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The issues of intersonic and supersonic fracture become the frontier of dynamic fracture mechanics. We describe in this paper the recent progresses in obtaining the analytical continuum solution for the initial-boundary valued problem of intersonic fracture under mode II loading, and construct an plausible analytical solution for mode III supersonic fracture.

Conventional strain-based mechanics theory does not account for contributions from strain gradients. Failure to include the strain gradient contributions can lead to underestimates of stresses and size-dependent behaviors in small-scaled structure [1]. This paper focus on the structural size effects on torsion of cylinders. The torsional stiffness of cylinders can be higher than conventional expectation when the cylinder size is in the nanometer - or micron-scale. Following the Saint-Venant theory of torsion, we established the equation of torsion in terms of the warping function on the basis of the nano-mechanical theory of elasticity. The torsional equations contain two higher order material length scale parameters and two conventional Lame constants. The equilibrium equation is a fourth order partial differential equation which can be reduced to two second order equations. Two formulations in terms of pseudo warping function and stress function are presented. Closed-form solutions for circular and thin wall section and series solutions for rectangular microbars have been obtained. The total torque depends only on the stresses conjugated to the strain and is only implicitly dependent on the higher order stress metrics. The solution reveals that the torsional rigidity is dependent on the higher order length scale parameters and strain gradients and increases asymptotically upward when the cylinder size is reduced to the size of the higher order length scale material parameters. The increase is most marked for thin walled cylinders, stiffening to more then 10 times the conventional value when the cylinder size is near that of the higher order length scaled parameters.

A major challenge in rock mechanics has been the realistic modeling that can reveal the progressive accumulation of damage and shear localization in a brittle rock under compression. The Rock Failure Process Analysis code (RFPA2D) is an efficient tool and realistic model to simulate such complexities. A key assumption of the code is that the heterogeneity of elastic moduli and failure strength are characterized by the Weibull distribution with two parameters (m and σ0 ). However, these two parameters do automatically not relate to the microstructural parameters, such as grain size and microcrack statistics. Therefore, the purpose of this paper is to elucidate the micromechanical basis of these Weibull parameters, specifically how they depend on microstructural attributes such as grain size and crack statistics. Secondly, a methodology was developed to quantitatively determine the relevant micromechanical parameters for input into the RFPA2D code. Finally, the methodology was implemented by quantifying the microcrack geometry and statistics of real rock and simulating its uniaxial compression and progressive failure behavior. The simulated result agrees well with the experimental study.

In the present paper, axisymmetric smooth and notched specimens of aluminium alloy LY12CZ were monotonic tension tested to study the ductile fracture behavior and evaluate the suitability for the critical void growth ratio, VGC of the material, from the micro and macro points of view. It's found that the material would change fracture morphology from tensile to shear failure in the various stress states; the ductile fracture parameter VGC is sensitive to the fracture morphology which is applicable for the case of tensile failure while not suitable for the case of the shear failure, i.e. the case of smooth tensile specimens.

Potentially both global and local approaches may be used to predicting the effect of loading history on cleavage fracture toughness distribution of ferritic steels. In this paper the dramatic increase in the apparent lower shelf fracture toughness of A533B steel following warm pre-stressing (WPS) has been predicted using these approaches. Extensive experimental evidence suggesting significant enhancement in fracture toughness of ferritic steels within the lower shelf temperatures following WPS are used to verify and compare the applicability and the extent of validity of the models. The global approach is based on the distribution of toughness data described by Wallin statistical model in conjunction with the Chell model for WPS effect. The local approach on the other hand is a Beremin type model that uses the Weibull stress to predict the WPS effect. Weibull stresses would essentially reflect the WPS effect on redistribution of stress-state around the crack tip. Predictions for apparent toughness using the two approaches are discussed in the light of the suggestion that residual stresses are the main cause of the enhancement, at least for the material and geometry used in this study.

In this paper elastic stress field in an elliptic inhomogeneity embedded in orthotropic media due to non-elastic deformation is determined by the complex function method and the principle of minimum strain energy. Two complex parameters are expressed in a general form, which covers all characterizations of the degree of anisotropy for any ideal orthotropic elastic body. The stress acting on the long side of ellipse can be considered as a crack driving force and applied in failure and fatigue analysis of composites. For some special cases, the resulting solutions will reduce to the known results.

