Linear-nonlinear stiffness responses of carbon fiber-reinforced polymer composite materials and structures: a numerical study

The stiffness response or load-deformation/displacement behavior is the most important mechanical behavior that frequently being utilized for validation of the mathematical-physical models representing the mechanical behavior of solid objects in numerical method, compared to actual experimental data. This numerical study aims to investigate the linear-nonlinear stiffness behavior of carbon fiber-reinforced polymer (CFRP) composites at material and structural levels, and its dependency to the sets of individual/group elastic and damage model parameters. In this regard, a validated constitutive damage model, elastic-damage properties as reference data, and simulation process, that account for elastic, yielding, and damage evolution, are considered in the finite element model development process. The linear-nonlinear stiffness responses of four cases are examined, including a unidirectional CFRP composite laminate (material level) under tensile load, and also three multidirectional composite structures under flexural loads. The result indicated a direct dependency of the stiffness response at the material level to the elastic properties. However, the stiffness behavior of the composite structures depends both on the structural configuration, geometry, lay-ups as well as the mechanical properties of the CFRP composite. The value of maximum reaction force and displacement of the composite structures, as well as the nonlinear response of the structures are highly dependent not only to the mechanical properties, but also to the geometry and the configuration of the structures

A note on the conceptual design of polymeric composite automotive bumper system

In this paper, a conceptual design approach to the development of polymeric-based composite automotive bumper system is presented. Various methods of creativity, such as mindmapping, product design specifications, brainstorming, morphology chart, analogy and weighted objective methods are employed for the development of composite bumper fascia and for the selection of materials for bumper system. The evaluation of conceptual design for bumper fascia is carried out using weighted objective method and highest utility value is appeared to be the best design concept. Polymer-based composites are the best materials for bumper fascia which are aesthetically pleasant, lighter weight and offer many more substantial advantages

Temperature profile of produced gas in oil palm biomass fluidized bed gasifier: effect of fibre/shell composition ratio

Malaysia is known to be one of the largest palm oil producers and also generates huge amounts of oil palm biomass, which is mainly treated as bio waste. One of the efficient methods to recycle this potential oil palm biomass could be gasification technology. Gasification is a process involving conversion of solid carbonaceous fuel into combustible gas using directly heated biomass. From processing of Fresh Fruit Bunch (FFB) (a biomass example), Empty Fruit Bunch (EFB) fibre, shell etc. are produced. In this study, a laboratory scale fluidized bed was developed, an appropriate fibre/shell composition ratio was studied and analysis on profiles of gas produced in the oil palm biomass fluidized bed gasifier was conducted. The effects of fibre/shell composition ratio and rate of reaction on temperature profiles were investigated. Temperature reaction rate and calorific value of oil palm biomass with gas compositions were also analyzed

Simulation and analysis for harvesting Dioscorea hispida tubers

This study discussed an analysis and simulation of fixture stand structure that will use for data collection of force required for harvesting the tubers of Dioscorea hispida. The tubers were surrounded by roots which were well gripped to the soil which made harvesting process difficult. Therefore, a new tool fixture equipped with digital force gauge device to gripped stem dioscorea hispida is required. Imada digital force measurement gauges are state-of-the-art, instruments capable of the highly accurate measurements required in quality testing to determine the strength or functionality of a part or product. The information from the experiments is used to model and simulate the tool in Computer Aided Design (CAD) environment. The solid modelling software Solidworks was used for the design, modelling and simulation of the equipment and the finite element analysis to determine the stress affected on various fixture designs

Microstrip to Parallel-Strip Nonlinear Transition Balun with Stubs and DGS for UWB Dipole Antenna

Three tapered baluns with nonlinear transition are developed for harmonic suppression in dipole antenna. The first balun consists of an exponential profile with the size of a quarter–wavelength for both the height and width with a wideband characteristic. However, for some applications such as narrowband harmonic suppression antennas and wideband-to-narrowband reconfigurable antennas, the suppression of higher operating band is desired. By employing stubs-filter and a defected ground structure (DGS), two narrowband tapered baluns are produced. They are named as an exponential balun-stub and an exponential balun-DGS, respectively, that operate from 1 to 2 GHz. A simulated and measured results that based on the reflection coefficient is found to be better than -10 dB from 1 to 2 GHz. The employment of the stubs and DGS have enabled these baluns to have the capability to reject the unwanted higher frequency band from 2.0 to 10 GHz. Finally, the proposed baluns are employed as a feeding circuit for an ultra wideband (UWB) circular dipole antenna that produces a reasonable outcome

The influence of equi-biaxially fabric prestressing on the flexural performance of woven e-glass/polyester reinforced composites

