Toughness stress-strain curve

Creep is the change in shape of a material while subject to a stress it is time-dependent. Elasticity, the ability of a fiber to return to its original dimensions upon release of a deformation stress, is described by the tenacity of the 5deld point on the stress-strain curve. Toughness, the ability of a fiber to absorb work before it ruptures, is evaluated from the area under the total stress-strain curve. The toughness index is defined as one-half the product of the stress and strain at break... 

The abihty of a fiber to absorb energy during straining is measured by the area under the stress—strain curve. Within the proportional limit, ie, the linear region, this property is defined as toughness or work of mpture. For acetate and triacetate the work of mpture is essentially the same at 0.022 N/tex (0.25 gf/den). This is higher than for cotton (0.010 N/tex = 0.113 gf/den), similar to rayon and wool, but less than for nylon (0.076 N/tex = 0.86 gf/den) and silk (0.072 N/tex = 0.81 gf/den) (3). 

Fig. 4. Types of stress—strain curves (a) soft and weak (b) hard and brittle (c) soft and tough (d) hard and strong and (e) hard and tough.

Fig. 41. Typical stress—strain curve. Points is the yield point of the material the sample breaks at point B. Mechanical properties are identified as follows a = Aa/Ae, modulus b = tensile strength c = yield strength d = elongation at break. The toughness or work to break is the area under the curve.

Stress-strain curves at the conditions of product application. If applicable, this would usually indicate the toughness of material by sizing up the area under the curve (Chapter 2). It would also show the proportional limit, yield point, corresponding elongations, and other relevant data. 

As previously described (Chapter 2), the area under short-term stress-strain curves provides a guide to a material s toughness and impact performance (Fig. 7-6). The ability of a TP to absorb energy is a function of its strength and its ductility that tends to be inversely related. The total absorbable energy is proportional to the area within the lines drawn to the appropriate point on the curve from the axis. The material in area A is... 

Fig. 7-6 Toughness tends to relate to the area under the stress-strain curve.

The phenomena of brittle and tough fracture give rise to fairly characteristic stress-strain curves. Brittle fracture in materials leads to the kind of behaviour illustrated in Figure 7.1 fairly uniform extension is observed with increasing stress, there is minimal yield, and then fracture occurs close to the maximum on this graph. 

Figure 7.1 Typical stress-strain curves for (a) a brittle plastic and (b) a tough plastic with yield point, showing the parameters used for the evaluation of degradation in tests...

Impact strength is a measure of the energy needed to break a sample—it is not a measure of the stress needed to break a sample. The term toughness is typically used in describing the impact strength of a material but does not have a universally accepted definition although it is often described as the area under stress-strain curves. 

How can you estimate relative toughness of polymer samples from stress-strain curves ... 

The comparison of the mechaiucal properties of the UPy samples and the PEG controls demonstrates that the introduction of our biomimetic module into the network dramatically enhanced the polymer mechanical properties. As shown in the stress-strain curves (Fig. 10.8), the network containing the biomimetic crosslinker has significantly higher modulus, tensile strength, and toughness than the... 

Figure 5.112 Idealized stress-strain curve for a tough ceramic-matrix composite. Reprinted, by permission, from R. W. Davidge and 1. J. R. Davies, in Mechanical Testing of Engineering Ceramics at High Temperatures, B. F. Dyson, R. D. Lohr, and R. Morrell, eds., p. 251. Copyright 1989 by Elsevier Science Publishers, Ltd.

It is important to note that the behavior of polymers below the yield point is Hookean and essentially reversible for short-term service. Thus this range, which is associated with stretching and bending of covalent bonds, is called the elastic range. The area under the stress-strain curve is a measure of toughness. 

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