Thermoplastic Research Articles

Thermal Stability of Encapsulated Carbon-Based Multiporous-Layered-Electrode Perovskite Solar Cells Extended to Over 5000 h at 85 °C.

The key to the practical application of organometal-halide crystals perovskite solar cells (PSCs) is to achieve thermal stability through robust encapsulation. This paper presents a method to significantly extend the thermal stability lifetime of perovskite solar cells to over 5000 h at 85 °C by demonstrating an optimal combination of encapsulation methods and perovskite composition for carbon-based multiporous-layered-electrode (MPLE)-PSCs. We fabricated four types of MPLE-PSCs using two encapsulation structures (over- and side-sealing with thermoplastic resin films) and two perovskite compositions ((5-AVA)x(methylammonium (MA))1-xPbI3 and (formamidinium (FA))0.9Cs0.1PbI3), and analyzed the 85 °C thermal stability followed by the ISOS-D-2 protocol. Without encapsulation, FA0.9Cs0.1PbI3 exhibited higher thermal stability than (5-AVA)x(MA)1-xPbI3. However, encapsulation reversed the phenomenon (that of (5-AVA)x(MA)1-xPbI3 became stronger). The combination of the (5-AVA)x(MA)1-xPbI3 perovskite absorber and over-sealing encapsulation effectively suppressed the thermal degradation, resulting in a PCE value of 91.2% of the initial value after 5072 h. On the other hand, another combination (side-sealing on (5-AVA)x(MA)1-xPbI3 and over- and side-sealing on FA0.9Cs0.1PbI3) resulted in decreased stability. The FACs-based perovskite was decomposed from these degradation mechanisms by the condensation reaction between FA and carbon. For side-sealing, the space between the cell and the encapsulant was estimated to contain approximately 1,260,000 times more H2O than in over-sealing, which catalyzed the degradation of the perovskite crystals. Our results demonstrate that MA-based PSCs, which are generally considered to be thermally sensitive, can significantly extend their thermal stability after proper encapsulation. Therefore, we emphasize that finding the appropriate combination of encapsulation technique and perovskite composition is quite important to achieve further device stability.

Friction stir spot welding of recycled scrap thermoplastics

There is a real demand for sustainable lightweight structures because of the growing environmental concerns. One important solution is developing structures through recycled scrap/waste thermoplastic materials. The current work studies the friction stir spot weldability of recycled thermoplastics, which will help to analyze the potential of friction stir-based welding techniques towards developing these sustainable structures. The combined behavior of recycling-welding procedures is investigated, as they may cause degradations; to ensure that the base thermoplastic polymer's chemical, thermal, and mechanical properties are retained. Scrapped milk bottles made from HDPE material are used as a case study. The highest lap-shear load of 1528 N was achieved at the optimum welding conditions of 1600 rpm rotational speed, 1 mm plunge depth, and 60 s dwell time. Fractographic studies (macroscopic and SEM-based) suggested four types of fracture morphologies depending on welding conditions used. The DSC results showed no significant differences in melting temperature and crystalline content of the polymeric material. The TGA tests showed no significant thermal degradations. The FTIR analysis of all the samples (bottle, recycled sheet, weld material) exhibited characteristic HDPE peaks. All these results suggest combined-welding recycling had a minimal impact on the polymeric structure. Thus, friction stir spot welding (FSSW) technique joins recycled thermoplastic scrap/waste materials with high lap-shear load and without any significant polymer degradations.

