The effects of physical aging on the tensile property of notched samples and the endothermic peak at glass transition region of polyphenylquinoxaline films were studied.
The physical aging behavior of atactic polystyrene (aPS) films achieved under different drawing conditions has been studied by optical birefringence and modulate differential scanning: calorimeter (m.d.s.c.). The resu...The physical aging behavior of atactic polystyrene (aPS) films achieved under different drawing conditions has been studied by optical birefringence and modulate differential scanning: calorimeter (m.d.s.c.). The results show that on annealing at specific temperature below glass transition temperatue (T-g), the enthalpy relaxation (Delta H) and T-g decrease with increasing of birefringence (Delta n). On the other baud, the effect of molecular draw ratio (MDR) is confusing: Delta H and T-g decrease with increasing of MDR in the early stage of aging, but the MDR's effect become unobvious with the development of aging. It may be concluded that the ordered domain generated by the drawing below or above glass transition temperature will affect the development of physical aging behavior. The viewpoint of cohesional entanglement is used to account for the above observations.展开更多
The random, block, and alternative copolymers of poly ether sulfone(PES) and poly ether ether sulfone(PEES) were synthesized v/a three kinds of methods. The chemical structures of the three kinds of copolymers wer...The random, block, and alternative copolymers of poly ether sulfone(PES) and poly ether ether sulfone(PEES) were synthesized v/a three kinds of methods. The chemical structures of the three kinds of copolymers were characterized by ^13C NMR. Three kinds of PES/PEES copolymers( Tg =215 ℃ ), which were almost identical in composition but different in sequence distribution, were used. Their physical aging process was studied by differential scanning calorimetry(DSC) at three aging temperatures ranging between Tg -15 ℃ and Tg -25℃. The experimental results reveal that the alternative copolymer shows a lower enthalpy relaxation time 〈T〉 and apparent activation energy when compared with the random and block copolymers. The result of the electron-microscopy investigation of the three copolymers that were treated at 200 ℃ for 96 h indicates that the molecular aggregation of the copolymers changed from a randomly coiled amorphous phase to an ordered phase, and the ordered structure of the alternative copolymer was more distinct than that of the random phase. The experimental results of this study suggest that the motion of the sagments is affected by the different molecular-chain sequence distribution.展开更多
Poly(lactic acid) (PLA) is a promising bio-based environmentally-friendly plastic. Nevertheless, the physical aging-induced brittleness of PLA limits its widespread applications. Blending with immiscible ductile polym...Poly(lactic acid) (PLA) is a promising bio-based environmentally-friendly plastic. Nevertheless, the physical aging-induced brittleness of PLA limits its widespread applications. Blending with immiscible ductile polymer is an effective way to toughen PLA. However, the underlying details of the toughening mechanism and, in particular, the effect of physical aging are not well understood. Herein, atomic force microscopy (AFM) based nanomechanical mapping technology was utilized to visualize the differences in the deformation mechanisms between unaged and aged PLA/poly(ε-caprolactone) (PCL) blend upon uniaxial drawing. Results show that physical aging has a significant effect on the microscopic Young’s modulus and its distribution of PLA matrix, resulting in a highly heterogeneous response of the PLA/PCL blend to external stress and affecting the mechanical properties of the PLA phase under different extensions. This work provides a new experimental basis for understanding the effect of physical aging on the mechanical properties of PLA-based materials.展开更多
The power-law relationship between creep rate decay and time is one of the intrinsic characteristics of metallic glasses.In the current work,a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) high-entropy metallic glass was select...The power-law relationship between creep rate decay and time is one of the intrinsic characteristics of metallic glasses.In the current work,a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) high-entropy metallic glass was selected as the model alloy to test the influences of physical aging and cyclic loading on the power-law creep mechanism,which was probed by the dynamic mechanical analysis in terms of the stochastic activation,and contiguous interplay and permeation of shear transformation zones.It is demonstrated that a notable discrepancy appears between thermal treatment and mechanical treatment on the power-law creep mechanism of this high-entropy metallic glass.On the one hand,physical aging below the glass transition temperature introduces the annihilation of potential shear transformation zones which contribute to creep.On the other hand,cyclic loading can tailor the“forward”jump operations competing with the“backward”ones of shear transformation zones by controlling the interval time(recovery time).The current research offers a new pathway towards understanding the creep mechanism of high-entropy metallic glasses.展开更多
Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace ...Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.展开更多
The crazing of polyphenylquinoxaline (PPQ-E) films during in situ stretching has been observed by SEM. The crazing phenomena and craze morphology of PPQ-E films were interpreted. The strain values at critical crazing ...The crazing of polyphenylquinoxaline (PPQ-E) films during in situ stretching has been observed by SEM. The crazing phenomena and craze morphology of PPQ-E films were interpreted. The strain values at critical crazing and yielding and the craze stability of PPQ-E samples depend on the thermal-dealing condition for the samples. From the point of view of cohesional entanglements and energy absorbed by samples, the experiment results were explained.展开更多
In order to predict the mechanical performance of the polyvinyl chloride (PVC) at a high operating temperature, a series of short-term tensile creep tests (one- tenth of the physical aging time) of the PVC are car...In order to predict the mechanical performance of the polyvinyl chloride (PVC) at a high operating temperature, a series of short-term tensile creep tests (one- tenth of the physical aging time) of the PVC are carried out at 63 ℃ with a small constant stress by a dynamic mechanical analyzer (DMA). The Struik-Kohlrausch (SK) formula and Struik shifting methods are used to describe these creep data for various physical aging time. A new phenomenological model based on the multiple relaxation mechanisms of an amorphous polymer is developed to quantitatively characterize the SK parameters (the initial creep compliance, the characteristic retardation time, and the shape factor) determined by the aging time. It is shown that the momentary creep compliance curve of the PVC at 63℃ can be very well fitted by the SK formula for each aging time. However, the SK parameters for the creep curves are not constant during the aging process at the elevated temperatures, and the evolution of these parameters and the creep rate versus aging time curves at the double logarithmic coordinafes have shown a nonlinear phenomenon. Moreover, the creep master curves obtained by the superposition with the Struik shifting methods are unsatisfactory in such a case. Finally, the predicted results calculated from the present model incorporating with the SK formula are in excellent agreement with the creep experimental data for the PVC isothermally aged at the temperature relatively close to the glass transition temperature.展开更多
Aggregation-induced emission(AIE)luminogens are attractive dyes to probe poly-mer properties that depend on changes in chain mobility and free volume.When embedded in polymers the restriction of intramolecular motion(...Aggregation-induced emission(AIE)luminogens are attractive dyes to probe poly-mer properties that depend on changes in chain mobility and free volume.When embedded in polymers the restriction of intramolecular motion(RIM)can lead to their photoluminescence quantum yield(PLQY)strong enhancement if local microviscosity increases(lowering of chain mobility and free volume).Nonethe-less,measuring PLQY during stimuli,i.e.heat or mechanical stress,is technically challenging;thus,emission intensity is commonly used instead,assuming its direct correlation with the PLQY.Here,by usingfluorescence lifetime as an absolutefluorescence parameter,it is demonstrated that this assumption can be invalid in many commonly encountered conditions.To this aim,different poly-mers are loaded with tetraphenylenethylene(TPE)and characterized during the application of thermal and mechanical stress and physical aging.Under these con-ditions,polymer matrix transparency variation is observed,possibly due to local changes in refractive index and to the formation of microfractures.By combin-ing different characterization techniques,it is proved that scattering can affect the apparent emission intensity,while lifetime measurements can be used to ascertain whether the observed phenomenon is due to modifications of the photophysi-cal properties of AIE dyes(RIM effect)or to alterations in the matrix optical properties.展开更多
Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties.Dynamic mechanical relaxation behavior of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_...Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties.Dynamic mechanical relaxation behavior of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass was investigated by dynamic mechanical analysis(DMA)and the mechanical spectra could be well described by the quasi-point defects(QPD)theory.Compared to typical metallic glasses,the intensity of theβrelaxation of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass is lower due to the sluggish diffusion.At the same time,the correlation factor is higher than that of conventional metallic glasses and this is ascribed to the high configuration entropy.In parallel,physical aging below the glass transition temperature leads to a decrease of atomic mobility,caused by a decrease of the concentration of defects.展开更多
Evolution of deformation and relaxation behaviors of a prototypical Cu_(46)Zr_(46)A_(l8)metallic glass was explored by extensive creep tests under both physical aging and cyclic loading.Deep insights into the microstr...Evolution of deformation and relaxation behaviors of a prototypical Cu_(46)Zr_(46)A_(l8)metallic glass was explored by extensive creep tests under both physical aging and cyclic loading.Deep insights into the microstructure-induced dynamic heterogeneity which accommodates creep deformation were successively revealed via experimental measurements and spectral analyses.An annihilation of local defects within metallic glass with increasing annealing time and cyclic numbers was observed through the reduction of amplitude in both activation energy spectra and relaxation-time spectra,which were also accompanied by an ascending value of β_(KWW).It is further found that the corresponding deformation units within the metallic glass do not disappear permanently,but are recoverable over the course of cyclic loading.The apparent suppressed relaxation process can be gradually alleviated with increasing resuming time between two consecutive cycles,behaving differently from physical aging,which indicates a notable discrepancy between thermal treatment and mechanical treatment.展开更多
The purpose of this work is to investigate the dynamic fracture properties of glassy polycarbonate (PC) with different aging times. The optical method of caustics is adopted in which the shadow spot patterns are rec...The purpose of this work is to investigate the dynamic fracture properties of glassy polycarbonate (PC) with different aging times. The optical method of caustics is adopted in which the shadow spot patterns are recorded by a high speed camera during the dynamic fracture process. Then, the dynamic crack propagation, the stress intensity factor (SIF) and the dynamic fracture toughness of aged PC are obtained through an analysis of the characteristic size of caustic pattern. Moreover, by combining with the investigation of the fracture surface and the energy release rate analysis, the influence of aging time on the dynamic fracture behavior is discussed. Results show that the dynamic fracture toughness and critical energy release rate of PC decreases with aging time for short aging times, whereas they have little change or even increase for longer aging times. Therefore, aging modifies the mechanical properties especially the dynamic fracture properties of PC nonlinearly, not linearly as generally thought of.展开更多
Physical aging is currently a major obstacle for the commercialization of PIM-1 membranes for gas separation applications.A well-known approach to reversing physical aging effects of PIM-1 membranes at laboratory scal...Physical aging is currently a major obstacle for the commercialization of PIM-1 membranes for gas separation applications.A well-known approach to reversing physical aging effects of PIM-1 membranes at laboratory scale is soaking them in lower alcohols,such as methanol and ethanol.However,this procedure does not seem applicable at industrial level,and other strategies must be investigated.In this work,a regeneration method with alcohol vapors(ethanol or methanol)was developed to recover permeability of aged PIM-1 membranes,in comparison with the conventional soaking-in-liquid approach.The gas permeability and separation performance,before and post the regeneration methods,were assessed using a binary mixture of CO_(2) and CH_(4)(1:1,v:v).Our results show that an 8-hour methanol vapor treatment was sufficient to recover the original gas permeability,reaching a CO_(2) permeability>7000 barrer.展开更多
文摘The effects of physical aging on the tensile property of notched samples and the endothermic peak at glass transition region of polyphenylquinoxaline films were studied.
