Conventional Carbon Fiber Reinforced Polymer Research Articles

Analytical model for RC beams with embedded prestressed Fe-SMAs

Prestressed iron-based shape memory alloy (Fe-SMA) strengthening is an effective means to enhance the performance of reinforced concrete (RC) structures. The applied prestress level significantly influences the strengthening efficiency. However, the absence of a reliable model predicting the applied prestress hinders the efficient design of prestressed Fe-SMA strengthening solutions. To fill this gap, the current study proposes an analytical model, with which a constant zone and a transfer zone are identified in strengthened RC beams. The constant zone, with zero interfacial shear stress, sustains a constant prestress level, while the transfer zone, experiencing non-zero shear stress, gradually reduces the Fe-SMA tensile stress from the prestress level to zero. Validated through experiments, the proposed model accurately predicts the applied prestress levels and prestress-induced deflections in RC beams strengthened with Fe-SMAs and more conventional carbon fiber reinforced polymers (CFRPs). Further analysis reveals that the transfer zone length ranges from 4 to 7 characteristic lengths, and it is proportional to the logarithm of the applied prestress level. Simplifying a constant prestress level within the beam span yields sufficiently accurate prestress analysis.

Study of CFRP Laminate Gradually Modified throughout the Thickness Using Thin Ply under Transvers Tensile Loading.

The use of thin-ply composite materials has rapidly increased due to their tailorable mechanical properties and design flexibility. Considering an adhesively bonded composite joint, peel stress stands out as a key contributor leading to failure among other primary stress factors. Therefore, the reinforcement of carbon fiber-reinforced polymer (CFRP) laminates throughout the thickness could be considered as an approach to improve the joint strength. Using thin plies locally between the conventional CFRP layers in a laminate can enhance the strength, as the sudden change in stiffness means that the load transfer is not monotonous. Consequently, the following study examined the effect of altering thin plies gradually throughout the thickness on the behaviour of the CFRP laminates when subjected to transverse tensile loading. To achieve this goal, the CFRP laminates were gradually modified by using different commercially accessible prepreg thin plies, leading to an improved overall structural performance by reducing stress concentrations. Besides conducting an experimental study, a numerical assessment was also carried out utilizing Abaqus software with a Representative Volume Element (RVE) at the micro scale. The comparison of reference configurations, which involved various thin plies with different thicknesses and traditional CFRP laminates, with the suggested gradual configuration, demonstrated a notable enhancement in both strength and material cost. Furthermore, the proposed RVE model showed promising capability in accurately forecasting the strength of fabricated laminates.

Bio-Based Pultruded CFRP Laminates: Bond to Concrete and Structural Performance of Full-Scale Strengthened Reinforced Concrete Beams.

This paper presents an experimental study about the use of innovative bio-based pultruded carbon-fiber-reinforced polymer (CFRP) laminates for structural strengthening. The bio-based laminates were produced in the framework of an applied research project (BioLam) using a resin system with 50% (wt.%) bio-based content, obtained from renewable resources. In the first part of the study, their tensile and interlaminar shear properties were characterized and compared with those of conventional oil-based CFRP laminates. In the second part of the study, the bond behavior to concrete of both types of CFRP laminates applied according to the externally bonded reinforcement (EBR) technique was assessed by means of single-lap shear tests performed on CFRP-strengthened concrete blocks; the experimental results obtained from these tests were then used in a numerical procedure to calibrate local bond vs. slip laws for both types of laminates. The final part of this study comprised four-point bending tests on full-scale EBR-CFRP-strengthened reinforced concrete (RC) beams to assess the structural efficacy of the bio-based laminates; these were benchmarked with tests performed on similar RC beams strengthened with conventional CFRP laminates. The results obtained in this study show that the (i) material properties, (ii) the bond behavior to concrete, and (iii) the structural efficacy of the developed bio-based CFRP laminates are comparable to those of their conventional counterparts, confirming their potential to be used in the strengthening of RC structures.

