A study on penetration fracture characteristics of glass plates subjected to impact loadings

In this study, a comparison between theoretical solutions and experimental results are examined for fracture conditions in the case of float glass plates subject to static loadings. The ranges from fracture-generated initiations to critical penetration energies are confirmed according to the impactor mass under high velocity, and an analytical method is presented to determine the fracture strength and penetration strength. Also, fracture patterns are investigated according to impact velocities.     

7075铝合金板淬火残余应力模拟及实验研究

铝合金板在淬火过程中产生较大的残余应力,导致构件出现变形、翘曲。采用准耦合法对7075铝合金板在淬火过程中的温度场和应力场进行数值模拟,利用盲孔法对淬火后的残余应力分布进行实验测量。结果表明,7075铝合金板淬火后残余应力呈现出外压内拉的分布状态,淬火过程中形成的较大温度梯度造成的不均匀塑性变形是应力产生的主要因素,铝板表层和心部冷却速度的变化导致了应力分布状态的转变。实验结果验证了准耦合模拟方法的可行性,研究结论为残余应力控制提供重要依据。     

Second-order continuity tensor and stiffness degradation of aluminum alloy 2024T3 under large strain at room temperature

A symmetric second-order continuity tensor is proposed to characterize anisotropic damage of anisotropic materials based on the hypothesis of equivalent elastic strain energy. On the basis of the equivalent elastic strain energy hypothesis, the relation between the effective elastic properties and the continuity tensor has been formulated. The current formulation does not require the assumption that the principal coordinate system of damage must coincide with that of the material. In a two-dimensional damage analysis, the state of damage can be represented by a Mohr’s circle of continuity. The proposed damage characterization technique has been successfully applied to an example case, where aluminum alloy 2024T3 specimens were strain-damaged by uni-axial tension. The experimental results show that the effects of strain damage can cause degradation of the material stiffness. On the other hand, the overall elastic orthotropy of the material does not increase with the degree of damage. The proposed continuity tensor has been found to be capable of describing this phenomenon. The principal values and the principal directions of the continuity tensor have been determined. The mean value of the principal values can represent the magnitude of the damage, while the principal direction of the continuity tensor may provide information about the damage mechanism.     

Continuous out-of-plane deformation measurements of AA5083-H116 plates subjected to low-velocity impact loading

An optical system based on structured light and close-range photogrammetry has been developed and is in this study used to continuously measure the full-field out-of-plane deformation of aluminium plates subjected to low-velocity impact loading. During testing, square AA5083-H116 aluminium plates with thickness 5 mm were mounted in a circular frame and impacted by a 30 mm diameter blunt-nose projectile with velocities ranging from 7 to 11 m/s, while the out-of-plane deformations were measured at the opposite side. A fringe pattern was projected onto the rear target surface by a slide projector and the variation in the pattern during penetration was observed by a high-speed camera recording 10,000 images per second. The recorded images were subsequently computer processed to provide full-field topography information of the target surface during deformation. Degradation of measurement data due to impact induced vibration has been evaluated and reduced to a minimum by isolating the optical system from the mechanical experiment. The out-of-plane deformation measurements were compared to non-linear finite element simulations, and the agreement between experimental and predicted results was in general found to be good.     

Numerical analysis of static performance comparison of friction stir welded versus riveted 2024-T3 aluminum alloy stiffened panels

Most researches on the static performance of stiffened panel joined by friction stir welding（FSW） mainly focus on the compression stability rather than shear stability. To evaluate the potential of FSW as a replacement for traditional rivet fastening for stiffened panel assembly in aviation application, finite element method（FEM） is applied to compare compression and shear stability performances of FSW stiffened panels with stability performances of riveted stiffened panels. FEMs of 2024-T3 aluminum alloy FSW and riveted stiffened panels are developed and nonlinear static analysis method is applied to obtain buckling pattern, buckling load and load carrying capability of each panel model. The accuracy of each FEM of FSW stiffened panel is evaluated by stability experiment of FSW stiffened panel specimens with identical geometry and boundary condition and the accuracy of each FEM of riveted stiffened panel is evaluated by semi-empirical calculation formulas. It is found that FEMs without considering weld-induced initial imperfections notably overestimate the static strengths of FSW stiffened panels. FEM results show that, buckling patterns of both FSW and riveted compression stiffened panels represent local buckling of plate between stiffeners. The initial buckling waves of FSW stiffened panel emerge uniformly in each plate between stiffeners while those of riveted panel mainly emerge in the mid-plate. Buckling patterns of both FSW and riveted shear stiffened panels represent local buckling of plate close to the loading corner. FEM results indicate that, shear buckling of FSW stiffened panel is less sensitive to the initial imperfections than compression buckling. Load carrying capability of FSW stiffened panel is less sensitive to the initial imperfections than initial buckling. It can be concluded that buckling loads of FSW panels are a bit lower than those of riveted panels whereas carrying capabilities of FSW panels are almost equivalent to those of riveted panels with identical geometries. Finite elem     

An estimation method for the Shock Response Spectrum propagating into plates subjected to hypervelocity impact

The present work regards the prevision through Finite Element Analysis (FEA) codes of the Shock Response Spectrum (SRS) levels on thin plates subjected to Hypervelocity Impact (HVI).     

