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S Hashemi - One of the best experts on this subject based on the ideXlab platform.
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Effect of temperature on fracture properties of an amorphous poly(ethylene terephthalate) (PET) film
Journal of Materials Science, 2002Co-Authors: A. Arkhireyeva, S HashemiAbstract:Fracture behaviour of an amorphous polyethylene terephthalate (PET) film with a glass transition temperature (Tg) of 72°C and a thickness of 0.21 mm was studied between 23 and 70°C using Double Edge Notched Tension (DENT) specimens. Within this temperature range, DENT specimens fractured by ductile tearing of the Ligament region after Ligament region had been fully yielded. The load-displacement curves obtained for different Ligament Lengths were geometrically similar to one another. On the basis of these, Essential Work of Fracture (EWF) methodology was used to determine fracture toughness of the PET film as a function of temperature. A linear relationship was obtained between the total specific work of fracture, wf, and Ligament Length, L, at temperatures under consideration. Results showed that specific essential work of fracture, we, is independent of temperature but the specific non-essential work of fracture (β wp) increases with increasing temperature and drops in value near the glass-transition temperature. A linear relationship was also found for yielding (wy) and necking/tearing (wnt) components of wf as a function of Ligament Length. The specific essential work components were found to be temperature dependent and whilst component wey decreased component went increased with increasing temperature. The contribution of went to we was substantially greater than that of wey at all temperatures.
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Influence of temperature on plane stress ductile fracture of poly(ethylene terephthalate) film
Plastics Rubber and Composites, 2001Co-Authors: A. Arkhireyeva, S HashemiAbstract:AbstractDouble edge notched poly(ethylene terephthalate) (PET) specimens of varying Ligament Lengths and 0·125 mm thickness have been pulled to complete fracture between 23 and 160°C. Within this temperature range, propagation of the crack was always stable, producing load–displacement curves at various Ligament Lengths that were geometrically similar to one another. Essential work of fracture (EWF) analysis was used to study the effect of temperature on fracture toughness. A linear relationship was obtained between specific total work of fracture W f and Ligament Length over the entire temperature range under consideration. The slope of the line, which is termed specific non-essential work of fracture βw p , showed a maximum near the glass transition temperature of the material (T g ≈ 93°C). Beyond this point, βw p decreased sharply with increasing temperature. The intercept of the line at zero Ligament Length, which is referred to as specific essential work of fracture w e , showed three types of variat...
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determination of the fracture toughness of polybutylene terephthalate pbt film by the essential work method effect of specimen size and geometry
Polymer Engineering and Science, 2000Co-Authors: S HashemiAbstract:The fracture behavior of PBT films of thicknesses 0.125, 0.175, 0.275, 0.375 and 0.5 mm was investigated according to Essential Work of Fracture (EWF) method. Single edge and double edge notched specimens of varying Ligament Lengths were tested in tension producing load-displacement traces that were typical of ductile failure. A linear relationship was obtained between the total specific work of fracture (w f ) and Ligament Length (L). This linearity was maintained as Ligament Length exceeded the plastic zone size or one third of sample width. It was found that while the specific essential work of fracture (w e ) was independent of thickness, the specific non-essential work of fracture (βw p ) decreased with increasing thickness. It was found also, that work of fracture parameters were independent of the specimen width for the range of thicknesses used in the present study. Nevertheless, for a sample width of 20 mm, a lower w e and a higher βw p value was obtained. Good agreement was found between values of w e obtained from SENT and those obtained from DENT specimens; the value of βw p was consistently higher for SENT specimens.
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work of fracture of pbt pc blend effect of specimen size geometry and rate of testing
Polymer Engineering and Science, 1997Co-Authors: S HashemiAbstract:Fracture behavior of PBT/PC blend was studied at room temperature using two specimen geometries (SENT and DENT) and a wide range of specimen sizes and crosshead speeds. It was found that the fracture of all SENT and DENT specimens is completely ductile and stable. A linear relationship was obtained between the specific total work of fracture, w f , and the Ligament Length, L. Extrapolation of this linear relationship to zero Ligament Length gave the specific essential work of fracture, w e , which for PBT/PC blend was 35 ± 5 kJ/m 2 and was almost insensitive to geometry and the dimensions of test specimens as well as testing rate.
