Load-displacement Graphs Research Articles

Large Deformation Studies on Combined Shell Structures

The combinations of shell structure give discontinuity to their load path and hence play major role in load deformation behaviour of shell structures. In this paper thin metal shells are studied for combination of shell geometries for large deformation. The study is conducted on four categories of shell structures which are the combination of simple cylinder, frusta and half sphere. The large deformation was obtained by axially compressing these geometrical shells between two flat plates. The geometrical shell behaviour to large deformation was understood with load displacement graph for different geometrical changes. The associated change in mode of deformation is presented and discussed.

Quasi Static Axial Crushing of Foam Filled Thin Walled Circular Tubes

Objective: Thin walled circular tubes are used in many practical situations to absorb impact energy, the axial impact of these thin-walled tubes absorb deformation energy at nearly constant load resulting in high energy absorption. This paper investigates the dynamic progressive buckling response of empty and foam filled tubes under quasi static loading conditions and validation of results using non linear finite element code LS-DYNA. Method/Analysis: In the experimental study, aluminium 6063-T5 thin walled circular tubes are integrated with low density polyurethane foam and quasi static loading is conducted on both empty and foam filled tubes to determine the buckling response and deformation shape under impact. The load-displacement graph obtained is used to determine the energy absorbed by the thin walled structure. The numerical analysis of a similar loading condition is simulated using LS-DYNA and a systematic comparison between the finite element model and experimental deformed shapes, load-displacement, number of folds, energy absorption is done. Findings: The integration of low density foam in empty aluminium tube increased the energy absorption by 1.4% with an additional stability in the deformation and satisfactory agreements were achieved between the finite element model and experimental deformed shapes, load-displacement, number of folds, energy absorption with an error less than 15%. Applications/Improvements: One potential application of polyurethane foams is that it can be used as reinforcement in energy absorbing structures, hence an understanding of the response of the system in different loading condition is necessary to improve the crashworthiness. The experimental results are correlated to FEM to reduce the time spend on experimental testing.

Static load behavior and energy absorption of safety guardrails for construction works

One of the requirements which must be met by the temporary edge protection systems (TEPS) is to stop a worker who walks, stumbles, falls and knocks against the system. The effect of the worker’s crash with the protection system is a dynamic type stress applied as an impact. The capacity of the system to withstand the impact depends on its ductility and its ability to absorb energy. The area enclosed by the load-displacement graph of a TEPS when the load is statically applied is an indicator of its ductility and its ability to absorb energy. In Europe, the EN 13374 standard specifies the requirements to be fulfilled by the TEPS. For systems placed in floor slabs with a slope smaller than 10° (class A systems), the standard indicates that the testing should be performed using static loads. In this work, TEPS manufactured from steel, wood, injected plastic, and composites have been tested with the static loads test system specified in the EN 13374 standard for assessing class A systems. Subsequently, the areas enclosed in the load-displacement diagram have been tested and have been compared with the estimated values of impact energy.

Experimental Study on Injected Anchors for the Seismic Retrofit of Historical Masonry Buildings

ABSTRACTThis article reports the results of a research study on the behavior of injected anchors in historical masonry under cyclic loads. Laboratory tests with masonry specimens (bricks and mortar with low characteristics to replicate real historical masonry) were conducted to analyze the response of steel anchors injected using a special sock and with different types of mortar (cement and lime based). The test benches replicate the real condition of the use of these anchors: they allow simulation of the connection of masonry panels (T and L connections) or the anchor of steel ties to contrast the arch thrust. Monotonic and cyclic pullout tests were conducted on short and long anchors to define the loss of strength under cyclic loads for different situations. The results yielded load-displacement graphs, steel bar deformation graphs of the anchors’ length, a qualitative bond stress curve, and a comparison among maximum strengths obtained under several conditions.

