Carbon Fiber Reinforced Epoxy Composites Research Articles

Multiobjective optimization of carbon fiber–reinforced epoxy composite properties using nonparametric modeling

Carbon fiber–reinforced epoxy composites are widely used in the marine and aviation sectors due to their superior mechanical properties. As research into these materials progresses, the demand for materials with even more complex and superior properties has increased. Traditional trial-and-error methods are limited to optimizing single factors and are plagued by heavy workloads and prohibitive costs when applied to multifactor composite designs. Addressing these problems, this study introduces a nonparametric multiobjective optimization process for composite materials. This approach employs a Gaussian process (GP) to establish a multiobjective regression model and uses nondominated sorting genetic algorithm II (NSGA II) to determine the Pareto front. Pareto solutions were ranked in accordance with their similarity to ideal solutions and on the basis of predetermined preference weights. The results demonstrate variations in optimal outcomes contingent on the weight values assigned. The differences between the optimized results and experimental validations reached 12.9%, with the minimum deviation being 0.6%. The effectiveness of the proposed method was demonstrated. The strategy combines GP and NSGA II to extend design methods for small samples and materials with multiple attributes. This method enables the simultaneous optimization of multiple conflicting objectives, offering greater efficiency than addressing them individually.

Tribological synergy of copper‐based metal–organic frameworks, carbon fibers and SiO2 in modifying the friction and wear properties of epoxy composites

AbstractCopper‐based metal–organic frameworks is anticipated to find applications in the field of friction materials owing to its plentiful surface‐active groups and distinctive framework structure. In this study, copper‐based metal–organic frameworks was synthesized through ultrasound‐assisted method and incorporated alone into carbon fiber reinforced epoxy composites or together with SiO2 nanoparticles towards the goal of improving the composites' friction and wear properties. It is revealed that copper‐based metal–organic frameworks alone cannot improve the friction and wear of carbon fiber reinforced epoxy composites simultaneously. The combination of copper‐based metal–organic frameworks and SiO2 nanoparticles was more effective in enhancing both the mechanical and tribological properties of studied composites. The composite material exhibits a friction coefficient of 0.104 under the specified test conditions of 10 MPa and 3.75 m/s. Additionally, the specific wear rate is impressively low, measuring only 5.64 × 10−7 mm3 N/m. Through morphological and chemical analysis on the worn surfaces and transfer films, the functioning mechanism of copper‐based metal–organic frameworks in modifying the mechanical and tribological properties was discussed. It was discovered that a tribological synergy exists between short carbon fibers, copper‐based metal–organic frameworks, and SiO2 fillers, leading to a shift in the wear mechanism of the composite materials from abrasive wear to adhesive wear. Concurrently, a shear‐prone transfer film forms on the surface of the counter steel surfaces. Findings of the present study pave a new route of designing high performance epoxy based tribo‐composites by using metal–organic frameworks.Highlights Cu‐BDC nanosheets were synthesized using ultrasound‐assisted techniques and incorporated as tribological fillers in EP composites. The combined use of Cu‐BDC, SiO2, and SCF fillers synergistically enhances the mechanical and tribological properties of EP composites. The composite material exhibits a friction coefficient of 0.104 under the specified test conditions of 10 MPa and 3.75 m/s, the specific wear rate is impressively low, measuring only 5.64 × 10−7 mm3N/m. During the sliding friction process of the composite materials, Cu‐BDC and SiO2 play a crucial role in reducing SCF pull‐out wear through their anchoring effect. The dynamic coordination bond structure of Cu‐BDC contributes to the formation of uniform and continuous transfer films on counter metal surfaces.

Influence of MoS2 nano-filler additions on wear behavior of carbon fiber reinforced epoxy composites

In this research work, two body wear and three-body wear performance of carbon fabric reinforced HTR 212 epoxy resin(CF/Epoxy) composites are experimentally evaluated. Carbon fabric/epoxy resin composite panels with MoS2 nano-filler additions of 0.1, 0.2, 0.4 and 0.7 weight percentage are developed by Vacuum Assisted Resin Transfer Molding process. Two Body Wear test is conducted on the prepared specimen in accordance with ASTM G-99, whereas Three Body Abrasive wear test is conducted as per ASTM G-65. Experimental Tests are conducted for sliding and abrading distances in multiples of 250 m up to 1500 m. Results reveal that Carbon fabric/epoxy resin composites with 0.7 weight percent of MoS2 show 18% reduction in two body wear compared to a decrease of 35% in Three Body abrasive wear at 1500 m abrading distance. Scanning Electron Microscopy is used to study the surface morphology of the tested samples and to know the mode of damage at the surface.

