Resin Cracking Research Articles

UV/thermal dual-cured MWCNTs composites for pipeline rehabilitation: Mechanical properties and damage analysis

Deformation and damage in underground pipelines remain challenging to monitor over the long term due to sensor degradation caused by corrosive substances present in the pipelines. This study investigates the potential of incorporating multi-walled carbon nanotubes (MWCNTs) into ultraviolet-cured-in-place pipe (UV-CIPP) material, a widely adopted trenchless repair technique, to enhance performance and enable deformation monitoring. A UV/thermal dual-curing strategy is introduced to mitigate the significant reduction in light transmittance caused by the inclusion of MWCNTs in the composite material. The addition of MWCNTs led to a 94.86 % reduction in light transmittance through glass fibers. However, this issue was effectively resolved through the incorporation of thermal curing, allowing for the production of ultra-high-strength composites using only three layers of fibers within a short curing time. Under optimal conditions (0.2 wt% MWCNTs with the impregnation layer on top), the flexural strength and modulus reached 442.75 MPa and 15.58 GPa, respectively, marking improvements of 14.01 % and 45.2 % over the base material. Additionally, the hardness on the composite's backside increased by 10.95 % compared to the front, indicating enhanced reinforcement. The tensile strength of braided glass fibers improved by 42.31 % and 197.54 % with the addition of 0.2 wt% and 1.0 wt% MWCNTs, respectively. Failure modes varied based on the location of the sensing layer, but all specimens eventually failed due to resin cracking, delamination of the MWCNTs-impregnated layer, and fiber fractures. The UV/thermal dual-cured composite material developed for pipeline rehabilitation in this study exhibits ultra-high strength and shows significant potential for multifunctional sensing applications.

Infrared–Resin Crack Measurement and Preventive Work Technology for Maintenance

The use of thermography as a nondestructive evaluation technique is increasingly popular for maintaining concrete structures. Most inspections merely evaluate the locations and shapes of defects on surfaces. To address this shortcoming, it proposes an inspection method and preventive work using a coating-type resin sensor combined with an infrared camera. No method has been developed to assess the depth of defects. In this approach, infrared-reactive resin is applied. Thermographic images of the target area are captured sequentially. Temperature curves obtained at each pixel during the cooling process are analyzed using Fourier transform to differentiate defect states in various parts of the temperature distribution. The temperature change is found to be correlated with the defect size. Approximately 5% aluminum powder is mixed into the applied gel resin. Because of its specific gravity, it tends to concentrate in areas damaged by compression failure or to float. This report discusses technologies related to identification of defects and measuring their size in infrared-reactive resin, with examination of the effectiveness of measures to prevent scattering and collapse of defects caused by structural degradation. A concentric loading test on reinforced concrete columns confined by gel resin ties is described herein. Test variables include concrete compressive strength of 232–244 N/mm<sup>2</sup>, both below and above the equipment hole that caused the defect, and to measure the relation, a comparison with test specimens that are free of defects.

Thermo-oxidative aging induced multi-scale shrinkage and damage in 3D angle-interlock woven composites

The deterioration of resin and interface in composites deteriorate during high-temperature service, would impact both the thermal stability and overall performance significantly. This paper focused on the experimental characterization of multi-scale damage and resin shrinkage within composites induced by thermo-oxidative aging using Micro-CT, SEM and Confocal Interferometric Microscopy (CIM), and exploring the coupling mechanism between them. The results show that damage distribution and propagation are affected by the hierarchical structure of 3-D angle-interlock fabric. Macro-CIM shows that maximum resin shrinkage depth depends on the resin width and aging time. Resin shrinkage profile evolution demonstrated the accelerating effect of resin crack on shrinkage. Micro-CIM shows that macro yarn cracks form through the accumulation of micro resin cracks in resin-rich areas and fiber/resin interface debonding. The formation of fiber/resin interface crack is tied to the resin shrinkage state, only occurring when the surrounding resin shrinkage slope exceeds a specific threshold value.

