Tear behavior

ASTM D4533 Standard Test Method for Trapezoid Tearing Strength of GeotextUes. 

A precut specimen is subjected to a tensile force to continue or propagate a tear. This test is not used internationally but it is still popular in America (Table 7.11). 

Fixation of upper clamp Free swivel or universal joint 

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Tensile and Tearing Behavior. As shown in Figure 4, the tensile and tear strengths increased with increasing PMMA content measurements of tear strength were not feasible at PMMA contents > 30%. In any case, the incorporation of PMMA at even relatively low levels greatly improves the rather low strengths of the unmodified PU. 

Elastomers in the first category show the simplest tearing behavior and are therefore described first. For these materials, once fracture has been initiated, a tear propagates at a rate dependent on two principal factors the strain energy release rate, G, and the temperature, T. The former quantity represents the rate at which strain energy is converted into fracture energy as the crack advances. It is defined by a relation analogous to Eq. (10.4) ... 

Azemi, S. and Thomas, A. G. (1988). Tear Behavior of Carbon Black-Filled Rubbers . L. L Amin and K.T. Lau (Eds.). Proceedings International Rubber Technology Conference, Penang, Malaysia 147. Kuala Lumpur Rubber Research Institute of Malaysia. 

The tear properties of rubber depend on tear rate and temperature. At low rates, tear has a knotty appearance, whereas tearing at high speeds proceeds steadily, and the torn surfaces are much smoother. In the absence of reinforcement or crystallization, tear behavior is dominated by hysteretic properties in the viscous phase of the rubber. It is related directly to the relaxation of stress that occurs at the tip of the growing tear. 

Hamed GR, Huang MY (1998) Tensile and tear behavior of anisotropic double networks of a black-filled natural rubber vulcanizate. Rubber Chem Technol 71(5) 846-860... 

Film. Blown film manufactured from PB has a high tensile strength and exhibits good resistance to tear, impact, and puncture (47). Such film also exhibits hard-elastic behavior that is, it can recover its original length even after extensive stretching. Some properties of PB film are given in Table 5. 

For both the tongue and Elmendorf test methods, it is important to observe the behavior of the specimen as the tear is propagated. In cases where the yams in the test direction are much stronger than the perpendicular yams, it is sometimes difficult or impossible to propagate the tear in the desired direction. In this case, a crosswise tear results. Tear resistance is primarily a function of fabric constmction. Loose, open weaves such as cheesecloth tend to resist tear, whereas tight weaves tend to tear easily. In the open weave, the concentrated force field at the point of tear is dissipated by the compliance of the fabric stmcture to accommodate the stress field, thereby distributing the force over a greater number of yams. 

There are other types of impact tests for shock loading where energy is required to cause complete failure is reported. Each has their specific behaviors that can be related to specific product performance requirements. Tests include ball burst, ball or falling dart using different weights and heights, bag drop, bullet-type instantaneous impact, Charpy, dart drop, Mullen burst, tear resistance, and tub (2). 

The morphology of the agglomerates has been problematic, although some forms of network-like structures have been assumed on the basis of percolation behavior of conductivity and some mechanical properties, e.g., the Payne effect. These network stmctures are assumed to be determining the electrical and mechanical properties of the carbon-black-filled vulcanizates. In tire industries also, it plays an important role for the macroscopic properties of soft nano-composites, e.g., tear. 

This behavior is similar to the cut growth and fatigue behavior of rubber compounds. The rate of the growth of a cut is a function of the tearing energy [38,39] which itself is proportional to the stored elastic energy density in the test piece. The exact value depends on the shape of the test piece. 

Behavioral and environmental modifications may significantly improve dry eye, especially in mild cases. Evaluate the patient s environment for air drafts. Consider adding a humidifier in low-humidity areas. Schedule regular breaks from computer work or reading. Lower the computer screen to below eye level to decrease lid aperture. Evaluate medication use and make therapeutic substitutions to medications that do not exacerbate dry eye. Spectacle sideshields or goggles may reduce tear evaporation.30... 

The polyurethane formulation Involved a proprietary crossllnkable system based on poly(propylene glycol) and methylene dllsocyanate (NCO/OH ratio = 1.0). For studies of viscoelastic, energy absorption, and fatigue behavior, the weight fractions of PUMA were 0, 0.25, 0.50, 0.75, and 1.0 for studies of tensile and tear strength, the ratios were 0, 0.10, 0.20, 0.25, 0.30, and 0.40. Reactants were mixed at room temperature, degassed, poured Into a mold, and cured at 60 C for 48 hr. 

Such effects are likely to be important. The use of SP interactions to create bioinspired material properties (e.g., see Chap. 9) implies that the ultimate yield behavior of SP materials could depend on the mechanical response of supramolecular interactions. Paulusse and Sijbesma (2004) have also shown that ultrasound-generated shear stresses can mechanically tear apart coordination SPs, damage that is subsequently repaired during dynamic equilibration once the shear stresses are removed. The mechanical response of supramolecular interactions within materials has potentially important consequences in the context of self-repairing materials, where the mpture of sacrificial supramolecular interactions protects a permanent, underlying materials architecture. The dynamic repair of the SP component in... 

The correlation between the TEARS assay and MDA dnring oxidation of edible oils may be complicated by the presence of tocopherols (e.g. Vitamin E, 21) . An evaluation was carried of MDA, determined by an independent method , and TEARS as indices for direct oxygen uptake of edible oils and unsatnrated fatty acids. The linear increase of MDA and TEARS with oxygen consumption of soybean oil, in a closed vessel at 170 °C, stops when the latter value reaches 500 p.molL, when both MDA and TEARS start to decrease on further O2 consumption. The same process carried out at 40 °C, using 2,2 -azobis(2,4-dimethylvaleronitrile) (171) as initiator, shows linearity up to 1500 p,molL O2 consumption . A similar behavior is observed for nnsatnrated fatty acids snch as oleic, linoleic and linolenic acids . On the other hand, depletion of Vitamin E (a-tocopherol, 21) and its analogs y- and 5-tocopherol (172, 173) present in the oil show a linear dependence on O2 consumption of the oil, np to 1800 p,molL . This points to the consumption of these antioxidants, and especially 21, as a good index for the O2 uptake in oils at high temperature. The determination of the tocopherols is carried ont by HPLC-FLD (Xex = 295 nm, Ah = 325 nm) . ... 

Diagnosing an anxiety disorder in children can be difficult, because children often are unable to recognize and describe anxiety in themselves. Instead, they may complain of somatic symptoms. Younger children may exhibit behavioral changes such as tearfulness, diffi-... 

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