Adjusting the pH of sizing agents to achieve superior interfacial and mechanical properties of carbon fiber reinforced epoxy composites.

Interfacial properties were crucial in determining the mechanical properties of carbon fiber reinforced polymer composites (CFRPs). Applying appropriate sizing agents could effectively improve the interfacial properties of CFRPs. However, the influence of the pH of the sizing agent on the interfacial properties of CFRPs was still unclear. In this work, the above issues were elucidated by adjusting the pH of the diethanolamine-modified E51(E51@DEA) sizing agent to investigate its impact on the interfacial properties of CFRPs. The molecular weight and emulsion particle diameter of E51@DEA increased with increasing pH of the sizing agent, despite the presence of identical chemical functional groups. The best interfacial enhancement was observed for E51@DEA-pH 7. T700/E51@DEA-pH 7 exhibited ILSS and IFSS values of 102.24 and 113.45 MPa, respectively. This showed an increase of 76% and 37% when compared with T700. Additionally, the compressive and tensile strength of T700/E51@DEA-pH 7 also improved by approximately 13% and 30%, respectively. The suitable molecular chain length of the sizing agent and the high roughness of the surface of CFs were regarded as the contributing factors. This work further provided an effective and simple strategy for adjusting sizing agents to better improve the interfacial properties of CFRPs.

Panoramic View of Interface-Related Thermo-oxidative Aging of Carbon Fiber-Reinforced Epoxy Composites

Panoramic View of Interface-Related Thermo-oxidative Aging of Carbon Fiber-Reinforced Epoxy Composites

Investigation of fracture behavior and mechanical properties of epoxy composites supported with MWCNTs microscopically

Adding of a multi-walled carbon nanotubes (MWCNTs) to epoxy resin has shown promising results in improving fracture toughness in bulk epoxy and carbon fiber-reinforced epoxy composites (CFRP). using a hand layup proceeding followed by the so called vacuum bagging process method, carbon fiber-reinforced polymer multi-wall carbon nanotubes (MWCNTs) was added to an epoxy resin with a weight percentage mixing of 1% wt., 1.25% wt., and 1.5 % wt. MWCNTs. Furthermore, the specimen underwent analysis via Fourier-Transform Infrared (FTIR) spectroscopy, and X-ray Diffraction (XRD) spectroscopy, the composites were subjected to a microscopic examination using a Scanning Electron Microscope (SEM). FTIR and XRD verified the folding and unfolding of the polymer, in addition, the mechanical properties including tensile strength, bending stress, and impact behavior were investigated as well as the hardness test. The obtained results showed a significant improvement of about (40 %) in tensile strength, (53 %) in bending stress at 1 % wt. MWCNTs, and (70 %) percentage increment in the strength of Impact at 1.25 % wt. MWCNTs. And the gained hardness was about 40.5 HV which were compared with a reference substance named Carbon Fiber (CF) without any addition of nano materials. Carbon nanotubes have demonstrated their potential to enhance the mechanical properties of fiber-reinforced polymers, so this investigative study employs comprehensive characterization techniques, and demonstrates significant improvements in mechanical properties for the modified polymeric composite materials supported with nano materials.

Development of high‐strength carbon fiber/thermoplastic epoxy resin composites and it's recyclability

