“…Recently, KWW model was used to predict relaxation behavior of some polymer materials at high temperature and, in addition, the results of the model provided good matching with experimental data. 24,25,86,87 To predict experimental responses of PLA and PLA/HA, the KWW model equation is given below where t represents time, τ0 is relaxation time, and β is stretched exponent in the limits of 0<β<1, the stretching exponent β is associated with distribution width of relaxation time, and σ0 is stress level at starting point of relaxation test.…”
Section: Discussionmentioning
confidence: 99%
“…The curves showed that KWW function predicted adequately changing of the relaxation time with temperature: the effect of the glass transition temperature on relaxation behavior of PLA and PLA/HA was similar to that reported in Schiavi and Prato. 24 Figure 15.Stress versus relaxation time for PLA. Symbols: experimental data in in relaxation tests on specimens subject to tension up to maximum ɛmax = 0.015 and various minimum stress σmin MPa, at various temperatures T ℃.Figure 16.Stress versus relaxation time for PLA/HA.…”
Section: Discussionmentioning
confidence: 99%
“…It is possible to find some examinations related to anomalous relaxation on polymer materials; however, a few focused on the effects of temperature. 22–27…”
Relaxation behavior provides specific information that indicates stress development with elapsed time for the determination of material characterization and constituting of material modeling. In addition, anomalous relaxation behavior of polymeric materials enables experimental analysis of some theoretical variables in constitutive equation. Equilibrium stress is one of the most prevailing variables in material modeling and it is generally considered as unmeasurable. In this study, evolution of equilibrium stress was examined with relaxation tests of two semi crystalline polymer materials, one of which was found to reach precise equilibrium stress levels. In accordance with this purpose, extensive relaxation tests were conducted on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites specimens at a wide range of temperatures from 23 ℃ and 55 ℃, and stress levels from 1 MPa to 50 MPa for poly(lactic acid) and 51 MPa for poly(lactic acid)/hydroxyapatite nanocomposites. All the specimens were subjected tensile loading–unloading and partial retraction process. The starting points of the relaxation test were chosen on unloading segment of stress–strain curves. Evolution of stress may decay, increase or decay then increase depending on the test point on unloading curves. Relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites was simulated using viscoplasticity theory based on overstress for polymeric materials. Experimental results of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites were matched with numerical results of viscoplasticity theory based on overstress for polymeric materials, and viscoplasticity theory based on overstress for polymeric material model was found to have an aptitude for predicting anomalous relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Additionally, the effect of temperature on relaxation time was investigated with using Kohlraush–Williams–Watts time-decay function. Modeling capability of Kohlrausch–Williams–Watts model was reasonable to predict short-term simple relaxation of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Responses of the model showed that interaction between relaxation time and environmental temperature was related to transition from glass state to rubbery state.
“…Recently, KWW model was used to predict relaxation behavior of some polymer materials at high temperature and, in addition, the results of the model provided good matching with experimental data. 24,25,86,87 To predict experimental responses of PLA and PLA/HA, the KWW model equation is given below where t represents time, τ0 is relaxation time, and β is stretched exponent in the limits of 0<β<1, the stretching exponent β is associated with distribution width of relaxation time, and σ0 is stress level at starting point of relaxation test.…”
Section: Discussionmentioning
confidence: 99%
“…The curves showed that KWW function predicted adequately changing of the relaxation time with temperature: the effect of the glass transition temperature on relaxation behavior of PLA and PLA/HA was similar to that reported in Schiavi and Prato. 24 Figure 15.Stress versus relaxation time for PLA. Symbols: experimental data in in relaxation tests on specimens subject to tension up to maximum ɛmax = 0.015 and various minimum stress σmin MPa, at various temperatures T ℃.Figure 16.Stress versus relaxation time for PLA/HA.…”
Section: Discussionmentioning
confidence: 99%
“…It is possible to find some examinations related to anomalous relaxation on polymer materials; however, a few focused on the effects of temperature. 22–27…”
