Time to fracture

Equation (8.46) applies to the motion until fracture is complete. After this the form of (8.45) applies. Kipp and Grady (1985) have shown that the time to fracture (time from inception to completion of failure at the fracture zone) depends on the material and kinematic properties of the problem according to... 

Further, if one considers the distance the tensile unloading wave can propagate over the time to fracture f from (8.46), a lower bound criterion for the fragment size can be established... 

Fig. 1.19 Potential-pH diagram for copper in solutions containing and (NH4>2S04 (after Mattson ) with superimposed times to fracture Tf of direct-loaded a-brass wires held at various potentials in the solution of pH 7-2 the specimen without external polarisation had Ff = 3y h (after Hoar and Booker S)...

Table 4 Time to fracture of branched PEs tested in long-term tensile tests at 50 °C in a 10% aqueous solution of Igepal (CO-630, notched specimen). Number of branches/1000 carbon atoms 18. Isothermal crystallization at 115°C/lh [85]...

Molecular tl iy for fracture could be traced ba k to an application of the rate-process theory to fracture teiomena (65) and al the similar line of thou t Beuche (1) developed his theory for fracture in p<%mer. Zhurkov (66,67) derived independently the same equation to the Beuche s one the time to fracture. Based on this equation the activation energies for the fracture were estimated from the experimental results on the time to fracture under the unaxial load (20,68). Change of deformation potential in a stressed chain was discussed by Kausch (J9.20). Fracture developement has been discussed from the a >ects of micromori lr of polymers by Peterlin (J5, 69-71), Kausch (19,20) and DeVries(/7,61, 72). 

Ffe. 21. Stress dependence of time to fracture of craze matter in PS (from Ref. [34], courtesy of Pergamon Press)... 

Fig. 7. Rate dependence of time-to-fracture values, tf, based on crack tip strain gage measurements for all materials investigated.

The essential parameters for the calculation of Kj are the time-to-fracture, tf, and the materi modulus, E. Values for tf were determined via crack tip strain gage signals according to a procedure described in [5, 6], The testing rate dependence of tf values are shown in Fig. 7. for materials investigated. Adequate values for the rate dependent modulus E (as well as for the rate dependent Poisson s ratio which enters into the proper definition of in Eq. 2) of the various engineering polymers used in this study, were determined experimentally [4]. At example of data is shown for POM in Fig. 8. 

Zhurkov and Tomashevsky proposed a direct relationship between ATab the time to fracture of a loaded specimen. If we stipulate as a fracture criterion the requirement that a certain nmnber A/ of molecular chains must fracture for the remaining intact chains to be unable to carry the load, the time to fracture, tf, becomes. 

For a body containing small flaws of length a, the stress-time to fracture initiation relationship is given by ... 

Figure 2. Minimum creep rate (a) and time to fracture (b) versus stress for the monolithic alloys and their short fiber composites.

Fig. 2b shows the variation of the time to fracture with the stress for the same specimens tested in Fig. 2a. The results for AZ 91 alloy and its composite demonstrate the creep life-times of the composite may be up to one order of magnitude longer than those for the monolithic alloy although this difference decreases with increasing applied stress so that ultimately there is very little difference at stresses >100 MPa. By contrast, the creep life of the QE 22 + Saffil composite is markedly shorter than that of the unreinforced alloy at stresses > 100 MPa. The presence of a reinforcement leads to a substantial decrease in the overall ductility of matrix alloy. Thus,...

Results of Fracture-Toughness Tests over the Range of Test Speeds. Figure 4 shows the stress intensity factor, KImax, versus test speed for all the materials tested. The test speed is the true opening displacement rate of the specimen when fracture occurs. It is measured by the optical device, and it can be up to 14 m/s. Typical times to fracture vary from 10 s at the lowest speeds to -150 xs at the highest. 

Figure 17. Biaxial flexural strength, as a function of stress rate (a) and predicted flexural strength as a function of time to fracture (b) for UST dental porcelain, with and without ion exchange, in artificial saliva at 37°C. In a),(Jjo is the scaling parameter and n is the slow crack growth, SCG, susceptibility coefficient. Inert strength was determined at 100 MPa/s in air with a drop of silicone oil on the tensile surface to inhibit the occurrence of SCG. In (b), the slope of fitted curve is related with n. Data from [63,71]...

A more recent test (DlB-test) utilises a solution containing 5 g/1 804, 0.5 g/1 of CT and lg/1 of SCN (added as potassium salt). This test has the advantage that the test solution is less aggressive and the amount of hydrogen that is developed during the test is comparable with that produced in practice on the surface of prestressing tendons within the ducts in defective conditions. The time to fracture required is 2000 h. All types of steel that caused damage in field, failed in this DIB standard test within 2000 h [6]. 

SCC materials data have often been presented in the form of diagrams showing time to fracture as a function of nominal stress. The diagrams show that a minimum (threshold stress) is necessary to eause SCC. However, a better measure of eritieal stress is the critical stress intensity factor (see Section 7.12.3). 

Figure 7.62 Dependence of time to fracture on stress for different stainless steels in 42% boiling MgCl2 solution. (Adapted from Fontana and Greene [7.1].)...

Stress Cracking Resistance (Constant Tensile Load) - data Polymer Solids and Polymer Melts R. Lack, W. Grellmann Constant Tensile Test Method Table 4.24 Time to fracture as a function of medium and applied load (unit MPa) or the stress intensity factor K (unit MPa mm ) for thermoplastic materials by means of the constant (tensile) load method (using notched samples incl. FNCT and PENT). ... 

Material Specification Medium T [°C] Load [MPa] Time to fracture [s] Ref. 

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