The fracture toughness is a critical material property for the pyrolytic carbon materials used in mechanical heart-valve prostheses; however, making accurate toughness measurements has traditionally been problematic due to difficulties in fatigue precracking specimens. In this work, a simple, effective, and reliable precracking method is presented where a sharp precrack is "popped in" from a ra...

Fracture toughness tests were conducted for an A533B-1 steel by using chevron-notched compact specimens in the temperature range from the lower shelf regime up to the transition temperature in order to assess the R-curve for cleavage fracture. The applicability of these specimens to the simple fracture toughness test without introducing fatigue pre-cracks was examind. The following are the summ...

This paper presents a probabilistic assessment model for linear elastic fracture mechanics (LEFM). The model allows the determination of the failure probability of a structure subjected to fatigue loading. The distributions of the random variables for civil engineering structures are provided, and the relative importance of these random variables is determined. An example of a bridge detail is ...

In this paper fracture surface of the fatigue delamination have been investigated. Fatigue delamination tests were performed on the crabon/epoxy under different stress ratios. Samples were cut from the DCB specimens and analyzed in Laser Confocal Scanning Microscope. The analysis was used to measure the roughness values. Different fractographic features observed in the study are discussed.

introduction: file fracture is one of the main procedural mishaps in endodontic treatment. the aim of this in vitro study was to compare the fracture rate of three niti rotary systems; hero 642, mtwo and flexmaster in artificial canals. methods and materials: in this study, bovine long bone was used. after primary preparation of bones, longitudinal sections with 4-cm diameter were cut and encod...

Mechanisms for fatigue crack closure under plane strain conditions have recently been identified at very low (near-threshold) stress intensities in terms of effects of excess corrosion deposits or fracture surface roughness in promoting premature closure of the crack. In the present paper, a geometric model is presented for crack closure induced by fracture surface roughness. This model specifi...

The cyclic fatigue resistance of K3 and EndoSequence files was compared by rotating files against a highly polished surface inclined at 15 degrees to the horizontal. For each brand, files with a 25 tip in .04 and .06 taper and files with a 40 tip in .04 and .06 taper were tested at both 300 and 600 rpm. A 3-mm axial movement simulated a clinical pecking motion at 1 cycle per second. The number ...

The design of clinical trials allows for limited insights into the fatigue processes occurring in resin composites and the factors involved therein. In vitro studies, in contrast, can fundamentally narrow study interests to focus on particular degradation mechanisms and, to date, represent the major contributors to the state of knowledge on the subject. These studies show that microstructural f...

In this paper, and its companion Part 2 [Dong and Atluri (2013b)], the Symmetric Galerkin Boundary Element Method (SGBEM), and the SGBEMFEM alternating/coupling methods, are compared with the recently popularized Extended Finite Element Method (XFEM), for analyzing fracture and fatigue crack propagation in complex structural geometries. The historical development, and the theoretical/algorithmi...

We report a case of two hemiarthroplasties (HAs) that underwent an unexpected mechanical failure. Two patients affected by femoral fractures were treated with an HA. At 5 and 7 years after surgery, they showed a breakage of the HA at the head-stem junction. We analyzed macroscopically and microscopically (by a scanning electron microscopy) the surfaces of the broken prostheses. In both cases, a...