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SOLID MECHANICS
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FLUID MECHANICS
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Year Range:

2012

Volume 2

partial Issue 3 | May 2012 | 03xxxx

partial Issue 2 | March 2012 | 02xxxx

Issue 1 | January 2012 | 01xxxx

2011

Volume 1

Theoretical and Applied Mechanics Letters is jointly published by the Chinese Society of Theoretical and Applied Mechanics and American Institute of Physics. The Chinese Society of Theoretical and Applied Mechanics is the sole distributor of the print and electronic versions in Mainland China, and American Institute of Physics is the sole distributor of the print and electronic versions outside Mainland China.

Select this Article		Current understanding of ultra-high cycle fatigue Qingyuan Wang, Muhammad Kashif Khan, and Claude Bathias Theor. Appl. Mech. Lett. 2, 031002 (2012); http://dx.doi.org/10.1063/2.1203102 (6 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The fatigue life of numerous aerospace, locomotive, automotive and biomedical structures may go beyond 10⁸ cycles. Determination of long life fatigue behavior becomes extremely important for better understanding and design of the components and structures. Initially, before the invention of ultrasonic fatigue testing, most of the engineering materials were supposed to exhibit fatigue life up to 10⁷ cycles or less. This paper reviews current understanding of some fundamental aspects on the development of accelerated fatigue testing method and its application in ultra-high cycle fatigue, crack initiation and growth mechanisms of internal fracture, S-N diagram, fatigue limit and life prediction, etc.

Select this Article		Very high cycle fatigue for GCr15 steel with smooth and hole-defect specimens Zhengqiang Lei, Aiguo Zhao, Jijia Xie, Chengqi Sun, and Youshi Hong Theor. Appl. Mech. Lett. 2, 031003 (2012); http://dx.doi.org/10.1063/2.1203103 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Very high cycle fatigue (VHCF) properties of a low temperature tempering bearing steel GCr15 with smooth and hole-defect specimens are studied by employing a rotary bending test machine with frequency of 52.5 Hz. Both smooth and hole-defect specimens break in VHCF regime with some difference in fatigue crack initiation. For smooth specimens, a fine granular area (FGA) is observed near the grain boundary in the fracture surface of the specimens broken after 10⁷ cycles. But no FGA is observed in the hole-defect specimens broken in VHCF regime, and the VHCF crack does not initiate from the small hole at the surface as it does at low or high cycle fatigue regime. Internal stress is employed to explain the VHCF behavior of these two types of specimens. At last, an advanced dislocation model based on Tanaka and Mura model is proposed to illustrate the internal stress process and to predict fatigue crack initiation life with FGA observed in the fracture region.

Select this Article		Correlation of crack growth rate and stress ratio for fatigue damage containing very high cycle fatigue regime Chengqi Sun and Youshi Hong Theor. Appl. Mech. Lett. 2, 031004 (2012); http://dx.doi.org/10.1063/2.1203104 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A model is proposed to correlate the crack growth rate and stress ratio containing very high cycle fatigue regime. The model is verified by the experimental data in literature. Then a formula is derived for the effect of mean stress on fatigue strength, and it is used to estimate the fatigue strength of a bearing steel in very high cycle fatigue regime at different stress ratios. The estimated results are also compared with those by Goodman formula.

Select this Article		Improving fatigue strength of bainite/martensite dual-phase steels in very high cycle fatigue regime by refining microstructures Yangbo Liu, Shouxin Li, Zhengou Yang, Jingyu Cui, Jialin Gu, and Bingzhe Bai Theor. Appl. Mech. Lett. 2, 031005 (2012); http://dx.doi.org/10.1063/2.1203105 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Very high cycle fatigue behaviors of two bainite/martensite dual-phase steels were investigated. One of the steels was cyclic rapid heat treated and its microstructures were refined. Fatigue strength of the steel is 225 MPa higher than that without refining. Observation of fracture surfaces show that the fatigue cracks initiate at bainites for non-refined steel and at non-metallic inclusions for the refined steel. The size of inclusions is much smaller than that of bainites which results in the improvement of fatigue strength.

Select this Article		Fatigue life assessment of a high strength steel 300 M in the gigacycle regime Hongqian Xue, Pingli Liu, Peng Chen, and Jie Wang Theor. Appl. Mech. Lett. 2, 031006 (2012); http://dx.doi.org/10.1063/2.1203106 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The fatigue behavior of a high strength steel 300 M in the gigacycle regime was investigated. Fully reversed tension — compression fatigue tests at ambient temperature were performed using an ultrasonic fatigue system operating at 20 kHz. The staircase test method was employed to obtain accurate values of the mean fatigue strength corresponding to fixed numbers of cycles up to 10⁹. These results were compared to the curve which is estimated by the data tested in the mid-long life regime on conventional servo hydraulic test machine at 20 Hz. Results indicate that the fatigue strength determined from ultrasonic fatigue testing is lightly higher than conventional testing in the range of 10⁶–10⁷ cycles. It is obvious that nucleations of fractures tend to occur below the surface, if fractures happen after more than 10⁷ cycles. All the fractured specimens fails from internal SiO₂ inclusions or smaller carbides and carbide clusters.

