Out Of Plane Stiffness Research Articles

Experimental study on the blast resistance of polyurea-coated aramid fabrics

This paper investigates overpressure attenuation capacity and failure mechanism of the polyurea-coated aramid fabric (PCAF) subjected to air-blast loading experimentally. The peak overpressure, arrival time and positive pressure duration of shock waves on the blast and back side of PCAFs were obtained in tests and analyzed. In addition, the failure mode and mechanism were revealed with the electron scanning microscope (SEM), meanwhile the effect of polyurea type, coating position and thickness ratio on the blast resistance were discussed. The results show that in the cases of scaled distances of 1.84 and 2.32 m/kg1/3, PCAFs, one-layer polyurea coated on three-layer aramid woven fabrics, can attenuate the peak overpressure by about 70 %, delay the arrival time by about 0.7 ms, and shorten the positive pressure duration by 10 %-50 %. This is due to the increased out-of plane stiffness and closure of interweaving apertures of the aramid fabric. Furthermore, perforation is the main failure mode of aramid fabrics, in which the tensile breakage in weft yarn and the frictional slip in warp yarn, while the failure modes of PCAF mainly include fracture and exfoliation, with both weft and warp yarns breakage and polyurea failure. It was concluded that the degree of infiltration between the polyurea and fabric affects mechanical properties of the fiber, changing the failure mode of PCAF. In terms of the extent of damage, the PCAF exhibits a superior blast resistance when the polyurea coated on the back side. The blast resistance of PCAF increases first then decreases with an increase in the thickness of the polyurea layer under the same areal density.

Single-layer PtSe2 adsorbed with non-metallic atoms: geometrical, mechanical, electronic and optical properties and strain effects.

Recently, single-layer PtSe2, possessing high carrier mobility and optical response, has been successfully fabricated. To further expand its application scope and find new physics, in this work, we functionalized it via the adsorption of non-metallic atoms X (X = H, B, C, N, O, and F) to form hybrid systems X-PtSe2, and their geometrical, mechanical, electronic, and optical properties as well as strain tuning effects were studied deeply. Calculations show that the energy stability of X-PtSe2 systems is significantly enhanced, and they also hold higher thermal and mechanical stability. Particularly, X-PtSe2 systems present excellent in-plane tenacity and out-of plane stiffness against deformations, which make them more applicable for designing nanodevices. Intrinsic PtSe2 is a semiconductor, while the X-PtSe2 system can be a band-gap narrowed semiconductor or metal, thus expanding the application scope for PtSe2, and the odd-even effect of electronic phase variation related to the atomic number is found. Besides, the wavelength range of optical adsorption is increased in X-PtSe2 systems, implying that its optical response region is wide, providing more options for developing optoelectronic devices. Moreover, it is shown that strain can flexibly tune the electronic property of X-PtSe2 systems, especially enhancing the optical absorption ability substantially, beneficial for their applications in solar devices.

Mechanical properties of 3-D printed truss-like lattice biopolymer non-stochastic structures for sandwich panels with natural fibre composite skins

A full mechanical characterisation of three types of 3-D printed lattice cores was performed to evaluate the feasibility of using additive manufacturing (AM) of lightweight polymer-based sandwich panels for structural applications. Effects of the shape of three selected lattice structures on the compression, shear and bending strength has been experimentally investigated. The specimens tested were manufactured with an open source fused filament fabrication-based 3-D printer. These sandwich structures considered had skins made of polypropylene (PP)-flax bonded to the polylactic acid (PLA) lattice structure core using bi-component epoxy adhesive. The PP-flax and the PLA core structures were tested separately as well as bonded together to evaluate the structural performance as sandwich panels. The compression tests were carried out to assess the in-plane and out of plane stiffness and strength by selecting a representative number of cells. Shear band and plastic hinges were observed during the in-plane tests. The shear and three-point bending tests were performed according to the standard to ensure repeatability. The work has provided an insight into the failure modes of the different shapes, and the force-displacement history curves were linked to the progressive failure mechanisms experienced by the structures. Overall, the results of the three truss-like lattice biopolymer non-stochastic structures investigated have indicated that they are well suited to be used for potential impact applications because of their high-shear and out of the plane compression strength. These results demonstrate the feasibility of AM technology in manufacturing of lightweight polymer-based sandwich panels for potential structural uses.