AbstractThe realization of the recycling of epoxy resin composites has important practical significance for “carbon peak, carbon neutrality” and resource conservation, and recycling. In this study, high‐strength carbon fiber fabric reinforced thermoplastic epoxy (TPE) composites (CFF/TPE) were successfully fabricated by a laminated hot‐pressing process, and both CFF and TPE were efficiently recycled via an ultrasonication‐assisted solvent method. The CFF/TPE composites present mechanical properties (tensile strength: 705 MPa, flexural strength: 711 MPa) by optimizing the process parameters, which are comparable to those of carbon fiber reinforced thermosetting epoxy. Moreover, the tensile strength retention rates of recycled CFF and TPE are 92% and 89%, respectively. The recycled CFF can be completely reprocessed through the same hot‐pressing process, and the recycled CFF/TPE composite exhibited high efficiency reuse and excellent mechanical properties (high strength of reaching 94% of CFF/TPE). This approach provides a new strategy for the facile production of high‐performance carbon fiber reinforced epoxy composites with high efficiency recycling.Highlights Recyclable carbon fiber fabric reinforced thermoplastic epoxy composites (CFF/TPE) are fabricated by a laminated hot‐pressing process. The composite exhibits excellent mechanical properties, which is comparable to that of carbon fiber reinforced thermosetting epoxy. The carbon fiber fabric and thermoplastic epoxy can be efficiently recycled via a simple ultrasonication‐assisted solvent method, and resued.

Chemical recovery of carbon fibers from composites via plasma assisted solvolysis

In this work plasma assisted solvolysis using nitric acid is proposed for chemical recovery of carbon fibers from carbon fiber-reinforced epoxy resin composites (CFRCs). Complete decomposition of the epoxy matrix could be achieved, regardless the composites’ geometry. The efficiency of the process was examined in terms of a) process duration, b) resin decomposition rate and c) materials properties. SEM and EDX data showed that the recovered fiber surfaces are almost free of epoxy resin residuals and their tensile strength was comparable to that of typical virgin carbon fiber. The process decomposition efficiency is very high without requiring additional organic solvents or high temperature / pressure, stressing the potential of this method for viable recycling of CFRCs.

Effects of porosity on ultrasonic attenuation coefficient, shear properties and failure mechanisms of CF/EP laminates

Carbon fiber reinforced epoxy composite (CF/EP) laminates with porosity ranged from 0% to 2.5% were prepared under inadequate curing pressures, and then applied to ultrasonic, metallographic and mechanical testings. Porosity was evaluated using an ultrasonic attenuation model, which was established by taking consideration of surface losses, material attenuation coefficient and void attenuation coefficient. Shear properties were determined via short beam shear (SBS) method and porosity-related failure mechanisms were characterized using ultrasonic B-Scan and metallographic analysis. The results show that there is a third-order polynomial correlation between porosity level and ultrasonic attenuation coefficient. The shear strength approximately drops by 15%, 30%, 40% and 45% with porosity level up to 1.0%, 1.5%, 2.0% and 2.5% respectively. The detrimental effects of Porosity can be attributed to the reduced bonding area between plies or among fiber-resin area as well as the crack initiation and propagation.

Investigation of the influence of Halloysite Nanotubes (HNTs) on the low-velocity impact behavior of carbon fiber-reinforced epoxy composites

This study explores the impact of incorporating Halloysite Nanotubes (HNTs) nanoparticles on the low-velocity impact (LVI) behavior of carbon fiber (CF) laminate epoxy nanocomposites. The objective of this investigation was to observe the effects of different nanotube loadings (0.5[Formula: see text]wt.% and 0.7[Formula: see text]wt.%) on CF composites and assess their impact resistance. To achieve this, the CF was subjected to Electrophoretic Deposition (EPD) process to introduce the HNTs. Vacuum-assisted Resin Transfer Molding (VaRTM) was employed to fabricate the CF-reinforced epoxy-based laminated nanocomposites with incorporated HNTs. LVI tests were conducted following the ASTM-D-7136 standard, utilizing impact energies of 10[Formula: see text]J and 15[Formula: see text]J. Subsequently, the damaged areas within the composites were examined using optical microscopy (OM) and scanning electron microscope (SEM). The findings of this investigation revealed a significant enhancement in impact damage resistance with the addition of HNTs. The highest damage resistance and minimal energy absorption were observed at a loading of 0.7[Formula: see text]wt.% HNTs. The results reveal that incorporating 0.7[Formula: see text]wt.% HNTs substantially reduces delamination damage, influenced by absorbed impact energy. As well it composite underscores enhanced interlaminar bonding through 0.5[Formula: see text]wt.% and 0.7[Formula: see text]wt.% HNTs modification. Hence, we confidently assert that the addition of HNTs nanoparticles to CF/epoxy composites has considerably influenced the impact response of the nanocomposites.