Effect of sand coating on durability and micro-structural deterioration of GFRP rebar under alkaline environment attack

The objective of this study is to investigate the consequences of the sand-coated layer on the durability of glass fiber reinforced polymer (GFRP) rebars under four alkali solution concentrations and three temperatures. A total of 464 GFRP rebars specimens were manufactured to undergo accelerated corrosion experiments and mechanical performance test. Among them, 438 specimens were used to test the residual tensile strength of GFRP rebars after 120 days of immersion; 26 specimens were applied for surface observation and microscopic testing to analyze the degradation and damage process of GFRP rebars. SEM and digital camera were used to examine the micro-structure of samples either with or without sand layer covering. The unidirectional tensile strength experiment was conducted to test the remaining tensile strength of GFRP rebars after corrosion. The experimental results indicate that sand coating provides better protection and restraint in GFRP rebar durability reduction, resulting in a lower rate of fiber loosening and resin cracking and flaking when exposed to a solution over a pH of 12.5. As the failure of GFRP rebars ranges from local damage to cracking of the peripheral sand protective layer, the pH value of 12.5 is considered a critical alkali solution concentration. Based on experimental results, an improved model was proposed to predict the short-term and long-term residual strength values of GFRP rebars. The calculation results indicate that the predict values are in good agreement with the experimental ones, and the proposed model can be used to predict the residual strength of GFRP rebars.

Study on interlaminar fracture toughness of unidirectional composites

Carbon fiber composite is widely used in the nuclear industry and other fields due to their lightweight and high strength. There are various forms of failure in composite, including resin cracking, fiber fracture, and resin fiber interface debonding. At the initial stage of damage, they all exhibit the form of microcracks. As cracks propagate and fuse, they ultimately lead to macroscopic fracture of composite components. For safety reasons, it is necessary to study the fracture toughness of composite. This article uses a combination of winding method and double cantilever beam method to study the interlayer fracture toughness characteristics of high-strength (or high modulus) fiber epoxy resin composite under type I load. Choose a more suitable propagation GIC as a measurement metric. The results indicate that under the same resin matrix, the interlayer fracture toughness of high-strength fiber composite is much higher than that of high modulus fibers, which is related to the high surface chemical activity of high-strength fiber monofilament. Finally, combined with finite element analysis, its application in laminated structures was briefly analyzed.

Products and bromine migration characteristics of non-metallic components of waste printed circuit boards pyrolysis in a fluidized bed pyrolyzer

This study investigated non-metallic components (NMCs) of waste printed circuit boards (WPCBs) pyrolysis in a fluidized bed pyrolyzer (FBP). The pyrolysis temperature was set at 350–750 °C. K2CO3, ZnO, CaO and Fe2O3 were added at the temperature of 650 °C to stabilize Br. The characterization of pyrolysis char, pyrolysis oil and pyrolysis gas were analyzed. Migration and transformation of Br in NMCs pyrolysis was investigate. Brominated epoxy resin cracking and Br fixation mechanism were proposed. Pyrolysis oil yield reached the highest at 650 °C. Phenols were the main components of pyrolysis oil, it increased with temperature and reached the highest at 650 °C. The proportion of esters and ketones were 2–4% and 2–3%, respectively. The secondary cracking during pyrolysis correlated the secondary release of CO2, CO, CH4 and H2. Br mainly distributed in pyrolysis oil in the form of HBr and reached the maximum at 550 °C. Organic bromides was mainly bromophenols in pyrolysis oil. Br distributed in pyrolysis char was mainly inorganic bromines in the form of brominated salts. Bromines in pyrolysis gas were mainly CH3Br, C2H5Br, C3H7Br, C3H5Br. K2CO3, CaO effectively promoted Br fixation through neutralization reaction, direct elimination and dissociation adsorption. ZnO, Fe2O3 promoted bromides cracking.

X-ray microtomography analysis of the damage mechanisms in 3D circular braided carbon fiber/epoxy resin composite tubes under axial impact compression

The dynamic behavior of three-dimensional (3D) circular braided composite tubes with different braided parameters was experimentally investigated subjected to axial impact compression using a Split Hopkinson Pressure Bar (SHPB). The damage characterization of the post-impacted tubes was examined using scanning electron microscope (SEM) and X-ray micro-computed tomography (micro-CT). The influence of braided parameters and strain rate, including braided angle, the number of braided layer and axial yarn, on the dynamic mechanical properties, progressive crush characteristics and failure mechanism of 3D braided composite tubes was analyzed in detail. It was found that the smaller braided angle and the larger numbers of braided layers contributed to better axial dynamic properties. The compressive strength, stiffness and specific energy absorption (SEA) of 3D five direction (3D5D) tubes with axial yarn were larger than those of 3D four direction (3D4D) tubes without axial yarn. Meanwhile, the dynamic mechanical response and damage patterns of braided tubes exhibited significant strain rate effects. The impact compression failure mechanisms of braided tubes were mainly fiber tows crushing, fiber breakage, fiber buckling, shear fracture, resin cracking, interfacial cracks, fiber-matrix debonding, etc.

