Flexural Strength Results Research Articles

Strength of Continuous Fibres Reinforced Composites

The strength values of continuous fibre/plastic composites, with different fibre-matrix bond strengths, different fibre and matrix failure strains, different failure types, obtained on coupon of different dimensions, have been analysed. The analysis has been based on the results of tensile, compression and flexural strength of carbon/epoxy, carbon/polyester and glass/polyester composites. Strength results have been correlated with the component characteristics and to the failure processes during testing. The effect of strength decrease with an increase in coupon dimensions has been considered as size effect, applying the Weibull statistical theory and Wisnom fibre model of noncatastrophic failure. Strength results obtained in different tests have been mutually compared and the influence of non-linear elastic behaviour of carbon fibres has been included to explain flexural strength.

Effect of moisture content on the properties of silanized jute‐epoxy composites

AbstractThe composites investigated in this article were epoxy resins reinforced with jute‐fibers. The jute‐fibers were modified with an epoxyfunctional‐γ‐glycidoxypropyltrimethoxy‐silane (A‐187 from Osi‐Specialtis GmbH, Germany), which works as a coupling agent between fiber and matrix. The introduction of the coupling agent distinctly influences the mechanical properties of the composite: Dynamic modulus was doubled, damping was reduced by about 50%, and the Wöhler curves showed fatigue limits increased by about 20%. The investigations pointed out further that the moisture uptake of composites with silanized fibers was reduced by about 10–20%. Moisture at equilibrium and kinetics of absorption increase with increasing fiber content. Finally, the application of the coupling agent caused a reduction of moisture effects on mechanical properties. Tensile strength, tensile modulus, and fatigue strength under repeated tensile stress were reduced up to 30%. This tendency was not duplicated in the results for flexural strength and flexural modulus.

Novel composites utilizing raw wool and polyester resin

Considerable research has been conducted with natural fibres as a source of reinforcement for organic matrices. These fibres have included wood pulp, sisal, hemp and numerous other plants [1–3]. However, little attention has been given to natural animal fibres such as wool and hair. Traditionally, wool fibres have been spun into multilayer fibres in the form of threads, which are then knitted into cloth and utilized for the manufacture of garments. As a composite, wool fibres have been combined with polyester fibres and spun into multistrand yarn as threads, again for use in garments. The major engineering application of these composites has been for thermal insulation for the human body. In general, the mechanical properties were not considered relevant for cloth applications. This study seeks to investigate the mechanical properties of a new form of wool–polyester composite, i.e. the reinforcement of raw wool fibres (before spinning into thread or yarn) with a polyester resin matrix for use in structural applications not associated with clothes. Raw wool is one of the major export commodities of a number of countries, including Australia. It is one of the oldest naturally renewable fibres in use. It is epidermal in origin and grown naturally on the bodies of sheep. The wool is obtained by shearing the fleece from the sheep, and then graded, washed and combed to remove any extraneous matter such as grease, dirt, moisture and vegetable matter. The fibres are generally entangled and crimped. In this study, the wool fibres were supplied by the CSIRO Division of Wool Technology. The fibre was classified as fine, clean carded wool, i.e. washed and combed with all foreign matter removed. The composite matrix was prepared from polyester resin with 1% hardener (methyl ethyl ketone peroxide). Samples of composite sheets were prepared in the laboratory from skeins of wool laid alternatively with layers of resin mixture, and placed in a rectangular mould. This was repeated until the required fractions of wool and resin were achieved. The top of the mould was sealed and hydraulic pressure of 1.2 MPa was applied for a period of 24 h. The pressure was then reduced to 0.6 MPa, the sample sheet was removed and excess solid resin trimmed. The composite so obtained was cured in air. This process was repeated for sample sheets containing wool by mass of 40, 30, 20 and 10 g and a ‘‘control’’ sheet of polyester resin. All test pieces had the wool aligned in the longitudinal direction except for the 40 g (55% mass fraction) transverse samples. Wool composite samples were prepared for a range of fibre fraction by wool mass content corresponding to mass fractions of 21, 40, 52 and 55%. Specimens were cut from the prepared sample sheets for use in three test procedures: flexural (36 test pieces), tensile (36 test pieces) and Izod impact with 48 test pieces. All specimens were conditioned for 24 h at 22 2 8C at a relative humidity of 52 5%. An Instron hydraulic testing machine (model 1114) was used for both the flexural and tensile testing. Automatic data collection was employed to allow further processing of the test data. Flexural test pieces were cut into rectangular shapes measuring approximately 150 mm 3 15 mm (of various thickness, approximately 26 mm) using a rotary saw. Three-point bending tests with a span of 50 mm were conducted. The flexural strength (modulus of rupture) was calculated as 3Pl=2bd2 where P is maximum load, b is test piece width, d is test piece thickness and l is test piece span length. Impact test specimens were cut into rectangular shapes using a rotary saw and notched with a milling machine cutter. Tests and sample dimensions followed the conditions outlined in AS1146 [4]. Impact testing was conducted using a Material Forge model TM 52004 impact tester (an Izod type test). The results from the mechanical tests are given in Table I. These results indicated that there is little influence on the tensile stress or modulus of elasticity with increasing fraction of wool content. However, when the fibres were laid in a transverse position to the tensile load the tensile stress was approximately one half of that for the parallel loading case with the 55% wool fibre test pieces. Moreover, the modulus of elasticity of the transverse samples was similar to that of the parallel fibre samples. The variation of flexural strength with increasing fibre content is shown in Fig. 1. Flexural strength results are also shown for a control sample with 0% fibres, and transverse aligned fibres with 55 wt % wool fibre. The maximum value of flexural strength was at the

