Mixed-Mode Delamination Failures of Quasi-Isotropic Quasi- Homogeneous Carbon/Epoxy Laminated Composite

This chapter characterised the delamination behaviour of a quasi-isotropic quasi-homogeneous (QIQH) multidirectional carbon/epoxy-laminated composite. The delaminated surface constituted of 45°//0 layers. Specimens were tested using mode I double cantilever beam (DCB), mode II end-notched flexure (ENF) and mixed-mode I+II mixed-mode flexure (MMF) tests at constant crosshead speed of 1 mm/min. Results showed that the fracture toughness increased with the mode II component. Specifically, the mode I, mode II and mixed-mode I+II fracture toughness were 508.17, 1676.26 and 927.52 N/m, respectively. When the fracture toughness values were fitted using the Benzeggagh-Kenane (BK) criterion, it was found that the best-fit material parameter, η, was attained at 1.21. Furthermore, fibre bridging was observed in DCB specimens, where the steady-state fracture toughness was approximately 80% higher compared to the mode I fracture toughness. Finally, through scanning electron micrographs, it was found that there was resin-rich region at the crack tip of the specimens. In addition, fibre debonding of the 45°layer was found to be dominant in the DCB specimens. Significant shear cusps were noticed in the ENF specimens. As for the MMF specimens, matrix cracking and fibre debonding of the 0°layer were observed to be the major failure mechanisms

Non-Fickian Absorption Characteristics of Adhesive Joints: Capillary Effects and Residual Properties

Mechanical performance of polymer-based adhesive joints is generally susceptible to moisture absorption. This study quantifies the effects of moisture content on the strength, stiffness, and energy properties of adhesive bonded joints. For this purpose, moisture absorption characteristics of structural adhesive joints (Araldite 2015) with different thicknesses (0.5, 1.0, and 1.5 mm) were firstly established under accelerated aging condition (deionized water at 60 oC). A thickness-dependent non-Fickian moisture absorption model was then used to characterize the moisture absorption of the adhesive joints. Results suggested that the moisture absorption of the adhesive joints was governed by the capillary action. Subsequently, adhesive joints with aluminum 6061 adherent and 0.5 mm-thick Araldite 2015 adhesive compound were subjected to dry, 0.1, 0.15, 0.18, and 0.2 pct of moisture content. The specimens were tested in shear and tension loadings at 1 mm/min. The resulting variations in the mechanical properties were fitted using a residual property model. It was noticed that all properties degraded upon moisture attack. For strength and energy properties, the degradation was more severe in tension. As for the stiffness, the decrease in the property was similar in both tensile and shear. The results from this study showed that moisture attack is an important aspect to be considered when designing for the service lifetime of adhesive bonded structures

Mechanical properties of bamboo and bamboo composites: a review

This article discuses on the studies that have been done by previous researchers on the mechanical properties of bamboo. Nowadays, natural fibre composites have gained the attentions of many industries as alternative materials due to their various advantages such as sustainable, abundant, low cost and good specific strength. With the current emphasis on environmental friendliness and sustainability, natural fibre composites are more preferred over conventional fibre which is normally non-biodegradable. Bamboo is a type of natural fibre composites that are widely used in many industries such as in construction and furnishing. Hence, it is crucial to study the mechanical properties of bamboo to make sure it is safe for certain applications. However, there are many factors that determine the mechanical properties of bamboo such as species, age and so on. This journal compiles and reviews on some of the researches on the mechanical properties of pure bamboo and bamboo composites such as their tensile properties, compressive properties, impact strength and fracture toughness. The reviews include how the researchers set up their experiments, the bamboo species used and the results obtained. Since bamboo are constantly exposed to harsh environment such as rain and river, the effect of moisture/ water content on the mechanical properties of bamboo are also reviewed and it exposed that moisture content has drastic effect on the mechanical properties of bamboo

Moisture absorption effects on mode II delamination of carbon/epoxy composites

It is necessary to consider the influence of moisture damage on the interlaminar fracture toughness for composite structures that are used for outdoor applications. However, the studies on the progressive variation of the fracture toughness as a function of moisture content M (%) is rather limited. In this regard, this study focuses on the characterization of mode II delamination of carbon/epoxy composites conditioned at 70 °C/85% relative humidity (RH). End-notched flexure test is conducted for specimens aged at various moisture absorption levels. Experimental results reveal that mode II fracture toughness degrades with the moisture content, with a maximum of 23% decrement. A residual property model is used to predict the variation of the fracture toughness with the moisture content. Through numerical simulations, it is found that the approaches used to estimate the lamina and cohesive properties are suitable to obtain reliable simulation results. In addition, the damage initiation is noticed during the early loading stage; however, the complete damage is only observed when the numerical peak load is achieved. Results from the present research could serve as guidelines to predict the residual properties and simulate the mode II delamination behavior under moisture attack

The influence of woven density on tensile properties of hybrid kenaf/glass composites

The synergy of natural fibre and synthetic fibre reported to overcome natural fibre drawback. This study focus on, plain weave of kenaf fibre with different weaving density effects on its tensile properties in hybridization with non-woven mat glass. The weaving density directly affect composites fibre loading, increased in weaving density hence increase fibre loading and composite weight. Two type of woven kenaf fabrics were weaved by lab scale self-designed hand loom, varies in warp direction. For comparison purposes, kenaf composite for both type of woven kenaf fabricated by compression moulding. The tensile properties and its failure mechanism were revealed in this study. Kenaf composite with higher woven density shows slightly reduce it tensile strength even though increased in composite fibre loading. Both kenaf composites achieved tensile strength at 83.85 MPa and 75.61 MPa respectively. However, tensile modulus calculated as comparable for both composites with results as 8.92 MPa and 8.29MPa. Hybrid kenaf/glass composites however exhibits, drastic drop in tensile strength and modulus effect of weaving density. Drop in tensile strength about 28% with increased in weaving density, hybrid kenaf low woven density tensile strength measured at 85.5 MPa meanwhile hybrid kenaf high weaving density composites dropped to 51.7 MPa. Tensile modulus for the composites measures at 9.88 MPa and 6. 75 MPa for low and high woven density hybrid composites respectively. Failure mechanism analysis has found that fracture was dominantly by kenaf yarn in both parameters