Understanding friction and wear properties of carbon fiber/epoxy stitched composites

Due to its low friction coefficient and wear rate, and good self-lubrication, carbon fiber reinforced polymer (CFRP) composite is used as friction material. The easy interlaminar delamination and low impact damage tolerance of conventional CFRP laminates lead the friction materials to wear seriously, which causes the early-stage failure. Here, carbon fiber/epoxy stitched composites were prepared by the resin transfer molding technology. Effects of load and stitch parameters on the friction and wear properties of stitched composites under dry conditions were investigated through experiment and simulation. The coefficients of friction (COFs) of composites increase linearly at the initial stage, and then decrease from a maximum peak to a relatively stable state value. Samples with a high stitch density and a small stitch spacing along the sliding direction has low COF values and wear rates. With the increase of the normal load, COFs and the wear rate both decrease first and then increase. The wear tracks on the surface of CF/EP stitched composites are generated by comprehensive effects of cutting, adhesive and fatigue wears. This study provides comprehensive characterization and deep understanding of friction and wear properties of carbon fiber/epoxy stitched composites, which will broaden the CFRP application as frication material.

Using Harris Hawk algorithm for experimental study on the hole dilation mechanism during Micro-machining (μM) of Graphene nanoplatelets/Carbon fiber (GnP/C) reinforced polymeric composite

This article highlights the hole generation mechanism in the Graphene nanoplatelets/Carbon fiber (GnP/C) reinforced polymeric composite. The lower conductivity of conventional carbon fiber reinforced polymer (CFRP) composites restricts the μEDM (Micro Electrical discharge machining) test. This limitation is overwhelmed by adding highly conductive GnP powder in the CFR (epoxy) polymer composites. The generation of the drilled hole is possible through the increase in the electrical conductivity of the samples. During μEDM, in order to examine the quality of machined holes in terms of hole dilation (HD), different process constraints such as voltage (80, 120, 160 V), pulse on time (30, 40, 50 s), and weight percentage of GnP (0.25, 1, 1.75%) are evaluated (HD). The hole dilation was significantly influenced by GnP concentration and voltage alteration during the micromachining process. Analysis of Variance (ANOVA) results confirmed that the GnP concentration (67.51%) was the most prominent factor affecting hole dilation. The high-resolution microscopy test was performed to investigate the hole machined surface and damages occur during the micromachining test. The variation in the thermal nature of carbon fabric and resin generates internal stress between the composite material, which results in micro-cracks developed in the laminates. The varying parameters were controlled and optimized through a recently developed nature-inspired metaheuristics algorithm based on the conduct of Harris Hawk (HH). The optimal parametric condition for the hole dilation is voltage (level 1–80 volt), pulse duration (level 1–30 μs), and GnP concentration% (Level 1–0.25). The findings of the validation test demonstrate the application potential of the proposed Harris Hawk algorithm.

A study of the fracture mechanisms of hybrid carbon fiber reinforced polymer laminates reinforced by thin‐ply

AbstractThe main stress component which creates delamination in bonded single lap joints with composite adherends is the transverse tensile stress. Therefore, the following study investigates the behavior of composite laminates (reference and hybrid laminates reinforced by thin‐ply) under transverse tensile loading. Texipreg HS 160T700 and NTPT‐TP415 were used as the conventional carbon fiber reinforced polymer (CFRP) and thin‐ply respectively. Hybrid composite laminates were studied using different amounts of thin‐ply, applied through the thickness. The manufactured laminates, of unidirectionally stacked construction, were tested under transverse tensile loading. Digital image correlation was performed to investigate the average peel strain distribution for the composite and to better understand the phenomena associated to the use of hybrid laminates. Experimental results show that the reinforced hybrid composite laminates, created using thin‐plies, present higher failure load compared to the reference conventional CFRP or thin‐ply laminates. This was found to be due to the higher ductility enabled by the presence of thin‐plies. Distributing a constant amount of thin‐ply through the thickness was found to increase the laminate transverse strength, as the thin‐ply laminates act as a barrier against crack propagation. A representative volume element was studied for each configuration since this numerical method brings the opportunity to investigate the studied configurations in microscale.

