Evaluation of effectiveness of polymer coatings in reducing blastinduced deformation of steel plates

Incorporating elastomers such as polymers in protective structures to withstand high energetic dynamic loads,has gained significant interest.The main objective of this study is to investigate the influence of a Polyurea coating towards the blast-induced response in steel plates.As such,Polyurea coated steel plates were tested under near-field blast loads,produced by the detonation of 1 kg of spherical nitromethane charges,at a standoff distance of 150 mm.Mild steel(XLERPLATE 350)and high-strength steel(BIS80)plates with thicknesses of 10 mm were Polyurea coated with thicknesses of 6 mm and 12 mm on either the front(facing the charge)or the back face.The deformation profiles were measured using 3D scanning.Numerical simulations were performed using the non-linear finite element code LS-DYNA.The strain-dependent behaviour of the steel and Polyurea were represented by Johnson-cook and Money-Rivlin constitutive models,respectively.The numerical models were validated by comparing the plate deflection results obtained from the experiments and were then used in the subsequent parametric study to investigate the optimum thickness of the Polyurea coating.The results indicate that back face coating contributes towards an approximately 20%reduction in the residual deformation as well as the absence of melting of the Polyurea layer,while the front-face coating can be used a means of providing additional standoff distance to the steel plates.

ON THE REFINED FIRST-ORDER SHEAR DEFORMATION PLATE THEORY OF KARMAN TYPE

A new refined first-order shear-deformation plate theory of the Karman type is presented for engineering applications and a new version of the generalized Karman large deflection equations with deflection and stress functions as two unknown variables is formulated for nonlinear analysis of shear-deformable plates of composite material and construction, based on the Mindlin/Reissner theory. In this refined plate theory two rotations that are constrained out in the formulation ate imposed upon overall displacements of the plates in an implicit role. Linear and nonlinear investigations may be mode by the engineering theory to a class of shear-deformation plates such as moderately thick composite plates, orthotropic sandwich plates, densely stiffened plates, and laminated shear-deformable plates. Reduced forms of the generalized Karman equations are derived consequently, which are found identical to those existe in the literature.

KRMN-TYPE EQUATIONS FOR A HIGHER-ORDER SHEARDEFORMATION PLATE THEORY AND ITS USE IN THE THERMAL POSTBUCKLING ANALYSIS

arman-type nonlinear large deflection equations are derived occnrding to theReddy's higher-order shear deformation plate theory and used in the thermal postbuckling analysis The effects of initial geometric imperfections of the plate areincluded in the present study which also includes th thermal effects.Simply supported,symmetric cross-ply laminated plates subjected to uniform or nomuniform parabolictemperature distribution are considered. The analysis uses a mixed GalerkinGolerkinperlurbation technique to determine thermal buckling louds and postbucklingequilibrium paths.The effects played by transverse shear deformation plate aspeclraio, total number of plies thermal load ratio and initial geometric imperfections arealso studied.

A MIXED VARIATIONAL FORMULATION FOR LARGE DEFORMATION ANALYSIS OF PLATES

A mixed vuriational formulation for large deformation analysis of plates is introduced. In this formulation the equilibrium ami compatibility equations are satisfied identically by means of stress functions and displacement components, respectively, and the constitu,lye equations are satisfied in a least square sense. An example is solved and the results are compared with those available in the literature.Further, the functional is particularized for buckling analysis of plates and a simple example is solved to illustrate the theory.

Time-varying nonlinear dynamics of a deploying piezoelectric laminated composite plate under aerodynamic force

Using Reddy’s high-order shear theory for laminated plates and Hamilton’s principle, a nonlinear partial differential equation for the dynamics of a deploying cantilevered piezoelectric laminated composite plate, under the combined action of aerodynamic load and piezoelectric excitation, is introduced. Two-degree of freedom(DOF)nonlinear dynamic models for the time-varying coefficients describing the transverse vibration of the deploying laminate under the combined actions of a first-order aerodynamic force and piezoelectric excitation were obtained by selecting a suitable time-dependent modal function satisfying the displacement boundary conditions and applying second-order discretization using the Galerkin method. Using a numerical method, the time history curves of the deploying laminate were obtained, and its nonlinear dynamic characteristics,including extension speed and different piezoelectric excitations, were studied. The results suggest that the piezoelectric excitation has a clear effect on the change of the nonlinear dynamic characteristics of such piezoelectric laminated composite plates. The nonlinear vibration of the deploying cantilevered laminate can be effectively suppressed by choosing a suitable voltage and polarity.

ANALYTICAL RELATIONS BETWEEN EIGENVALUES OF CIRCULAR PLATE BASED ON VARIOUS PLATE THEORIES

Based on the mathematical similarity of the axisymmetric eigenvalue problems of a circular plate between the classical plate theory（CPT）, the first-order shear deformation plate theory（FPT） and the Reddy＇s third-order shear deformation plate theory（RPT）, analytical relations between the eigenvalues of circular plate based on various plate theories are investigated. In the present paper, the eigenvalue problem is transformed to solve an algebra equation. Analytical relationships that are expressed explicitly between various theories are presented. Therefore, from these relationships one can easily obtain the exact RPT and FPT solutions of critical buckling load and natural frequency for a circular plate with CPT solutions. The relationships are useful for engineering application, and can be used to check the validity, convergence and accuracy of numerical results for the eigenvalue problem of plates.