An efficient approach to manufacturing carbon nanosheets from lignite and their impact on the mechanical performance of semi-crystalline thermoplastic composites with comprehensive benchmarking

Lignite-derived carbon nanosheets (CNS) offer a novel approach to producing carbon-based nanomaterials with unique advantages over other precursors. The primary mechanism successfully demonstrated the transformation of lignite into CNS by thermo-chemical treatment process through acid treatment (HNO3), catalyst impregnation (FeCl3), and carbonization (1000 °C, 5 min) steps resulting in the enrichment in the carbon content by maintaining the desired efficiency to be used as a filler in compounding process. Moreover, the produced CNS had superior characteristics in terms of carbon content reached 70 % and thermal stability even at 1000 °C compared to lignite. Subsequently, a comprehensive benchmarking study was conducted to achieve high compatibility and uniform dispersion between semi-crystalline thermoplastics such as HomoPP, CopoPP, PA6 and PA6,6 with CNS using a high-speed thermokinetic shear mixer. CNS exhibited enhanced compatibility with thermoplastics, leading to improved mechanical properties such as tensile and flexural modulus inpolymer composites. The benchmark studies revealed that a loading ratio of 0.5 wt% of CNS exhibited optimal reinforcement efficiency. Notably, PA6 matrix demonstrated the most significant improvement in yield strength, increasing by 12 %, while PA6,6 showed the highest increase in tensile modulus at 25 %. Similarly, PA6,6 exhibited the most notable improvement in flexural modulus with a substantial increase of 17 %. Conversely, HomoPP matrix displayed the highest improvement in flexural strength, increasing by 13 %. Furthermore, the incorporation of CNS into the polymer leads to an increase in the crystallization temperature from 182 °C to 194 °C for PA6-0.5 % CNS. These findings highlight the potential of CNS as versatile materials with promising polymer applications such as automotive and aviation.

The synergistic effect and origin of strength in carbon fiber reinforced PAEK, PEEK, and PEKK high‐performance thermoplastic composites manufactured by multi‐scale aqueous dispersion coating

AbstractHigh‐performance thermoplastic composites of polyketones [poly‐aryl‐ether‐ketone (PAEK), poly‐ether‐ether‐ketone (PEEK), poly‐ether‐ketone‐ketone (PEKK)] reinforced with continuous carbon fiber (CF) were consolidated using towpreg produced by multi‐scale aqueous dispersion coating technique. An intra‐matrix trend of composite strength and void fraction was studied to identify the composite with maximum strength free of voids for each polyketone matrix. The CF/PAEK composite with a flexural strength of ~2047 MPa and ILSS of ~99 MPa with a fiber volume fraction of ~67% had the maximum strength free of voids among CF/PAEK composite and all polyketone composites studied. The highest crystallinity (34.5%), and the highest amount of hydrogen bonding and bonds formed between CF, PI nanoparticle, and PAEK explained the origin of strength in CF/PAEK composite. The maximum strength among CF/PEEK and CF/PEKK composite free of voids had a flexural strength of ~1861 MPa, ~1981 MPa; ILSS of ~74 MPa, ~60 MPa; fiber volume fraction of ~61% and ~ 65%, respectively. The polyimide (PI) nanoparticles layer on CF formed the fiber matrix interface, supported hydrogen bonding in all polyketone composites, and formed bonds with CF and matrices of PAEK and PEEK establishing a synergistic effect.Highlights Intra‐matrix trend of strength and voids in polyketone composites studied. Void‐free, high‐performance, high fiber volume fraction composites developed. CF/PAEK composite had maximum strength among polyketone composites studied. PI nanoparticles formed bonds with CF and matrices of PAEK and PEEK. CF/PAEK composite strength originates from crystallinity, H bond, and bonding.

Effect of Electrochemical Aryl Diazonium Salt Modification on Interfacial Properties of CF/PEEK Composites.

The interfacial properties between carbon fiber (CF) and thermoplastic resin are relatively weak, which can be problematic for composites in structural applications. Improving the surface roughness of CF is regarded as an effective way to enhance the interface of composites. However, most CF modifying methods are complex and time-consuming, which cannot meet the demand for industrial production. Therefore, it is of great significance to research a fast technique of CF surface modification to strengthen the interface of composites. Herein, a one-pot reaction based on the aryl diazonium salt modification was applied to enhance the interface between CF and poly ether ether ketone (PEEK) resin. Carbon nanotubes (CNTs) were linked to CF by p-phenylenediamine (PPD) via cyclic voltammetry (CV). The surface morphology, chemical characteristics and surface energy of modified CF illustrated the effectiveness of this method, and the interfacial properties of as-prepared modified CF/PEEK demonstrated the increased tendency. All the CF was treated within 5 min and the interfacial shear strength (IFSS) of CF/PEEK was increased to the maximum of 99.62 MPa by aryl diazonium salt modification. This work may shed some light on the industrialized application of CF reinforced high-performance engineering thermoplastic composites.

