Preparation and Characterization of Silicon-containing Polyarylacetylene/montmorilloite Nanocomposites

Dimethylphenylpropargyl ammonium bromide (DMPPAB) was synthesized and used to modify pristine montmorillonite (MMT) by a cation exchange process. The organically modified montmorillonite (OMMT) was verified and used to mix with a silicon-containing polyarylacetylene (PSA) as well as MMT. The PSA/MMT and PSA/OMMT nanocomposites were prepared by solution under sonication and melting intercalation processes, respectively, and then cured by a step heating process. The thermal and flexural properties of the cured PSA and nanocomposites were studied by thermogravimetric and dynamic mechanical analysis. The results showed that the intercalation of DMPPAB into the MMT galleries made the d-spacing enlarge. During PSA curing, the cure heat of PSA caused the MMT and OMMT to delaminate and exfoliate in the PSA matrix. The glass transition temperature of the cured PSA and nanocomposites were higher than 500?°C. The inner acetylenic groups in the PSA resin could further crosslink above 300?°C. The temperature at 5% mass loss of the cured PSA decreased by 4.6% with 3% mass fraction of OMMT loading, and the char yield of the cured PSA changed only slightly. The flexural strength of the cured PSA was augmented with addition of MMT or OMMT, but the flexural modulus of the cured PSA decreased slightly. The flexural strength of the cured nanocomposite increased from 20.1?MPa to 30.1?MPa when 3% mass fraction of OMMT was added into the PSA matrix.     

Interphase characterization in epoxy resin/carbon fibre composites

In this paper, interphase properties of carbon fibre/epoxy resin single-fibre model and unidirectional (UD) composites are reported. To study the contribution of the carbon fibre surface chemistry and morphology and of the resin itself to the overall properties of the composites, untreated, oxidized and sized fibres are used with bi- and tetrafunctional, diglycidylether of Bisphenol A, DGEBA and tetraglycidyl 4,4'-diaminodiphenylmethane, TGDDM-based resins, cured with amine and anhydride hardeners. Adsorption measurements and single fibre contact angle experiments, as well as the pull-out test were applied to characterize the surface of carbon fibre and the interfacial shear strength with different matrices. It was shown that the presence of the size on the surface can drastically affect the wettability as well as the starting rate of the cure reaction of epoxide in the vicinity of the fibre surface, as revealed by FTIR microscopy. Different elastic-plastic behavior of model composites before debonding is found for untreated, oxidized and sized fibres, due to the various interphase structures formed. Both micro-and macromechanical properties of the composites are found to be significantly affected by the matrix properties. The role of the surface treatment of fibers becomes especially important in high performance resin systems.     

In situ observation of interfacial debonding process induced by matrix crack propagation in two-dimensional unidirectional model composites

Interfacial debonding behavior is studied for unidirectional fiber reinforced composites from both experimental and analytical viewpoints. A new type of two-dimensional unidirectional model composite is prepared using 10 boron fibers and transparent epoxy resin with two levels of interfacial strength. In situ observation of the internal mesoscopic fracture process is carried out using the single edge notched specimen under static loading. The matrix crack propagation, the interfacial debonding growth and the interaction between them are directly observed in detail. As a result, the interfacial debonding is clearly accelerated in specimens with weakly bonded fibers in comparison with those with strongly bonded fibers. Secondary, three-dimensional finite element analysis is carried out in order to reproduce the interfacial debonding behavior. The experimentally observed relation between the mesoscopic fracture process and the applied load is given as the boundary condition. We successfully evaluate the mode II interfacial debonding toughness and the effect of interfacial frictional shear stress on the apparent mode II energy release rate separately by employing the present model composite in combination with the finite element analysis. The true mode II interfacial debonding toughness for weaker interface is about 0.4 times as high as that for a stronger interface. The effect of the interfacial frictional shear stress on the apparent mode II energy release rate for the weak interface is about 0.07 times as high as that for the strong interface. The interfacial frictional shear stress and the coefficient of friction for weak interface are calculated as 0.25 and 0.4 times as high as those for strong interface, respectively.     