Investigation into Thermomechanical Response of Polymer Composite Materials Produced through Additive Manufacturing Technologies.

This paper presents the static mechanical behavior and the dynamic thermomechanical properties of four market-available reinforced and non-reinforced thermoplastics and photopolymer materials used as precursors in different additive manufacturing technologies. This article proposes a characterization approach to further address development of aeronautic secondary structures via 3D-printed composite materials replacing conventional manufactured carbon fiber reinforced polymer (CFRP) composites. Different 3D printing materials, technologies, printing directions, and parameters were investigated. Experimental results showed that carbon-reinforced ONYX_R material exhibits a transition point at 114 °C, a 600 MPa tensile strength, and an average tensile strain of 2.5%, comparable with conventional CFRP composites manufactured via autoclave, making it a suitable candidate for replacing CFRP composites, in the aim of taking advantage of 3D printing technologies. ONYX material exhibits higher stiffness than Acrylonitrile-Butadiene-Styrene Copolymer (ABS), or conventional Nylon 6/6 polyamide, the flexural modulus being 2.5 GPa; nevertheless, the 27 °C determined transition temperature limits its stability at higher temperature. Daylight High Tensile (further called HTS) resin exhibits a tensile strength and strain increase when shifting the printing direction from transversal to longitudinal, while no effect was observed in HighTemp DL400 resin (further called HTP).

A feather-inspired interleaf for enhanced interlaminar fracture toughness of carbon fiber reinforced polymer composites

Carbon fiber reinforced polymer (CFRP) composites with lightweight, high-strength and high-modulus properties are in high demand across the fields of aerospace engineering , urban mass transit, new energy and architectural design . However, most CFRP composites suffer from delamination owing to the weak interlayer which plays an important role to transfer perpendicular load to plies. Here, inspired by natural hierarchical structures of feathers, a novel interleaf towards conventional CFRP composites was rationally designed and experimentally proved to be effective for significant enhancement of anti-delamination performance. Interestingly, ZnO nanorods grown on the electrospun nanofibrous mats and carbon fiber bundles formed a kind of cross-scale structure system. It was very similar to the natural hierarchical structures of feathers with rachis, barbs and barbules. Experimental results verified that the introduced hierarchical structures assuredly enhanced the interlayer toughening performance via substantial energy dissipation . When compared with original CFRP composites, the obtained CFRP composites with a feather-inspired interleaf exhibited significantly improved mechanical performance in Mode I and Mode II interlaminar fracture toughness . The proposed bio-inspired design philosophy and feasible fabrication method are anticipated to provide an industry-friendly way to effectively improve the mechanical performance of traditional CFRP composites and promote potential large-scale applications of bio-inspired CFRP composites in the broad engineering field. TOC: Inspired by natural hierarchical structure of feathers, a novel interleaf was designed and fabricated to enhance the mechanical performance of CFRP laminates, which provides a promising and versatile design strategy for the effective mechanical improvement of laminated composites.

Carbon fiber-reinforced polyamide composites with efficient stress transfer via plasma-assisted mechanochemistry