Influence of cell size on out of plane stiffness and in-plane compliance character of the sandwich beam made with tunable PCTPE nylon honeycomb core and hybrid polymer nanocomposite skin

Sandwich structures with honeycomb core find specific application in impact resistance and energy absorption applications. However, such studies were limited to cores with metallic honeycomb, which had limited energy absorption abilities apart from extrinsic weight. The current work aims to fabricate hybrid sandwich beams made with PCTPE (Plasticized Co-polyamide Thermoplastic Elastomer) nylon using Fused Filament Fabrication (FFF). The cell size was varied from 10 to36 mm with a variation of longest diagonal. The face sheets were prepared with High-density polyethylene (HDPE) matrix with equal loading of Graphite nanoplatelet and Nano-diamond hybrid filler system. The face sheets were joined to honeycomb core to prepare sandwich panel with tailored made adhesive. It was observed that during out of the plane test, for 10 mm cell the SEA (specific energy absorption) was 1.15 kJ/kg, which decreased upto and 69% for 36 mm respectively. During the in-plane flexural test, the minimum flexural modulus showed by 36 mm longest diagonal cell was 31 MPa, which had increased further by 24, 50, 62, 67 and 76% for 27, 21, 15, 12 and 10 mm respectively, indicating elastic nature and damping ability of sandwich beam. The free vibration analysis was performed on by taking cantilever configuration. The experimentally obtained results were then validated using Ansys-14 simulation. It was concluded that PCTPE nylon core exhibited dual properties of stiffness and compliance for the period of out-plane testing and in-plane respectively, with a threshold limit of 36 mm cell size.

Installation Technology of Webs in the Construction of PC Box-Girder Bridge with Corrugated Steel Webs

In the construction of prestressed concrete(PC) box-girder bridge with corrugated steel webs used cast-in-place cantilever method, the key component-corrugated steel webs are fabricated in factory first and then transported to the construction site. Because of the low out-of plane stiffness, corrugated steel webs are easy to deform in the construction, which brings many difficulties for construction. The precision of installing the corrugated steel web has a direct effect on the cross-section shape of the box-girder. So it is a key step to monitor the orientation and installation of corrugated steel web during construction. Based on the experience of some PC box-girder bridges with corrugated steel webs having been built, a method to control the installation accuracy of corrugated steel webs is proposed and some quality assurance measures are introduced in order to ensure the accuracy, reliability and security of the installation of corrugated steel web. The method can be taken as a reference in the construction of this kind of bridge.

Construction process analysis for a single-layer folded space grid structure in considering time-dependent effect

A new long-span space grid structure system, “single-layer folded space grid” (SFSG), is applied in the Shenzhen Universiade Stadium. Compared with regular single-layer grid, the out-of plane stiffness and bearing capacity of the structure is improved with bending and uplifting of the structural units in SFSG, and the span capacity of the structure is then enhanced. Because of the large structural dimension, the construction process including assembling, closure and brace-unloading should be divided into many stages. As a result, there is very strong time-dependent effect for the structural stress state in construction. In this paper, based on matrix mechanics model of space grid structures, a time-dependent analysis method considering temperature variation during construction is presented based on matrix mechanics model to optimize the closure scheme. A combined brace element is presented to accurately simulate the mechanic character of temporary braces. In this way, the whole construction process of assembling, closure and brace-unloading are effectively and accurately analyzed for the SFSG structure of Shenzhen Universiade Stadium. The displacement state, stress distribution, and force changes in temporary braces are obtained to provide instruction for the design and control of construction process.

