试验确定自增强圆筒的表面裂纹K1因子和疲劳扩展规律

本文提供了一种可以进行自增强处理的圆筒试样,通过实验用柔度法确定了该试样的表面裂纹的应力强度因子,介绍了含表面裂纹试样的柔度测试技术,导出了柔度与表面裂纹尖端前缘各点的应力强度因子的关系式,该式可作为各种含表面裂纹试样柔度法测表面裂纹 K_1因子的参考,本文还测定了不同自增强程度下,自增强圆筒的表面裂纹疲劳扩展规律。     

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介绍降载柔度单试件法测量柱试件ＣＯＤ阻力曲线的基本原理和运用微机采集与处理数据的方法,测定圆试件ＨＱ６０钢的ＣＯＤ阻力曲线,试验结果表明用降载柔度法测量圆柱试件ＣＯＤ阻力曲线有高很精度。     

AN ANALYTICAL SOLUTION OF SECOND－ORDER WAVE FORCE ON A VERTICAL CIRCULAR CYLINDER

ＡＮＡＮＡＬＹＴＩＣＡＬＳＯＬＵＴＩＯＮＯＦＳＥＣＯＮＤ－ＯＲＤＥＲＷＡＶＥＦＯＲＣＥＯＮＡＶＥＲＴＩＣＡＬＣＩＲＣＵＬＡＲＣＹＬＩＮＤＥＲＺｈｏｕＺｈｉ－ｌｉ（邹志利）（ＤａｌｉａｎＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌｏｇｙ，Ｄａｌｉａｎ）Ｄａｉ...     

VARIATIONAL PRINCIPLE AND GENERALIZED VARIATIONAL PRINCIPLE IN HYDRODYNAMICS OF A CLASS OF NON－NEWTONIAN FLUID

ＶＡＲＩＡＴＩＯＮＡＬＰＲＩＮＣＩＰＬＥＡＮＤＧＥＮＥＲＡＬＩＺＥＤＶＡＲＩＡＴＩＯＮＡＬＰＲＩＮＣＩＰＬＥＩＮＨＹＤＲＯＤＹＮＡＭＩＣＳＯＦＡＣＬＡＳＳＯＦＮＯＮ－ＮＥＷＴＯＮＩＡＮＦＬＵＩＤＳｈｅｎＭｉｎ（沈敏），ＳｕｎＱｉ－ｒｅｎ（孙其仁）（Ｓ...     

FORCED OSCILLATIONS OF BOUNDARY VALUE PROBLEMS OF HIGHER ORDER FUNCTIONAL PARTIAL DIFFERENTIAL EQUATIONS

ＦＯＲＣＥＤＯＳＣＩＬＬＡＴＩＯＮＳＯＦＢＯＵＮＤＡＲＹＶＡＬＵＥＰＲＯＢＬＥＭＳＯＦＨＩＧＨＥＲＯＲＤＥＲＦＵＮＣＴＩＯＮＡＬＰＡＲＴＩＡＬＤＩＦＦＥＲＥＮＴＩＡＬＥＱＵＡＴＩＯＮＳＪｉｎＭｉｎｇＺｈｏｎｇ（靳明忠），ＤｏｎｇＹｉｎｇ（董莹），Ｌｉ...     

OBLC Domain Decomposition for Artificial Compressible Equation

ＯＢＬＣＤＯＭＡＩＮＤＥＣＯＭＰＯＳＩＴＩＯＮＦＯＲＡＲＴＩＦＩＣＩＡＬＣＯＭＰＲＥＳＳＩＢＬＥＥＱＵＡＴＩＯＮＬｉｎＭｉｎｇｓｅｎ（林明森）；ＨｕａｎｇＬａｎｃｈｉｅｈ（黄兰洁）（ＲｅｃｅｉｖｅｄＤｅｃ．１７，１９９４；Ｃｏｍｍｕｎｉｃａｔｅｄｂｙ...     

UNCONDITIONAL STABLE SOLUTIONS OF THE EULER EQUATIONS FOR TWO－AND THREE－D WINGS IN ARBITRARY MOTION

ＵＮＣＯＮＤＩＴＩＯＮＡＬＳＴＡＢＬＥＳＯＬＵＴＩＯＮＳＯＦＴＨＥＥＵＬＥＲＥＱＵＡＴＩＯＮＳＦＯＲＴＷＯ－ＡＮＤＴＨＲＥＥ－ＤＷＩＮＧＳＩＮＡＲＢＩＴＲＡＲＹＭＯＴＩＯＮＧａｏＺｈｅｎｇｈｏｎｇ（高正红）（ＲｅｃｅｉｖｅｄＪａｎ．１２，１９９５，Ｃ...     