Carbon fiber-reinforced polymers (CFRPs) show excellent mechanical strength and lightweight. However, conventional CFRPs require high loading of carbon fibers (CFs) to improve their mechanical properties due to poor polymer–CF interfacial adhesion. We propose a dry and ecofriendly method to fabricate high-performance CFRPs by improving interfacial adhesion. The plasma-assisted mechanochemistry (PMC) process can create physical and chemical linkages between polymers and carbon fillers via application of a mechanical force and plasma treatment. We use carbon nanotubes as bridge materials to increase the effective interfacial area and promote mechanical interlocking. The PMC-treated CFRPs exhibit reduced C-factor and increased degree of entanglement, indicating efficient stress transfer the polymer to the filler. Additionally, the PMC process can provide the significantly improved mechanical properties of CFRPs even at low CF loading. Notably, the PMC-treated CFRPs showed continuously increasing tensile strength, Young's modulus, and elongation at break with increasing CF content up to 30 wt%, which has not been observed previously for CFRPs. As a result, the tensile strength, Young's modulus, and elongation at break of the PMC-treated composites with a CF content of 30 wt% increased by 47.1%, 43.0%, and 91.7%, respectively, compared to those of the conventional composites. We believe that this simple approach opens a new route to the fabrication of high-performance CFRPs exhibiting extraordinary mechanical properties.

Engineering the electrospinning of MWCNTs/epoxy nanofiber scaffolds to enhance physical and mechanical properties of CFRPs

A cost-effective approach to improve the physical and mechanical properties of carbon fiber reinforced polymer (CFRP) prepreg composites, where electrospun multiwalled carbon nanotubes (MWCNTs)/epoxy nanofibers were synthesized and incorporated in between the layers of conventional CFRP prepreg composite has been presented. MWCNT-aligned epoxy nanofibers were successfully produced by an optimized electrospinning process. Nanofibers were deposited directly onto prepreg layers to achieve improved adhesion and interfacial bonding, leading to added strength and improvements in other mechanical properties. Thus, interlaminar shear strength (ILSS) and fatigue performance at high-stress regimes increased by 29% and 27%, respectively. Barely visible impact damage (BVID) energy increased significantly by up to 45%. The thermal and electrical conductivities were also enhanced significantly due to the presence of the highly conductive MWCNT networks between the CFRP layers. The presented method was capable of uniformly depositing high contents of MWCNTs at interlaminar ply interface of prepregs to strengthen/enhance CFRP properties, which has not been previously shown to be possible due to high resin viscosity caused by randomly oriented MWCNTs in epoxy system.

Thermally stable and highly recyclable carbon fiber-reinforced polyketone composites based on mechanochemical bond formation

Compounding polyketone (PK) with carbon fibers (CFs) can provide composites that exhibit excellent properties. However, the thermal stability of PK itself is poor, limiting practical applications at high temperatures. Herein, a novel process is proposed to improve the thermal stability of PK-based carbon fiber-reinforced polymers (CFRPs). The plasma-assisted mechanochemistry (PMC) process creates mechanochemical bonds between materials under dry conditions, reducing polymer chain mobility at high temperatures and increasing the stiffness. Compared with conventional PK-based CFRPs, PMC-processed CFRPs have significantly higher glass transition temperatures and storage modulus, resulting in improved thermal stability. The tensile strength remained >90% after annealing at 150 °C for 1000 h. Moreover, despite repeated thermal hysteresis, the recycled PK-based CFRPs showed tensile strength, Young's modulus, and elongation at break that were >90% of initial values. This work provides a feasible and ecofriendly strategy to expand the applications and promote repeated recycling of PK-based CFRPs.

Experimental Study of a New Strengthening Technique of RC Beams Using Prestressed NSM CFRP Bars

The reinforcement of structural elements subjected to bending with carbon fiber reinforced polymers (CFRP) located on the underside of the element to be reinforced (known as near surface mounted or NSM) is an effective technique that provides environmentally sustainable solutions in the field of civil engineering. Introducing preloads on the reinforcing elements allows us to maximize the high performance of CFRPs, besides recovering deformations. A new technique to perform the pre-stressing of CFRP bars in NSM configuration is described in this paper. The technique introduces the preload on the rods after they have been placed in the grooves, and with a system that acts and reacts against the beam itself. We also present the results of a testing campaign conducted to determine the effectiveness of said technique. Breakage of the control beams (without reinforcement) was ductile, while breakage of reinforced beams was explosive. Pre-stressing the reinforcing elements allowed us to increase the bearing capacity of the beams 170% compared to the control beams, also resulting in an increase in the rigidity of the reinforced elements and a decreased cracking of the beam. The results however are only slightly better than those of a conventional CFRP NSM reinforcement, due to the appearance of cavities in the groove where the adhesive didn’t manage to penetrate.