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Fracture toughness evaluation of ductile polymeric films
Journal of Materials Science, 1997Co-Authors: S HashemiAbstract:The energy for complete fracture in double edge-notched tension test specimens has been measured for a wide range of polymer films. Results indicated that the variation of the total specific work of fracture, wT, with Ligament Length, L, can be described by two straight lines, both of the form wT = we + β wpL, thus giving upper and lower intercept values at zero Ligament Length (i.e. we) for each film. The first term, we, is the energy absorbed per unit area of fracture, whereas the second term, wp, is the energy absorbed per unit volume of plastic deformation remote from the fracture surface. The lower we value was obtained from the extrapolation of the data within the mixed mode region (plane-stress/plane-strain) where the maximum net-section stress exceeded 1.15 times that of the tensile yield stress, σy, of the material, and the upper value was ascertained by extrapolating the data within the plane stress region where the net-section stress was 1.15 σy. It appears that the transition from plane stress to plane strain mode of fracture in thin films occurs at a Ligament Length much greater than 5B, where B is the specimen thickness. Moreover, it was found that the linearity of the data within the plane-stress region was not affected when Ligament Length values exceeded the plastic zone size. Moreover, variation of the extension to break with Ligament Length, for both pure plane stress and the mixed mode regions, was also linear; and the extrapolation values at zero Ligament Length were identified as crack opening displacements. Essential work estimated from the crack opening displacement agreed reasonably well with the extrapolated values.
Steven F. Viegas - One of the best experts on this subject based on the ideXlab platform.
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Prediction of Ligament Length and Carpal Diastasis During Wrist Flexion-Extension and After Simulated Scapholunate Instability
The Journal of hand surgery, 2013Co-Authors: Rita M. Patterson, Naoya Yazaki, Clark R. Andersen, Steven F. ViegasAbstract:Purpose To determine the role of the carpal Ligaments during wrist flexion-extension and to understand whether maintaining integrity of only the dorsal scapholunate Ligament (SLL) is adequate for maintaining stability of the scapholunate joint. Methods This study combined motion analysis and manual digitization of Ligament attachment regions to generate predictions of carpal Ligament Length and implied strain during wrist motion and Length changes after simulated Ligamentous injury. Results We modeled 13 Ligaments and 22 Ligament segments (subportions). We measured Ligament Length change with respect to wrist angle. A total of 11 segments had minimum stretch or elongation from neutral wrist position over the entire wrist range of motion for any Ligament cut condition. The remaining 11 segments had more than 10% stretch in some portion of flexion-extension. In general, Ligaments had increased stretch during wrist flexion and after cutting the entire SLL and the dorsal intercarpal Ligaments off the scaphoid. Conclusions Disruption of the membranous and palmar portions of the SLL and the dorsal intercarpal Ligament off the scaphoid did not result in the development of an increased 3-dimensional scapholunate gap, as measured by differences in Ligament Length calculations between the scaphoid and lunate. This may indicate a predynamic instability condition (before clinical signs and x-ray findings) that is stabilized by the dorsal SLL, preventing the increase in the 3-dimensional scapholunate gap. This may also support surgical treatment recommendations, which suggest that repair of the dorsal component only of the SLL will be effective. Disruption of the dorsal intercarpal Ligament off the scaphoid or lunate did not result in further significant changes. Therefore, the dorsal SLL has an important role in preventing scapholunate Ligament instability. Clinical relevance These results provide insight into the abnormal kinematics as various Ligaments are compromised.
