Preventing Repeat Victimization: A Systematic Review

This report presents a systematic review, including a statistical meta-analysis, of the effects of initiatives to prevent repeat victimization

Moisture effects on the bending fatigue of laminated composites

This paper investigated the effect of moisture ingress on the bending fatigue of laminated composites. An accelerated testing method was developed to investigate the correlation between composite fatigue and moisture diffusion effects. Unidirectional and cross-ply laminated CFRP composites were manufactured in autoclave, and then submerged in both fresh and seawater for various periods until moisture saturation. Quasi-static and cyclic tests were carried out in both air and wet environment, and the failure mechanisms were investigated using visual and microscopic methods. Additionally, a robust 2D Finite Element model (FEA) was developed to simulate the fatigue crack propagation based on virtual crack closure technique (VCCT), while a 3D FEA model was developed to investigate the edge effect on fatigue crack propagation. The experimental observations gave a good agreement with the FEA models. The study showed that the bending fatigue failure was due to the so-called buckling-driven delamination, and the fatigue life was reduced significantly owing to the combination of edge effect and capillary effect. The fatigue test indicated that the fatigue resistance was degraded one stress level due to the water ingress, e.g. from 80% ultimate flexural strength (UFS) to 65% UFS. Therefore, a 4-step fatigue failure theory was proposed to explain the moisture effects on the crack propagation under bending fatigue

Effects of hygrothermal stress on the failure of CFRP composites

This paper investigates the hygrothermal effects on the failure mechanisms in bending of carbon fibre reinforced polymer (CFRP) composites. Accelerated diffusion testing was carried out by immersion at 50 °C constant temperature and 70 bar hydrostatic pressure to study the effects of fresh or sea water diffusion into pre-preg CFRP laminates. Consequently the composite laminates were tested in bending after 1 and 3 months’ immersion. A three-dimensional finite element analysis (FEA) model was developed to couple the moisture diffusion, hygrothermal expansion and bending. Optical and field emission scanning electronic microscope (SEM) were employed to analyse the failure mechanisms of CFRP composites in bending after immersion. The study showed that the mechanical properties are significantly reduced after short term immersion due to the edge effects, while the damage to the fibre/polymer interface becomes more significant to laminate degradation after longer-term immersion

Multi-scale modelling of moisture diffusion coupled with stress distribution in CFRP laminated composites

Laminated composite structures operating in a marine environment are subject to moisture ingress. Due to the slow diffusion process of moisture, the distribution of moisture is not uniform so that the laminates can develop hygrothermal stresses. An accurate prediction of the moisture concentration and the associated hygrothermal stress is vital to the understanding of the effect of marine environment on failure initiation. The present paper investigates the time-dependent moisture diffusion and the stress distribution in carbon fibre reinforced polymeric (CFRP) composites by means of experimental study and Finite Element Analysis (FEA). Samples were made from CFRP pre-preg autoclave-cured, and then immersed in fresh water and sea water at a constant 50 °C for accelerated moisture diffusion. Laminates with [0]16, [90]16, [±45]4s lay-up sequences were investigated. A multiscale 3D FEA model was developed to evaluate the interfacial stresses between polymer matrix and carbon fibre and the stress distribution in the composite laminates. The analysis revealed that both the stress distribution and stress level are time-dependent due to moisture diffusion, and the interphase between fibres and matrix plays an important role in both the process of moisture diffusion and the stress/strain transfer. The interlaminar shear stresses of the laminates induced by hygrothermal expansion exhibited a significant specimen edge effect. This is correlated with the experimental observations of the flexural failure of laminates

The effects of unequal compressive/tensile moduli of composites

Abstract This paper investigates the effects of unequal compressive and tensile moduli of carbon fibre reinforced plastic (CFRP) composites. The basic assumption is based on the statistics that the compressive modulus is a fraction lower than the tensile modulus. Data evaluated by Finite Element Analysis (FEA) model, Classical Laminate Theory (CLT) model, and experiment are used to investigate these effects. The terms of compressive modulus are successfully introduced into the Tsai–Wu failure criterion for the production of failure envelops, into the Classical Beam Theory (CBT) and CLT for the investigation of flexural behaviour as well as the fibre microbuckling model for the analysis of compressive failure. The study shows that the failure criteria shift from stress domain to strain domain when the compressive modulus is considered, and the strain dominated failure criteria could generally provide more accurate prediction in composite material. Therefore it is proposed to apply strain dominated failure criteria for composite design, testing and certificate.Abstract This paper investigates the effects of unequal compressive and tensile moduli of carbon fibre reinforced plastic (CFRP) composites. The basic assumption is based on the statistics that the compressive modulus is a fraction lower than the tensile modulus. Data evaluated by Finite Element Analysis (FEA) model, Classical Laminate Theory (CLT) model, and experiment are used to investigate these effects. The terms of compressive modulus are successfully introduced into the Tsai–Wu failure criterion for the production of failure envelops, into the Classical Beam Theory (CBT) and CLT for the investigation of flexural behaviour as well as the fibre microbuckling model for the analysis of compressive failure. The study shows that the failure criteria shift from stress domain to strain domain when the compressive modulus is considered, and the strain dominated failure criteria could generally provide more accurate prediction in composite material. Therefore it is proposed to apply strain dominated failure criteria for composite design, testing and certificate

