Key Engineering Materials Vols. 334-335

Abstract: Microstructure and mechanical properties of ternary PP/POE/nano-CaCO3 composites were investigated. Two different phase structures were obtained mainly by adjusting processing sequence. The one-step process led to the isolated distribution of elastomer and CaCO3 particles in PP matrix, while the two-step one attained an encapsulated microstructure. In comparison with binary blends of PP/POE or pure PP, toughness of the ternary composites was significantly increased. Meanwhile, their stiffness and tensile strength kept nearly unchanged or slightly enhanced, implying that there is a synergistic effect between nano-CaCO3 and POE components.

Abstract: The scratch behavior of a set of model soft thermoplastic olefin systems containing at least 65 wt% of ethylene-propylene rubber (EPR) in polypropylene was analyzed using a standardized progressive load scratch test. It was found that raising the ethylene content in the EPR introduces crystalline phases, as evidenced by differential scanning calorimetry, and significantly alters the scratch behavior. A strong effect was also observed by changing the rate at which the scratch test was applied. This paper will discuss these effects based on the scratch damage mechanisms observed.

Abstract: The present work synthesized conductive composites consisting of waterborne polyurethane (WPU) and carbon black (CB). Besides the low percolation threshold (0.7
0.95wt%), the composites are quite sensitive to organic solvent vapors regardless of their polarities as characterized by the drastic changes in conductivity. In the case of polar solvents, negative and positive vapor coefficient phenomena of the composites were successively observed with a rise in CB content. It was found that different mechanisms are responsible for the broad applicability of the composites as candidates for gas sensing materials owing to the different interactions among the matrix polymer, the filler particles and the solvent molecules.

Abstract: Microcapsules self-repairing polymeric composites belong to a new kind of smart materials. In this work, microcapsules used for polymeric composites self-repairing were prepared by in-situ polymerization. Optical microscopy, scanning electronic microscopy (SEM), fourier transfer infrared spectroscopy (FT-IR), and thermal gravity analysis (TGA) were used to determine the properties of prepared microcapsules such as grain size and their distribution, wall thickness, content of core materials and thermal performances of microcapsules. Results showed that the average grain size was 210 μm and the wall thickness was in the range of 1.8-5 μm depending on agitation rate. Thermal analysis indicated that the repairing agent’s core materials were encapsulated in microcapsules.

Abstract: This paper explores the so-called “margin failures” observed in loaded curved bi-layer structures. Hemispherical bi-layer model test specimens consisting of glass shells with varying margin geometry filled with epoxy resin, simulating brittle crowns on tooth dentine, are loaded with compliant indenters along the (convex) axis of symmetry. Using this unique setup, the influence of margin geometry on margin failure is examined. Nearly all previous studies have utilised hard spherical indenters of various radii, and examined crack initiation and evolution at the contact point. However, the modes of fracture observed in this traditional contact problem, surface cone cracking or flexure-induced radial cracking initiate close to or inside the (small) contact area, and thus not explain the margin failures commonly observed by dentists. Crack growth at the margins distant from the contact zone cannot be generated under indentation using hard spherical indenters. The use of a compliant (soft) indenter distributes the indentation force over a large contact area, generating a compressive zone underneath the contact, and effectively inhibiting the modes of fracture typically observed using hard indenters (radial and cone cracking). Consequently, significant tensile stresses at the support margin become dominant, and the focus shifts to fracture initiating at the support margins. In this study, cylindrical indenters composed of PTFE Teflon, with a modulus several orders of magnitude lower than the indented materials, are used to examine margin fracture in brittle crown like structures. The specific focus is the effect of margin geometry – Chamfered; Round; Shoulder margins are examined, and their influences on crack initiation and damage evolution are reported.

Abstract: This paper uses Finite Element Analysis to examine stresses in loaded curved bi-layer structures. The model system consists of glass shells, both constant thickness and tapered, filled with dental composite. These systems, simulating brittle crowns on tooth dentine, are loaded with ultra-compliant disk indenters, and hard spherical indenters for comparison, along the (convex) axis of symmetry. The resulting maximum principal stress patterns are analysed. Previous studies have generally utilised hard spherical indenters of various radii indenting constant thickness coatings, and examined stresses leading to crack initiation. However, the peak stresses observed in this traditional contact problem – inducing surface cone cracking or flexureinduced radial cracking - occurred close to or inside the (small) contact area, and do not explain the margin failures in dental crowns commonly observed by dentists. Furthermore, the effect of varying coating thickness, especially tapering towards thinner margins, has not previously been examined. The use of an ultra-compliant indenter distributes the indentation force over a large contact area, generating a compressive zone underneath the contact, and consequently, previously insignificant stresses at the support margin become dominant, and the focus shifts to the support margin, rather than the area close to the contact. In this study, balsa wood is used as the disk indenter model material, with a modulus several orders of magnitude lower than the indented materials. Stress patterns from the same systems indented by hard spherical indenters are included for comparison. The specific focus is the effect of tapered coatings, examining stress patterns from several geometries. Results confirm not only a shift in the peak maximum principal stress from the near-contact area (under hard spherical indenters) to the margin area (under ultra-compliant indenters), but also show that coating taper can have a significant influence on the margin stress under a soft indenter. In the same systems indented by a hard indenter, coating taper has very little effect on the more localised stresses induced.

Abstract: Fiber Reinforced Plastics (FRPs) are now under research as crush element because of its contribution in energy absorption. The 3D-textile braiding was introduced in this study as a reinforcement form of fibers. The CFRP square tubes with rectangular cross section were tested in quasi-static experiments. The results show that 3D structure was effective in holding back the propagation of the central crack and the composite tube with a design on the corners could perform better energy absorption capability.

Abstract: Fiber reinforced composite
materials
have been applied widely to many structures, because they have some advantages like easy handling, high specific strength, etc. The numerical method like finite element method has been applied to design and to evaluate the material properties and behavior as the development of Computer Aided Engineering. It is very difficult to calculate with accuracy not only in structural scale but also in detail material scale (for example, the order of fiber diameter) by the traditional FEM, because
composite
materials like woven fabric composites have the geometrical complexity
and the large difference between above mentioned scales.
The development of multi-scale analysis method is one of the major topics in computational mechanics. Mesh superposition
is one of multi-scale analysis methods and is an effective method to solve the problems which have the large difference between the structure scale and the reinforcement scale. We have expanded the finite element mesh superposition method with 3 scales
and have defined as M3 (Macro-Meso-Micro) method. In this paper, we have proposed a new approach method combined with M3 method and homogenized method to obtain the mechanical properties and to simulate the behavior of woven fabric composites. In addition, the elastic-plastic mechanics and the damage mechanics
have been introduced into M3 method to investigate the effects of matrix-crack on the structural and material properties. From the numerical results, it is revealed that it is very useful for the evaluation of mechanical properties of composite materials.

Abstract: This paper describes an on-going study to investigate the efficacy of a steel-composite hybrid pipe material for applications in highly corrosive and extreme pressure conditions. The study, covering aspects of costs, design and qualification testing, has been carried out using an actual 10-in condensate steel pipeline as the basis for comparison. On the whole it has been concluded that the hybrid pipe material has the potential to substitute metal pipelines where corrosion resistance and high pressure are major drivers, although assessment is continuing.