Mechanical, Dielectric and Flame-Retardant Properties of GF/PP Modified with Different Flame Retardants.

With the rapid development of electronic information technology, higher requirements have been put forward for the dielectric properties and load-bearing capacity of materials. In continuous glass fiber-reinforced thermoplastic composites, polypropylene matrix is a non-polar polymer with a very low dielectric constant and dielectric loss, but polypropylene is extremely flammable which greatly limits its application. Aiming at the better application of flame retardant-modified continuous glass fiber-reinforced polypropylene composites (FR/GF/PP) in the field of electronic communication, the effects of four different kinds of flame retardants (Decabromodiphenyl ethane (DBDPE), halogen-free one-component flame retardant (MONO), halogen-free compound flame retardant (MULTI), and intumescent flame retardant (IFR)) on the properties of FR/GF/PP were compared, including the mechanical properties, dielectric properties and flame-retardant properties. The results showed that among the FR/GF/PP, IFR has the highest performance in mechanical properties, MULTI has better performance in LOI, DBDPE and IFR have better performance in flame retardant rating, and DBDPE and IFR have lower dielectric properties. Finally, gray relational analysis is applied to propose an approach for selecting the optimal combination (flame retardant type and flame-retardant content) of comprehensive performance. In the application exemplified in this paper, the performance of IFR-3-modified GF/PP is optimized.

Challenges to Improve Extrusion-Based Additive Manufacturing Process of Thermoplastics toward Sustainable Development.

This review aims to present the different approaches to lessen the environmental impact of the extrusion-based additive manufacturing (MEX) process of thermoplastic-based resins and protect the ecosystem. The benefits and drawbacks of each alternative, including the use of biomaterials or recycled materials as feedstock, energy efficiency, and polluting emissions reduction, have been examined. First, the technological option of using a pellet-fed printer wascompared to a filament-fed printer. Then, common biopolymers utilized in MEX applications are discussed, along with methods for improving the mechanical properties of associated printed products. The introduction of natural fillers in thermoplastic resins and the use of biocomposite filaments have been proposed to improve the specific performance of printed items, highlighting the numerous challenges related to their extrusion. Various polymers and fillers derived from recycling are presented as feeding raw materials for printers to reduce waste accumulation, showing the inferior qualities of the resulting goods when compared to printed products made from virgin materials. Finally, the energy consumption and emissions released into the atmosphere during the printing process are discussed, with the potential for both aspects to be controlled through material selection and operating conditions.

Fabrication and mechanical properties of a high-performance PEEK-PEI hybrid multilayered thermoplastic matrix composite reinforced with carbon fiber

This paper presents a method for manufacturing a hybrid matrix composite material reinforced with a woven carbon fiber that combines the properties of two thermoplastic polymers: PEEK (polyether-ether-ketone) and PEI (polyether-imide). The manufacturing process involves a multilayer architecture and a single hot-pressing consolidation step. Experimental tests — including uniaxial tensile tests, delamination tests in Mode I and impact tests at low velocities — were conducted to compare the resulting laminate with single matrix materials (PEEK/CF and PEI/CF).The improvements in strain to failure by 48 % in tensile tests with fiber orientation at ±45∘ and in delamination force by 13 % in low velocity impact tests with respect to PEI/CF show that the heterogeneous matrix blend maintains the crystalline content and excellent elastoplastic response of PEEK while taking advantage of the affordability, lower processing temperature and toughness of PEI.

Discovery of periplasmic solute binding proteins with specificity for ketone bodies: β-hydroxybutyrate binding proteins.

