Micromechanics Study of Fatigue Damage Incubation Following an Initial Overstrain

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Yibin Xue ◽  
Amanda M. Wright ◽  
David L. McDowell ◽  
Mark F. Horstemeyer ◽  
Kiran Solanki ◽  
...  
Keyword(s):  
Plastic Strain ◽  
Shear Strain ◽  
Equivalent Plastic Strain ◽  
Strain Range ◽  
Maximum Strain ◽  
Plastic Shear ◽  
Cyclic Plastic ◽  
Intermetallic Particles ◽  
Plastic Shear Strain ◽  
The Matrix

Understanding and quantifying the effects of overloads/overstrains on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multistage fatigue model under variable amplitude loading. Micromechanical simulations are conducted on a 7075-T651 Al alloy to quantify the cyclic microplasticity in the matrix adjacent to intact or cracked, life-limiting intermetallic particles. An initial overstrain followed by constant amplitude cyclic straining is simulated considering minimum to maximum strain ratios of 0 and −1. The nonlocal equivalent plastic strain at the cracked intermetallic particles reveals overload effects manifested in two forms: (1) the cyclic plastic shear strain range is greater in the cycles following an initial tensile overstrain than without the overstrain and (2) the initial overstrain causes the nonlocal cumulative equivalent plastic strain to double in subsequent tensile-going half cycles and triple in subsequent compressive-going half cycles, as compared with cases without an initial tensile overstrain. The cyclic plastic zone at the microdiscontinuity corresponds to that of the maximum strain during the initial overstrain and the nonlocal cyclic plastic shear strain range in the matrix near the intact or cracked inclusion is substantially increased for the same remote strain amplitude relative to the case without initial overstrain. These results differ completely from the effects of initial tensile overload on the response at a macroscopic notch root or at the tip of a long fatigue crack in which the driving forces for crack formation or growth, respectively, are reduced. The micromechanical simulation results support the incorporation of enhanced cyclic microplasticity and driving force to form fatigue cracks at cracked inclusions following an initial tensile overstrain in a fatigue incubation model.

scholarly journals The Application of “Strain Range Partitioning Method” to Torsional Creep-Fatigue Interaction

1976 ◽  
Vol 98 (3) ◽  
pp. 244-248 ◽  
Author(s):  
S. Y. Zamrik ◽  
O. G. Bilir
Keyword(s):  
Plastic Strain ◽  
Shear Strain ◽  
Creep Strain ◽  
Strain Range ◽  
304 Stainless Steel ◽  
Strain Component ◽  
Strain Partitioning ◽  
Plastic Shear ◽  
Torsional Fatigue ◽  
Plastic Shear Strain

The method of strain range partitioning was applied to a series of torsional fatigue tests conducted on tubular 304 stainless steel specimens at 1200°F (649°C). Creep strain was superimposed on cycling strain, and the resulting strain range was partitioned into four components; completely reversed plastic shear strain, plastic shear strain followed by creep strain, creep strain followed by plastic strain and completely reversed creep strain. Each strain component was related to the cyclic life of the material. The paper describes the experimental procedure used to achieve strain partitioning and the torsional test results are compared to those obtained from axial tests. The damaging effects of the individual strain components were expressed by a linear life fraction rule. The shear strain plastic component showed the least detrimental factor when compared to creep strain reversed by plastic strain. In the latter case, a reduction of torsional fatigue life in the order of magnitude of 1.5 was observed.

Automated Measurement of Near-Surface Plastic Shear Strain

2014 ◽  
Vol 3 (3) ◽  
pp. 1-16 ◽  
Author(s):  
G. Trummer ◽  
K. Six ◽  
C. Marte ◽  
A. Meierhofer ◽  
C. Sommitsch
Keyword(s):  
Shear Strain ◽  
Surface Plastic ◽  
Automated Measurement ◽  
Plastic Shear ◽  
Near Surface ◽  
Plastic Shear Strain

Impact of Low Temperatures on Solder Joint Failures

2002 ◽  
Vol 124 (2) ◽  
pp. 135-137 ◽  
Author(s):  
Boris Mirman
Keyword(s):  
Solder Joint ◽  
Shear Strain ◽  
Low Temperatures ◽  
Solder Joints ◽  
Failure Criteria ◽  
Plastic Shear ◽  
Plastic Packages ◽  
Plastic Shear Strain ◽  
Thin Plastic ◽  
The Impact

An experiment with solder joints of thin plastic packages, cycled between −10° and 110°C, has demonstrated that the majority of solder joint failures occurred at the low temperatures. In this experiment, the low temperatures caused high peeling stresses in the heel area of solder joints and, as usual, relatively low plastic shear strain (as compared with these strains at high temperatures). This fact suggests that the impact of solder peeling stresses on the solder failure is noticeably higher than is anticipated by applying the commonly used failure criteria.

Size Effect of Shear Fracture Energy of Concrete in Uniaxial Compression Based on Gradient-Dependent Plasticity

2006 ◽  
Vol 312 ◽  
pp. 299-304 ◽  
Author(s):  
X.B. Wang
Keyword(s):  
Plastic Deformation ◽  
Fracture Energy ◽  
Shear Strain ◽  
Characteristic Length ◽  
Deformation Curve ◽  
Plastic Shear ◽  
Dependent Plasticity ◽  
Plastic Shear Strain ◽  
Relative Stress ◽  
Total Fracture

Gradient-dependent plasticity where a characteristic length is involved into yield function is adopted to calculate the thickness of shear band (SB) and the distribution of plastic shear strain in SB. The characteristic length reflecting the heterogeneous extent of texture only controls SB’s thickness. The local plastic shear strain in SB is highly non-uniform. The total fracture energy is the sum of pre-peak and post-peak fracture energies. The pre-peak part is described by the nonlinear Scott model and depends on the height of specimen. The post-peak part is calculated through the derived post-peak relative stress-plastic deformation curve. If the inclination angle of SB is not influenced by the height, then the slope of post-peak relative stress-plastic deformation curve and the post-peak fracture energy are independent of the height. The total fracture energy is linearly size-dependent as the pre-peak fracture energy is linearly related to the height. The slope of postpeak relative stress-plastic deformation and the total fracture energy are verified through previous experiments for normal concrete in uniaxial ompression.

