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Carbon fiber reinforced thermoplastic (CFRTP) composites, known for their excellent mechanical properties and environmental sustainability, are highly sought‐after in aerospace, energy, and many other fields. Grinding could be used to realize the high‐accuracy and low‐damage machining of CFRTP components. However, due to the temperature sensitivity and water absorption of CFRTP, dry and flood lubrication grinding could cause thermal damage and hygrothermal aging, respectively. In addition, these methods could lead to dust and excessive cutting fluids harmful to the environment. Addressing these bottlenecks, this study is the first to propose using oil‐on‐water minimum quantity lubrication (OoW‐MQL) to grind CFRTP. Experiments including various lubricating conditions and grinding parameters were performed to investigate the grinding performance. Experimental results showed that OoW‐MQL with the oil–water proportion of 1:1 outperformed the other lubricating conditions, achieving the best surface quality with the lowest grinding forces and temperatures. The optimal oil–water proportion remained almost unchanged under different grinding parameters. Furthermore, importance analysis using the extreme gradient boosting (XGBoost) algorithm demonstrated that oil–water proportion was the most critical factor affecting surface roughness. This study proves the feasibility of OoW‐MQL and provides technical guidance for high‐quality grinding of CFRTP. Highlights: Oil‐on‐water minimum quantity lubrication (OoW‐MQL) was proposed to grind carbon fiber reinforced thermoplastic (CFRTP) composites.The experimental results of grinding forces, grinding temperatures, surface roughness and surface morphologies were analyzed, which proved that OoW‐MQL with oil–water proportion (1,1) had outstanding lubricating and cooling capability.The effect of grinding parameters on the optimal oil–water proportion was proved to be negligible through comparative tests under grinding parameters of high force and high temperature.Quantitative analysis using the extreme gradient boosting (XGBoost) algorithm identified the oil–water proportion as the most critical factor influencing surface roughness. [ABSTRACT FROM AUTHOR]

Grinding could be used to enhance accuracy and quality of carbon fiber‐reinforced poly‐ether‐ether‐ketone (CF/PEEK) composites. However, the grinding mode, namely up‐grinding (UG) or down‐grinding (DG), is usually neglected while unbefitting grinding mode choice may cause inferior surface quality. To investigate effects of grinding modes on grinding performance of anisotropic CF/PEEK, grinding experiments in UG and DG were carried out under different fiber orientation angles θ. Experimental results indicated that maximum grinding temperatures and normal grinding forces in UG were lower than DG regardless of the abrasive grit sizes. Material removal mechanisms of CF/PEEK affected by grinding mode were revealed by analyzing morphologies of surface, chip and grinding wheel. When θ = 0°, the dominant mechanisms in DG were extrusion fracture and fiber deformation, while they were interface shear debonding and bending fracture in UG. When θ = 90°, the dominant mechanisms in DG included interface layer separation and bending fracture, while they were shear and extrusion fracture of well‐supported fibers in UG. Thus, UG was more favorable for material removal, obtaining lower surface roughness values, fewer machining defects and less wheel wear than DG. This study will provide technical guidance for high‐quality grinding of carbon fiber‐reinforced thermoplastic composites. Highlights: The effects of grinding modes (DG and UG) on the grinding performance of anisotropic CF/PEEK composites were investigated.Material removal mechanisms of CF/PEEK affected by grinding mode were revealed under different fiber orientation angles.The maximum grinding temperatures and normal grinding forces in UG were lower than DG.UG was more favorable for material removal in grinding, and could produce better ground surface quality than DG. [ABSTRACT FROM AUTHOR]

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Recently, thermoplastic resins were used as matrix to synthesize carbon fiber‐reinforced thermoplastic (CFRTP) for recycling it easily. In this study, a CFRTP with excellent mechanical properties and heat resistance was synthesized using a polyether ether ketone (PEEK) as a matrix resin. The PEEK resin was modified to form cross‐linked structures through Friedel–Crafts reaction alkylation. The synthesis temperature of CFRTP was optimized considering the mechanical properties of PEEK, and its heat resistance was enhanced because of the cross‐linked structures. Further, the cross‐linked PEEK resin was partially used as a matrix resin, and the mechanical properties of the CFRTP were enhanced. We plan to develop a method for recycling CFRTP using PEEK and crosslinked PEEK for synthesizing C/C composites by focusing on the high heat resistance of the crosslinked PEEK containing a large amount of carbon and reducing mass loss after heat treatment. Highlights: CC bonds were introduced into the polyether ether ketone (PEEK) resin by Friedel–Crafts reaction alkylation.Thermal properties of PEEK were enhanced by hypercrosslinking reaction.Optimization of synthesized temperature was investigated to fabricate carbon fiber‐reinforced thermoplastic (CFRTP).Mechanical properties were enhanced CFRTP modified with hypercrosslinking reaction. [ABSTRACT FROM AUTHOR]

With the rapid development of transportation and electronic equipment industries, lightweight requires reliable joining technology for metal/polymer. Preheating before welding is a potential way to improve the tensile properties of the joint and reduce the risk of defect formation. In this study, thermal assistance friction stir lap welding (TA‐FSLW) in joining 6061‐T6 aluminum alloy and carbon‐fiber‐reinforced thermoplastic (CFRTP) is investigated. The welds are evaluated by OM image segmentation and statistical calculation, temperature detection in thermal imaging, SEM and EDS of the fracture, tensile, and hardness analysis. From the quantitative analysis results of the width of the CFRTP side‐melting zone and the area of Al alloy fragments in the welding zone, the movement of the polymer chain in the CFRTP of joint is intensified by thermal assistance, which reduces the thickness of the melting zone on the side of the composite material. The area of metal fragments ranges from 100 to 2 × 106 μm2. The microscopic analysis results indicate that preheating enhances the initial thermal motion of molecules. Gaseous polymers are dissociated from the molten state, reducing the number of bubbles in the composite material. Small size fragments are inserted into the molten CFRTP and mechanical interlocking is enhanced due to the uniform interweaving of metals and polymers. A maximum tensile strength of 39.97 MPa is achieved, which increases by 37.6% compared with the conventional FSLW. Highlights: Thermal assistance friction stir welding technology is applied to the welding of aluminum alloy with carbon‐fiber‐reinforced thermoplastic.The number and area of aluminum alloy fragments are counted and analyzed by the metal segmentation counting algorithms.Thermal assisted technology reduces the thickness of the melting zone of CFRTP and enhances the material flow and refinement of aluminum alloy fragments. [ABSTRACT FROM AUTHOR]

