Some Physical Processes Involved in Deformation and Fracture

<p>The effects of strain rate, of moisture content, and of tracheid structure on the transverse fracture properties of Pinus Radiata have been studied. Small rectangular blocks were loaded to failure in transverse tension, with the conditions of fracture being varied as follows: (i) strain raite - at 2 x 10 caret-6 sec caret-1, and from 10 caret-5 to 10 caret 2 sec caret-1 in decade steps , (ii) moisture content - airdry (12.7%) and saturated, and (iii) structure - springwood and summerwood. Microscopical examination (both scanning electron and optical) of the surfaces produced by the facture showed that the cellular level, either of two types of failure could occur. These are called transwall and intrawall; transwall is the longitudinal splitting of a tracheid wall, and intrawall is a splitting between adjacent tracheids.</p>

Some Physical Processes Involved in Deformation and Fracture

<p>The effects of strain rate, of moisture content, and of tracheid structure on the transverse fracture properties of Pinus Radiata have been studied. Small rectangular blocks were loaded to failure in transverse tension, with the conditions of fracture being varied as follows: (i) strain raite - at 2 x 10 caret-6 sec caret-1, and from 10 caret-5 to 10 caret 2 sec caret-1 in decade steps , (ii) moisture content - airdry (12.7%) and saturated, and (iii) structure - springwood and summerwood. Microscopical examination (both scanning electron and optical) of the surfaces produced by the facture showed that the cellular level, either of two types of failure could occur. These are called transwall and intrawall; transwall is the longitudinal splitting of a tracheid wall, and intrawall is a splitting between adjacent tracheids.</p>

A rare case of Diastematomyelia with syrinx and tethered cord in a newborn

Diastematomyelia or Split cord syndrome is a rare form of spinal dysraphism characterized by longitudinal splitting of spinal cord, conus medullaris or filum terminale to a variable extent. Presence of SCM is suggested by certain superficial markers like skin pigmentation, hemangioma, lipoma, dermal sinus and hypertrichosis. Meningocele or myelomenigocele may also be present. Affected children usually present with progressive sensorimotor symptoms and bowel and bladder dysfunction. Development of sensorimotor symptoms and progressive loss of function emphasis the need for antenatal diagnosis of the spinal deformities which paves way for early intervention and management thus minimizing the morbidity.

The Influence of Wire Type Indentation on Longitudinal Splitting in Pre-Stressed Concrete

The important characteristic in the creation of longitudinal splitting cracks in pretensioned concrete members has found to be the geometry of the pre-stressing wire indents. Longitudinal splitting along prestressing tendons can result in severe splitting of prestressed member in the field under loading over time. The research evaluated the influence of wire type indentation on the longitudinal splitting in prestressed concrete members fabricated with different concrete mixtures and different compressive strength of concrete. A key objective was to find the best type of wire to avoid failures in the field. A study was conducted at Kansas State University to understand the effect of wire type on the longitudinal splitting between prestressing steel and prestressed concrete. Three different types of wires will be presented in this paper denoted as “WB”, “WF” and “WQ”. The wires have different parameters which include indent depth, indent width, indent sidewall angle, indent pitch and indent volume.

The energy-absorbing characteristics of tubular sandwich structures

The energy-absorbing response of sandwich structures with exceptionally high levels of energy absorption is investigated. The sandwich panels are produced by fixing small composite tubes onto metal facings with surface features that reflect the internal geometry of the tubing. Small diameter tubes are employed to manufacture the cores, since it is well established that the specific energy absorption (SEA) characteristics of a composite tube increase as the inner dimension (diameter or wall-to-wall) to thickness ratio decreases. Tests have been undertaken on tubular arrays based on both circular and square composite tubes. The effect of varying the areal density of the tubular array within the core was investigated by systematically increasing the number of tubes from one to nine. An examination of the composites during the crushing process indicated that all of the tubes failed in a splaying process, involving significant fracturing of fibers and longitudinal splitting. The measured values of SEA remained relatively constant in most cases as the areal density of the tubular arrangement was increased, suggesting that cores could readily be designed to absorb known levels of applied external energy. Arrays based on circular tubes offered higher energy-absorbing characteristics than their square counterparts, with values in excess of 100 kJ/kg being recorded in some cases. It is believed that these tubular sandwich structures offer potential for use in components that are subjected to extreme dynamic loading, such as those associated with impact and blast.

Optimization Technique and Practice of Stratified Injection in Low and Medium Permeability Thin Interlayer Reservoirs

Reservoir S is a typical medium and low permeability thin interlayer reservoir. It is developed by co-production of directional Wells and separate injection of directional Wells. The comprehensive water content of the oilfield is 54%. Therefore, it is urgent to optimize the injection method of stratified injection distribution in this reservoir, so as to improve the degree of water driving and recovery. In this paper, the reservoir engineering and numerical simulation methods are adopted to introduce the impact factor of injection-production correspondence rate, modify the previously used fine injection matching model, and use the model to quantitatively analyze the sensitivity of key parameters such as longitudinal splitting coefficient, pressure recovery rate and injection-production correspondence rate. The results show that it is very important to select the influencing factors for the injection and production response ratio of medium and low permeability thin interlayer reservoirs, which directly affects the effect of stratified water injection. At present, this research technology has been widely applied in S oilfield, and the water injection effect is very significant, effectively improving the recovery rate of the implementation area by 2%, which provides experience for the water injection development of similar reservoirs.