Anisotropic hardening theory and the Bauschinger effect

1981 ◽  
Vol 16 (2) ◽  
pp. 85-95 ◽  
Author(s):  
D W A Rees
Keyword(s):  
Shear Strain ◽  
Bauschinger Effect ◽  
Published Data ◽  
Strain History ◽  
Pure Aluminium ◽  
Plastic Shear ◽  
Anisotropic Hardening ◽  
Plastic Shear Strain ◽  
Hardening Theory ◽  
Yield Loci

A review of anisotropic hardening theory is presented with particular reference to the Bauschinger effect in reversed torsion and anisotropic yield loci in σ, τ space associated with plastic shear strain history. The Bauschinger effect is obtained experimentally from a series of torsion tests on En3B steel tubes prestrained to a maximum of 10 per cent plastic shear strain. The effect, measured from the stress in reversed torsion at the proportionality limit, is analysed from the theory. It is shown to be consistent with experimental observations made on the translation and contraction of an initial yield locus, that are in marked contrast to the rigid translation of kinematic hardening rules. The degree of shear prestrain is shown to considerably influence the magnitude of the effect, an observation in full support of a theoretical Bauschinger parameter. The present test data together with existing published data for commercially pure aluminium 1100-F and the aluminium alloy Noral 19 S confirm that the controlling parameter is a scalar coefficient of plastic prestrain. The investigation supports a scalar function that is parabolic in the second invariant of plastic prestrain. The effect of yield point definition is examined and a comparison between theoretical and experimental yield loci is presented.

A New Approach to Measure Strain During Friction Stir Welding Using Visioplasticity

2011 ◽  
Author(s):  
Mohamadreza Nourani ◽  
Abbas S. Milani ◽  
Spiro Yannacopoulos
Keyword(s):  
Friction Stir Welding ◽  
Plastic Strain ◽  
Shape Change ◽  
Equivalent Plastic Strain ◽  
Leading Edge ◽  
Strain Range ◽  
New Approach ◽  
Friction Stir ◽  
Tool Shoulder ◽  
Tool Pin

During modeling of the friction stir welding (FSW) process, the prediction of strain range experienced by the material is important as it affects the microstructure and mechanical properties of the final weld [1–7]. For aluminum alloys, this range has been reported very scarcely and/or scattered widely in the literature (the range of the maximum equivalent plastic strain has been reported to be from 2.4 to 184 [8–24]). A new approach is proposed in this article for measuring strain during friction stir welding using visioplasticity. In this approach, strains are calculated from changes in the boundaries of a small cylindrical Al-30% SiC composite marker mounted in the advancing side of mid-plane of adjacent plates during welding. The marker shape change is observed by a “stop action” (freeze-in) technique midway the process. COMSOL numerical modeling is then used to compute the strain distribution using the observed boundary changes compared to the initial marker boundaries. As an illustrative example, the method is applied to the results reported by London et al. [25] for the friction stir welding of 6.35 mm thick 7050 aluminum plates, welded with tool RPM of 350, welding speed of 1.69 mm/sec, tool pin diameter of 8 mm, tool shoulder diameter of 24 mm, and tool tilt angle of 3 degrees. A lower and upper bound of cumulative equivalent plastic strain of 14.1 and 20.3, respectively, were found to be in the neighborhood where the marker enters the severe deformation zone at mid-plane of plates in front of the leading edge of the pin.

Biaxial Tensile Test of High Strength Steel Sheet for Large Plastic Strain Range

2012 ◽  
Vol 504-506 ◽  
pp. 59-64 ◽  
Author(s):  
Tomoyuki Hakoyama ◽  
Toshihiko Kuwabara
Keyword(s):  
Plastic Strain ◽  
High Strength Steel ◽  
Deformation Behavior ◽  
Equivalent Plastic Strain ◽  
Strain Range ◽  
High Strength ◽  
Test Material ◽  
Strain Rates ◽  
Stress Space ◽  
Plastic Strain Range

Deformation behavior of high strength steel with a tensile strength of 590 MPa under biaxial tension was investigated for a work equivalent plastic strain range of 0.002 0.16. The test material was bent and laser welded to fabricate a tubular specimen with an inner diameter of 44.6mm and wall thickness of 1.2 mm. Using a servo-controlled tension-internal pressure testing machine, many linear stress paths in the first quadrant of stress space were applied to the tubular specimens. Moreover, biaxial tensile tests using a cruciform specimen were performed to precisely measure the deformation behavior of the test material for a small strain range following initial yielding. True stress-true plastic strain curves, contours of plastic work in stress space and the directions of plastic strain rates were measured and compared with those calculated using selected yield functions. The plastic deformation behavior up to an equivalent plastic strain of 0.16 was successfully measured. The Yld2000-2d yield function most closely predicts the general work contour trends and the directions of plastic strain rates of the test material.

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