To distinguish the grinding performance of the multidirectional (MD) and unidirectional (UD) carbon fiber‐reinforced thermoplastic (CFRTP) composites, MD and UD carbon fiber‐reinforced poly‐etherether‐ketone (CF/PEEK) composites were employed in this study. Different ply stacking sequences and process parameters were set for grinding experiments. Subsequently, the surface morphologies and roughness were observed and measured. Experimental results indicated that the variations of grinding forces with grinding parameters of MD‐CF/PEEK and UD‐CF/PEEK were consistent. However, the heat transfer mechanism and the effects of grinding parameters on the maximum grinding temperatures were different between the two composites. The grinding forces and temperatures of MD‐CF/PEEK were slightly lower than UD‐CF/PEEK, and MD‐CF/PEEK reached better surface quality under the same parameters, indicating that the grinding performance of MD‐CF/PEEK was not the simple superposition of UD‐CF/PEEK. In addition, the chip formation and material removal mechanism of CF/PEEK were investigated. The grinding performance of MD‐CF/PEEK was primarily dependent on the θ elements of laminate while the grinding performance of UD‐CF/PEEK was closely related to the fiber orientation angles during grinding. This study established a more in‐depth understanding into the grinding performance of MD‐CF/PEEK and provided technical guidance for high‐quality grinding of CFRTP. Highlights: The grinding performance of the multidirectional (MD) and unidirectional (UD) carbon fiber‐reinforced poly‐etherether‐ketone (CF/PEEK) is compared.The grinding forces and temperatures of MD‐CF/PEEK are slightly lower than that of UD‐CF/PEEK, and the MD‐CF/PEEK reach a better surface quality under the same grinding parameters.The grinding performance of MD‐CF/PEEK is primarily dependent on the θ elements of laminate, and the change of layering order is not a critical factor.The grinding performance of UD‐CF/PEEK is closely related to the fiber orientation angles during the grinding process.The surface quality of MD‐CFRTP can be effectively improved by reducing the grinding depth and feed speed, and increasing the grinding wheel speed. [ABSTRACT FROM AUTHOR]

Polymer/metal hybrid lightweight structures are increasingly employed in automotive, aerospace and electronics industries. Friction stir welding (FSW) is applied for the effective welding of metals and thermoplastic materials. For the welding of dissimilar materials, due to the significant property differences, it is hard to achieve high strength welded joints with smooth appearance. In this article, the influence of pin length is studied by experiments for the friction stir lap welding (FSLW) of Al alloy and carbon-fiber-reinforced thermoplastic (CFRTP). Tensile tests, OM, SEM and EBSD are carried out to evaluate the welding performance. Results indicate that the joint with smooth surface topography is obtained at the pin length of 2.5 mm with a peak temperature of 250.3 °C and the CFRTP matrix PEI thermal decomposition temperature residence time of 47.6 s. From OM and SEM micro analysis, the width of the bonding area is 3.02 mm and a thin uniform interaction layer is formed in the joint. EBSD confirms that the Al alloy in the stirring zone is refined after recrystallization. It is difficult to form a stacked layered structure in the bottom of joint, so the property of the joint is improved. The tensile strength is 32.9 MPa, which is 63.1% of CFRTP. [ABSTRACT FROM AUTHOR]

Dissimilar joining between carbon fiber reinforced thermoplastic (CFRTP) and metal has attracted attention of transportation equipment industry for reduction of weight and cost by multi-material structure. Friction stir spot welding (FSSW) between anodized A5052 (AO-A5052) and carbon fiber reinforced thermoplastic (CFRTP) was investigated for the improvement of joining strength. Average tensile shear strength of AO-A5052/CFRTP joint was 2505 N and more than 500 N higher than that of untreated-A5052/CFRTP joint. In the AO-A5052/CFRTP joint, probe plunge induced cracks and microwrinkles in the anodic oxide layer on the weld surface. Matrix resin was immersed into the cracks and the microwrinkles underneath of the shoulder of the welding tool. Reinforced carbon fiber and matrix resin was immersed into large crack at the outer peripheral corner of probe. Thus, those increased the joining strength by mechanical anchoring effect. Thermal stress test and machining stress test were performed for revealing the mechanism of cracking of anodic oxide layer. Although thermal stress did not generate cracks in the anodic oxide layer, machining stress by probe plunge generated cracks in the anodic oxide layer. The generated cracks in anodic oxide layer underneath of the shoulder were distorted to the rotating direction of welding tool by the friction stirring. [ABSTRACT FROM AUTHOR]

As a lightweight material with high performance, carbon fiber‐reinforced thermoplastic plastic (CFRTP) is being implemented increasingly in aerospace, automotive, new energy, and so forth. The connection between CFRTP and metals, which are still used in these areas, is an inevitable problem. Among the various connection techniques, laser welding of CFRTP to metal is attractive due to high efficiency, excellent strength, and no contact. This paper presents the most recent research on laser welding CFRTP and metals in three aspects: (a) the principle of laser welding CFRTP to metals and the influence of process parameters on joint quality including laser power, defocus distances, scanning speed, clamping pressure, and beam shape, (b) the joint enhancement mechanisms and methods, and (c) numerical simulations of temperature and stress fields of laser‐connected CFRTP to metals. The findings show that joint strength is significantly influenced by process parameters and that the maximum joint strength can be achieved by choosing the right parameters. Apart from the conventional techniques of texturing the metal surface, applying a suitable layer of resin, and applying chemical treatment, other novel joint improvement measures have also been used, including the use of blue laser and CFRTP embedded in the metal. The temperature field and residual stresses can be successfully simulated by finite elements, which can be useful when studying new processes and choosing parameters for metal laser welding and CFRTP. Highlights: We review the progress from parameters, simulations, and enhancements.The main parameters have essential effects on the dimensions and strength of joints.FEM (Finite Element Method) is applied to simulate the temperature and stress of the laser welding.Joints can be reinforced by surface pre‐texturing, adding resin, and grafting. [ABSTRACT FROM AUTHOR]

Induction welding is a suitable and promising technique for assembling thermoplastic composite structural components. In this work, a magneto-thermal coupling model has been developed to simulate the induction welding process of carbon fiber–reinforced thermoplastic composite L-shaped stringers. To verify the accuracy and applicability of this model, a series of experiments were conducted, and an infrared thermometer was utilized to calibrate the simulation temperature field. The accuracy and applicability of the model for the induction welding process were validated by comparing the experimental results with the simulated results. Specifically, the induced current density and the magnetic field distribution during induction heating were examined, and the temperature distribution of the carbon fiber–reinforced thermoplastic composite L-shaped stringers during heating was analyzed. It was found that the temperature field on the induction element was distributed in a semi-elliptical shape, extending from the boundary to the middle and intersecting in a butterfly shape at the center. Furthermore, the evolution of the temperature field under different process parameters was investigated, focusing on the influence of coil current and heating time. Based on the simulation results, the optimum process parameters were the coil current of 4 A and the heating time of 40 s. [ABSTRACT FROM AUTHOR]

Metal‐polymer hybrid joints can contribute to weight reduction and have potential use in transportation industries. In this work, laser texturing was used to enhance bonding strength of laser‐welded 304 stainless steel/carbon fiber reinforced thermoplastics (CFRTP) joint. The tight relationship between surface texture spacing and porosity characteristic as well as tensile property of joint was systematically investigated. The temperature field distribution during welding process was simulated and the mechanism of porosity suppression depending on grid spacing was discussed. The result showed that the number of pores at cross‐section decreased first and then rose with the increase of micro‐structure spacing, which corresponded to the variation trend of bonding strength and was inconsistent with the evolution of connecting area. The joint achieved the minimum porosity defect and reached maximum fracture load of 2594 N when the grid spacing was 1.2 mm, while the maximum joint width of 9.28 mm was obtained when 0.4 mm spacing was adopted, indicating that the joint quality rather than mechanical interlocking governed the mechanical property of joint. Appropriate interface contact conductance (TCC) related to texture spacing could optimize the interface heat dissipation rate, and was the key factor to efficiently control the shrinkage porosity. The TCC of small or large grid spacing was too high or too small, resulting in failure of the heat transfer path through the interface to metal during cooling process. Moreover, the proper texture spacing improved the uniformity of joint strain distribution in tensile‐shear testing, which benefited joint strength. Highlights: Laser‐textured grid pattern spacing affected number and distribution of pores.Heat dissipation rate varied with various spacing at joint interface.1.2 mm spacing texture reduced stress concentration during tensile process. [ABSTRACT FROM AUTHOR]

