Buckling Mode Research Articles

Incremental Deformations and Bifurcation of Elastic Solids Reinforced by Fibers With Intrinsic Extensional, Flexural, and Torsional Elasticity

Abstract We present a model for incremental deformations of an elastic solid reinforced by a single family of fibers that offer resistance to extension, flexure, and torsion. The theory is cast in the setting of small-on-large deformations and provides a framework for the multiscale analysis of bifurcation of equilibria in fibrous composites. The model is based on a theory of three-dimensional Cosserat elasticity in which fiber kinematics are controlled by a rotation field that is weakly coupled to the bulk deformation through a pointwise fiber-materiality constraint. Fiber–matrix interaction forces are explicitly accounted for via the attendant Lagrange multipliers. We demonstrate the utility of the model by investigating the onset of bifurcation in an incompressible fiber-reinforced elastic half-plane. In particular, we study the influence of axial fiber stiffness, flexural stiffness, and fiber–matrix interaction forces on planar buckling modes. We envisage a model for the study of buckling problems of biological and industrial relevance with a view to gaining better insight into the roles of fiber bending, twisting, and fiber–matrix interaction forces in regulating the buckling of fibrous composites.

Local buckling behaviour of web perforated cold-formed steel lipped channel columns

To connect beams and bracings with storage rack uprights, closely spaced perforations are provided along the web, flanges, and rear flanges of uprights. These perforations can significantly lower the ultimate capacity of such compression members with the possible influence of its natural buckling modes. This capacity reduction can depend on various parameters such as (a) geometrical shape, proportioning of cross-section, and stiffeners; (b) perforation shape, size, spacing, and location; (b) slenderness of member, cross-section, and elements of cross-section; and (d) material properties. A thorough understanding of the influence of the above-mentioned factors is necessary for the accurate strength prediction of perforated Cold-formed steel (CFS) compression members. Even though the current design standards are updated for the accurate strength prediction of unperforated CFS compression members, they do not collectively account for the influence of all the aforementioned factors on the load-carrying capacity of the perforated CFS members, particularly for the local buckling capacity. Though the Direct Strength Method (DSM) of design is the most accepted method for accurate strength prediction of CFS members even for complex cross-sectional shapes, recent research on the strength evaluation of perforated CFS members using DSM has emphasized the need for refinement in DSM. The Modified Direct Strength Method (MDSM), which accounts for the simultaneous buckling of flanges and web, includes the cross-section aspect ratio and cross-section slenderness to predict more accurately the local buckling design strength. However, it was developed only for unperforated specimens. Hence, a systematic experimental and numerical investigation was done to understand the influence of the perforation in the local buckling behavior of the lipped channel section. In total, 14 specimens, including 2 unperforated and 12 web perforated CFS lipped channel stub columns were physically tested with fixed support conditions. The Finite Element Analysis using ABAQUS software was used to conduct an extensive parametric numerical study. The results were used to compare the strength curves of DSM and MDSM and the modification in the design curves has been proposed by considering the erosion in strength due to the presence of perforation.

Influence of geometric imperfections on the seismic performance of unanchored liquid storage tanks

This paper investigates the inelastic buckling of imperfect unanchored cylindrical steel tanks subjected to seismic loads. A pushover-based seismic analysis was conducted considering the impulsive hydrodynamics pressures on the wall and base plate of the tank. Material and geometric nonlinearities were considered in the seismic analysis of the tanks. Three types of imperfections were analyzed: imperfections due to impacts, imperfections located at the bottom of the tank wall, and imperfections with the first buckling mode shape. The buckling analysis was performed for two tank geometries (one slender and one broad), and the effect of the imperfections was correspondingly evaluated. The considered imperfection amplitudes were established according to the New Zealand seismic design code for storage tanks. Additionally, amplitudes that exceed the normative limit were evaluated to further analyze the sensitivity to imperfection. The analysis revealed that geometric imperfections reduce the peak ground acceleration needed to induce buckling failure. Specifically, the critical peak ground acceleration for the slender tank decreased from 0.195 g to 0.180 g for the slender tank and from 0.600 g to 0.535 g for the broad tank. This buckling capacity reduction due to geometric imperfections were about 8 % and 11 % for the slender and the broad tanks, respectively.

