Fretting Fatigue Behavior of Riveted Al 6XXX Components

The riveting is widely used for fitting together two or more elements of structure in the same or different materials. In these assemblies the stress field is complex, we have to consider the effect of the geometrical discontinuity, the contact, the tightening, the material properties and the applied load. The current work focus on the study of fretting fatigue crack formation in common 6XXX aluminum alloys, used in land transportation equipments, and uncovering characteristic origins of crack by experimental and numerical methods based on multi-axial fatigue life models. 3D finite element models were validated by the experimental results obtained with strain gauges. The influences of the contact friction coefficient at the fretting surface, the fastening forces and the remote stress applied in the fretting fatigue experiments on the crack origins are discussed by the comparison of the different numerical results.

Dynamic Behavior of Cracked Cantilevered Pipes Conveying Fluid

In this article, the effects of the non-propagating open cracks on the dynamic behaviors of a cantilevered pipe conveying fluid are studied. The model divides the pipe into a number of segments from the crack sections and assembles all segments each by each by a rotational spring which has no mass. The stiffness of the spring is obtained through linear fracture mechanics. In order to obtain the modal functions which satisfy the boundary conditions and geometrical discontinuity conditions at the crack’s location, a simple approach is used. That is adding polynomial functions to the modal functions of the uncracked beam. The equations of motion for the cracked cantilevered pipe conveying fluid is derived based on the extended Lagrange equations for systems containing non-material volumes. Not only the virtual work done by the discharged fluid, but also that done by the fluid at the crack position due to the geometrical discontinuity conditions are considered in the present equations of motion. In this article, several numerical examples are given. The comparisons of solutions of the present equations with that of model in existence show that the present work is better. The influences of the relative depth, the position ratio of the cracks, the flow velocity on the eigenvalues are depicted.

Fracture Assessment of Welded Joint With Geometrical Discontinuity Using the Weibull Stress

Recently the Weibull stress is used as a fracture driving force parameter in fracture assessment. The Weibull stress is derived from a statistical analysis of local instability of micro cracks leading to brittle fracture initiation. The critical Weibull stress is expected to be a critical parameter independent of the geometrical condition of specimens. Fracture toughness test using 3-point bending and tensile tests of welded joint specimens with geometrical discontinuity were conducted in order to study the applicability of fracture assessment procedure based on Weibull stress criterion. Steel plates prepared for this study had tensile strength of 490 MPa for structural use. Two kinds of welded joint specimens, “one-bead welded joint” and “multi-pass welded joint” were prepared for fracture toughness test by using gas metal are welding. In tensile test specimen, corner flaws were introduced at the geometrical discontinuity part at where stress concentration is existed. Three dimensional elastoplastic finite element analyses were also carried out using the welded joint specimen models in order to calculate the Weibull stress. The critical loads for brittle fracture predicted by the Weibull stress criterion from CTOD test results of one-bead and multi-pass welded joint specimens show fairly good agreement with experimental results of welded joint specimens with geometrical discontinuity.

Importance of pin geometry on pin-on-plate wear testing of hard-on-hard bearing materials for artificial hip joints

The contact mechanics between the pin and the plate used in simple wear screening tests were investigated in this study. Both soft-on-hard, such as ultra-high molecular weight polyethylene (UHMWPE)-on-metal or UHMWPE-on-ceramic, and hard-on-hard, such as metal-on-metal, bearing couples were considered. The effect of the pin geometry and the misalignment between the pin and the plate were investigated on the predicted contact pressure distribution at the bearing surfaces using the finite element method. It was demonstrated that in the case of soft-on-hard bearing couples, neither the geometrical discontinuity of the pin surface nor the misalignment could cause a significant increase in the contact stress. However, for hard-on-hard combinations, even with a very small misalignment of 0.5° between the pin and the plate, the geometrical discontinuity could lead to a more than tenfold increase in the predicted contact stress. This elevated contact stress may lead to a large scatter in the wear data and, even more importantly, structural damage of the bearing surfaces.