Mainul Islam

Manufacture of Syntactic Foams Using Starch as Binder: Post-Mold Processing

Syntactic foam manufacturing method, ‘post-mold processing,’ based on the buoyancy of hollow microspheres was studied for potential building material applications. The post-mold processing involves mixing starch particles and ceramic hollow microspheres in water. It was found starch particles tend to adhere to hollow microspheres, forming agglomerations, during mixing. It was also found that “volume fraction of starch particles on a microsphere making a relative density of 1.0” (VFSMRD) is an indicator for mixture volume transitions. Both the maximum total volume expansion of mixture and a transition in formation, after phase separation, of mixture volume in water referred to as “top phase” in a mixing container were taken place at a calculated VFSMRD. It was found that hollow microsphere size effect on attracting starch particles was relatively high but IBVMS effect was not significant. Also, no effect of water volume for a given diameter of cylindrical container was found. Starch-microsphere inter-distance was discussed and considered to be an important parameter affecting starch content in an agglomeration. A Simple Cubic cell model for the starch-microsphere inter-distance was adopted to quantitatively explain various effects on starch content in agglomeration such as hollow microsphere size, initial bulk volume of hollow microspheres (IBVMS), and water volume. Further, the following were found for manufactured syntactic foams: (a) volume fraction of starch in foam is of linear relation with starch content before mixing for a given experimental data range and (b) shrinkage is relatively high for small hollow microspheres with high starch content.

Sandwich composites made of syntactic foam core and paper skin: Manufacturing and mechanical behavior

Novel sandwich composites made of syntactic foam core and paper skin were developed as potential building materials. Interface bonding between core and skin was controlled by varying starch content. Two different microsphere size groups were employed for syntactic foam core manufacturing based on the pre-mold processing method. Properties of skin paper with starch adhesive on were found to be affected by drying time of starch adhesive. Mechanical behavior of manufactured sandwich composites in relation with properties of constituent materials was studied. Skin paper contributed to increase up to 40% in estimated flexural strength over syntactic foams, depending on starch content in adhesive between syntactic foam core and paper skin. Small microsphere size group for syntactic foam core was found to be advantageous in strengthening of sandwich composites for a given starch content in adhesive. This finding was in agreement with calculated values of estimated shear stress at interface between skin and core. Failure process of the sandwich composites was discussed in relation with load–deflection curves. Cracking of syntactic foam core was detected to be the first event in sandwich composite failure sequence. Hygroscopic behavior of syntactic foam panels was investigated. Moisture content in the foam was measured to be high for high starch content in the foam panels. No significant moisture effect on flexural strength of syntactic foam panels after being subjected to moisture about 2 months was found for both microsphere size groups. However, substantial decrease (28%) in flexural modulus was found for the foam panels made of large microspheres although not much moisture effect was found on that of small microspheres.

Quantitative and qualitative analyses of mechanical behavior and dimensional stability of styrene-based shape memory composites

The effect of glass fiber reinforcement on the mechanical properties and geometrical shape stability during the thermomechanical cycle of the shape memory polymer composite has been investigated. A substantial improvement in the mechanical properties due to glass fiber reinforcement has been realized. However, unexpected deformation has been observed during heating process, particularly in the first thermomechanical cycle. This unanticipated deformation negatively affects the geometrical shape stability of the composite, and as a consequence the geometry preciseness of the structural parts manufactured with shape memory polymer composites will be reduced. In this article, the unanticipated thermal deformation in the shape memory polymer composites during the heating has been observed experimentally, and constitutive relationships to describe this behavior have been developed. Furthermore, an application of a constant tensile load during the heating process on the shape memory polymer composite part was found to be a reliable solution to reduce the thermal distortion effect and improve the geometric stability of the composite. The results showed that developed constitutive relations have shown a good agreement with the experimental results. Furthermore, the proposed applied tensile load has shown significant improvement in the shape memory polymer composite samples’ geometrical shape stability when subjected to a temperature increase.

Temperature Effects on Full Scale FRP Bridge Using Innovative Composite Components

Numerous large-scale demonstrator projects around the world have shown the viability of composite materials for bridge applications. Most of the projects have been directed towards the better understanding of bridge behaviour in strength and serviceability. However, the behaviour under different environmental conditions and longer term effects on durability are yet to be fully understood. This paper presents the results of an investigation on effects of temperature change into the structural behaviour of a FRP demonstrator trial bridge. It was installed at the University of Southern Queensland, Toowoomba Campus using innovative sandwich composites. It has been found that temperatures in different locations of the bridge vary for different locations within the bridge. The variation is found to reverse during day and night time. Based on the meas-ured temperature variation, some important recommendations are provided on the effects of temperature for innovative fibre composite bridge.

Compressive strength characterization of polyester based fillers

This paper investigates the compressive properties of polyester based fillers with different proportions of resin, sand and fly ash. The research program aims at developing a polymer based filler for a glass fibre reinforced polymer (GFRP) tube to be used as a structural rehabilitation system. It has been initiated to improve fundamental understanding of this material and to provide the knowledge required for its broad utilization. In this development, sample trial mixes were considered based on several weight percentages of polyester resin, fly ash and sand. These weight percentages were selected after analyzing volumetric properties of sand. The effect of resin (binder), sand and fly ash contents on the compressive strength of polyester based fillers with respect to age is reported. It has been found that at the age of 7 days all the batches reached about 90% of the compressive modulus. The experimental compressive stress-strain curves reported here were compared with established analytical models for normal strength concrete.