This paper studies the effect of the Columbic force on piezoelectric fracture. Bound charges emerge on the upper and lower surfaces of a permeable crack when a piezoelectric solid with the crack is subjected to far-field mechanical/electric loading. Taking into account the Columbic force between the bound charges, we obtain a non-linear equation governing the normal component of electric displacement D2(x1)on the crack faces. The results show that D2(x1)is, in general, not a constant along the crack faces and depends on the mechanical/electric loading conditions, the crack profile and the material properties outside and inside the crack. Furthermore, we examine the Columbic force under low mechanical/electric loads and then discuss the effect of the Columbic force on the fracture behaviour of piezoelectric materials.

The ground fissure is one of primary geological disasters in Xi’an, China. The extension pattern and deformation failure area near fissure are studied through the FEM of elastic-plastic fracture mechanics in this paper. The results show the crack extension is not completely tension crack, it is mixed mode when the confined aquifer was pumped. The extents of earth surface deformation and stress concentration of beyond plate are larger than that of the bottom one. It is consistent with observational results.

Graphite has been developed as heat resistant material. To apply a reliable structural design using graphite, it is very important to investigate thermal shock characteristics. The common experimental methods of thermal shock fracture toughness are quenching and arc discharging heating methods. This paper describes experimental technique to evaluate the thermal shock fracture toughness using laser irradiation and proposes that a critical value of laser power can be a measurement to evaluate heat resistant materials. The laser source is CO2 laser having maximum power of 4.0kW. The range of laser beam is from 1.0 to 2.7 kW and the beam duration is fixed at 1sec. K and C type thermocouples were used to measure the temperature distribution of a thermal shock fracture toughness specimen. In this study, the temperature distribution of specimen surfaces and critical laser power was investigated. After test, the surface phenomenon of specimen is examined using radiography and SEM. It is concluded that the critical laser power causing fracture can be the major factor of thermal shock fracture toughness of ATJ graphite.

In practical engineering, the cracks are always mixed mode. The research on the mixed fracture criterion has an important significance in fracture mechanics and engineering. Stress state of the mixed mode cracks is complicated. A new unified strength theory considering the effects of all the three principal stresses is generalized into the fracture mechanics in this paper. The complex stress states are common characteristics between the mixed mode cracks and the unified strength theory. A unified fracture function criterion is established by using the unified strength theory in this paper. In the unified fracture function, the difference between tension and pressure and the effect of the intermediate principal stress σ2 are considered. With the variation of α = σt/ σc and failure parameter b , a series of mixed mode crack criteria are formed, and can be applied for many materials. The J-integral is calculated through FEM. According to the relation between the result and the stress intensity factor, Klc can be obtained. Then it is used in the unified fracture function. The unified fracture criterion is compared with those of other mixed mode criterions.

Accurate crack propagation simulation requires critical fracture parameters to be known a priori. For elastic-plastic materials, two fundamental parameters are the separation energy and the peak stress required to generate new crack surfaces. In general, both are difficult to quantify since direct determinations are not possible in experiments. For inhomogeneous materials, such as graded materials, determination is even more complex since these parameters vary spatially. In this paper, a novel method based on an inverse analysis technique is proposed to estimate the fracture parameters of elastic-plastic and graded media. The method utilizes the Kalman filter to process measured data and extract best estimates of the unknown parameters. The accuracy of the method is examined in a verification study where a dynamically propagating crack in double cantilever beam type specimen is modeled. In the study, time variation records of crack opening displacement, opening strain, crack advance distance, and load point reaction force are used as possible measurements. Despite large noises in data, the results confirm accurate estimation. The estimates improve when multiple measurements are supplied to the inverse technique.