Experimental Investigation of a Novel CFRP-Steel Composite Tube-Confined Seawater-Sea Sand Concrete Intermediate Long Column

In order to fully utilize sea sand in offshore engineering, a novel carbon fiber-reinforced polymer (CFRP)-steel composite tube-confined seawater-sea sand concrete (FCTSSC) column structure has been developed. This study conducts experimental investigations on FCTSSC intermediate long columns for the first time. It investigates the failure modes and the impact of the external CFRP layers number on the axial compression performance. The results reveal that the FCTSSC intermediate long column specimens exhibit the failure modes of global buckling and localized steel tube bulging. After CFRP restriction, the ultimate load bearing capacity of the specimens increased from 12.51% to 20.87%. The ultimate load bearing capacity, its enhancement percentage, and peak lateral deformation are all positively correlated with the external CFRP layers number. Finally, a summary and assessment were conducted on the applicability and accuracy of the existing load bearing capacity models, providing a reference for subsequent research.

Some Unfamiliar Structural Stability Aspects of Unsymmetric Laminated Composite Plates.

It is widely recognized that certain structures, when subjected to static compression, may exhibit a bifurcation point, leading to the potential occurrence of a secondary equilibrium path. Also, there is a tendency of deflection increment without a bifurcation point to occur for imperfect structures. In this paper, some relatively unknown phenomena are investigated. First, it is demonstrated that in some conditions, the linear buckling mode shape may differ from the result of geometrically nonlinear analysis. Second, a mode jumping phenomenon is described as a transition from a secondary equilibrium path to an obscure one as a tertiary equilibrium path or a second bifurcation point. In this regard, some non-square plates with unsymmetric layer arrangements (in the presence of extension-bending coupling) are subjected to a uniaxial in-plane compression. By considering the geometrically linear and nonlinear problems, the bucking modes and post-buckling behaviors, e.g., the out-of-plane displacement of the plate versus the load, are obtained by ANSYS 2023 R1 software. Through a parametric analysis, the possibility of these phenomena is investigated in detail.

Development and application of out-of-plane deformable X-shaped brace for energy dissipation and thermal stress mitigation: An experimental and numerical study

Exoskeleton systems are increasingly employed in both new and existing buildings to enhance seismic performance. Addressing the critical challenges of energy dissipation and thermal stress mitigation in these systems, an out-of-plane deformable X-shaped energy dissipation brace (OPD-XEDB), integrating an out-of-plane X-shaped brace with a shear-type metallic damper, was proposed in this study. A seismic design methodology for OPD-XEDB was firstly developed, ensuring effective energy dissipation of the damper before any potential brace buckling. Following this methodology, two specimens, exhibiting distinct failure modes of damper shear fracture and brace buckling, were designed and subjected to quasi-static loadings to explore their energy dissipation mechanisms. Upon these experimental results, a numerical model incorporating buckling and pinching behaviors was proposed and calibrated, effectively capturing the hysteretic responses of the specimens. This model was then employed in a comprehensive numerical analysis, validating the effectiveness of design methodology and determining the optimal specifications for the OPD-XEDB in a prototype building. Ultimately, thermal analysis and nonlinear time history analysis were conducted on the prototype building. The thermal analysis proved the effectiveness of the OPD-XEDB's out-of-plane configuration in mitigating thermal stress by out-of-plane deformation, significantly mitigating thermal stress in braces and interconnected moment frames by 96.59–96.66 %. The time history analysis revealed that the dampers in OPD-XEDBs dissipated 11.6–23.2 % of total seismic energy, effectively preventing substantial buckling in the X-shaped braces. This energy dissipation mechanism led to a remarkable 79.7 % reduction in steel consumption for post-earthquake retrofitting, thereby significantly enhancing the seismic resilience of the primary structure.

Probability model evolution laws and mechanisms of non-linear buckling capacity of single-layer spherical gridshells with topology-constrained initial imperfections

