Quasi-static Transverse Loading Research Articles

Characterization of failure of single carbon nanotube fibers under extreme transverse loading

Carbon nanotube (CNT) fibers have been extensively investigated along the longitudinal direction and are well-known for their high axial tensile strength and modulus. However, after being manufactured into textiles or composites, these fibers are usually subjected to transverse loading during their normal service life. Deformation and failure of CNT fibers induced by external loads in the transverse direction lack examination. This study integrated single-fiber quasi-static and dynamic transverse loading techniques with scanning electron microscopy (SEM) and high-speed imaging, respectively. An extreme condition was considered as the indenter was a sharp razor blade. Failure behavior of single CNT fibers transversely loaded by the blade at different velocities was visualized, and axial mechanical response of these fibers was measured. The fracture surface of CNT fibers was examined by SEM. Additional experimental investigations were performed on commercialized two organic (aramid and ultrahigh molecular weight polyethylene) and two inorganic (ceramic and glass) fibers. It is revealed that CNT fibers experienced initial contact with the blade, followed by partial incision, and ultimately tensile failure. Furthermore, the energy dissipation and dispersion capabilities of CNT fibers per unit mass were demonstrated to surpass that of commercialized high-performance fibers during extreme transverse loading. As the loading rate increased, the energy dissipation of CNT fibers was further improved by 2.1 times. Such high performance of CNT fibers in resisting extreme transverse loading was presumably attributed to the high hardness, strength, and stiffness of CNTs in the transverse direction and weak intermolecular interactions in the axial direction. This study expands material characterization of CNT fibers in the transverse direction and reveals the fundamental failure mechanism of CNT fibers in the harsh environment, which is deemed useful to develop the fiber-scale model for textiles and composites.

Elevated thermal conditioning effect on flexural strength of GFRP laminates: An experimental and statistical approach

This study aims to investigate the flexural strength and damage formation in glass fibre reinforced polymer (GFRP) laminates for different thicknesses (2, 3 and 4 mm), small span length variations (50.8 and 56 mm), crosshead speeds (1 and 10 mm/min), thermal conditioning duration (3 and 6 h) and thermal conditioning temperatures (27 °C (room temperature), 50 °C, 100 °C and 150 °C). A closed muffle furnace used for thermal conditioning of GFRP specimens. A quasi-static transverse load applied using four-point bend method. GFRP plates are translucent; hence high-intensity background light is used to observe the formed damage and its extent after four-point bend test. The most effectively influencing parameters among GFRP laminate thickness, span length, thermal conditioning temperature, thermal conditioning time and crosshead speeds on the flexure strength of GFRP plates analysed by adopting the two-parameter Weibull distribution statistical method. Flexural strength of the GFRP laminates severely degraded when the exposed elevated temperature approached the glass transition temperature (Tg) 100 °C. Exposure duration affected the flexural strength. GFRP composites exposed for 6 h showed comparatively better flexural strength regain than those GFRP specimens exposed for 3 h. GFRP laminate thickness showed a more significant influence on the flexural strength compared to small span length variation. GFRP laminate with 2 mm thickness showed highest flexural strength compared to 3 mm and 4 mm thick GFRP specimens while the span length 50.8 mm showed higher flexural strength compared to GFRP laminates with 56 mm span length. Crosshead speed also affected the flexural strength and GFRP specimens tested at 10 mm/min showed higher flexural strength compared to specimens tested at 1 mm/min. For specimens tested at room temperature the cumulative failure probability curves agglomerated at a single region in the graph. However, as the temperature and laminate thickness increased these curves dispersed over the entire graph. Experimental flexural strength showed good agreement with the theoretical flexural strength calculated from gamma function.

Experimental Investigation of Transverse Loading Behavior of Ultra-High Molecular Weight Polyethylene Yarns

