Two kinds of tough ductile heatresisting thermoplastic, namely bisphenol A polysulfone (PSF) and polyethersulfone (PES) were used to toughen thermoset epoxy resin. A systematic study on the relationship between the mo...Two kinds of tough ductile heatresisting thermoplastic, namely bisphenol A polysulfone (PSF) and polyethersulfone (PES) were used to toughen thermoset epoxy resin. A systematic study on the relationship between the molecular weight and the terminal group of the thermoplastic modifier and the fracture toughness of the modified resin was carried out. The morphology of PSF modified epoxy resin was surveyed. With the same kind of PSF the structure of the epoxy resin and the toughening effect of PSF was also investigated. The fractography of PSF, particle modified epoxy was examined in detail with SEM. The contribution of every possible energy absorption process has been discussed. Crack pinning mechanism seems to be the most important toughening mechanism for tough ductile thermoplastic PSF particle modified epoxy system.展开更多
A plane-strain unit-cell finite element model was proposed to study the effects of resin/sand interface adhesive and resin cohesive strength on the overall tensile strength of resin sand,as well as the fracture modes....A plane-strain unit-cell finite element model was proposed to study the effects of resin/sand interface adhesive and resin cohesive strength on the overall tensile strength of resin sand,as well as the fracture modes.The main micro-scale characteristics of the numerical model were extracted from the micrograph of resin sand specimens by three-dimensional X-ray microscopy(3 D-XRM).The extended finite element method(XFEM)and cohesive behavior method were employed to explicitly describe the resin fracture and sand/resin interface debonding,separately.The corresponding experimental observation of micro-scale failure behavior based on the scanning electron microscopy(SEM)was presented for a comparison.The numerical results show that the initial failure of the model occurs at the sand/resin interface,followed by consequent resin failure.Dependent on the resin cohesive strength,the location of resin failure varies from the central zones to resin neck arc zones.A typical mixed mode fracture is observed,which is consistent with the corresponding micro-scale experimental observation.When the resin cohesive strength ranges between 8 and 12 MPa,the resin cracks occur at the central zone of resin bridges and propagate perpendicularly to the tensile direction until through cracks happen.At a higher range(between 12 and 16 MPa),interface cracks cross with resin cracks,bonding bridges of resin sand are broken.The interface adhesive strength has a more significant effect on the overall tensile strength of resin sand than the resin cohesive strength.The overall tensile strength of resin sand increases first then keeps stable with the increase of the resin cohesive strength.This work attempts to establish a numerical model which accurately describes the complicated mixed mode fracture of resin sand,which is beneficial to understand deeply the fracture mechanism of resin sand.展开更多
The geometries of resins with single-layer （SG）, double-layer （DG） and triple-layer （TG） were calculated with the quantum chemistry method. The geometries and net charges of atoms were obtained. The calculated a...The geometries of resins with single-layer （SG）, double-layer （DG） and triple-layer （TG） were calculated with the quantum chemistry method. The geometries and net charges of atoms were obtained. The calculated average distances between layers were 0.5348 nm and 0.5051 nm and the action energies were -9.6355 kJ/mol and -32.2803 kJ/mol for resins DG and TG, respectively. Higher electronegative polar atoms can easily form hydrogen bonds with hydrogen atoms of other resin molecules, resulting in resin aggregates. The minimum cross-sectional diameters of resin molecules are too large to enter the pores of zeolite, so they are likely to crack on the surface of zeolite.展开更多
Quasi-static and high strain rate compressive experiments on vinyl ester casting were carried out by means of MTS (Material Test System) and Hopkinson bar. The behaviors of the compressed unstable and fracture of the ...Quasi-static and high strain rate compressive experiments on vinyl ester casting were carried out by means of MTS (Material Test System) and Hopkinson bar. The behaviors of the compressed unstable and fracture of the resin casting at different strain rates were investigated.The results indicate that the response behavior of the resin casting is controlled by different mechanisms at different strain rate, and some mechanical properties of vinyl ester casting are rate-dependent: the casting are destroyed in toughness model under strain rate 3.3×10 -4～6.6×10 -3/s, while the casting are destroyed in brittleness model under strain rate 950～5800/s. The yield stress, yield strain energy density are all increased with the increasing strain rates at quasi-static as well as at high strain rates. What is interesting is that the yield strain decreased with the strain rates increasing at quasi-static while increased at high strain rates. It is considered that the casting occurred forcing high elastic deformation at high strain rates. The damage of the specimens is mainly controlled by axial stress before unstable deformation, while mainly controlled by shear stress after unstable deformation, and then developed to fracture finally. This progress is rate-dependent: the development of the cracks inside the castings increased with the strain rate increasing.展开更多
基金Sponsored by the National Natural Science Foundation of China
文摘Two kinds of tough ductile heatresisting thermoplastic, namely bisphenol A polysulfone (PSF) and polyethersulfone (PES) were used to toughen thermoset epoxy resin. A systematic study on the relationship between the molecular weight and the terminal group of the thermoplastic modifier and the fracture toughness of the modified resin was carried out. The morphology of PSF modified epoxy resin was surveyed. With the same kind of PSF the structure of the epoxy resin and the toughening effect of PSF was also investigated. The fractography of PSF, particle modified epoxy was examined in detail with SEM. The contribution of every possible energy absorption process has been discussed. Crack pinning mechanism seems to be the most important toughening mechanism for tough ductile thermoplastic PSF particle modified epoxy system.