Investigation of the quasi static penetration resistance behavior of carbon fiber reinforced laminate HDPE composites

Abstract In this paper, a study on the quasi-static penetration resistance behaviour of unidirectional carbon fiber fabric/High Density Polyethylene (HDPE) composite with two different thicknesses which are laminated 4L and 12L (4 layers & 12 layers), i.e., HC = 3.1 mm and 9.3 mm, is presented using the quasi-static punch shear test (QS-PST) methodology for the experiments. The penetration resistance is usually shown by a load–displacement graph, integral of which is the energy dissipated by the composite during penetration. The penetration energy varies with the diameter of the support span which can be equal or higher than the punch diameter. During tests, a flat punch of diameter 7.6 mm with a range of support spans 8.89 mm–50.8 mm has been used and QS-PST experiments are carried out for varying support span to punch diameter ratios (i.e., SPR = 1.16, 1.33, 1.67, 2.00, 2.33, 2.67, etc.). Their damage mechanisms for different SPRs and thickness are documented. Stiffness, peak force, deflection, damage area, and energy dissipation results are presented in detailed form.

Biomechanical properties of lumbar endplates and their correlation with MRI findings of lumbar degeneration

How stiffness and strength of the human lumbar endplate vary with location, spinal level, and its correlation with MRI findings of lumbar degeneration, has not been reported in detail. 27 lumbar spines (16 male, 11 female, 31–49yrs) were harvested from cadavers without history of lumbar lesion or trauma. Disc and endplate degeneration was evaluated from MRI. Micro-CT was used to evaluate endplate microstructure. Indentation tests were performed to quantify stiffness and strength at 23 sites on each endplate from load-displacement graphs. Results showed that stiffness and strength increased from the centre of the endplate towards its periphery. There was no general age-related reduction in endplate stiffness or strength, although strength decreased slightly with age opposite the inner annulus. Disc degeneration was associated with a 39–46% decrease in stiffness, and a 21–30% decrease in strength, with effects being greatest near the endplate periphery. The presence of Modic changes had a similar effect. Strength and stiffness consistently increased at lower spinal levels, and were consistently greater in the inferior endplate (relative to the vertebra). Gender had little influence, although stiffness in the peripheral endplate was greater in males. BV/TV, SMI, Tb.Th and BMD were positively correlated with strength. We conclude that endplate properties reflect compressive stresses within adjacent intervertebral discs. Weaker and softer endplates may indicate reduced mechanical loading in decompressed discs that are stress-shielded by the neural arch. Preoperative MRI evaluation of endplate integrity could reduce the risk of implant subsidence following inter-body fusion.

Fracture Behaviours in Compression-loaded Triangular Corrugated Core Sandwich Panels

The failure modes occurring in sandwich panels based on the corrugations of aluminium alloy, carbon fibre-reinforced plastic (CFRP) and glass fibre-reinforced plastic (GFRP) are analysed in this work. The fracture behaviour of these sandwich panels under compressive stresses is determined through a series of uniform lateral compression performed on samples with different cell wall thicknesses. Compression test on the corrugated-core sandwich panels were conducted using an Instron series 4505 testing machine. The post-failure examinations of the corrugated-core in different cell wall thickness were conducted using optical microscope. Load-displacement graphs of aluminium alloy, GFRP and CFRP specimens were plotted to show progressive damage development with five unit cells. Four modes of failure were described in the results: buckling, hinges, delamination and debonding. Each of these failure modes may dominate under different cell wall thickness or loading condition, and they may act in combination. The results indicate that thicker composites corrugated-core panels tend can recover more stress and retain more stiffness. This analysis provides a valuable insight into the mechanical behaviour of corrugated-core sandwich panels for use in lightweight engineering applications.

Tearing of Thin Polymer Sheets with Wrinkling

In this paper, the tearing behavior of thin polymer sheets was studied experimentally and numerically. First, the specific essential work of fracture for thin biaxially oriented polyethylene terephthalate (Mylar) was measured experimentally. Double-edged notched tensile specimens of Mylar with three different thicknesses and varying ligament lengths were tested. Load-displacement graphs were formed, and the total internal energy was evaluated, from which the specific fracture energy was determined. Next, a finite element analysis was performed to predict the tearing response of polymer sheets. The finite element model incorporated a user-defined cohesive element to properly represent the structural behavior of a thin polymer sheet in the presence of damage, including the propensity of the sheet to wrinkle. The results indicated that the measured specific essential work-of-fracture values were nearly identical for the three separate thicknesses, which confirmed that it is indeed a material property of the Mylar itself. The developed user cohesive element accurately simulated the tearing of thin polymer sheets, producing well-matched nominal stress–strain curves to those by experiments. Analyses were also performed for the double-edged notched tensile configuration with different lengths and a corner-loaded square sheet configuration with a center cut, which showed that the wrinkle deformation significantly affected the tearing behavior of thin polymer sheets.