POSS-polyurethane prepolymer strengthened and toughened CF/epoxy resin composites for room and simulated Arctic ambient temperature

As an important material candidate for automotive, aviation, and aerospace, the wide application of carbon fiber-reinforced epoxy resin composites (CFRPs) was important. However, restricted by the low toughness. Herein, octaaminopropyl cage polysilsesquioxane-polyurethane prepolymer (POSS-PU) was synthesized by in-situ polymerization of PU on the POSS, and then employed as the modifier for epoxy resin (EP). Compared to pristine EP, the toughness of the 7.5 wt% POSS0.5-PU/EP was increased by 115.3 % without compromising the tensile strength and Tg. The unnotched impact strength, interlaminar shear strength (ILSS), and flexural strength of the CFRPs prepared from the modified EP were increased by 73.5 %, 7.5 %, and 42.4 %, compared to CF/EP. Additionally, the mechanical properties of CFRPs maintained a substantial improvement under low-temperature, and the CF/7.5 wt% POSS0.5-PU/EP was increased by 72.9 % (impact strength) and 21.7 % (ILSS), compared to those of CF/EP. Compared to the improvement in the toughness of CFRPs at room temperature, the retention rate of toughness enhancement at low temperature was approximately 100 %. CFRPs prepared by POSSx-PU/EP offered outstanding mechanical properties and hence showed great potential for future industrial applications.

Effect of ceramic particles on the mechanical and tribological properties of short carbon fibre reinforced epoxy composites

Effect of ceramic particles on the mechanical and tribological properties of short carbon fibre reinforced epoxy composites

Effect of Fiber Stacking Sequence on Mechanical Property of Polymeric Composite through VARTIM Method and Metallographic Examination

Because of higher specific modulus/strength, lower weight, good corrosion resistance with design flexibility and easy production, carbon fiber reinforced epoxy composites are widely used for many structural applications. Glass woven (plain) and carbon fabric (plain) were studied. Thus, glass fabric-reinforced epoxy composites (GFRCs) and carbon fabric-reinforced composites (CFRCs) were fabricated throughVacuum Assisted Resin Transfer moulding (VARTM) methodology. Firstly, manufacturing unit/control system, preparation stages and some elements used in manufacturing the epoxy based composites are reviewed. Then, effects of stacking sequence of fibers on mechanical properties were investigated and a comparison was made on two types of fabrics on hardness/deformation depth through Stereo Microscope (SM). The experimental results exhibited that the hardnesses measured were around 40.6 HB and 52.4 HRB for GFRP and CFRP, respectively. Improvements in carbon fiber were about 29% in comparison to glass fiber. Further, both hybrid composites made from glass and carbon fiber, the hardnesses values were reduced. In case of C2/G2/C2 hybrid composites, reduction rate was about 9.3% in comparison to C6 fiber reinforced laminate composite. Moreover, it is clearly revealed that there were extensive deformation regions reflecting the white areas because top layer was in G2/C2/G2 samples, but there was no such a white area in C2/G2/C2 composite.

Dual rapid self-healing and easily recyclable carbon fiber reinforced vitrimer composites

Traditional carbon fiber reinforced epoxy composites (CFRECs) pose significant challenges to sustainable development due to their non-self-healable and non-recyclable nature, which causes environmental pollutions. To address these challenges, our research focuses on the design of carbon fiber reinforced vitrimer (CF/vitrimer) composites system with dual self-healing properties (self-healing resin and self-healing interface) and dual recyclable capabilities (recycling vitrimer resin and recycling CF). On the one hand, the scratch on the vitrimer resin exhibited rapid self-healing properties (achieving ˃ 95 % recovery within 5 min). Additionally, the self-healing interface was constructed between the functionalized CF and the vitrimer resin, and even after undergoing five self-healing cycles, the self-healing interface maintained a self-healing efficiency of 77.4 %. On the other hand, the CF/vitrimer composites could be easily and effectively degraded in ethylene glycol, resulting in recycled vitrimer resin and recycled CF. These results not only indicate the potential for developing other types of self-healing CF/vitrimer composites but also highlight their contributions to sustainable development.

