Search results

The safety assessment of engineering structures under repeated variable dynamic loads such as seismic and wind loads can be considered as a dynamic shakedown problem. This paper aims to extend the stress compensation method (SCM) to perform lower bound dynamic shakedown analysis of engineering structures and a double-closed-loop iterative algorithm is proposed to solve the shakedown load.

The construction of the dynamic load vertexes is carried out to represent the loading domain of a structure under both dynamic and quasi-static load. The SCM is extended to perform lower bound dynamic shakedown analysis of engineering structures, which constructs the self-equilibrium stress field by a series of direct iteration computations. The self-equilibrium stress field is not only related to the amplitude of the repeated variable load but also related to its frequency. A novel double-closed-loop iterative algorithm is presented to calculate the dynamic shakedown load multiplier. The inner-loop iteration is to construct the self-equilibrated residual stress field based on the certain shakedown load multiplier. The outer-loop iteration is to update the dynamic shakedown load multiplier. With different combinations of dynamic load vertexes, a dynamic shakedown load domain could be obtained.

Three-dimensional examples are presented to verify the applicability and accuracy of the SCM in dynamic shakedown analysis. The example of cantilever beam under harmonic dynamic load with different frequency shows the validity of the dynamic load vertex construction method. The shakedown domain of the elbow structure varies with the frequency under the dynamic approach. When the frequency is around the resonance frequency of the structure, the area of shakedown domain would be significantly reduced.

In this study, the dynamical response of structure is treated as perfect elastoplastic. The current analysis does not account for effects such as large deformation, stochastic external load and nonlinear vibration conditions which will inevitably be encountered and affect the load capacity.

This study provides a direct method for the dynamical shakedown analysis of engineering structures under repeated variable dynamic load.

While additive manufacturing via melt-extrusion of plastics has been around for more than several decades, its application to complex geometries has been hampered by the discretization of parts into planar layers. This requires wasted support material and introduces anisotropic weaknesses due to poor layer-to-layer adhesion. Curved-layer manufacturing has been gaining attention recently, with increasing potential to fabricate complex, low-weight structures, such as mechanical metamaterials. This paper aims to study the fabrication and mechanical characterization of non-planar lattice structures under cyclic loading.

A mathematical approach to parametrize lattices onto Bèzier surfaces is validated and applied here to fabricate non-planar lattice samples via curved-layer fused deposition modeling. The lattice chirality, amplitude and unit cell size were varied, and the properties of the samples under cyclic-loading were studied experimentally.

Overall, lattices with higher auxeticity showed less energy dissipation, attributed to their bending-deformation mechanism. Additionally, bistability was eliminated with increasing auxeticity, reinforcing the conclusion of bending-dominated behavior. The analysis presented here demonstrates that mechanical metamaterial lattices such as auxetics can be explored experimentally for complex geometries where traditional methods of comparing simple geometry to end-use designs are not applicable.

The mechanics of non-planar lattice structures fabricated using curved-layer additive manufacturing have not been studied thoroughly. Furthermore, traditional approaches do not apply due to parameterization deformations, requiring novel approaches to their study. Here the properties of such structures under cyclic-loading are studied experimentally for the first time. Applications for this type of structures can be found in areas like biomedical scaffolds and stents, sandwich-panel packaging, aerospace structures and architecture of lattice domes.

This work presents an experimental approach to study the mechanical properties of non-planar lattice structures via quasi-static cyclic loading, comparing variations across several lattice patterns including auxetic sinusoids, disrupted sinusoids and their equivalent-density quadratic patterns.

This study sets out to compare the response of three‐dimensional (3D) woven composites subjected to high strain rate (HSR) compression loading with the dynamic response.

The 3D composites were manufactured using Kevlar woven fabrics with epoxy resin system utilising vacuum bag moulding approach. Samples were subjected to HSR compression loading in three directions using a modified split Hopkinson's pressure bar.

Peak stress and stiffness of 3D composites were higher for dynamic loading when compared with static loading in case of both in‐plane direction and out‐of‐plane direction. The peak stress and modulus increased with the increase in strain rate for both in‐plane direction and out‐of‐plane direction. Peak stress and dynamic modulus were higher when the samples were loaded in the fill direction compared with the warp direction loading. The failure strain in through‐the‐thickness direction was far higher than in in‐plane warp and fill direction.