Polyhydroxyalkanoates are a class of biodegradable, thermoplastic polymers which represent a major carbon source for various bacteria. Proteins which mediate the translocation of polyhydroxyalkanoate breakdown products, such as β-hydroxybutyrate (BHB)-a ketone body which in humans serves as an important biomarker, have not been well characterized. In our investigation to screen a solute-binding protein (SBP) which can act as a suitable recognition element for BHB, we uncovered insights at the intersection of bacterial metabolism and diagnostics. Herein, we identify SBPs associated with putative ATP-binding cassette transporters that specifically recognize BHB, with the potential to serve as recognition elements for continuous quantification of this analyte. Through bioinformatic analysis, we identified candidate SBPs from known metabolizers of polyhydroxybutyrate-including proteins from Cupriavidus necator, Ensifer meliloti, Paucimonas lemoignei, and Thermus thermophilus. After recombinant expression in Escherichia coli, we demonstrated with intrinsic tryptophan fluorescence spectroscopy that four candidate proteins interacted with BHB, ranging from nanomolar to micromolar affinity. Tt.2, an intrinsically thermostable protein from Thermus thermophilus, was observed to have the tightest binding and specificity for BHB, which was confirmed by isothermal calorimetry. Structural analyses facilitated by AlphaFold2, along with molecular docking and dynamics simulations, were used to hypothesize key residues in the binding pocket and to model the conformational dynamics of substrate unbinding. Overall, this study provides strong evidence identifying the cognate ligands of SBPs which we hypothesize to be involved in prokaryotic cellular translocation of polyhydroxyalkanoate breakdown products, while highlighting these proteins' promising biotechnological application.

EFFECTS OF DIFFERENT COOLANT MEDIA ON THE COOLING PERFORMANCE OF INJECTION MOLD PRODUCT

The injection molding process involves heating a thermoplastic polymer above its melting point and injecting it into a mold. The polymer then cools and solidifies to form the final part. The process consists of four stages: clamping, injection, cooling, and ejection. Among these stages, cooling plays a crucial role as it requires an efficient cooling system to transfer heat from the mold at a consistent rate, ensuring high-quality final products. This project specifically focuses on investigating the impact of different cooling media used in the cooling system for the mold. The aim is to compare the effectiveness of various cooling media on the cooling performance of the injection-molded product. Different types of coolants, including water, oil, or other solution mixtures, have been considered for their ability to reduce or regulate the temperature of the system. CAD modeling was prepared for the case study, along with a pre-designed conformal cooling channel and gating system. After conducting the simulation analysis, water emerged as the most effective coolant, demonstrating superior results compared to other coolant options. The results also highlight the feasibility of using alternative coolants that offer comparable cooling performance.

Recyclable multiscale composite structural supercapacitor

AbstractThis study presents a proof‐of‐concept for a fully recyclable and sustainable composite structural supercapacitor. The fabricated device shows promising energy storage capabilities and mechanical strength. Generally, structural supercapacitors capacitance is considerably lower than non‐load‐bearing mono‐functional supercapacitors and are made via thermoset polymer electrolyte. Here, the device is fabricated using an optimized solid electrolyte composition of carbon aerogel modified carbon fibers, fumed silica, lithium salt, and a thermoplastic polymer matrix. The supercapacitor exhibits a high capacitance of 5225 mFg−1 (193 mFcm−2) at 1 mVs−1 scan rate and a large voltage window of 4 V. A simple dissolution/reprecipitation method is used to demonstrate the recycling feasibility, with minimal mechanical degradation (<10%) in the polymer matrix and no chemical structure changes in the electrolyte. This work establishes a promising ecologically‐sound structural energy storage technology with favorable performance compared to prior studies.Highlights A proof‐of‐concept fully recyclable composite structural supercapacitor is made. Thermoplastic‐based robust polymer electrolytes are fabricated. Recycling via dissolution and re‐precipitation of components is demonstrated. Comparison to prior structural supercapacitors shows favorable performance.

