The essential work of fracture through the wall of a uPVC pipe

The specific essential work of fracture, w _e, has been measured for a relatively thick walled uPVC pipe as a function of position through the wall of the pipe. w _e was highest at the surface of the pipe and decreased significantly at the centre of the pipe wall. The variation in w _e through the wall of the pipe correlated with the processing level of the uPVC material as measured by the critical temperature, T _c. The variability in the measured values of w _e was substantially higher in the centre of the pipe where the processing levels were lower. This was likely to be a result of the variability in the microstructure of the material where poor processing had introduced regions of poor fusion of primary PVC particles.     

The fracture behaviour of uPVC at both ambient and high hydrostatic pressures

Fracture measurements have been made using a high pressure technique on three batches of uPVC corresponding to distinct levels of gelation.K _c values correlate with methylene chloride attack in the established manner, but are low in comparison with room pressure values measured at comparable strain rates. This is linked with the presence of stress whitening on the fracture surface at room pressure, its absence at high pressure, and its diminution at room pressure when testing speed is increased, when lowK _c values are also recorded. The results are successfully interpreted in terms of a multiple craze slow crack growth model, in which cracking in the tests at room pressure and slow speed is assumed to start at theK _c measured at high pressure, and slow crack growth follows as the load on the specimen continues to increase until the specimen fails catastrophically. A reasonable choice of parameters then gives a good prediction of the observed collapse loads.     

Essential work of fracture analysis of the tearing of a ductile polymer film

The fracture behaviour of a 0.5 mm thick ethylene-propylene block copolymer, previously evaluated using the essential work of fracture method, has been analyzed again in more detail, using different plots, allowing the determination of the crack initiation displacement and stress. In such plots is evidenced that the specific essential work of fracture, w_e, corresponds to the energy just up to crack initiation value that can be related with J₀. Also, it has been found a novel relationship between the plastic term, βw_p and the crack initiation stress, σ_i.     

Effect of test conditions on the essential work of fracture in polyethylene terephthalate film

The tear resistance of polyethylene terephthalate film is characterized by the essential work of fracture method in mode I as a function of test speed and temperature. Attempts to extrapolate tearing resistance found by the method of essential work to commercial slitting processes are discussed. Limitations of the essential work of fracture method with regards to specimen size are evaluated. Based on the findings modifications to the test protocol are suggested.     

Failure mechanics of uPVC cyclically pressurized water pipelines

An extensive investigation has been directed towards explaining fatigue failure of pressurized water pipelines under service conditions, in terms of laboratory studies of the base material (unplasticized polyvinyl chloride, uPVC). It is established that many such failures are located in the regime to which linear elastic fracture mechanics can be applied, with encouraging predictive accuracy. Only failures at very low stress levels are not reliably explained by these methods, which nevertheless provide direction for further study.     

Temperature and deformation rate dependence of the work of fracture in polycarbonate (PC) film

Single edge notched polycarbonate (PC) specimens of thickness 0.175 mm were pulled to complete fracture at temperatures between 25°C and 100°C and at loading rate values of 2, 5 and 50 mm/min. A duckbill-shaped yielded zone was formed ahead of the crack tip in all the specimen tested. Propagation of the crack within the yielded zone was always stable. The method of essential work of fracture (EWF) was used to study the effects of temperature and loading rate on fracture toughness. The specific essential work of fracture, w _e, was found to be independent of both temperature and loading rate. The non-essential work of fracture, w _p, increased with increasing temperature but showed no systematic variation with respect to loading rate. Moreover, plastic constraint factor, m, also increased with increasing temperature. A linear temperature dependence was obtained for both w _p and m giving the extrapolated values of w _p = 0 and m = 0.5 at –23°C.     

Fractal fracture of polyarylatesulfone film specimens

Donetsk Physicotechnical Institute, Ukrainian Academy of Sciences, Donetsk. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 4, pp. 116–120, July – August, 1995.     