It is of interest to understand damage and failure mechanisms of microcracks and their evolution as a function of loading history, especially in the case of complex loading. Owing to their superior mechanical and physical properties, carbon nanotubes (CNTs) seem to hold a great promise as an ideal reinforcing material for composites of high-strength and low-density. HOWEVER, In most of the experimental results, only modest improvements in the strength and stiffness have been achieved by incorporating carbon nanotubes in polymers. There are many factors that influence the overall mechanical property of CNT-reinforced composites, e.g. the weak bonding between CNTs and matrix, the waviness and agglomeration of CNTs. In the present paper, we use the Mori-Tanaka method to evaluate the effect of these factors on the moduli of CNTs-CNT-reinforced composites. It is established that the waviness and agglomeration may significantly reduce the stiffening effect of CNTs, while the interface between the matrix and CNTs influence the moduli of CNTs-reinforced composites little.In this paper, the frictional sliding of microcracks under complex triaxial loading is analyzed, and the obtained results are incorporated into the constitutive relation of microcrack-weakened brittle materials.

A virtual crack vector model is proposed in this paper to simulate the branched crack propagation and simplify its calculation of energy release rate. An energy gradient fracture criterion is constructed based on this model. It can take account of the effects of biaxial loads or T-stress on brittle mixed mode fracture and agrees well with the test data of biaxial tensile fracture and the specially conducted experiment of the influences of ox on the mixed mode fracture of plexiglas. Considering its advantage of predicting initial propagation angle and critical fracture stress independently without the determination of the core region radius, it can be used as a practical fracture criterion for brittle mixed mode fracture under biaxial tension.

Reduced activation ferritic (JLF-1) steel is one of the leading candidates for blanket/first-wall structures in D-T fusion reactors. In fusion applications, structural materials will suffer the effects of repeated temperature changes. Therefore, a database of tensile strength and fracture toughness are very important as the temperature is 400 ° C and it's TIG welded joint. In this paper, fracture toughness JIC and KIC) and tensile tests were carried out at room temperature (RT) and at elevated temperature (400 ° C). The tensile properties of the TIG welding joint of JLF-1 steel was also investigated. It was shown that the tensile strength and fracture toughness values of the JLF-1 steel are slightly decreased with as increase in temperature. The fracture toughness values of JLF-1 steel at room temperature and at 400°C show excellent JIC values of about 530 kJ/m2 and 340 kJ/m2, respectively.

In order to perform elastic-plastic fracture mechanical analyses, fracture resistance curves for concerned materials are required. A standard CT specimen was used to obtain fracture resistance curves. However the fracture resistance curve by the standard CT specimen was very conservative to evaluate the integrity of the structure. Also the fracture resistance curve was affected by the specimen geometry, crack plane orientation, reverse cyclic loading and dynamic strain aging. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen. For these purpose, fracture tests using the real-scale pipe specimen and standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. From the result of the pipe and the standard CT specimen tests, it was observed that the fracture resistance curve of the standard CT specimen test was conservative compare to that of the pipe specimen test.

The brittle-ductile character is one of the important mechanical indexes of rocks and also one of the important affecting factors of rockburst. Both conventional and true triaxial tests have shown that the brittle-ductile character of rocks varies with the variation in rocks stress state and stress path, but these two kinds of tests have revealed totally different laws of brittle-ductile transition. This present paper analyses the results from two tests firstly and then summarizes the effect of rock’s brittle-ductile transition character on rockburst and finally points out the deficiency in present studies of rockburst.

This paper presents the results of an experimental and numerical study carried out to investigate the effect of warm pre-stressing on cleavage fracture in ferritic steels using cracked and notched specimens. It is shown that the local approach based on Weibull theory predicts the increase in toughness following warm pre-stressing in highly constrained geometries. The observed effect of pre-loading in low constraint specimens such as round notched bars is less. The local approach could not predict the differences and it is suggested that the variation of triaxiality factor, the ratio of hydrostatic stress to Von Mises, in the plastic zone, is a contributing factor.

Research studies for mode I cracks have shown that fracture toughness or the critical value of J for fracture initiation, Jcrit is not merely a material property but depends also on the geometry and loading configurations. The geometry dependency of fracture toughness can be attributed to the effect of the crack tip constraint. In this paper, the constraint effect is studies for the initiation stage in mode II ductile crack growth. Two major mechanisms of ductile fracture: 'void growth and coalescence' and 'shear band localization and de-cohesion' are considered. A boundary layer model is simulated using the finite element method and the effect of far-filed T-stress on the relevant stress parameters near the crack tip is studied. It is shown that the initiation of the ductile crack growth in mode II is influenced significantly by T for the mechanism of void growth and coalescence and is insensitive to T for the mechanism of shear localisation and de-cohesion.

