Advanced Materials Research Vols. 41-42

Abstract: A special test setup was designed and used in compression shear test of unidirectional carbon fiber composites to study the effect of short fiber interleaves (SFIs) on the interlaminar shear behavior. The comparative tests for two kinds of double-notched compression specimens, with and without SFIs, were carried out to determine the interlaminar shear strength and modulus (ILSS and ILSM) and to examine the failure characteristics. To determine ILSM of the specimens with SFIs an inversion analysis method was proposed based on comparing compression displacement of specimens with and without SFIs. The experimental results show that SFIs makes ILSS decreasing due to lower interface strength, and the complex damage process of SFIs leads to a considerable increase of interlaminar shear compliance.

Abstract: A micro-mechanical model and simulation for the damage behavior of short fiber interleaves (SFIs) were developed based on Mori-Tanaka method and an equivalent approach to interface debonding (Fitoussi etc 1990). The damage evolution and the stress-strain relation of SFIs have been predicted in the cases of interlaminar shear, out-of and in-plane tension, respectively. The simulation indicates that the damage always starts from the interface debonding of fibers perpendicular to load and the matrix cracking in the direction parallel to fibers, and then rapidly spreads to more fibers during loading. The strength and the ultimate strain in out-of-plane tension are much lower than that in interlaminar shear and in-pane tension. The strength and failure probability of interface bonding are the most considerable factors to affect the damage and failure of SFIs. The comparison of the simulation with the interlaminar shear test shows a good agreement.

Abstract: Corrosion rates and anode polarization curves of RE-Ni-W-P-SiC-PTFE composite coatings in various concentrations of sulfuric acid and hydrochloric acid solutions have been studied. Results show that corrosion law of the RE-Ni-W-P-PTFE-SiC composite coatings in various concentrations of sulfuric acid solutions is identical. The corrosion rates of the composite coatings are increased with increasing sulfuric acid concentration while the corrosion rates are decreased with increasing concentration of hydrochloric acid. Anode polarization curves of RE-Ni-W-P-SiC-PTFE composite coatings in various concentrations of sulfuric acid and hydrochloric acid solutions have showed that anode polarization electric current density of the composites at 200°C or 500°C heat treatment was below that at other heat treatment, it is clear that the composite coatings at 200°C or 500°C heat treatment has better corrosion resistance.

Abstract: The flexural behaviour of 6-ply unidirectional hybrid fibre-reinforced polymer (FRP) matrix composites containing a mixture of E-glass and S2-glass fibres was investigated. A high performance epoxy system comprising of Kinetix® R240 epoxy resin (combined with Kinetix® H160 epoxy hardener) was utilised for the composite matrix. Flexural testing was conducted in accordance with Procedure A of the ASTM D790-03 test standard on a universal testing machine equipped with a three-point bend test rig. In addition to varying the stacking configurations of the composite prepregs, the influence of span-to-depth ratio on the flexural properties and failure mechanisms was also studied. The failure mechanisms of the resulting fractured specimens were characterised using optical microscopy and compared with those noted by the authors in previous work.

Abstract: The blast-resistant of an aluminum foam sandwich structure under impact has been investigated. Plastic deformation and load distributions in each of the sub-layers during and after impact were calculated by the material point method with the consideration of strain rate effect on deformation of the aluminum foam. The numerical results from the 3D material point method modeling show that the blast-resistant capability of the aluminum foam sandwich structure is excellent, and the energy absorbability of the structure would be underestimated if the strain rate effect on the aluminum foam is ignored.

Abstract: Effects of the concentrations of solid particles in the bath and plating conditions on chemical components and polarization curves of oxygen separating out were studied by use of PARSTAT2263 electrochemistry testing instrument made by Research Center of Princeton and EPMA-1600 electron probe X-ray diffraction. And the results show that kinetic parameters of oxygen evolution of the obtained Al/Pb-WC-ZrO2 composite electrode materials are a=771mV, b=140mV, i0=3.11×10-6A·cm-2, and oxygen overvoltage is η=1009mV. The contents of WC and ZrO2 particles in the Al/Pb-WC-ZrO2 composite coating are 10.02wt% and 3.55wt% respectively when plating conditions are as follows: WC:50g/L,ZrO2:40g/L, bath temperature: 20°C, electric current density: 1.5A/dm2, plating time: 2h.