Influence of nanographene filler on sliding and abrasive wear behaviour of Bi-directional carbon fiber reinforced epoxy composites

This study investigated the tribological performance of composites, i.e., made of epoxy resin reinforced with bi-directional carbon fibres and graphene nanoparticle additions at different concentrations using pin-on-disc and abrasion tribotesters. The composites were developed using the hand lay-up technique. The sliding test was performed at different applied loads (30 N, 40 N and 50 N) by keeping the sliding distance of 603 m and the sliding speed of 3.35 m/s. The weight loss, specific wear rate and coefficient of friction were determined as a function of load and sliding distance with the fiber-matrix (weight fraction maintained at 60:40). The result shows that the specific wear rate and coefficient of friction varied considerably during the running period and reached stable values at the steady state region. It is also observed that the fiber-matrix bonding characteristics impact the wear properties, and the specific wear rate decreases with the increase in load. The wear surfaces were examined and assessed using scanning electron microscopy (SEM), and fiber breakage, fiber fragmentation and adhesive wear are observed. In addition, the dry sand abrasion test was carried out for 5 min (100 rpm) with silica sand as the abrasive media using a chlorobutyl rubber wheel as the liner for the steel disc. The results reveal that the abrasion loss is decreased with an increase in the concentration of nanographene from beyond 0.8 wt% due to the increase in hardness. The SEM images of worn surface features very well support the abrasion tests.

Pyrolysis Kinetics Analysis and Prediction for Carbon Fiber-Reinforced Epoxy Composites.

Carbon fiber-reinforced epoxy resin composites have poor high temperature resistance and are prone to thermal damage during service in the aerospace field. The purpose of this study was to evaluate the thermal decomposition (pyrolysis) characteristics of carbon fiber-reinforced epoxy composites and reasonably predict their thermal decomposition under arbitrary temperature conditions. The kinetic analysis was conducted on the thermal decomposition of carbon fiber-reinforced epoxy resin composites (USN15000/9A16/RC33, supplied by Weihai GuangWei Composites Co., Ltd. Weihai City, Shandong Province, China) under a nitrogen environment, and an improved model of pyrolysis prediction suitable for the arbitrary temperature program was developed in this work. The results showed that the carbon fiber-reinforced epoxy composites begin to degrade at about 500 K, and the peak value of the weight loss rate at the respective heating rate appears in the range of 650 K to 750 K. A single-step reaction can characterize the thermal decomposition of carbon fiber-reinforced epoxy composites in a nitrogen atmosphere, and a wide variety of isoconversional approaches can be used for the calculation of the kinetic parameters. The proposed model of pyrolysis prediction can avoid numerous limitations of temperature integration, and it shows good prediction accuracy by reducing the temperature rise between sampling points. This study provides a reference for the kinetic analysis and pyrolysis prediction of carbon fiber-reinforced epoxy composites.

Effects of CNT microstructural characteristics on the interfacial enhancement mechanism of carbon fiber reinforced epoxy composites via molecular dynamics simulations

Numerous studies have concentrated on improving the mechanical properties of carbon fiber reinforced polymer composite (CFRP) through the modification of carbon fiber (CF) with carbon nanotubes (CNTs). However, most of them were confined to describing experimental phenomena. In this study, molecular dynamics (MD) simulation was used to systematically reveal the effect of CNT nanostructures on the interfacial reinforcement of CF/epoxy. An all-atom modeling method was used to provide a quantitative description of the CF-CNT/polymer interface characteristic structure. Computational results indicate that nanotubes can protect the intra- and intermolecular interactions of epoxy segments from being destroyed, thereby preventing the initiation and propagation of micro-defects during interfacial deterioration. The mechanical competition between the interface and polymer bulk leads to different failure mechanisms, and the strengthened interface region has fewer atoms leaving the equilibrium state during tensile deformation. The insertion of CNTs on the fiber surface, specifically increasing their length, diameter, distribution density, or orientation, can improve interfacial tensile strength (up to +62.11 %) and delay the detachment of epoxy molecules from the CF. Additionally, MD outcomes were verified by synthesizing CNTs onto CF using an electric field-assisted flame synthesis approach, leading to improvement in IFSS (+62.67 %) and ILSS (+27.78 %).

