Bio-Based Hyperbranched Toughener From Tannic Acid and Its Enhanced Solvent-Free Epoxy Resin with High Performance

It is essential to design economic and efficient tougheners to prepare high-performance epoxy resin;however,this has remained a huge challenge.Herein,an eco-friendly,low-cost,and facile-fabricated bio-based hyperbranched toughener,carboxylic acid-functionalized tannic acid(CATA),was successfully prepared and applicated to the preparation of solvent-free epoxy resins.The mechanical performance,morphology,structural characterization,and thermal characterization of toughened epoxy resin system were studied.The toughened epoxy resin system with only 1.0wt%CATA reached the highest impact strength,111%higher than the neat epoxy resin system.Notably,the tensile strength and elongation at break of toughened epoxy resin systems increased moderately with increasing CATA loading.Nonphase-separated hybrids with significant toughening effect were obtained.Additionally,the thermal stabilities of toughened epoxy resin systems decreased with increasing CATA loading.This study provides an eco-friendly,cost-effective,and facile approach for the preparation of high-performance,solvent-free epoxy resins with potential for practical applications in sealing integrated circuits and electrical devices fields.

Preparation and Performance of Short Carbon Fiber and Flake Graphene Reinforced Polycarbonate Composites: Effects of Different Tougheners

Different tougheners including methyl methacrylate-butadiene-styrene terpolymer (MBS, core-shell type), maleic anhydride (MAH) grafted ethylene-octene copolymer (EOM), and MAH grafted polyethylene wax (PEM) were investigated for toughening the polycarbonate (PC) composites reinforced by short carbon fiber (SCF) and flake graphene (FG). The effects of tougheners on the preparation, thermal conductivity and mechanical properties of PC composites were studied. Scanning electron microscopy was used for characterizing the impact fracture surfaces of the composites. The results showed that introducing tougheners into the carbon reinforced PC composites was beneficial to improving the processability, and PEM was more effective than EOM and MBS. Meanwhile, the through-thickness and the in-plan thermal conductivity decreased to some degree due to the isolated island effects of tougheners. Moreover, the brittle PC composites with high flexural stress could be easily toughened by tougheners. In contrast, PEM had better toughening function than EOM and MBS, and correspondingly, the stiffness of the composites was the lowest for the PEM toughened systems. The fractography revealed that dense and uniformly distributed carbon fillers dispersed in matrix PC and circular cavities coexisted in the composites. The naked fiber length gradually increased as the ductility of composite materials improved.

Influence of Different Tougheners on the Properties of PC/PBT Alloy

This paper focuses on the influence of glycidyl methacrylate functionalized polyolefin elastomer (SOG-03) on the properties of PC/PBT alloys, and also made a contrastive analysis with ethylene-methyl acrylate-glycidyl methacrylate terpolymer (EMA-co-GMA) and methyl methacrylate-butadiene-styrene terpolymer (MBS), the common toughener in PC/PBT alloy. The impact performance test results of PC/PBT alloys with different addition of SOG-03 showed that the brittle-ductile transition began when SOG-03 content reached 3 wt%. The microstructure, differential scanning calorimeter (DSC) and multi-extrusion process results of PC/PBT alloys all showed that SOG-03 tends to be dispersed in PBT phase and the dispersed SOG-03 presents typical rubber-toughened polymer morphology. The toughening efficiency of MBS on PC/PBT alloy was much lower than EMA-co-GMA and SOG-03, and showed a worse processing stability after multi-extrusion process and long-term thermal ageing properties. The EMA-co-GMA and SOG-03 toughened PC/PBT alloys showed an equivalent toughness, while the PC/PBT alloy with SOG-03 showed a better processing stability during the multi-extrusion process and long-term thermal ageing property when the thermal aging time is more than 600 h.

Progress in Research on Structural Ceramic Materials Toughened by Graphene

Graphene has excellent mechanical properties and unique physical/chemical properties,which make it have a good strengthening and toughening effect on structural ceramic materials.In recent years,it has received widespread attention and research.This article reviews the mixing and sintering processes in the preparation of graphene/ceramic com-posites,as well as the toughening mechanism of graphene on ceramic materials.It also looks forward to how to further enhance the toughening effect of graphene.

