Composite Circular Tubes Research Articles

Experimental Investigation on the Crashworthiness of Braided Glass/Epoxy Tubes Subjected to Axial Impacting

This paper presented an experimental study on the low-velocity impact response of triaxial braided composite circular tubes, which were fabricated with S-glass/epoxy composite. The impact responses were recorded and analyzed in terms of impact load-displacement curves and specific energy absorption. In addition, four basic failure modes called delaminating, splaying, fragmental fracture and progressive folding were founded. The levels of the mean impact load and specific energy absorption (SEA) are determined by the energy absorption mechanisms, which are related to the dominant failure modes of the tubes. In general, delamination which exhibits the poor energy absorbing performance is the dominant failure mode for all the specimens. Impact test results showed that all three types of tubes had almost the same SEA. Compared to the quasi-static test results, the first peak load and the mean load decrease at about 50% and 10% respectively, SEA generally decreases at an average level 10%.

Crashworthiness characteristics of flax fibre reinforced epoxy tubes for energy absorption application

The study reported here entailed an experimental investigation of the crashworthiness characteristics of natural flax fibre reinforced epoxy composite circular tubes from the point of view of energy absorption. The specimens tested under uniaxial compression include three inner diameters (36, 54 and 82mm), three numbers of plies (1, 2 and 3) and three length-to-diameter ratios (1, 1.5 and 2). A total of 81 hollow tubes were tested (three specimens for each type) and the energy absorption capabilities of the specimens were evaluated. The parameters measured were the maximum crushing load, maximum stress, total absorbed energy, specific absorbed energy and crush force efficiency. The failure modes of the specimens were analysed from photography. Test results indicate that flax fibre reinforced epoxy composite tube has the potential to be used as energy absorber.

The Effect of Reinforcement-Length of Carbon Fiber Reinforced Bonding Composites on Circular Tubes under Flexural Condition

This paper presents an experimental investigation on flexural performance of carbon fiber reinforced bonding composite circular tubes with different length of reinforcing pieces. Four kinds of composites bonded tubes with different reinforcing pieces length 20mm, 30mm, 40mm and 50mm were carried out. The flexural strength and modulus of bonged composite samples tested were investigated. The experiment result indicates that the length of reinforcing pieces has some effects on the flexural performance of bonding composite circle tubes. The average flexural strengths of samples reinforced 20mm, reinforced 30mm, reinforced 40mm and reinforced 50mm are 41%, 45%, 49% and 51% of average flexural strength of boned samples without bonding, respectively. The bonding strength will improve when the length of reinforcing pieces increases. The modulus does not change when reinforcing length was greater or equal than 30mm. The main typical failure modes of tested specimens are adhesive cohesive failure and interlamination failure between prepreg and adhesive film.

The Effect of Bonding Length on the Flexural Performance of Carbon Fiber Epoxy Matrix Composite Tubes

This paper attempts to explore the influence to flexural performance of carbon fiber epoxy matrix composite circular tubes which were bonded in four different bonding Length with adhesive. Under the different bonding length, i.e. 20, 25, 35 and 40mm, the flexural performance of carbon fiber epoxy matrix composite circular tubes which were bonded were tested. It is shown that the bonding length affect the flexural properties of composite tubes. The flexural strength and elastic modulus of specimens CFRL50 increase about 18.11% and 36.95% respectively, compared to specimens CFRL20. The flexural properties of bonding composite tubes increased with the increasing length of reinforced pieces L2. Embedded bonding technology can provide a good bonding performance for composite circle tubes.

Experimental Investigation on Composite Circular Steel Columns - Taguchi’s Approach