Modified essential work of fracture model for polymer fracture

The well-known essential work of fracture model, describing the linear relationship between fracture energy and un-cracked ligament length, is further extended to allow for any non-linearity in the relationship as this can potentially lead to a large error in determination of the essential work of fracture. Two different polymers, described in the literature, were chosen to show how the essential work of fracture of a polymer can still be determined in cases when a non-linearity exists in the relationship between fracture energy and ligament length. The new model specifies the condition under which the linear relationship exists, and the condition under which the non-linearity needs to be considered.     

Factors affecting cathodic-protection interference

A 3D theoretical simulation and analysis of DC stray-current corrosion (SCC) is introduced. The use of boundary element analysis system (BEASY) has allowed cathodic protection (CP) interference to be assessed in terms of the normal current density, which is directly proportional to the corrosion rate. Different real structures consisting of pipelines and/or well casings are simulated to investigate the factors affecting four types of CP interferences, namely, anodic, cathodic, combined and induced, with special emphasis on the cathodic one. The results reveal that the application of impressed current CP systems creates DC SCC on other nearby unprotected structures. This is an inherent potential problem with the application of such systems which dominates with decreasing soil conductivity, and/or increasing the anode current density and its proximity to the protected structures. On the contrary, SCC can be reduced by using multi-groundbed anodes. In addition, it is found that the cathodic interference is more serious than anodic one, and the combined and induced interferences can also cause severe corrosion. Finally, it can be concluded that the BEASY software is a very helpful tool for future planning before installing any structure, where it gives the possible CP interferences on any nearby unprotected metallic structures.     

Factors affecting the severity of work related traffic crashes in drivers receiving a worker's compensation claim

Aim

To examine factors that contribute to the severity of work related crashes in New South Wales, Australia.

Methods

Workers’ Compensation data was linked to police crash records for the period 1998-2002. Multivariate analysis was carried out to assess the relationship between relevant risk factors and the severity of injury (permanent disability or death) in drivers who had received a claim for a work related crash.

Results

Age, gender, occupation, duty status, vehicle type, licence status, fatigue, speeding and location of the crash were independently associated with the severity of the crash. Drivers aged 65 years and older were nearly twice (OR: 1.824, 95% CI: 1.106-3.007) as likely to be permanently injured or die as a result of a work related crash compared to the younger age group (15-24 years old). The risk to older drivers was even higher in crashes occurring while on duty. Drivers involved in traffic crashes while commuting were more likely to be severely injured (OR: 1.28, CI: 1.15-1.42) than those on duty. Compared to car drivers, taxi drivers were more than twice (OR: 2.38, CI: 1.726-3.296) as likely to be severely injured.

Conclusions

The findings contribute to bridging the gap in knowledge in the area of work related crashes and highlight the higher risk of permanent disability and death in older drivers, taxi drivers and commuters.     

Factors affecting motion integration

The perceived direction of motion of a featureless contour inside a circular aperture is always perpendicular to the contour's orientation, regardless of its true motion (the aperture problem). This study investigates the circumstances under which unambiguous feature motion (of line terminators, single dots, or truncations of a D6 pattern) in adjacent apertures can alter the perceived direction of such featureless contours. We find that integration mechanisms responsible for motion capture are fairly robust against misorientations and contrast manipulations of individual components, are sensitive to differences in spatial frequencies, and scale with pattern size. Motion capture is not diminished when a D6 profile is substituted for the square-pulse profile of a line and is independent of the visibility of the apertures, indicating that object interpretations and three-dimensional analyses of a scene are less important than has been postulated previously. These results have strong implications for the neuronal hardware underlying the integration of motion signals across space and provide a framework for global motion models.     

Factors affecting bonding of metals

Abstract

Adhesives have several advantages over mechanical fastening, and the use of bonding is steadily increasing in many applications. Bonding of primary structures in aircraft has been used for many years and much more research has been directed towards aluminium than any other material. Joint performance depends on the alloy, pretreatment, primer, and adhesive. Many studies of these variables have been made, often making use of modern surface analytical techniques. Informative studies have also been carried out on titanium and steel. Hot, humid conditions, especially combined with stress, can be especially damaging to metal joints. A full understanding of the factors that provide the best resistance to this damaging effect has not yet been achieved. However, stable oxide layers with the correct topography appear critical and selection of the correct pretreatment is therefore of paramount importance.

