Jifeng Zhang

Effects of Nano-Aluminum Nitride on the Performance of an Ultrahigh-Temperature Inorganic Phosphate Adhesive Cured at Room Temperature

Based on the optimal proportion of resin and curing agent, an ultrahigh-temperature inorganic phosphate adhesive was prepared with aluminum dihydric phosphate, aluminium oxide (α-Al2O3), etc. and cured at room temperature (RT). Then, nano-aluminum nitride (nano-AlN), nano-Cupric oxide (nano-CuO), and nano-titanium oxide (nano-TiO2) were added into the adhesive. Differential scanning calorimetry was conducted using the inorganic phosphate adhesive to analyze the phosphate reactions during heat treatment, and it was found that 15 wt % nano-AlN could clearly decrease the curing temperature. Scanning electron microscopy was used to observe the microphenomenon of the modified adhesive at ultrahigh-temperature. The differential thermal analysis of the inorganic phosphate adhesive showed that the weight loss was approximately 6.5 wt % when the mass ratio of resin to curing agent was 1:1.5. An X-ray diffraction analysis of the adhesive with 10% nano-AlN showed that the phase structure changed from AlPO4(11-0500) to the more stable AlPO4(10-0423) structure after heat treatment. The shear strength of the adhesive containing 10% nano-AlN reached 7.3 MPa at RT due to the addition of nano-AlN, which promoted the formation of phosphate and increased the Al3+.

Investigation of mechanical performances of composite bolted joints with local reinforcements

Abstract Four different local reinforcement schemes used in composite bolted joints were studied. In numerical study, a set of 3-D failure criteria was used and the progressive failure analysis was implemented via user-defined subroutine vectorized user-material (VUMAT), which was programmed by the commercial finite element (FE) software ABAQUS. In the experiment, test specimens were manufactured with different local reinforcement schemes, and the mechanical performances of these specimens were tested under tensile loads. Failure modes of these specimens were observed and mechanical performances of test specimens with local reinforcement were studied. It was found that the numerical results agreed well with the experiment. It was also found that local reinforcement schemes influenced the mechanical performances of bolted joints obviously and that the tensile strength of composite bolted joints could be improved significantly by burying laminate slices.

Study of the Effect of Curing Residual Stress on the Bonding Strength of the Single Lap Joint Using a High-Temperature Phosphate Adhesive

High-temperature phosphate adhesives are widely used in the aerospace and nuclear power industries. However, complex residual stresses can result when the curing temperature parameters are unreasonable due to the brittleness of the adhesive. To reveal the curing temperature mechanism affecting the bonding strength of the phosphate adhesives, several curing temperature curves (CT-1~6) were designed for the single lap joint (SLJ) using phosphate adhesive. The residual stress helped to reveal the relationship between the curing temperature parameters and the bonding performance. In this process, the residual stress of the silicon carbide joint was measured using micro-Raman spectroscopy, and the tensile strength of the joint was tested. A cohesive zone model (CZM) was established with Abaqus® to verify the results, and the numerical results from the model agreed well with the experimental values. The residual stress and adhesive strength were obviously affected by curing temperature. The reasonable curing temperature curves have the benefits of reducing the residual stress and improving the bonding strength.

Preparation, Mechanical and Thermal Properties of Poly(Butylene Terephthalate) and Its Nanocomposites Prepared from Cyclic Butylene Terephthalate

Polymerized cyclic butylene terephthalate (pCBT) casts and pCBT/nano-silica composites generated from cyclic butylene terephthalate (CBT) were manufactured. The mechanical properties of pCBT casts with various ratio of catalyst were investigated through three-point bending test, and the thermal properties of the samples were tested by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). Moreover, the fracture morphologies of pCBT as well as its nano-silica composites were observed by SEM. From the study, suitable catalyst content for CBT resin was determined and pCBT/nano-silica composites were found to have better thermal performances compared with neat pCBT.

Study on the Factors of Residual Thermal Stress on Single Lap Joint

This paper discussed the residual thermal stress on single lap joint of various materials. Finite element method (FEM) was adopted to simulate the experimental phenomena. The adherend and adhesive were the main research objects. Mismatch of adherend, adhesive thickness, temperature variation which were the three key factors on the residual thermal stress were analyzed. While, four kinds of materials that include C/SiC, SiC, high temperature nickel based alloy GH1035 (GH1035) and high temperature boron fiber reinforced epoxy composite (composite) formed seven approaches for numerical analysis. The results showed that the adhesive with the C/SiC has the best performance and the best thickness of every approach was determined. Moreover, the ladder temperature is better than other temperature styles.