Composite circular steel tubes- with and without epoxy infill for three different grades of concrete are tested for ultimate load capacity and axial shortening , under axial monotonic loading for compression. Steel tubes are compared for different lengths, cross sections and thickness. Specimens were tested separately after adopting Taguchi’s L9 (Latin Squares) Orthogonal array in order to save the initial experimental cost on number of specimens and experimental duration. DOE (Design of Experiment) approach was adopted. Results were generated using Taguchi’s method-a new technique to get mean effects plot. Analysis was carried out using ANOVA (Analysis of Variance) technique with the assistance of Mini Tab v15- a statistical soft tool. Results were verified after conducting preliminary nine combination experiments as per L9 orthogonal array and linear regression models were developed. Comparison for predicted and experimental output is obtained from linear regression plots. To know the implications of different factors on circular composite columns with and without epoxy, surface contours were also generated. From this research study it is concluded that ,Regression models which were developed with minimum number of experiments based on Taguchi’s method predicted the axial load carrying capacity very well and reasonably well for at ultimate point. Cross sectional area of steel tube has most significant effect on ultimate load carrying capacity. Also it is observed that, as length of steel tube increased- load carrying capacity decreased.

Flexural Behavior of Concrete-Filled FRP-Steel Composite Circular Tubes

Three large-scale concrete-filled FRP-steel composite circular tubes and a control steel tube were tested to investigate flexural behavior. The effects of FRP and composite with different types of FRP with various ultimate strains were investigated. The study demonstrated the important effect of FRP, and showed that the load-displacement curves of FRP-steel composite tube beams could be divided into four stages: elastic stage, plastic stage, hardening stage and residual stage. An additional decline stage was gained for multi-fiber with different ultimate strains and steel composite tube concrete beams. FRP could increase the ultimate bearing capacity and bring the hardening stage after steel tube yielding, and a certain degree of stiffness would be achieved to avoid the “zero stiffness”. The composite of a variety of FRP could relax fracture failure for the FRP-steel composite steel concrete beams, realized the successive rupture of fiber in batches and changed the failure modes.

A study on crushing behaviors of composite circular tubes with different reinforcing fibers

In this study, the failure modes and energy absorption capabilities of different kinds of circular tubes made of carbon, Kevlar, and carbon–Kevlar hybrid fibers composites with epoxy resin have been evaluated. The relationship between the crushing parameters (specific energy absorption, maximum peak load, mean crushing load) and the material properties for different fibers and patterns was also investigated. The fabric carbon/epoxy tubes had the best energy absorption capability (specific energy absorption of 81.7%). In contrast, the tubes made of Kevlar showed the worst energy absorption capability. Based on the linear regression analysis results, the crushing parameters generally showed good correlation with the compressive strength and shear modulus. In particular, the specific energy absorption of the tubes with the brittle fracture mode revealed the strongest correlation with the compressive strength (R-square value = 0.90).

Dynamic Progressive Damage Modeling of Fiber-reinforced Composites Under Different Strain Rates

A dynamic progressive damage model is developed to simulate the crash dynamic behavior of laminated composites. Experimental results are taken from various types of uni-axial quasi-static and dynamic tests on unidirectional plies. The model is an integration of four major components: rate-dependent material model, stress analysis, failure analysis, and material property degradation rules. Material properties of a glass/epoxy unidirectional ply under quasi-static and dynamic loading conditions; in longitudinal, transverse, and shear loadings and at various strain rates, ranging from 0.001 to 100 s-1 which are typical strain-rate range during automobile crash accidents, are fully characterized. The material properties, including strain-rate-dependent effects, are derived. The dynamic behavior of composite specimens exhibited strain-rate dependency, when compared to the static properties. Based on the results obtained, the empirical material model functions are proposed in terms of strain rates. In addition, stress-based dynamic failure criteria including different failure modes of a unidirectional ply under multi-axial states of stress and the strain-rate-dependent behavior of material are developed. The developed failure criteria are used to quantify the damage evolution and corresponding reduction in the stiffness and strength in different modes based on associated rate-dependent material property degradation rules. The developed models are programmed as a user-defined subroutine in LS-DYNA, a nonlinear, explicit dynamic code. The predictive capability of the model is validated by numerical simulations of two representative composite specimens; quasi-isotropic composite flat specimens under tensile dynamic loading and circular composite tubes under axial impact against experimental results. The predictions of the model correlate well with the results obtained by experiments.