This research offers a detailed probability analysis of the non-linear buckling capacity (NBC) of single-layer gridshells (SLGs), impacted significantly by stochastic initial geometric imperfections during construction. Employing the constrained stochastic imperfection modal method, which adeptly incorporates topology constraints of actual initial imperfection scenarios. The key factors, such as the imperfection simulation method, imperfection amplitude, number of rings, and the rise-to-span ratio, are evaluated through systematic numerical analysis. The results reveal that the traditional random imperfection method cannot obtain the actual bimodal distribution of the NBC, and it can overestimate the maximum and minimum NBCs by 5.16 % and 52.49 %. Furthermore, the joint well-formedness is introduced to quantify the joint local stiffness, and it is found to have a highly intertwined correlation with the structural non-linear buckling mode. The evolution mechanism of probability models can be elucidated through the joint initial deviations leading to changes in joint well-formedness (i.e., local stiffness), based on which it is concluded that an imperfection amplitude of 1/1500 of the structural span should be recommended to be the imperfection amplitude acceptance limit to fully utilize the structural global buckling capacity; significant deviations in primary rib joints and inner ring joints markedly affect the NBC more than those in non-primary rib joints and outer ring joints. The aforementioned conclusions are essential for revising guidelines for permissible joint deviations and assessment methodologies for critical joints throughout the construction.

Harnessing unconventional buckling of tube origami metamaterials based on Kresling pattern

Kresling tube metamaterials are well known to exhibit a chirality-dependent exotic mechanical feature: a shortening or lengthening in the direction of the tube’s axis produces a relative rotation of the two polygonal bases of the tube. This property can be easily grasped by fabricating a single-storey Kresling tube using cardboard. What has not been stressed much, if not even recognized, in the literature is the fact that such a mechanical feature is not depending only on the (chiral) geometrical pattern and unaffected by the in-plane/bending stiffness of facets and the creases’ resistance to folding. Assuming to neglect the bending stiffness of facets, in the present contribution we prove, through some numerical simulations based on a discrete model taking into account inertial terms, that only when the in-plane-to-folding stiffness ratio is large the Kresling tube exhibits the aforementioned exotic feature as described in the literature. We also prove that a low in-plane-to-folding stiffness ratio reveals: (i) an unconventional buckling mode, both for axial shortening and lengthening, which resembles the mechanism of a camera diaphragm; (ii) a kind of auxetic behavior, i.e. a stenosis in a shortening test.

Symmetry breaking and high-order instability of telephone cord buckles triggered by in-plane gradients of thin films

Buckle delaminations are ubiquitous in natural and artificial systems including tectonic plates, biological tissues, film structures, and two-dimensional materials. Although the formation and manipulation of various buckle delaminations have been extensively investigated in the past few decades, understanding complex buckle delamination patterns is still a challenge. Here we report on the symmetry breaking and high-order instability of telephone cord (TC) buckles triggered by in-plane gradients of thin films, including strain gradient and thickness gradient. Our experimental observations reveal the unique morphological profile of the asymmetric TC buckle due to the strain gradient. Impact of in-plane strain gradient on morphological changes of TC buckles is elucidated by simulations of buckling and delamination of the thin film. Phase diagrams for five buckle delamination morphologies, i.e., symmetric TC buckle, asymmetric TC buckle, symmetric bilateral branched buckle, asymmetric bilateral branched buckle, and unilateral branched buckle with respect to average strain and strain gradient (or thickness gradient) have been numerically established. This work could promote a better understanding of complex buckle delamination patterns with symmetry breaking and high-order instability and controllable fabrication of ordered buckle delamination patterns by regulating in-plane gradients of thin films.

The role of unit cell topology in modulating the compaction response of additively manufactured cellular materials using simulations and validation experiments

Additive manufacturing has enabled a transformational ability to create cellular structures (or foams) with tailored topology. Compared to their monolithic polymer counterparts, cellular structures are potentially suitable for systems requiring materials with high specific energy-absorbing capability to provide enhanced damping. In this work, we demonstrate the utility of controlling unit-cell topology with the intent of obtaining a desired stress–strain response and energy density. Using mesoscale simulations that resolve the unit-cell sub-structures, we validate the role of unit-cell topology in selectively activating a buckling mode and thereby modulating the characteristic stress–strain response. Simulations incorporate a linear viscoelastic constitutive model and a hyperelastic model for simulating large deformation of the polymer under both tension and compression. Simulated results for nine different cellular structures are compared with experimental data to gain insights into three different modes of buckling and the corresponding stress–strain response.