Highly improved interfacial affinity in carbon fiber-reinforced polymer composites via oxygen and nitrogen plasma-assisted mechanochemistry

Compounding polymers with carbon fibers (CFs) is a highly effective means of producing polymer composites with enhanced mechanical properties. However, in most conventional carbon fiber-reinforced polymer (CFRP) composites, mechanical improvements are limited by low interfacial affinity between the polymer and the CFs. The plasma-assisted mechanochemistry (PMC) process described herein resulted in covalent bonds between the polymer matrix and CFs, greatly increasing the interfacial affinity between the two materials and allowing the efficient transfer of stress from the polymer to the CFs. Polyketone (PK) and CFs were compounded via PMC processing under O2, N2, and Ar plasmas, and carbon nanotubes (CNTs) were introduced at the PK/CF interface. The resulting PK/CNT/CF composites exhibited significantly improved mechanical properties, especially when treated with O2 and N2 plasmas. The tensile strength and Young's modulus of O2 plasma-treated composites increased by 20% and 31%, respectively, compared to those of conventional composites. This approach is generally applicable to the development of high-performance CFRP composites.

Thermo-Mechanical Buckling of CFRP Cylindrical Shells with FGPM Coating

In this paper, the buckling behaviors of cylindrical shells made of a new kind of carbon fiber reinforced polymer (CFRP) and coated with functionally graded polymeric material (FGPM) are investigated. The fundamental equations of a moderately-thick shell are established within the framework of Reddy’s higher-order shear deformation theory (HSDT). The material model is derived by combining the conventional micro-mechanical CFRP model with the hybrid FGPM model. Micro-crack damage in CFRP core is included via the damage variables. The buckling compressive stresses of the shells exposed to the thermal environment are obtained by the Galerkin’s method. The solutions reveal that the lay-up sequence of the laminas and the thickness ratio of the FGPM coating to CFRP core have significant influence on the computed results. The variation of the buckling loads with respect to the content of carbon fiber and distributed profile of the FGPM components follows some nonlinear laws. The structural instability induced by damages appear to be more remarkable with the increased shell thickness. However, this effect can be reduced by optimizing the ply angles of the stacking laminas. More factors, such as geometric parameters, numbers of fiber layers, lamina stacking sequences, damage, material properties and thermal loads, are also discussed in detail.

Numerical study on the bond between CFRP rod panels (CRPs) and concrete

In this study, finite element (FE) models are developed to examine the interfacial behavior of a new retrofitting system comprised small diameter carbon fiber reinforced polymer (CFRP) rods spaced apart a distance larger than the rod diameter. The CFRP rod panel (CRP) is adhesively bonded to the concrete surface. The study explores several key parameters, including bond-slip (τ-δ) relation, effective bond length, rod diameter (D), and rod spacing-to-diameter (S/D) ratio. The models were validated against previous double-lap CRP-concrete block tests. A bilinear (τ-δ) model that provides a good correlation to the failure loads of the entire range of specimens was established. The effective bond length was found for two commonly used CRPs, and was 85 mm for one with D = 2 mm and S = 6.35 mm, and 115 mm for that with D = 4 mm and S = 9.50 mm. A parametric study using 20 FE models was carried out, considering four rod dimeters (1–4 mm) and five S/D ratios (2.2–3.18). It was found that although debonding failure consistently governs; decreasing (D) or increasing (S/D) ratio increases the ultimate strength. The effect of (S/D) ratio is more pronounced for D = 1 mm than other diameters. The study also found that debonding load of CRP is 51% higher than that of an externally bonded conventional CFRP plate of similar cross-sectional area and mechanical properties.