Ultra-high molecular weight polyethylene (UHMWPE) Dyneema® SK-76 fibers are widely used in personnel protection systems. Transverse ballistic impact onto these fibers results in complex multiaxial deformation modes such as axial tension, axial compression, transverse compression, and transverse shear. Previous experimental studies on single fibers have shown a degradation of tensile failure strain due to the presence of such multi-axial deformation modes. In this work, we study the presence and effects of such multi-axial stress-states on Dyneema® SK-76 yarns via transverse loading experiments. Quasi-static transverse loading experiments are conducted on Dyneema® SK-76 single yarn at different starting angles (5°, 10°, 15°, and 25°) and via four different indenter geometries: round (radius of curvature (ROC) = 3.8 mm), 200-micron, 20-micron, and razor blade (ROC ~2 micron). Additionally, transverse loading experiments were also conducted for a 0.30 cal. fragment simulating projectile (FSP) and compared to other indenters. Experimental results show that for the round, 200-micron indenter, and FSP geometry the yarn fails in tension with no degradation in axial failure strain compared to the uniaxial tensile failure strain of SK-76 yarn (2.58%). Whereas for the 20-micron indenter and razor blade, fibers fail progressively in transverse shear followed by progressive strength degradation of the yarn. Strength degradation of yarn occurs at relatively low strains of 0.6–0.7% with eventual failure of the yarn at approximately ~1.8% and ~1.5% strain for the 20-micron indenter and razor blade, respectively. Breaking angles (range of 10°–30°) are observed to have little effect on the failure strain for all indenter geometries.

Experimental investigation on energy absorption of auxetic structures

The human being has always been looking for optimal use of his surrounding materials and over the years, has managed to invent various structures with special properties. Lattice structures are widely used in various applications due to their lower weight and desirable compressive strength. An example of these structures is the honeycomb that is very popular and many studies have been done about it. A new type of lattice structures is auxetic structure that has negative Poisson’s ratio due to its geometry. This characteristic has caused auxetic structures to have unique properties such as high shear strength, indentation resistance and energy absorption. Investigation of energy absorption of auxetic structures is a subject that has not been studied in researches. In this study, the ability of some auxetic structure for absorbing energy is investigated at quasi-static and low velocity impact transverse loading. Specimens with three types of geometries (re-entrant, arrowhead and anti-tetra chiral) are fabricated using additive manufacturing method (3D printing). Discussion about energy absorption and failure mechanisms of all three structures were carried out and compared in both types of loading.

On the instability of multiple annular delaminations of axisymmetric laminates with arbitrary boundary conditions subjected to transverse load

Herein, the damage problem of quasi-isotropic composite laminates subjected to a quasi-static transverse load has been studied analytically. The damage was modeled as multiple equal-sized annular delaminations of equal-interval in the thickness direction without any opening during transverse loading. This simplified damage shape was adopted according to the typical damage morphology of impact-tested laminates. Closed-form expressions of the responses, such as a deflection and an energy release rate, were developed in terms of the applied force, dimensions of the plates, and damage under arbitrary boundary conditions based on the Mindlin plate theory. Though their applicability is limited owing to an assumption of linearity, the closed-form expressions provide fundamental information, particularly at the initiation and early growth of the damage, on the effects of the boundary conditions, dimensions, fundamental material properties, and ply thickness of the composite laminates.

Experiment and modified model for CFRP/steel hybrid tubes under the quasi-static transverse loading

Composite/metal hybrid structure has both the advantages of light weight and high strength of composite materials and the advantages of low cost and easy connection of metals, which has great prospects for automotive applications. It is significant to investigate the energy absorption characteristics and theoretical analysis of Composite/Metal hybrid structures under transverse loading. Our study uses the example of CFRP/steel hybrid tube to explore bending deformation behaviour and energy absorption characteristics of the structure by experiment and theoretical analysis based on three-point test. Here, the effects of different winding sequences and thickness (4-ply, 8-ply, and 12ply) of CFRP were performed at three-point bending test, and all specimens were guided by metal tubes to stabilise bending collapse, and the influence of winding sequences on energy absorption and bending resistance is greater than that of numbers of winding layers. The result showed that the specific energy absorption of CFRP/steel hybrid tube with [±45°/90°/90°]2 winding modes was the best, which was 21.4% higher than that of Large-Diameter (LD) steel tube. The bending theoretical model of composite/metal hybrid tube based on Poonaya’s model was performed to predict bending behaviour of hybrid tube. The theoretical result is in good agreement with the experiments, and the bending collapse behaviour is related to the hinge lines formed by CFRP with different angles. The bending theoretical model was modified by considering the hardening behaviour of the material, and can be applied to study on bending behaviour of CFRP/metal hybrid tube by the validation of the CFRP/Al hybrid tube.

