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2018 Vol. 39, No. 5 Published: 2018-10-28

	439	Advances on Nanosecond Pulse Laser Ablation of Amorphous Alloys

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.032
		Amorphous alloys are a new class of structural materials with long range atomic disorder. These alloys possess a series of superior mechanical and physical properties, and can be applied in fields of defense, airspace and so on. However, in these applications, amorphous alloys are prone to fail when exposed to high-energy laser or space plasma. Meanwhile, their structure response to high-energy laser irradiation is also of scientific significance. Therefore, the laser ablation of amorphous alloys has attracted increasing attention in recent years. This short review focuses on the nanosecond pulse laser ablation of amorphous alloys in atmosphere and water environments. We present relevant experimental and theoretical progresses about typical phenomena in ablation, such as melting, hydrodynamic instability，explosive boiling，bubble dynamics and so on. The review ends with the key aspects that deserve further investigations.
		2018 Vol. 39 (5): 439-452 [Abstract] ( 283 ) HTML (1 KB) PDF (0 KB) ( 281 )

	453	Evaluating nearly singular integrals accurately and efficiently based on sphere subdivision method

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.016
		The boundary element method (BEM) has been widely used for solving engineering and scientific problems. Compared with the finite element method (FEM), the BEM is more attractive for its dimension reduction feature and higher accuracy. Accurate and efficient evaluation of nearly singular integrals is of crucial importance for successful implementation of the BEM. The nearly singular integrals in BEM have been studied for a long time, and many methods have been proposed. However, none of them can evaluate these integrals accurately and efficiently. In this paper, a method based on sphere subdivision technique is proposed for evaluating nearly singular integrals. With the method, the nearly singular integrals can be evaluated accurately and efficiently for cases of arbitrary type fundamental solution, arbitrary shape of element and arbitrary location of source point. In the proposed method, the minimum and maximum distances between the source point and the integration element are firstly computed, which determine the beginning and ending of sphere radius. Then triangular and quadrilateral sub-elements can be obtained by subdividing the integration element through a sequence of spheres with exponential increasing radius. Finally the obtained sub-elements are turned into arc-shape ones, i.e. the triangular and quadrilateral sub-elements are changed to flabellate and annular sub-elements, respectively. The sphere subdivision is performed in 3D Cartesian coordinate system, thus the proposed method is suitable for any elements. In addition, fundamental solution is a function of the distance between the source point and the field point, so in the same level of accuracy, the number of Gaussian point can greatly decrease in circular direction for evaluating nearly singular integrals on sub-elements. Because of exponential growth of sphere radius, the integration can be of the same level of accuracy in the radial direction. The numerical examples have demonstrated that the proposed method has much better stability and accuracy than conventional methods.
		2018 Vol. 39 (5): 453-461 [Abstract] ( 207 ) HTML (1 KB) PDF (0 KB) ( 271 )

	462	Circumferential evanescent guided waves in functionally graded cylindrical curved plates

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.025
		Evanescent wave modes are substantially different from the propagating modes，which are associated with non-real wavenumbers and decay exponentially or damped with propagation distance. Such modes with complex wavenumbers play an important role in the detection of the shape and size of defects, but it is very difficult to obtain the complex solutions of the dispersion equation which correspond to evanescent waves, especially for demanding cases such as those involving composite materials and curved structures. An improved orthogonal polynomial method is proposed to deal with the problems of evanescent guided waves in a functionally graded cylindrical curved plate in this paper. The proposed method can convert the complex differential equations with variable coefficients into an eigenvalue problem and obtain all the purely real, purely imaginary and complex solutions but without iterative process. The validity of the proposed method is illustrated by specific numerical examples. Three dimensional full dispersion curves of the guided waves in various graded cylindrical curved plates are obtained, and the effects of different radius-thickness ratios and graded fields on the dispersion characteristics of guided evanescent waves are illustrated. The displacement amplitude and stress distributions are also discussed to analyze the specificities of the evanescent guided waves. Numerical results show that there are only purely real and purely imaginary branches for circumferential SH waves, but for circumferential Lamb-like waves there are purely real, purely imaginary and complex branches. Most complex branches collapse onto the minima of purely imaginary branches and local inflection points occasionally appear on higher order real branches. Complex branches exhibit both local vibration and local propagation, and they will turn into real branches with increasing frequency. Both the radius-thickness ratio and the graded field have significant effects on dispersion curves. With the increase of the radius-thickness ratio, the decay of evanescent waves is faster. All the results presented in this work can provide theoretical guidance for ultrasonic nondestructive evaluation.
		2018 Vol. 39 (5): 462-471 [Abstract] ( 151 ) HTML (1 KB) PDF (0 KB) ( 310 )