A study of cumulative fatigue damage in aluminum alloy 2024-T4

Experimental data were generated using 2024-T4 aluminum alloy specimens under stress ratios of ?1 and ?0.5 for low-high, low-high-mixed, high-low and high-low-mixed stress sequences.Analysis of the data using Kramer's equation has indicated that the predicted cumulative fatigue damage and fatigue life are in close agreement with experimental results for low-high and low-high-mixed stress sequences under all stress ratios, whereas the theoretical values for high-low and high-low-mixed stress sequences under all stress ratios are more conservative than those obtained experimentally.It is suggested that development of Kramer's equation be studied thoroughly for possible modification.     

A theoretical and experimental study of hemispherical shells subjected to axial loads between flat plates

The quasi-static loading of an open hemispherical shell along its axis of symmetry through a rigid flat plate is considered with particular reference to large deformations and buckling.Deformation patterns which are symmetric and non-symmetric about the axis are studied analytically and experimentally for models of different materials and radius to thickness ratios varying between 36 and 460.     

Dynamic response of aluminum honeycomb sandwich panels subjected to hypervelocity impact by porous volcanic rock projectile

The dynamic response and damage behavior of aluminum honeycomb sandwich panels (HC/SPs) subjected to hypervelocity impact by volcanic rock projectiles were investigated by hypervelocity impact tests and hydrocode simulations. The experiments were conducted using a two stage light gas gun and the results showed that the failure modes in HC/SPs subjected to hypervelocity impact by volcanic rock projectiles mainly took forms of front-face denting and circular perforation, honeycomb core collapsing and rapture, rear-face petal-ling and perforation etc. A 3D discrete configuration of the porous volcanic rock projectiles was set up. The hypervelocity impact behavior of the HC/SPs was investigated through hydrocode modeling, within a Lagrange-SPH coupling method in LS-DYNA solver. It was found that the dynamic response and failure modes in the HC/SPs were significantly influenced by the impact location and the impact velocity of the volcanic rock projectile.

     

Visioplasticity analysis of 2024 aluminum alloy extrusions

Visioplasticity studies were conducted on axisymmetric extrusions of 2024 aluminum alloy extruded in the temperature range of 300–537°C. Two types of flow pattern occurred: (a) the usual type consisting of a single maximum in the transverse grid lines located at the extrusion axis; and (b) an uncommon wavy-type with two maxima located symmetrically about the axis. The occurrence of the latter pattern was accentuated as the temperature was lowered or the extrusion speed increased. Good agreement was obtained between computed and experimental positions of the transverse grid lines for both types of flow pattern using flow function analysis. The width of the deformation zone in the double maximum pattern was reduced compared with the single maximum pattern; it moved downstream at the die entrance and upstream at the exit. Derived values of the shear strain and principal strain suggest that the double maximum pattern observed here is determined more by material behavior than by lubrication conditions.     

Buckling and vibration of stiffened plates subjected to partial edge loading

The buckling and vibration characteristics of stiffened plates subjected to in-plane partial and concentrated edge loadings are studied using finite element method. The initial stresses are obtained considering the pre-buckling conditions. Buckling loads and vibration frequencies are determined for different plate aspect ratios, edge conditions and different partial non-uniform edge loading cases. The non-uniform loading may also be caused due to the supports on the edges. The analysis presented determines the stresses all over the region for different kinds of loading and edge conditions. In the structural modelling, the plate and the stiffeners are treated as separate elements where the compatibility between these two types of elements is maintained. The vibration characteristics are discussed and the results are compared with those available in the literature. Buckling results show that the stiffened plate is less susceptible to buckling for position of loading near the supported edges and near the position of stiffeners as well.     

Numerical and experimental studies on characteristic surface temperature variations of aluminum plates facing different directions

This paper is a part of the work in developing a software that predicts IR signatures from objects in the scene by considering the direct and diffuse solar irradiations, the atmospheric convection and the conduction within objects. The thermal information of the objects and their background is essential for understanding the IR signature characteristics from the scene. The thermal contrast between the objects and the background is then used to obtain their infrared radiation contrast which is the important signal in identifying the objects. We considered the composite heat transfer modes including conduction, convection and spectral solar irradiation on the objects within a scene to calculate the surface temperature distribution. The radiative energy components included in the thermal analyses are consisted of the direct and diffuse solar irradiances and sky thermal irradiation, while the thermal conduction within the object is approximated as one-dimensional heat transfer into the depth. The measured diurnal surface temperature variations on the three different test plates facing east, south and west respectively are fairly well compared with the modeled results obtained from the software developed in this study and a commercial software. A complete set of measured data including the plate temperature together with the detailed weather information and the irradiation data can be valuable reference for future study.     