This paper presents a new computer program called DIFAR (or dynamic incremental failure analysis of rock) that can simulate fracture process of brittle rocks under dynamic impacts. The program is based on a linear elastic finite element method incorporated with a failure criterion for damage checking. Modulus is reduced once the failure criterion is satisfied. In addition, Weibull distribution of the modulus and strength of the elements are used for modeling the mesoscopic heterogeneity. The failure criterion is a Mohr-Coulomb type of condition with a tensile cut-off, in which strength parameters are functions of the strain rate. More importantly, the whole fracture process of rock fragmentation can be simulated, including initiation, propagation, and coalescence of microcracks. The program DIFAR has been used to simulate elastic wave propagation and nonlinear fragmentation, and validity and efficiency of this program is demonstrated. The program can be considered as a dynamic counterpart of the RFPA, a failure analysis program for static loads, developed at Northeastern University, China.

The influence of a biasing electric field on the propagation of the lowest-order antisymmetrical a0 Lamb wave modes in a bi-layered piezoelectric plate is investigated in this paper. It is found that the velocity shifts for the a0 mode due to presence of the bias field on the 10- µm LiNbO3 film structure are comparable with those observed in surface acoustic waves and Lamb waves in LiNbO3 plates. The fractional change in phase velocity of the layered piezoelectric structure is a linear function of the biasing electric field and can be used in voltage sensors.

The present paper introduces the experimental study on soft rock (analogized with mortar)under dynamic uniaxial compression at the strain rates from 10 -5 to 101s-1. It is indicated that thecompressive strength of the soft rock increase with the increasing strain rate and the rising rates are higher than that of hard rock. The Young's moduli and Poisson's ratio of the soft rock increase with the increasing strain rate, but the rising rates are less than that of compressive strength. In addition, the mechanism of the strain rate effect of the soft rock is primarily analyzed based on the SEM results.

By contrast with static fracture toughness determination, the methodology for dynamic fracture toughness characterization is not yet standardized and appropriate approaches must be devised. The accurate determination of the dynamic stress intensity factors must take into account inertial effects. Most methods for dynamic fracture toughness measurement are experimentally complex. However, dynamic fracture toughness determination using strain measurement is extremely attractive in terms of experimental simplicity. In this study, dynamic fracture toughness tests using strain measurement are performed. High rate tension and charpy impact tests are carried out for titanium alloy, maraging steel and Al alloys. In the case of evaluating the dynamic fracture toughness using high rate tension and charpy impact tests, load or energy methods are used commonly. The consideration about inertial effects is essential, because load or energy methods are influenced by inertia. In contrast, if the position for optimum response of strain is provided, dynamic fracture toughness evaluation using strain near crack tip is more accurate. To obtain the position for optimum response of strain, a number of gages were attached at angles of 60°. Reliability for experimental results is evaluated by Weibull analysis. The method presented in this paper is easy to implement in a laboratory and it provides accurate results compared to results from load or energy methods influenced by inertia.

The Indonesian railway transportation has adventages in term of capacity, efficiency, trafic, and safety compared to the other types of land transportations. At present, the Indonesian Railway Company has 519 locomotives, and 1643 passenger cars, that transport about 184 million man-trip each year[1,2]. Unfortunately, the rate of train collisions in Indonesian railway system was very high. In the last ten years, 2352 train accidents have happened which claimed 997 lives and left 2638 people injured. The record shows that 110 of those accidents were train to train collisions[1]. This paper consider the structural impact behavior of Indonesian passenger railway car subject to collision forces. This characteristic is very important parameter for passenger protection during the course of collision[3-5]. The vehicle structure should be able to absorb the huge impact energy or impact force to ensure the passenger safety[6-9]. The impact energy of cars-train is evaluated using the principle of multibody dynamics[10,11]. The vehicle structure under impact load is analyzed using the finite element method. The principal of symmetry is adopted, so the collision scene could be simulated as collision between the vehicle with a rigid wall. The analysis result shows that the structure is collapse at the passenger area (saloon) which is in agreement with the real collision. Modification is proposed to protect the passenger area by introducing crush zone area and impact energy absorber.