SYNTHESIS OF A HYPERBRANCHED POLYETHER EPOXY THROUGH ONE- STEP PROTON TRANSFER POLYMERIZATION AND ITS APPLICATION AS A TOUGHENER FOR EPOXY RESIN DGEBA

A novel liquid hyperbranched polyether epoxy （HBPEE） based on commercially available hydroquinone （HQ） and 1,1,1-trihydroxymethylpropane triglycidyl ether （TMPGE） was synthesized through an A2 ＋ B3 one-step proton transfer polymerization. In order to improve the toughness, the synthesized HBPEE was mixed with diglycidyl ether of bisphenol A （DGEBA） in different ratios to form hybrids and cured with triethylenetetramine （TETA）. Thermal and mechanical properties of the cured hybrids were evaluated. Results show that addition of HBPEE can improve the toughness of cured hybrids remarkably at 〈 20 wt% loading, without compromising the tensile strength. However, the glass transition temperature （Tg） of the cured hybrids decreases with increasing HBPEE content. Fracture surface images from scanning electron microscope show oriented fibrils in hybrids containing HBPEE. The formation and orientation of the fibrils can absorb energy under impact and lead to an improvement of toughness. Furthermore, based on the morphology of fractured surfaces and the single Tg in each hybrid, no sign of phase separation was found in the cured hybrid systems. As a result, the toughening mechanism could be explained by in situ homogeneous toughening mechanism rather than phase separation mechanism.

Impact-abrasive Wear Behavior of ZTA and NbC Reinforced Fe60 Matrix Composites

The impact-abrasive wear behavior of ZTA(zirconia toughened alumina)particle(ZTAp)and NbC particle(NbCp)reinforced Fe60 matrix composites(ZTAp-NbCp/Fe60)were investigated.Specimens of pure Fe60 matrix material,NbCp reinforced Fe60 composite(NbCp/Fe60)and ZTAp-NbCp/Fe60 with different contents of ZTAp were prepared through vacuum sintering and tested on an MLD-10B Impact Wear Rig.As revealed by the results,NbCp could strengthen Fe60 matrix,and had fine grain strengthening effect on Fe60matrix.When the mass fraction of ZTAp was 5%-15%,the impact-abrasive wear performance of ZTAp-NbCp/Fe60 composites was better than that of Fe60 and NbCp/Fe60.When the mass fraction was 15%,the ZTApNbCp/Fe60 had the best performance.ZTAp could weaken the impact and wear effect of abrasive particles on the composite and protect the matrix.Cracks occured at the interface and at defects in the ZTAp.The former leaded to ZTAp shedding,while the latter leaded to ZTAp fracturing.In both cases,the performance of the composite material would decrease.

A Review of Experimental Research on the Mode I Fracture Behavior of Bamboo

Bamboo is an eco-friendly material with light weight,high strength,short growth cycle and high sustainability,which is widely used in building structures.Engineered bamboo has further promoted the development of modern bamboo structures due to its unrestricted size and shape.However,as a fiber-reinforced material,fracture damage,especially Mode I fracture damage,becomes the most likely damage mode of its structure,so Mode I fracture characteristics are an important subject in the research of mechanical properties of bamboo.This paper summarizes the current status of experimental research on the Mode I fracture properties of bamboo based on the three-point bending(TPB)method,the single-edge notched beam(SENB)method,the compact tension(CT)method and the double cantilever beam(DCB)method,compares the fracture toughness of different species of bamboo,analyzes the toughening mechanisms and fracture damage modes,discusses the applicability of different theoretical calculation methods,and makes suggestions for future research priorities,aiming to provide a reference for future research and engineering applications in related fields.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SiC_W/BAS (BaAl_2Si _2O_8) GLASS-CERAMIC COMPOSITE

BAS (BaAl 2Si 2O 8) glass ceramic was prepared by a sol gel process and the SiC W/BAS composites were fabricated by hot pressing. The transformation from hexacelsian to celsian, the microstructure and mechanical properties of the composites was investigated. The results show that the transformation promoted by adding celsian seeds is retarded in the composite by the presence of SiC whisker. SiC whisker has a good effect of improving the mechanical properties of BAS glass ceramic matrix. The toughening mechanisms are crack deflection and whisker fracture. The strengthening mechanism is loading transition. The amorphous phase at SiC W/BAS matrix interface damages the fracture toughness and high temperature strength of the composites.