Mechanical Behavior of High-Performance Yarns Transversely Loaded by Different Indenters

In this study, we performed off-axis transverse loading experiments to study the stress concentration developed in a high-performance yarn with different indenters. A universal testing machine was utilized to perform quasi-static transverse loading experiments on Twaron® yarns. Seven different round indenters possessing radius of curvature ranging from 0.20 to 4.50 mm were employed in the experiments. In addition, post-mortem failure analysis was performed on the recovered specimens via a scanning electron microscope. From the transverse loading experiments, the results showed that, as the radius of curvature of the indenters increased, the concentrated load decreased, causing the failure surfaces to change from a combination of kink band, snapped-back, and localized shear to only fibrillations. The concentrated stresses were predicted by a strain energy model when loaded by an indenter with a radius of curvature smaller than 1.59 mm. For indenters larger than 1.59 mm, the specimens failed in fibrillation, the concentrated stresses agreed well with the stresses predicted by quasi-static circular curved beam theory.

Plastic collapse and energy absorption of empty circular aluminum tube under transverse quasi-static loading

This paper presents an experimental investigation on plastic collapse and energy absorption of empty circular aluminum tubes under quasi-static transverse loading. Tubular structures being a critical demand as material saving, high energy absorption and good strength characteristics were of major concerns due to its wall thinness, and so, its various diameter-to-thickness (D/t) ratios and span lengths. Studies found that empty circular Al-tube structure subjected to transverse standard three-point bending loading undergone three plastic deformation phases, starting with crumpling phase, crumpling and buckling phase, and lastly the structural collapse. The results found that energy absorption of empty aluminum tubes for a constant D/t ratio decreases as span length. On the contrary, the energy absorption of empty aluminum tubes for a given constant span length increases with the increase in D/t ratio.

Orthotropy as a driver for complex stability phenomena in cylindrical shell structures

By applying a quasi-static transverse load, shallow cylindrical shells can be snapped between two inverted stable states. This dynamic transition, initiated at either a limit point (fold) or a subcritical bifurcation, traverses a region of instability. The ensuing large displacements are attractive for shape adaptation of multi-functional engineering structures. Previous research on isotropic cylindrical shells has indicated the presence of isolated regions of stability in the otherwise unstable transition region. While these regions are theoretically attractive for multi-stage snap-morphing, they are difficult to attain in practice by means of a single control parameter. In this paper, we study the effect of orthotropic material properties on the structural stability and snap-through behavior of shallow cylindrical shells. In addition, we explore complex stability phenomena created by material orthotropy, which are attractive for multi-stage morphing. The problem is analyzed in a robust manner using a technique known as generalized path-following, which combines the mathematical domains of finite element analysis and numerical continuation. The present study shows, in particular, that laminates comprising layers of different directional material properties provide the ability to tailor the elastic bifurcation behavior of cylindrical shells. For example, the lamination scheme can be varied to add isolated regions of stability or entirely remove them; to induce snaking that allows transitioning between the two inverted cylindrical shapes through a series of snaps; and finally, to create groupings of multiple unique stable configurations that can be attained via additional shape control.

Plastic collapse and energy absorption of circular filled tubes under quasi-static loads by computational analysis

This study presents the finite element analysis of plastic collapse and energy absorption of polyurethane-filled aluminium circular tubes under quasi-static transverse loading. Increasing focuses were given to impact damage of structures where energy absorbed during impact could be controlled to avoid total structure collapse of energy absorbers and devices designed to dissipate energy. ABAQUS finite element analysis application was utilized for modelling and simulating the polyurethane-filled aluminium tubes, different set of diameter-to-thickness ratios and span lengths, subjected to transverse three-point-bending load. Different sets of polyurethane-filled aluminium tubes subjected to the transverse loading were modelled and simulated. The failure modes and mechanisms of filled tubes and its capabilities as energy absorbers to further improve and strengthening of empty tube were also identified. The results showed that plastic deformation response was affected by the geometric constraints and parameters of the specimens. The diameter-to-thickness ratio and span lengths had shown to play crucial role in optimizing the PU-filled tube as energy absorber.

Electromechanical behavior of carbon nanotube fibers under transverse compression

Although in most cases carbon nanotube (CNT) fibers experience axial stretch or compression, they can also be subjected to transverse compression, for example, under impact loading. In this paper, the electromechanical properties of both aerogel-spun and dry-spun CNT fibers under quasi-static transverse compressive loading are investigated for the first time. Transverse compression shows a nonlinear and inelastic behavior. The compressive modulus/strength of the aerogel-spun and dry-spun CNT fibers are about 0.21 GPa/0.796 GPa and 1.73 GPa/1.036 GPa, respectively. The electrical resistance goes through three stages during transverse compressive loading/unloading: initially it decreases, then it increases during the loading, and finally it decreases upon unloading. This study extends our knowledge of the overall properties of CNT fibers, and will be helpful in promoting their engineering applications.