Other strength parameters of 3D composites could be studied.

The study provided the strength comparison of 3D composites in different situations.

The paper provide data on 3D composites for engineering applications.

The purpose of this paper is to propose and analyse computationally a new concept for mechanical interlocking between metal and plastics. The approach utilizes some of the ideas used in the spot‐clinching joining process and is appropriately named “clinch‐lock polymer metal hybrid (PMH) technology.”

A new approach, the so‐called “direct‐adhesion” PMH technology, is recently proposed Grujicic et al. to help meet the needs of automotive original equipment manufacturers and their suppliers for a cost‐effective, robust, reliable PMH technology which can be used for the manufacturing of load‐bearing body‐in‐white (BIW) components and which is compatible with the current BIW manufacturing‐process chain. Within this approach, the necessary level of polymer‐to‐metal mechanical interconnectivity is attained through direct adhesion and mechanical interlocking.

In an attempt to fully assess the potential of the clinch‐lock approach for providing the required level of metal/polymer mechanical interlocking, a set of finite‐element based sheet‐metal forming, injection molding and structural mechanics analyses is carried out. The results obtained show that stiffness and buckling resistance levels can be attained which are comparable with those observed in the competing injection over‐molding PMH process but with an ∼3 percent lower weight (of the polymer subcomponent) and without the need for holes and for over‐molding of the free edges of the metal stamping.

The paper presents a useful discussion of clinch‐lock joining technology's potential for fabrication of PMH load‐bearing BIW components.

The main purpose of this study was to evaluate the mechanical behaviour of layered fibrous carbon-fibre reinforced plastic (CFRP) under complex low-speed bending and impact loads and subsequent cyclic tensile loads.

A comprehensive approach was adopted to study the damage accumulation processes using state-of-the-art testing and diagnostic equipment. In the course of the study, a microstructure analysis of damages caused by a transverse impact and cyclic tension was performed.

A dependence of residual fatigue life of the studied composite material on the intensity of the preliminary impact bending was established. Temperature field distribution fields on the surface of the sample during tests were shown. Data on damage accumulation processes were presented, which were obtained during the registration of acoustic emission signals.

A connection was established between changes of registered acoustic response signals and thermal imaging camera data, which was supported by the results of an experimental study. The results of the comprehensive approach showed a qualitative correlation.

The feasibility of advanced viscoplastic models for non‐linear boundary element analysis of metallic structural components with dependence on thermomechanical history is investigated. Several numerical examples are presented using the boundary element implementation of two different internal state variable viscoplastic models to the solution of time‐dependent inelastic problems arising in creeping metallic structural components under the combined action of high temperature loading gradients and quasi‐static mechanical loading conditions. To demonstrate the efficiency of the implemented viscoplastic models, the results obtained using the direct boundary element methodology are compared with those obtained by both analytical and finite element solution as well as, for different numerical results of plane strain thermoviscoplastic deformation problems under general thermomechanical loading.

A growing response in the development of hybrid composites to conquer the deficiency of neat composites has provoked doing this work. Thermoplastic Polycarbonate material offers better impact toughness with low structural weight. There is a little/no information available over the selected sandwich hybrid composite prepared from woven E-Glass and polycarbonate sheet. The purpose of this paper is to understand the response of the novel hybrid structure under tensile, flexural, interlaminar shear and impact loading conditions.

The hand-layup technique is used for fabricating the hybrid composites in the laminate configuration. The hybrid composites are prepared with a total fiber content of 70 percent weight fractions. The effect of the percentage of reinforcement on mechanical properties is evaluated experimentally as per American society for testing materials standard test methods. The damaged mechanisms of failed samples and fractured surfaces are well analyzed using vision measuring system and scanning electron microscopy.

A decline in densities of hybrid composites up to 22.5 percent is noticed with reference to neat composite. An increase in impact toughness up to 40.73 percent is marked for hybrid laminates owing to the ductile nature of PC. Delamination is identified to be the major mode of failure apart from fiber fracture/pull-out, matrix cracking in all the static loading conditions.

The response of novel hybrid composite reported has been explored for the first time in this paper. The outcome of experimental work revealed that hybridization offered lightweight structures with improved transverse impact toughness as compared to conventional composite.