Effects of material of metallic frame on the penetration resistances of ceramic-metal hybrid structures

The effects of metallic material on the penetration resistances of ceramic-metal hybrid structures against vertical long-rod tungsten projectiles were studied by artillery-launched experiments and numerical simulation.Hybrid structures with rectangular cores in transverse orthogonal arrangement and slidefitting ceramic inserts of zirconia toughened alumina prisms were fabricated with titanium alloy TC4(Ti6 Al4 V),AISI 4340 steel and 7075 aluminum alloy panels,respectively.The results showed that the hybrid structure of Ti6A14V exhibited the highest penetration resistance,followed by that of 7075 aluminum alloy with the same area density.The penetration resistance of the hybrid structure of AISI4340 steel was the lowest.The underlying mechanisms showed that the metallic material of a ceramicmetal hybrid structure can directly affect its energy absorption from the impact projectile,which further affects its penetration resistance.Different metallic frames exhibited different failure characteristics,resulting in different constraint conditions or support conditions for ceramic prisms.The high penetration resistance of the Ti6Al4V hybrid structure was due to its stronger back support to ceramic prisms as compared with that of AISI 4340 steel hybrid structure,and better constraint condition for ceramic prisms by metallic webs as compared with that of 7075 aluminum alloy hybrid structure.The results of mass efficiency and thickness efficiency showed that the Ti6Al4V hybrid structure has advantages in reducing both the thickness and the mass of protective structure.In addition,because the ceramic-metal hybrid structures in the present work were heterogeneous,impact position has slight influence on their penetration resistances.

EFFECT OF TRIAXIAL STRESS CONSTRAINT ON THE DEFORMATION AND FRACTURE OF POLYMERS

One purpose of this paper is to give a brief overview on the research status of deformation,fracture and toughening mechanisms of polymers,including experimental,theoretical and numerical studies.Emphasis is on the more recent progresses of micromechanics of rubber particle cavitation and crazing,and the de- velopment of fracture criteria for ductile polymers. The other purpose is to study the effect of triaxial stress constraint on the deforma- tion and fracture behavior of polymers.Polycarbonate(PC),acrylonitrile-butadiene- styrene(ABS)and PC/ABS alloy are considered in this investigation.A series of circumferentially blunt-notched bars are used to experimentally generate different tri- axial stress fields.The fracture surfaces of specimens with different notch radius are examined by scanning electron microscope(SEM)to study the fracture and tough- ening mechanisms of polymer alloy.It is shown that the triaxial stress constraint has a significant effect on the deformation,fracture and toughening of PC,ABS and PC/ABS alloy.We will also discuss the extent to which a micromechanies criterion proposed by the first author can serve as a fracture criterion for ductile polymers. A new ductile fracture parameter is emphasized,which can be employed to evaluate the fracture ductility of polymers.Stress state independence of the parameter for the PC,ABS and PC/ABS alloy has been experimentally verified.

Microstructure and Mechanical Properties of CaCO_3 Whisker-reinforced Cement

Composite Portland cement （PC） played an important role in various kinds of construction engineering owing to low hydration heat,low-cost,and application of solid industrial waste,but its brittleness and low strength limited its use in stress-bearing locations.The aim of this study is to improve the toughness and fracture resistance by incorporating CaCO3 whisker in cement matrix.Effect of different content of calcium carbonate whiskers on the mechanical properties of PC was investigated.The results showed that the flexural strength,impact strength and split tensile strength were increased by 39.7%,39.25% and 36.34% at maximum,respectively.Microstructure and elements of the whiskers in hardened cement were observed and analyzed by SEM/EDS.The mechanisms of the reinforcement of CaCO3 whisker on cement were also discussed,and the conclusion was that the improvement could be correlated to energy-dissipating processes owing to crack bridging,crack deflection,and whisker pull-out at the crack tips.