By employing the Stroh formalism for plane anisotropic thermoelasticity, closed-form solutions for the orders of stress and heat flux singularities of multi-material wedges have been obtained. Several different boundary conditions are considered in this paper such as insulated or isothermal as well as free-free or fixed-fixed or free-fixed or fixed-free wedge boundaries. The solutions show that the singular orders are influenced by the wedge configurations (n wedge angles), boundary conditions, elastic constants and heat conduction coefficients, but are independent of the thermal moduli.

This paper aims to assess the effect of shape irregularity on contact damage in a brittle coating on a stiff metal substrate. Hertzian contact damage in a dental porcelain layer over a Ni-Cr alloy substrate in both curved and flat geometries was studied using finite element analysis and experimental investigation. Three failure modes were examined with varying porcelain layer thickness: cone cracking at the top surface of the porcelain, interface cracking at the layer/substrate interface and plastic deformation below the contact area in the substrate. It is shown that curvature has very little effect on the initiation of surface cone cracks in this system, but substantial effect on the initiation of interface radial cracks. In particular, curvature reduces the critical load for the onset of interface cracks

This paper deals with a Mode III interfacial edge crack in a magnetoelectroelastic bimaterial subjected to line singularities such as an out-of-plane line force, a line electric charge, a line magnetic charge and a straight screw dislocation. The surfaces (including crack surfaces) of the bimateral are assumed to be electrically open and magnetically closed. The closed-form analytical solution to the problem is obtained by employing the complex variable approach in conjunction with the conformal mapping technique. The intensity factors of stress, electric displacement and magnetic induction are given explicitly. The obtained results can be used as the Green's function to solve more complicated problems.

A surface strain measurement approach to understanding of delamination processes of thermal barrier coatings (TBCs) under heat cycle conditions was described in this paper. Heat cycle tests between the high temperature ranged from 1473K to 1073K and the relatively low temperature (573K) was carried out on thermal barrier coated type 304 stainless steel specimens. 8mass%Y2O3- ZrO2 and Al2O3 coatings were used for the TBCs. The surface strain behavior during the heat cycle test was measured using a laser speckle strain/displacement gauge (SSDG). It was found that the thermal expansion of a substrate was almost reflected on a surface strain if a delamination wasn't initiated, while the value of a surface strain decreased to the value of the thermal expansion of a ceramics-coating if the delamination of the ceramics-coating was initiated. The state of a subsurface delamination was able to be nondestructively inferred by the surface strain behavior. The delamination life of a ceramics-coating in the specimen with a low-pressure-plasma-sprayed (LPPS) bond-coating was found to be longer than that with an atmospheric-plasma-sprayed (APS) bond-coating. The large roughness of a bond-coating was also found to be effective in improving the delamination life of a ceramics-coating owing to the restriction of a crack propagation parallel to the interface between the ceramics-coating and the bond-coating.

Multi-layer thin films are widely used in micro-sensor and microelectronics products. These electronic devices contain several metal or polymer thin films and reliability of these systems is strongly dependent on the interfacial adhesion of these thin films. Due to the thermal stress, residual stress or elastic mismatch, the delamination between layers sometimes occurs. Therefore, it is important to evaluate the interfacial strength precisely. Peel tests are simple way to estimate an interfacial strength and, in fact, widely used in industrial field. Recently, a new simple but functional device for peel tests has developed in our group. This test method is called 'Multi-stages peel test'. There are two features in this device. At first, peeling tips can be observed continually and it becomes easy to measure a peeling angle. Second is that the peeling angle can be varied by attaching dead weights on the specimen. This dead weight works as a shear force at the peeling tip and the peeling angle can be changed variously. Therefore, the fracture tests under various phase angles are possible. In this paper, Multi-stages peel test is applied to the evaluation of interface strength of multi-layer thin films that are composed of Cu, Cr, PI and Si layers. By considering the energy balance during the peel test, the interfacial strength independent of the thickness can be obtained.

