Load-elongation curves, and

The trapezoid test method (ASTM Dll 17) is recommended for determining the tear resistance of nonwoven fabrics. An outline of a trapezoid is marked on a 7.5 x 15 — cm specimen, and the nonparallel sides are clamped in the jaws of the tensile-testing machine. The load is applied to the specimen in such a way that the tear propagates across the specimen width. The value of the breaking load is obtained from the load—elongation curve and is determined primarily by the bonding or interlocking of the fibers of the composite structure. 

The clear separation of transformation from spherulitic to fibrous structure and the drawing of fibrous structure observed with nylon 6 are not found with polyethylene or polypropylene. This could lead to the conclusion that in these polymers the deformational process is basically different from that in nylon 6. But, closer inspection of material drawn to gradually increasing draw ratios reveals a closer similarity than one can derive from load-elongation curves and direct observation of necking. 

Figure 11.2 Comparison of the nominal stress-elongation curve (load-elongation curve) and the true stress-elongation curve...

The area of the polar diagram is related to variables such as refining and wet press pressure. The load-elongation curve during tensile testing also shows marked differences in the two directions (Figure 4.8). 

Figure 4.8 The load-elongation curves for paper in the machine and cross machine directions.

Figure 3. Load-elongation curves of (a) nylon 6 and (b) linear polyethylene...

Figure 8.14 (a) The load-elongation curve of TPV measured at 23°C and the elongation speed of 200 mm min f The SEM images of TPV samples drawn at (b) strain = 1.7, (c) strain = 5.5, (d) strain = 7.4. (Reproduced from Reference (28) with permission from Elsevier Science.)... 

This experience so clearly demonstrated on the brittle composite materials can be applied immediately to the deformation of fully drawn fibrous material which may be extended up to fracture. If one stops a little before rupture and removes the load completely, the sample will slowly approach almost zero strain. The deformation is nearly completely recoverable. The next loading yields a lower load-elongation curve. One... 

The mechanical properties of the polylmide film were measured in tension tests. To do this polylmide films were cast and cured on glass substrates. The films were removed and tensile test specimens were stamped from the films using a die. The specimens were then pulled to fracture at a cross-head speed of 10 mm/min. The mechanical properties obtained from the load-elongation curves are given in Table I. 

Stretching a hair fiber in water and the curve at the top of the chart represents stretching at 65% RH. In the Hookean region of the load-elongation curves, the stress (load) is approximately linear to the strain (elongation), and the ratio of stress to strain in this region is the elastic modulus (Es), commonly called Young s modulus. The elastic modulus is usually expressed in dynes per square centimeter and may be calculated from this simple expression ... 

Load-elongation [45] and stress-relaxation [46] measurements may be used to follow the course of the reduction of keratin fibers by mercaptans. Extension in the postyield region is resisted primarily by the disulfide bonds [45], Therefore, this region of the stress/strain curve holds special significance to the reduction reaction. 

The load/elongation curve of a spider drag hne silk of length 25.3 mm and diameter 4.20 p,m is shown in Figure 13.32. From the graph determine ... 

Fig. L(a) Three common working definitions of the yield point for metals. (1) Load maximum (2) tangent method, (3) firoofistress" or "strain-offset method. (The proof-strain is commonly taken to be 0 /%, but is quite arbitrary.) (b) Load elongation curves for polymers. (I) Brittle, (2) strain softening, (3) cold-drawing, (4) strain-hardening, (5) rubbery. Typical definitions of the yield point are marked by arrows on curves (2), (3) and (4). Any one polymer can show behaviour raiding from (1) to (5) depending on test conditions, e.g. temperature, strain-rate, tension...

Fig. 13.18 Continued, (b) Load-elongation curves of sheets and halyards after a period on intial loading. From Gleistein catalogue.

From the load/elongation curves obtained fin- each spedmoi, its tenacity (Ntex ), breaking extension (%), modulus (N) and s )edfic modulus (Ntex ) were determined in the three major directions, i.e. machine direction (MD), [Pg.312]

Rectangular specimens cut out circumferentially and longitudinally from a graft waU can be tested on a tensile apparatus. Hasegava and Azuma, and Lee and WUson have used this procedure on both synthetic grafts and natural vessels. The output is a load-elongation curve similar to that shown in Fig. 14.3, and the curve can be used to obtain the same parameters as for the tube. 

Fig. 41.4 The effects of a local application of TGF-beta and EGF on structural properties of the femur-graft-tibia complex after ACL reconstraction. The load-elongation curves of the femur-graft-tibia complexes in the knees with growth factor (GF) application, with fibrin sealant alone (sham), and without growth factor or fibrin sealant (control) groups and the normal femur-ACL-tibia complex (normal ACL). A combined application of TGF-betal and EGF significantly improved mechanical strength of the femur-graft-tibia complex at 12 weeks after ACL reconstruction (From Ref. [43]))...

Fig. 4.47 A schematic illustration of the yield drop and serration in the load elongation curve...

Yield stress may be regarded most simply as the minimum stress at which permanent strain is produced when the stress is subsequently removed. Although this deformation is satisfactory for metals, where there is a clear distinction between elastic recoverable definition and plastic irrecoverable deformation, in polymers the distinction is not so straightforward. In many cases, such as the tensile tests discussed above, yield coincides with the observation of a maximum load in the load-elongation curve. The yield stress then can be defined as the true stress at the maximum observed load (Figure 11.8(a)). Because this stress is achieved at a comparatively low elongation of the sample, it is often adequate to use the engineering definition of the yield stress as the maximum observed load divided by the initial cross-sectional area. 

In some cases there is no observed load drop and another definition of yield stress is required. One approach is to determine the stress where the two tangents to the initial and final parts of the load elongation curve intersect (Figure 11.8(b)). An alternative is to attempt to define an initial linear slope on the stress-strain curve and then to draw a line parallel to this that is offset by a specified straia, say 2 per cent. The interception of this line with the stress strain curve then... 

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