	472	FIXED-GIRD SHAPE OPTIMIZATION METHOD FOR OPENING STRUCTURES VIA SMOOTHLY DEFORMABLE IMPLICIT CURVES

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.023
		Shape optimization of the holes in opening structures can effectively alleviate the hole-edge stress concentration, which has high requirements for the stress analysis precision and the geometrical ability of hole-edge curves. However, the existing fixed-grid shape optimization approaches could not meet the above two requirements very well. In view of this, the finite cell method is adopted in this work for high-precision numerical analysis within fixed meshes, and the smoothly deformable implicit curve is used to describe the boundary to be optimized. After the establishment of optimization model and the derivation of analytical sensitivity analysis formulas, the hole shape optimization design framework is finally built with high precision and high efficiency. Through the optimization of holed structures under different load boundary conditions, it is shown that the proposed method has the advantages of no mesh updating, simple sensitivity derivation, high analytical precision and large design space.
		2018 Vol. 39 (5): 472-481 [Abstract] ( 205 ) HTML (1 KB) PDF (0 KB) ( 277 )

	482	Strain burst model and intermittent plastic flow of single crystal nanopillar under displacement loading mode

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.017
		The micro-compression tests revealed significant strain bursts during plastic deformation of single crystal nanopillar, showing special intermittent plastic flow behaviors. In this paper, a three-stage formulation of the strain burst phenomenon is presented according to the experimental observations of single-crystal Au pillars with a diameter of several hundred nanometers under displacement loading mode. A continuum mechanics model with the second-order work parameter is then developed to describe the intermittent plastic flow within crystal plasticity framework, and their finite element implementation is realized. By comparing to the experimental results, the newly proposed theoretical model is verified to be able to describe the strain bursts and plastic flow of face-centered cubic single crystal under displacement loading mode, with a reasonable accuracy in predicting the plastic deformation behavior of nanopillars. In addition, the second-order work criterion is effective in judging the occurrence of strain bursts event under the condition of displacement loading. Using this model, the randomness, size dependency and rate sensitivity of strain bursts during the plastic deformation of nanopillars are further investigated in detail.
		2018 Vol. 39 (5): 482-491 [Abstract] ( 175 ) HTML (1 KB) PDF (0 KB) ( 270 )

	492	DYNAMIC RESPONSE OF TUNNEL LINING UNDER ENDOGENOUS FUNCTION IN SATURATED POROELASTIC HALF-SPACE

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.011
		Based on Biot’s theory of two-phase medium, a high-precision indirect boundary integral equation method is utilized to solve the transient dynamic response of elastic tunnel embedded in a saturated poroelastic half space under internal blast loading. Response time history about the ground displacement, tunnel hoop stress, radial displacement and pore pressure of surrounding rock under blast load are given by calculating, and analyzed the difference of time history response between the saturated half space and the whole space. The results show that the embedded depth has large effect on dynamic response of the shallow buried tunnel-surrounding rock system; the boundary drainage condition has little impact on the time history response under blast load. With the increase of porosity, the influence of blast load on surrounding saturated rock is reduced while the blast effects on the tunnel is increased. When the direct waves and reflected waves by tunnel surfaces are strengthened by the reflected waves from the half-space surface, the tunnel vault is obviously affected by the surface reflection wave and the amplitude of hoop stress and radial displacement of surrounding rock are much larger than the tunnel in a whole space.
		2018 Vol. 39 (5): 492-503 [Abstract] ( 120 ) HTML (1 KB) PDF (0 KB) ( 280 )