Study on crack propagation of adhesively bonded DCB for aluminum foam using energy release rate

Aluminum foam with initial crack, which has a closed cell form adhesively bonded, is studied to compare and analyze the crack propagation behavior by using both experimental and finite element analysis techniques. The specimen is loaded in Mode I type of fracture as 15 mm/min speed of a displacement control method. The experimental results were used to accommodate the finite element analysis performed with commercial software ABAQUS 6.10. First, using a video recording, five steps of experiment were selected at random and then the energy release rate was calculated. The estimated energy release rate was then used as fracture energy into the finite element analysis. Comparing the experimental axial load-displacement graphs and the finite element analysis results, roughly equivalent peak values were observed in the cohesive strength of the aluminum foam double cantilever beam. However, force versus displacement patterns showed somewhat different: little deformation was observed in aluminum foam, whereas adhesive parts in double cantilever beam were significantly deformed.

An Experimental on Honeycomb Core in the Axial Direction under the Quasi-Static Loading

This paper focuses on the quasi-static response of the aluminum honeycomb core based on an experimental work. The load-compression and energy absorb characteristics of the out-of-plane aluminium honeycomb core are studied for three varieties of the core cell sizes which are 0.01905, 0.0127 and 0.00635 m. The crushing tests were conducted on the Instron machine with a displacement control of 5 mm/min. The initial part in the load-displacement graph shows linear elastic characteristic, followed by a non-linear elastic-plastic regime before it collapses. Based on the observation, the cell sized 0.01905 m shows the global buckling collapse, but the cell sized 0.0127 and 0.00635 m collapse as progressive buckling mode. The cell size 0.00635 m shows highest energy absorption due to it has the highest density and it collapses like the progressive buckling mode compared with the others specimen.

The analysis of the deformation of single node in a modular scaffolding system

The increasingly complex engineering structures of scaffoldings require optimal designing in terms of safety, economy and erection. This approach requires detailed knowledge of the static-strength properties of elements, as well as knowledge of their interconnections. The paper deals with the laboratory tests of deformations in modular scaffolding nodes for the following loads: torque of the ledger, shearing and bending in the horizontal plane. The original grip was used in the study, which allows to load the node with aforementioned loads. The result of research is a description of the deformation of the nodes and the load-displacement graphs. The studies presented in the paper indicate that graphs are repeatable, which is not obvious in the case of nodes assembled manually. This means that it can be used as a basis for the verification of non-linear numerical analysis, which will have to take into account such issues as the material nonlinearities, geometric nonlinearities, contact and friction.

접착제로 접합된 이중외팔보 알루미늄폼의 파괴 거동에 관한 연구

In this study, closed-cell aluminum foam with an initial crack was investigated to produce an axial load-time graph. Using the 10-kN Landmarks of MTS Corporation, a 15-mm/min velocity of mode I shape was applied to the aluminum foam specimen using the displacement control method. ABAQUS 6.10 simulation was used to model and analyze the identical model in three dimensions under conditions identical to those of the experiment. The energy release rate was calculated on the basis of an axial load-displacement graph obtained from the experiment and a transient image of the crack length, and then an FE model was analyzed on the basis of this fracture energy condition. The relation between load and displacement was discussed; it was found that the aluminum foam deformed somewhat less than the adhesive layer owing to the difference in elastic modulus.