Parameter Study of Numerical Simulation for Tensile Properties of Multi-Layer SMATed Alloys

Strength and ductility are very important to marine engineering. Because of their remarkable mechanical properties, nanocrystalline metals have been the focus of much research in recent years. Based on surface mechanical attrition treatment (SMAT) and warm co-rolling technologies, the resulting material performances amazingly exhibit high strength and exceptional ductility. Therefore, this method is a promising avenue for advanced materials for marine engineering. Cohesive finite element method (CFEM) is employed to investigate the tensile performance of multi-layer SMATed alloys. With the results of simulation and experiment compared, simulation parameters have been studied . According to comparing different simulation results, the model parameters, normal direction strength and tangential direction strength in CFEM are studied.

Electrical and Mechanical Properties of Short-Carbon-Fiber Reinforced Polymerized Cyclic Butylene Terephthalate Composites

Polymerized cyclic butylene terephthalate (pCBT) resin casts filled with short carbon fibers were prepared by the melt-mixing approach. The electrical conductivity of short-carbon-fiber (SCF) reinforced thermoplastic pCBT resin casts were investigated with a special attention paid to the properties in the percolation threshold region and the mechanical properties of the composites were also studied. The percolation threshold value of the novel material system was determined which was also verified by SEM images and the thermoelectric behavior of the specimens. Even though the electrical properties of SCF/pCBT composites enhanced significantly, the material becomes more brittle than neat pCBT and all the specimens appear brittle fracture during the mechanical test. Moreover, fiber pull-out is the main damage form in three-point-bending test.

Preparation and Characterization of In Situ Polymerized Cyclic Butylene Terephthalate and its Composites

A fatal disadvantage of continuously reinforced thermoplastic composites is the high melt viscosity of the matrix which hampers impregnation. However, the melt viscosity of low molecular weight CBT resin can reach extremely low value, which simplifies impregnation and enables the use of thermoset production methods. The thermal analysis, rheological analysis and mechanical property on the polymerization and crystallization of CBT into poly (cyclic butylene terephthalate) (PCBT) at different ratios of catalyst were investigated in this paper. The continuous glass fiber (GF) reinforced PCBT composite with over 70% fiber volume content was prepared via in situ polymerization, and the mechanical property of the PCBT was studied. The best impregnation time was decreased and the degree of crystallinity was increased respectively with catalyst fraction increasing. The tensile/flexural strength and modulus of PCBT resin and GF/PCBT composites were enhanced when the catalyst fraction increased from 0.3% to 0.6%.

Residual Stress Measurement in Inorganic Phosphate Adhesive Joint by Raman Spectroscopy

This paper deals with the determination of residual stress in SiC adherend bonded with inorganic phosphate adhesive using Raman and fluorescence spectroscopy in a micro-Raman system. To determine the stress mode in the specimen, we descript the corresponding relation between the Raman effect and residual stress. The laser with wavelength at 532nm and 785nm was respectively applied to test hundreds of test points on the SiC adherend and selected 785nm wavelength laser as the illuminant. Meanwhile, Raman imaging was used to analyze the surface of SiC and inorganic phosphate adhesive. Meanwhile, we determined the unreliability of estimating by Si peak. Taking E2-TO peak as reference, residual stress of six selected points was obtained. Then, we summarized the mechanism of compressive stress, and analyzed the stress change regulation.

Study on the Tensile Properties of Glass Fiber Reinforced Poly Cyclic Butylene Terephthalate Composites under and after High Temperature

A fatal disadvantage of continuously reinforced thermoplastic composites is the high melt viscosity of the matrix which hampers impregnation. However, the melt viscosity of low molecular weight cyclic butylene terephthalate resin can reach extremely low value, which simplifies impregnation and even allows for the use of thermoset production techniques resin transfer moulding. To solve the problem of the glass fiber reinforced poly cyclic butylene terephthalate composites applied in the environment of high temperature, the specimens of composite laminates were tested under and after different temperature. It has been observed that the tensile properties of GF/PCBT composites decrease with increasing temperature between room 25°C and 150°C and tend towards stability after the high temperature.