	504	Numerical simulation on the impact of debris on the penetration resistance of thin aluminum alloy plate

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.012
		Using ABAQUS finite element software, the numerical simulation model of blunt-nosed projectile and debris impacting 2A12-T4 aluminum alloy plate is established by using appropriate material parameters and criteria. By changing the relative position between the projectile and debris, the influence rule and mechanism of the debris on the penetration resistance of the target plate impacted by projectile are studied. The physical process and failure mechanism of target impacted by target are analyzed by numerical simulation. Based on the numerical simulation results, it can be found that the effect of debris on the penetration resistance of target is affected by the velocity of projectile and the mutual position between projectile and debris. For the ballistic resistance of target, there is an optimum value for the contact area between the projectile and the fragment, and also the damage area of the target plate will be reduced if the contact area is too large or too small, thus reducing the energy absorption of the target in the impact process.
		2018 Vol. 39 (5): 504-512 [Abstract] ( 135 ) HTML (1 KB) PDF (0 KB) ( 290 )

	522	Rapid Element-free method for circular plate on elastic base subjected to concentrated force

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.014
		This article use the Element-free Galerkin Method to discussed circular plate on elastic base subjected to concentrated force,during which a new kind of node distribution and node integration form were proposed,and on this basis the correlation parameter of the weight function and solution of the concentrated force are also discussed.The results of examples show that the proposed method has high efficiency and accuracy.
		2018 Vol. 39 (5): 522-529 [Abstract] ( 133 ) HTML (1 KB) PDF (0 KB) ( 266 )

	530	Mechanical Behavior and Failure Mechanism of Ice at Cryogenic Temperatures under Uniaxial Compression

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.026
		By using an Instron 5848 material testing machine and a split Hopkinson pressure bar (SHPB) with cooling chambers, a series of uniaxial compression experiments were carried out to explore the mechanical behaviors and failure mechanism of polycrystalline ice at temperatures of -10/ -20 /-30℃ and at strain rates in the range of 10-4S-1 to 102S-1. The reliability and effectiveness of the experimental results were analyzed. The experimental results show as follows. The compressive strength of ice is sensitive to temperature and strain rate obviously. It also increases with the increase of strain rate and the decrease of temperature. There is a linear relationship between the compressive strength and the logarithm of strain rate. The increase of strain rate enhances the strengthening effect of the compression strength due to the decrease of temperature. Within the studied strain rate and temperature scope, the ice mainly has three types of failure modes, namely expansion, longitudinal splitting and holistic crushing. The different ice failure modes and the increase of compressive strength are caused by the energy of the crack tip can not be released in time, the increase of the hydrogen bond strength and the friction resistance of the crack slipping in the ice.
		2018 Vol. 39 (5): 530-538 [Abstract] ( 212 ) HTML (1 KB) PDF (0 KB) ( 262 )

	539	Accuracy of the extended boundary element method analyzing the stress fields of V-notched/cracked structures

		DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.027
		According to the theory of linear elasticity, the numerical methods are difficult to calculate the singular stress field in a V-notch/crack tip region. In this paper, the extended boundary element method (XBEM) is proposed to determine the singular stress field near a V-notch/crack tip. Firstly, a small sector around the V-notch/crack tip is dug out from the V-notch/crack structures. The displacement and stress components in the small sector are expressed as the asymptotic series expansions with respect to the radial coordinate from the tip. The amplitude coefficients in the series expansions are taken as the basic unknowns. Secondly, the boundary element method is used to analyze the V-notch/crack structure removed the small sector. Consequently, the complete displacement and stress fields of the V-notched/cracked structure are solved by combining the boundary element analysis and the asymptotic series expansions of the stress field, where the extended boundary element method has the characteristics of the semi-analytic approach. The XBEM is suitable for the stress analysis of general V-notched/cracked structures, and its solution can accurately describe the displacement and stress field from the notch/crack tip to the whole region. Finally, two numerical examples are given to demonstrate the effectiveness and accuracy of the XBEM.
		2018 Vol. 39 (5): 539-551 [Abstract] ( 143 ) HTML (1 KB) PDF (0 KB) ( 258 )

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