Cyclic Softening and Over-Softening of a 1 Percent Cr-Mo-V Steel at Elevated Temperature

1981 ◽  
Vol 23 (6) ◽  
pp. 305-308
Author(s):  
T. Gardiner
Keyword(s):  
Shear Stress ◽  
High Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Stress Range ◽  
Continuous Cycling ◽  
History Effect ◽  
Initial Cycle ◽  
Range Variation ◽  
Total Shear

Detailed results are presented of shear stress range variation during cycling of 1 per cent Cr-Mo-V test specimens within controlled total shear strain limits at 565°C. The cyclic softening induced during continuous and two-step cycling are compared. A saw-toothed pattern for the strain was maintained for each cycle giving a constant straining rate. Normal cyclic softening was found throughout the tests but another phenomenon of over-softening occurred during the two-step tests when high strain cycles took place first. A permanent history effect had been produced within the steel. This over-softening did not depend on the straining rate of the cycling or the magnitude of the initial cycle ratio. The generally accepted method of determining cyclic stress-strain curves using continuous cycling is shown to be invalid when over-softening is present.

Strain-Based Fatigue Test and Reliability Research of 42CrMo Alloy Steel

2010 ◽  
Vol 97-101 ◽  
pp. 856-860
Author(s):  
Nan Xu ◽  
Xiu Hua Ren ◽  
Wei Qiang Wang
Keyword(s):  
Fatigue Test ◽  
Alloy Steel ◽  
Strain Range ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Range Data ◽  
Stress Range ◽  
Probability Models ◽  
Total Strain Range

The strain-based fatigue tests of 42CrMo alloy steel were conducted by controlling six sets of total strain range, and stress range data was obtained under each strain range. The results of fatigue test revealed that fatigue performance of 42CrMo alloy steel was of tremendous dispersivity all though materials were strictly chosen, heat-treated and machined. Cyclic stress-strain (CSS) curves were compared with monotonic tensile curve, which showed that 42CrMo alloy steel quenched and tempered was a kind of cyclic softening material. Evaluation results revealed that LND was the best probability function to describe cyclic stress of strain fatigue for 42CrMo steel. Cyclic stress range under the median and high probability was evaluated by means of stochastic performance probability models.

Effect of Tensile Dwell on Low Cycle Fatigue of Cast Superalloy Inconel 792-5A at 800°C

2011 ◽  
Vol 488-489 ◽  
pp. 735-738
Author(s):  
Miroslav Šmíd ◽  
Karel Obrtlík ◽  
Martin Petrenec ◽  
Jaroslav Polák
Keyword(s):  
High Strain ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Lower Stress ◽  
Secondary Cracks ◽  
Continuous Cycling ◽  
Cast Superalloy ◽  
Strain Cycling

Effect of tensile dwell on low cycle fatigue of cast Inconel 792-5A is studied in symmetrical strain cycling at 800°C. Cyclic hardening/softening curves, cyclic stress-strain curves (CSSC) and fatigue life curves were obtained in continuous cycling and in cycling with tensile dwells. Dwells have slight effect on hardening/softening curves at high strain amplitudes. CSSC in cycling with dwells is shifted to lower stress amplitudes. No significant effect of dwells on Basquin curves is observed. Density of slip markings in continuous cycling is significantly higher in comparison with cycling with dwells. Samples cycled with dwells are typical of high density of secondary cracks, although sporadic slip markings were also found.

Rate Dependent Constitutive Equations of Cyclic Softening

1985 ◽  
Vol 40 (7) ◽  
pp. 653-665
Author(s):  
J. S. Mshana ◽  
A. S. Krausz
Keyword(s):  
Stress Relaxation ◽  
Low Temperature ◽  
Constitutive Equations ◽  
Strain Softening ◽  
Structural Characteristics ◽  
High Stress ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Stress Softening

Constitutive equations of cyclic strain and stress softening for materials with low internal stress levels are derived from the rate theory. The study shows that over the high stress and low temperature range where the description of plastic flow in cyclic softening can be approximated with activation over a single energy barrier, cyclic strain softening is well related to stress relaxation process while cyclic stress softening is related to creep process. The material structural characteristics for cyclic strain softening, cyclic stress softening and stress relaxation are identical. Subsequently, it is shown that cyclic stress and strain softening within the high stress and low temperature range can be evaluated from the constitutive equations using the material structural characteristics measured from a simple stress relaxation test.