Effect of the micro-structure on the compressive failure behavior of three-dimensional orthogonal woven composites

The failure behavior of three-dimensional orthogonal woven composites (3DOWCs) under in-plane axial compression has been experimentally and numerically investigated. The micro-structure at the intersecting points of the fabric reinforcement, which is induced by the tow force in the weaving process, is introduced. The strength and the induced damage along the warp and weft directions were investigated. The micro-structure of the 3DOWC including the details of the tow waviness and resin distribution was accurately obtained through a multiscale modeling approach. Resin cracking and the local stress concentration were captured by the numerical models, and they showed good correlations with the experimental results. The fiber undulation in the region of the tow intersection concentrated stress, which led to fiber fracture in the compression process. The main load-carrying tow, namely, the warp and weft tow along each direction, had different forms of undulation, which should be the reason for the decreasing compression-carrying capacity of the 3DOWC. With increasing Z-binder tow force, the level of fiber straightness decreased and the failure mode transformed from macroscopic brooming type to fiber microbucking. The inclination angle of the through-thickness fracture path suggested that fracture was induced by the shear failure in the load-carrying tows.

Aging behaviour of encapsulated assemblies of epoxy resin under accelerated thermal cycling

Epoxy potting materials are inevitably exposed to cyclic temperature environments during use. Under temperature load, thermal stress concentration occurs inside the epoxy encapsulation layer and leads to interface debonding and resin cracking, which eventually leads to the failure of the encapsulated component. In view of this, the effects of thermal cycling on epoxy resin and its encapsulated assemblies were investigated in this work. The surface morphology was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), the mechanical properties were measured by the Shore hardness tester and universal electronic extensometer, and the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to explore the thermogravimetric and thermal stability of epoxy resin under thermal cycling. The electrical properties of encapsulated assemblies of epoxy resin were measured by broadband dielectric spectroscopy and breakdown voltage. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the changes of the epoxy molecular structure before and after thermal cycling. Based on the aforementioned results and analysis, an aging mechanism of epoxy resin under an alternating thermal cycle was proposed.

Evaluation of the interfacial crack suppression effect by the resin crack arrester

Evaluation of the interfacial crack suppression effect by the resin crack arrester

High‐performance fiber‐reinforced composites with a polydopamine/epoxy silane hydrolysis‐condensate bilayer on surface of ultra‐high molecular weight polyethylene fiber

AbstractA bilayer structure with polydopamine (PDA) transition layer and 3‐glycidyl ether oxy‐propyl trimethoxy silane (GOPTS) hydrolysis‐condensate strengthened layer on the surface of ultra‐high molecular weight polyethylene (UHMWPE) fiber is prepared to improve the damage resistance of composites and more efficient stress transmission in composites. PDA is covered on the surface of UHMWPE fiber and then GOPTS is hydrolyzed and condensed to form inorganic ‐O‐Si‐O‐ with epoxy groups on the PDA layer. In addition, the surface activated nano‐SiO2 is dispersed in the epoxy resin to increase the strength of the matrix resin. The results show that the interfacial shear strength (IFSS), the impact strength, the flexural strength and flexural modulus of UHMWPE‐PDA‐GOPTS/EP‐SiO2 increase by 99.1%, 54.1%, 76.8%, and 36.6% respectively compared with unmodified UHMWPE/EP. The chemical compositions of the treated fiber surface are characterized by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (ATR‐FTIR). With the help of the scanning electron microscopy, the interface failure and reinforcement mechanism of the composites are further explored due to UHMWPE fiber shear yield deformation, UHMWPE fiber fracture, matrix resin cracking and the relative sliding friction between the fiber and matrix.

Synergistic effect of acidic environmental exposure and fatigue loads on FRP tendons

The synergistic effect of acidic environmental exposure and fatigue loads on fiber-reinforced polymer (FRP) tendons was investigated in this study. The fatigue behavior of basalt FRP tendons under cyclic loads and exposed to air, water, and acid was evaluated. Three types of fatigue tests, that is, air, water spraying, and acid spraying tests, were performed at 40 °C. Another set of preconditioned specimens was prepared by immersing in an acid solution without stress for a designated period. Fatigue stresses of 25%fu–65%fu (where fu is the tensile strength) were applied at a stress ratio of 0.5. The failure mechanism was analyzed at macroscopic and microscopic scales. The results showed that water spraying had the most negligible impact on fatigue behavior, and the acid spraying specimens exhibited 58% faster degradation than the water spraying specimens. Moreover, the synergistic effect of the acid and cyclic stress facilitated the failure process of the acid spraying specimens by 43% compared to the preconditioned specimens. The internal pressure generated by the ingress liquid accelerated resin cracking and fiber–matrix interface debonding. Furthermore, the synergistic effect of the acid and fatigue loads accelerated degradation, owing to the combined effect of internal pressure and chemical corrosion.