Proposed Qualification Test Procedure to Identify Prestressed Concrete Ties That May Be Susceptible to End-Splitting Cracks

Prestressed concrete ties could develop end-splitting cracks along tendons due to lateral bursting stresses. The lateral bursting stresses can form due to Hoyer effect (change in diameter of the prestressing tendons due to Poisson’s ratio, the jacking force in the tendons, geometrical features, and indent characteristics of the prestressing tendons. End-splitting cracks can occur immediately after de-tensioning procedure in some cases, but they also can be developed during the first weeks after de-tensioning procedure due to sustained lateral stresses exerted by the prestressing tendons. The ability of concrete to resist these bursting stresses without cracking is primarily the function of the thickness of concrete cover, the type of concrete mixture used and the maximum compressive strength of the concrete. The test purpose was to identify tie designs that may be susceptible to end-splitting cracks. The Qualification test will be great tool to identify tie designs that have ability to form end-splitting cracks. The System Qualification Test involves six pre-tensioned concrete prisms with the same prestressing tendons and concrete mixture that is used in the concrete ties, except that the edge distance for the prisms is reduced by approximately 25 percent. If this reduction in edge distance results in longitudinal splitting cracks along the prestressing tendons, then the system (tie design and material selection) may be susceptible to concrete end-splitting cracks. In this case, changes to the design and/or material selection should be made prior to mass production of ties.

Degradation of Glass Fiber Reinforced Polymer (GFRP) Material Exposed to Tropical Atmospheric Condition

Fibre reinforced polymers (FRPs) have emerged as popular materials for structural application in recent decades due to numerous of advantages. Despite the growing body of research on the use of glass fibre reinforced polymers (GFRP) composites in repairing and retrofitting the important structures such as oil and gas pipelines, the lack of comprehensive data on the long-term degradation mechanism for these materials is still impeding their widespread use in open-air structures repairs particularly in tropical climate locations such as Malaysia. Therefore, this paper presents an experimental investigation to determine the influence of tropical atmospheric condition on tensile properties of the GFRP. In this study, a set of GFRP samples were fabricated using epoxy resin as polymer matrix and woven E-glass fibres as reinforcing materials. These samples were exposed to tropical atmospheric condition in Malaysia for a period of four months. Tensile test was carried out for each sample before and after four-months period of exposure. The experimental tensile test results recorded a 15% reduction in tensile strength after 4 months of exposure as compared to its original strength. Further, the dominant failure mode of the exposed sample was characterized with longitudinal splitting of the fibres without completely breaking out. Overall, the tropical atmospheric condition has a noticeable impact on the GFRPs tensile strength degradations over the exposure duration.

Transitional Channel Flow: A Minimal Stochastic Model

In line with Pomeau’s conjecture about the relevance of directed percolation (DP) to turbulence onset/decay in wall-bounded flows, we propose a minimal stochastic model dedicated to the interpretation of the spatially intermittent regimes observed in channel flow before its return to laminar flow. Numerical simulations show that a regime with bands obliquely drifting in two stream-wise symmetrical directions bifurcates into an asymmetrical regime, before ultimately decaying to laminar flow. The model is expressed in terms of a probabilistic cellular automaton of evolving von Neumann neighborhoods with probabilities educed from a close examination of simulation results. It implements band propagation and the two main local processes: longitudinal splitting involving bands with the same orientation, and transversal splitting giving birth to a daughter band with an orientation opposite to that of its mother. The ultimate decay stage observed to display one-dimensional DP properties in a two-dimensional geometry is interpreted as resulting from the irrelevance of lateral spreading in the single-orientation regime. The model also reproduces the bifurcation restoring the symmetry upon variation of the probability attached to transversal splitting, which opens the way to a study of the critical properties of that bifurcation, in analogy with thermodynamic phase transitions.

Analysis of the three dimensional structure of the kidney glomerulus capillary network

The capillary network of the kidney glomerulus filters small molecules from the blood. The glomerular 3D structure should help to understand its function, but it is poorly characterized. We therefore devised a new approach in which an automated tape collecting microtome (ATUM) was used to collect 0.5 μm thick serial sections from fixed mouse kidneys. The sections were imaged by scanning electron microscopy at ~ 50 nm/pixel resolution. With this approach, 12 glomeruli were reconstructed at an x–y–z resolution ~ 10 × higher than that of paraffin sections. We found a previously undescribed no-cross zone between afferent and efferent branches on the vascular pole side; connections here would allow blood to exit without being adequately filtered. The capillary diameters throughout the glomerulus appeared to correspond with the amount of blood flow within them. The shortest path (minimum number of branches to travel from afferent to efferent arterioles) is relatively independent of glomerular size and is present primarily on the vascular pole size. This suggests that new branches and longer paths form on the urinary pole side. Network analysis indicates that the glomerular network does not form by repetitive longitudinal splitting of capillaries. Thus the 3D structure of the glomerular capillary network provides useful information with which to understand glomerular function. Other tissue structures in the body may benefit from this new three dimensional approach.