The material properties of underfill and substrate in flip chip package have temperature-dependent and moisture-sensitive characteristics. During the solder reflow process, the CTE mismatch in the package causes thermal stresses, which may reduce the reliability of the flip chip package. The package reliability can be improved by varying the die thickness, the fillet angle and the thickness of the underfill and by changing the underfill material. In this paper, the temperature- dependent properties of the underfill were established first. The flip chip reliability was then analyzed by finite element code ANSYS. Both underfill A and underfill B were used in the analysis. The results show that better reliability of the flip chip package was obtained for underfill A, for larger fillet angle of the underfill, for thinner die in the package, and for larger Young's modulus of underfill with linear elastic assumption. Also a hygrothermal preconditioning before thermal cycling reduces the reliability of the flip chip package.

This paper presents a design and performance tests of in-plane gimbal-structured Z-axis gyroscope. The device is manufactured by conventional surface micro machining process using 15µm-thickness epitaxially grown polysilicon. The total size of the device is 4.8mm x 4.8mm in area including 1mm x 1mm core gyro structure and pads for wire bonding. It is designed as two-gimbaled structure which separates inner and outer gimbals. This leads two nearly identical modes of gyroscope, i.e. driving and sensing mode, to mechanically decoupled ones, resulting in enhanced performance. Experiments are accomplished through frequency analysis and dynamic tests using a detection circuit, a vacuum chamber and a rate table. Through experiments, it is confirmed that the designed gyroscope has 0.003 deg/sec resolution, 0.00095 deg/sec/ Hz noise equivalent density, 0.57 % FSO nonlinearity error and 0.02 deg/sec bias stability.

The compactly supported radial basis functions (RBFs) is modified and used to the wave propagation in the anisotropic materials. An example to simulate the wave propagation in composite material is used in the paper to verify this method. In this example, stress wave propagation histories are obtained. The comparison between results by this method and by finite element method is also made. And the agreement with two results shows that this method can be used to simulate the wave propagation history in anisotropic material efficiently.

This present paper makes preliminary discussions on the application of Numerical Manifold Method to P- version adaptive analysis and deduces the displacement functions with various orders in elements and the expression of element's stiffness matrix, and codes the program for adaptive analysis with language C. Two numerical examples are studied and their results verity that the method and programs being given on this paper are accurate.

In finite element method, the order of complete polynomial of the interpolation function is related to the number of nodes in the element. This paper presents a four-node quadrilateral element with quadratic function on it. The presented displacement functions maintain C0-continuity. Meanwhile, the element stiffness matrix is derived from the displacement functions. Test problems show that high accuracy can be achieved by the use of the new displacement function on the element.

In this paper, the moving least-square (MLS) method, one of the most promising meshless methods, is modified to construct whole field meshless approximation for coupled electromechanical problems. Based on this method, the crack propagation behavior and the elasto-electric fields near a crack tip in a PZT-5H piezoelectric ceramic under mechanical, electrical and mechanical-electrical mixed loads are investigated. The numerical results show that for a negative applied electric field, the hoop stress will be maximum at a certain angle other than 00 when the ratio of the electric field to tensile stress is relatively high, which makes the crack turn away from its original growth path.

This paper describes the application of the coupled FE-BEM (finite element-boundary element method) for the numerical harmonic analysis of the linear dynamic behaviour of a magnetostrictive Terfenol-D rod in water. The magnetostrictive rod is three-dimensionally modeled to transduce applied electric current in a helical coil around the rod to mechanical displacement. The steady-state resonance response of the displacement is shown.

To increase the accuracy of R-F method, it is necessary to solve the problems of the linear expansion of failure function and non-normal variables. In this paper, the improved FOSM method was applied to calculate the failure probability of welded pipes with cracks. The examples show that this method is simple, efficient and accurate for reliability safety assessment of welded pipes with cracks. It can save more time than the Monte Carlo method does, so that the improved FOSM method is recommended for general engineering reliability safety assessment of welded pipes with cracks.

A numerical algorithm using equal-order linear finite element and fractional two-step method is presented in this paper, which is used for analysis of incompressible viscous fluid flow with free surface problems. In order to avoid severe mesh distortions, ALE method is used for dealing with the free surface sloshing. For numerical integration, the fractional step method is employed, which is useful because the same linear interpolation functions for both velocity and pressure could be carried out in the finite element formulation. The present algorithm has been applied to some examples and proved to be accurate and more efficient.