Effect of void content on the strength of composite laminates

An experimental program was conducted to assess the effect of void content on the static strength and fatigue life of composite laminates under flexural loading. The fabrication procedure used to produce carbon/epoxy laminates with reasonably uniform void content and constant fiber fraction is described. A fracture criterion correlating the ultrasonic attenuation to the strength of composite laminates is presented. Good correlation with experimental results of interlaminar shear and flexural strength was obtained. The fatigue test results and the proposed theory indicate that voids have a strong detrimental effect on the fatigue life of composite structures if the void content is above a critical value. The proposed theory provides the basis of an experimental program aimed at determining the maximum allowable ultrasonic attenuation of a composite laminate for a specific loading condition.

A penetration test to evaluate wood decay and its application to the Loggia monument

Facing the problem of restoration and consolidation of wooden beam floors and roofs of historical buildings and ancient masonry houses, it is important to evaluate wood decay in a reliable way. The techniques usually adopted require the taking of samples, laboratory tests, radiographs or ultrasound analysis, while tests in situ are usually based on yard practice and generally give only some qualitative information about wood condition. In the present work a method and an operative technique are proposed which make penetration measurements possible. The test can be regarded as an extension of the dynamic penetration test used for soil investigation and it is based on the pentration of a graduated rod, which advances by means of repeated blows of a rebound hammer. A preliminary study was done to identify and prepare the most suitable equipment. An attempt to find a possible correlation between wood flexural strength and penetration test results was also done and the correlation curve for spruce wood seems to give a reliable result. This technique was proposed and adopted for a broadbased investigation of the roof vault of the Palazzo della Loggia, a 16th century building in Brescia (Italy), and it gave useful indications of the extent and depth of the decay of the supporting wood structure.

Interface analysis of Si-C-O fibre/magnesium aluminosilicate matrix composites

Interface characteristics of Si-C-O (NicalonR) fibre-reinforced glass ceramic matrix composites were studied using scanning Auger microscopy (SAM). Composites with and without the cation additions of Ba, Nb, Zr, Li and Li-Zr-Nb to the magnesium aluminosilicate (MAS) matrix were fracturedin situ under ultrahigh vacuum. SAM depth profiles and flexural strength results showed the compositional effects of the additives in the fibre-matrix interface region.

Some statistical considerations of steel fiber composites

Because of the decisive influence of the fabrication method on the strength and durability of fiber composites, the design of fiber concrete elements should be based on statistical considerations of their properties. The paper presents a statistical analysis of compressive and flexural strength results of both plain and steel fiber concrete. Fiber concrete results in compression and flexure show larger standard deviations and greater departure from normal distribution. However, there is no need to test more specimens than that required for plain concrete, although the method of compaction should be specified for flexural strength design. Fibers increase compressive strength, and the difference observed from that of plain concrete is not due to chance. No relation exists between maximum load in flexure and the debonding behavior of the fibers.

Wider highway tendency shown in road building: U. S. Department of Agriculture Press Service No. 194

This work aims to develop a technology with an instant demoulding ability for making precast architectural tiles with an aesthetically pleasing appearance. To achieve this, double-layer composite consisting of a wet-mixed self-compacting glass mortar as the surface-layer and a dry-mixed mortar as the base-layer was designed. The performance of the surface-layer prepared with recycled glass cullet with different particle sizes, and the effects of aggregate types and contents on the base-layer mortar were investigated. The results suggest that the non-porous nature and smooth surface of the glass cullet decreased the water absorption and reduced the strength of the mortars. The flexural and pull-out strength results demonstrated that all the architectural tiles produced exhibited good interfacial adhesion between the two layers and complied with the standard requirements for “Terrazzo tiles” for internal and external applications.