Relaxation behavior provides specific information that indicates stress development with elapsed time for the determination of material characterization and constituting of material modeling. In addition, anomalous relaxation behavior of polymeric materials enables experimental analysis of some theoretical variables in constitutive equation. Equilibrium stress is one of the most prevailing variables in material modeling and it is generally considered as unmeasurable. In this study, evolution of equilibrium stress was examined with relaxation tests of two semi crystalline polymer materials, one of which was found to reach precise equilibrium stress levels. In accordance with this purpose, extensive relaxation tests were conducted on poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites specimens at a wide range of temperatures from 23 ℃ and 55 ℃, and stress levels from 1 MPa to 50 MPa for poly(lactic acid) and 51 MPa for poly(lactic acid)/hydroxyapatite nanocomposites. All the specimens were subjected tensile loading–unloading and partial retraction process. The starting points of the relaxation test were chosen on unloading segment of stress–strain curves. Evolution of stress may decay, increase or decay then increase depending on the test point on unloading curves. Relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites was simulated using viscoplasticity theory based on overstress for polymeric materials. Experimental results of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites were matched with numerical results of viscoplasticity theory based on overstress for polymeric materials, and viscoplasticity theory based on overstress for polymeric material model was found to have an aptitude for predicting anomalous relaxation behavior of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Additionally, the effect of temperature on relaxation time was investigated with using Kohlraush–Williams–Watts time-decay function. Modeling capability of Kohlrausch–Williams–Watts model was reasonable to predict short-term simple relaxation of poly(lactic acid) and poly(lactic acid)/hydroxyapatite nanocomposites. Responses of the model showed that interaction between relaxation time and environmental temperature was related to transition from glass state to rubbery state.
“…The first is an ultrafast photocurrent in a photoconductive switch or semiconductor using electric-field carrier acceleration or the photo-Dember effect [30]- [32], and the second method is, THz waves are generated by nonlinear optical effects such as optical rectification (limited to femtosecond laser excitation), difference-frequency generation (DFG) [33], optical parametric oscillation [34], [35], or ambient air-plasma generation [36], [37]. y Terahertz Quantum-cascade lasers (THz QCL): For the THz QCL method, the THz waves are emitted by means of electron relaxation between subbands of quantum wells [38], [39], and there are semiconductor-based THz sources [40], [41] and powerful continuous-wave THz sources [33], [42], [43]. The first THz QCL was developed in 1994 and had a lasing frequency of about 70 THz.…”
Section: Co-word Analysis and Co-citation Network Analysis A Co-mentioning
Terahertz is a high-tech technology that has been developed rapidly in recent years. Relevant research has been extensively carried out in physics, chemistry, communication, biology, agricultural food safety testing, industrial non-destructive testing, biochemical, medical, and biological imaging. To provide a summary of the research trend in the field, there is a need to analyze the literature by scientometrics. In this work, we have an overview of the literature in the terahertz field, and then analyze the literature from the aspects of terahertz source, terahertz detector, terahertz spectroscopy and imaging, and terahertz applications respectively. The focus of this work is to automatically extract the trend by co-words and cocitation network analysis, and the comparative point of view is used to understand two closely related but different fields of terahertz basic research and terahertz application research. Through the scientific basis measurement, the research characteristics of these two fields, including annual outputs, active journals, key authors, key research directions and hotspots, important research projects and the countries behind them are immediately obtained. INDEX TERMS Terahertz, scientometrics, measurement, applications.
“…[54,55] These IPNs have the potential to be used as actuators, for noise and vibration damping, [49] and in shape memory and self-healing applications. [1][2][3][4] Understanding and modeling their stress relaxation behavior is therefore essential.…”
The stress relaxation behavior of acrylic-polyurethane (PU)-based graftinterpenetrating polymer networks (IPNs) was characterized via dynamic mechanical analysis (DMA) and modeled using finite element method (FEM) analysis. Stress relaxation of glassy IPN specimens was experimentally studied under flexural testing, while rubbery IPN specimens were tested in tension. The effects of varying the styrene content in the acrylic copolymer phase, compatibility of the two phases in IPNs, and changing the concentration of acrylic copolymer and PU were studied. A higher percentage of styrene content resulted in higher homogeneity of IPN specimens, and decrease in initial modulus for acrylic copolymer specimens. Additionally, glassy IPN specimens with 90% styrene shows resistance to relaxation as high as acrylic copolymer samples. Experimental results were used to develop a numerical model to study stress relaxation response of specimens. While polymer systems have been
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