Comparison of the properties of Nextel 720/SiC composites at room temperature and 1300°C

Continuous Nextel 720 fibers reinforced SiC composites with PyC interface are fabricated by LPCVI at 1000°C for 200 h using SiCH₃Cl₃ as precursor. The mechanical properties at RT and 1300°C are measured by three-point bending. The microstructures of the interface are characterized by TEM. The results indicate the composites have the metal-like behavior of fracture, whether they are at RT or high temperature. The RT and 1300°C strengths are 310 MPa and 140 MPa, respectively. The RT and 1300°C strains are 0.32% and 0.12%, respectively. The loss of flexural strength and strain of the Nextel 720/SiC composites at high temperature result from stronger residual thermal stress caused by the mismatch of CTE between fibers and matrix. A gap appears between fibers and PyC interface after the 1300°C test, which could be resulted from 7.7% compressive strain of PyC interface caused by the residual thermal stress and 0.1% sintering shrinkage of Nextel 720 fiber.     

Void content and interfacial properties of composite laminates under different autoclave cure pressure

With an identical temperature profile, various cure pressures were applied to determine the effect of cure pressure on void distribution and interlaminar shear strength (ILSS) of [0]₁₀ T800/X850 composite laminate. Void shape, distribution, and void content within the composite laminates were characterized using optical microscope. The ILSS was evaluated using short-beam three-point bending tests and their interface debonding failure and fracture surfaces were determined using scanning electron microscope. The experimental results indicated that long strips voids are generated in the low-pressure curing stage. The voids mainly exist in the two forms of rod-like shape and spherical shape, and their number and size decrease as the cure pressure increases. The influence of cure pressure on the void content and ILSS shows a different trend in two stages: when the cure pressure is lower than 0.4 MPa, the ILSS decrease by 5.21% with 1% increase in void content, and their relationship is inversely linear. However, when the cure pressure is higher than 0.4 MPa, the void content is less than 1% and ILSS increase slightly by 1.69% when the cure pressure goes from 0.4 to 0.6 MPa, the influence of cure pressure on void content and ILSS is clearly presented.     

Polymerization,structure and track recording properties of CR-39 cured with UV photoinitiators

CR-39 monomer was cured isothermally at temperatures from 54.5 to 115°C with UV sensitive photoinitiators to high conversions. The use of photoinitiators allowed the cure of CR-39 isothermally at high temperatures and eliminated the danger of thermal runaway present in the conventionally used thermal initiation with peroxides. It was found that the properties of the UV photoinitiated CR-39 were similar to the conventionally polymerized resin.     

冲击下花岗岩界面动态摩擦特性实验研究

 为研究岩石界面动态摩擦性能,对房山花岗岩进行了冲击速度42.2~130.6 m/s、倾斜角为20°和30°的横剖试样斜撞击实验。倾斜角为20°的为对比实验,研究不发生滑动时的界面性能;在倾斜角为30°的实验中,靶和飞片撞击界面发生相对滑动,用于研究发生界面滑动时的动态摩擦性能。基于此,研究了正应力在317~685 MPa、界面相对滑移速度在2.76~24.88 m/s时花岗岩界面滑动态摩擦状态。其结果可以初步揭示地震过程板块动态摩擦过程摩擦强度急剧降低的现象。     

Modelling of the transverse strength of fibre reinforced epoxy composite at low and high temperature

Process-induced thermal residual stresses and matrix failure of unidirectional carbon fibre reinforced composites (CFRP) have been investigated by finite element analysis (FEA). We used a partial discrete FEA model based on a unidirectional composite consisting of a microscopic area of fibres and matrix surrounded by a homogenised composite area. The FEA provided information about the stress state in the matrix and the fibre–matrix interface. The transverse strength of the composite was calculated regarding matrix failure and fibre matrix debonding. The influence of the temperature on the Young's modulus, the non-linear stress–strain behaviour and the strength of the matrix were investigated in detail. Following this approach it was possible to incorporate the resulting microresidual stresses on the transverse strength of the composite. Tensile tests of the neat resin and of the composite were performed in the temperature range of ?40°C to 60°C. The results of the FEA modelling are in good agreement with the experimental results of the transverse tests.     