High-rise tower structures supported by side frame structure and viscous damper in chemical industry can produce plasticity under dynamic loads, such as wind and earthquake, which will heavily influence the long-term safety operation. This paper aims to systematically study the optimization design of these structures by free vibration and dynamic shakedown analysis.

The transfer matrix method and Euler–Bernoulli beam vibration are used to study the free vibration characteristic of the simplified high-rise tower structure. Then the extended stress compensation method is used to construct the self-equilibrated stress by using the dynamic load vertexes and the lower bound dynamic shakedown analysis for the structure with viscous damper. Using the proposed method, comprehensive parametric studies and optimization are performed to examine the shakedown load of high-rise tower with various supported conditions.

The numerical results show that the supported frame stiffness, attached damper or spring parameters influence the free vibration and shakedown characters of high-rise tower very much. The dynamic shakedown load is lowered down quickly with external load frequency increasing to the fundamental natural frequency of the structure under spring supported condition, while changed little with the damping connection. The optimized location and parameter of support are obtained under dynamical excitations.

In this study, the high-rise tower structure is simplified as a cantilever beam supported by a short cantilever beam and a damper under repeated dynamic load, and linear elasticity for solid is assumed for free vibration analysis. The current analysis does not account for effects such as large deformation, stochastic external load and nonlinear vibration conditions which will inevitably be encountered and affect the load capacity.

This study provides a comprehensive method for the dynamical optimization of high-rise tower structure by combining free vibration and shakedown analysis.

In order to use the BS EN 15058-3 principle more scientifically to design the welding structure of rail vehicles, a method of stress state assessment of welding joints meeting the requirements of BS EN 15058-3 is proposed by using IIW-2008 and ASME-BPVC-VIII-2:2015 standard.

The stress state evaluation process of two standards is studied, and the stress state evaluation method of two standards is programmed by computer language. Among them, ASME standard can evaluate the stress state of welding structures without defects and with defects. In order to verify the feasibility of the method, under the fatigue load of en13749 standard, the method is applied to the welding structure design of the rail car frame.

The results show that the evaluation based on IIW-2008 standard is stricter, and the stress factor of the weld between the crossbeam and the traction pull rod seat is the largest, the value is 0.881, and the stress state grade is medium. With the increase of the number of defects, the stress level of the welded joint increases and the fatigue life decreases.

This study can provide a reference for the welding design of rail vehicles and other complex structures and has a certain engineering guiding significance.

The occurrence of multiple hazards in extreme conditions is not unknown nowadays, but the sustainability of the reinforced concrete structures under such scenarios form competitive challenges in civil engineering profession. Among all, fire following earthquake (FFE) is categorized under multiple extreme load scenarios which causes sequential damages to the structures. This paper aims to experiment a full-scale RC frame sub-assemblage for the FFE scenario and assess each stage of damage through the nondestructive testing method.

Two levels of simulated earthquake damages, i.e. immediate occupancy (IO) level and life safety (LS) level of structural performance were induced to the test frame and then, followed by a realistic compartment fire of 1 h duration. Also, the evaluation of damage to the RC frame after the fire subsequent to the earthquake was carried out by obtaining the ultimate capacity of the frame. Ultrasonic pulse velocity and rebound hammer test were conducted to assess the structural endurance of the damaged frame. Cracks were also marked during mechanical damages to the test frame to study the nature of its propagation.

Careful visual inspection during and after the fire test to the test frame were done. To differentiate between concrete chemically affected by the fire or physically damaged is an important issue. In situ inspection and laboratory tests of concrete components have been performed. Concrete from the test frame was localized with thermo-gravimetric analysis. The UPV results exhibited a sharp decrease in the strength of the concrete material which was also confirmed via the DTA, TGA and TG results. It is important to evaluate the residual capacity of the entire structure under the FFE scenario and propose rehabilitation/retrofit schemes for the building structure.

The heterogeneity in the distribution of the damage has been identified due to variation of fire exposure. The study only highlights the capabilities of the methods for finding the residual capacity of the RC frame sub-assemblage after an occurrence of an FFE.

It is of find kind of research work on full-scale reinforced concrete building. In this, an attempt has been made for the evaluation of concrete structures affected by an FFE through nondestructive and destructive methods.