Fracture Toughness of Composite and Unfilled Restorative Resins

Fracture toughness, critical strain energy release rate, and critical stress intensity factor were determined for experimental and commercial restorative resins. A composite resin had lower resistance to arack initiation than an unfilled acrylic resin. The data were consistent with surface failure observed in single-pass wear studies of these resins.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66920/2/10.1177_00220345770560070801.pd

Stress field around arbitrarily shaped cracks in two-dimensional elastic materials

The calculation of the stress field around an arbitrarily shaped crack in an infinite two-dimensional elastic medium is a mathematically daunting problem. With the exception of few exactly soluble crack shapes the available results are based on either perturbative approaches or on combinations of analytic and numerical techniques. We present here a general solution of this problem for any arbitrary crack. Along the way we develop a method to compute the conformal map from the exterior of a circle to the exterior of a line of arbitrary shape, offering it as a superior alternative to the classical Schwartz-Cristoffel transformation. Our calculation results in an accurate estimate of the full stress field and in particular of the stress intensity factors K_I and K_{II} and the T-stress which are essential in the theory of fracture.Comment: 7 pages, 4 figures, submitted for PR

A new look at energy release rates for quasistatically propagating cracks in inelastic materials

A mapping technique is used to derive an integral expression for the energy release rate for a quasistatically propagating crack. The derivation does not depend on any assumptions in regard to the contitutive behavior of the material. It leads to a contour integral around the crack tip, plus an area integral over the region enclosed by this contour. Only the stress and displacement fields appear in the integrands. Although for stationary crack solutions known to the authors the area integral is not convergent, for propagating crack solutions in elastoplastic material, the integrals are convergent, and lead to zero energy release rate. This confirms conclusions by Rice from an independent point of view.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42773/1/10704_2004_Article_BF00012388.pd

Influence of welding residual stresses on stable crack growth in tubular K-joints under compressive fatigue loadings

Tubular bridge design has to deal with fatigue issues. The fatigue susceptibility of these bridges, composed of circular hollow section profiles welded together in K-joints, is mainly due to stress concentrations, to welding imperfections and to tensile residual stresses induced by the welding process. Since these residual stresses are unknown for K-joints, measurements were carried out in vicinity of weld toes using the incremental hole-drilling method, X-ray diffraction and neutron diffraction in particular. Re-sults from these techniques show that on the first millimeters from the surface, the most important tensile re-sidual stresses are oriented perpendicular to the weld and reach the yield strength. According to experimental investigations on two large scale specimens, it is established that tensile residual stresses have a strong influ-ence down to a depth of 2-3 mm from the surface, allowing cracks to propagate in compressive joints. Prelim-inary Finite Element Analyses are presented in this paper

Analysis and simulations for a phase‐field fracture model at finite strains based on modified invariants

Phase‐field models have already been proven to predict complex fracture patterns for brittle fracture at small strains. In this paper we discuss a model for phase‐field fracture at finite deformations in more detail. Among the identification of crack location and projection of crack growth the numerical stability is one of the main challenges in solid mechanics. Here we present a phase‐field model at finite strains, which takes into account the anisotropy of damage by applying an anisotropic split of the modified invariants of the right Cauchy‐Green strain tensor. We introduce a suitable weak notion of solution that also allows for a spatial and temporal discretization of the model. In this framework we study the existence of solutions and we show that the time‐discrete solutions converge in a weak sense to a solution of the time‐continuous formulation of the model. Numerical examples in two and three space dimensions illustrate the range of validity of the analytical results

Analysis of bioactivities and chemical composition of Ziziphus joazeiro Mart. using HPLC–DAD

AbstractThe aim of this study was to evaluate the chemical profile and antioxidant, antimicrobial and antiparasitic activities of the hydroalcoholic extract of the leaves of Ziziphus joazeiro Mart. (HELZJ). The antioxidant DPPH and FRAP assays and chemical profile were determined by colorimetric methods and HPLC/DAD. The antiparasitic, antibiotic and antibiotic-modifying activity were evaluated by microdilution assays. The HPLC–DAD assay showed the presence of mostly tannins and flavonoids, such as caffeic acid and quercetin. The levels of polyphenols and flavonoids were 183.136mg/g extract and 7.37mg/g extract, respectively. DPPH and FRAP showed low antioxidant activity for the extract. The antibacterial and antifungal activities were not of clinical relevance, showing MIC>1024μg/mL. However, synergism was observed between HELZJ and the antibiotics amikacin and gentamicin, which resulted in decreased bacterial drug resistance. EHFZJ showed low toxicity in fibroblasts in vitro, while antiparasitic results against Trypnosoma cruzi, Leishmania braziliensis and Leishmania infantum were not clinically relevant. Thus, our results indicate that Z. joazeiro Mart. (HELZJ) could be a source of plant-derived natural products that could lead to the development of promising new antibiotic compounds for infectious diseases

On the Path of a Quasi-static Crack in Mode III

A method for finding the path of a quasi-static crack growing in a brittle body is presented. The propagation process is modelled by a sequence of discrete steps optimizing the elastic energy released. An explicit relationship between the optimal growing direction and the parameters defining the local elastic field around the tip is obtained for an anti-plane field. This allows to describe a simple algorithm to compute the crack path

Physiological-based cord clamping in very preterm infants — Randomised controlled trial on effectiveness of stabilisation

Aim: To test whether stabilising very preterm infants while performing physiological-based cord clamping (PBCC) is at least as effective as the standard approach of time-based delayed cord clamping (DCC). Methods: A randomised contr