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Prediction of Ligament Length During Wrist Flexion Extension
ASME 2008 Summer Bioengineering Conference Parts A and B, 2008Co-Authors: Rita M. Patterson, Naoya Yazaki, Clark R. Andersen, Newt H. Scott, Steven F. ViegasAbstract:Direct measurement of Ligament Length in the wrist is difficult due to constrained space and short Length of many Ligaments. No prior studies have reported measurements of Ligament Length between the carpal bones of the wrist. In this presentation, we have combined high precision motion analysis of the carpal bones, subsequent manual digitization of the Ligament attachment regions, and a simulated Ligament wrapping model, to generate predictions of carpal Ligaments’ Length and implied strain during wrist motion.Copyright © 2008 by ASME
Guillermo Enrique Eliçabe - One of the best experts on this subject based on the ideXlab platform.
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Optimal Ligament Lengths in impact fracture toughness estimation by the essential work of fracture method
Polymer Testing, 2005Co-Authors: Valeria Pettarin, Patricia Maria Frontini, Guillermo Enrique EliçabeAbstract:This work presents a statistical analysis of the confidence in fracture parameters of polymers estimated through the essential work of fracture (EWF) methodology under impact conditions. Fracture toughness parameters—essential, we, and non-essential work of fracture, wp—are obtained from the experimental relationship between specific total work of fracture wf and Ligament Length of the tested samples l: we is obtained from the y-intercept and wp from the slope of wf versus l in cases where a linear fit is suitable. The distribution of Ligament Lengths within a fixed number of samples to be tested under impact loading conditions is determined in order to minimize the uncertainty of the estimated parameters when linear reduction of the data is assumed. The statistical approach applied to two different polymeric materials shows that the uniform Ligament Length distribution along the Ligament range is not the optimal one. We propose an optimal distribution of Ligament Lengths to be tested that depends on the distribution of error standard deviations of the measured work of fracture along the l-axis.
Patricia Maria Frontini - One of the best experts on this subject based on the ideXlab platform.
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On the applicability of the essential work of fracture method to thick abs Se(b)-specimens
2013Co-Authors: P. Luna, E. Lievana, Celina Raquel Bernal, Patricia Maria Frontini, Yiu-wing MaiAbstract:This paper deals with the application of the EWF methodology to thick ABS SEN(B)-specimens in order to study its applicability to conditions other than plane stress. Different loading regimes were induced by varying the testing temperature. Post-mortem fracture surface appears to be completely stress whitened, indicating ductile fracture. Load-line displacement plots display geometric similarity over a well-defined range of Ligament Lengths for which the application of the EWF methodology was in principle possible. At the same time crack growth was observed to initiate before maximum load and the complete Ligament yielding. Over a critical Ligament Length gross yielding occurred and the total specific work of fracture was found independent of Ligament Length. Below this critical Ligament Length, EWF methodology seemed to be still applicable and it was possible to extrapolate reliable we values. Besides, the EWF was simulated by elastic-plastic FEM analysis. Numerical results were consistent with experimental findings.
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Optimal Ligament Lengths in impact fracture toughness estimation by the essential work of fracture method
Polymer Testing, 2005Co-Authors: Valeria Pettarin, Patricia Maria Frontini, Guillermo Enrique EliçabeAbstract:This work presents a statistical analysis of the confidence in fracture parameters of polymers estimated through the essential work of fracture (EWF) methodology under impact conditions. Fracture toughness parameters—essential, we, and non-essential work of fracture, wp—are obtained from the experimental relationship between specific total work of fracture wf and Ligament Length of the tested samples l: we is obtained from the y-intercept and wp from the slope of wf versus l in cases where a linear fit is suitable. The distribution of Ligament Lengths within a fixed number of samples to be tested under impact loading conditions is determined in order to minimize the uncertainty of the estimated parameters when linear reduction of the data is assumed. The statistical approach applied to two different polymeric materials shows that the uniform Ligament Length distribution along the Ligament range is not the optimal one. We propose an optimal distribution of Ligament Lengths to be tested that depends on the distribution of error standard deviations of the measured work of fracture along the l-axis.