Optimization-free design of stiffened thin-walled structures guided by data-rich buckling modes

Regarding the buckling resistance design of thin-walled structures, the conventional iterative optimization approaches pose significant challenges for engineering professionals and create a high barrier for structural designers. This study introduces a novel approach for the anti-buckling design of stiffening ribs, which is based on the solved linear buckling modes rather than on the buckling load factors (BLFs) as in traditional iterative optimization methods. Specifically, the design process begins with a linear buckling analysis of the pre-stiffened part to extract the first-order eigenmode shape. Subsequently, normal vectors are calculated for both the pre-buckling geometric model and the buckled mode shape. By analyzing the normal deflection angle, a group of characteristic points is identified, and these points would be used to serve as guidelines for determining the layout of the stiffening ribs. We validate the effectiveness and efficiency of the proposed protocol through numerical examples spanning from 2D to 3D space considering different loading conditions. Our approach eliminates the need for tedious parametric modeling and high computational cost associated with conventional optimization-based methods. It is particularly well-suited for engineering applications that solely require linear buckling analysis.

Post-buckling behavior of variable-arc-length elastica pipe conveying fluid including effects of self-weight and pressure variation

This paper investigated the post-buckling behaviors of a variable-arc-length (VAL) elastica pipe caused by internal transporting fluid motion, accounting for the effects of the self-weight and variation of internal fluid pressure. Both weak-form and strong-form formulations of the VAL elastica pipe were developed. The weak-form formulation was derived by the virtual work principle, and later solved using the nonlinear finite element method (FEM). The strong-form formulation was derived using equilibrium of the force and moment equations, the geometrical relationship of the differential pipe segment, and the energy conservation of the transported fluid. Because of the large displacement analysis, the variation in the internal pressure inside the pipe was considered, which was taken into account by energy conservation based on the Bernoulli principle. Then, the set of nonlinear governing first-order differential equations, corresponding to the two-point boundary value problem, was conveniently solved using the shooting optimization method (SOM). The numerical results obtained from the presented FEM and SOM analyses independently verified each other, with good agreement between these two methods. The parametric study considered the effects of gravity load (pipe and fluid self-weights) and internal fluid pressure on the post-buckling characteristics of the VAL pipe. The numerical results showed that without the pipe and internal fluid weights, the transporting fluid exerted an axial compressive force on the pipe, causing post-buckling phenomena. Beyond the critical state, the support rotation and the length of the VAL pipe increased as the internal fluid velocity decreased. Finally, by including the effect of self-weight, the mode exchange of the odd buckling modes (1st and 3rd modes) was found from the load-displacement path.

A comparative analysis of compressive and wear failure of laser-powder bed fused Stainless Steel 316L produced with different hatch spacing in stripe and contour patterns

The selection of hatch spacing is crucial in additive manufacturing processes to produce a defect free Stainless Steel 316L (SS) components, especially in laser powder bed fusion (LPBF) process. Improper selection of hatch spacing could lead to various failure regimes (like vertical cracking, porosity, and un-melted particles) in Stainless Steel 316L (SS) component produced through laser powder bed fusion (LPBF). Further, the failure regimes have a direct impact on the hardness, compression strength, friction, and wear properties of LPBF SS components. The present study has taken substantial efforts to analyse the impact of various hatch spacing (0.08 mm, 0.10 mm. and 0.12 mm) in stripe and contour patterns, in terms of morphology, mechanical, and tribological properties of LPBF SS components. Also, the present study elucidates how variations in hatch spacing influences the features like particle fusion, crack formation, density, hardness, surface roughness, compression, and wear properties. The stripe pattern with low hatch spacing of 0.08 mm showed better particle fusion and high surface roughness; whereas the high hatch spacing has produced voids, un-melted powder particles, and cracks in the stripe and contour pattern. High densities and hardness values were attributed to the stripe patterns with more effective melting and fusing of powder particles. XRD analysis revealed the stable phase compositions across various hatch spacing with a predominant FCC crystal structure. Residual stress distribution was significantly influenced by the hatch spacing for both stripe and contour patterns. Importantly, the low hatch space leads has promoted the tensile residual stress formation and vice versa for the higher hatch spacing. Stripe patterns showed higher compression strengths with buckling and shear mode as a compression failure. The stripe pattern demonstrated a low specific wear rate (SWR) and coefficient of friction (COF) compared to the contour pattern, with respect to the various hatch spacing. Furthermore, the simulated body fluid (SBF) lubrication regime played a significant role in reducing the COF. Patches, groves, furrows, and craters demonstrated the abrasive and adhesive failure for both stripe and contour pattern, which is further detailed in the article.

