Scaling aspects of quadrangular plates subjected to localised blast loads—experiments and predictions

A series of experimental results on clamped mild steel quadrangular plates of different thicknesses (1.6, 2.0, 3.0 and 4.0 mm) and varying length-to-width ratios (1.0–2.4) subjected to localised blast loads of varying sizes is reported. Disc shaped explosive charges of varying charge diameter-to-plate width ratios (0.2–0.37) and charge heights (1.8–14 mm) are centrally positioned on quadrangular plates to provide impulses resulting in mid-point deflections in the range from two plate thicknesses to central plate tearing. The effects of varying both the loading conditions and the plate geometries on the deformation are described. A modified dimensionless number is presented for the quadrangular plate response when subjected to localised circular blast loading. In addition, numerical predictions are carried out and compared with experiments for a limited selection of plate geometries.     

Buckling analysis of Reissner–Mindlin plates subjected to in-plane edge loads using a shear-locking-free and meshfree method

Buckling study of plates subjected to uniformly uniaxial, biaxial in-plane compression and pure shear loads using an efficient novel meshfree method is presented in this paper. The moving Kriging (MK) interpolation technique satisfying the Kronecker delta function property is employed to construct the shape functions. To allow for the effect of transverse shear deformation on thick plates, the first-order Reissner–Mindlin plate theory (FSDT) is adopted. The new formulation enables us to eliminate shear-locking demonstrated by various numerical examples involving both thin and moderately thick plates. It is found that the results achieved by the present approach match well with those obtained by other existing numerical approaches and analytical solutions, which illustrates the applicability, the effectiveness and the accuracy of the method.     

A generalized high-order global–local plate theory for nonlinear bending and buckling analyses of imperfect sandwich plates subjected to thermo-mechanical loads

The available plate theories have been generally calibrated using linear strain–displacement expressions. Furthermore, many of them do not consider the transverse normal stress continuity and the transverse flexibility of the sandwich plates. Majority of the investigations performed so far in the buckling analysis of the sandwich plates, have been restricted to linear buckling analysis of the perfect sandwich plates based on theories that either violate the continuity condition of the transverse stresses at the layer interfaces or do not satisfy the mentioned condition when nonlinear strain–displacement expressions are used. Therefore, their results may be unreliable for nonlinear stress and buckling (especially in the postbuckling region) analyses. In the present paper, nonlinear strain–displacement expressions are employed for imperfect sandwich plates subjected to thermo-mechanical loads to propose an accurate global–local theory that satisfies the continuity of all of the transverse stress components. The theory is presented in a compact matrix form. Compatible Hermitian elements with C¹ continuity are employed to enhance the results. Buckling and wrinkling loads are detected employing a criterion previously published by the author. Comparisons made in the paper with results reported by well-known references, confirm the accuracy and the efficiency of the proposed theory and the relevant solution algorithm.     

Inverse identification of time-harmonic loads acting on thin plates using approximated Green’s functions

In this paper, a non-iterative technique is proposed for the transverse load identification on Kirchhoff plates using approximate Green’s functions (AGFs). In this way, we firstly employ the recently introduced meshless method to construct the AGFs, as the combination of a series of Trefftz basis, i.e. Exponential basis functions (EBFs), and the fundamental solutions of the governing equation. As will be explained, using a proper set of EBFs, as well as a collocation technique, enables us to construct the AGFs for different types of domain shape and boundary conditions. In the second step, a set of artificially generated results, in the absence of realistic experimental results, are used to express the plate’s response field, i.e. deflection or velocity fields, as a series of AGFs through a collocation technique. It will be shown how the constant coefficients of the response series are related to the intensity of the reconstructed force at a set of selected points. The proposed method is capable of constructing both distributed and concentrated loads with desirable accuracy. This ability is shown in the solution of three sample problems of the static and time-harmonic force recovery.     

Microstructure and microhardness of an AlFe alloy subjected to severe plastic deformation and aging

A nanocrystalline structure was produced in an Al-11 wt.% Fe alloy with the use of the novel technique of severe plastic deformahon of ingots by torsion under high imposed pressure. This technique allows a large departure of materials from equilibrium. The microstructure of the alloys was studied with the use of TEM and EDS. The severe plastic deformation led to solid solubility extension of iron in the aluminum matrix, dispersion and dissolution of second phase particles, grain size reduction into the nanometer range, and partial amorphization. Microhardness of the alloy increased substantially after the deformation due to the grain refinement and the solid solubility extension. Aging of the severe plastically deformed samples at 100 °C led to further increase of the microhardness due to the decomposition of the supersaturated solid solution and precipitation-induced hardening.     