In this study, a highly efficient method for preparing Al/CFRTP/Al composite laminates by roller preparation was proposed. Three different surface treatments, namely, anodic oxidation, laser texture and surface modification, were used to improve the strength of the metal‐fiber interface. Results show that composite laminates can be prepared efficiently by using reasonable roll pressing technology. The composite laminates with a thickness of 3 mm has good shear strength when the reduction amount is 0.02 mm. Laser texturing increases the contact area at the laminate interface. The surface roughness of Al alloy sheet is improved after laser texture. Moreover, the matrix in the fiber layer of the laminate can be embedded in the gullies formed by the laser texture to form a mechanical interlocking structure. The shear strength of the laminates was further increased when the laser scanning spacing was 2 mm. The highest shear strength of the laminate is 52.4 MPa after using a coupling agent to modify the surface of the Al alloy sheet. X‐ray photoelectron spectroscopy analysis showed that a new chemical bond was generated at the interface between CFRTP and the Al alloy sheet modified with silane coupling agent, thereby forming a molecular bridge among different materials. Mechanical interlocking structure and the generation of new chemical bonds cause the interface to need to absorb more energy during the failure process, which is conducive to the improvement of the interface strength. Highlights: Propose roller pressing to prepare Al/CFRTP/Al composite laminates.Effect of laser texture of the laminates interface is clarified.Mechanism of coupling agents at the interface has been elucidated.Efficient preparation of thermoplastic fiber metal laminates has been achieved. [ABSTRACT FROM AUTHOR]

A series of numerical material tests based on homogenization theory are carried out to characterize the anisotropic elastoplastic and hardening behavior of thermoplastic resin reinforced in one direction by carbon fibers (UD-CFRTP), and a new constitutive model is proposed to describe the characteristic material behavior. First, macroscopic stress-strain curves are obtained from numerical material tests (NMTs) conducted on a unit cell model, i.e., a representative volume element of periodic microstructures, to which uniaxial and combined stress states are applied under various conditions of stress ratios and stress paths. Using the obtained NMTs results, the initial shape of the yield surface and its evolution are investigated in detail. The results suggest that even if a resin has isotopic hardening characteristics, UD-CFRTP exhibits complex anisotropic post-yielding or, equivalently, hardening behavior. Then, a constitutive model that can describe such material behavior is originally formulated, and a step-wise identification strategy is presented to determine the material parameters. Finally, by carrying out verification analyses, we confirmed that the macroscopic stress-strain curves represented by the proposed model can be fitted to those obtained by NMTs with sufficient accuracy for practical use and that the performance of the proposed model is much better than that of a conventional constitutive law.

The induction welding has been recognized as one of potential and high-efficiency joining methods for thermoplastic composite materials. In this study, a numerical simulation model with containing both induction wielding heat transfer and joint tensile failure process for CF/PPS-Al alloy interlocking induction welding was established based on software COMSOL Multiphysics and Abaqus/Explicit. The CF/PPS-Al7075 interlocking welding joints with special designed macro-scale interlocking were tested under tensile loads, and the corresponding single-lap shear strength, energy absorption, and failure mechanisms were investigated by combining the experimental and numerical approaches. Finally, the influence of macro-scale interlocking geometric parameters on joint tensile strength was also discussed. The results indicate that the proposed model can effectively predict the temperature distribution in the welding process and the tensile failure process of the joint. It is also presented that the addition of macro-scale interlocking features can effectively improve the ultimate load (47%) of the CF/PPS-Al alloy induction welded joints. Meanwhile, the number of addition PPS films in the welding zone and the inclination angle have greater contribution on the tensile strength of the welded joints. [ABSTRACT FROM AUTHOR]

This study evaluated the Mode I interlaminar delamination fracture toughness of s-CF/PA6 (short Carbon Fiber/Polyamide 6) laminates molded by FDM (Fused Deposition Molding) type 3D printer, using DCB (Double Cantilever Beam) tests on two different configurations. We also tested and compared dried and undried specimens. Fracture surface observations by scanning electron microscope revealed the mechanism of toughness development and factors affecting interlaminar delamination fracture toughness. The results showed that angle ply exhibit higher toughness than cross ply. The toughness of dried specimens was higher than that of the non-dried specimens. These results were highly variable. One reason for this is the difference in adhesion states and voids between layers. One possible cause of insufficient welding is a molding area temperature during molding. In addition, insufficient welding may occur if the filaments are printed when they are not sufficiently dry. As for voids, there is a possibility that they can be improved by adjusting the 3D printer. [ABSTRACT FROM AUTHOR]

• An elastic-plastic model considering plastic deformation was established, and its accuracy was verified through off-axis tensile tests and simulations. Additionally, a comparison was made between the predictions of the elastic-plastic model considering plasticity and those of the elastic model not considering plasticity. • The effect of stiffness parameters on the mechanical response was explored and the optimal stiffness parameters were determined. • The elastic-plastic-damage model is established and applied to simulate the low-velocity impact mechanics response and damage behavior of thermoplastic composite CFRTP. By incorporating the plastic deformation and Puck damage criteria law, a three-dimensional elastic-plastic-damage model has been established to predict the behavior of carbon fiber reinforced thermoplastic (CFRTP) composites under low-velocity impacts. The model has been integrated into ABAQUS/Explicit, and off-axis tensile test were conducted to ascertain appropriate parameters for the elastic-plastic model. Additionally, finite element modeling of off-axis tensile were employed to assess the precision of the model parameters and to contrast the variance of accounting for plastic deformation against neglecting it. The effectiveness of the elastic-plastic-damage model, incorporating damage considerations, was confirmed through an analysis of the mechanical response and progressive damage of CFRTP during low-velocity impact tests. Compared to the elastic-damage model that does not consider plastic deformation, the elastic-plastic-damage model, which takes plastic deformation into account, exhibits higher prediction accuracy. Both simulation and experimental results indicate that delamination and matrix cracking are the dominant damage patterns observed in CFRTP at relatively low impact energies (≤16.20 J). [ABSTRACT FROM AUTHOR]

In this study, quasi-isotropic (QI) laminates were fabricated using two types of PA6/CF thin-ply prepregs with different fiber/matrix interfacial properties, and Charpy impact tests and falling weight impact tests were conducted. The effects of layer thickness of prepreg and interfacial properties on the impact energy absorption performance were investigated by clarifying the fracture mode and propagation during impact. The layer thickness of each ply was set to 40, 80 and 120 μm by using thin-ply prepreg with the thickness of about 40 μm made by tow-spreading technology. Charpy impact values were higher for PA6/CFsmooth, where interface fracture was dominant, the values significantly increased as the layer thickness of the prepreg increased. On the other hand, the Charpy impact values of PA6/CFrough, where cohesive fracture is dominant, did not change significantly with increasing prepreg layer thickness. The results of the drop-weight impact test indicate that the layer thickness of the prepregs changing the fracture mode depends on the fiber/matrix interfacial properties. It is clear that the layer thickness at which the "thin-ply effect = reduced delamination" induced by changes in the layer thickness constituting the QI material is affected by the fiber/matrix interfacial properties. From the viewpoint of impact energy absorption, similar to the results of the Charpy impact test, it was shown that more impact energy can be absorbed when large scale delamination occurred.

