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Thermal Shrinkage (thermal + shrinkage)
Selected AbstractsShape Memory Effect of Bacterial Poly[(3-hydroxybutyrate)- co -(3-hydroxyvalerate)],MACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2005Young Baek Kim Abstract Summary: A bacterial poly[(3-hydroxybutyrate)- co -(3-hydroxyvalerate)] biosynthesized by Pseudomonas sp. HJ-2 was found to be a shape memory polymer. Permanent shapes were set by annealing at room temperature the samples that had been pre-treated above 95,°C in specified shapes. The temporary shapes were set by stretching and holding the elongated samples. Thermal shrinkage began at 45,°C and stopped at 75,°C to recover to their permanent shapes. Apparently, the orientation induced the formation of hard segments that were responsible for setting the temporary shapes. The shape memory effect of this polymer was explained based on the DSC and XRD results at different phases. The recovery of a coil shape upon heating a strip of HJ-2 PHB35V, demonstrating the polymers shape memory effect. [source] Residual compressive behavior of alkali-activated concrete exposed to elevated temperaturesFIRE AND MATERIALS, Issue 1 2009Maurice Guerrieri Abstract This paper reports the effect of elevated temperature exposures, up to 1200°C , on the residual compressive strengths of alkali-activated slag concrete (AASC) activated by sodium silicate and hydrated lime; such temperatures can occur in a fire. The strength performance of AASC in the temperature range of 400,800°C was similar to ordinary Portland cement concrete and blended slag cement concrete, despite the finding that the AASC did not contain Ca(OH)2 , which contributes to the strength deterioration at elevated temperatures for Ordinary Portland Cement and blended slag cement concretes. Dilatometry studies showed that the alkali-activated slag (AAS) paste had significantly higher thermal shrinkage than the other pastes while the basalt aggregate gradually expanded. This led to a higher thermal incompatibility between the AAS paste and aggregate compared with the other concretes. This is likely to be the governing factor behind the strength loss of AASC at elevated temperatures. Copyright © 2008 John Wiley & Sons, Ltd. [source] A numerical model for the time-dependent cracking of cementitious materialsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2001G. P. A. G. van Zijl Abstract A unified finite element formulation is presented for the analysis of the time-dependent cracking of cementitious materials. The rate-type constitutive law incorporates linear visco-elasticity and continuum plasticity. The former accounts for the bulk creep via a Maxwell chain, while the latter describes crack initiation and propagation via a softening, anisotropic Rankine yield criterion. The rate dependence of bond ruptures leading to fracture is accounted for by considering the viscosity of the cracking process. This contribution to the cracking resistance also regularises the localisation process. It is demonstrated how other important phenomena in cementitious materials, such as stress-dependent hygral and thermal shrinkage, can be incorporated into the computational framework. Copyright © 2001 John Wiley & Sons, Ltd. [source] Muscle fiber properties and thermal stability of intramuscular connective tissue in porcine M. semimembranosusJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2009Liisa Voutila Abstract BACKGROUND: Strips can be easily peeled from raw destructured pork (M. semimembranosus, SM muscle) by hand but in normal meat these strips break. In general, destructured meat is pale in color. Porcine SM muscles have thick muscle fibers which could predispose them to destructuration. This study investigated whether the onset and peak temperatures of thermal shrinkage (To and Tp) of intramuscular connective tissue from SM muscles were associated with muscle fiber thickness, capillary density or extracellular space. We also investigated whether these muscle fiber properties of destructured muscles differed from those of normal muscles. RESULTS: The destructured and normal muscles were similar in muscle fiber cross-sectional area, capillary density, extracellular space and sarcomere length. To correlated negatively with sarcomere length. The water content of differential scanning calorimetry samples consisting of intramuscular connective tissue was higher in destructured muscles than in normal muscles. CONCLUSION: Muscle fiber properties (muscle fiber cross-sectional area and sarcomere length) and capillary density are similar in destructured and normal SM muscles. To and Tp of intramuscular connective tissue are similar in destructured and normal muscles. Muscle fiber properties show no association with the thermal shrinkage properties of intramuscular connective tissue. Copyright © 2009 Society of Chemical Industry [source] Effects of film and substrate dimensions on warpage of film insert molded partsPOLYMER ENGINEERING & SCIENCE, Issue 6 2010Seong Yun Kim Three-dimensional flow and structural analyses were carried out for film insert injection molding to investigate warpage of film insert molded (FIM) parts with respect to variation of film and substrate thickness. Asymmetry of temperature distribution in the thickness direction was increased with increasing film thickness but decreased with increasing substrate thickness. Asymmetry of the in-mold residual stress distribution in the FIM specimen was generated by the nonuniform temperature distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of the ejected FIM specimen was determined by relaxation of the asymmetric in-mold residual stress distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of FIM specimens annealed at 80°C for 30 min showed complex behavior, and the behavior was understood by using factors such as degree of warpage of the ejected part, thermal shrinkage of the inserted film, and retardation of heat transfer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers [source] Ejection force modeling for stereolithography injection molding toolsPOLYMER ENGINEERING & SCIENCE, Issue 4 2002Giang T. Pham Stereolithography (SL) molds have proven effective for short injection molding runs. However, they are susceptible to failure because of their poor mechanical properties, especially at elevated temperatures. A majority of these failures occur during the ejection stage, as a result of excessive ejection forces. An ejection force model was developed by combining the effects of thermal shrinkage and mechanical interlocking due to stair-steps on the surface of SL tools. Finite element analyses were performed to validate and complement the ejection force equation. Measured forces and temperatures from injection molding experiments indicated that the ejection force model is valid for SL molds of both circular and non-circular shape. The average differences between measured and predicted ejection forces were approximately 10%. [source] | |||||||||||||