Energy absorption properties of braided glass/epoxy tubes subjected to quasi-static axial crushing

Quasi-static axial compression tests were performed to study the failure mechanisms and energy absorption capabilities of braided composite circular tubes. The effect of braiding parameters and chamfer initiators on energy absorption was investigated. The braided preforms consisted of various triaxial architectures using S-glass. It was found that tubes with external chamfers were crushed progressively, but unchamfered tubes failed catastrophically. The crushing response of glass/epoxy braided tubes can be categorised into four basic modes: splaying, fragmental fracture, progressive folding and catastrophic failure. The levels of the mean crush load and specific energy absorption are determined by the energy absorption mechanisms, which are related to the dominant failure modes of the tubes. The specific energy absorption of the braided tubes with these four different failure modes follows the sequence of splaying, fragmentation, progressive folding and catastrophic failure.

Experimental optimization of composite collapsible tubular energy absorber device

A four-phase program to improve the specific energy absorbed by axially crushed composite collapsible tubular energy absorber devices was undertaken. In the first phase, examining of the crushing behaviour of non-triggered tubes was carried out. The second phase is aimed at obtaining the best position for the triggered wall. The third phase focuses on the effects of material sizing in order to understand the influence of triggered wall length on the responses of composite circular tubes to the axial crushing load. The results of these three phases of the study contribute to the fourth whose objective is to optimize the shape geometry of the cross-section area to further improving in tube energy absorption capability. The experimental results demonstrated the strong potential benefits of optimizing the material distribution. The sizing and shape optimization of composite collapsible tubes exhibited a pronounced effect on their capability to absorb high specific energy under axial compressive load.

Modeling of Prestressed Concrete-Filled Circular Composite Tubes Subjected to Bending and Axial Loads

This paper presents a nonlinear model used to predict the load–deflection responses and axial load–moment interaction curves of pretensioned concrete-filled circular composite tubes. The model accounts for the prestressing effect, which not only improves serviceability, but also activates a confinement mechanism of the concrete core restrained by the tube. The enhanced performance of confined concrete is considered. In the compression side, the tube is modeled as a biaxially loaded membrane, subjected to longitudinal compressive and hoop tensile stresses, and failure is detected using the Tsai–Wu biaxial strength envelope. Progressive failure of layers of fibers at various directions within the tube leads to stiffness degradation, and is modeled using the classical lamination theory–ultimate laminate failure approach. The model is verified using experimental results and used in a parametric study to evaluate the effects of prestress level, amount and material type of prestressed reinforcement, and thickne...

Effect of geometry on the crushing behaviour of laminated corrugated composite tubes

This paper is devoted to study the effect of corrugation geometry on the crushing behavior, energy absorption, failure mechanism, and failure mode of woven roving glass fibre/epoxy laminated composite tubes. A comprehensive experimental program has been carried out on two geometrically different types of composite tubes subjected to axial compressive loading conditions. A cylindrical composite tube has been fabricated and tested in order to provide a means of comparison with corrugated composite tube. Both are tested under the same condition to establish the effect of corrugation geometry. The results showed that the initial failure was dominated by interfacial failure, while a folded zone grows progressively down in a form of mushrooming failure. The results also showed that radial corrugated composite tube (RCCT) exhibited good energy absorption capability than circular composite tube (CCT).

Contribution of Failure Mechanisms to Crush Energy Absorption in a Composite Tube

The main energy absorbing mechanisms during quasi-static crush of a circular composite tube have been investigated using an axisymmetric finite element model. Failure mechanisms such as material failure, delamination, friction between plies and friction between a metallic initiator and the tube are explicitly represented in the model. A Design of Experiments (DOE) study is performed to estimate the contribution of each of these mechanisms on the total energy absorbed. The results confirmed that friction between the tube and the initiator was the dominant mechanism, representing approximately 50% of the total energy absorption. The delamination mechanism did not absorb significant amounts of energy, but the presence of delamination had a strong effect on the bending stiffness and the deformation of the tube, which in turn affected strongly the total energy absorbed. The results of this study not only provide a better understanding of tube crush behavior, but also guide the development of better models for design of composite crush tubes.