Laser surface texturing is generally a promising approach to enhance the adhesion property of a metal-thermoplastic hybrid structure, and the effect is related to groove configuration. Laser joining of a carbon fiber-reinforced thermoplastic (CFRTP) composite to a 6061 Al alloy under various groove configurations was carried out, aimed to investigate the effect of groove width and depth on interfacial morphology, mechanical properties, and fracture behavior of CFRTP/Al joints. Tensile shear force was tested, and fracture surface and interface morphology were observed by scanning electron microscopy. Besides, the numerical simulation of the temperature field was conducted to reveal the joining mechanism. The results indicate that the tensile shear strength of the CFRTP/Al joint gradually increases with the increase of groove width and reaches a peak value of 22.8 MPa when the width is 0.5 mm. As the groove width is further increased, the tensile shear strength of the CFRTP/Al joint decreases. Compared to groove width, the tensile shear strength of the CFRTP/Al joint presents a similar variation trend with the increasing groove depth on the Al alloy surface. When the groove depth reaches 0.6 mm, the maximum joint strength is 24.33 MPa. After the Al alloy is laser-textured, the surface fracture mode of the CFRTP/Al laser joint features a mixed fracture mode including a cohesive fracture and an interface fracture. This study provides a deeper understanding of the effect of groove configuration on the laser joining of the CFRTP/Al hybrid structure and potentially lays a foundation for the adjustment of a suitable groove configuration toward obtaining the desired effect. [ABSTRACT FROM AUTHOR]

Dissimilar components composed of CFRTP (Carbon Fiber Reinforced Thermoplastic Polymer) and TC4 titanium alloy are increasingly applied in the aerospace field. The scanning mode offers a significant influence on the quality of laser joining joint between CFRTP and TC4 titanium alloy. Therefore, the laser joining between TC4 titanium alloy with surface microgrooves and CFRTP has been implemented under oscillating laser joining mode and linear laser joining mode respectively in the present research. The temperature distribution is qualitatively explored based on the established mathematical model of laser joining between CFRTP and TC4 titanium alloy. The interface morphology and the joining strength of CFRTP/TC4 titanium alloy lap joints under oscillating laser joining and linear laser joining are compared. The results indicate that the simulated temperature distribution shows good agreement with the experimental results. Compared with linear laser joining, the oscillating laser joining weakens the heat concentration and creates a heating zone with larger area and more uniform temperature distribution. The interface morphology of laser joining CFRTP/TC4 titanium alloy joints obtained by oscillating laser joining presents better resin filling and fewer bubble defects due to the temperature variation of the form of unequal amplitude oscillations, with the resin filling ratio of 92.20% and the porosity of 3.78%. In contrast, the linear laser scanning mode with a large number of large-sized bubbles in the filling resin and small-sized fusion gaps distributed at the interface holds a resin filling rate of 60.11% and a porosity of 32.89%. By adopting the joining method with oscillating laser scanning mode, higher quality joints can be obtained with the joining strength of 24.48 MPa. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced thermoplastic polymer (CFRTP) laminates can be used in packaging electronics components to reduce weight and shield external disturbance. The CFRTP structures in operation are inevitably to suffer dynamic loading conditions such as falling rocks, tools and impacts. In this study, a strain rate dependent material model for accurately evaluating the dynamic response of CFRTP laminates with different stacking sequence was proposed. The model was composed of three components: a strain rate dependent constitute model, a strain rate related damage initiation model and an energy-based damage evolution model. The strain rate effect of modulus and strength was described by a stacking sequence related matrix, and the damage initiation model could describe the matrix, fiber and delamination damage of CFRTP laminates without introducing cohesive elements. The material model was implemented into finite element software ABAQUS by user defines subroutine VUMAT. The low velocity impact tests of CFRTP laminates with quasi-isotropic and angle-ply stacking sequence were used to provide validation data. The dynamic response of CFRTP laminates from numerical results were highly consistent with the experimental results. The mechanical response of CFRTP laminates were affected by stacking sequence and impact energy, and the numerical error of proposed material model significantly decreased with the increasing impact energy especially for the laminae with damage occur. [ABSTRACT FROM AUTHOR]

Repairing delamination damage is critical to guarantee the structural safety of carbon fiber-reinforced thermosetting composites. The popular repair approaches, scarf repair and injection repair, can significantly restore the in-plane mechanical performance. However, the out-of-plane properties become worse due to the sacrifice of fiber continuity in these repairing processes, leading to the materials being susceptible under service loads. Here, we propose a novel in situ delamination repair approach of controllable thermal ablation in damage removal, achieving a high repair efficiency without impairing the fiber continuity in carbon fiber/epoxy panels. The epoxy resin in the delaminated region was eliminated under the carbonization temperature in a few minutes, allowing the carbon fiber frame to retain its structural integrity. The healing agent, refilled in the damaged region, was cured by the Joule heating of designed electrodes for 30 min at 80 °C, yielding the whole repair process to be accomplished within one hour. For the delaminated carbon fiber/epoxy panels with thicknesses from 2.5 to 6.8 mm, the in-plane compression-after-impact strength after repair could recover to 90.5% of the pristine one, and still retain 74.9% after three successive repair cycles of the 6.8 mm-thick sample. The simplicity and cost-saving advantages of this repair method offer great potential for practical applications of prolonging the service life of carbon fiber-reinforced thermosetting composites. [ABSTRACT FROM AUTHOR]

Tensile axial fatigue tests were carried out using carbon fiber‐reinforced thermoplastics (CFRTP) plate with a hole notch up to very high cycle fatigue (VHCF) regime, where number of loading cycles was 2 × 107. The fatigue test was periodically interrupted, and fatigue damage accumulation around the hole notch was non‐destructively detected by two positron annihilation methods. Positron annihilation lifetime spectroscopy was applied to obtain positron lifetime and Doppler broadening method to obtain S‐parameter. Both parameters increased with increasing fatigue loading cycles. Fatigue damage detected by two positron annihilation methods was attributed to the expansion of free volume in the polymer matrix. The estimated size of free volume was sub‐nanoscale according to the experimental value of the positron annihilation lifetime. SEM and μCT scan revealed that the macroscopic fatigue damages, such as surface cracking, transverse cracking and delamination, increased with increasing fatigue loading cycles, which indicated that sub‐nanoscale and macroscopic fatigue damages progressed simultaneously. Consequently, it can be concluded that the positron annihilation methods can be used for the non‐destructive fatigue damage detection of CFRTP. Highlights: Fatigue damage of CFRTP was detected by two kinds of positron annihilation methods.Positron lifetime and S‐parameter increased with increasing loading cycles up to 2 × 107.Microscale or nanoscale fatigue damages in CFRTP were related to macroscopic damages. [ABSTRACT FROM AUTHOR]