The effects of stoichiometry and structure on the dynamic torsional properties of a cured epoxy resin system

The dynamic torsional characteristics of a difunctional, bisphenol-A-type epoxy resin cured with different amounts of metaphenylene diamine, using two cure cycles, were determined in torsion at four frequencies between ?150° and 200°C. Besides two prominent relaxations, α and β, a third broad, but not very intense, relaxation has been shown to be present in all samples in the intermediate temperature range and has been designated the α transition. An analysis of the data on the temperature and frequency dependence of these relaxations allows some insight into their possible molecular origins. The torsional moduli were found to be related to the molecular packing, as reflected in their densities.     

Rupture of molecules upon fracture of adhesive joint between two polymer samples

The surfaces formed after fracture of the joint of two polystyrene (PS) samples have been studied by attenuated total reflection Fourier-transform infrared spectroscopy. The adhesive joint between samples was created by pressing them one against another and holding at a pressure of 0.8 MPa and a temperature of 80°C, which is ～23°C lower than the glass transition temperature of PS. It has been found that, after the joint fracture, the concentration of molecule ends formed after the rupture of carbon-carbon bonds in the back-bone of the PS molecule increases.     

Direct Resinification of Two (1→3)-β-D-Glucans,Curdlan and Paramylon,via Hot-Press Compression Molding

Abstract

Hot-press compression molding was attempted to resinify two renewable source-derived linear (1→3)-β-D-glucan polymers, i.e., paramylon or curdlan via the generation of reactive aldehyde groups that tend to crosslink with hydroxyl groups of the glucans. As for the paramylon, the optimal molding temperature was found to be around 220?°C, keeping the pressure at 20?MPa for 3?min, due to its highly crystalline structure. On the other hand, the curdlan resin was producible in the temperature range of 180–240?°C at the same pressure and pressing time. Dynamic mechanical analysis revealed a large temperature dependence of the loss modulus, E’’, for the paramylon-based polymer resin whereas the semi-crystalline curdlan resin was stable in terms of both the storage and loss moduli, E’ and E’’, up to 160?°C. The vaporization of the water formed during the molding, due to the thermal decomposition, and the adsorption of moisture due to the hydrophilic property of the paramylon affected the thermal stability. The curdlan resin exhibited flexural strength and modulus extremely superior to those of regenerated and esterified curdlan films, and even a little superior to those of polyamide-12. The strain at break was comparable to the yield strain of an epoxy resin. On the other hand, the paramylon-based polymer resin was producible, but the resinification property and thermal stability of the paramylon resin was inferior to the curdlan resin due to the former’s highly crystalline structure.     

Mechanical and Tribological Properties of Self-Reinforced Polyphenylene Sulfide Composites

25%, 50%, and 75% polyphenylene sulfide (PPS) long fiber reinforced PPS resin were prepared by a hot pressing method. Neat resin PPS and PPS fiber samples were also prepared to compare with the self-reinforced PPS composites. The reinforcing fibers were preheat treated at 240°C for 24 h. The tribological properties of the self-reinforced PPS composites against an AISI 1045 steel ring were determined by a block on ring type friction tester. Differential scanning calorimetry (DSC) results indicated that a higher degree of crystallinity was retained in the self-reinforced PPS composites than in neat PPS resin after hot pressing. Therefore, the addition of PPS fiber improved both the mechanical and tribological properties of PPS resin significantly. Dynamic mechanical analysis (DMA) demonstrated that the PPS fibers increased the glass transition temperature (Tg) of the PPS resin. SEM images of the fracture surfaces indicated that the toughness of the samples increased with increasing PPS fiber content. Additionally, PPS fibers improved the tribological properties of PPS resin by significantly reducing the friction coefficient and wear rate.     