基金This work was Supported by the National Basic Research Project-Macromolecular Condensed State
文摘The physical aging behavior of atactic polystyrene (aPS) films achieved under different drawing conditions has been studied by optical birefringence and modulate differential scanning: calorimeter (m.d.s.c.). The results show that on annealing at specific temperature below glass transition temperatue (T-g), the enthalpy relaxation (Delta H) and T-g decrease with increasing of birefringence (Delta n). On the other baud, the effect of molecular draw ratio (MDR) is confusing: Delta H and T-g decrease with increasing of MDR in the early stage of aging, but the MDR's effect become unobvious with the development of aging. It may be concluded that the ordered domain generated by the drawing below or above glass transition temperature will affect the development of physical aging behavior. The viewpoint of cohesional entanglement is used to account for the above observations.
文摘The random, block, and alternative copolymers of poly ether sulfone(PES) and poly ether ether sulfone(PEES) were synthesized v/a three kinds of methods. The chemical structures of the three kinds of copolymers were characterized by ^13C NMR. Three kinds of PES/PEES copolymers( Tg =215 ℃ ), which were almost identical in composition but different in sequence distribution, were used. Their physical aging process was studied by differential scanning calorimetry(DSC) at three aging temperatures ranging between Tg -15 ℃ and Tg -25℃. The experimental results reveal that the alternative copolymer shows a lower enthalpy relaxation time 〈T〉 and apparent activation energy when compared with the random and block copolymers. The result of the electron-microscopy investigation of the three copolymers that were treated at 200 ℃ for 96 h indicates that the molecular aggregation of the copolymers changed from a randomly coiled amorphous phase to an ordered phase, and the ordered structure of the alternative copolymer was more distinct than that of the random phase. The experimental results of this study suggest that the motion of the sagments is affected by the different molecular-chain sequence distribution.
基金the National Natural Science Foundation of China(No.52073261).
文摘Poly(lactic acid) (PLA) is a promising bio-based environmentally-friendly plastic. Nevertheless, the physical aging-induced brittleness of PLA limits its widespread applications. Blending with immiscible ductile polymer is an effective way to toughen PLA. However, the underlying details of the toughening mechanism and, in particular, the effect of physical aging are not well understood. Herein, atomic force microscopy (AFM) based nanomechanical mapping technology was utilized to visualize the differences in the deformation mechanisms between unaged and aged PLA/poly(ε-caprolactone) (PCL) blend upon uniaxial drawing. Results show that physical aging has a significant effect on the microscopic Young’s modulus and its distribution of PLA matrix, resulting in a highly heterogeneous response of the PLA/PCL blend to external stress and affecting the mechanical properties of the PLA phase under different extensions. This work provides a new experimental basis for understanding the effect of physical aging on the mechanical properties of PLA-based materials.
基金the National Natural Science Foundation of China(NSFC,No.51971178)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(No.2021JC-12)+3 种基金the Natural Science Foundation of Chongqing(No.cstc2020jcyj-jq X0001)sponsored by Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2021015)financial support from MICINN(grant PID2020112975GB-I00)Generalitat de Catalunya(grant 2017SGR0042)。
文摘The power-law relationship between creep rate decay and time is one of the intrinsic characteristics of metallic glasses.In the current work,a La_(30)Ce_(30)Ni_(10)Al_(20)Co_(10) high-entropy metallic glass was selected as the model alloy to test the influences of physical aging and cyclic loading on the power-law creep mechanism,which was probed by the dynamic mechanical analysis in terms of the stochastic activation,and contiguous interplay and permeation of shear transformation zones.It is demonstrated that a notable discrepancy appears between thermal treatment and mechanical treatment on the power-law creep mechanism of this high-entropy metallic glass.On the one hand,physical aging below the glass transition temperature introduces the annihilation of potential shear transformation zones which contribute to creep.On the other hand,cyclic loading can tailor the“forward”jump operations competing with the“backward”ones of shear transformation zones by controlling the interval time(recovery time).The current research offers a new pathway towards understanding the creep mechanism of high-entropy metallic glasses.