Displacement rate effects on the mode II shear delamination behavior of carbon fiber/epoxy composites

This paper studies the influence of displacement rate on mode II delamination of unidirectional carbon/epoxy composites. End-notched flexure test is performed at displacement rates of 1, 10, 100 and 500 mm/min. Experimental results reveal that the mode II fracture toughness GIIC increases with the displacement, with a maximum increment of 45% at 100 mm/min. In addition, scanning electron micrographs depict that fiber/matrix interface debonding is the major damage mechanism at 1 mm/min. At higher speeds, significant matrix-dominated shear cusps are observed contributing to higher GIIC . Besides, it is demonstrated that the proposed rate-dependent model is able to fit the experimental data from the current study and the open literature generally well. The mode II fracture toughness measured from the experiment or deduced from the proposed model can be used in the cohesive element model to predict failure. Good agreement is found between the experimental and numerical results, with a maximum difference of 10%. The numerical analyses indicate crack jump occurs suddenly after the peak load is attained, which leads to the unstable crack propagation seen in the experiment

Influence of ball burnishing on surface quality and tribological characteristics of polymers under dry sliding conditions

In this paper, the application of ball burnishing as a new surface treatment process for polymers is investigated. The polymers used were polyoxymethylene (POM) and polyurethane (PUR). The lowest surface roughness value achieved for POM was 0.44 µm (45% decrease) and for PUR was 0.46 µm (42% decrease). The lowest coefficient of friction value achieved was 0.22 (32.9% decrease) for POM and 0.24 (28.8% decrease) for PUR. The lowest specific wear rate value achieved was 0.31×10 -6 mm 3/N m (38.6% decrease) for POM and 0.41×10 -6 mm 3/N m (37.9% decrease) for PUR

Stress analysis of femur and femoral stems for hip arthroplasty

Osteoarthritis is the major reason that causes hip problem. According to Cristofolini (1997), there are more than 800,000 hip replacements being implanted worldwide annually. It is important to know the performance of hip prostheses especially the stability and the longevity. In this project, numerical simulation based on finite element method is used to analyze the mechanical behavior of femur-implant system. Finite element analysis is carried out on three-dimensional model of a human femur on both full and half models. This is to investigate the behavior of an intact femur under loading. Then, the analysis is repeated for an Anatomic Medullary Locking (AML) hip prosthesis, which is of one type of cementless hip prosthesis, implanted inside the femur. This is only done on half femur model. Both the stem and the head are made by Cobalt Chromium Molybdenum (CoCrMo). After that, the analysis is carried out on a cemented hip prosthesis. The cement is made by polymethylmethacrylate (PMMA), which is of flexible polymeric cement. The hip prosthesis model used for analysis is of Charnley type. The study on the stem length effect is then done. Lastly, the analysis is repeated for cancellous with different density. The cortical, cancellous, metal and cement are assumed to be linear, elastic, isotropic and homogeneous. Linear elastic analysis is adapted and maximum principal stress/strain and von Mises stress are the criterions that are of concern. Results show that both full and half femur modeling give similar stress distribution. Besides, the treated femur is always understressed at the upper most region of the femur. Cemented type of total hip replacement (THR) gives a better stress distribution on the femur compared to cementless type. In addition, hip prosthesis with shorter stem induces the stresses more evenly on the femur. Also, different cancellous density does not significantly affect the stresses

Impact behavior of short and continuous fiber-reinforced polyester composites

In this study, the impact strengths of E-glass, coir, oil palm as well as E-glass/coir and E-glass/oil palm hybrid polyester composites were studied. All types of composites were reinforced with fiber volume fractions of 30%, 40%, and 50% and fiber lengths 3, 7, and 10 mm. Composite laminates reinforced with longitudinal and transverse coir fiber mats were also studied. The number of fiber mats varied from 1, 2, 3, and 4 layers for non-spaced fiber mats and 2, 3, and 4 layers for 1.5 mm spaced fiber mats. Besides, coir-polyester composite with addition of sand filler was studied as well, with 40%, 50%, and 60% of volume fractions and fiber lengths of 3, 7, and 10 mm. Results show that impact strength improves with fiber content and fiber length. In addition, longitudinal fiber mats always exhibit better impact toughness compared to transverse fiber mats. Impact strength is improved with the number of fiber layers but worsened by the fiber spacing. As for coir/polyester concrete, low fiber content and fiber length improve the impact strength. The fractured surfaces were inspected under scanning electron microscope to investigate the fracture mechanisms in each type of composites

Effect of fibre orientation on the scratch characteristics of E-glass fibre-reinforced polyester composite

Recent patents on newly developed composites show that the application of fibres can be used to enhance the structural integrity of polymers. In this work, the scratch behaviour of E-glass fibre-reinforced polyester composites is investigated. The composites are prepared for different fibre orientations, longitudinal, transverse and random. The scratch force is lower for polyester composites with longitudinal orientated fibres compared to transversely aligned orientation. The introduction of glass fibres increases the scratch hardness of polyester