• A non-contact temperature measurement method was proposed to monitor real-time temperature to unveil the laser ablation mechanism of CFRTP. • A novel FE model has been developed for laser cleaning of the three-dimensional woven CFRTP that takes into account anisotropic heat transfer. • The influence of three key laser cleaning parameters on the cleaning quality was elucidated through statistical methods. • The mechanical property enhancement of bonded joints can be attributed to the improved wettability and higher surface free energy. The outstanding mechanical properties of carbon fiber reinforced thermoplastic polymer (CFRTP) have led to its widespread application in many industrial sectors. In response to the engineering challenge of repairing large non-critical CFRTP structural components in situ, an infrared fiber laser surface cleaning technology is proposed to treat the bonding interface and enhance the tensile strength of polypropylene (PP)-based CFRTP single-lap bonded joints. Specifically, through single-factor and orthogonal experiments, the impact of different process parameters on the properties of the bonded joints was identified first. Then, online temperature monitoring was performed to elucidate the laser treatment mechanism of the CFRTP sample interface. Surface morphology of the laser-treated samples further indicates that when the temperature of the sample surface surpasses the resin decomposition temperature with extended holding time, the resin could be removed from the surface more thoroughly. Additionally, a novel three-dimensional woven finite element (FE) model, accounting for anisotropic heat transfer, was established to predict the surface temperature and cleaning quality of CFRTP. The FE model incorporates the anisotropic heat transfer characteristics of carbon fibers, thus accurately simulating the heat transfer behaviors between carbon fibers and the resin matrix. The laser ablation mechanism is elucidated by examining the surface ablation morphologies and peak surface temperatures. A comparison between experimental results and FE simulations demonstrated a notable coherence in the trend of surface morphology variations, with discrepancies in peak surface temperatures ranging from 3.29 % to 24.63 %. The experimental tests proved that the shear strength of single-lap bonded joints reaches its maximum value when the laser power is 35 W, the scanning speed is 2500 mm/s, and the number of scans is four. The enhancement of the mechanical properties of bonded joints can be attributed to the improved wettability and higher surface free energy of the laser-treated samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anodic oxide film was proposed to improve bonding reliability of steel/CFRTP. • Interfacial structure of stainless steel/CFRTP joint was observed by TEM. • DFT calculation was adopted to study bonding mechanism between oxide film and CFRTP. Metal-carbon fiber reinforced thermoplastic (CFRTP) hybrid joints have demonstrated its effectiveness in achieving lightweight design concept in engineering application. However, it is difficult to produce high-reliability joint due to differences in physical as well as chemical properties between metal and CFRTP. In this study, porous oxide film was prepared by anodizing treatments with various anodic oxidation times on steel surface to enhance joint performance of laser-welded steel/CFRTP. The maximum steel/CFRTP joint fracture load of 1960 N was reached, which was three times as much as that obtained with pretreated steel. The results indicated that porous structure was introduced into steel surface by anodization process, which resulted in better wettability of molten CFRTP and higher surface roughness, thus contributing to the enhancement of joint area as well as mechanical interlocking at the interface, further improving joint performance. Meanwhile, more Cr-O-C chemical bonds were produced because Cr-rich oxide film formed after anodizing contributed to interfacial chemical reaction. The chemical bond between oxide film and CFRTP was proved through density functional theory (DFT) calculation. Additionally, with the increase of anodic oxidation time, chemical bond content and surface roughness first enhanced and then reduced, which suggested that the porous structure prepared with 20 min anodizing time could best improve the interfacial mechanical interlocking, and promote the chemical bonding as well as steel/CFRTP joint interfacial bonding. [ABSTRACT FROM AUTHOR]

The lightweight design concept in structural applications has generated interest in hybrid structures of carbon-fiber-reinforced thermoplastics (CFRTP) and metals as attractive structure components. However, these hybrid structures face challenges due to the significant differences in physical and chemical properties between CFRTP and metals, resulting in limited strength and rendering them unsuitable for advanced transportation. To address these limitations, the current research focuses on creating a biomimetic texture on A6061-T6 (6061) surfaces using femtosecond laser to manufacture high-strength hybrid structures, inspired by organismal body surfaces. The CFRTP and 6061 were joined by friction stir spot welding (FSSW). The femtosecond laser treatment produces double-scale roughness on 6061 surfaces and causes carbon to absorb into alumina. These changes in physical and chemical structures enhance the compatibility between 6061 and CFRTP. The biomimetic rough aluminum surface creates effective mechanical interlock at the interface with CFRTP, preventing the initiation and propagation of fracture cracks. The presence of absorbed carbon enhances the Al-O covalency, which influences the bonding behavior at CFRTP/6061 interfaces. The improved compatibility, mechanical interlock, and enhanced bonding behavior synergistically strengthen the joint strength of CFRTP/6061 hybrid structure modified by the biomimetic papilla structure. Current biomimetic design strategy inherits the remarkable natural wisdom and is expected to provide valuable insights for the development and application of CFRTP/metal hybrid structures. • The biomimetic papilla structure inspired by organismal body surfaces was textured on 6061 for high-reliability CFRTP/6061 hybrid structures. • The evolutions in failure mechanism of the hybrid strcutures were uncovered. • The improving compatibility, achieving mechanical interlock, and evolving bonding behavior strengthened the joint strength. • The modified CFRTP/6061 hybrid structures achieved the high joint strength of 37.06 MPa and joint efficiency of 69.92 %. [ABSTRACT FROM AUTHOR]

This paper presents a method to improve the laser bonding joint strength between carbon fiber reinforced thermoplastic composite (CFRTP) and aluminum alloy (Al). In this method, the CFRTP with preset aluminum alloy sheet is attained by the compression molding method after the aluminum alloy sheet is preset between the polyetheretherketone (PEEK) and carbon cloth. The CFRTP with preset aluminum alloy sheet is connected to the aluminum alloy by laser heat source, and the maximum load of the joint can reach 4264 N. Microstructure and fracture surface morphology of joint are observed and analyzed. The results indicate that the interface of the preset aluminum alloy sheet and CFRTP reveals an extensive diffusion of elements compared with the interface of aluminum alloy and CFRTP due to the effect of hot pressing. The fracture failure mode of the lap structure between aluminum alloy and CFRTP is mixed fracture with adhesion fracture as the main component. The fracture position of preset aluminum alloy sheet and aluminum alloy lap structure is observed near the weld seam fusion line, and numerous dimples are found on the fracture surface of aluminum alloy. The increase in joint bonding force is mainly attributed to the collective effect of two lap structures; during the stretching process, the interface between aluminum alloy and CFRTP first undergoes fracture, and then, preset aluminum alloy sheet undergoes plastic fracture failure. [ABSTRACT FROM AUTHOR]

The effect of the layer thickness of prepreg on the tensile properties and failure behavior of quasi-isotropic (QI) laminates of thermoplastic CFRP consisting of carbon fiber and polyamide 6 was investigated. The layer thickness of each ply was set to 40, 80 and 120 μm by using thin-ply prepreg with the thickness of approximately 40 μm made by tow-spreading technology. As a result, that so-called "Thin-ply Effect" reported for thermosetting CFRP was not remarkable in this study of thermoplastic CFRP composed of CF/PA6. The tensile stress linearly increased with tensile strain up to the maximum tensile stress independent of the layer thickness. The tensile strength and modulus hardly changed with the layer thickness, although the delamination was interestingly inhibited with decrease of layer thickness. However, although the effect of the layer thickness of the prepreg was slight until the maximum tensile stress was reached, the failure behavior at the final breaking was significantly different depending on the layer thickness. Thinner layers inhibited delamination, and as the layer thickness increased, delamination became the dominant failure mode. Therefore, it was clarified that the effect of the layer thickness of prepreg appeared in the fracture behavior at the final failure after reaching the maximum tensile stress in the QI laminates of CF/PA6.