基金supported by the National Outstanding Youth Science Fund Project (Grant No. 12125206)Basic Science Center for “Multiscale Problems in Nonlinear Mechanics”(Grant No. 11988102)+1 种基金General Project of National Natural Science Foundation of China (Grant No. 11972345)CAS Project for Young Scientists in Basic Research (Grant No. YSBR-096)。
文摘Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.
基金This work was supported by the National Key Projects for Fundamental Research--"Macromolecular Condensed State",The State Science and Technology Commission of China and by the Science Foundation of PPLAS
文摘The crazing of polyphenylquinoxaline (PPQ-E) films during in situ stretching has been observed by SEM. The crazing phenomena and craze morphology of PPQ-E films were interpreted. The strain values at critical crazing and yielding and the craze stability of PPQ-E samples depend on the thermal-dealing condition for the samples. From the point of view of cohesional entanglements and energy absorbed by samples, the experiment results were explained.
基金Project supported by the National Natural Science Foundation of China (Nos. 10672095 and 11072137)the Shanghai Leading Academic Discipline Project (No. S30106)
文摘In order to predict the mechanical performance of the polyvinyl chloride (PVC) at a high operating temperature, a series of short-term tensile creep tests (one- tenth of the physical aging time) of the PVC are carried out at 63 ℃ with a small constant stress by a dynamic mechanical analyzer (DMA). The Struik-Kohlrausch (SK) formula and Struik shifting methods are used to describe these creep data for various physical aging time. A new phenomenological model based on the multiple relaxation mechanisms of an amorphous polymer is developed to quantitatively characterize the SK parameters (the initial creep compliance, the characteristic retardation time, and the shape factor) determined by the aging time. It is shown that the momentary creep compliance curve of the PVC at 63℃ can be very well fitted by the SK formula for each aging time. However, the SK parameters for the creep curves are not constant during the aging process at the elevated temperatures, and the evolution of these parameters and the creep rate versus aging time curves at the double logarithmic coordinafes have shown a nonlinear phenomenon. Moreover, the creep master curves obtained by the superposition with the Struik shifting methods are unsatisfactory in such a case. Finally, the predicted results calculated from the present model incorporating with the SK formula are in excellent agreement with the creep experimental data for the PVC isothermally aged at the temperature relatively close to the glass transition temperature.
基金Ministero dell’Universitàe della Ricerca,Grant/Award Number:20179BJNA2。
文摘Aggregation-induced emission(AIE)luminogens are attractive dyes to probe poly-mer properties that depend on changes in chain mobility and free volume.When embedded in polymers the restriction of intramolecular motion(RIM)can lead to their photoluminescence quantum yield(PLQY)strong enhancement if local microviscosity increases(lowering of chain mobility and free volume).Nonethe-less,measuring PLQY during stimuli,i.e.heat or mechanical stress,is technically challenging;thus,emission intensity is commonly used instead,assuming its direct correlation with the PLQY.Here,by usingfluorescence lifetime as an absolutefluorescence parameter,it is demonstrated that this assumption can be invalid in many commonly encountered conditions.To this aim,different poly-mers are loaded with tetraphenylenethylene(TPE)and characterized during the application of thermal and mechanical stress and physical aging.Under these con-ditions,polymer matrix transparency variation is observed,possibly due to local changes in refractive index and to the formation of microfractures.By combin-ing different characterization techniques,it is proved that scattering can affect the apparent emission intensity,while lifetime measurements can be used to ascertain whether the observed phenomenon is due to modifications of the photophysi-cal properties of AIE dyes(RIM effect)or to alterations in the matrix optical properties.
