Eta factor – η CMOD , used to calculate the plastic component of the J-integral from the applied load and crack mouth opening displacement (CMOD) – differed from literature solutions and is specimen size-dependent. The error associated with the calculation of the J-integral is estimated to be < 5% with the obtained η CMOD , while the use of literature solutions for η CMOD result in significant non-conservative overestimates of the experimental J-integral. It is recommended that fracture testing be limited to a specific specimen geometry associated with a FEA-derived η CMOD solution. The crack growth correction to the J-integral measurement was also obtained, and is recommended to be derived from the η pin (also referred to as η LLD, derived from the load-displacement of the pin boundary), which can be used alongside the η CMOD for experimental calculation of the J-integral in standard single-specimen fracture testing. Friction at the pin-specimen interface results in significant non-conservative bias error in the J-integral, and a rolling pin-clevis contact is recommended with a pin diameter twice that of the specimen width to mitigate pin contact plasticity and damage. [ABSTRACT FROM AUTHOR]

Abstract: Rolling contact fatigue cracks in railway track called squats are studied in this paper. In the first part, the effects of an elastic foundation (sleepers and the ballast) on stress intensity factors obtained at a crack tip are studied. A simplified finite element model (FEM) and an extended finite element model (XFEM) were created to investigate these effects, the XFEM model being limited in geometrical size, but more able to model crack growth. Both FEM and XFEM confirmed that an elastic foundation leads to an additional bending stress which increases the crack growth rate significantly. Field results also authenticate that squat form cracks appear on timber sleepers more commonly than on concrete ones. These results indicate that considering these bending stresses in a FE model, is important to achieve a more realistic model of squat development. In the second part, a short crack of 250μm length is simulated to investigate how variations of traction ratio (TR), friction coefficient between the crack faces (FC) and the crack angle affect SIFs when the rail is mounted on an elastic foundation. Simulations show that a crack on a rail laid on elastic foundation (clips, sleepers and ballast) can lead to significantly higher SIFs in many conditions and consequently raises crack growth rate. This indicates that foundation stiffness is as important as water entrapment and friction coefficient between the crack faces. [Copyright &y& Elsevier]