In this study, the synergistic effects of a hybrid surface treatment involving hydrochloric acid (HCl) immersion and silanization on friction stir spot welding (FSSW) of aluminum and carbon fiber reinforced thermoplastic (CFRTP) were investigated. Maximum tensile shear strength of 10.2 kN and maximum cross-tension strength of 1.92 kN were achieved. An unloading test and a miniature tensile test revealed that the fracture behavior changed from interfacial to CFRTP fracture due to increased interfacial strength with the hybrid treatment and utilization of the CFRTP strength enhanced the joint strength. The nanostructures at the interface with HCl immersion treatment indicated that the interfacial properties were improved mechanically in addition to the chemical enhancement by silanization. Owing to the hybrid treatment, aluminum and CFRTP were efficiently joined by the adhesion behavior of spreading melted plastic resin during the FSSW process.

Long molding times and the impossibility of remelting or reforming carbon fiber-reinforced plastics (CFRPs) that contain thermosetting resin after molding have led researchers to focus on carbon fiber-reinforced thermoplastics (CFRTPs) made with thermoplastic resin. Compared to CFRPs, CFRTPs are easier to recycle, but they generally exhibit strength properties that are inferior to those of CFRPs due to poor adhesion between the carbon fiber and the resin. To address this issue, we devised a new surface modification method (using a titania solution) to improve adhesion between fiber and the resin. Fragmentation and tensile tests were used to evaluate the effect of the surface modification method on CFRTP adhesion. The results indicate that surface modification can enhance adhesion in CFRTP, which may improve the material's mechanical properties. [ABSTRACT FROM AUTHOR]

Laser joining merges as a novel technique for the connection of carbon fiber reinforced thermoplastics composite (CFRTP) and metal. Besides, machining grooves on the metal surface presents a surface pre-treating method to enhance the strength of laser joining joint between CFRTP and metal. In this study, the laser joining of CFRTP and Ti6Al4V alloy is performed with different groove dimensions. The effect of groove dimension on interface morphology and failure load is analyzed. In addition, the formation mechanism of the interface and the fracture mode of the joint are further elucidated. The results indicate that the structurally sound connection and maximum failure load are attained with an appropriate groove dimension (groove width: 0.7 mm, groove depth: 0.25 mm, and aspect ratio: 0.36). At a narrower groove, the bubbles inside the resin caused by thermal decomposition of the matrix resin are obtained, while at a deeper groove, the gaps and holes are observed in the interface of the joint, both resulting in a lower failure load. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced thermoplastic (CFRTP) composites grinding temperatures could even exceed the glass transition temperature (Tg) of the material due to heat accumulation, combined with the unknown material removal mechanism, resulting in machining defects. To investigate the grinding temperature distribution and maximum temperatures of carbon fiber-reinforced poly-ether-ether-ketone (CF/PEEK) composites, as a typical kind of CFRTP, an analytical temperature model considering the anisotropy was proposed based on the moving heat source theory, verified by the experimental results measured by the infrared camera. Further, the material removal mechanism under temperature treatments (below and above Tg) was also studied. In high temperatures (above Tg), there were many defects on surfaces after grinding, including resin smearing, severe deflection, fiber distortion, and grinding wheel clogging. Therefore, to reduce the grinding temperature below Tg, the vortex tube cooling-assisted grinding method was proposed in the research. The proposed method could reduce the grinding temperature in the grinding area, suppress resin smearing, improve the surface quality, enhance the elastic modulus and nano-hardness of the workpiece, and reduce the clogging of grinding wheels. This study provided a better understanding of the CF/PEEK grinding temperature characteristics and suggested a method to improve the grinding quality. [Display omitted] • An analytical temperature model for CF/PEEK grinding considering material anisotropy was developed. • The material removal mechanism in CF/PEEK grinding under temperature treatments (below and above Tg) was revealed. • The temperature characteristics of CF/PEEK depended on grinding parameters, fiber orientations and temperature treatments. • The cooling-assisted grinding improved the grinding quality and mechanical properties, reducing the grinding wheel clogging. [ABSTRACT FROM AUTHOR]

The γ-aminopropyltrimethoxysilane (γ-APS) and γ-(2,3-epoxypropoxy) propyltrimethoxysilane (γ-GPS) single or bilayer silane film was produced to improve the tensile property of laser-welded 304 stainless steel/CFRTP joint in this work. The bonding mechanism at joint interface was investigated through experiments as well as density functional theory (DFT) calculation. Si-O-Fe covalent bonds were formed between steel and different silane films. Hydrogen bonds were induced at the interfaces of silane coating/polymer sides. The binding energy calculation results suggested that the binding between γ-APS silane coupling agent and steel was more stable than that of γ-GPS and steel. The binding energy of −3.37 eV between amino group in γ-APS and carbonyl group in CFRTP was greater than the binding energy of −4.84 eV between epoxy group in γ-GPS and amide group in CFRTP, which indicated stronger interaction was obtained between γ-GPS and polymer compared to the interaction between γ-APS and polymer. The bilayer silane coating could combine the dominant functional groups of silane monolayer film to obtain stable bonding on both metal side and CFRTP side. Moreover, compared with silane single film, longer silane oligomer molecular chain length was provided by bilayer silane film, resulting in more entanglement sites between silane film and CFRTP and the increased joint mechanical property. The steel/CFRTP hybrid joint reached maximum tensile shear strength of 17.2 MPa, which was further increased by 115.0% and 79.2% than that obtained by γ-APS and γ-GPS silane single coating, respectively. [Display omitted] • Bilayer silane film was proposed to improve bonding reliability of steel/CFRTP. • Different bonding mechanisms between silane film and metal or CFRTP was elucidated. • Bonding energies between various functional groups were calculated. [ABSTRACT FROM AUTHOR]

