Tensile measurement

Polyurethane elastomers are known for their high elongation, tensile strength and modulus properties. The combination of these properties provides toughness and durability in fabricated parts. Cast elastomers extended with butanediol can maintain these tensile properties when the use temperature is about 80 C. When these elastomers are subjected to higher temperatures, reduction in the tensile properties are observed due to the weakening of physical bonds in the elastomer. 

The tensile properties measured on the unaged and heat-aged elastomer materials made from HER and butanediol are given in Table 8.16. 

The 100, 200 and 300% tensile modulus values of unaged elastomers are higher for HER than for the butanediol elastomer. Analysing the 100, 200 and 300% modulus values of 100 °C heat-aged samples showed that HER elastomer retained about 95-97% of its original unaged values compared to 75-76% for butanediol. At 120 °C, there was 93-94% modulus retention for HER whilst 85-88% was observed for butanediol. When 

Energy to break (kN/m) (area under stress-strain curve) 110 124 111 104 92 100 98 91 

Note The values in the parenthesis are the percentages of properties retained after the heat ageing, nd Not determined  

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In addition to transport properties, the adhesive properties are characterized by tensile measurements. For instance, the peel strength is deterrnined by measuring the force required to pull the adhesive from a substrate at a constant speed in a controUed temperature and humidity environment. 

In the matrix of PLA/ polycaprilactone (PCL)/OMMT nano-composites, the silicate layers of the organoclay were intercalated and randomly distributed (Zhenyang et at, 2007). The PLA/PCL blend significantly improved the tensile and other mechanical properties by addition of OMMT. Thermal stability of PLA/PCL blends was also explicitly improved when the OMMT content is less than 5%wt. Preparation of PLA/thermoplastic starch/MMT nano-composites have been investigated and the products have been characterized using X-Ray diffraction, transmission electron microscopy and tensile measurements. The results show improvement in the tensile and modulus, and reduction in fracture toughness (Arroyo et ah, 2010). 

Very recently, Williams, Billington Pearson (1992) have examined the effect of reinforcement by silver or silver-tin alloy on the mechanical properties of three glass-ionomer cements. Measurements of compressive, flexural, tensile (measured by the diametral compressive procedure) and shell strength are given in Table 5.17. These results show that the effect of reinforcement varies from cement to cement but, in general, increases it. 

Figure 33 Correlation of T2 from H NMR with ultimate elongation (tensile) measurement for thermally aged samples at the indicated temperatures, and for 22°C y-irradiated at 200 Gy/h. Reproduced from Harris et al. [86]. Copyright 2003, John Wiley 8t Sons, Inc.

Tear strength is only applicable to flexible materials and is very little used to monitor ageing simply because tensile strength will serve perfectly well. There are circumstances where compression stress-strain properties would be relevant but the relatively bulky test pieces will be subject to the limitation of oxygen diffusion in any accelerated tests and changes can probably be estimated from tensile measurements. Similarly, shear stress-strain is very rarely used for monitoring ageing. 

Product Identification was by GC/MS, NMR, and IR. Fundamental crosslinking chemistry was explored using swell measurements on simple solution copolymers and swell and tensile measurements with vinyl acetate (VAc), vinyl acetate/butyl acrylate (VAc/BA) or vinyl acetate/ethylene (VAE) emulsion copolymers. Polymer synthesis 1s described In a subsequent paper (6). Homopolymer Tg was measured by DSC on a sample polymerized In Isopropanol. Mechanistic studies were done 1n solution, usually at room temperature, with 1, 2 and the acetyl analogs 1, 2 (R =CH3). 

Tensile Tests. Polymers were padded on filter paper at lOX add-on, cured at 150°C for 3 or 10 min, and tested as In Tappi Useful Method UH656. Tensile measurements on padded samples were done with 1" strips on an Instron Tester after conditioning In a constant temperature and humidity room. Wet, methyl ethyl ketone (MEK) and perchloroethylene (PCE) tenslles were run after brushing the sample with IX aqueous Aerosol OT or solvent. 

Lap shear testing Shear can be applied in a number of ways cyclic, intermittent, static (or constant), or increasing. A simple overlap shear test is described in ASTM-D-1002. This can be illustrated again using two strong microscope slides. Here, the microscope slides are adhered in parallel to one another except offset. After the appropriate set-up time, the top and bottom of the slide combination are attached to the shear tensile-measuring device and the experiment is carried out. 