Stability assessment of CIPP liner under varied boundary conditions: A theoretical and simulation study

The buckling of liners carries significant implications, including hampered medium transmission, structural damage, and the risk of leaks, adversely affecting production, economy, and the environment. The interface performance between Cured-in-place-pipe (CIPP) liners and host pipes is pivotal for overall structural stability. However, this interface's influence has been underestimated in engineering practices and laboratory research. This study introduces two novel hydrostatic pressure buckling models, enhancing constrained arch and energy-based Glock models, while considering both free and bonded boundary conditions. Subsequently, a validated 3D finite element model of CIPP lined pipes is established from full-scale tests. Through comprehensive sensitivity analysis, the study investigates the influence of diameter-to-wall thickness ratio (DR) and annular gap on liner buckling under free boundary conditions. Additionally, it explores the effects of DR value and ovality ratio on buckling behavior under bonded conditions. Results reveal distinct buckling and post-buckling modes under different boundary conditions. The proposed theoretical analysis method accurately predicts critical buckling pressure within a 10 % error margin, validated through experiments and numerical simulations, offering practical guidance for assessing repaired pipe stability.

Experimental and numerical study on energy absorption performance of truncated origami materials

In this study, a truncated origami structure, originated from the Miura-ori structure, was designed. The compressive behaviors of this structure subjected to x2-direction (in-plane) and x3-direction (out-of-plane) compression were studied both experimentally and numerically. The structure with a smaller truncated ratio value, e, was more similar to a dense solid. Representative specimens of the Miura-ori and the truncated origami designs were fabricated and tested under both quasi-static and dynamic (v = 7 m/s) conditions. Compared to the Miura-ori structure, the truncated origami showed higher specific energy absorption (SEA) and less load drop between the initial peak force and mean crushing force. In both loading directions, the SEA increased as the truncated ratio decreased for the truncated origami specimens, which was comparable under both quasi-static and dynamic loading. The truncated origami was extrapolated to a numerical model with 5 × 5 × 5 cells to mimic a block of material, and the effects of truncated ratio and loading velocity were investigated. As the e decreased, the deformation mode gradually changed from rigid folding and progressive deformation to plate buckling mode under quasi-static compression. This change was accompanied by an increase in both SEA and overall strength. The truncated origami exhibited the best energy absorption performance when e = 0.4. Under quasi-static compression in the x2- and x3-direction, the SEA of truncated origami is 3.2 and 1.6 times that of Miura-ori metamaterial, respectively. The truncated origami materials with a truncated ratio of 0.8 remained velocity-insensitive up to 25 m/s and displayed similar strength and deformation modes as under quasi-static loading. At a speed of 50 m/s the deformation became more localized, and the SEA increased significantly. The auxetic and expansion behaviors were significantly diminished under higher impact velocities.

Topologically protected hierarchical buckling modes of compressed thin films on Winkler substrates

Patterns created by buckling of thin films on substrates have important applications in many fields such as functional devices and surface engineering. Introducing hierarchy to such patterns may further enhance their functionalities. However, unpredictable geometrical and material defects may disturb the formation of patterns. It is thus attractive to construct robust hierarchical buckling patterns that are insensitive to defects. Here, inspired by the construction of topologically protected localized states insensitive to defects in wave mechanics, a thin film of finite length bonded on a simple Winkler substrate is quantitatively designed by just varying its width continuously. Under the action of specific compressive stresses within such a continuous thin film owing to thermal mismatch between the film and substrate, there really exists a hierarchical film-buckling mode generated by topologically protected localization. Conditions under which the topologically protected localization exists are given explicitly, and the underlying mechanism is intuitively demonstrated from the mechanical point of view. Moreover, an analytical solution for the decay rate of localization is obtained as a satisfactory second-order approximation, from which the associated influencing factors are clearly identified. This work is expected to provide a theoretical guidance for the design and optimization of hierarchical patterns in film/substrate systems via the concept of topology.