Degradation of torsional behaviors of 3-D braided thin-walled tubes after atmospheric thermal ageing

Degradations of torsional behavior is a key issue to the evaluation of the 3-D braided tubes in thermal-oxidizing environment for a long-term service. Here we report the effect of thermal oxygen ageing on torsional behaviors of 3-D carbon fiber/ epoxy resin braided composite tubes. The torsional behaviors of the 3-D braided tubes were quasi-statically tested after ageing at 110 °C and 180 °C for 8, 16 and 32 days respectively. Three-dimensional digital image correlation (3D-DIC) technique was used to display shear strain distribution. A microstructure finite element analysis (FEA) model was established to reveal the torsional damage mechanisms. We found that both temperature rise and ageing time extension will decrease the shear modulus and torque strength. Temperature has a greater influence on modulus and torque strength degradation than ageing time does. Ageing at 110 °C, resin crack and yarn breakage are the main torsional damages, while at 180 °C, yarn pull-out emerges as a further torsional damage.

Low Velocity Impact Behaviour Analysis of Different Fibre Stacking Sequences of Glass Fibre Reinforcement Composite.

Furthering understanding the damage deformation behaviour involved in the impact test of Fibre-reinforced composite material is important in designing for the structural components. Thus, this study presents the damage effect of different stacking sequence of glass fibre reinforce polymer (FRP) composite on low-velocity impact test (LVI). The glass FRP composites were fabricated using vacuum-assisted resin transfer moulding process, which is capable of producing constant thickness with high volume fractions of composite laminates as compared to the traditional wet hand lay-up method. The physical and impact properties were determined according to the ASTM D7137 standards. It was found that, bi-axial glass FRP composite can afford the energy until 90J and without the post perforation occurred, which mean that from the LVI test, the architecture weave of bi-axial glass FRP composite was showed high performance as compared to the unidirectional glass FRP composite. Lastly, component failures such as resin cracking, fibre breakage, fractured knit, fibre buckling, and delamination were also highlighted in this paper.

Structural performance of composite tidal turbine blades

Tidal turbine blades experience a significant bending moment in the root area during their long-term operation in a sea water environment. This necessitates using fibre reinforced polymer as the blade material to provide the required strength/stiffness. In this study, a design methodology based on hydrodynamic and Finite Element models with a view to examine the mechanical properties of composites was developed to evaluate the structural response of two commercial scale turbine blades (1.5 and 0.35 MW). Using the output from the hydrodynamic model, Finite Element stress analysis was conducted in order to determine the likelihood of blade failure. To incorporate appropriate failure modes with the blade model, failure analysis was conducted on the composite test coupons. The results of stress analysis show that the blade root area experiences high stress values with failure modes such as resin cracking, fibre/matrix interfacial de-bonding, delamination and fibre breakage. It is also predicted that the glass fibre composite blades require three times thicker laminates than a carbon fibre composite blade of similar design to maintain the same safety factor. Reasonable agreement between the numerically and experimentally determined strain fields on a small-scale blade indicates that the result of Finite Element stress analysis is valid.

Effect of carbon/Kevlar asymmetric hybridization ratio on the low-velocity impact response of plain woven laminates

The ply structure has a significant effect on the impact resistance and failure behavior of composite laminates. In this paper, carbon/Kevlar hybrid fabric reinforcements were prepared with different Kevlar ratio (0%, 25%, 50%, 75%, 100%) by replacing carbon fabric plies on the non-impact side by Kevlar plies. The low-velocity impact tests for all configurations were carried out under 15 J and 25 J energy respectively. The results show that the maximum deflection, impact duration, impact absorption energy and absorption energy efficiency of hybrid laminates increased with the Kevlar hybrid ratio, whereas the peak force presented a decreasing trend, which indicates that the adding of Kevlar layer makes the laminates more ductile than non-hybrid carbon structure. The damage mechanism of the carbon fiber ply was brittle fiber fracture, resin cracking and resin shedding, while the fibers pull-out and tows splitting was found in Kevlar ply. The critical structural damages start from the non-impact side and evolve to the impact side. And the rules of internal crack volume distribution with Kevlar plies are consistent with the trend of external damage area on the non-impact side. It is suggested that in order to take into account the peak strength and excellent structural resilience, Kevlar asymmetric-hybrid ratio of 25% is the most appropriate. The reason is that an appropriate small ratio of Kevlar cushion ply can not only effectively avoid the tensile fracture at non-impact side happened in the non-hybrid carbon structure, but also withstand enough impact load by maintaining a high carbon fiber content.