THE ANALYTICAL STUDY ON THE LASER INDUCED REVERSE－PLUGGING EFFECT BY USING THE CLASSICAL ELASTIC PLATE THEORY（II）──REVERSE－BULGE MOTION

ＴＨＥＡＮＡＬＹＴＩＣＡＬＳＴＵＤＹＯＮＴＨＥＬＡＳＥＲＩＮＤＵＣＥＤＲＥＶＥＲＳＥ－ＰＬＵＧＧＩＮＧＥＦＦＥＣＴＢＹＵＳＩＮＧＴＨＥＣＬＡＳＳＩＣＡＬＥＬＡＳＴＩＣＰＬＡＴＥＴＨＥＯＲＹ（ＩＩ）──ＲＥＶＥＲＳＥ－ＢＵＬＧＥＭＯＴＩＯＮ￥(周益春，...     

NUMERICAL STUDIES FOR A MODEL DESCRIBING COMPLEXITY

ＮＵＭＥＲＩＣＡＬＳＴＵＤＩＥＳＦＯＲＡＭＯＤＥＬＤＥＳＣＲＩＢＩＮＧＣＯＭＰＬＥＸＩＴＹＨｕａｎｇＸｉｎ（黄欣）ＬｉｕＺｅｎｇ－ｒｏｎｇ（刘曾荣）（Ｄｅｐｔ．ｏｆＭａｔｈ．ＳｕｚｈｏｕＵｎｉｖｅｒｓｉｔｙ，Ｓｕｚｈｏｕ，Ｊｉａｎｇｓｕ）（ＬＮＭ，Ｉ...     

Bending problems of Non-Homogeneous Cylindrical Orthotropic Circular Plate

ＢＥＮＤＩＮＧＰＲＯＢＬＥＭＳＯＦＮＯＮ－ＨＯＭＯＧＥＮＥＯＵＳＣＹＬＩＮＤＲＩＣＡＬＯＲＴＨＯＴＲＯＰＩＣＣＩＲＣＵＬＡＲＰＬＡＴＥＱｉｎＳｈｅｎｇ－ｌｉ（秦圣立）（ＱｕｆｕＮｏｒｍａｌＵｎｉｃｅｒｓｉｔｙ，Ｑｕｆｕ，Ｓｈａｎｄｏｎｇ）（Ｒｅｃｅｉ...     

A delamination gage for carbon fiber composites

A graphite crack gage familiar to fracture testing of nonconductive polymeric materials has been adapted to measure delamination growth in carbon fiber composites. The gage consists of a continuous graphite film whose conductance changes linearly with respect to crack length. The development of an insulation technique so that the electrical film may be applied to carbon fiber composites is described. Further constraints on the gage design occur due to the narrow profiles of conventional delamination specimens. These limitations are reviewed in detail along with appropriate methods for manufacturing and calibration of the gage for delamination experiments. A simple shunt voltage measurement circuit is described along with a derivation of the relationship of crack length to voltage. Two example applications are provided: stable delamination growth in a conventional double cantilever beam (DCB) specimen and dynamic delamination growth in a single-edge-notched (SEN) strip. The electrical delamination length measurements from the DCB tests were found to compare well with the location of the delamination front determined by microscopy and radiography. These results give confidence in dynamic delamination results where growth rates exceeding 1000 m/s were measured. Sample evaluations of delamination toughness are made using the experimental data; compliance methods are used in the case of the DCB analysis, and dynamic finite element methods are used in the case of the SEN strip analysis.     

Two-dimensional analysis of progressive delamination in thin film electrodes

By employing the two-dimensional analysis, i.e., plane strain and plane stress, a semi-analytical method is developed to investigate the interfacial delamination in electrodes. The key parameters are obtained from the governing equations, and their effects on the evolution of the delamination are evaluated. The impact of constraint perpendicular to the plane is also investigated by comparing the plane strain and plane stress. It is found that the delamination in the plane strain condition occurs easier, indicating that the constraint is harmful to maintain the structure stability. According to the obtained governing equations, a formula of the dimensionless critical size for delamination is provided, which is a function of the maximum volumetric strain and the Poisson’s ratio of the active layer.     

Effects of voids on postbuckling delamination growth in unidirectional composites

This work examines the effects of manufacturing induced voids on the postbuckling behavior of delaminated unidirectional composites. In the finite element model developed, a through-width delamination is introduced close to one surface of a flat panel, and a void is placed in the delamination plane ahead of each delamination front. The panel is subjected to compression in the fiber direction. The postbuckling delamination growth is studied by calculating the strain energy release rate (SERR) using the virtual crack closure technique. Local stress analyses of the region near the delamination front are also performed to further investigate the void effects. It is found that although the presence of void does not significantly alter the postbuckling transverse displacement of the delaminated panel, the induced stress perturbation by the void affects the SERR. The Mode II SERR as well as the total SERR increase depending on the size of the void and its distance from the delamination front. Since the Mode I SERR shows non-monotonic behavior with the applied load, the effects of voids are studied on its maximum value.     

