Interlaminar shear strength properties

Table 1 Interlaminar shear strength properties of phenolic composites...

It is critical that surface treatment conditions be optimized to composite properties since overtreatment as well as undertreatment will degrade composite properties. Typically composite interlaminar shear strength (ILSS), in-plane shear, and transverse tension ate used to assess the effectiveness of surface treatment. More recently damage tolerance properties such as edge delamination strength, open hole compression, and compression after impact have become more important in evaluating the toughness of composite parts. 

ISO 3597-4 2003 Textile-glass-reinforced plastics - Determination of mechanical properties on rods made of roving-reinforced resin - Part 4 Determination of apparent interlaminar shear strength... 

In addition to the direct measurements of fiber-matrix interface properties discussed in Section 3.2, a number of testing techniques have been devised to assess the fiber-matrix interface bond quality by inference from the gross mechanical properties such as interlaminar shear strength (ILSS), translaminar or in-plane shear strength, and transverse tensile strength. These testing techniques invariably employ... 

As with tensile properties, both compressive strength and modulus depend on the fiber content and hber orientation (see Table 5.8). The interlaminar shear strength reported in Table 5.8 is a measure of the shear strength in the thickness direction of the SMC sheet. It is determined by three-point flexural testing of beams with short span-to-depth ratios and is considered to be a quality-control test for molded composites. 

The function of the resin matrix material in filament-wound structures is to help distribute the load, maintain proper fiber position, control composite mechanical and chemical properties, and provide interlaminar shear strength. Either a thermosetting or a thermoplastic resin material may be selected. Thermosetting resins may be selected for application in a wetwinding process or as part of a prepreg resin system. 

Both fiber-matrix interphase-sensitive mechanical tests (interlaminar shear strength, 90° flexure) and interphase-insensitive tests (0° flexure) were conducted on high volume composite samples fabricated from the same materials and in the same manner as discussed above to see if the interphase and its properties altered the composite mechanical properties and in what manner. A summary of the data is plotted as a bar graph in Fig. 7. The first set of bars represents the difference in fiber-matrix adhesion measured between the bare fibers and the sized fibers by the ITS. The composite properties plotted on the figure also show increased values for the epoxy-sized material over the bare fiber composite. 

As there are no fibers aligned in the through-thickness direction of 2-D fiber-reinforced composites, a possible mode of failure is by shear between the fabric plies. Hence, interlaminar shear strength is an important property. Tests were conducted using the ASTM D2344-84 short beam method. The average interlaminar shear strength from five samples was measured to be 62 MPa at room temperature. 

In fibre-reinforced glass matrix composites, 3-D parts offer greater potential than uni-directionally reinforced composites (in 1-D or 2-D fibre lay-up), discussed in Chapter 19, because of their potentially better interlaminar shear strength and isotropic properties. A... 

Polymer composites. The composite research at the Institute is led by Prof. Wu Renjie, Deputy director of the Institute. Chen, et al. (14), studied the effect of oxidation of carbon fiber on the wettability by the binder resin. With the aid of ESCA, they showed that the Q/C ratio on the fiber surface increased with the oxidation time. The interlaminar shear strength also increased correspondingly. Cai Weizhen and her colleagues showed me their exceptional setup for a carbon-fiber composite study. They built their own torsion pendulum for the study of dynamic mechanical properties of the composite and a contact angle goniometer for the study of the composite interface. It was apparent that surface treatment of carbon fiber was their major concern. 

D2344-84 Apparent interlaminar shear strength of parallel fibre composites by short beam method D3039-76 Tensile properties of fibre—resin composites... 

Carbon fibers are surface treated by the manufacturers using proprietary processes to improve the bond between resin and fiber. For control purposes, it is usual to measure the three point interlaminar shear strength (ILSS) and the choice of resin, volume fraction, span/depth ratio, mode of failure and time of treatment (Table 9.1) are important parameters. As the fiber modulus increases, longer treatment times will be required to obtain the same level of ILSS and overtreatment can result in loss of properties, particularly impact strength (Figure 20.15). 

The effect of surface treatment on the mechanical properties of carbon-fibre composites Brittle fibres in a brittle matrix can have appreciable toughness because the cracks can get diverted along the fibre-matrix interface. If the bond is weak the composite will not support loads in shear or compression, but when the bond is too strong, the material will be brittle. These aspects are illustrated in Fig. 6, where it is seen that the interlaminar shear strength reaches a plateau but the notched tensile strength decreases... 

A 5-harness satin (5-HS) weave will have its warp yarns running over four weft yarns and under one weft yarn as shown in Fig. 9.5. Other n-HS weaves used in composite materials include 8-HS, where the warp yarn passes over seven weft yarns and under one, and 12-HS where the warp yarn passes over eleven weft yarns and under one. It can easily be understood that the more yarn passes over the other yarn, the straighter and less crimped will be the yarns present in the fabric. The straighter the segments, the more the fabric composite behaves as a lamina in a laminated composite, increasing the inplane properties at the expense of out-of-plane properties and interlaminar shear strength - and of course vice versa. 

Improved mechanical properties. The addition of small size and low loading of nanoparticles will enhance the matrix-dominated properties such as stiffness, fracture toughness and interlaminar shear strength of conventional fiber-reinforced composites. 

Most FRP bars exhibit relatively low interlaminar shear strength, as there is generally no reinforcement between layers of axial fibres. Therefore, the performance of FRP bars for shear loads relies mainly on the matrix properties. Shear resistance can be improved by braiding or winding fibres in the transverse direction of the bar or by introducing continuous strand mats in the fibre architecture (ACI Committee 440, 2006). 

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