Evaluation of Shear Strength for Reinforced Flat Plates Embedded with GFRP Plates

Abstract In this study, The purpose of this study is to experimentally investigate the shear behavior of reinforced flat plate embedded with GFRP(glass fiber reinforced polymer) plate with openings. The GFRP shear reinforcement is manufactured into a plate shape with several openings to ensure perfect integration with concrete. The test was performed on 7 specimens. the parameters include the type of reinforcement and amount of the shear reinforcement., From the test, we analysed the crack, failure mode, Strain, load-displacement graph. a calculation of the shear strength of reinforced flat plate with GFRP plate based on the ACI 318-11 was compared with the test results. The results of the experiment indicate that GFRP plate is successfully applied as a shear reinforcement in the flat plate under punching shear. Keywords :shear reinforcement, flat plate, glass fiber reinforced polymer(GFRP), shear strength. † Corresponding author: Tel: +82-31-201-2542; E-mail: kimhc@khu.ac.krReceived March 13 2014; Revised March 27 2014;Accepted March 28 2014Ⓒ2014 by Computational Structural Engineering Institute of KoreaThis is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons. org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Effect of trigger configuration on the crashworthiness characteristics of natural silk epoxy composite tubes

In the current study, the quasi-static compression test over natural silk epoxy composite tubes was performed using two different trigger mechanisms. The natural silk epoxy composite tubes used in this study consisted of 12 layers of woven natural silk as reinforcement and a thermoset epoxy resin as matrix. The natural silk epoxy composite tubes had lengths of 50mm, and they were associated with external triggers, including four steel pieces located on the downside flat plate fixture and a plug trigger. The failure modes of the natural silk epoxy composite tubes were investigated using representative photographs taken during the quasi-static compression test. In addition to the load–displacement graphs, the crashworthiness characteristics of the natural silk epoxy composite tubes were exported. The results showed that the four-piece trigger mechanism changed the manner in which failure progressed i.e. from catastrophic to progressive. Plug trigger caused a significant reduction in load carrying capacity and energy absorption capability of specimens. The four-piece trigger retained energy absorption capability of specimens similar to the non-triggered ones, while both the reduction of peak load and increase in crash efficiency of these were observed to be significant.

Geometrical metallic shell behavior study under compression

The loading response of shell structures depends on their shapes. The individual shape behaves uniquely to the loading, and different shapes give different load displacement graphs. If these geometries are combined, then their load displacement graphs can be different. It may happen that their combined behavior can be harnessed to be used as better energy absorber in a controlled manner, which they cannot if they are used individually. Experiments were conducted on two separate geometries as well by joining them with weld. The first geometry was the top cylindrical and frusta bottom. The second geometry was the shape of inverted bell crater and half-spherical shells. Combining these two shapes produced the third geometrical shape. The large deformation was obtained by crushing these geometrical shells between two flat plates. The finite element analysis was used to simulate the crush phenomenon. The behavior of the geometrical shell to large deformation was understood with load displacement graph for different samples. The energy absorbed by the different samples was calculated and compared. The parameters, like material and thickness, were varied for the samples to see their effect on the large deformation behavior. Moreover, friction role is discussed on the crush phenomenon. This paper also gives an idea on the different parameters which can affect the energy-absorbing capacity of the combined geometrical shells.

Effect of Strain Rate Upsetting Process on Mechanical Behaviour of Epoxy Polymer

The advantages of polymer materials such as high strength and stiffness to weight ratio, corrosion resistance and manufacturing flexibility have increased the industry demands to utilize them in high performance applications. Designing polymer structures depends on a high understanding of their hyper-elastic behaviour, therefore investigating the mechanical behaviour of polymers is necessary. In this paper, the nonlinear behaviour of epoxy polymer is examined under upsetting test. The main aim of the study is to analyse the effect of strain rate on the mechanical behaviour of epoxy polymer. The cylindrical polymer epoxy specimen, 20mm in length and in diameter, was manufactured. The upsetting tests provided quasi-static compressive loads which were adjusted in the loading rates of 0.1, 1, 50, 100, 200 and 500 mm/min. The loadings were continued until complete fracture was observed. Each loading rate was repeated for at least 3 specimens to ensure a reasonably good statistical sampling. The average data of each test is used to produce the load-displacement graphs of the specimens, from which stress-strain curves are extracted to show the behaviour of epoxy polymer. The results show a 37% increase of yield stresses when the loading rate is increased from 0.1 to 500 mm/min and the yield strains increase by 26%. The stress-strain curves are nonlinear where the slope increases when the loading rate is raised from 0.1 to 100 mm/min but then decreases when the rate is further raised from 100 to 500 mm/min. The maximum load that can be sustained is increased with loading rate. This can be due to the microstructure deformation response of epoxy polymer. This polymer is categorised as large-strain material by showing exhibiting large deformations under different rates of compression loading.