Buckling of delaminated bi-layer beam-columns

An improved analytical model is presented to analyze the delamination buckling of a bi-layer beam-column with a through-the-width delamination. Both the transverse shear deformation and local delamination tip deformations are taken into consideration, and two delaminated sub-layers as well as two substrates in the intact (un-delaminated) regions are modeled as individual Timoshenko beams. A deformable interface is introduced to establish the continuity condition between the two substrates in the intact regions. Consequently, a flexible joint is formed at the delamination tip, and it is different from the conventional rigid joint given in most of studies in the literature, in which the local delamination tip deformations are completely ignored. In contrast to the local delamination buckling in our previous study (Qiao et al., 2010), the present model accounts for the global deformations of the intact region in the delaminated composite beam-column, thus capable of capturing the buckling mode shape transitions from the global, to global–local coexistent, and to local buckling for asymmetric delamination as the interface delamination increases. Good agreement of the present analytical solutions with the full 2-D elastic finite element analysis demonstrates the local deformation effects around the delamination tip and verifies the accuracy of the present model. Parametric studies are conducted to investigate the effects of loading eccentricity, delaminated sub-layer thickness ratio, and interface compliance on the critical buckling load for the delaminated composite beam-column. Transitions of buckling modes from the global to local delamination buckling are also disclosed as the thickness of one sub-layer reduces from the thick sub-layer to a thin film. The developed delamination buckling solution facilitates the design analysis and optimization of laminated composite structures, and it can be used with confidence in buckling analysis of delaminated composite structures.     

Study on failure process of delaminated stiffened composite plates under compression

Failure behavior of the delaminated stiffened composite plates under compression is studied by the finite element method, based on a Global-Local variational model. A virtual crack closure technique and a self-adaptive grid moving scheme are proposed to predict the delamination growth process. The contact effect along the delamination front is considered. The numerical results show that the influences of the distribution and location of the stiffeners, the configuration and size of the delamination, the boundary condition and the contact upon the failure behavior of the plates are significant. The project supported by the National Natural Science Foundation of China (59975014)     

Direct determination of interlaminar stresses in polymeric adhesive layer

A method for direct measurement of shear and normal displacements, and a simple way of determining the distribution of the respective average stresses along an interlaminar adhesive layer (IAL), were successfully examined on a symmetrical doubler model. Experimental data proved to be in agreement with available analytical solutions for this model in the elastic stage. The method was also examined beyond the elastic linear range and may be used to follow up the initiation of delamination.     

A crack tip tracking algorithm for cohesive interface element analysis of fatigue delamination propagation in composite materials

A novel approach is proposed for the use of cohesive elements in the analysis of delamination propagation in composite materials under high-cycle fatigue loading. The method is applicable to delamination propagation within the Paris-law regime and is suitable for the analysis of three-dimensional structures typical of aerospace applications. The major advantages of the proposed formulation are its complete independence of the cohesive zone length – which is a geometry-dependent parameter – and its relative insensitivity to mesh refinement. This is only possible via the introduction of three nonlocal algorithms, which provide (i) automated three-dimensional tracking of delamination fronts, (ii) an estimation of direction of crack propagation and (iii) accurate and mesh-insensitive integration of strain energy release rate. All calculations are updated at every increment of an explicit time-integration finite element solution, which models the envelopes of forces and displacements with an assumption of underlying constant cyclic loading. The method was implemented as a user-defined subroutine in the commercial finite element software LS-Dyna and supports the analysis of complex three-dimensional models. Results are presented for benchmark cases such as specimens with central cut plies and centrally-loaded circular plates. Accurate predictions of delamination growth rates are observed for different mesh topologies in agreement with the Paris-laws of the material.     

NUMERICAL ANALYSIS OF DELAMINATION GROWTH FORSTIFFENED COMPOSITE LAMINATED PLATES

A study of postbuckling and delamination propagation behavior in delaminated stiffened composite plates was presented. A methodology was proposed for simulating the multi-failure responses, such as initial and postbuckling, delamination onset and propagation, etc. A finite element analysis was conducted on the basis of the Mindlin first order shear effect theory and the von-K6rm~n nonlinear deformation assumption. The total energy release rate used as the criteria of delamination growth was estimated with virtual crack closure technique (VCCT). A self-adaptive grid moving technology was adopted to model the delamination growth process. Moreover, the contact effect along delamination front was also considered during the numerical simulation process. By some numerical examples, the influence of distribution and location of stiffener, configuration and size of the delamination, boundary condition and contact effect upon the delamination growth behavior of the stiffened composite plates were investigated. The method and numerical conclusion provided should be of great value to engineers dealing with composite structures.     

Two-dimensional analyses of delamination buckling of symmetrically cross-ply rectangular laminates

The conventional approach to analysis the buckling of rectangular laminates containing an embedded delamination subjected to the in-plane loading is to simplify the laminate as a beam-plate from which the predicted buckling load decreases as the length of the laminate increases. Two-dimensional analyses are employed in this paper by extending the one-dimensional model to take into consideration of the influence of the delamination width on the buckling performance of the laminates. The laminate is simply supported containing a through width delamination. A new parameter β defined as the ratio of delamination length to delamination width is introduced with an emphasis on the influence of the delamination size. It is found that (i) when the ratio β is greater than one snap-through buckling prevails, the buckling load is determined by the delamination size and depth only; (ii) as the ratio β continues to increase, the buckling load will approach to a constant value. Solutions are verified with the well established results and are found in good agreement with the latter.