Thermal stress measurement in steel plate strengthened by CFRP and aluminum alloy plates

In steel members strengthened by carbon-fiber reinforced polymer (CFRP) plates, the thermal stresses are introduced in the steel members, the CFRP plates and the adhesive layers when temperature changes because the linear thermal expansion coefficients of steel and CFRP are mismatched. As so far, the authors proposed a technique to reduce the thermal stress in steel members strengthened by CFRP plates, which involves bonding aluminum alloy plates with CFRP plates. In the proposed method, the thermal stress in steel member can be reduced so that there are negligible levels of stress in steel member when the cross sectional areas of CFRP and aluminum plates are designed to correspond to the coefficient of thermal expansion of steel, even though the thermal stresses are introduced in the CFRP and aluminum plates. In this study, to confirm the maintaining the thermal stress reduction in steel member by proposed method, thermal stress measurement in steel plate strengthened by CFRP and aluminum plates was carried out about 21 months. In this research, the thermal stress introduced in the steel plate strengthened by CFRP plates was also measured. Furthermore, to assume the thermal shear and normal (peel) stresses in adhesive layers, FE analysis with plane stress element was employed. As the result, it was shown the thermal stresses in steel plate with CFRP plate were able to calculate by using composite theory and measured temperature. Furthermore, in steel plate strengthened by CFRP and aluminum plates, the thermal stress introduced in steel plate was negligible-small through the all-season. It was found the thermal stresses in steel plate with CFRP plates as well as CFRP and aluminum plates were also estimated by using composite theory and measured temperature. In the steel plate strengthened by CFRP and aluminum plates, the thermal shear and normal stresses in adhesive layer glued to steel plate become smaller than that in the conventional CFRP bonded specimen. However, the shear stress in adhesive layers between CFRP and aluminum plates in proposed method was higher than the thermal stress in adhesive layers between CFRP plates in conventional method.

Flexural behavior of preloaded reinforced concrete beams strengthened by prestressed CFRP laminates

This study focuses on evaluating flexural behavior of preloaded reinforced concrete beams (RC) strengthened with pre-tensioned (prestressed) carbon fiber reinforced polymer (CFRP) laminates. A technique for tensioning and application of pre-tensioned CFRP laminates strengthening system were developed. In order to verify the effectiveness, a total of twelve RC beam specimens were strengthened and tested under monotonic three-point loading up to failure. For comparison purposes, one unstrengthened control (as-built) RC beam and another specimen strengthened with conventional non-tensioned CFRP laminates were tested. The other ten RC beam specimens were strengthened with pre-tensioned CFRP laminates and the performance was compared to the control specimens. Several influential experimental parameters were considered including: (i) pre-tensioned strain level, (ii) CFRP reinforcement ratio, and (iii) sustained loading level. Experimental results indicated that the first two parameters of pre-tensioning strain and CFRP reinforcement ratio had significant influence on both flexural strength and stiffness of the strengthened beams. However, experimental results indicated that the level sustained load had less influence, especially when failure mode is in the form of CFRP laminates rupture. Also, the behavior of retrofitted beams was simulated using nonlinear finite element analyses. Good correlation between experimental and numerical results was achieved. Results indicated that in cases where sustained loads were larger than 40% of the control beam ultimate load, the capacity of strengthened beams was notably reduced. However, this negative effect could be avoided by maintaining the pre-strain level to 3000.0∼4000.0με.