Observation of transcrystalline growth of PLA crystals on sisal fibre bundles and the effect of crystal structure on interfacial shear strength

Hot-stage microscopy was used to characterise crystal growth at the interface between sisal fibre bundles and a polylactic acid (PLA) matrix in order to better understand the mechanical properties of sisal fibre–PLA composites. Cooling rates and crystallisation temperatures and times were varied to influence crystalline morphology at the interface. Single sisal fibre bundles were evaluated in their as received state or treated with 6 wt.% caustic soda solution for 48?h at room temperature. A microbond shear test was used to characterise the shear strength of the interface as a function of fibre surface treatment. These tests were performed on sisal fibre bundles carefully embedded in flat films of PLA supported on card mounts. Fibre bundles in a PLA matrix were cooled from 180?°C at rates from 2 to 9?°C/min and then crystallised isothermally. For as received fibre bundles uneven growth of PLA spherulites occurred at all cooling rates and crystallisation temperatures. For caustic soda treated fibres, uneven spherulitic growth was observed at crystallisation temperatures at and above 125?°C. In contrast, transcrystalline growth was observed for samples cooled to 120?°C at cooling rates from 2 to 6?°C/min and then allowed to crystallise. The microbond shear strengths of untreated and caustic soda treated fibre bundles were evaluated using Weibull statistics and the caustic soda treated fibres exhibited higher interfacial shear strengths in comparison to untreated fibres, reflecting the development of a transcrystalline layer at the fibre to matrix interface.     

长亚甲基链段改性固化剂的制备与性能

采用二官能度环氧树脂对己二胺进行改性,得到了含多段长亚甲基链段的柔性固化剂。利用红外光谱表征其基本结构。采用环氧树脂E-44与之进行固化,通过不同温度下固化时间对力学强度影响的分析,初步确定其最佳固化条件为80 ℃,6 h。通过热重分析检测不同固化比例下固化产物的热稳定性,并采用差示扫描量热法研究该固化剂的固化动力学参数、反应活性、最佳固化温度及时间。对其固化物拉伸剪切强度进行测试,测试结果表明:在固化比例为1:0.5时,在-196 ℃、室温、60 ℃下的拉伸剪切强度分别为16.84,14.73和13.52 MPa,基本满足实际应用的需求。     

Deformation and annealing behaviour of a low carbon high Mn TWIP steel microalloyed with Ti

ABSTRACT

A low carbon high Mn, Ti microalloyed dual phase TWIP steel has been processed through cold rolling and annealing. X-ray diffraction reveals the maximum austenite (≈92%) in HRACST sample whereas, the 50CD sample shows 29% ferrite. The microstructure of HRAC and HRACST samples reveal austenite grains with annealing twins and deformation induced ferrite (DIF). The higher amount of DIF along with deformation twins form during cold deformation. Annealing at 500°C shows recovery, whereas at 700°C shows partial recrystallisation and at 900°C reveals almost full recrystallisation. TEM microstructures of the 900°C for 30?min samples reveal annealing twins with TiC particle. Strong Brass {110}<112> and Goss{110}<001> texture components are observed in HRAC, HRACST and 50CD samples. Goss Twin (GT) {113}<332> and Copper Twin (Cu-T) {552}<115> components are observed in 50CD sample. Addition of Ti results in an average grain size of 20?μm. Maximum YS (1176?MPa) and UTS (1283?MPa) values with the lowest ductility of 11% have been obtained for the 50CD sample which is related to the formation of extensive deformation twin and a higher fraction of DIF. 700°C-30?min and 700°C-60?min samples show an increase in ductility (23% and 34%, respectively) with a marginal decrease in tensile strength (1054?MPa). Annealing at 900°C shows ductility restoration up to 60% with higher tensile strength compared to HRACST sample. Ductile fracture of HRAC and HRACST samples transform to brittle fracture in the 50CD sample. Annealing at 900°C for 30?min shows ductile fracture with some (Fe, Mn)S and TiC particles.     

Measurements of the complex shear modulus of polymers under hydrostatic pressure usina the quartz resonator method

Abstract

The quartz resonator method measures the complex shear modulus or compliance of viscoelastic materials in the frequency range from 50 kHz to 140 MHz at temperatures between ?150°C and 300°C and pressures up to 1 GPa. This method can be applied to viscous fluids or polymer melts -even in their glassy or seminystalline regime.

The phase diagram of poly(diethylsiloxane) PDES (a mesophase polymer) was determined for two samples with different molecular weight at pressures up to 400 MPa and temperatures between 20°C and 100°C. Phase transitions are indicated by a sharp bend in the shear compliance although the volume effect of the mesophase-isotropic transition vanishes around 80 MPa.