Toughening mechanism of lined Al_2O_3-ZrO_2 multiphaseceramics in SHS composite pipes

Hypoeutectic and hypereutectic Al2O3-ZrO2 multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis （SHS） process. The microstructure of the ceramics was observed by means of SEM and EPMA. The fracture toughness of the multiphase ceramics was tested by using the Vickers indentation method. The fracture toughness of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.96 MPa·m^1/2 and that of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.23 MPa·m^1/2. The toughening mechanisms were systematically investigated by means of SEM and XRD. The results show that the bridging toughening mechanism, stress induced ZrO2 transformation toughening mechanism, and microcrack toughening mechanism are the predominant toughening mechanism.

SPECIAL EFFECT OF ULTRA-FINE RUBBER PARTICLES ON PLASTIC TOUGHENING

According to the present theories of plastic toughening, it is impossible to enhance the toughness, stiffness and/orheat resistance of plastics simultaneously by using rubber. A series of novel nano-rubber particles (UFPR) were introduced,which were prepared through irradiating common rubber lattices and spray drying them. Epoxies toughened with UFPRshowed a much better toughening effect than those with CTBN, and the heat resistance of epoxy was unexpectedly elevated.For polypropylene toughening, UFPR can improve the toughness, stiffness and heat resistance of PP simultaneously. Thesespecial toughening effects overcome the deficiencies in rubber toughening technology and are worth further investigating.

A Review on Binderless Tungsten Carbide: Development and Application

WC-Co alloys have enjoyed great practical significance owing to their excellent properties during the past decades.Despite the advantages,however,recently there have been concerns about the challenges associated with the use of Co,i.e.price instability,toxicity and properties degeneration,which necessitates the fabrication of binderless tungsten carbide(BTC).On the other hand,BTC or BTC composites,none of them,to date has been commercialized and produced on an industrial scale,but only used to a limited extent for specialized applications,such as mechanical seals undergoing high burthen as well as high temperature electrical contacts.There are two challenges in developing BTC:fully densifying the sintered body together with achieving a high toughness.Thus,this review applies towards comprehensively summarize the current knowledge of sintering behavior,microstructure,and mechanical properties of BTC,highlighting the densification improving strategies as well as toughening methods,so as to provide reference for those who would like to enhance the performance of BTC with better reliability advancing them to further wide applications and prepare the material in a way that is environment friendly,harmless to human health and low in production cost.This paper shows that the fabrication of highly dense and high-performance BTC is economically and technically feasible.The properties of BTC can be tailored by judiciously selecting the chemical composition coupled with taking into careful account the effects of processing techniques and parameters.

DESIGN AND PREPARATION OF SILICON NITRIDE COMPOSITE WITH HIGH FRACTURE TOUGHNESS AND NACRE STRUCTURE

A new way of designing and preparing silicon nitride ceramic composite with high fracture toughness and nacre structure has been proposed. To mimic the laminated structure of nacre, Si_3N_4 matrix ceramic layer can be obtained through compacting rolling method. To mimic the secondary toughening of nacre structure, SiC whisker is added into Si_3N_4 and acts as the secondary toughening phase. Boron nitride (BN)is selected to mimic the organic layer in nacre so as to form the weak interfaces between Si_3N_4 layers. Alumina is added into BN to adjust the bonding strength of the interface.The Si_3N_4 sheets are stacked into the die after coating with BN. After the removal of the organic matter in them, the green body is hot pressed at 1820℃for 1.5 hours under N_2 atmosphere. The fracture toughness of the so-made Si_3N_4 composite at room temperature is 20.36MPa m￣(1/2), the three-point bending strength at room temperature is 651.47MPa. The crack spreads and deflects along the interface between BN and Si_3N_4 layer and extends through the BN layer into Si_3N_4 layer. The improvement of the fracture toughness may be due to the staircase-shape-like crack which provides the long crack path, the fracture and deformation of Si_3N_4 layer, and the pullout of SiC whiskers from the Si_3N_4 layer.