• Micro-texture under different texturing direction had different effect on joint. • Stress at the TC4/CFRTP interface was simulated. • Different Micro-texture provided different mechanical resistance during tensile test. Hybrid structure of titanium alloy and carbon fiber reinforced thermoplastic composite (CFRTP) provided a new direction for lightweight and laser had a great prospect for application in joining metal/plastic. In this work, before laser joining TC4 (Ti6Al4V) and CFRTP (PA66), three groove micro-structures in different texturing direction (0°, 45°, 90°) were prepared on the TC4 surface respectively by nanosecond laser. The effect of different groove texturing was studied. Research results showed that the existence of three groove texturing increased the affinity between TC4 and molten CFRTP to the same extent. The resin-carbon fiber mixture adhered to the surface of TC4 after laser texturing increased obviously. However, the groove micro-structure had different impact on the tensile performance of the joint. The maximum tensile shear strength could reach 10.9 MPa, which was increased by 111 % compared with the untreated when the groove micro-texturing direction was perpendicular to the tensile direction (0° texturing) while the 90° textured joint performance was only increased by 42.9 %. The FEA results revealed that micro-texturing provided mechanical resistance for the joint during the tensile process and 0° micro-texturing provided the largest mechanical resistance followed by 45° and 90° micro-texturing. [ABSTRACT FROM AUTHOR]

• FSSW of Al and CFRTP joint were studied with surface treatment and interfacial adhesion. • The combination of laser ablation and interfacial PA6 film significantly enhanced the interfacial bonding of the joint. • A bond force of 10.282 kN was shown for the Al/CFRTP joints at FSSW 2000 rpm–3 mm–10 s. The multiple material design of lightweight structural components of new energy vehicles imposes high demands on the joint of Al alloy and CFRTP composite. This study explored the fabrication of high joint strength between Al alloy 6061 and CFRTP PA6 composites through the laser ablation on Al alloy surface and friction stir spot welding (FSSW) process. By experimental optimization of the FSSW parameters, including rotational speed, displacement, and dwelling time, a remarkable tensile shear force of 10.282 kN was achieved under the rotational speed of 2000 rpm, displacement of 3 mm, and dwelling time of 10 s. The interfacial morphology of the Al alloy/CFRTP joint was characterized in detail. The microstructure analysis revealed a number of physical anchoring areas formed at the joint interface of laser-ablated Al alloy and CFRTP PA6. The PA6 resin of the CFRTP could be fully melted and effectively fill the grooves on the laser-ablated Al alloy surface due to the compression load and heat output at a high rotational speed and dwelling time. [ABSTRACT FROM AUTHOR]

Repairing delamination damage is critical to guarantee the structural safety of carbon fiber-reinforced thermosetting composites. The popular repair approaches, scarf repair and injection repair, can significantly restore the in-plane mechanical performance. However, the out-of-plane properties become worse due to the sacrifice of fiber continuity in these repairing processes, leading to the materials being susceptible under service loads. Here, we propose a novel in situ delamination repair approach of controllable thermal ablation in damage removal, achieving a high repair efficiency without impairing the fiber continuity in carbon fiber/epoxy panels. The epoxy resin in the delaminated region was eliminated under the carbonization temperature in a few minutes, allowing the carbon fiber frame to retain its structural integrity. The healing agent, refilled in the damaged region, was cured by the Joule heating of designed electrodes for 30 min at 80 °C, yielding the whole repair process to be accomplished within one hour. For the delaminated carbon fiber/epoxy panels with thicknesses from 2.5 to 6.8 mm, the in-plane compression-after-impact strength after repair could recover to 90.5% of the pristine one, and still retain 74.9% after three successive repair cycles of the 6.8 mm-thick sample. The simplicity and cost-saving advantages of this repair method offer great potential for practical applications of prolonging the service life of carbon fiber-reinforced thermosetting composites.

The application of carbon fiber reinforced thermoplastic matrix composites (CFRTP) is constantly increasing in various industrial sectors due to their mechanical properties and advantages compared to thermoset matrix composite. Nevertheless, CFRTP machining generates a current problem due to the anisotropy of these materials, the difficulty of impregnation of the reinforcement in the matrix, and its low melting temperature. For this reason, the study of conventional operations such as milling to achieve geometries with a good surface quality and reduced cosmetic defects is a line of research of great interest. In this article, a comparison of five cutting tools with different geometries has been made in CFRTP milling. The surface quality and the formation of visual defects such as fiber pull-out have been evaluated for each tool and combination of cutting parameters. In this sense, 16.42 μm in terms of Rz is the minimum average value for the complete experiment obtained for a conventional tool (tool A). However, surface qualities in terms of Rz close to 20 μm and minimum cosmetic defects have been obtained with a hybrid tool (tool C) with −10° helix angle and 8 teeth with a combination of cutting parameters of 0.07 mm/tooth and 3000 rpm, being the most complete tool of the experiment. [ABSTRACT FROM AUTHOR]

A new interlaminar shear test method has been proposed based on the double-notch compression test method, in which the test specimen shape with a modified overlap length of the notches is proposed, and the interlaminar shear strain is measured by two-dimensional digital image correlation (2D-DIC) analysis. In order to obtain the interlaminar shear properties in the elastic and non-linear regions of randomly oriented strand thermoplastic composites, we adopted a 2D-DIC analysis system using a bi-telecentric lens, which can accurately measure the strain in a small field of view, and a test system including an interlaminar shear test jig, which can apply a compressive load to the end face of the specimen at high perpendicularity. It is necessary to provide an overlap of the double-notch of 1 mm or more in order to simultaneously obtain the strain in the elastic region and the non-linear region from the actual test results. When numerical analysis by finite element method (FEM) was carried out on four types of test specimen with different shapes used in this research, by using the interlaminar shear property data obtained from actual tests on the optimum test specimen, there was a high level of agreement with the 2D-DIC analysis results for the shear stress – strain diagrams and the interlaminar shear strain distribution. Therefore, the benefits of the test specimen shape and dimensions in the new test method and the validity of the interlaminar shear property values that can be obtained using this method have been confirmed. [ABSTRACT FROM AUTHOR]

Recently, carbon fiber reinforced thermoplastics (CFRTP) have been widely used for various applications instead of carbon fiber reinforced thermosetting plastics (CFRP). Some matrix resins of CFRTP are crystalline polymers such as polyamide (PA), polyetheretherketone (PEEK), and polyimide. In this study, carbon fiber reinforced polyamide 6 was used, and the effect of crystal state of PA6 on the mechanical properties of CFRTP was investigated. To understand the crystal state of PA6, Differential scanning calorimetry (DSC) analysis was carried out, and an increase in the heat treatment time increased the crystallinity of PA6. The results of bending tests showed that there was a relationship between bending strength and crystallinity, however, longer heat treatment time decreased Young's modulus. The results of acoustic emission (AE) analysis and fractography showed that 30-h heat treatment made the matrix resin of CFRTP more brittle. To investigate the reason for this behavior, the DSC analysis of CFRTP was carried out. After the 30-h heat treatment, the crystal state was different compared to that of other materials. Therefore, bending properties are affected by the crystal state. Consequently, the crystal state must be considered to create CFRTP with desired properties. [ABSTRACT FROM AUTHOR]