Finite element analysis for thick composite structures is rather complicated. Two-dimensional modeling, which is relatively easy to make, can cause inaccurate result since the plane stress condition cannot be applied, while three-dimensional modeling is hard to make. In the three- dimensional modeling, it is difficult to model all the layers with different material properties and ply orientation in the structure. In this paper, an equivalent modeling is proposed and numerically tested for analysis of thick composite structures. The method has been verified for the modeling of composite plate and circular composite tube in order to find their bending deflection and natural frequency. MSC/NASTRAN and PATRAN are used for the calculation. It has been confirmed that three-dimensional analysis must be conducted for thick structures and the equivalent modeling is proven to be accurate when layers with same characteristics are properly grouped. The proposed modeling technique has been applied to analyze hingeless composite rotor hub system designed by Korea Aerospace Research Institute (KARI). Detailed three-dimensional modeling for this structure is almost impossible to make due to its complex geometry of thick composite structures. Using the proposed equivalent modeling technique, failure analysis was performed based on stress/strain criterion and the safety of each part was checked. Deflection of the hub system was validated comparing with the result from the simple analytical beam model, and the numerical result will be used for the next design cycle of the composite hub system.

Recently, the world is preparing for new revolution, called, ‘IT(Information Technology), NT(Nano-Technology), and BT(Bio-Technology).’ NT can be applied to various fields such as semiconductor-micro technology. Ultra precision processing is required for NT in the field of mechanical engineering. Because of radical advancement of electronic and photonics industry, necessity of ultra precision processing is on the increase for the manufacture of various kernel parts. In this paper, stability of ultra precision cutting unit is investigated and this unit is the kernel unit in ultra precision processing machine. According to alteration of shape and material of hinge, stability investigation is performed. Hinge shapes of micro stage in UPCU (Ultra Precision Cutting Unit) are designed in two types, where, hinge shapes are composed of round and rectangularity. Elasticity and strength are analyzed on micro stage with respect to hinge shapes by FE analysis. The micro stage in ultra precision processing machine has to keep hinge shape under cutting condition with 3-component force (cutting component, axial component, and radial component) and to reduce modification against cutting force. Then we investigated its elasticity and strength under these conditions. The material of the micro stage is generally used for duralumin with small thermal deformation. Since the elasticity and the strength quiet become important, the stability of the micro stage is investigated. Used materials are composed of aluminum of low strength and cooper with medium strength and spring steel with high strength. Through this stability investigation, trials and errors are reduced in design and manufacture at the same time, and we are accumulated foundation data for a unit control.

Fine blanking process with V-ring was simulated with FEM. The geometric parameters of the die, the punch, the serrated ring and the sheet are modeled. In this paper, some other assumptions are made for the analysis. The workpiece is considered as elastic-plastic material, while the tools are defined as rigid bodies. The damage model taking into account the influence of hydrostatic stress is used to simulate material fracture in blanking. The stress status and forming process are analyzed. Authors also investigated the effect of distance from tooth to die edge on roll-over high. The simulation can reflect the laws of fine blanking process.

In this paper, the buckling behavior of elastically restrained orthotropic web plates is investigated. In general, the pultruded FRP structural member is composed of flat plate elements and each plate element is elastically restrained against rotation by adjacent plate components. For finding the local buckling strength of composite flexural member considering the elastic restraint at the juncture of plate components, the orthotropic web plate is modeled as an elastically restrained orthotropic plate under linearly distributed in-plane forces. For the derivation of buckling equation, the power series solution technique is employed. For the plate having different mechanical properties, the parametric studies are conducted by varying the degree of restraint along the longitudinal edge under compression. By using the results obtained, simplified form of equation is also developed so that the practicing engineers can evaluate the buckling stress of such a plate for the preliminary design of FRP flexural members.

This paper presents the analytical investigations pertaining to the elastic buckling behavior of orthotropic composite plates. By the pultrusion process the structural shapes composed of orthotropic plate components are readily available in the construction market. When the member is utilized for the flexure, lateral-torsional buckling and local buckling behaviors must be taken into consideration. In the local buckling analysis, flange and web local buckling analyses must be conducted in the design of such a member. For finding the web buckling strength, the buckling equation for the orthotropic plate under linearly distributed in-plane forces is derived by using the Rayleigh-Ritz method. The boundary conditions of plate are assumed that the loaded edges are simply supported and the unloaded edges are simply supported or fixedly supported. The buckling coefficient of a plate having different orthogonal mechanical properties is found by using the numerical technique and the minimum buckling coefficient is suggested. In addition, simplified form of equation for predicting the minimum buckling coefficient for the plate is proposed. Brief discussion on the design criteria relating to the web local buckling is also provided.