Observations of the Effect of Creep Relaxation on High-Strain Fatigue

1966 ◽  
Vol 8 (3) ◽  
pp. 310-321 ◽  
Author(s):  
H. G. Edmunds ◽  
D. J. White
Keyword(s):  
Room Temperature ◽  
High Strain ◽  
Hold Time ◽  
Published Data ◽  
Preliminary Design ◽  
Test Environment ◽  
Continuous Cycling ◽  
Molybdenum Steel ◽  
Endurance Tests ◽  
Early Indication

Results are presented of high-strain endurance tests on 2‡ per cent chromium, 1 per cent molybdenum steel. As well as continuous cycling at room temperature and 600°C, the tests covered hold times of 30 minutes and 300 minutes at maximum strain at 600°C. For the shorter hold times, strain ranges extended down to less than ±0.1 per cent and for the longer hold times down to ±0.24 per cent. In a few tests an attempt was made to modify the test environment in order to gain an indication whether corrosion effects are likely to be important in such tests. It is argued that, for preliminary design purposes (pending the outcome of comprehensive endurance tests), extrapolation from high strains to low may be dangerous and that it may be preferable to use relatively simple creep data to gain an early indication of likely endurance properties with hold time. Such an interpretation is not inconsistent with the present or previously published data.

Rapid cycle-dependent softening of equal channel angularly pressed Sn–Ag–Cu alloy

2008 ◽  
Vol 23 (10) ◽  
pp. 2630-2638 ◽  
Author(s):  
Q.S. Zhu ◽  
Z.G. Wang ◽  
Q.L. Zeng ◽  
S.D. Wu ◽  
J.K. Shang
Keyword(s):  
Grain Boundary ◽  
Cast Alloy ◽  
Intermetallic Phase ◽  
Crack Density ◽  
Sharp Decrease ◽  
Surface Damage ◽  
Cyclic Stress ◽  
Grain Boundary Sliding ◽  
Cyclic Softening ◽  
Boundary Area

Cyclic stress–strain response of an equal channel angularly pressed Sn-3.8Ag-0.7Cu alloy was investigated to seek a mechanistic understanding of cyclic softening in Sn-rich alloys. The equal channel angular pressing (ECAP) was applied to modify the microstructure of the solder alloy by breaking up the needlelike Ag3Sn intermetallic phase into fine granules and by reducing the large β-Sn dendrites into smaller and equiaxed grains. The extruded alloys were subjected to strain-controlled fatigue test at various strain amplitudes. It was found that the extruded alloy exhibited a sharp decrease of the stress amplitude within the initial few cycles compared with the as-cast alloy. After only a few cycles, the alloy suffered from noticeable surface damage. In situ scanning electron microscopy observations of the cyclic bending specimens revealed an approximately logarithmic relationship between crack density and the number of cycles. A theoretical model of microcrack accumulation was constructed to explain the rapid cyclic softening behavior. The predicted results, based on the model, agreed well with the experimental data and indicated that the rapid softening had resulted from an increased tendency for grain boundary cracking in the ECAPed microstructure due to the increase in the grain boundary area per unit volume and the reduced resistance of Ag3Sn to grain boundary sliding.

Cyclic behaviour of materials

1970 ◽  
Vol 5 (3) ◽  
pp. 185-192 ◽  
Author(s):  
K J Miller
Keyword(s):  
Strain Rate ◽  
Strain Curve ◽  
Cyclic Hardening ◽  
Fatigue Behaviour ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Static Tests ◽  
Static Test ◽  
Cyclic Behaviour ◽  
Incremental Step

The effect of strain rate on the cyclic behaviour of two materials is presented. For the material that cyclically hardens (En 32B) a decrease in strain rate decreases the maximum cyclic hardening of the material, whilst for a material that cyclically softens (En 25) a decrease in the rate of deformation increases the maximum cyclic softening. It is concluded that the effect of strain rate on the cyclic stress-strain curve should be more closely studied than the effect of frequency since the frequency may be constant whilst the straining rate may vary considerably in plastically deformed zones. For those zones that suffer low strain rates the inclusion of time-dependent deformation processes can maximize the degree of softening or minimize the degree of hardening, thereby creating a greater localization of the plastic strain which should increase strain-concentration factors. Finally it is argued that it is better to predict fatigue behaviour from an incremental-step high-strain fatigue test on a single specimen than from static-test data. For the same reasons correlations between static tests and fatigue tests should be discouraged, especially for those materials that exhibit marked cyclic softening.