Glued-in rods for timber structures—An experimental study of softening behaviour

A test method to obtain the strength and the fracture characteristics of the bond of glued-in rods for timber structures is presented. Test results from a series of tests using the proposed method are also given. The test method makes it possible to record the complete stress-displacement response of small test specimens. This response includes the softening behaviour after peak stress,i.e. the decreasing stress at increasing deformation. The test series include three adhesives, two rod-materials, four load-to-grain angles and two timber qualities with different densities. A method to evaluate the fracture-softening behaviour is also proposed. The fracture softening is evaluated by using only a part of the stress-displacement curve. The part used in the evaluation is determination in terms of the slope of the descending part of the stress-displacement curve.

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Résumé L’article traite d’une nouvelle méthode d’essai destinée à déterminer la résistance et les caractéristiques de rupture du joint de colle de barres collées, utilisées dans les constructions en bois. Les résultats d’une série d’essais effectués avec la méthode proposée sont également indiqués. La méthode d’essai permet de déterminer l’ensemble de la relation contrainte-déformation pour les petits échantillons. Cette relation comprend le comportement isoadoucissant après contrainte maximale, c’est-à-dire la réduction de la contrainte pendant l’augmentation de la déformation. La série d’essais porte sur trois types de colle, deux matériaux de barres, quatre différents angles entre charge et orientation des fibres, ainsi que deux qualités de bois différentes, de densités différentes. Une nouvelle méthode d’évaluation du comportement iso-adoucissant est également indiquée en utilisant seulement une partie de la courbe contrainte-déformation. La partie utilisée pour l’évaluation est déterminée par la pente de la partie descendante de la courbe contrainte-déformation.

     

Perforation of AA5083-H116 aluminium plates with conical-nose steel projectiles—experimental study

The interest regarding use of aluminium alloys in lightweight protective structures is today increasing. Even so, the number of experimental and computational investigations giving detailed information on such problems is still rather limited. In this paper, perforation experiments have been performed on AA5083-H116 aluminium plates with thicknesses varying between 15 and 30 mm impacted by 20 mm diameter, 98 mm long, HRC 53 conical-nose hardened steel projectiles. In all tests, initial and residual velocities of the projectile were measured and a digital high-speed camera system was used to photograph the penetration and perforation process. Based on these measurements, impact versus residual velocity curves of the target plates were constructed and the ballistic limit velocity of each target was obtained. An analytical perforation model from the open literature is then used to predict the ballistic limit velocity, and excellent agreement with the experimental data is found. The experimental results are finally compared to similar experiments on steel and concrete targets, and the capacity of the different materials is evaluated in relation to total weight.     

Effect of displacement current in magneto–electro-elastic plates subjected to dynamic loading

Dynamic response of moderately thick magneto?Celectro-elastic plate using magnetic vector potential in finite element formulation is presented in this paper. Dynamic loading generate time varying electric and magnetic fields in magneto?Celectro-elastic continuum. Displacement current is associated with the generation of magnetic field due to time varying electric field. The non-conservative electric field is represented using electric scalar potential and magnetic vector potentials. Studies are carried out for CCCC, CCFC, CFFC and FCFC boundary conditions of the plate excited with time-harmonic mechanical excitation, the frequency range being chosen based on the critical frequency of the plate analyzed. The magnetic flux density in longitudinal x-direction is not affected by the electric displacement current for all the boundary conditions. The longitudinal y-direction and transverse direction components of magnetic flux density are showing variations for FCFC boundary condition when displacement current is accounted. The effect of displacement current is significant when two opposite edges of the plate are clamped.     

The influence of core properties on the perforation resistance of sandwich structures – An experimental study

The aim of this study is to investigate the perforation resistance of a range of foam-based sandwich structures. Nine foams, based on a crosslinked PVC, a linear PVC and PET, have been combined with thin glass fibre reinforced plastic skins to produce a range of lightweight sandwich structures, Initially, the mechanical properties of the different foams are characterised. Here, a new test geometry is used to evaluate the toughness characteristics and strengths of the foams under shear loading, a condition similar to that encountered during the impact perforation event.The influence of the plastic collapse stress of the foam in determining the failure thresholds of the front and rear composite skins is established. Here, an existing model has been used to successfully predict failure of the top surface composite skin in the sandwich structures. In addition, the force associated with perforating the lightweight core has been shown to be strongly dependent on the shear strength of the polymer foam. Finally, the perforation resistance of the sandwich structure has been shown to be closely linked to the Mode II work of fracture of the foam material. Here a unique relationship has been established between these two parameters, with all of the experimental points lying on one curve.     

