Under Cyclic Tension

1 True Axial Stress versus Strain Relation 

Strain increases with the cycle or the applied true strain. This quantity also decreases with the increasing alloying content, that is, relatively larger quantity of recovered volume strain for BD13 than for BD16. 

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Figure 19.18 True stress-strain relationship under cyclic tension. (From Reference 10 with permission from Elsevier Inc.)...

The resistivity data are shown in Fig. 4 for the second specimen under cyclic tension-compression mode with 0.2% constant strain amplitude. In the first 50 cycles the rate of increase, dpm(e)/dN, at 5 T is about 8x 10 nfi-cm/cycle. At relatively low fields (S = 1 to 2 T), the rate of increase was about 80% of that at 5 T. This means dpm e)/dN was rather insensitive to magnetic field. Between 50 and 400 cycles, dpm(s) dN was reduced to 1.7x 10" nfi-cm/cycle at 5 T. After 400 cycles, the rate was reduced even further. The cyclic strain was not continued to the point of saturation of the resistivity. Increasing the number of cycles, the mode of the stress-strain curve was changed from almost plastic to elastic. At N = 600, the peak load values of tension and compression increased from about 29 to 65 MN/rn. 

In order to demonstrate the predictability of the above model, the macroscopic behavior of the SMPF is estimated and the prediction is compared with the test result. In the following, three such predictions and/or comparisons are made. The first one investigates the effect of the heating rate on fully constrained stress recovery. The second one evaluates the effect of the amount of the amorphous phase and the crystalline phase on the stress-strain behavior under cyclic tension. The last one examines the growth of the crystalline phase due to stress induced crystallization. In all cases, the SMPF has a diameter of 0.04 mm. The material parameters for the stress recovery and strain hardening modeling as well as for the amorphous and crystalline subphase modules and for crystalline phase shp systems are summarized in Tables 5.2 to 5.4, respectively. 

Bai, S.-L. and Wang, M. 2003. Plastic damage mechanisms of polypropylene/polyamide 6/ polyethylene octane elastomer blends under cyclic tension. Polymer 44 6537-6547. 

M. J. Reece, F. Guiu, and M. F. R. Sammur, Cyclic Fatigue Crack Propagation in Alumina under Direct Tension-Compression Loading, J. Am. Ceram. Soc., 72[2], 348-352 (1990). 

Opposite indications come from the work of Anderson et al. [26], reporting the results of combined tension or compression and torsion cyclic loading on [ 30/90]s aramid/epoxy mbes. Under combined tension and shear loading, a phase shift equal to 180° induces a fatigue strength reduction of about 25%, and the strength... 

Endurance ratio n. The ratio of the endurance limit, under cyclic stress reversal, to the short-time, static strength of a material. If the mode of stress is not specified, tension/compression may be presumed. 

The challenges inherent in the measurement of stress-strain response of thin film materials by means of direct tensile testing are commonly more than offset by the distinct advantage that properties characterizing deformation resistance of the material in the plastic range can be determined under isothermal conditions for a relatively simple state of stress on the specimen. However, these techniques are not readily amenable to modifications that can accommodate uniaxial compression, simple shear stress, equi-biaxial stress or states stress on the specimen. As a result, it is difficult to draw conclusions concerning the dependence of plastic response on stress path history. It is noted that results for some cyclic tension-compression experiments were reported by Hommel et al. (1999). 

Modulus, dynamic Ratio of stress to strain under cyclic conditions that is calculated from either free or forced vibration tests in shear, compression, or tension. 

Steel Under Earthquake Excitations Reinforcing steel in external reinforced crmcrete jackets for the retrofit and strengthening of existing reinforced concrete or steel members comes mainly in the form of bars. Usually, the stress-strain behavior under tension-compression is cmcial to assess the longitudinal bars contribution. The stress-strain behavior under tension is of interest for the transverse reinforcement (stirmps). Steel dowels and stud shear connectors may involve shear (or tensile) behavior of steel- or bond-related issues. External steel plates may be considered under multiaxial loading (i.e., in cases of shear strengthening in order to estimate their yield stress). Bond-related issues may concern bar-concrete interfaces, bar-resin-concrete interfaces (NSM applications), or plate-resin-concrete interfaces under cyclic loading. 

Several criticisms of these parameters have recently been pointed out. First, they have no specific association with a material plane (i.e., they are scalar parameters), despite the fact that cracks are known to nucleate on specific material planes. With traditional parameters it is difficult to account for the effects of crack closure under compressive loading. Traditional parameters have not been successful at unifying experimental results for simple tension and equibiaxial tension fatigue tests. Finally, a nonproportional loading history can always be constmcted for a given scalar equivalence parameter that holds constant the value of the scalar parameter, but which results in cyclic loading of material planes. For such histories, scalar parameters incorrectly predict infinite fatigue life. 

To conclude the analysis of the influence of biaxiality ratios, it is worth mentioning the work by Perevozchikov et al. [19]. They investigated the fatigue behavior of unidirectional glass/epoxy mbular samples under the combined effect of shear stresses and transverse tension or compression stresses and reported the negative effect of cyclic shear stress components in the case of both tensile and compressive transversal stress. It was also shown that the increase of Xu ratio induced a reduction in the fatigue strength. 

Fujii T, Lin F, Morita Y. Fatigue behavior of plain woven glass-fabric laminates under tension/torsion combined loading (Effect of shear stress and cyclic condition on fatigue failure). Nippon Kikai Gakkai Ronbunshu, A Hen/Trans Jpn Soc Mech Eng Part A 1994 60 650—7 [in Japanese]. 

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