Experimental assessment of barely visible impact damage carbon fiber reinforced epoxy composite using ultrasound method

Background Carbon fiber reinforced epoxy (CFRP) is susceptible to impact damage which could resulted in reduction of the mechanical properties. This paper studies the architecture of barely visible impact damage (BVID) to comprehend the extent of damage on quasi-isotropic CFRP laminates of varying thickness (i.e. 16, 24 and 32-ply laminates of 3, 4 and 5 mm respectively). Methods Quasi-static indentation is chosen to produce BVID on CFRP laminates, followed by using non-destruction evaluation method, namely conventional contact-type ultrasonic testing (UT) and C-mode scanning acoustic microscopy (C-SAM) method. Results The findings revealed (1) the size and shapes of the BVID on CFRP laminates, (2) no damage was found at the center of the impact point, and (3) the bridging between the point of impact to the outer damaged diameter due to the consequence of diverse orientation of carbon fiber strips which exhibit excellent mechanical properties before structural failure. Conclusions The results concluded that the UT and C-SAM method can identify both the pristine region and the internal damaged structures in CFRP laminates.

Pyrolytic performance and kinetics study of epoxy resin in carbon fiber reinforced composites: Synergistic effects of epoxy resin and carbon fiber

Pyrolysis is recognized as a sustainable approach for recycling carbon fiber reinforced polymers (CFRP), ensuring enhanced process efficiency and resource utilization. To unveil the pyrolysis mechanism of epoxy resin and its synergistic interaction with carbon fiber in different scenarios, we conducted pyrolysis experiments on pure epoxy resin diglycidyl ether of bisphenol A cured with 4,4'-Diaminodiphenylmethane (C-epoxy), as well as three kinds of carbon fiber-resin mixtures, using TG and Py-GC/MS techniques. Isoconversional analysis (Friedman method) of C-epoxy degradation revealed three reaction stages within the temperature range of 280–540 °C, each corresponding to activation energies of 158 kJ/mol at α = 5%, 179–190 kJ/mol at the plateau of α = 10–60%, and 190–236 kJ/mol for α values surpassing 60%. The multi-Gaussian distributed activation energy model (DAEM) aptly characterized C-epoxy’s thermal decomposition, featuring two Gaussian peaks with similar contributions of 0.58 and 0.42, and activation energy distributions of 217.76 ± 3.92 kJ/mol and 233.36 ± 21.42 kJ/mol, respectively, which are close to the activation energies from isoconversional analysis at α = 10–60% and α > 60%, respectively. The presence of carbon fiber significantly influenced the kinetic parameters of epoxy resin pyrolysis, with the extent of change linked to the mixing methodology applied. Notably, carbon fiber decreased the activation energy of the reaction while accelerating the rate of weight loss. However, the synergistic effects vary depending on different synergistic scenarios. By analyzing the product distribution obtained through an analytical pyrolyzer coupled with a gas chromatography–mass spectrometry set-up (Py-GC/MS), we proposed a pyrolysis mechanism for epoxy resin, encompassing three key stages: cleavage of N–C and NC–COH bonds, phenolic O–C and vicinal C–C bonds, and disruption of the isopropylidene bridge on bisphenol A. The influence of carbon fiber on epoxy resin pyrolysis product distribution was relatively modest, manifesting predominantly within the mixture obtained by premixing before curing. Here, carbon fiber exhibited a dual effect, inhibiting oxygen-containing diphenyl products while promoting oxygen-containing monophenyl products. Ultimately, our study provides essential kinetic data for multidimensional simulation and theoretical guidance pertaining to the pyrolysis recycling of widely used carbon fiber-reinforced epoxy resin composites.

Exploring the Iosipescu method to investigate interlaminar shear fatigue behavior and failure mechanisms of carbon fiber reinforced composites

Iosipescu method, commonly adopted to determine the static shear properties of composite material, is extended to analyze the shear fatigue properties of carbon fiber reinforced epoxy composites. Following the results of the ultimate shear strength (τ) and interlaminar shear modulus (G13) in the static tests, this work conducted interlaminar shear fatigue tests with two stress ratios and four stress levels to obtain the S-N and stiffness degradation curves. The S‐N curves of the stress level versus logarithmic fatigue life exhibit a good linear relationship, and the specimens display a better fatigue performance at the stress ratio of 0.1 than −1. A significant three-stage cumulative damage evolution characteristic was found in the fatigue stiffness degradation process. In addition, the damage evolution, dominated by the propagation of matrix microcracks along the fiber direction inside the material, that is, debonding and delamination of the interface, was captured and analyzed via microscopic observation of the damaged zone on the specimen surface. Understanding the revealed processes of shear fatigue failure is crucial for ensuring the safe utilization of composite structures.