An experimental study of a schrödinger cat decoherence with atoms and cavities

Abstract

The dynamics of quantum decoherence have been experimentally studied for the first time. A single circular Rydberg atom prepares in a high-quality superconducting cavity a ?Schrödinger cat‘ state of the radiation field. This highly non-classical state is a quantum superposition of two coherent components with different classical phases. A second atom probes the cavity state after a tunable delay. The decay of the quantum correlations between the two atoms reveals the evolution of the initial quantum superposition into a mere statistical mixture. The time scale of this process decreases when the separation beween the two components increases. A simple theoretical model of the experiment is presented. The excellent agreement with the experimental signals confirms in a striking way the decoherence approach.     

The influence of boundary conditions on the loading of rectangular plates subjected to localised blast loading – Importance in numerical simulations

A series of localised blast loading experiments are performed in order to understand how the experimental set-up influences the impulse imparted to a plate. The imparted impulse is measured using a ballistic pendulum. The experimental results show that for both rigid and deformable plates the impulse measured by a ballistic pendulum increases as the height of the boundary (clamps) increases. Significantly, it is found that although the measured impulse varies as a function of the boundary height, the plate deformation is unchanged. This suggests that not all of the impulse measured by the ballistic pendulum resulted in plate deformation. Therefore, in numerical and analytical modelling, the total impulse from the ballistic pendulum should not simply be applied as a centrally localised pressure load.     

An experimental–numerical study of moisture absorption in an epoxy

It is well known that moisture absorption impairs the mechanical and physical properties of polymers. Conventionally, the material’s hygric strains are described as the product of a constant coefficient of moisture expansion (CME) and moisture concentration. This hypothesis, however, has not been thoroughly examined experimentally. In this paper, the hygro-mechanical response of a DGBA based epoxy is reported as a function of moisture uptake. Cylindrical specimens are made of epoxy with an axially located optical fiber that contains a 23 mm Bragg grating sensor (FBG). Strain data from the sensor and from a micrometer are combined with experimental absorption curves to determine the resin’s CME. The data indicate that diffusion and CME depend on moisture. Analysis of the experiments is carried out by numerical simulations of heat transfer, moisture diffusion and elastic stress analysis of the single fiber composite. The simulated results correlate well with the experimental data.     

An experimental study of on‐line computer control techniques applied to a double pipe heat exchanger

Abstract

Three different on‐line computer control methods, namely the identification and optimizing control technique, the direct design method and the digital form of P‐I‐D control, are applied to control the response of a double pipe heat exchanger. The relative merits of the methods are studied and discussed.

The experimental work is accomplished by the use of a HP‐1000 model 5L microcomputer. A digital voltmeter; the HP‐3456A, is used for reading and transferring data from the process to the computer. A data acquisition system, the HP‐3497A, contains a thermocouple relay and a D/A converter which can read input data from a thermocouple and also convert digital outputs to 4–20 mA signals required by control elements.

Results indicate that the identification and optimizing control technique gives superior performance in most cases, but requires longer computation time. Digital form of the P‐I‐D control requires the least computation time but yields poor performance and is limited in its potential for application to multivariable systems or to tracking problems.     

Wet thermo-mechanical behavior of steel–CFRP joints – An experimental study

The long term durability of CFRP strengthened steel structures is a key parameter for their safe use and effective design. Strengthened members can be subjected to different environmental conditions and loading scenarios during their service life, the effect of which on the failure mechanism of the strengthened member requires fundamental investigations. This paper presents an experimental investigation into the effects of wet thermo-mechanical loading on the bond strength and the failure mode of steel–CFRP single lap joints. A total of thirty four steel–CFRP single lap shear specimens were prepared and exposed to different combinations of wet thermal cycle ranges and sustained loads. The results show that these conditions (wet thermal cycles and sustained loads) have little impact on the bond strength of steel–CFRP lap joint when applied separately. However, when applied simultaneously, the bond strength of the joint is significantly reduced with failure observed at less than 30% of the static strength under temperatures that are well below the glass transition temperature of the adhesive.     

The dynamic responses of lamellar and equiaxed near β-Ti alloys subjected to multi-pass cross rolling

This work gives a comparison on the microstructural characteristics, textural discrepancies, and twinning behaviors of lamellar and equiaxed near β-Ti alloys during multi-pass cross rolling with a rolling reduction of 20%, 50% and 80%. The results showed that the restoration mechanism of the alloy in β phase is strongly dependent on the α morphologies, and in comparison, strain path has weaker influences on the grain refinement of the β matrix. Therefore, the texture intensities of both α and β phases were weakened owing to the dynamic recrystallization(DRX) of the two phases in the equiaxed microstructure. While,with regard to the lamellar microstructure, dynamic recovery(DRV) of the β phase predominated, forming elongated β subgrains. Besides, the α and β matrix in lamellar microstructures obeyed the Burgers orientation relationship, which was gradually broken down until the final reduction. Lastly, the{1101} twinning exhibits a strong size effect. With the continuous DRX of α phases, the α -twinning is suppressed owing to progressive grain refinement. The activation of β-twinning, namely{332} ?113?and {112} ?111?, in near β-Ti alloys is heavily dependent on the deficient β-stabilizing elements and the local stress concentration. These findings provide an effective way to obtain ultra-fine grain microstructures of this alloy.     