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May 2012

Volume 2, Issue 3 (partial)

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Select this Article		Special subject on very high cycle fatigue Qingyuan Wang Theor. Appl. Mech. Lett. 2, 031001 (2012); http://dx.doi.org/10.1063/2.1203101 (2 pages) Full Text: Read Online (HTML) \| Download PDF
		Abstract Unavailable

Select this Article		Effect of low cycle fatigue pre-damage on very high cycle fatigue Zhiyong Huang, Qingyuan Wang, Danièle Wagner, and Claude Bathias Theor. Appl. Mech. Lett. 2, 031007 (2012); http://dx.doi.org/10.1063/2.1203107 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Carbon-manganese steel is often applied in components of pipes in nuclear plant. Ultrasonic fatigue tests following low cycle fatigue (LCF) cycles damaged are used to study the strength of very high cycle fatigure (VHCF). The comparison of test results of simple VHCF and cumulative fatigue (LCF plus VHCF) shows that LCF load influences the following VHCF strength. Continuum damage mechanics model is extended to VHCF region. The effect of LCF load on VHCF is studied by an improved cumulative damage model.

Select this Article		Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading Nu Yan, Qingyuan Wang, Xishu Wang, Q. Chen, and N. Kawagoishi Theor. Appl. Mech. Lett. 2, 031008 (2012); http://dx.doi.org/10.1063/2.1203108 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading frequency (20 kHz) were investigated and compared with the results under conventional loading of rotating bending (50 Hz). The growth of a crack retarded at about 500 µm in surface length under ultrasonic loading, while at about 20 µm under rotating bending. Although striations being a typical fracture mechanism were observed under conventional loading, most of fracture surface was covered with many facets under ultrasonic loading. These facets were also observed under rotating bending in nitrogen gas. The difference in growth mechanism depending on the loading frequency and the retardation of a crack growth under ultrasonic loading may be caused by the environment at the crack tip due to high crack growth rate under ultrasonic loading.

Select this Article		The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy Yuli Gu, Chunhu Tao, Yuhuai He, and Changkui Liu Theor. Appl. Mech. Lett. 2, 031009 (2012); http://dx.doi.org/10.1063/2.1203109 (5 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy are systematically studied. The results show that fatigue fracture still occurs above the cycle of 10⁸ for tests carried out at the frequency of f = 20 kHz and stress ratio R = −1, so the traditional fatigue limit at cycle of 10⁷ is not appropriate for fatigue design. Fatigue fracture surfaces are perpendicular to stress axis for cylindrical and plate specimens, and the fatigue cracks originate from the extra surface of the specimens. Fatigue crack is apt to propagate from cutting direction to forward direction, which occurs mainly in the second propagation stage at higher stress amplitude. There is an obvious frequency effect for DZ125 superalloy. The higher the test frequency is, the more serious the effect of frequency on fatigue behaviors of the alloy. After the frequency correction, the ultra-high cycle fatigue S-N curve well coincide with the traditional fatigue S-N curve.

Select this Article		Very high cycle fatigue behavior of bridge steel welded joint Chao He, Yongjie Liu, Donghui Fang, and Qingyuan Wang Theor. Appl. Mech. Lett. 2, 031010 (2012); http://dx.doi.org/10.1063/2.1203110 (5 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Very high cycle fatigue (VHCF) behaviors of bridge steel (Q345) welded joints were investigated using an ultrasonic fatigue test system at room temperature with a stress ratio R = −1. The results show that the fatigue strength of welded joints is dropped by an average of 60% comparing to the base metal and the fatigue failure still occurred beyond 10⁷ cycles. The fatigue fracture of welded joints in the low cycle regime generally occurred at the solder while at the heat-affected zone (HAZ) in the very high cycle regime. The fatigue fracture surface was analyzed with scanning electron microscopy (SEM), showing welding defects such as pore, micro-crack and inclusion were the main factors on decreasing the fatigue properties of welded joints. The effect of welding defects on the fatigue behaviors of welded joints was discussed in terms of experimental results and finite element simulations.

Select this Article		Vibration analysis of fluid-conveying nanotubes embedded in an elastic medium considering surface effects Yuhang Li, Bo Fang, Jiazhong Zhang, and Jizhou Song Theor. Appl. Mech. Lett. 2, 031011 (2012); http://dx.doi.org/10.1063/2.1203111 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An analytical model is developed to study the surface effects on the vibration behavior including the natural frequency and the critical flow velocity of fluid-conveying nanotubes embedded in an elastic medium. The effects of surface elasticity and residual surface stress are accounted through the surface elasticity model and the Young-Laplace equation. A Winkler-type foundation is employed to model the interaction of nanotubes and the surrounding medium. The results show that the surface effects have more prominent influences on the nature frequency with smaller nanotube thickness, larger aspect ratio and larger elastic medium constants. Both surface layers and the elastic medium enhance the stability of nanotubes. This study might be helpful for designing the fluid-conveying nanotube devices in NEMS and MEMS systems.

