Breaking strength/stress

Important physical properties include the density, melt flow index, crystallinity, and average molecular weight. Mechanical properties of a polymer, such as modulus (the ratio of stress to strain), elasticity, and breaking strength, essentially follow from the physical properties. 

It is common that mechanochemical degradation involves scission of the macromolecule, so one basic question would be to inquire about the level of stress necessary to separate two chemical moieties which have been attached by a covalent bond. Besides the academic interest, the breaking strength of a covalent bond is associated with the ultimate properties of engineering materials and has attracted considerable attention since the beginnings of quantum chemistry. 

Equation (73) is based on the observed shift in vibrational frequency. Since these measurements are usually carried out at a level of stress which is well below the theoretical breaking strength of the chain, they may correspond to the initial portion of the curve in Fig. 20 which also predicts a linear decrease of U(a) on the level of stress. 

TENSILE STRENGTH. The rupture strength (stress-strain product at break) per unit area of a material subjected to a specified dynamic load it... 

Determination of tensile strength at break, tensile stress at yield, elongation at break, and stress values of rubber in a tensile test Physical testing of rubber Part A2 Method for determination of tensile stress-strain properties... 

Figure 7. Observed relationship between breaking stresses and free radicals. No the number of free radicals produced with no degradation N,-, same but with degradation

Materials in the form of fibers are often vastly stronger than the same materials in bulk form. Glass fibers, for examples may develop tensile strengths of 7 MPa (1,000,000 psi) or more under laboratory conditions, and commercial fibers attain strengths of 2,800 to 4.8 MPa (400,000 to 700,000 psi), whereas massive glass breaks at stresses of about 7 MPa (1000 psi). The same is true of many other materials whether organic, metallic, or ceramic. 

Reversals represent zones of variations in breaking strength. The areas immediately adjacent to either side of a reversal are more likely to break under stress than are other... 

Materials science associated with fracture mechanics has mainly been confined to composite materials such as concrete, ceramics and metals. Much of the emphasis of the research has been on preventing fatigue and failure rather than designing for it to occur. The way a structure deforms and breaks under stress is crucial for properties such as flow and fracture behaviour, sensory perception of structure, water release and the mobility and release of active compounds. In the case of foods, the ability to break down and interact with the mouth surfaces provides texture and taste attributes. The crack propagation in a complex supramolecular structure is highly dependent on the continuous matrix, interfacial properties and defects and the heterogeneity of the structure. Previous structure-fracture work has dealt with cellular plant foods, and it has been demonstrated that the fracture path differs between fresh and boiled carrots due to cellular adhesion and cell wall strength as well as cell wall porosity and fluid transport (Thiel and Donald 1998 Stoke and Donald 2000 Lillford 2000). 

Fig. 3.15. Collapse of the computer simulaion data for stress (cr) - strain (n /L ) in fractured triangular network with bond-bending forces (/ = 0.1) for two diflFerent linear sizes L (= 50 and 70). The randomness in the bond-breaking strength is assumed to be uniform (a = 0). nb denotes the number of broken bonds and is taken to be 1.75 here (Sahimi and Arbabi 1993).

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