The brittle to ductile transition of single crystal materials—An indentation model

A model for the brittle to ductile transition of brittle single crystal materials under indentation has been investigated. Continuous dislocation pile-ups against the wedge tip are used to explain the plastic deformation. The indentation depth is attributed to the dislocation pile-ups. The critical indentation depth p _cof brittle to ductile transition is proposed. Thus, the single crystal material is in brittle mode during the indentation loading if the indentation depth is greater than p _c. Otherwise, it is ductile. Micrographs support this modeling. Indentation on the surfaces of (100) or (110) in fcc and bcc single crystal materials is compared. The parameter Sis proportional to the number of dislocations and to the reciprocal of wedge angle. The value of Sis smaller for (100) than for (110) in fcc structure, but the trend of bcc structure is opposite. The shape of indenter is similar to that of grinding particles consisting in cutting tools. In order to maintain cutting efficiency in ductile mode, the cutting tool must be replaced if the grinding particles are blunt.     

Mixed mode stable tearing of thin sheet?AI 6061-T6 specimens: experimental measurements and finite element simulations using a modified Mohr-Coulomb fracture criterion

In this investigation, a combined experimental and computational approach with a Modified Mohr Coulomb (MMC) fracture criterion employing post-initiation element softening is used to simulate stable crack propagation under Mode I, Mode III and combined Mode I/III loading conditions. Results from the studies demonstrate that good correlation exists between the measured load-displacement and the numerically predicted response when the stiffness of the specimen fixture is included in the FE model. The numerical results were able to capture most of the experimentally observed features during crack propagation, such as through-thickness slant fracture, necking, tunneling and local specimen twist, thus confirming that the MMC criterion is suitable for predicting in-plane and out-of-plane tearing of sheets. It was found that in order to predict correctly the load-displacement curve as well as the fracture plane, different amount of softening is needed for Mode I and Mode III loading cases. This observation can be justified on the micro-mechanical level, while there is a competition between the mechanisms of dimple and shear fracture.     

Field intensity factors around inclusion corners in 0–3 and 1–3 composites subjected to thermo-mechanical loads

A super inclusion corner apex element for polygonal inclusions in 0–3 and 1–3 composites is developed by using numerical stress and displacement field solutions based on an ad hoc finite element eigenanalysis method. Singular stresses near the apex of inclusion corner under thermo-mechanical loads can be obtained by using a super inclusion corner apex element in conjunction with hybrid-stress elements. The validity and the applicability of this technique are established by comparing the present numerical results with the existing solutions and the conventional finite element solutions. As examples of applications, a square array of square inclusions in 0–3 composites and a rectangular array of rectangular inclusions in 1–3 composites are considered. All numerical examples show that the present numerical method yields satisfactory solutions with fewer elements and is applicable to complex problems such as multiple singular points or fields in composite materials.     

The wear and fracture behaviour of ultra high molecular weight polyethylene subjected to γ-irradiation in an atmosphere of acetylene

The wear and mechanical properties of GUR 1020 (Perplas IMP 2000-2) Ultra High Molecular Weight Polyethylene (UHMWPE) subjected to -irradiation in an atmosphere of acetylene, were evaluated for a range of processing conditions of irradiation, annealing and ageing. The results were compared with those obtained for the virgin UHMWPE material and material processed using conventional -irradiation in nitrogen. Cross-linking produced by irradiation in acetylene, followed by subsequent annealing was found to be significantly more effective in improving the mechanical and wear properties of UHMWPE compared to when the material was irradiated in nitrogen. Gel fraction analysis on its own, while being able to detect the degree of cross-linking, was found to be insufficient in determining the effectiveness of the cross-links and the resulting mechanical properties of the UHMWPE material. The results suggest that -irradiation in an atmosphere of acetylene may provide significant advantages over conventional UHMWPE processing and irradiation cross-linking techniques.     

Optical methods for complete stress determination — An experimental alternative to finite-element analysis

Experimental optics provides an interesting alternative to finite-element analysis (FEA) for estimating stress distribution in bodies subjected to load. Complete determination of the state of stress in a two-dimensional transparent model of the body was performed, using modern interferometry in combination with conventional photoelasticity. Stress concentrations and singularities may be evaluated in the same experimental set-up by means of the methods of caustics.The present approach eliminates the effect of limited optical quality of the model material, which is an advantage in engineering applications of the methods proposed. In contrast to most testing procedures using interferometry, this technique provides particularly simple handling of equipment and ease in evaluation. The paper describes an application to restorative dentistry of these methods of experimental stress analysis.