Investigation of penetration mechanics of PW Kevlar fiber reinforced HDPE composites

In this article, a study on the quasi-static penetration resistance behavior of plain weave Kevlar/high density polyethylene composite with varying thicknesses, i.e. HC = 3.1–9.4 mm, is presented using the quasi-static punch shear test methodology for the experiments. The penetration resistance is usually shown by a load–displacement graph, integral of which is the energy dissipated by the composite during penetration. The penetration energy varies with the diameter of the support span which can be equal or higher than the punch diameter. During tests, a flat punch of diameter 7.6 mm with a range of support spans 8.89 to 50.8 mm has been used and quasi-static punch shear test experiments are carried out for varying support span to punch diameter ratios (i.e. SPR = 1.16, 1.33, 1.67, 2.00, 2.33, 2.67, etc.). Their damage mechanisms for different support span to punch diameter ratios and thickness are documented. Stiffness, peak force, deflection, damage area and energy dissipation results are presented in detailed form.

Nonlinear Finite Element Analysis of an R/C Frame Under Lateral Loading

Recent developments in computer technology have made possible the use of finite element methods for 3D modeling and analysis of reinforced concrete structures. In this study, the failure behavior and crack formation of an R/C frame under monotonic and reversed-cyclic lateral loading are studied by 3D nonlinear finite element analysis using ANSYS software. Modeling the nonlinear behavior of concrete material as well as the reinforcing steel embedded within concrete is a difficult task. Different methodologies and modeling options are considered in the computer model. The application of reversed cyclic displacement loading and the execution of nonlinear analyses are explained in detail. Load-displacement relationships and concrete crack profiles are obtained in order to compare with the experimental data and observed crack profile. The analysis results compared well with the experimental data based on the comparison of load-displacement graphs. The failure mode of the frame is identified by the crack profiles displayed on the structure.

Modelling and Experimental Study of Mechanical Behaviour of Walls Produced by Different Knitting

Abstract This study aims to investigate the shear behavior and resistance of brick walls produced by various knitting types. For this purpose, 15 samples were produced using Holland knitting, block knitting, cross knitting, lock knitting, and plain knitting. The samples were forced in experiments to collapse and in the non-linear region, the changes in the samples related with shear forces and shear rigidity of the wall sections were determined. In the performed experimental study, the standard sliding resistance test technique for the masonry wall samples has been determined as recommended in ASTM Standard 1391-81. The numerical modeling was carried out by the finite elements method with the program package Ansys, taking into account the local mechanical parameters of bricks and mortar. The behavior of the experimental samples and the cracks occurred during the experiments were analyzed and shear stress graphs and load-displacement graphs were derived. The modeling with the Ansys program was compared with the experimental results and the most appropriate wall knitting type could be proposed.

Investigation on the effect of hybridisation and weathering behaviour of natural fibre polymer composites

The performance and behaviour of various natural fibres and their hybrids with synthetic glass fibre composites were investigated in this work. The composites were fabricated using moulding method. The tensile compressive and flexural strength of the fabricated composites were tested using universal testing machine (UTM). From the load-displacement graph obtained from UTM, the effect of fibres and its hybridisation with glass fibre on the ultimate stress and the displacement on loading were analysed. The impact strength of the un-notched composites was analysed using charpy impact tester. The water immersion tests were also conducted to ensure the weathering behaviour/suitability of this moulded composite under some moisture conditions. From the experimentations it was concluded that the natural fibres can become a best competitor to eliminate or decrease the use of conventional fibre reinforcement. In general, the hybridisation of natural fibre composites enhances the mechanical properties.