Elastic recovery test

The elastic recovery test is used for the determination of the elastic recovery of the bituminous binders in a ductilometer at a given temperature. It is primarily applicable to modified 

The test is carried out in accordance to CEN EN 13398 (2010) and ASTM D 6084 (2006), or AASHTO T 301 (2013), by using the same apparatus, mould and procedure as in the ductility test. The testing temperature is usually 25°C. The only difference is that the bituminous specimen is not stretched until rupture but only up to a predetermined elongation (200 mm by CEN EN 13398 2010). 

The bitumen thread thus produced is cut in the middle to obtain two halves of thread. After a predetermined time for recovery has elapsed (30 min by CEN EN 13398 2010), the shortening of the half threads is measured (by a ruler) and expressed as the percentage of the elongation length. 

The test is performed on two specimens, and their arithmetic mean, rounded up to 1%, is taken as the representative elastic recovery value of the bituminous binder. The difference between the two measurements should be less than 5% in absolute value. Otherwise, a third specimen is tested and the representative elastic recovery is the arithmetic mean of the two values that differ the least. If the third value differs by more than 5% in absolute value, the test is repeated with two new samples. 

The elastic recovery test, because of its similarity to the ductility test, is also sometimes called the modified ductility test. 

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With the appearance of modified bitumen, there was a necessity to establish supplementary tests. Thus, cohesion tests, the elastic recovery test and storage stability tests have been added. 

It should be pointed out that the same apparatus is used for the elastic recovery test. For details, see Section 4.6. 

AASHTO T 301.2013. Elastic recovery test of asphalt materials by means of a ductilometer. Washington, DC American Association of State Highway and Transportation Officials. 

Elastic recovery tests (a) loading-unloading curve and (b) elastic recovery results. 

Hardness is essentially a measure of stiffness and in principle can be related to modulus. For plastics, the term hardness refers to resistance to indentation but depending on the test method the measurement is made either with the indentation load applied or after its removal when elastic recovery has taken place. The standard methods are given in ISO 868 (Shore) [6] and ISO 2039 (Ball indentation and Rockwell) [7]. However, Vickers microhardness is more satisfactory for monitoring degradation of rigid materials. 

Plasticity test determines the deformation or flow of a rubber compound having little elastic recovery. It should be remembered that elasticity is present even in an un-vulcanized rubber and the energy will be stored in the compound during deformation and then released when the force is removed. Rubber before vulcanization is in between a plastic and an elastic state when warmed up it becomes more plastic and less elastic. From commercial points of view, the plasticity tests are of little significance, but are important because their results assist in determining the processibility of the material and are used frequently for process control purposes. 

More modem versions of the Defo test have vacuum preparation of the test piece and computerised control but although they measure both the viscous and elastic components, it is still a compression test at low shear rate. Isayev et al27 described an instrument and method to discriminate between materials by measuring the elastic recovery at very short times. 

Observations of the specificity of indentations, excluding measurement of the magnitude of Vickers pyramid penetration, enable a description of the properties of minerals, ceramic materials, or other brittle bodies (Vigdo-rovich and Yelenskaya, 1967 A. Szymanski et al., 1969). The action of elastic-recovery forces after removal of the pressure often causes perturbation in the structure of the test surface, around the site subjected to loading (Fig. 6.3.1). This is described in Section 6.2. 

The amorphous phase appearing above 20 GPa at room temperature (see above) has also recently been studied by X-ray diffraction [135] and Raman scattering [132,133]. Serebryanaya et al. [135] identify the structure as a three-dimensionally polymerized Immm orthorhombic lattice, but find that compression above 40 GPa gives a truly amorphous structure. In contrast to the orthorhombic three-dimensional polymer structure discussed in the last section, the best fit here is found for (2+2) cycloaddition in two directions, with (3+3) cycloaddition in the third, and thus some relationship to the tetragonal phase. From the in situ X-ray data a bulk modulus of 530 GPa is deduced, about 20% higher than for diamond. Talyzin et al. [132, 133] find that this phase depolymerizes on decompression into linear polymer chains, unless the sample is heated to above 575 K under pressure. A strong interaction with the diamond substrate is also noted, such that only films with a thickness of several hundred nm are able to polymerize fully [ 132]. Hardness tests were also carried out on the polymerized films, which were found to be almost as hard as diamond and to show an extreme superelastic response with a 90% elastic recovery after indentation [133]. 

A variety of rheological tests can be used to evaluate the nature and properties of different network structures in foods. The strength of bonds in a fat crystal network can be evaluated by stress relaxation and by the decrease in elastic recovery in creep tests as a function of loading time (deMan et al. 1985). Van Kleef et al. (1978) have reported on the determination of the number of crosslinks in a protein gel from its mechanical and swelling properties. Oakenfull (1984) used shear modulus measurements to estimate the size and thermodynamic stability of junction zones in noncovalently cross-linked gels. 

Direct information on elastic recovery, relative hardness, work of indentation, and strain rate-stress relationship (Fig. 2.15) can provide a comprehensive fingerprint of a particular sample resulting, for example, from a change in either a production process or a wear test procedure. It is ideally suited to the comparison of one sample with a control or reference. The wider assumptions that are needed to derive indirect... 

Fliestand and Smith (1984) proposed three indices referred to as Tabletting Indices. The three indices are a strain index, bonding index and the BFI, which was described in the section on Capping. The strain index is a measure of the strain present in a material following compaction and is a measure of elastic recovery calculated by a dynamic indentation hardness test. The bonding index is a measure of the material s ability to deform plastically and form bonds and is the ratio of a compact s tensile strength and indentation hardness. 

The texture of bread was evaluated based on an instrumental Texture Profile Analysis (TPA). Bread slices (height 30 mm) were compressed with a universal testing machine (Zwick 1445, Ulm, G) to 15 mm with two repeating cycles. The crumb firmness and the elastic recovery were evaluated as described in ref. 8. The modulus of deformability of starch and flour gels was evaluated as described in ref. 7. 

Although the data on tensile elastic recovery are not normally specified for commercial purposes, they may be required in the assessment of the suitability of a given type of fiber for particular purposes and are often quoted in manufacturers publications and the technical press. .. It is recognised that values for the tensile elastic recovery of a fiber may vary considerably with the conditions of test, and no single set of conditions will define adequately the behaviour of the fiber. Consequently the tensile elastic recovery should be measured for at least two widely differing conditions of extension or relaxation time, one of which is a preferred set of conditions, the other being appropriate to the purposes of testing. 

BS 4029, 1978, specifies a method of test for the measurement of tensile elastic recovery of all types of single filaments or fibers when subjected to tensile strain applied by a CRE type machine. No special pretreatments such as mechanical cycling or relaxation of internal stresses by immersion in boiling water are specified, although it is acknowledged that they may be required for some special purposes. The determination of elastic recovery from a given stress (specific stress) is not included. 

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