The problem addressed in this paper is the elastic local buckling of thin-walled compression members whose plate components are tapered in thickness along the longitudinal direction. In the design of structural system in construction, shipbuilding, and aerospace industries, such structural plate components are frequently encountered. The elastic buckling analysis of transversely isotropic plates with varying thickness and various boundary conditions is performed to derive the buckling equation of thin-walled members composed of tapered plate components. In the analytical solution, the energy approach is adopted. The analytical results are presented in a graphical form in which the plate buckling coefficients are suggested with respect to the width ratio of plate elements and the degree of taper. In addition, using the buckling equations of plates with specific boundary conditions, the simplified form of equation for the local buckling coefficient of structural members such as L-section, T-section, and Box-section is suggested.

This paper introduces temperature effect to rock model. It sets up a thermo-visco-elastic-plastic rock model. Based on the rock model which consists of spring, dashpot and plastic elements under the condition of un-axial compression, the behaviors of the thermo-visco-elastic-plastic in rock are discussed, and the equations of the constitutive, creep, unload and relaxation have been obtained. This model can reflect the rock or rock mass average thermo-rheology character. Meanwhile, this study gives a explanation of the significances of this kind of model in the practical use.

Analytical solutions of stress fields in functionally graded circular hollow cylinder with finite length subjected to axisymmetric pressure loadings on inner and outer surfaces are presented in this paper. The cylinder is simply supported at its two ends. Young's modulus of the material is assumed to vary continuously in radial direction of the cylinder. Moreover, numerical results of stresses in functionally graded circular hollow cylinder are appeared.

In this paper, a simple conformal load-bearing antenna structure smart skin with a multi-layer sandwich structure composed of carbon/epoxy, glass/epoxy, and a dielectric polymer was designed and fabricated. The mechanical properties of each material in the designed smart skin were obtained from experiments. Tests and analyses were conducted to study the behavior of the smart skin under compressive loads. The designed smart skin failed due to buckling before compression failure. The stresses of each layer and the first failed layer of the smart skin were predicted using MSC/NASTRAN. The finite element model was verified by comparing the numerical results from geometrical linear/nonlinear analyses with the measured data. The numerically predicted structural behavior of the smart skin agreed well with the experimental data. The results showed that the carbon/epoxy layer took charge of most of the compressive load, and the first failure occurred in the dielectric layer while the other layers remained safe. A numerical model was used to obtain design data from the parametric study. The effect of changing the design variables on the buckling and compressive behavior of the smart skin was also investigated. As a result, it was confirmed that the transverse shear moduli of the honeycomb core had a serious impact on the buckling load of the smart skin when the shear deformation was considerable.

In this paper, a simple but highly accurate analytical method to evaluate stress intensity factors based on an element overlay technique is presented. When a crack exists in a structure, we need to analyze its global deformation as well as local deformation field around the tip of the crack. This naturally leads us to a consideration on some kind of multi-scale analysis strategies. Thus, we adopt the element overlay technique (S-FEM) which is a kind of multi-scale methodologies. In this paper, we present i) numerical implementation of element overlay technique (S-FEM), ii) method to calculate stress intensity factors (virtual crack closure-integral method, VCCM), iii)accuracies of evaluated stress intensity factors and iv) some discussions.

This paper compiles solutions of plastic η factors for standard and non-standard fracture toughness testing specimens, via detailed three-dimensional (3-D) finite element (FE) analyses. Fracture toughness testing specimens include a middle cracked tension (M(T)) specimen, SE(B), single-edge cracked bar in tension (SE(T)) and C(T) specimen. The ligament-to-thickness ratio of the specimen is systematically varied. It is found that the use of the CMOD overall provides more robust experimental estimation than that of the LLD, for all cases considered in the present work. Moreover, the estimation based on the load- CMOD record is shown to be insensitive to the specimen thickness, and thus can be used for testing a specimen with any thickness.