Mechanical Properties of Abaca-Glass Fiber Composites Fabricated by Vacuum-Assisted Resin Transfer Method.

The application of natural fiber-reinforced composites is gaining interest in the automotive, aerospace, construction, and marine fields due to its advantages of being environmentally friendly and lightweight, having a low cost, and having a lower energy consumption during production. The incorporation of natural fibers with glass fiber hybrid composites may lead to some engineering and industrial applications. In this study, abaca/glass fiber composites were prepared using the vacuum-assisted resin transfer method (VARTM). The effect of different lamination stacking sequences of abaca–glass fibers on the tensile, flexural, and impact properties was evaluated. The morphological failure behavior of the fractured-tensile property was evaluated by 3D X-ray Computed Tomography and Scanning Electron Microscopy (SEM). The results of mechanical properties were mainly dependent on the volume fraction of abaca fibers, glass fibers, and the arrangement of stacking sequences in the laminates. The higher volume fraction of abaca fiber resulted in a decrease in mechanical properties causing fiber fracture, resin cracking, and fiber pullout due to poor bonding between the fibers and the matrix. The addition of glass woven roving in the composites increased the mechanical properties despite the occurrence of severe delamination between the abaca–strand mat glass fiber.

I-fiber implantation robot for composite parts

I-fiber implantation is a new stitching technology that can effectively enhance the interlayer performance of laminated composites. This paper presents and evaluates the design and implementation of the I-fiber robot implantation system integrated for producing high-performance fiber preforms for advanced composites. The system was constructed and validated through I-fiber robot implantation experimentation. It was demonstrated that automated I-fiber implantation could be achieved by use of an industrial robot. The programming method and computer-aided manufacturing software of the I-fiber implantation robot were feasible and effective. The double-cantilever-beam (DCB) experiments showed that the implantation of I-fiber significantly improved the interlaminar fracture toughness of the laminated composite, where the maximum load value increased by up to 106%. The DCB load–displacement curve presented a zigzag shape, where the peaks and valleys were the location points of the I-fiber break. It was also found that for the reinforced laminated composite without an I-fiber head, the delamination failure was manifested as resin cracking and I-fiber pullout, while for the I-fiber with a certain head length, the I-fiber failure mechanism was brittle fracture. I-fiber with a certain head length could significantly improve the interlayer performance of the composite. In addition, DCB experiments also revealed that the implantation matrix had little effect on the interlayer performance of I-fiber reinforced composites, and the failure load value and the I-fiber implantation volume showed an obvious proportional relationship.

In Situ Detection of Water Leakage for Textile-Reinforced Composites.

By incorporating electrically conductive yarns into a waterproof membrane, one can detect epoxy resin cracking or liquid leakage. Therefore, this study examined the electrical conductivity variations of several yarns (metallic or carbon-based) for cracking and water detection. The first observations concerned the detectors’ feasibility by investigating their conductivity variations during both their resin implementation processes and their resin cracking. Throughout this experiment, two phenomena were detected: the compression and the separation of the fibres by the resin. In addition, the resin cracking had an important role in decreasing the yarns’ conductivity. The second part of this study concerned water detection. Two principles were established and implemented, first with yarns and then with yarns incorporated into the resin. First, the principle of absorption was based on the conductivity variation with the yarns’ swelling after contact with water. A short circuit was established by the creation of a conductive path when a drop of water was deposited between two conductive, parallel yarns. Through the influence of the yarns’ properties, this study explored the metallic yarns’ capacity to better detect water with a short circuit and the ability of the carbon-based yarns to detect water by the principle of absorption.

Drill bit with clip-edges based on the force control model for reducing the CFRP damage

Carbon fiber reinforced plastic composites are popular in the aviation industry, and it is inevitable to drill holes within strict damage tolerances during assembly. However, drilling damages often occur at the drill-exit of carbon fiber reinforced plastic for lacking back support. This paper aims to study the drilling damages formation of carbon fiber reinforced plastic, and further proposes a novel drill structure for reducing the damages. According to the damage formation of drill-exit fibers, the mathematical model is established to analyze the tool-fibers cutting process and fiber deflection. Then based on the cutting model, the multi-edge control force cutting method is proposed, and it is an effective method to cut off fibers with deflection control and damage reduction. In order to carry out the cutting effect, a novel clip-edges drill structure is proposed. The geometric analysis of the novel structure reveals that the structure can cut the fibers from both sides and reduce fiber resin cracking. Finally, comparative experiments are carried out in drilling carbon fiber reinforced plastic, and the novel drill bit with clip-edges drill structure can reduce drilling exit damage and obtain more high-quality holes.