基金financially supported by the National Natural Science Foundation of China(No.51971178)the Fundamental Research Funds for the Central Universities(Nos.3102019ghxm007 and 3102017JC01003)+4 种基金Astronautics Supporting Technology Foundation of China(No.2019-HT-XG)the Natural Science Foundation of Shaanxi Province(No.2019JM-344)the Construction Project of Postgraduate Course of Northwestern Polytechnical Universitythe financial support from MINECO(grant FIS2017-82625-P)Generalitat de Catalunya(grant 2017SGR0042)。
文摘Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties.Dynamic mechanical relaxation behavior of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass was investigated by dynamic mechanical analysis(DMA)and the mechanical spectra could be well described by the quasi-point defects(QPD)theory.Compared to typical metallic glasses,the intensity of theβrelaxation of Zr_(35)Hf_(17.5)Ti_(5.5)Al_(12.5)Co_(7.5)Ni_(12)Cu_(10)high entropy bulk metallic glass is lower due to the sluggish diffusion.At the same time,the correlation factor is higher than that of conventional metallic glasses and this is ascribed to the high configuration entropy.In parallel,physical aging below the glass transition temperature leads to a decrease of atomic mobility,caused by a decrease of the concentration of defects.
基金supported by the NSFC(Grant No.51971178)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(Grant No.2021JC-12)+2 种基金the fund of the State Key Laboratory of Solidification Processing in NWPU(Grant No.SKLSP202017)financial support from MICINN(Grant FIS2017-82625-P)Generalitat de Catalunya(Grant 2017SGR0042)
文摘Evolution of deformation and relaxation behaviors of a prototypical Cu_(46)Zr_(46)A_(l8)metallic glass was explored by extensive creep tests under both physical aging and cyclic loading.Deep insights into the microstructure-induced dynamic heterogeneity which accommodates creep deformation were successively revealed via experimental measurements and spectral analyses.An annihilation of local defects within metallic glass with increasing annealing time and cyclic numbers was observed through the reduction of amplitude in both activation energy spectra and relaxation-time spectra,which were also accompanied by an ascending value of β_(KWW).It is further found that the corresponding deformation units within the metallic glass do not disappear permanently,but are recoverable over the course of cyclic loading.The apparent suppressed relaxation process can be gradually alleviated with increasing resuming time between two consecutive cycles,behaving differently from physical aging,which indicates a notable discrepancy between thermal treatment and mechanical treatment.
基金supported by the National Basic Research Program of China(973 Program)(No.2010CB731503)
文摘The purpose of this work is to investigate the dynamic fracture properties of glassy polycarbonate (PC) with different aging times. The optical method of caustics is adopted in which the shadow spot patterns are recorded by a high speed camera during the dynamic fracture process. Then, the dynamic crack propagation, the stress intensity factor (SIF) and the dynamic fracture toughness of aged PC are obtained through an analysis of the characteristic size of caustic pattern. Moreover, by combining with the investigation of the fracture surface and the energy release rate analysis, the influence of aging time on the dynamic fracture behavior is discussed. Results show that the dynamic fracture toughness and critical energy release rate of PC decreases with aging time for short aging times, whereas they have little change or even increase for longer aging times. Therefore, aging modifies the mechanical properties especially the dynamic fracture properties of PC nonlinearly, not linearly as generally thought of.
基金Faiz Almansour is grateful to the Department of Research&Development,Saudi Aramco for funding and supporting his Ph.D.studies.M.Alberto is grateful to EPSRC for funding under the research grant number EP/S032258/1R.Bhavsar to EPSRC under grant number EP/M001342/1.
文摘Physical aging is currently a major obstacle for the commercialization of PIM-1 membranes for gas separation applications.A well-known approach to reversing physical aging effects of PIM-1 membranes at laboratory scale is soaking them in lower alcohols,such as methanol and ethanol.However,this procedure does not seem applicable at industrial level,and other strategies must be investigated.In this work,a regeneration method with alcohol vapors(ethanol or methanol)was developed to recover permeability of aged PIM-1 membranes,in comparison with the conventional soaking-in-liquid approach.The gas permeability and separation performance,before and post the regeneration methods,were assessed using a binary mixture of CO_(2) and CH_(4)(1:1,v:v).Our results show that an 8-hour methanol vapor treatment was sufficient to recover the original gas permeability,reaching a CO_(2) permeability>7000 barrer.