The flexural properties of plain-weave woven fabric-reinforced composites have been investigated to clarify the effects of equi-biaxially fabric prestressing on flexural characteristics. The prestressed composite samples were manufactured by applying the symmetrical tension load to both warp and weft yarns prior to matrix curing. The fabricated samples were tested under different fabric orientation angles, i.e. from warp to bias direction. The decline in the flexural properties of the prestressed composite due to matrix creep was checked. From three-point bending tests, the prestressed samples exhibited a maximum increase in the flexural performance, such as the strength and modulus, of ∼16% at a prestressing level of 50 MPa when compared with unprestressed counterparts. The level of improvement in the flexural properties reduced with increasing fabric orientation angle. The creep was induced in the prestressed matrix and subsequent decline in the improved flexural properties was indicated in the prestressed samples. The decline in flexural properties occurred mostly during the short-term creep

Curing behaviour of unsaturated polyester resin and interfacial shear stress of sugar palm fibre

Studies on the effect of cobalt of unsaturated polyester resin and the effect of treated sugar palm fibre with sodium hydroxide on single fibre strength and interfacial shear strength (IFSS) are presented in this paper. 1% of methyl ethyl ketone peroxide was used as the initiator, while cobalt of variable percentages (0.05%, 0.1%, 0.2%, 0.4 %,0.6%, 0.8% and 1%)was used as the hardener. The effects on glass transition and exothermic reaction of unsaturated polyester were studied for post curing temperature determination using differential scanning calorimetry by heating the samples at 10ºC/min heating rate from 30ºC to 120ºC with flowing of purge nitrogen gas atmosphere . For the single fibre test and IFSS, the treatment was carried out using sodium hydroxide solution with 1% concentration for one hour soaking time. Based on the optimisation percentage of cobalt, it was found that the higher the percentage of cobalt, the faster the sample tested to gel and cured. Treated sugar palm fibre exhibited better single fibre strength and IFSS between the matrices compared to untreated fibre due to the effectiveness of the alkali treatment. This can be attributed to the rearrangement of fibrils along the direction of tensile force and the removal of the coating layer and impurities after the alkaline treatment

Harmonic Suppression Dual-band Dipole Antenna with Parasitic Elements and a Stub

A dual-band harmonic suppression dipole antenna suitable for energy harvesting system is presented in this paper. A linear dipole with two parasitic elements is designed and fabricated with a capability to eliminate the harmonic of higher order modes. At first, the antenna resonates at 900 MHz and 2.7 GHz. Therefore, a parasitic element is added into each of the dipole’s arm to tune the second frequency band to 2.4 GHz to fit into wireless application. However, the presence of two parasitic elements has generated an unwanted harmonic at 4.0 GHz. Thus, a stub has been integrated into the antenna’s terminal (feed line) to suppress the 4.0 GHz frequency. This technique is suitable for developing a multiband antenna with harmonic suppression. The antenna is fabricated on a FR-4 board with the size of 72×152 mm2 which operates efficiently at 0.8 GHz and 2.4 GHz which is suitable for wireless communication applications. The prototype can suppress the undesired harmful harmonics present within the frequency range of 3 to 5 GHz. The antenna has a good potential to be used in a rectenna system with a dual-band frequency operation but with better performance. Simulation and measurement results obtained are in a good agreement, which have confirmed the proposed design concept

The mechanical performance of sugar palm fibres (Ijuk) reinforced phenolic composites

Sugar palm fibres are one of the natural fibres which have many features and need further study to understand their properties. The aim of this work is to investigate the flexural, compressive and impact properties of sugar palm fibres reinforced phenolic composites. Sugar palm fibres were used as a filler (particle size 150 μm) and with loading of 0, 10, 20, 30, and 40 vol.%. The fibres were treated by sea water and then fabricated into composites by hot press technique. Flexural, compressive, and impact tests were carried out as per ASTM D790, ASTM D695-08a, and ASTM D256 standards, respectively. Scanning electron microscopy (SEM) was used to investigate the morphology and the interfacial bonding of the fibres-matrix in composites. The results show that the mechanical properties of the composites improve with the incorporation of fibres. The composite of 30 vol.% particle loading exhibit optimum values which are 32.23 MPa, 61.66 MPa, and 4.12 kJ/m2 for flexural, compressive, and impact strength, respectively. This was because good compatibility of fibre-matrix bonding. Consequently, sugar palm fibre is one of the prospective fibres and could be used as a potential resource to reinforcement polymer composite

Creep test rig for cantilever beam: Fundamentals, prospects and present views

Cross arms in transmission tower are made up of Chengal wood, which degrade and collapse after a long period of service. This is due to creep deformation, and the rate of degradation is expedited due to exposure to extreme tropical climate. Hence, it is crucial to comprehend the early creep stage, which leads to structural failure. Apart from that, there are several research and industrial application gaps of these cross arms. For instance, creep life analysis of actual cross arms is still unexplored. In this study, the state-of-the-art is related to creep experiments and creep test rig designs, espacially on the creep test of a cantilever beam setup. The experimental methodologies implemented two vital approaches, conventional and accelerated techniques. The specific creep experiments on cantilever beam structure are emphasized and suggested in the manuscript as the building blocks for future design of cantilever creep test rig. This helps to guide future development design of cantilever beam creep test rig by fulfilling the specific criteria related to creep fundamentals, numerical modelling analysis, test operation for data evaluation, and development process. At the end, the challenges and improvements on the criteria existing design of test rigs are elaborated