Analysis of impact response and damage evolution in multi‐scale of novel 3D carbon fiber‐reinforced polyetheretherketone composites

AbstractThermoplastic composites have a high application demand in aerospace, marine military and other cutting‐edge industry. However, it poses a considerable obstacle in achieving three‐dimensional (3D) thermoplastic composites because of the inadequate infiltration of highly viscous thermoplastic resins. In this paper, high‐toughness Polyetheretherketone (PEEK) resin‐based 3D orthogonal carbon fiber thermoplastic composites were designed and obtained. Low‐velocity impact test was conducted on 3D orthogonal woven composite (3DOWC) under the energy levels of 5 and 10 J, and its performance was compared with that of the 2D unidirectional layup composite (2DULC) and the 2D plain layup composite (2DPLC). The results showed that 3DOWC possessed superior elastic energy absorption capacity and less damage morphology compared to 2D composites. 3DOWC had the highest contact force value of 2420.25 N at 10 J, which is 36.83% higher than that of 2DPLC. Furthermore, a finite element model in multi‐scale was established to investigate the damage evolution and failure mechanism of the 3D orthogonal woven CF/PEEK composites. The damage morphology observed in both experimental and numerical findings demonstrated that the matrix shedding, while the yarn fractured on the nonimpact side beneath the impact point. Additionally, enhancing the tensile strength of the yarn in the bottom layer can lead to further improvement in impact resistance. This work provides an innovative method for manufacturing 3D thermoplastic composites and lays the foundation for the impact simulation analysis of such composites.Highlights A novel approach was introduced for fabricating 3D carbon fiber/PEEK composites, which exhibits remarkable resistance to impact. A comprehensive investigation was conducted to evaluate the impact properties of 3D thermoplastic composite compared to 2D composite. A finite element model in multi‐scale including failure criteria was established to simulate the damage evolution.

Deep reinforcement learning for optimal control of induction welding process

Optimizing induction welding (IW) process parameters for the application of joining thermoplastic composites is challenging as it requires achieving complex spatiotemporal thermal characteristics along the weld-line to obtain desired weld quality. We formulate an optimal control problem which captures these requirements and seeks to optimize the IW coil speed using a fast-acting dynamic IW process model. We develop a novel Deep Reinforcement Learning (DRL) framework to solve this computationally challenging control problem and demonstrate via simulation study that the learned DRL feedback control policy results in better spatiotemporal thermal characteristics as compared to the current state-of-the-art.

Three-dimensional heat transfer analysis of Hot Gas Torch (HGT)-assisted Automated Fiber Placement (AFP) for thermoplastic composites

Automated Fiber Placement (AFP) is a key additive manufacturing process for the production of complex composite structures. This study focuses on the in-situ AFP process for thermoplastic composites with Hot Gas Torch (HGT), which includes heating, consolidation, and solidification steps. Temperature control is critical to achieving high quality parts as it affects bond quality, crystallization, and solidification. However, previous studies have oversimplified convective heat transfer by assuming a constant coefficient, resulting in discrepancies between simulations and experiments. This paper introduces a novel distribution function to model the convective heat transfer coefficient, thereby improving temperature predictions. An optimization loop is used to determine the parameters of the function, which ensures agreement with experimental data. The proposed approach accurately predicts the temperature distribution, which is validated against unseen experimental results. By incorporating the distribution of the convective heat transfer coefficient, this study improves the understanding of heat transfer mechanisms in AFP for thermoplastic composites, leading to improved manufacturing processes and part quality.