基金Fundamental Research Funds for the Central Universities(WUT:2018III066GX)Nature Science Foundation of Hubei Province(2017CFC809)+1 种基金China Postdoctoral Science Foundation(No.2018M632933)the Foreign Science and Technology Cooperation Project of Hubei Provenience(Grant No.2013BHE008).
文摘A plane-strain unit-cell finite element model was proposed to study the effects of resin/sand interface adhesive and resin cohesive strength on the overall tensile strength of resin sand,as well as the fracture modes.The main micro-scale characteristics of the numerical model were extracted from the micrograph of resin sand specimens by three-dimensional X-ray microscopy(3 D-XRM).The extended finite element method(XFEM)and cohesive behavior method were employed to explicitly describe the resin fracture and sand/resin interface debonding,separately.The corresponding experimental observation of micro-scale failure behavior based on the scanning electron microscopy(SEM)was presented for a comparison.The numerical results show that the initial failure of the model occurs at the sand/resin interface,followed by consequent resin failure.Dependent on the resin cohesive strength,the location of resin failure varies from the central zones to resin neck arc zones.A typical mixed mode fracture is observed,which is consistent with the corresponding micro-scale experimental observation.When the resin cohesive strength ranges between 8 and 12 MPa,the resin cracks occur at the central zone of resin bridges and propagate perpendicularly to the tensile direction until through cracks happen.At a higher range(between 12 and 16 MPa),interface cracks cross with resin cracks,bonding bridges of resin sand are broken.The interface adhesive strength has a more significant effect on the overall tensile strength of resin sand than the resin cohesive strength.The overall tensile strength of resin sand increases first then keeps stable with the increase of the resin cohesive strength.This work attempts to establish a numerical model which accurately describes the complicated mixed mode fracture of resin sand,which is beneficial to understand deeply the fracture mechanism of resin sand.
文摘The geometries of resins with single-layer （SG）, double-layer （DG） and triple-layer （TG） were calculated with the quantum chemistry method. The geometries and net charges of atoms were obtained. The calculated average distances between layers were 0.5348 nm and 0.5051 nm and the action energies were -9.6355 kJ/mol and -32.2803 kJ/mol for resins DG and TG, respectively. Higher electronegative polar atoms can easily form hydrogen bonds with hydrogen atoms of other resin molecules, resulting in resin aggregates. The minimum cross-sectional diameters of resin molecules are too large to enter the pores of zeolite, so they are likely to crack on the surface of zeolite.
文摘Quasi-static and high strain rate compressive experiments on vinyl ester casting were carried out by means of MTS (Material Test System) and Hopkinson bar. The behaviors of the compressed unstable and fracture of the resin casting at different strain rates were investigated.The results indicate that the response behavior of the resin casting is controlled by different mechanisms at different strain rate, and some mechanical properties of vinyl ester casting are rate-dependent: the casting are destroyed in toughness model under strain rate 3.3×10 -4～6.6×10 -3/s, while the casting are destroyed in brittleness model under strain rate 950～5800/s. The yield stress, yield strain energy density are all increased with the increasing strain rates at quasi-static as well as at high strain rates. What is interesting is that the yield strain decreased with the strain rates increasing at quasi-static while increased at high strain rates. It is considered that the casting occurred forcing high elastic deformation at high strain rates. The damage of the specimens is mainly controlled by axial stress before unstable deformation, while mainly controlled by shear stress after unstable deformation, and then developed to fracture finally. This progress is rate-dependent: the development of the cracks inside the castings increased with the strain rate increasing.