Optimal structural design of a planar parallel platform for machining

Parallel manipulators have many advantages over traditional serial manipulators. These advantages include high accuracy, high stiffness and high load-to-weight ratio, which make parallel manipulators ideal for machining operations where high accuracy is required to meet the requirements that modern standards demand. Recently, the finite element method has been used by some workers to determine the stiffness of spatial manipulators. These models are mainly used to verify stiffness predicted using kinematic equations, and are restricted to relatively simple truss-like models. In this study, state-of-the-art finite elements are used to determine the out of plane stiffness for parallel manipulators. Euler–Bernoulli beam elements and flat shell elements with drilling degrees of freedom are used to model the platform assembly. The main objective of this study is to quantify the stiffness, particularly the out of plane stiffness, of a planar parallel platform to be used for machining operations. The aim is to obtain a design that is able to carry out machining operations to an accuracy of 10 μm for a given tool force. Reducing the weight of a parallel manipulator used in machining applications has many advantages, e.g. increased maneuverability, resulting in faster material removal rates. Therefore the resulting proposed design is optimized with respect to weight, subject to displacement and stress constraints to ensure feasible stiffness and structural integrity. The optimization is carried out by means of two gradient-based methods, namely LFOPC and Dynamic-Q.

A high frequency coin-tap method of non-destructive testing

A high frequency version of the coin-tap method of non-destructive testing has been investigated. The technique involves tapping the structure with a very light striker of mass typically below 1 g and monitoring the sound produced by the tap. The low striker mass increases the frequency range of the excitation compared to that obtained in the conventional version of the test, which means that the membrane resonance of the layer above a defect such as a disbond or delamination is excited. This results in a large increase in the amplitude of motion produced. The method has been tested on aluminium plates with flat-bottomed holes, the results being considerably better than those obtained using the conventional coin-tap method, a defect 50 mm in diameter and 7 mm deep being at the margin of detectability whereas with the conventional method, a 50 mm diameter defect 5 mm deep was not detectable. However, the results on a honeycomb specimen with fibre-reinforced plastic skins were not as good as those with the conventional coin-tap method. This is because the frequency range of the excitation is reduced by the low out of plane stiffness of the fibre reinforced plastic, while the membrane resonance frequency is high due to the large in-plane stiffness and low density. The method may therefore be useful on structures fabricated from metals or un-reinforced plastics.

鋼構造柱梁接合部の歪集中に関する実験的研究 (その 2)

The purpose of the paper is to investigate the effect of the out of plane stiffness of the column flange on the strain concentration of beam-to-column connections in steel structures under increasing alternative loading. The test specimens are H-TYPE (the shape of the column cross section is H), and are small-scale ones. They are manufactured by machineworks from the rolled steel plate (thickness; 65 mm, SS 41). The specimens are made so as to represent the part of the beam flange without stiffening plates. The increasing alternative load is subjected to the end of the beam flange. Strain and displacement in the plastic region of the beam flange are calculated by MOIRE analysis. The characteristics of the strain concentration of beam-to-column connections are influenced considerably by the characteristics of the plastic out of plane deflection of the column flange. In regard to the beam flange of beam-to-column connections which did not generate the plastic out of plane deflection of the column flange, summary of the results are shown below. (1) The amplitude of the strain at the end of the joint is larger than the amplitude of the strain at the middle of the joint. (2) In regard to the strain distribution from which subtract the initial residual strain at every loop, the reversal of the strain concentration occurs. (3) When the stress surpasses the past largest range, the strain concentration ratio increases rapidly. (4) Mean stress-mean strain relations at the beam flange near the joint to the column flange are almost equal to material stress-strain relations. (5) Elastic strain distribution and plastic strain distribution are almost independent. These distributions are approximated by parabola. (6) The elastic strain concentration ratios are constant.