Equivalent Finite Element Modeling of Thick Composite Structures for Analysis of Composite Hingeless Hub System

Finite element analysis for thick composite structures is rather complicated. Two-dimensional modeling, which is relatively easy to make, can cause inaccurate result since the plane stress condition cannot be applied, while three-dimensional modeling is hard to make. In the three- dimensional modeling, it is difficult to model all the layers with different material properties and ply orientation in the structure. In this paper, an equivalent modeling is proposed and numerically tested for analysis of thick composite structures. The method has been verified for the modeling of composite plate and circular composite tube in order to find their bending deflection and natural frequency. MSC/NASTRAN and PATRAN are used for the calculation. It has been confirmed that three-dimensional analysis must be conducted for thick structures and the equivalent modeling is proven to be accurate when layers with same characteristics are properly grouped. The proposed modeling technique has been applied to analyze hingeless composite rotor hub system designed by Korea Aerospace Research Institute (KARI). Detailed three-dimensional modeling for this structure is almost impossible to make due to its complex geometry of thick composite structures. Using the proposed equivalent modeling technique, failure analysis was performed based on stress/strain criterion and the safety of each part was checked. Deflection of the hub system was validated comparing with the result from the simple analytical beam model, and the numerical result will be used for the next design cycle of the composite hub system.

Design of Braided Composites for Energy Absorption

This paper describes a model for simulating the crushing behavior and predicting the energy absorption characteristics of triaxially braided composite tubes. The crushing model uses the finite element code ABAQUS along with a material module that describes the constitutive behavior of the braid material. The constitutive behavior includes the effects of damage accumulation, and scissoring and jamming of the braider tows. To facilitate the model development, extensive material tests and tube crushing experiments were performed.Crushing tests were conducted on braided carbon fiber/epoxy-vinyl ester composite circular tubes, which were supplied by USCAR’s Automotive Composites Consortium. All tests were conducted quasi-statically, and plug-type initiators were used to trigger the progressive crushing. Experimental results show that the profile of the load-displacement curve and the overall energy absorption can be significantly affected by the fiber architecture and the fillet radius of the plug-type initiat...

Effects of Braiding Parameters on Energy Absorption Capability of Triaxially Braided Composite Tubes

The effects of two different braiding parameters, the braiding angle and the axial yarn content, on the crush failure characteristics and specific energy absorption capability of two-dimensional (2D) triaxially braided composite circular tubes were studied. Quasi-static axial compression was employed for these crush tests. The crushing appearance and failure modes in the crushing zones were examined by optical microscopy. The results showed that the triaxially braided carbon composite tubes were crushed by a progressive splaying mode. The average width of the splaying fronds increased with increasing braiding angle, but decreased with increasing axial yarn content. The tube with 200 braiding angle showed the highest specific energy absorption among the tubes with various braiding angles. And the tubes using 6k-12k fiber tows as the axial yarn exhibited higher specific energy absorption among the tubes with various axial yarn content.

P27 Review of measurement, assessment, analysis and reporting of visual acuity in clinical trials in ophthalmology

This paper is devoted to study the effect of corrugation geometry on the crushing behavior, energy absorption, failure mechanism, and failure mode of woven roving glass fibre/epoxy laminated composite tubes. A comprehensive experimental program has been carried out on two geometrically different types of composite tubes subjected to axial compressive loading conditions. A cylindrical composite tube has been fabricated and tested in order to provide a means of comparison with corrugated composite tube. Both are tested under the same condition to establish the effect of corrugation geometry. The results showed that the initial failure was dominated by interfacial failure, while a folded zone grows progressively down in a form of mushrooming failure. The results also showed that radial corrugated composite tube (RCCT) exhibited good energy absorption capability than circular composite tube (CCT).

Bending of fibre-reinforced composite thin-walled tubes

The present paper reports on the bending of thin-walled fibre-reinforced composite circular tubes under certain end-clamping conditions, simulating the oblique collision of structural elements of impacted vehicles. The fracture mechanism of the crushed composite tubes is quite different from that of metallic components loaded under the same conditions. Energy absorption in the present case is achieved by material fragmentation; i.e., the mechanism of fracture dominates the phenomenon, rather than plastic deformation. The effect of clamping conditions on the energy absorbing efficiency of the shell is also examined.

The collapse of a viscous tube

The collapse of a composite circular viscous tube owing to external pressure and surface tension is considered. It is shown that, for small surface tension, the collapse time, at which the tube closes, is very sensitive to the viscosity of the inner tube.