An exploration of the ballistic resistance of multilayer graphene polymer composites

The response of multilayer graphene/polyvinyl alcohol (MLG/PVA) films were studied under quasi-static (Q.S.) and dynamic edge-clamped transverse loading. The 10 μm thick films, reinforced by ∼35 vol.% MLG and measuring 85 mm square were fabricated by liquid exfoliation of the graphene followed by filtration of the MLG/PVA dispersion. The responses of the MLG/PVA films were compared with those of equal areal mass films of pure PVA and aluminum. The moderately conductive (∼10−2 S cm−1) MLG/PVA films had a Young’s modulus approximately twice that of PVA and a low strain rate (10−3 s−1) peak strength that was about 50% higher. Moreover, while the MLG/PVA films had a tensile strength lower than the Al films, they had a higher load carrying capacity compared to the Al films and were stiffer than the PVA films under Q.S. transverse loading. The ballistic limit of the MLG/PVA films was ∼50% higher than the Al films but the higher ductility of the parent PVA resulted in the pure PVA films having a higher ballistic resistance. The ballistic resistance of the MLG/PVA is well predicted by a membrane stretching analysis and this enables us to present an outlook on the ballistic resistance potential of graphene/PVA composites comprising aligned large flakes.

Precast Fiber-Reinforced Concrete Barriers with Integrated Sidewalk

Three concepts of bridge barriers with integrated sidewalk were designed, built, and tested. Two precast barriers were designed with high-performance fiber-reinforced concrete (HPFRC)—the former with a tensile strain-softening material and the latter with a tensile strain-hardening material. Use of HPFRC allowed a significant reduction of concrete sections and reinforcement of precast barriers. Moreover, a new connection method was developed to anchor barriers to the bridge slab. One high-performance concrete (HPC) cast-in-place barrier was also designed as a reference. All barriers were submitted to quasi-static transverse loading up to failure and exceeded CSA PL2 and AASHTO TL4 design load requirements. Finite element models used at the design process provided an accurate reproduction of test results in terms of stiffness, ultimate strength, cracking pattern, and displacement. A numerical parametric study was conducted with the validated models to evaluate the effect of key economical and construction characteristics of the precast barriers.

Blast dynamics of beam-columns via analytical approach

Problems involving forced transverse vibrations of beam-columns have many applications in different fields of engineering. This paper presents an analytical procedure allowing the prediction of the blast dynamic response of a beam-column to a combined action of axial and transverse loads. The solution is based on the continuous formulation and the Euler–Bernoulli beam theory. The response of the beam-column in the quasi-static, dynamic and impulsive regimes is analysed using the developed analytical model. The analysis shows that the number of modes of vibration needed to produce an accurate estimate of the beam-column behaviour may vary depending on the loading regime. Various types of spatial load distributions and time histories of transverse loads commonly used in engineering practice for modelling of extreme loads are discussed. The significance of the axial force and the shape of the transverse load time history for the beam-column response is shown using the response spectrum and pressure–impulse diagram methods. The initial imperfections in the beam-column geometry and applied loads are introduced into the analysis and their effects are also examined. The results obtained by the analytical model are compared to the results of a nonlinear finite element analysis performed in ABAQUS. Certain discrepancies between the beam-column response yielded by the analytical solution and the finite element model were observed at high levels of axial force and quasi-static transverse loading conditions.

Interaction of inter- and intralaminar damage in scaled quasi-static indentation tests: Part 2 – Numerical simulation

A numerical study, accompanied by the experimental data from Part 1 of this paper, provides a clear picture of the global damage behaviour and local response of four scaled Carbon Fibre Reinforced Polymer (CFRP) laminates under quasi-static transverse loading. Interface elements with a cohesive formulation are employed to model delamination, matrix cracks and their interaction. The predictive damage from different numerical simulations with different levels of detail is presented, and the validity is illustrated both qualitatively and quantitatively. Specifically the number of inserted potential intralaminar crack paths is varied from no cracks, through single, then double, to multiple cracks. It is shown that the models with the capability to simulate multiple matrix cracks best predict the key aspects of barely visible damage of composite laminate during quasi-static loading.