When a sample is smaller than about 1 cm it becomes impractical to use tensile measurements to study network structure. The swelling behavior of small... 

In considering true transition points we have considered only one, the liquid/ solid point, to be of practical significance. The other two points considered to be of practical importance—namely, the attainment of 5% and 90% maximum tensile strength—we have called critical points as opposed to transition points. We have not been able, as yet, to find simple reliable tests to replace tensile measurements. 

It is worth pointing out that the most reliable stress-strain curves are obtained by uniaxial compression or shear, in order to avoid the craze formation that can occur in tensile measurements. 

In the case of siloxane elastomers, the testing of mechanical properties is of particular importance. Elongation or tensile measurements are used almost to the exclusion of other types of mechanical tests, probably because of their simplicity. In this way, structural information is obtained about the networks, such as their degrees of cross-linking.92 Measurements of the ultimate strength (modulus at rupture), and the maximum... 

CED is determined by calculation, using the Van Krevelen increment values (Van Krevelen, 1990). There is no apparent effect of the crosslink density on K, which seems to depend (as CED), only on the molecular scale structure (polarity, hydrogen bonding). The following results were obtained with quasi-static tensile measurements (10-3-10 4 s-1 strain rate) in a temperature range 200 K-Tg, using a bidimensional extensometer to determine E and v (from which K and G could be determined) (Verdu and Tcharkhtchi, 1996) ... 

A constant strain rate of 10% per minute was employed. Polymers were isolated by air drying or freeze drying and molded at 150°C into dumbbell speciments for the tensile measurements. Glass transition temperatures (Tg) were measured by differential scanning calorimetry. 

The existence of a non-zero intercept in Equation 1 is probably attributed less to experimental precision than to variable stress relaxation although little stress relaxation generally occurs in high speed tensile measurements (12), the Tedlar data clearly demonstrate how extensive this may be. Even with the other materials, the toughness contribution from beyond the linear region, though small, differed from material to material. This variable contribution from beyond the linear region is considered the major reason for the nonzero intercept. 

The mechanical properties were evaluated by two sets of tensile measurements. Typical stress-strain curves are shown in Figure 4. The modulus and stress decrease with increasing aging time. Similar results are observed for all aging samples at all three temperatures. Both testing methods provided essentially the same tensile data at 400% extension. The scatter of the tensile data is due to the experimental error associated with the measurement. 

Tensile, modulus, and elongation are measures of the strength of a rubber compound.They are measured on bow tie-shaped specimens that are clamped in a tensile measuring apparatus and stretched. 

The mechanical behavior of the hydrogels can be described by the theories of rubber elasticity and viscoelasticity, which are based on time-independent and time-dependent recovery of the chain orientation and structure, respectively. Mechanical properties due to rubber elastic behavior of hydrogels can be determined by tensile measurements, while the viscoelastic behavior can be determined through dynamic mechanical analysis. 

All tensile measurements were performed by the authors with microtomed ribbons of 0.1 mm thickness at ambient temperature. In Fig. 10 typical stress-strain curves for all three poly(ether ester) materials are plotted. All samples were extruded at a common undercooling of 60 °C. The initial tensile modulus increased from 14 MPa for material A to 62 MPa and 208 MPa for B and C, respectively. 

In those cases where plasticizers were added, this was generally effected by adding polymer and plasticizers to toluene/alcohol mixtures, evaporating the solvent, and finally drying the plasticized polymer at 80 °C under vacuum. Alternately, the polymer-plasticizer mixture could be prepared by direct addition of the plasticizer to the powdered base resin. Stress-strain measurements were made on microdumbbells obtained from compression-molded pads of. 020 mil thickness. Tensile measurements were conducted at strain rates of 1000% /min. 

Ross-Murphy, S.B. and Todd, T. 1983. Ultimate tensile measurements of filled gelatin gels. Polymer 24 481 86. 

The crystals have been solution grown in o-dichlorobenzene by Hasegawa and Geil. This technique and the resultant crystal morphology have been described by Geil (7). To prepare samples for tensile measurements several additional requirements must be met. First, the crystals must be dispersed in the solvent so no aggregates form, and the crystallization should be complete so that no amorphous debris remains. Furthermore, high purity solvents are necessary to avoid contamination of the gap upon evaporation of the solvent. In practice we have found it necessary to distill the solvents in several cases. 

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