3D-Matched-Filter Galaxy Cluster Finder I: Selection Functions and CFHTLS Deep Clusters

We present an optimised galaxy cluster finder, 3D-Matched-Filter (3D-MF), which utilises galaxy cluster radial profiles, luminosity functions and redshift information to detect galaxy clusters in optical surveys. This method is an improvement over other matched-filter methods, most notably through implementing redshift slicing of the data to significantly reduce line-of-sight projections and related false positives. We apply our method to the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep fields, finding ~170 galaxy clusters per square degree in the 0.2 <= z <= 1.0 redshift range. Future surveys such as LSST and JDEM can exploit 3D-MF's automated methodology to produce complete and reliable galaxy cluster catalogues. We determine the reliability and accuracy of the statistical approach of our method through a thorough analysis of mock data from the Millennium Simulation. We detect clusters with 100% completeness for M_200 >= 3.0x10^(14)M_sun, 88% completeness for M_200 >= 1.0x10^(14)M_sun, and 72% completeness well into the 10^(13)M_sun cluster mass range. We show a 36% multiple detection rate for cluster masses >= 1.5x10^(13)M_sun and a 16% false detection rate for galaxy clusters >~ 5x10^(13)M_sun, reporting that for clusters with masses <~ 5x10^(13)M_sun false detections may increase up to ~24%. Utilising these selection functions we conclude that our galaxy cluster catalogue is the most complete CFHTLS Deep cluster catalogue to date.Comment: 18 pages, 17 figures, 5 tables; v2: added Fig 5, minor edits to match version published in MNRA

3D FEA modelling of laminated composites in bending and their failure mechanisms

keywords: 3D keywords: 3D keywords: 3D keywords: 3D keywords: 3DAbstract This paper developed three-dimensional (3D) Finite Element Analysis (FEA) to investigate the effect of fibre lay-up on the initiation of failure of laminated composites in bending. Tsai-Hill failure criterion was applied to identify the critical areas of failure in composite laminates. In accordance with the 3D FEA, unidirectional ([0]16), cross-ply ([0/90]4s) and angle-ply ([±45]4s) laminates made up of pre-preg Carbon Fibre Reinforced Plastics (CFRP) composites were manufactured and tested under three-point bending. The basic principles of Classical Laminate Theory (CLT) were extended to three-dimension, and the analytical solution was critically compared with the FEA results. The 3D FEA results revealed significant transverse normal stresses in the cross-ply laminate and in-plane shear stress in the angle-ply laminate near free edge regions which are overlooked by conventional laminate model. The microscopic images showed that these free edge effects were the main reason for stiffness reduction observed in the bending tests. The study illustrated the significant effects of fibre lay-up on the flexural failure mechanisms in composite laminates which lead to some suggestions to improve the design of composite laminates

Kondo effect in a carbon nanotube with spin-orbit interaction and valley mixing: A DM-NRG study

We investigate the effects of spin-orbit interaction (SOI) and valley mixing on the transport and dynamical properties of a carbon nanotube (CNT) quantum dot in the Kondo regime. As these perturbations break the pseudo-spin symmetry in the CNT spectrum but preserve time-reversal symmetry, they induce a finite splitting $\Delta$ between formerly degenerate Kramers pairs. Correspondingly, a crossover from the SU(4) to the SU(2)-Kondo effect occurs as the strength of these symmetry breaking parameters is varied. Clear signatures of the crossover are discussed both at the level of the spectral function as well as of the conductance. In particular, we demonstrate numerically and support with scaling arguments, that the Kondo temperature scales inversely with the splitting $\Delta$ in the crossover regime. In presence of a finite magnetic field, time reversal symmetry is also broken. We investigate the effects of both parallel and perpendicular fields (with respect to the tube's axis), and discuss the conditions under which Kondo revivals may be achieved.Comment: 13 pages, 17 figure

DNA protection by histone-like protein HU from the hyperthermophilic eubacterium Thermotoga maritima

In mesophilic prokaryotes, the DNA-binding protein HU participates in nucleoid organization as well as in regulation of DNA-dependent processes. Little is known about nucleoid organization in thermophilic eubacteria. We show here that HU from the hyperthermophilic eubacterium Thermotoga maritima HU bends DNA and constrains negative DNA supercoils in the presence of topoisomerase I. However, while binding to a single site occludes ∼35 bp, association of T. maritima HU with DNA of sufficient length to accommodate multiple protomers results in an apparent shorter occluded site size. Such complexes consist of ordered arrays of protomers, as revealed by the periodicity of DNase I cleavage. Association of TmHU with plasmid DNA yields a complex that is remarkably resistant to DNase I-mediated degradation. TmHU is the only member of this protein family capable of occluding a 35 bp nonspecific site in duplex DNA; we propose that this property allows TmHU to form exceedingly stable associations in which DNA flanking the kinks is sandwiched between adjacent proteins. We suggest that T. maritima HU serves an architectural function when associating with a single 35 bp site, but generates a very stable and compact aggregate at higher protein concentrations that organizes and protects the genomic DNA