Abstract: With the increasing demands of energy efficiency and environment protection, composite materials have become an important alternative for traditional materials. Composite materials offer many advantages over traditional materials including: low density, high strength, high stiffness to weight ratio, excellent durability, and design flexibility. Despite all these advantages, composite materials have not been as widely used as expected because of the complexity and cost of the manufacturing process. One of the main causes is associated with poor dimensional control. General curved composite parts are often used as the structural components in the composite industry. Due to the anisotropic material nature, process-induced dimensional variations make it difficult for tighttolerance control and limit the use of composites. This research aims to develop a practical approach for the design of general curved composite parts and assembly. First, the closed-form solution for the process-induced dimensional variations, which is commonly called spring-in, was derived. For a general curved composite part, a Structural Tree Method (STM) was developed to divide the curve into a number of pieces and calculate the dimensional variations sequentially. This method can be also applied to an assembly of composite parts. The approach was validated through a case study. The method presented in this paper provides a convenient and practical tool for the dimensional and tolerance analysis in the early design stage of general curved composite parts and assembly, which is extremely useful for the realization of affordable tight tolerance composites. It also provides the foundation of Integrated Product/Process Development (IPPD) and Design for Manufacturing/Assembly (DFM/DFA) for composites.

Abstract: Process and properties of pulse electrodeposited RE-Ni-W-P-SiC composite coatings were studied. The results show that the deposited rate by pulse current is larger than that by direct current; the deposited coatings by pulse current are better than that by direct current in corrosion resistance and microhardness. And the corrosion resistance of the coatings with pulse current is better than that of stainless steel (1Cr18Ni9Ti). The duty ratio and the pulse frequency in the process of electrodeposition have a large influence on the deposition rate, the composition and the properties of coatings. SEM measurement shows that the crystals with pulse current are smaller and the surface is smoother than that by direct current. It is beneficial to make crystalline grain finer by mixing rare earth.

Abstract: The safe operation of both thermal and nuclear power plant is increasingly dependent upon structural integrity assessment of pressure vessels and piping. Furthermore, structural failures most commonly occur at welds so the accurate design and remnant life assessment of welded plant is critical. The residual stress distribution assumed in defect assessments often has a deciding influence on the analysis outcome, and in the absence of accurate and reliable knowledge of the weld residual stresses, the design codes and procedures use assumptions that yield very conservative assessments that can severely limit the economic life of some plant. However, recent advances in both the modeling and measurement of residual stresses in welded structures and components open up the possibility of characterising weld residual stresses in operating plant using state-of–the–art fully validated Finite Element simulations. This paper describes research undertaken to predict residual stresses in stainless steel welds in order to provide validated reliable, accurate Structural Integrity assessment of nuclear power plant components

Abstract: Structural health monitoring or damage detection has long been a research interest for its great potential for life safety and economic benefits to the industrialized world. Structural vibration behavior is an essential signature of the integrity of structures and hence has been used for damage detection. Structural vibration impedance by way of piezoceramic patch excitation offers a local damage detection technique. It has been known that temperature change has adverse effects on the measured impedance result and can complicate the damage analysis. It is believed that one way of temperature influence on vibration is through adding thermal prestress to the structure. Prestress affects vibration in different ways on different structures and application problems. For the impedance method, prestress comes not only from temperature change but also from other sources such as wind, gravity and working load. This paper deals with prestress effects in the context of local vibration behavior of structures. A theoretical analysis is given on how prestress affects the vibration. Experimental impedance measurement results for piezoceramic patch excited vibration of simple structures such as plates under prestress are presented.