Towards a unified methodology for the simulation of rupture in collision and grounding of ships

The aim of the work is the definition of a procedure for the numerical simulation of the response of ship structures under accidental loading conditions, which suffer various different modes of failure, such as tension, bending, tearing and crushing and in particular to investigate the effect of material modeling, i.e. material curve and rupture criterion as well as mesh size and strain rate effect on the results. To this end, different material models and simulation techniques were used for the simulation of eighteen indentation tests conducted by different research groups. The simulations were performed using the explicit finite element code ABAQUS 6.10-2. The tests refer to the quasi-static and dynamic transverse and in-plane loading of various thin walled structures which represent parts of a ship structure. Three rupture criteria are incorporated into VUMAT subroutine, which interacts with the explicit finite element code and refers to an isotropic hardening material that follows the J2 flow theory assuming plane stress conditions, in order to investigate the prediction and propagation of rupture. The focus is on investigating whether it is possible to define a unified methodology, which is appropriate for the simulation of all different tests. Consistency in the numerical results is observed with the use of an equivalent plastic strain criterion, in which formulation a cutoff value for triaxialities below −1/3 is included.

An elastic–plastic cohesive zone model for metal–ceramic interfaces at finite deformations

This study concerns an elastic–plastic cohesive zone model for metal–ceramic interfaces and the corresponding nonlinear finite element implementation for general boundary value problems that accounts for nonlinear traction separation constitutive relation including fine scale mechanisms of the bonded interfaces failure. The interfacial model, formulated in terms of geometrically nonlinear theory of plasticity, allows for localization of plastic deformation, ensuing damage and failure/fracture behavior of the interface at finite deformations. From the numerical simulations, fiber is modeled as a linearly elastic material while the constitutive relation of matrix material is modeled using large deformation of isotropic porous plastic material which includes the voids nucleate, grow and coalesce. Further, an extensive parametric study is conducted in which the effects of hardening/softening, cohesive yield stress and the damage displacement jumps in determining stress-strain response of the composite and fiber/matrix debonding process under quasi-static transverse loading. Moreover, the effects of initial yield stress and void volume fraction in the porous matrix are also considered. Results show there are significant effects of interface yield and failure/fracture as well as matrix porous plasticity on the overall deformational and failure response of composites.

Prediction Method of the Dent Depth of Composite Laminates Subjected to Quasi-Static Indentation

A method was developed to predict numerically the dent depth of composite laminates subjected to quasi-static indentation. A progressive damage analysis was conducted for composite laminates under quasi-static transverse compressive loading by using a strain based Hashin and Yeh failure criteria as well as the FEM, and a series of degraded elastic constants of the damaged zone were drawn from the numerical results. The effective elastic constants of the damaged zone of the laminates were reevaluated according to Sun’s explicit expression. Finally, the dent depth vs. indentation force curve was predicted based on Swanson’s contact theory. The numerical simulations on the static indentation tests of T700/BA9912, T700S/5228 and T700/QY9511 laminates were done via this method. The numerical results agree well with the test data in the terms of the contact force and the corresponding dent depth.

Fatigue residual strength of circular laminate graphite–epoxy composite plates damaged by transverse load

The research dealt with the relation between damage and tension–tension fatigue residual strength (FRS) in a quasi-isotropic carbon fibre reinforced epoxy resin laminate. The work was organized in two phases: during the first one, composite laminates were damaged by means of an out-of-plane quasi-static load that was supposed to simulate a low velocity impact; in the second phase, fatigue tests were performed on damaged and undamaged specimens obtained from the original composite laminates. During the quasi-static transverse loading phase, damage progression was monitored by means of acoustic emission (AE) technique. The measurement of the strain energy accumulated in the specimens and of the acoustic energy released by fracture events made it possible to estimate the amount of induced damage and evaluate the quasi-static residual tensile strength of the specimens. A probabilistic failure analysis of the fatigue data, reduced by the relative residual strength values, made it possible to relate the FRS of damaged specimens with the fatigue strength of undamaged ones.

Transverse impact behavior and energy absorption of three-dimensional orthogonal hybrid woven composites

Abstract The transverse impact behaviors of three-dimensional (3D) orthogonal hybrid woven fabric composites were tested on a modified split Hopkinson pressure bar (SHPB) apparatus. The load–displacement curves of the composites in transverse impact were obtained to analyze the strain rate sensitivity of energy absorption. It was found that energy absorption of the composites increases with the impact velocity (i.e., strain rate). The failure modes under quasi-static transverse loading are tensile failure on back side and compressive failure on the front side, while those in transverse impact are matrix cracking, fiber breakage and fiber pull-out. The 3D orthogonal woven composites have the same failure mode in the warp and weft directions. There is no delamination for the 3D orthogonal woven composites under transverse impact as observed in laminated composites.