In this study, the viscosity of unidirectional carbon fiber reinforced thermoplastic (CFRTP) laminates near their melting point was evaluated to discuss the relationship between the thermal fusion conditions and the flow of the fibers and matrix. The laminates were regarded as a fluid flowing in the direction perpendicular to the fibers. The microscopic flow of the fibers and matrix was observed during a parallel plate compression test conducted near the melting point. On the basis of this observation, the viscosity and flow properties were evaluated by the finite element method (FEM). The results of the parallel plate compression test showed that the test conditions and the decrease in the thickness of the laminates are related to the apparent viscosity of the unidirectional plate. In addition, cracks in the direction of the maximum shear stress were detected via in situ observation near the melting point of the matrix. The occurrence of this phenomenon depended on the apparent viscosity of the unidirectional laminates, and it was found that no cracks occurred when the apparent maximum viscosity of the unidirectional laminates was lower than a threshold. [ABSTRACT FROM AUTHOR]

Laser direct joining of carbon fiber reinforced thermoplastic (CFRTP) composite plate and titanium alloy plate with a thickness of 2 mm was performed with swing laser. Numerous air bubble of submillimeter size were observed inside the fusion zone of CFRTP and titanium alloy at the cross section of the joints. The air bubble characteristics were analyzed based on the morphology and size, while the formation mechanism of air bubble was further elucidated according to the nucleation mode, nucleation site and nucleation position. The results demonstrated that the nucleation modes of air bubble are substantially divided into homogeneous nucleation and heterogeneous nucleation, which is related to the nucleation sites. The nucleation mode presents a crucial factor influencing the position and morphology of air bubble. In addition, the air bubble characteristics are also determined by the clamp pressure and resin flow. The final morphology of air bubble is primarily represented by four typical types. [ABSTRACT FROM AUTHOR]

An experimental investigation on the joining process of 6061 aluminum alloy and carbon fiber reinforced thermoplastics composite (CFRTP) has been carried out with swing laser. The application of the swing laser is beneficial to obtain a larger bonding area. The effects of scanning speed are investigated on the interface formation and fracture load of the hybrid joint. In addition, the formation mechanism of the interface and the fracture mode of the hybrid joint are further elucidated. The results indicate that maximum failure load is obtained with appropriate process parameters (scanning speed: 20 mm/s, laser power: 2000 W), whereas the interface morphology under this process parameter demonstrates that the structurally sound connection between CFRTP and aluminum alloy is realized by the mechanical interlocking effect. At a higher scanning speed, the gaps in the interface caused by insufficient heat input per unit length result in a lower failure load, while at a lower scanning speed, the bubbles and gaps at the interface are observed as a result of resin decomposition and trapped pyrolysis gases in the interface, ultimately reducing the failure load of the joint. Moreover, the fracture mode of the hybrid joint is a mixed failure. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced thermoplastics (CFRTP) have great interest nowadays due to their excellent mechanical properties and lightness. However, in opposition to thermoset matrix composites, there is a lake in the research about machining processes of these materials. Their low glass transition temperature is a handicap when conventional machining is used. An alternative is abrasive water jet machining (AWJM) because it does not cause thermal damage. However, the surface quality produced by this process must be studied and related to the cutting parameters. This article studies the surface quality generated by water jet machining in a low melting point thermoplastic matrix composite material. The kind of thermoplastic used is a TPU (polyurethane). The combination of a high-strength material (carbon fiber) with a low-strength material (thermoplastic matrix) makes machining difficult and can generate a poor surface finish. The influence of cutting parameters has been evaluated through an ANOVA analysis. A mathematical model that relates the surface quality with the cutting parameters has been established by means of a response surface methodology (RSM). The combination of a hydraulic pressure of 250 MPa with a traverse speed of 300 mm/min and an abrasive mass flow of 170 g/min produces the best surface quality. Finally, the main flaws when CFRTP is water jet machined have also been identified. [ABSTRACT FROM AUTHOR]

This paper proposes a fusion bonding technology with electrical resistance heating for carbon fiber-reinforced plastic using polyphenylene sulfide thermoplastic resin with 60% carbon fiber (CFRTP), and suitable bonding conditions are investigated experimentally. The concept of the fusion bonding system is that the thermoplastic resin in the CFRTP sheet is heated to near its melting point of 280°C via electric charging after clamping two CFRTP sheets at high pressures, 310 kPa, using electrodes made from aluminum rods. The heating temperature was controlled using the electrical resistances (5-20 O) between the two CFRTP sheets which were controlled using the exposed carbon fiber (CF) on the CFRTP surface: a lower exposure rate gives a higher electrical resistance, e.g., 15 O for CF20% and 5 O for CF80%. In addition, the sample temperature was dependent on the electric current and the electric charging time. Two CFRTP sheets were successfully bonded using the fusion bonding system with the maximum strength of more than 30 MPa, where an electric current of 4.0 A was applied for 10 s. The bonding strength was attributed to changes in the material properties, especially the bonding resin. The hardened bonding resin was created from heat processing at 250°C, which led to a high bonding strength. [ABSTRACT FROM AUTHOR]

In this study, we propose a new surface generation model for carbon fiber reinforced thermoplastics (CFRTP) manufactured by the long fiber thermoplastic-direct (LFT-D) method. CFRTP are considered to be a next-generation structural material because of their high productivity as well as high mechanical strength and lightness. Conversely, CFRTP have a rough surface, which does not meet the automotive outer panel standard of a "class A surface." In the present study, we establish a surface roughness generation model based on a thermal shrinkage mismatch of thermoplastic resin to carbon fiber and non-uniform carbon fiber distribution. Furthermore, we construct a surface roughness estimation formula based on the model. In the calculation, a cross-sectional image of CFRTP is divided into many vertical segments. Subsequently, the thermal shrinkage of each segment is calculated with a standard deviation, an average, and a probability density of the amount of carbon fiber in each segment. The surface roughness of the manufactured CFRTP was measured using a surface profilometer. The result showed that the arithmetic surface roughness increased with the volume fraction of carbon fiber. We applied the surface roughness calculation to cross-sectional images of the specimens. Consequently, the estimated surface roughness showed the same tendency, in which the surface roughness increased with the volume fraction of carbon fiber. The slope of a regression line of the estimated surface roughness with respect to the volume fraction was 0.010, which was almost the same (0.011) as the slope of a regression line of the measured surface roughness. Furthermore, the estimation formula using a thermal shrinkage effective depth of 395 μm was able to estimate the surface roughness within a 3% average error. Using the estimation formula, it was predicted that the surface roughness increased with the standard deviation of the amount of carbon fiber in a segment. To confirm the reliability of the model and the formula, we measured the standard deviation of the amount of carbon fiber in CFRTP specimens, showing that the trend for CFRTP specimens matched the estimated values. [ABSTRACT FROM AUTHOR]

This study focuses on the influence of process-induced fiber bundle waviness (FBW) on the strength of unidirectional carbon fiber-reinforced thermoplastics (CFRTP) composites. Fiber bundle waviness is often observed in manufactured CFRTPs, which deteriorates the mechanical properties and induces the variation in properties. This study numerically investigates the flexural strength reduction of CFRTP with in-plane FBWs using the finite element method considering local fiber angles and local fiber volume fractions. Numerical results are verified by the experimental flexural test results. It is concluded that the present numerical modeling can predict the deterioration in mechanical properties owing to FBW, and the failure modes depend on FBW parameters. [ABSTRACT FROM AUTHOR]