Mechanical Properties and Microstructure of CaSO4 Whisker Reinforced Cement Mortar

Calcium sulfate whisker(CaSO4 whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO4 whiskers on the mechanical properties of the resulting cement mortar was also studied. The results showed that the flexural strength and compressive strength of the mortar specimen was improved as high as 28.3% and 8.5% by incorporating 5 wt% CaSO4 whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO4 whiskers were identified by X-ray diffraction(XRD) and scanning electron microscope(SEM). Conclusion can be drawn that CaSO4 whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO4 whisker on the reinforcement is mainly on three aspects: whisker pullout, crack deflection, and crack bridging. Mercury intrusion porosimetry(MIP) tests have confirmed that for 28 d cement mortar, the harmless pores increased from 9.33% to 10.62%, and the harmful pores decreased from 2.08% to 1.90%. Therefore, the whisker can optimize the pore size distribution of the resulting cement mortar.

Room-temperature mechanical properties of WSi_2/MoSi_2 composites

Five kinds of WSi_2/MoSi_2 composites were successfully prepared bymechanical alloying, IP and high temperature sintering techniques. And their hardness and fracturetoughness were measured by the Vickers indentation fracture mode through an Hv-10A type sclerometer.The microstructure and morphology were investigated by a JSM-56001V scanning electron microscope.Results show that the addition of 50% WSi_2 (in mole fraction) has remarkable hardening andtoughening effects on the MoSi_2 matrix, whose hardness value and fracture toughness value areincreased about 60% and 86%, respectively. For WSi_2/MoSi_2 composite, the hardening mechanisms arefine-grain and the second phase particles strengthening, and the toughening mechanisms includefine-grain, grain drawing, crack deflection, microbridge and bowing toughening.

TOUGHENING OF POLYCARBONATE WITH PBA-PMMA CORE-SHELL PARTICLES

The miscibility,mechanical properties,morphology and toughening mechanism of PC/PBA-PMMA blends wereinvestigated.The dynamic mechanical results show that PC/PBA-PMMA blend has good miscibility and strong interfacialadhesion.The Izod impact strength of blend PC/PBA-PMMA with 4%(volume fraction)PBA-PMMA core-shell modifier is16 times higher than that of pure PC.The core-shell volume fraction and thickness of the PMMA shell have effect on thetoughness of PC/PBA-PMMA blends.As PMMA volume fraction increases,the toughness of PC/PBA-PMMA blendincreases,and reaches a maximum value at 30% volume fraction of PMMA or so.The tensile properties of PC/PBA-PMMAblend with a minimum amount of PBA-PMMA modifier show that brittle-tough transition has no significant variance incomparison with that of pure PC.The scanning electron microscopic(SEM)observation indicates that the tougheningmechanism of the blend with the pseudo-ductile matrix modified by small core-shell latex polymer particles is the synergeticeffect of cavitation and shear yielding of the matrix.

A review of the strengthening–toughening behavior and mechanisms of advanced structural materials by multifield coupling treatment

The application of an external field is a promising method to control the microstructure of materials, leading to their improved performance. In the present paper, the strengthening and toughening behavior of some typical high-performance structural materials subjected to multifield coupling treatment, including electrostatic field, electro-pulse current, thermal field, and stress field, are reviewed in detail. In addition to the general observation that the plasticity of materials could be increased by multi-external fields, strength enhancement can be achieved by controlling atomic diffusion or phase transformations. The paper is not limited to the strengthening and toughening mechanisms of the multifield coupling effects on different types of structural materials but is intended to provide a generic method to improve both the strength and ductility of the materials. Finally, the prospects of the applications of multi-external fields have also been proposed based on current works.

Mechanical Behaviors of ZrO_2-Al_2O_3 Ceramic Composites with Y_2O_3 as Stabilizer

The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into the ZrO2 matrix where the quantity of additive Y2O3 is 3.5% (mole fraction), the growth of ZrO2 grains is efficiently inhibited, which helps the ZrO2 grains exist in a metastable tetragonal manner; thus higher strength and toughness are acquired. When the content of alumina is 20% (mass fraction), the bending strength and fracture toughness of the composites are 676.7 MPa and 10 MPa·m1/2 respectively, the mechanical behaviors are close to those prepared with ZrO2 and Al2O3 powders synthesized through wet chemical approach. The mechanical behaviors of the composites are well improved owing to the dispersion toughening of alumina grains and phase transformation toughening of zirconia grains.