Interlaminar strength

Fibers Transverse fracture Flexural strength Interlaminar shear Interlaminar... 

Axial compressive strength Axial tensile strength Circumferential tensile strength Interlaminar shear strength Circumferential modulus of elasticity Specific gravity... 

Flexural strength (77°F) Compression strength Interlaminar shear (77°F)... 

Interlaminar (longitudinal) shear modulus (Git) Longitudinal tensile strength Transverse tensile strength Interlaminar shear strength Longitudinal Poisson s ratio (piO Transverse Poisson s ratio (pj... 

Laminates ate a special form of composite material or reinforced plastic because the continuous reinforcing ply of fibrous material imparts significant strength in the x—j plane. The strength along the axis results from interlaminar bonding of resins. Very few fibers ate oriented in the direction, so it tends to be the weak link in this type of composite. 

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. 

The significance of interlaminar stresses relative to laminate stiffness, strength, and life is determined by Classical Lamination Theory, i.e., CLT stresses are accurate over most of the laminate except in a very narrow boundary layer near the free edges. Thus, laminate stiffnesses are affected by global, not local, stresses, so laminate stiffnesses are essentially unaffected by interlaminar stresses. On the other hand, the details of locally high stresses dominate the failure process whereas lower global stresses are unimportant. Thus, laminate strength and life are dominated by interlaminar stresses. 

A collection of the basic building block, a lamina, was bonded together to form a laminate in Chapter 4. The behavior restrictions were covered in the section on classical lamination theory. Special cases of laminates were discussed to learn about laminate characteristics and behavior. Predicted and measured laminate stiffnesses were favorably compared to give credence to classical lamination theory. Then, the strength of laminates was discussed and found to be reasonably predictable. Finally, interlaminar stresses were analyzed because of their apparent strong influence on laminate strength (and life). 

As already mentioned, the first pyrolysis cycle leads to an open porosity of about 20-30 %. This high porosity limits the interlaminar shear strength (ILS). A reduction in the porosity is possible by reimpregnation with polymers and subsequent pyrolysis or CVI (Chemical Vapour Infiltration). 

MPa. At the stress maximum or in the region where the stresses remain nearly constant a strong delamination occurred, which probably reduces the interlaminar shear strength dramatically. Therefore the high strain-values cannot really be used for design. 

The interlaminar shear strength (ILSS) is the value of the shear strength producing a delamination between two composite layers along the plane of their interface. The measurement is made by a three-point deflection test with the supports very close together. 

ISO 14130 1997 Fibre-reinforced plastic composites - Determination of apparent interlaminar shear strength by short-beam method ISO 15024 2001 Fibre-reinforced plastic composites - Determination of mode I interlaminar fracture toughness, GIC, for unidirectionally reinforced materials... 

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... 

Interlaminar shear strength (ILSS), AES atomic percent, contact angle, 0, and surface energy, y, data for untreated and electrochemically oxidized pitch-based carbon hber"... 

Gilbert, A.H., Goldstein, B. and Marom, G. (1990), A liquid droplet measurement technique as a means of assessing the interlaminar shear strength of fiber reinforced composites. Composites 21. 408-414. 

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... 

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