Jute/PP composites for covering honeycomb panels: Designability and mechanical behaviors

An approach involving low energy consumption was used to transform jute/polypropylene prepregs into a sustainable sandwich structure for automotive application. Fiber orientation and stacking sequence were modified to investigate their influence on the physical-mechanical properties of the prepregs as well as cyclic flexural properties, compression fatigue behaviors and 3D microstructure of honeycomb sandwich panels. The mechanical properties of the face sheets were comparable with GF-SMC; but since they are derived from natural fiber they present a more sustainable and renewable alternative to GF-SMC. Stacking sequence and fiber orientation were found remarkably factors for the limitation of structure and performance design. The honeycomb panels occurred fatigue failures under the compression cyclic loading for 131–547 times. The flexural and shear buckling modes correlated with each other and all the materials failed in a combination of face wrinkling, partial crushing and debonding. It was found that the prepregs could provide more possibilities for optimum structural design of honeycomb sandwich panels, benefiting for the applications in the automotive lightweight field.

Axial compressive stability design of longitudinal asymmetrical shuttle-shaped columns

Longitudinal asymmetrical shuttle-shaped column (LA-SSC) has found its wide application when subjected to combined axial compression and horizontal point load in practical engineering. This paper focuses on elastic and elasto-plastic buckling behaviors of the LA-SSC only under axial compression and the resulting outcome could provide an indispensable basis for further establishing buckling strength prediction of LA-SSC under axial compression and horizontal point load. At first, the elastic buckling behavior of tapered columns (TC) and longitudinal symmetrical shuttle-shaped columns (LS-SSC) are derived in theory and verified by finite element numerical results, and corresponding elastic buckling modes are discussed. Subsequently the elastic buckling load prediction of LA-SSCs is established first and the corresponding normalized slender ratio, as a key design parameter, is generalized. Finally, the stability capacity of LA-SSCs is involved in theoretical analysis and finite element (FE) numerical calculation under axial pressure. Through investigating the axial load-lateral displacement curves and axial stress distributions the buckled LA-SSCs, the effects of different parameters (such as overall length, plate thickness, and steel strength) on the axial compression stability capacity of LS-SSCs are explored. As a result, the complete design formulas for axial compression stability capacity of LA-SSCs are presented first and compared with current major design codes in various countries. It is observed that the proposed strength design formulas are in good correspondence with the FE numerical results. The proposed formulas could provide references and guidance for the axial compression buckling strength of LA-SSCs under axial compression and they further supply fundamentals for establishing the strength design recommendation of LA-SSCs under axial compression and bending moments.

Contact states of tubular strings during sinusoidal buckling transitions in a horizontal wellbore

Scholars working in the oil and gas industry have extensively researched the buckling behavior of downhole tubular strings. However, in most theoretical research, continuous contact between tubular strings and wellbores is assumed, which is not always true in experiments. To address this issue, a buckling model for a tubular string placed inside a horizontal wellbore using the beam-column model is built in this paper. Two contact states of the tubular string were considered: point contact and partial continuous contact. The model indicates that reducing the angular displacement of the wave peak position facilitates the tubular string's transition from point to partial continuous contact. Additionally, a higher gravity load or smaller radial clearance increases the likelihood of partial continuous contact. A new displacement calculation method has been proposed based on the buckling model. Using this method, the entire process of contact state changes of a tubular string is simulated under the sinusoidal buckling mode in this study. The results show that the contact state of the tubular string under sinusoidal buckling cannot be assumed to be a continuous contact state, and a theoretical foundation for various evaluations based on the buckling deformation of tubular strings is provided in this study.

Axial compression tests on CFRP strengthened CFS plain angle short columns

A comprehensive test program was performed to experimentally investigate the effect of CFRP strengthening on the axial strength and stability of CFS plain angle short columns subjected to monotonic axial compression. A total of 28 specimens were tested by varying the CFRP strengthening configurations for different column heights. Both uni-directional (CF_UD) and bi-directional (CF_BD) CFRP were considered. The influence of various parameters such as the type of CFRP, fiber orientation, and number of CFRP layers was investigated and discussed in detail. For single layer (ply) of CFRP, CF_UD-0° strengthening configuration resulted in maximum increase of axial capacity by 58.33% and 45.72% (in comparison to bare steel specimens), corresponding to 0.5 m and 1.0 m column lengths respectively. All the bare steel and skin-strengthened specimens failed predominantly due to torsional–flexural buckling mode. Additional layer of CFRP wrapping was found to enhance the axial capacity further and CF_UD-0°/BD was found to possess greater capacity in the case of double layer of CFRP. Adopting cardboard in-fill in addition to CF_UD-0° wrap has prevented the torsional mode of buckling and resulted in a peak increase of axial capacity by 192.55% and 240.61% corresponding to 500 mm and 100 mm long specimens, respectively.