Strength anisotropic tensile

A criterion has been developed based on the tensile normal stress and the anisotropic tensile strength on arbitrary planes about the crack tip. It is assumed that the crack grows along the plane on which the stress ratio is maximum (Buezek and Herakovich, 1985). A maximum stress criterion is also proposed (Gupta et al., 1993) for a crack which deflects along the interface... 

In 1977 Idemitsu Petrochemicals announced that immiscible blends of LDPE with HOPE, with EPDM, or with an atactic polypropylene, aPP, are suitable for the production of soft, thin films, with improved properties for packaging (Sakane et al. 1979). Similar blends, LDPE with HOPE, PP, and EP block copolymer, were proposed by Shin-Kobe Electric Machinery (1984) for films with good modulus, tear strength, and no sagging behavior. Also, Showa Denko (1983) found that immiscible, but lightly compatibilized, blends of LDPE with either HOPE or MDPE are suitable for films with uniform thickness and anisotropic tensile strength. 

Polyethylene, PE, blends from LDPE, HDPE, and MDPE were found suitable for manufacturing films with uniform thickness and anisotropic tensile strength... 

Polyethylene, PE, blends from LDPE, HDPE, and MDPE were found suitable for manufacturing films with uniform thickness and anisotropic tensile strength K. K. Showa Denko, Japanese Patent 157,837,20 Sep 1983, Appl. 15 Mar 1982 Japanese Patent 176,234, 15 Oct 1983, Appl. 09 Apr 1982... 

In addition to specific properties of interest for a particular application of a material, its elasticity, compressive and tensile strength, deformability, hardness, wear-resistance, brittleness and cleavability also determine whether an application is possible. No matter how good the electric, magnetic, chemical or other properties are, a material is of no use if it does not fulfill mechanical requirements. These depend to a large extent on the structure and on the kind of chemical bonding. Mechanical properties usually are anisotropic, i.e. they depend on the direction of the applied force. 

Polypropylene and polyethylene microporous films obtained by this method are available from Cel-gard48.5o,54,55 Ube. The dry process is technologically convenient because no solvents are required. However, only a uniaxial stretching method has been successful to date, and as a result, the pores are slitlike in shape and the mechanical properties of films are anisotropic. The tensile strength in the lateral direction is relatively low. 

The tensile strength of materials is dependent on the treatment and form of the material. Thus, the tensile strength of isotropic bulk nylon-6,6 is less than that of anisotropic oriented nylon-6,6 fiber. Inorganics and metals also form fibers and whiskers with varying tensile strengths (Table 14.1). Fibers are generally less crystalline and larger than whiskers. 

A major impetus was given to work, both academic and industrial, in the field of lyotropic systems by the development by duPont of commercial fibres having exceptionally high tensile strength and modulus through use of nematic anisotropic solutions of relatively rigid-chain aromatic polyamides. The earliest product to appear, Fibre B, was based upon poly (p-benzamide) (I)10), but was replaced by the fully commercial product, Kevlar, based upon poly (p-phenylene terephthalamide) (II) U). Arenka, from Akzo, also has the latter chemical repeating unit. 

Because of such orientation the products may be anisotropic in behaviour, with mechanical properties differing if measured in different directions (tensile strength will be higher in the direction of orientation, and impact strength also will be affected—fracture can take place more easily parallel to the direction of orientation). 

Rope represents a very useful form of fibrous product. A rope or cord consists of a bundle of fibers. The fibers may be continuous or they may be made of staple fibers, i.e. short, fine fibers. The tensile strength of a rope comes from the strength of individual fibers and the friction between them. The interliber friction prevents their slip past one another. Quite obviously, a rope or a cord has very anisotropic properties. It is strong in tension along the axis direction but not in the transverse or radial direction. Strength in compression is also very poor. 

---