Thermo-mechanically joined hybrids from carbon fiber-reinforced PA12 with die-cast alloy AlSi10Mg: how surface and interlayer design affect shear strength and fracture behavior

ABSTRACT Infrared radiation was used as a tool to heat laser-structured AlSi10Mg for subsequent fusion bonding with thermoplastic carbon fiber-reinforced PA12. When the two adherends are brought into contact, the bond is formed by melting of the surface-near polymer matrix and pressing it into the laser structure of the aluminum alloy. When investigating different fiber volume contents, the amount of fusible material was identified as a key parameter for the achievable bonding strength. Therefore, the best results were achieved with low fiber volume content (25 vol.-%) or under the use of an additional PA12 interlayer. Moreover, the influence of different surface texture parameters was investigated and the aspect ratio between structure depth and width was found to correlate best with the measured shear strengths. Aspect ratios from 0.18 to 1.15 increased the bond strength up to the interlaminar shear strength of the thermoplastic composite. Especially, aspect ratios of 0.61 or greater proved to be very effective, with resulting mean strength values of almost 30 MPa. While even lower ratios allowed higher loads on the joints compared with untreated surfaces, greater aspect ratios show lower bond strengths, as the laser structures were no longer completely filled with fused PA12.

Highly conductive and durable nanocomposite hard coatings of carbon fiber reinforced thermoplastic composites against lightning strikes

The growing use of thermoplastic composites (TPCs) like low-melting polyaryletherketone (LM-PAEK) matrices reinforced with unidirectional carbon fiber (CF) in aircraft structures presents a significant challenge in terms of lightning strikes and electromagnetic interference shielding during aircraft operations. This is due to the weak electrical conductivity of TPC structures, which results in widespread damage when struck by lightning. The repair and maintenance of these extended damaged sites can increase operational costs and loss of flights. Several lightning strike protection (LSP) systems have been developed and implemented to address these concerns. This study evaluated a highly conductive coating with a low filler rate for its effectiveness as an LSP solution for TPCs on exterior aircraft surfaces. The TPC panel without any coatings was first studied. Subsequently, the level of conductivity was increased by incorporating the nanoscale conductive fillers, silver-coated copper (Ag/Cu) nanoflakes, with a silver content of 20 wt.% (Ag20/Cu) and 30 wt.% (Ag30/Cu), correspondingly, into the coating at two loadings of 55 wt.% and 70 wt.% in an epoxy carrier for the surface coatings. The behavior of electrical and surface conductivity was thoroughly examined to understand the impact of Ag/Cu with a high aspect ratio and the effectiveness of the LSP solution. In addition, the spray-coated TPC panels underwent rigorous Zone 2A lightning strike testing using simulated lightning current, in agreement with the industry standard of Society of Automotive Engineers (SAE) Aerospace Recommended Practice (ARP) 5412B. Despite the higher resistance due to the lower conductive coating weight, the TPC panels with Ag30/Cu at loading of 70 wt.% achieved better results than those with Ag30/Cu at loading of 55 wt.%. This is evidenced by the minor structural delamination and CF breakage on the front surface, which proposes a new economic route for a sustainable post-processed LSP system in the aviation industry.

Crashworthiness optimization of variable stiffness B-pillar with thermoplastic composites

This study focuses on enhancing of crashworthiness and lightweight of the automotive B-pillar structure by using continuous carbon fiber reinforced thermoplastic composites (CFRTP) and optimized layer design. Firstly, the B-pillar is divided into four regions with variable stiffness. Quasi-static three-point bending test and numerical simulation are performed to calculate the stiffness of the structure. Then, the four regions of the B-pillar with different CFRTP layers are structurally designed to realize variable stiffness. Considering manufacturing requirements, a draping simulation is employed to predict potential layer defects. The results demonstrate that B-pillar structural performance is enhanced after the reorientation of CFRTP prepreg. Afterward, the crashworthiness of the CFRTP B-pillar considering the ply drop-off is evaluated and compared with the traditional Q235 steel counterparts. The results indicate that the CFRTP B-pillar exhibits superior crashworthiness but a substantial reduction in mass by 53.1%. Finally, the multi-island genetic algorithm (MIGA) is employed to achieve the optimal layer design scheme for lay-up optimization of the CFRTP B-pillar, and the crashworthiness of the CFRTP B-pillar with variable stiffness is further improved. The current work highlights a structural design strategy for CFRTP components for vehicles, which is crucial for the updating of automobile engineering.