Use of an elasto-plastic model and strain measurements of embedded fibre Bragg grating sensors to detect Mode I delamination crack propagation in woven cloth (0/90) composite materials

Mode I fracture analysis being employed to study delamination damage in fibre-reinforced composite structures under in-plane and out-of-plane load applications. However, due to the significantly low yield strength of the matrix material and the infinitesimal thickness of the interface matrix layer, the actual delamination process can be assumed as a partially plastic process (elasto-plastic). A simple elasto-plastic model based on the strain field in the vicinity of the crack front was developed for Mode I crack propagation. In this study, a double cantilever beam experiment has been performed to study the proposed process using a 0/90-glass woven cloth sample. A fibre Bragg grating sensor has embedded closer to the delamination to measure the strain at the vicinity of the crack front. Strain energy release rate was calculated according to ASTM D5528. The model predictions were comparable with the calculated values according to ASTM D5528. Subsequently, a finite element analysis on Abaqus was performed using ‘Cohesive Elements’ to study the proposed elasto-plastic behaviour. The finite element analysis results have shown a very good correlation with double cantilever beam experimental results, and therefore, it can be concluded that Mode I delamination process of an fibre-reinforced polymer composite can be monitored successfully using an integral approach of fibre Bragg grating sensors measurements and the prediction of a newly proposed elasto-plastic model for Mode I delamination process.

Development of fracture and damage modeling concepts for composite materials

An overview of proposed micro-crack based damage models for fibre reinforced composite plates is presented. A critical analysis has been performed on the potential application of those models for damage accumulation analysis of wide range fibre reinforced composite materials. The flaws and drawbacks of those models were critically analysed and presented in the text. Interestingly, it has been found that some proposed models can be extended or modified to address unresolved issues in crack propagation and damage accumulation in fibre reinforced composites. It can be concluded that the micromechanical approach alone is not sufficient to evaluate complete damage accumulation of composite and a significant theoretical modifications are required for existing brittle damage models before applying them to fibre reinforced composite materials. The goal of the current paper is an overview of the numerical approaches and approaches’ limitation of plate with multiply cracks problem. The used approaches is discussed and summarized. Equations for two or three dimensions of plate is given for studying effect of crack density on effective moduli. The insensitive effective moduli to the sizes, orientation and location of individual microcracks is also discussed. In addition, the problem associated with limitation of the exciting approaches with increasing cracks density conditions is summarized to approve that necessary modifications the numerical approach and corrections are required. Due to an increase interest in using a fracture mechanics based on microcracks numerical approaches to assess the damage of composite structures, the laminated composites selected as example. The micromechanics approach is not enough to evaluate damage and also most of current theoretical need modification for simulate real conditions.

Fabrication and Characterization of Unidirectional Silk Fibre Composites

Natural fibres offer a number of benefits as reinforcement for synthetic polymers since they have high specific strength and stiffness, high impact strength, biodegradability etc. The aim of this study is to fabricate and determine the performance of unidirectional silk fibre reinforced polymer composites. In the present initial study, alkali treated silk fibres were incorporated as reinforcing agent, while a mixture of 20% maleic anhydride grafted polypropylene (MAPP) and commercial grade polypropylene (PP) was used as matrix element. The unidirectional composites were fabricated by using hot compression machine under specific pressure, temperature and varying fibre loading. Tensile, flexural, impact and hardness tests were carried out by varying silk fibre volume fraction. Composites containing 45% fibre volume fraction had higher tensile and flexural strength, Young’s modulus and flexural modulus compared to other fabricated composites including those with untreated silk fibres. SEM micrographs were taken to examine composite fracture surface and interfacial adhesion between silk fibre and the matrix. These micrographs suggested less fibre pull out and better interfacial bonding for 40% fibre reinforced composites.

Mechanical and thermal properties of glass fiber–vinyl ester resin composite for pipeline repair exposed to hot-wet conditioning

Fiber-reinforced composites are a well-recognized option for repair and rehabilitation of the pipelines for the oil and gas industry. Infilled composite sleeve system provides an effective rehabilitation solution, where the sleeve acts as prime reinforcement without any direct contact with steel. However, the long-term performance of the repair is dependent, in part, on the effect of hygrothermal ageing of the composites. In this publication, glass transition temperature and mechanical properties are compared for glass-fiber reinforced vinyl ester composite, both as-manufactured and after hot-wet conditioning at 80℃. The tensile and shear strength reduced substantially during conditioning, whilst the elastic modulus was relatively stable. The average glass transition temperature of the composite dropped from the as-manufactured value of 110℃ to 97℃ and 101℃, after 1000 and 3000 h of conditioning, respectively, indicating that it is stable and that the composite is suitable for use as a pipeline repair material operating at 80℃. The results indicate that a 1000 h conditioning period, specified as a minimum period in ISO/TS 24817 is suitable for representing long-term properties for stiffness-based designs for the composite material and conditioning temperature investigated.

Smart structure for small wind turbine blade

Wind energy is seen as a viable alternative energy option for future energy demand. The blades of wind turbines are generally regarded as the most critical component of the wind turbine system. Ultimately, the blades act as the prime mover of the whole system which interacts with the wind flow during the production of energy. During wind turbine operation the wind loading cause the deflection of the wind turbine blade which can be significant and affect the turbine efficiency. Such a deflection in wind blade not only will result in lower performance in electrical power generation but also increase of material degradation due high fatigue life and can significantly shorten the longevity for the wind turbine material. In harnessing stiffness of the blade will contribute massive weight factor and consequently excessive bending moment. To overcome this excessive deflection due to wind loading on the blade, it is feasible to use shape memory alloy (SMA) wires which has ability take the blade back to its optimal operational shape. This paper details analytical and experimental work being carried out to minimize blade flapping deflection using SMA.