Hot Deformation Behavior of a Novel Ni-Cr-Mo-B Ultra-heavy Plate Steel by Hot Compression Test

Hot deformation behavior of a novel Ni-Cr-Mo-B heavy plate steel was studied by hot compression tests,which were conducted on a Gleeble-3800thermo-mechanical simulator corresponding to the temperature range of850-1 150℃ with the strain rates of 0.01-10s-1 and the true strain of 0.8.The results suggest that the majority of flow curves exhibit a typical dynamic recrystallization（DRX）behavior with an apparent single peak stress followed by agradual fall towards a steady-state stress.Important characteristic parameters of flow behavior as critical stress/strain for initiation of DRX and peak and steady-state stress/strain were derived from curves of strain hardening rate versus stress and stress versus strain,respectively.Material constants of the investigated steel were determined based on Arrhenius-type constitutive equation,and then the peak stress was predicted by the equation with the hot deformation activation energy of 379 139J/mol,and the predicted values agree well with the experimental values.Furthermore,the effect of Zener-Hollomon parameter on the characteristic points of flow curves was studied using the power law relation,and the ratio of critical stress and strain to peak stress and strain were found to be 0.91and0.46,respectively.

Design and energy absorption enhancement of vehicle hull under high dynamic loads

V-shape hulls are widely used in peacekeeping efforts such as demining vehicles in order to deflect the blast energy and reduce the effects of mine blast. Blast resistant design and energy absorption enhancement of V-shape plates were carried out using finite element analysis package ABAQUS. Various geometries of V-shape plates with and without interlayer of materials like Al-foams and honeycomb were employed to analyze their effects on the deformation of the plate and applied stresses and strains. The results obtained show that application of metallic foams leads to better response of the plate and consequently results in more energy dissipation, less dame to vehicle and enhances crew survivability.

Postbuckling behavior of 3D braided rectangular plates subjected to uniaxial compression and transverse loads in thermal environments

Postbuckling behavior of the 3D braided rectangular plates subjected to uniaxial compression combined with transverse loads in thermal environments is presented.Based on a micro-macro-mechanical model,a 3D braided composite may be treated as a cell system and the geometry of each cell is deeply dependent on its position in the cross-section of the plate.The material properties of the epoxy are expressed as a linear function of temperature.Uniform,linear and nonlinear temperature distributions through the thickness are involved.The lateral pressure(three types of transverse loads,i.e.transverse uniform load;transverse patch load over a central area;and transverse sinusoidal load)is first converted into an initial deflection and the initial geometric imperfection of the plate is taken into account.The governing equations are based on Reddy’s higher-order shear deformation plate theory with a von Kármán-type of kinematic nonlinearity.Two cases of the in-plane boundary conditions are also taken into account.A perturbation technique is employed to determine buckling loads and postbuckling equilibrium paths of simply supported 3D braided rectangular plates.The results reveal that the temperature rise,geometric parameter,fiber volume fraction,braiding angle,the character of the in-plane boundary conditions and different types of initial transverse loads have a significant effect on the buckling and postbuckling behavior of the braided composite plates.

Conjugate adaptive optics extension for commercial microscopes

We present what we believe is the first conjugate adaptive optics(AO)extension that can be retrofitted into a commercial microscope by being positioned between the camera port and the image sensor.The extension features a deformable phase plate(DPP),a refractive wavefront modulator,and indirect wavefront sensing to form a completely in-line architecture.This allows the axial position of the DPP to be optimized by maximizing an image quality metric,which is a cumbersome task with deformable mirrors as the correction element.We demonstrate the performance of the system on a Zeiss AxioVert 200M microscope equipped with a 20×0.75 NA air objective.To simulate sample-induced complex aberrations,transparent custom-made arbitrary phase plates were introduced between the sample and the objective.We demonstrate that the extension can provide high-quality full-field correction even for large aberrations,when the DPP is placed at the conjugate plane of the phase plates.We also demonstrate that both the DPP position and its surface profile can be optimized blindly,which can pave the way for plug-and-play conjugate-AO systems.

Discussion on the relationship between the Yanshanian Movement and cratonic destruction in North China

The relationship between the Yanshanian Movement, destruction of the North China Craton(NCC), and subduction of the western Pacific plate is crucial to reconstructing the middle-late Mesozoic tectonic evolution of the eastern Asian continent and margin. The Yanshanian Movement was a globally important change in crustal tectonics during the Middle-Late Jurassic.Previous research has systematically studied the formation and evolution of the Yanshanian Movement, focusing on the timing and location of tectonic movements, and the sedimentary and volcanic strata. However, the question of whether the tectonic activity occurred globally, and the characteristics of the Yanshanian Movement remain debated. The main argument is that if a tectonic movement can only be characterized by a regional or local disconformity, and if the tectonic movement occurred in an intracontinental setting, with extensive deformation but with no disconformity despite volcanic eruptions and magmatic intrusions, accompanied by changes in crustal structure and composition, should it be defined as a tectonic event or process? This question requires further analysis. The main aim of this study is to distinguish whether the Yanshanian Movement is a local feature of the eastern Asian continent, or a global tectonic event related to subduction of the Pacific Plate. In this paper, based on previous research, we discuss the spatial and temporal evolution of the Yanshanian Movement, the controlling tectonic mechanisms, and its relationship to the reactivation and destruction of the NCC and the subduction of the western Paleo-Pacific slab.We emphasize that the Yanshanian Movement in the Middle-Late Jurassic is distinct from the lithospheric thinning responsible for Early Cretaceous extension and magmatism related to the destruction of the NCC. The various tectonic stages were constrained by different dynamics and tectonic settings, or by different tectonic events and processes. Therefore, it is possible that the deformation and reactivation of the NCC contributed to its destruction, in addition to lithospheric thinning. Finally, we discuss whether the Yanshanian Movement was associated with the destruction of the NCC.