A review of polymeric bipolar plates for proton exchange membrane fuel cells: Materials, fabrication, applications, cost analysis, and current status

Bipolar plates play a crucial role in the performance and viability of proton exchange membrane fuel cells. Polymeric composites have demonstrated their potential as alternatives to graphite and metallic materials for bipolar plates due to their good corrosion resistance, lightweight nature, flexibility, and cost-effectiveness. However, these polymeric materials often suffer from low electrical conductivity. The incorporation of various electrically conducting fillers can improve the electrical conductivity of these materials. This work presents a comprehensive review of the utilization of polymeric materials-based composites for bipolar plates for proton exchange membrane fuel cells. Various aspects related to bipolar plates in proton exchange membrane fuel cells, including materials, fabrication techniques, applications, cost analysis, and the current status of proton exchange membrane fuel cells are discussed in this work. Both thermoplastic and thermoset-based composites are explored as matrix materials for bipolar plates, along with different conducting filler/reinforcement options, and their best results are also explored. The impact of traditional as well as emerging fabrication techniques on the performance of bipolar plates is evaluated, emphasizing the need to reduce the cost of bipolar plates for the commercialization of proton exchange membrane fuel cells. Furthermore, the paper also examines the applications and current status of proton exchange membrane fuel cells in India as well as worldwide.

Design on thermal-mechanism coordination for binding reinforcing mesh based on shape memory polymer

The traditional rebar binding devices require complex drive and transmission mechanisms, which leads to large volume and complex structure. In this paper, a cylindrical thermoplastic shape memory polymer (SMP) fixture is proposed to verify the rebar binding method of thermal-mechanism coordination. The SMP fixture is manufactured by the injection molding technology through selecting suitable-ratio Polylactic acid and Polycaprolactone (PCL) blend materials. Besides, an additional auxiliary device is presented to overcome the incomplete recovery disadvantage existing in the thermoplastic SMP and completely achieve binding the rebar. On this base, two different binding methods are proposed to compare the mechanical performance after fixing the rebar, and the external force/thermal contributions are tested and discussed in detail. The tested results show that the binding contribution of heat could reach 70% while the binding contribution of external force could reach 30% above the transition temperature (Tg ). The maximum tensile force that the binding rebar can withstand under the thermal-mechanism coordination action could reach up to 657.7 N, which is higher than the maximum tensile force of the wire binding. In addition, the maximum friction force between rebar and notches of fixture could reach up to 94.1 N, which further verifies the feasibility of thermal-mechanism coordination for binding reinforcing mesh based on SMP fixture.

An efficient machine learning-based model for predicting the stress-strain relationships of thermoplastic polymers with limited testing data

Thermoplastic polymers used in aeronautical structures such as poly-ether-ether-ketone (PEEK) usually exhibit nonlinear stress-strain relationships, which can be usually predicted by the physical and phenomenological models. For different thermoplastic polymers, however, existing models may encounter difficulties in reasonably predicting the stress-strain relationships. By reasonably using experimental data, the machine learning-based model can accurately predict the stress-strain relationships. In this paper, an efficient machine learning-based model is built to predict the stress-strain relationships of thermoplastic polymers by using the Kriging model, where limited testing data are merely used. Experiments of 69 specimens for PEEK are firstly performed under uniaxial tensile, where the temperatures range from 23 °C to 140 °C and the strain rates range from 10−3 s−1 to 10−1 s−1. Genetic algorithm is employed to train the proposed model based on the stress-strain relationships obtained from experiments. Moreover, the results predicted by the proposed Kriging-based model are compared with those obtained from the DSGZ (Duan-Saigal-Greif-Zimmerman) model. The results indicate that the Kriging-based model possesses better accuracy, lower complexity, and better robustness than the selected model, because the prior estimation is introduced by the assumption of Gaussian stochastic processes. In addition, the proposed model is also applied to Poly-Propylene (PP), PEEK at high temperatures, and polycarbonate (PC), it can be found that the Kriging-based model can also predict the stress-strain relationships of other amorphous and semi-crystalline thermoplastic polymers.