Strain/elongation diagrams

The relevant characteristic values are shown again in diagrammatic form in Fig. 2.4. Fig. 2.5 shows typical strain/elongation diagrams for selected plastics by way of example. The reliability of the MID is determined by the mechanics of the polymer basic body, so materials characterized by strength (elongation strain) and ductility are eminently suitable (see curves (b) and (c). Fig. 2.4). 

During the test, the load (F)-elongation (AL) diagram (Fig. 4.35) up to the break of specimen is recorded necessary to calculate the compressive stress ((j)-compressive strain (s) diagram using the geometric conditions of specimen Ao and equipment L or Lo (Eqs. 4.17. 19). In the case of compression measurement with extensometer ALq = ALq2 - ALqi is used otherwise the traverse path AL serves for the calculation of compression strain. For the determination of modulus of elasticity Ec a strain rate of 1 %/ min is applied and 2 mm/min are mostly used to perform the compression test. 

Fig. 30. Elongation and stress-relaxation of a semicrystalline PTMT film stress-strain/time diagram...

Fig. 3.4 Typical stress-strain (load-elongation) diagrams of various polymer types...

There is Httle difference between the wet and the dry stress—strain diagrams of hydrophobic fibers, eg, nylon, acryHc, and polyester. Hydrophilic protein fibers and regenerated cellulose exhibit lower tensile moduH on wetting out, that is, the elongations increase and the strengths diminish. Hydrophilic natural ceUulosic fibers, ie, cotton, linen, and ramie, are stronger when wet than when dry. 

Forming Limit Analysis. The ductihty of sheet and strip can be predicted from an analysis that produces a forming limit diagram (ELD), which defines critical plastic strains at fracture over a range of forming conditions. The ELD encompasses the simpler, but limited measures of ductihty represented by the percentage elongation from tensile tests and the minimum bend radius from bend tests. 

Figure 1 Schematic diagrams of various types of tensile tests F, force e strain or elongation.

Figure 15.4 gives the stress-strain diagrams for a typical fiber, plastic, and elastomer and the average properties for each. The approximate relative area under the curve is fiber, 1 elastomers, 15 thermoplastics, 150. Coatings and adhesives, the two other types of end-uses for polymers, will vary considerably in their tensile properties, but many have moduli generally between elastomers and plastics. They must have some elongation and are usually of low crystallinity. 

Fig. 13 Variation of 200% modulus (a), tensile strength (b), and elongation at break (c) with the amount of organoclay and XNBR. Stress-strain diagram of the organoclay-rubber composites (d)...

Tensile properties (tensile strength, elongation, modulus) were measured on an Instron tensile tester (ASTM D882-61T Method A). The tensile modulus was the slope of the initial straight portion of the stress-strain diagram. The heat-distortion... 

The strength properties of solids are most simply illustrated by the stress-strain diagram, which describes the behaviour of homogeneous brittle and ductile specimens of uniform cross section subjected to uniaxial tension (see Fig. 13.60). Within the linear region the strain is proportional to the stress and the deformation is reversible. If the material fails and ruptures at a certain tension and a certain small elongation it is called brittle. If permanent or plastic deformation sets in after elastic deformation at some critical stress, the material is called ductile. 

A very important diagram for fibres and yams is the stress—strain diagram, where the specific stress is plotted as a function of the elongation (extensional strain) in %. The curve starts at an elongation of zero and ends in the breaking point at the ultimate specific stress (=tensile strength or tenacity) and the ultimate elongation (=strain at break). 

Another example of the use of polarized radiation in imaging studies is the analysis of poly(vinylidene fluoride)(PVDF) films, which have been uniaxially elongated at different temperatures. Depending on the thermal, mechanical and electrical pretreatment, PVDF can exist in different modifications [59]. The crystal structure of the cmmpled 11(a) modification can be converted into the aU-tra s 1(P) form by tensile stress below 140°C (see Figure 9.27a). Figure 9.27b shows the stress-strain diagrams of PVDF films in the 11(a) form which have been elongated to 400 % strain at 100 and 150°C. The observed decrease in stress upon elevation of the... 

Figure 9.27 (a) Conformational changes occurring in the 11(a) l(P) transformation of PVDF (b) Stress-strain diagrams of PVDF films elongated to 400% strain at 100 and 150°C. Reproduced with permission from Ref [58] 2008,... 

Young s modulus, also referred to as elastic modulus, tensile modulus, or modulus of elasticity in tension is the ratio of stress-to-strain and is equal to the slope of a stress-strain diagram for the material. In the standard test method, ASTM D412, a force is apphed to a dog-bone-shaped sample of the cured adhesive. The force at elongation (strain) is measured. Most often, the elongation is 25-30% although for elastomeric materials it may be 100% or greater. 

Figure 11-14. Schematic representation of the tensile stress aw as a function of strain e at constant temperature for an elastomer E, a partially crystalline thermoplast T, and a hard-elastic thermoplast HT. The ductile region is la-II-III. The necking effect shown below the diagram is typical of normal thermoplasts, but does not occur with elastomers or hard-elastic thermpolasts. The diagram is not drawn to scale for example, elastomers show a much larger elongation at break than do thermoplasts.

Rgure 2 Load-elongation (stress-strain) diagram with typical cunres of a tensile test (A) with, and (B) without a maximum point (maximum tensile strength). 

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