Toughness index

The elasticity of a fiber describes its abiUty to return to original dimensions upon release of a deforming stress, and is quantitatively described by the stress or tenacity at the yield point. The final fiber quaUty factor is its toughness, which describes its abiUty to absorb work. Toughness may be quantitatively designated by the work required to mpture the fiber, which may be evaluated from the area under the total stress-strain curve. The usual textile unit for this property is mass pet unit linear density. The toughness index, defined as one-half the product of the stress and strain at break also in units of mass pet unit linear density, is frequentiy used as an approximation of the work required to mpture a fiber. The stress-strain curves of some typical textile fibers ate shown in Figure 5. 

Fig. 11. Normalized toughness index as a function of sub-Tg annealing time...

Mix details Fiber content and treatment First crack strength, Of (psi) First crack toughness, T (Ib-in.) I5 Co ho 30 Toughness index, Tjci (lb-in.)2 Equivalent flexural strength, CTb (psi) "... 

Furthermore, validation work of different fracture toughness indexes was performed within the FP-4 project REFEREE. In this project the influence of dynamic loading (used for the surveillance specimens) on the shift of fracture toughness was studied with respect to the shift obtained under quasi-static loading (as is the case under real conditions in the RPV). 

Fig. 5.17 In-plane tear and fracture toughness index against PCC content for the new composite and reference paper. Commercial copy is a geometric mean value. Abbreviations C new composite handsheets. Fibre components reg.cellulose regenerated cellulose, euca eucalyptus unrefined, sw fractionated refined softwood...

UTS, Eg, Normalized Toughness Index, Young s Modulus and Yield Stress as a Function of the Composite Thermal History... 

Probably the idea to use a dimensionless magnitude called the fracture index as a possible material characteristic was first published by Henager (1978). The test beam standardized by ASTM of cross-section 102x102 mm and of 305 mm span was used. It was loaded in its centre up to the total deflection of 1.9 mm. The toughness index (TT) was calculated as the ratio of area A+B to area A as it is shown in Figure 10.28. For plain concrete or mortar the value of TI is 1.0 or a little more, and for strongly reinforced fibre composite it may reach values of 30 or even 46. 

Figure 10.29 Schematic curve for determination of the flexural toughness indexes according to ASTM C 1018 (1997).

Examples of load-deflection curves in Figure 10.30 show the possible deficiencies of this type. Curve a describes a small strain hardening while curve a represents a rapid decrease of load after cracking and both are characterized by the same toughness index I5. Similarly, for curves b and b index I o is the same and only index I5 shows small difference, while the material s behaviour is completely different. Also, for curves c and c only I5 and I o are different while the values of I20 are the same. These examples prove that the determination of the toughness index is only a useful method of comparison for the effective material s behaviour with that of an idealized linear elastic-plastic material. However, it cannot be considered as a perfect material characteristic. 

TI(3) toughness index calculated as ratio of respective areas up to deflection 3 8 and 8 ... 

Henagei C. H. (1978) A toughness index of fibre concrete, in Proc. Int. RILEM Symp Testing and Test Methods of Fibre Cement Composites, R. N. Swamy ed., Sheffield Construction Press Ltd pp. 79—86. 

Fabrication of abrasive tools containing mesh diamonds, particularly with metal bonds, involves processing at temperatures of up to 900°C or even higher. The thermal stability of the crystals is therefore very important for such applications. The most common way to characterize thermal stabUity is to perform a toughness measurement after a high-temperature exposure— for example, 1100°C for 10 minutes in an inert atmosphere—yielding a thermal toughness index (TTl). The thermal stability of diamonds is mainly determined by the... 

The aim of the experiments was to investigate a simple test which could supply adequate information about the behaviour of SFRC. The basic concept was to use the ASTM approach of describing the matrix properties through the first crack strength (at LOP) and the fibre reinforcing effect through a toughness index. In addition crack distribution should be evaluated. 

In Fig. 6 demonstrated is dependence of the average number of the observed cracks on parameter r) /ci. Similar dependence can be observed for toughness index 1(10), where the coefficient of correlation for the same set of the results was found r = 0.727. 

One of the properties of concrete which is improved by the addition of fibres is energy absorption, it can be represented by the toughness index. The toughness index is calculated as the area under the normalized load-deflection curve out to the reference deflecion Dr Ti=(L/Lp)x(D/Dr)xlOO, where Dr=span/150, Lp=the peak of load. 

Figure 8.40 Effect of size of bundle (number of filaments) and supplementary material (metakaolin - MK Diatomite - DIA) on the retention of the /30 toughness index after accelerated ageing at S0°C for 84 days (plotted from data of Brandt and Glinicki [120]).

---