Static Flexural Tests Research Articles

Estimation of the flexural creep fracture strength of satin woven CFRP laminates1

This paper is concerned with the prediction of flexural creep fracture for CFRP laminates consisting of satin woven carbon fibers and a heat-resistant epoxy matrix with glass transition temperature Tg = 236° C. The flexural creep fracture tests were carried out under various stress levels at 50° C which is sufficiently below Tg. The static flexural tests were carried out at various deflection rates and temperatures. The master curve of flexural strength of CFRP was obtained by applying the reciprocation law of time and temperature to these experimental results. Furthermore, the flexural creep fracture of CFRP was estimated by utilizing the linear cumulative damage rule adapted to this master curve. The creep fracture predicted by the method mentioned above agrees fairly well with that measured by creep tests.

Effects of particle size on mechanical and impact properties of epoxy resin filled with spherical silica

AbstractEffects of particle size on the mechanical and impact properties of cured epoxy resins are studied. This resin was filled with spherical silica particles prepared by hydrolysis of silicon tetrachloride. Particles were sorted into five kinds of different mean sizes in the range from 6–42 μm. A static flexural and tensile tests and an instrumented Charpy type impact test were carried out. Flexural strength, tensile strength, and impact‐absorbed energy increased with a decrease in the particle size. Fractured surfaces were observed using a scanning electron microscope to clarify the initiation point of fracture.

朱子織CFRP積層板の曲げクリープ破壊寿命の予測

This paper is concerned with the prediction of flexural creep fracture for CFRP laminates consisting of satin woven carbon fibers and high temperature epoxy matrix, of which glass transition temperature Tg=236°C. The flexural creep fracture tests were practically carried out under various stress level at 50°C to be sufficiently lower than the Tg. On the other hand, the static flexural tests were carried out under various deflection rates and temperatures. The master curve of flexural strength of CFRP was obtained by applying the reciprocation law between time and temperature to these experimental results. Furthermore, the flexural creep fracture of CFRP was estimated by utilizing the linear cumulative damage rule adapted to this master curve. The creep fracture predicted by the method mentioned above is fairly well agreed with that measured by creep tests.

繊維強化複合材料はりの曲げ‐ねじり連成振動に関する研究

It is shown that the principal axis of elasticity (abbreviated to PAE) can be rotated from the structural axis by giving a specific fiber orientation or stacking sequence of a fiber composite beam. The theoretical results for PAE obtained by the use of the laminated plate theory agree with the experimental results for PAE of GFRP and CFRP laminated cantilever beams in the static flexural and torsional tests. It is illustrated from the flexural-torsion analysis and the static test that the angle of torsion at the free end of the beam is zero when the center of gravity of the beam with an eccentric mass coincides with the PAE. The natural frequencies of a beam involving an eccentric mass can be predicted by solving the characteristic equation of a simplified vibration equation of two degree-of-freedom system. The flexural-torsion coupling effects are discussed by using the coupling coefficient in the equation. Solving the vibration equation subjected to the sinusoidal excitation, it is proved that the torsional amplitude of the free end of the beam is zero when the center of gravity is on the PAE. The experimental results of the sinusoidal excitation test agree with the analytical solution of the vibration equation.

Structure and Properties of a Stampable Thermoplastic Composite

In this paper the structure of stamped glass fiber/polypropylene composites with different fiber/matrix interfaces is characterized and related to their short term mechanical behaviour. Optical microscopy and calorimetry are used to determine matrix and interface structure. Static tensile and flexural tests were performed but were less sensi tive to interface structure than impact. Extensive crystal nucleation observed on fibres, believed to be promoted by shear nucleation during stamping, did not correspond to a strong fibre/matrix interface.

Impact Properties of Three-Dimensional Braided Graphite/Epoxy Composites

An experimental study of the response and damage of three-dimensional braided graphite/epoxy composite due to sub-perforation velocity impact was carried out in this research. Simply supported square plates were impacted with an instrumented impact pendulum and also a projectile fired by a gas gun. Hemispherical nose impactors of two different diameters, 12.7 mm and 25.4 mm, were used in the pendulum tests. In addition, static flexure tests were performed. Impact damage was assessed using X-radiography, and compression after impact tests. Damages involved in impacted braided panel are matrix cracking in resin pockets, separation of fiber tows, and fiber tow breakage, mostly in fiber bundle crimp areas. A quasi-isotropic laminate was impact tested with pendulum for comparison of impact tolerance between the two composite systems.

Flexural Strength of Ferrocement

Static flexural tests were carried out on three types of ferrocement ; type A and type B to DnV rule, and a type with reinforcement only in tension side. Reinforcement content was systematically changed for these three types. Strength of ferrocement plate such as elastic modulus, cracking moment and maximum flexural moment were discussed assuming the ferrocement plate as a composite beam of mortar and steel, while ferrocement is assumed as a uniform material in many papers.Flexural moment, flexural elastic modulus and average crack spacing were discussed in terms of content and specific surface of reinforcement.Following conclusions were obtained ;(1) Flexural strength can be estimated on the basis of strength of mortar and reinforcement.(2) The moment at which cracks 0.02 to 0.025 mm wide are observed is about one and a half times of the estimated on strength of mortar.(3) From strength view point, optimum value of specific surface of reinforcement exists for structures of ferrocement of type A. For the value, cracking moment and maximum flexural moment are correlated to thickness of ferrocement plate, irrespective of type of structure.

Properties of Reinforced Abrasive Disks in Flexure

This paper deals with a study of the flexural behavior of thin, fiber-reinforced, resinoid abrasive disks. During use, these disks generally encounter a much higher ratio of flexural or bending stress to rotational stress than do straight grinding wheels. Material characteristics such as flexural modulus of elasticity, flexural strength, and flexural strain to fracture were evaluated for specimens machined from the disks at known orientations of each layer of fiber reinforcement. The effect of transverse loading on the abrasive disk was investigated by means of static flexural tests on randomly oriented disks. The failure load was predicted from considerations of beam theory and was found to agree well with experimental data.