scholarly journals Determination of Johnson Cook Parameters in Turning of Micro and Nano Reinforced Aluminum Composites using Trust Region Reflective Algorithm

2019 ◽  
Vol 8 (12) ◽  
pp. 1712-1716 ◽  
Keyword(s):  
Shear Stress ◽  
Composite Materials ◽  
High Strain ◽  
Base Alloy ◽  
Trust Region ◽  
Vital Role ◽  
Correct Prediction ◽  
Machining Parameters ◽  
Reinforced Composite

Accuracy of shear stress estimations plays a vital role in correct prediction of cutting forces in machining. In this study, efforts were directed to obtain better flow stress estimates through determination of novel Johnson Cook (JC) parameters for a number of micro and nano reinforced composite materials. Trust region reflective algorithm (non linear least squares) was used to determine optimum JC constants for each developed material subjected to varying machining parameters under high strain rate conditions. The newer JC constants yielded substantially better shear stress estimates as compared to base alloy JC constants; thus in turn improving cutting force predictability in machining of developed composite materials.

Practical Criterion for Estimation of Notch Fatigue Strength

2004 ◽  
Author(s):  
Hiroshi Matsuno ◽  
Yoshihiko Mukai
Keyword(s):  
Surface Layer ◽  
Fatigue Strength ◽  
Stress Ratio ◽  
Notch Root ◽  
Equivalent Stress ◽  
Cyclic Stress ◽  
Biaxial Stress ◽  
Combined Loading ◽  
Stress Range ◽  
Stress Cycling

In the present study, a practical criterion for the estimation of the fatigue strength of notched specimens is discussed from a practical standpoint of design and maintenance of machines and structures. First of all, a hypothesis of “Fatigue Plastic Adaption” is proposed as one idea that is available to combine microscopic and macroscopic approaches to fatigue plasticity. The hypothesis expresses that, at a surface layer and at a notch root, elastic deformation arising at the cyclic maximum stress is transformed into local and inhomogeneous plastic deformation. Based on the hypothesis, mechanical models are constructed in order to simulate cyclic stress behavior at the surface layer and at the notch root. As a result, “Equivalent Stress Ratio” is formulated as a parameter for correspondence of cyclic stress conditions between notched and unnotched specimens. Moreover, on the basis of the hypothesis of the plastic adaptation, the equation of the equivalent stress ratio is also derived for the case of biaxial stress cycling in torsion, and it is finally expanded for the general case of proportional multiaxial stress cycling. The published fatigue data concerning tension-compression, bending, torsion and their combined loading are rearranged on the diagram where an abscissa indicates the equivalent stress ratio and an ordinate indicates the stress range at the notch root. As the result, it is recognized that the relation between the equivalent stress ratio and the notch-root-concentrated stress range is shown by a certain curve proper to material in spite of difference of stress concentration factors, loading types and mean stresses. Consequently, a criterion for notch fatigue strength is described on the basis of the equivalent stress ratio, i.e., the notch-root-concentrated stress range at the fatigue strength of the notched specimen for any nominal stress ratio is identical with the fatigue strength of the unnotched specimen for the equivalent stress ratio.

A 3D Masonry-Like Model with Bounded Shear Stress

2017 ◽  
Vol 747 ◽  
pp. 20-27 ◽  
Author(s):  
Massimiliano Lucchesi ◽  
Barbara Pintucchi ◽  
Nicola Zani
Keyword(s):  
Shear Stress ◽  
Constitutive Equation ◽  
Convex Subset ◽  
Numerical Results ◽  
Stress Range ◽  
Symmetric Tensors ◽  
Elastic Materials ◽  
Linear Elastic ◽  
Non Linear

This paper deals with non linear elastic materials for which not all the stresses are admis-sible but only those which belong to the stress range, i.e. a closed and convex subset of the spaceof all symmetric tensors. The constitutive equation that has been formulated and explicitly solved issufficiently general to include, besides the so-called masonry-like materials, many others whose stressrange is obtained experimentally or is theoretically defined. The model, implemented into the finiteelement code MADY, has been used to analyze a masonry panel under a bi-directional monotonicallyincremental load and the obtained numerical results have been discussed.

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