Select this Article		Resonance frequencies and stability of a current-carrying suspended nanobeam in a longitudinal magnetic field R. D. Firouz-Abadi and A. R. Hosseinian Theor. Appl. Mech. Lett. 2, 031012 (2012); http://dx.doi.org/10.1063/2.1203112 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The resonance frequencies and stability of a nanobeam in a longitudinal magnetic field are investigated. To this aim, a three dimensional beam model is used in which the small-scale effect is taken into account based on the nonlocal elasticity theory. The Lorentz forces are obtained in terms of the local elastic rotations of the beam and the thermal stress due to current is modeled as an axial compressive force. Using the Galerkin method, the governing equations of motion are solved and the stability boundary of the nanobeam is determined.

Select this Article		LBM simulation of fluid flow in fractured porous media with permeable matrix Jinfang Gao and Huiling Xing Theor. Appl. Mech. Lett. 2, 032001 (2012); http://dx.doi.org/10.1063/2.1203201 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract To analyze and depict complicated fluid behaviors in fractured porous media with variably permeable matrix, an integrated discrete computational algorithm is proposed based on lattice Boltzmann method (LBM). This paper combines with the external force model and statistical material physics to effectively describe the feature changes while the fluid passes through the fractures within the permeable matrix. As an application example, a two dimensional rock sample is reconstructed using the digital image and characterized with different feature values at each LBM grid to distinguish pores, impermeable and permeable matrix by stating its local physical property. Compared with the conventional LBM, the results demonstrate the advantages of proposed algorithm in modeling fluid flow phenomenon in fractured porous media with variably permeable matrix.

Select this Article		Vortex structure simulation for supersonic mixing layers using nonlinear PSE method Xin Guo and Qiang Wang Theor. Appl. Mech. Lett. 2, 032002 (2012); http://dx.doi.org/10.1063/2.1203202 (4 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The method of nonlinear parabolized stability equations (PSE) is applied in the simulation of vortex structures in compressible mixing layer. The spatially-evolving unstable waves, which dominate the vortex structure, are investigated through spatial marching method. The instantaneous flow field is obtained by adding the harmonic waves to basic flow. The results show that T-S waves do not keep growing exponentially as the linear evolution, the energy transfer to high order harmonic modes, and that finally all harmonic modes get saturated due to nonlinear interaction. The mean flow distortion induced by the nonlinear interaction between the harmonic modes and their conjugate harmonic ones, makes great change of the average flow and increases the thickness of mixing layer. PSE methods can well capture the two- and three-dimensional large scale nonlinear vortex structures in mixing layers such as vortex roll-up, vortex pairing, and Λ vortex.

Select this Article		The effects of initial perturbation to mixing-layer noise Lin Zhou, Zhenhua Wan, Dejun Sun, and Mingjun Wei Theor. Appl. Mech. Lett. 2, 032003 (2012); http://dx.doi.org/10.1063/2.1203203 (5 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The far-field noise radiated from mixing layers is determined by the near-field flow dynamics which is sensitive to the initial perturbation of instability introduced physically or numerically. This study focuses on the effects of the phase delay in two initial perturbations, one at the fundamental wave number and the other at its subharmonic both calculated from linear instability analysis, on the sound generation in mixing layers. When different phase delays ?1 changing from zero to 2π is applied on the fundamental mode, we observe different vortex merging processes (e.g. vortex pairing or tearing). The strong nonlinear interaction in the merging process generates most of the noise from mixing layers. There shows a pattern in a period of 2π for the response of far-field sound to the change of ϕ₁. Similar effects on the dynamics and acoustics can be achieved by adding different phase delays ϕ₂ to the subharmonic mode instead, however, the response repeats in a period of only π for ϕ₂. The effects of the combination of different phase delays to other parameters, including the amplitude and wave number for each perturbations, are also investigated. All the results indicate a critical role of nonlinearity in the sound generation mechanism of mixing layers.

Select this Article		A solution to the hydrodynamic lubrication of a circular point contact sliding over a flat surface with cavitation Hans B. Löfgren Theor. Appl. Mech. Lett. 2, 032004 (2012); http://dx.doi.org/10.1063/2.1203204 (3 pages) Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This letter presents an analytical solution to the hydrodynamic lubrication of a circular point contact sliding over a flat surface with cavitation. The solution is found by solving the Reynolds equation with Reynolds boundary condition for cavitation. The cavitation boundary is shown to be straight lines directed 108.4° against the sliding direction. The result is experimentally verified in the limit of large values of viscosity, sliding velocity and radius of a spherical ball. The solution raises questions about the coupling between cavitation and film rupture and can be used as an independent check on the validity of numerical solutions.