Buckling of laminated sandwich plates subjected to partial edge compression

The buckling characteristics of sandwich plates having laminated stiff layers are studied for different types of partial edge loadings using a refined plate theory. With this plate theory, the through thickness variation of transverse shear stresses is represented by piecewise parabolic functions where the continuity of these stresses is satisfied at the layer interfaces by taking jumps in the transverse shear strains at the interfaces. The transverse shear stresses free condition at the plate top and bottom surfaces is also satisfied. It is quite interesting to note that this plate model having all these refined features requires unknown parameters only at the reference plane. To have a generality in the present analysis, finite element technique is adopted and it is carried out with newly developed triangular element, as existing finite elements cannot accommodate this plate model. So far, no solution exists in the literature for the problem of sandwich plate subjected to partial edge loading. The present analysis is first validated for the case of an isotropic plate subjected to partial edge compression and then it is extended to analyze sandwich plates. Few results are presented.     

On deformation and tearing of stiffened and un-stiffened square plates subjected to underwater explosion—a numerical study

In modern combat operations warships can be subjected to underwater blast loads capable of causing considerable structural damage. Research in the field of underwater explosion effects on structures has seen systematic developments since world war-I (WW-I) with the increased awareness that the possible underwater explosions and threats from the hunter killer “U” boats could now be countered. Most of the earlier investigations were conducted by military and these were classified. Cole [1] established empirical relations to model the underwater explosion (UNDEX) loading, which were the outcome of numerous experimental investigations done by the military agencies. In the present study the UNDEX load profile has been modeled as an exponentially decaying shock wave, which varies spatially and transiently. The failure modes in high strength (HS) and WELDOX Steel rectangular plates was predicted using an elasto-plastic model with isotropic hardening, strain rate effects and fracture criterion under clamped edge conditions. These models were implemented in the nonlinear finite element code ABAQUS/Explicit. The present study predicts and establishes the failure modes using a 3D FE analysis.     

Vibration and stability of angle-ply laminated composite plates subjected to in-plane stresses

Natural frequencies and buckling stresses of angle-ply laminated composite plates are analyzed by taking into account the effects of shear deformation, thickness change and rotatory inertia. By using the method of power series expansion of displacement components, a set of fundamental dynamic equations of a two-dimensional higher-order theory for thick rectangular laminates subjected to in-plane stresses is derived through Hamilton's principle. Several sets of truncated approximate theories are applied to solve the eigenvalue problems of a simply supported thick laminated plate. In order to assure the accuracy of the present theory, convergence properties of the fundamental natural frequency are examined in detail. Numerical results are compared with those of the published existing theories. The modal displacement and stress distributions in the thickness direction are obtained and plotted in figures. The present global higher-order approximate theories can predict the natural frequencies, buckling stresses and modal stresses of thick multilayered angle-ply composite laminates accurately within small number of unknowns which is not dependent on the number of layers.     

Evaluation of methods for reducing fretting fatigue damage in 2024-t3 aluminum lap joints

Fatigue strength of aluminum lap joints subjected to fretting can vary widely depending on the type of treatments applied to the faying surfaces. Many materials normally selected for their lubricity or good wear properties cannot be used in a bolted joint because of their interference with the load transfer requirements of the joint. Thus the best methods found in this evaluation in order of their effectiveness were bonded and shotpeened, bonded alone, shotpeened alone, and bonded steel wear pads. These techniques increased the fatigue strength at 10⁷ cycles of an untreated joint from 12 k.s.i. to a maximum of 23 k.s.i.     

Theoretical study of dynamic elastic buckling of columns subjected to intermediate velocity impact loads

Dynamic elastic buckling of simply supported columns subjected to intermediate velocity impact is theoretically studied in this paper. The dynamic buckling equation is set up. Theoretical solution of dynamic responses of columns subjected to a half-sine shape intermediate velocity impact load is derived. Based on the characteristics of the theoretical solution, a dynamic buckling criterion is proposed to determine the critical buckling condition and to estimate the dynamic buckling critical load. Theoretical results obtained in this study are compared with experimental data. They are also compared with numerical results obtained by other authors. Good agreements between them are observed.     

Thermal buckling of functionally graded rectangular plates subjected to partial heating

We present the thermal buckling analysis of functionally graded rectangular plates subjected to partial heating in a plane and uniform temperature rise through its thickness. The plate is simply supported for out-of-plane deformation and perfectly clamped for in-plane deformation. It is assumed that the functionally graded material properties such as the coefficient of linear thermal expansion and Young's modulus are changed individually in the thickness direction of the plate with the power law, while Poisson's ratio is assumed to be constant. Analytical developments consist of two stages. First, the nonuniform in-plane resultant forces are determined by solving a plane thermoelastic problem. Then the critical buckling temperatures of the plates with the predetermined resultant forces are calculated as the generalized eigenvalue problem which is constructed by using the Galerkin method. Finally, the effects of material inhomogeneity, aspect ratio, and heated region on the critical buckling temperatures are examined.