MST/475     

The work of fracture of epoxy resins

The work of fracture has been measured for some epoxy resins at liquid helium temperature, and when possible, at room temperature.     

Factors affecting the hygroexpansion of paper

Paper is a widely used packaging material and is nowadays regaining importance, e.g., as bio-based and biodegradable material. Moreover, new technologies such as polymer–fiber composites, printed electronics and the deep drawing of paper are developing. The process stability and also the resulting quality of paper converting processes such as coating, metallization, printing, and the printing of electronics are highly affected by the hygroexpansion of paper. In order to reduce production instability and to choose and develop paper substrates with ideal characteristics, critical parameters need to be known. This paper offers an extensive overview of those parameters, starting at a molecular and microscopic level with the effect of the constituents and morphology of single fibers, before moving on to paper contents, chemical modifications and additives and finally concluding with paper production and fiber network modification. It was found that the major influences are single fiber sorption, inter-fiber contacts, microfibril angle, fiber morphology (length, width, curliness) and fiber orientation. This review gives new ideas and insights for technologists working in research, development and production optimization of paper-based products.     

Damage work as ductile fracture criterion

This paper treats the ductile failure initiation in circumferentially-notched tension specimens and explores the local damage model that is able to represent the continuous degradation of the deforming material. With the aid of finite element calculations, the notched specimens have been simulated numerically and the whole strain-stress history for each geometry derived. This allows determination of the evolution of strain-stress fields until fracture occurs. Two damage models were evaluated: the Rice and Tracey cavity growth model and a model which combines the latter with the plastic strain work, to derive an intrinsic parameter called damage work. These models could predict the location where the crack will initiate as well as the crack initiation step which is reached for a relatively constant value of the critical damage.     

The work of fracture in semiductile polymers

The work to fracture in tension double-notched samples of some semiductile polymeric materials (rigid PVC, Orgalloy and Ultranyl) has been measured as a function of the ligament length. It was established that the work of fracture was proportional to the extent of the plastic zone that developed in the ligament area during crack propagation. It is proposed that the total energy density is made up of two terms, one distributed all over the plastic zone and the other localized in the vicinity of the fracture path. It is then shown that a linear relationship exists between the specific work of fracture and the ligament size, provided the height of the plastic zone linearly depends on the ligament length. The linear extrapolation of the specific work of fracture to nil ligament, yields a value that coincides with J _IC and therefore can be treated as a critical parameter. It is also shown that, at large ligaments, the dependence of the specific work of fracture on the ligament length reflects the post-yield behaviour of the material and it is influenced by the tendency of the height of the plastic zone to level off. Consequently, no specific meaning can be given to quantities obtained, according to the essential work of fracture theory, in the large ligament region, e.g. ligaments larger than three to five times the sample thickness.     

Essential work of fracture in polymer films

The fracture behaviour of two polymer films (100 m thick) has been investigated according to the essential work of fracture (EWF) approach in order to assess the validity of the linear relationship between the specific total work of fracture and the ligament length, postulated to exist by the EWF theory, and examine the transition from plane strain to plane stress conditions. Double edge notched specimens loaded in tension were used; ligaments were varied in the range 0.3 to 45 mm. No linear relationship was found and it was confirmed that a power law can be very accurately fitted to the experimental data. An annealed copper film (100 m thick) exhibited the same pattern of behaviour.     

Thin film fracture: Ti-coating-Be-substrate bond failure

The role of microstructure in the fracture of the bond between vapour-deposited thin film coatings and substrates will be modelled to a first approximation using classical fracture mechanics principles. Vapour-deposited coatings are composed of a grain structure with varying orientations. The effect of differing degrees of texture on the bond strength between the coating and its substrate will be considered in this analysis. Incorporated in stress calculations will be the residual stresses arising from the thermal contraction of the coating, an applied tensile stress normal to the coating surface (as that in an adherence pull test) and the critical stress needed for coating-substrate bond failure.