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the application of the essential work of fracture methodology to the plane strain fracture of abs 3 point bend specimens
Polymer, 2003Co-Authors: P. Luna, Patricia Maria Frontini, Brian Cotterell, C Bernal, Adrian P Cisilino, Yiu-wing MaiAbstract:The applicability of the EWF methodology to 3-point bend (SEB) specimens under conditions other than plane stress has been assessed experimentally. Different fracture conditions, pure plane strain and plane strain/plane stress transition, were obtained by varying the specimen thickness and testing temperature (20 and 80 8C). Post-mortem fracture surfaces appeared always completely stress-whitened, indicating ductile fracture. The load– line displacement plots are similar over a well-defined range of Ligament Lengths for which the application of the EWF methodology was in principle possible. Nevertheless, in experiments conducted at room temperature, crack growth was observed to initiate before maximum load and complete Ligament yielding. This behaviour was confirmed through plastic collapse analyses. A critical Ligament Length was found, over which the total specific work of fracture was dominated by edge effects. Below this critical Ligament Length, EWF methodology was still applicable and it was possible to extrapolate reliable wIe values. q 2002 Elsevier Science Ltd. All rights reserved.
Donald R Paul - One of the best experts on this subject based on the ideXlab platform.
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Fracture toughness of nylon-6 blends with maleated rubbers
Journal of Polymer Science Part B: Polymer Physics, 2004Co-Authors: O. Okada, H. Keskkula, Donald R PaulAbstract:The fracture toughness of blends of nylon-6 with maleated ethylene–propylene rubber and maleated styrene/hydrogenated butadiene/styrene triblock copolymer was investigated with a single-edge-notched three-point-bending instrumented Dynatup test. The blends for which the rubber particle size was less than 0.7 μm fractured in a ductile manner over the whole range of Ligament Lengths, whereas the blends with particles larger than 0.7 μm showed a ductile-to-brittle transition with the Ligament Length. In this regime, ductile fracture was observed for specimens with short Ligaments, whereas brittle fracture was seen for those with long Ligaments. The ductile fracture behavior was analyzed with the essential-work-of-fracture model, whereas linear elastic fracture mechanics techniques were used to analyze the brittle fracture behavior. The fact that the ductile fracture energy was larger for the blends with the styrene/hydrogenated butadiene/styrene triblock copolymer than for those with ethylene–propylene rubber was due to the larger dissipative energy density of the blends based on the styrene/hydrogenated butadiene/styrene triblock copolymer. Both the critical strain energy release rate (GIC) and the plane-strain critical stress intensity factor (KIC) increased as the rubber particle size decreased for both blend systems. The GIC and KIC parameters had similar values, regardless of the rubber type, when the rubber particle size was fixed. The transition Ligament Length was near the size criterion for plane-strain conditions for both blend systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1739–1758, 2004
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Fracture toughness of nylon 6 blends with maleated ethylene/propylene rubbers
Polymer, 2000Co-Authors: O. Okada, H. Keskkula, Donald R PaulAbstract:Abstract The fracture of blends of nylon 6 and maleated ethylene–propylene rubber was examined by both the Izod impact test and a single-edge notch three-point bend (SEN3PB) instrumented Dynatup test. The effects of EPR- g -MA content, Ligament Length, method of fracture surface measurement, sample thickness and fracture position in the molded bar on the fracture behavior were investigated. The data were analyzed by plotting the specific fracture energy (U/A) as a function of Ligament Length. The blends containing a high portion of EPR- g -MA in the rubber phase were found to be super tough over the whole range of Ligament Lengths and under all test conditions. However, a ductile-to-brittle transition was observed with Ligament Length for marginally tough blends which contained a low content of EPR- g -MA in the rubber phase and had a ductile–brittle temperature near or above room temperature; the specimens with short Ligament Length fractured in a ductile manner, while the specimens with long Ligaments showed brittle fracture. The transition Ligament Lengths were found to be dependent on the rubber particle size. The dual mode of fracture was rationalized by equations for ductile yielding and brittle crack propagation; values of yield stress and critical intensity factor were estimated from these model equations. The dissipative energy density, u d , was more sensitive to rubber particle size, sample thickness and location in the molded bar than the limiting specific fracture energy, u o . There is a good correlation between the standard Dynatup impact strength and the parameter u d for the gate end specimens.