Feather‐inspired carbon fiber reinforced polymers with nanofibrous fractal interlayer

Much work has been performed in improving carbon fiber‐reinforced polymer (CFRP) composites to prevent delamination, which is the major defect in laminated composites. Nevertheless, there is not much focus on improving conventional CFRP systems in terms of weight, especially when these are used in primary structures. This article explores whether lighter and at the same time stronger CFRP composites can be manufactured to replace conventional CFRP systems in major applications. Under this perspective, and having established the fundamentals for creating the next generation of light weight structural composites—the featherweight composites—this work introduces a feather‐inspired case which uses a controlled interlayer reinforcement in a fractal and reproducible manner at the macro‐, micro‐, and nano‐scales. By extensively describing the matrix system and the manufacturing processes and focusing on analytically and thermomechanically testing the CNT (Carbon Nanotubes) reinforced nanofiber interlayer system, it is shown that this feather‐inspired CFRP achieves significantly higher mechanical properties as well as potential weight savings. POLYM. COMPOS., 168–181, 2016. © 2014 Society of Plastics Engineers

Design criterion for fatigue strengthening of riveted beams in a 120-year-old railway metallic bridge using pre-stressed CFRP plates

This study presents a design criterion developed for fatigue strengthening of a 120-year-old metallic railway bridge in Switzerland and presents a pre-stressed un-bonded reinforcement (PUR) system developed to apply the strengthening. The PUR system uses carbon fiber reinforced polymer (CFRP) plates; however, unlike conventional pre-stressed CFRP reinforcement methods, preparation of the existing metallic bridge surface is not required. This decreases the time required for on-site strengthening procedures. The principle of the constant life diagram (CLD) and two fatigue failure criteria (Johnson and Goodman) are described. Analytical formulations are developed based on the CLD method to determine the minimum CFRP pre-stress level required to prevent fatigue crack initiation. The PUR system uses an applied pre-stress force to reduce the mean stress level (and stress ratio) to shift an existing fatigue-susceptible metallic detail from the ‘at risk’ finite life regime to the ‘safe’ infinite life regime. The applied CLD method is particularly valuable when the stress history of the detail is not known and it is difficult to assess the remaining fatigue life. Moreover, it is shown that the currently adopted approach in many structural codes which emphasizes stress range as the dominant parameter influencing fatigue life are non-conservative for tension–tension stress patterns (i.e., stress ratios of 0<R<1). Analyses show that the modified Johnson formula accurately reflects the combined effect of stress range, mean stress level, and material properties, and offers a relatively easy design procedure. Details of a retrofit field application on members of a riveted wrought iron railway bridge are given. A wireless sensor network (WSN) system is used for long-term monitoring of the on-site CFRP stress levels and temperature of the retrofitted details. WSN measurements indicate that increases in ambient temperature result in increased CFRP pre-stress levels.

Tornado-borne debris impact performance of an innovative storm safe room system protected by a carbon fiber reinforced hybrid polymeric-matrix composite

A new tornado safe room design is proposed using a recently developed Carbon-fiber reinforced Hybrid Matrix Composite (CHMC), or “CarbonFlex,” to withstand tornado-borne debris impacts. Test results reveal that the new CarbonFlex wall panel has superior impact resistance in comparison to conventional residential construction and some alternative residential tornado-resistant wall panel constructions observed in the literature and identified in the current work. Two CarbonFlex design groups successfully passed the high-debris impact tests at a missile speed of 44.7m/s (100mph), corresponding to a ground wind speed tornado of 111.7m/s (250mph) while the two other CarbonFlex wall panel designs passed tests at missile speeds of 40.2m/s (90mph), corresponding to ground wind speed tornados of 89.4m/s (200mph). Additionally, a control group wall panel design that was manufactured using a conventional carbon fiber reinforced polymer (CFRP), or more precisely a carbon fiber reinforced epoxy, indisputably failed two debris missile high-impact tests. The material processing parameters of CarbonFlex, i.e., the matrix thickness, hp, and an intermittent curing time, tc, show to be evidently influential on the impact resistance capability of the CarbonFlex panels where the resistance generally increases with smaller values of tc and with greater values of hp. The merits of using CarbonFlex over conventional building envelop components are quantified via vulnerability assessments of both conventional and the newly developed composite wall panel system under tornado transported debris impacts.