The pressure dependence of the glass relaxation process (in PVAc), was studied by measuring the change of the complex shear modulus with pressure at constant temperatures between 95°C and 145°C and pressures up to 600 MPa. Additionally to the relaxation process, also the pressure dependence of the real part of the shear modulus in the glassy region can be determined for testing the dislocation concept in the meandermodell by W. Pechhold.     

The variability of times to detect growth from individual Clostridium botulinum type E endospores is differentially affected by high pressure treatments

High pressure thermal (HPT) processing is a candidate technology for the production of safe and stable food. However, little is known about the effect of HPT or high hydrostatic pressure (HHP) treatments at ambient temperature on the variability of times to detect growth from individual spores. We investigated this effect by treating Clostridium botulinum type E spores with HHP (200–600?MPa, 20°C) and HPT (600?MPa, 80°C and 800?MPa, 60°C). Our results indicate that the mean detection times increase and the frequency distribution shifts toward longer times when HHP treatment intensity is increased. HPT treatments result in a highly scattered distribution. In contrast, pressure levels ≤300?MPa decrease detection times and heterogeneity of their distribution, which could lead to an increase in the potential risk originating from C. botulinum type E spores. Data provided here could help to refine risk assessment regarding this important food intoxicator.     

Interfacial debonding behavior of a rigid particle-filled polymer composite

Glass beads, non-modified and modified with coupling agent, were filled separately into high density polyethylene to obtain composite materials with different interfacial adhesion strengths. In situtensile tests reveal the damage mechanisms, which are mainly induced by the interfacial debonding. The interfacial debonding process is observed and studied. The debonding stress is found to be linearly related to the opening angle formed at two poles of the particles. Initial and final opening angles, in addition to the corresponding debonding stresses, are measured. The interfacial fracture energy obtained by using the Griffith fracture theory is found to be 0.028 J m^-2 and 0.058 J m^-2 for mechanical anchorage and physical entanglement across the interface, respectively. The stronger the interfacial adhesion, the smaller is the maximum opening angle and greater the debonding stress.     

Room vs. temperature studies of model composites: modes of failure of carbon fibre/epoxy interfaces

Laser Raman spectroscopy (LRS), transmission polarised optical microscopy (TPOM) and scanning electron microscopy (SEM) have been used to characterise the interface of model single-fibre composites. The composites consisted of single-carbon fibres embedded in epoxy resin. Local stress measurements as a function of applied strain were performed using LRS at both room temperature (RT) and 60?°C. Consecutively, the coupons were strained to failure and field emission SEM was used to study the fracture surfaces. In a parallel study, identical systems were subjected to incremental tension and fracture events were recorded as a function of applied strain. At RT, TPOM was used to provide additional insight in the local stress transfer. The stress transfer was found to depend on the combined effect of interfacial chemistry and thermal stresses. Thus, in the case of sized fibres, there is a distinct change in the interfacial failure mode at high temperature, whereas in the case of unsized fibres, the stress transfer is dominated by thermal stresses: at high temperature it is weak, due to the relief of the thermal stress field.     

Preparation of CuO nanoparticles by metal salt-base reaction in aqueous solution and their metallic bonding property

This article describes a method for preparing CuO nanoparticles in aqueous solution, and a demonstration of feasibility of metallic bonding with the use of the CuO particles. Colloid solution of CuO nanoparticles was prepared from Cu(NO₃)₂ aqueous solution (0.01 M) and NaOH aqueous solution (0.019 M) at 5–80 °C. Leaf-like aggregates with an average size of 567 nm composed of CuO nanoparticles were produced at 20 °C. The size of leaf-like aggregates decreased with increasing reaction temperature. Metallic copper discs could be bonded using the CuO nanoparticles under annealing at 400 °C and pressurizing at 1.2 MPa for 5 min in H₂ gas. A shear strength required for separating the bonded discs was 25.4 MPa for the CuO nanoparticles prepared at 20 °C, whose aggregates were the largest among the CuO particles examined. These results indicated that the formation of leaf-like aggregates of CuO nanoparticles led to efficient metallic bonding.