Mechanical and Self-Healing Performances of Crumb Rubber Modified High-Strength Engineered Cementitious Composites

High-strength engineered cementitious composite (HS-ECC) reinforced with polyethylene (PE) fiber characterizes wider crack widths than the conventional polyvinyl alcohol fiber-reinforced ECC (PVA-ECC), weakening the self-healing potential of HS-ECC. The properties of HS-ECC are tailored by introducing crumb rubber (CR), as artificial flaws can lower the matrix toughness and the crack width, leading to an enhanced self-healing potential of HS-ECC. In this study, CR is used to entirely replace silica sand (SS) with three equivalent aggregate-to-binder ratios of 0.2, 0.4, and 0.6, and two CR particle sizes (i.e., CR1 and CR2) are also considered to investigate the effects on density, compressive properties, and tensile performances of HS-ECC. Although CR substitution of SS influences adversely the mechanical strengths of HS-ECC, it can reduce the HS-ECC matrix fracture toughness, activate more microcracks, and reduce the crack width. Moreover, CR-modified HS-ECC specimens featuring the smallest crack width were preloaded to three specific strain levels, including 0.5%, 1.0%, and 2.0%, and then experienced wet–dry conditioning to exhibit effective mechanical and non-mechanical property recovery. The further hydration of binder materials enhances the interfacial bond stress and thus retains the mechanical performances of self-healed HS-ECC, which is expected to improve the practical application and benefit the sustainability of HS-ECC.

Segment Matrix Design and Drilling Test of Diamond Bit for Sapphire

This paper introduces the characteristics of sapphire and sapphire digging bits in LED field. The segment matrix design principle of bit and the rule of diamond selection are put forward. In addition, this paper analyzes the function of different metal powders and diamond parameters in the segment matrix. The results show that the finer grained (for example 80/100 mesh) diamond should be used with the concentrations of 30-60%. In the segment matrix, tin element can make the matrix more brittle and then the bit is sharper. Copper, silver and nickel element can enhance the matrix toughness and strength, cobalt and tungsten element can increase abrasive resistance. All of the above designs enable the sapphire bit to high sharpness and long life. A 4-inch sapphire bit was prepared for drilling sapphire crystal, the efficiency is increased by 8% than the Taiwan drill bit with the same specifications, the life is equal to Taiwan's drill bit, and the defect rate of sapphire bar is less than 0.5%, which satisfies the requirement of customers.

On the extent of fracture toughness transfer from 1D/2D nanomodified epoxy matrices to glass fibre composites

In this study, the effects of adding nanofillers to an epoxy resin (EP) used as a matrix in glass fibre-reinforced plastic (GFRP) composites have been investigated. Both 1D and 2D nanofillers were used, specifically (1) carbon nanotubes (CNTs), (2) few-layer graphene nanoplatelets (GNPs), as well as hybrid combinations of (3) CNTs and boron nitride nanosheets, and (4) GNPs and boron nitride nanotubes (BNNTs). Tensile tests have shown improvements in the transverse stiffness normal to the fibre direction of up to about 25% for the GFRPs using the ‘EP + CNT’ and the ‘EP + BNNT + GNP’ matrices, compared to the composites with the unmodified epoxy (‘EP’). Mode I and mode II fracture toughness tests were conducted using double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively. In the quasi-static mode I tests, the values of the initiation interlaminar fracture toughness, $$ G_{\text{IC}}^{\text{C}} $$GICC, of the GFRP composites showed that the transfer of matrix toughness to the corresponding GFRP composite is greatest for the GFRP composite with the GNPs in the matrix. Here, a coefficient of toughness transfer (CTT), defined as the ratio of mode I initiation interlaminar toughness for the composite to the bulk polymer matrix toughness, of 0.68 was recorded. The highest absolute values of the mode I interlaminar fracture toughness at crack initiation were achieved for the GFRP composites with the epoxy matrix modified with the hybrid combinations of nanofillers. The highest value of the CTT during steady-state crack propagation was ~ 2 for all the different types of GFRPs. Fractographic analysis of the composite surfaces from the DCB and ENF specimens showed that failure was by a combination of cohesive (through the matrix) and interfacial (along the fibre/matrix interface) modes, depending on the type of nanofillers used.

Bio-Inspired Laminates of Different Material Systems

Helicoidal laminates mimicking the laminar structure of the exoskeleton of crustaceans have been reported to resist higher out-of-plane loads than the common cross-ply and quasi-isotropic fiber-reinforced laminates. Some have reported that smaller inter-ply angle improves strength of helicoidal laminates but others have reported the opposite. A few important material parameters that dictate the failure mechanism of helicoidal laminates have recently been proposed based on proof-of-concept carbon fiber-reinforced laminates, which is not the best material system to benefit from a helicoidal configuration. This study investigates the out-of-plane loading performance of helicoidal laminates with various inter-ply angles, ply thicknesses, and materials. Result shows that the failure mechanism is dictated by the competition between spiraling matrix split and delamination followed by fiber breakage regardless of the laminate material system. Spiraling matrix split resistance decreases as pitch (ratio of inter-ply angle to ply thickness) and matrix toughness decreases. This study provides guidelines for the optimization of helicoidal laminates. Coexistence of spiraling matrix split and fiber damage is often seen on the failed laminate with the highest peak load. The optimal inter-ply angle provides the optimal spiraling matrix split resistance; so, neither spiraling matrix split nor fiber/delamination damage becomes dominant. Since resistance to spiraling matrix split decreases as pitch or matrix toughness decreases, the optimal inter-ply angle will increase for laminates with weaker matrix or thicker plies and vice versa.

Functionalization of Graphene and Its Influence on Mechanical Properties and Flame Retardancy of Jute/Poly(lactic acid) Composite

In this work, 9,10-dihydro-9-oxa-phosphaphenanthrene-10-oxide (DOPO) was covalently grafted onto the surface of graphene to get modified graphene (G-DOPO) firstly. The mechanical properties and flame retardancy of jute/poly(lactic acid) (PLA) composite with G-DOPO were studied. According to Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), it was confirmed that DOPO was grafted on the surface of graphene successfully. Thermogravimetric analysis (TGA) results demonstrated that the residue char of the composites increased with the addition of G-DOPO. The total heat release (THR) of the composite was significantly reduced and the limiting oxygen index (LOI) increased after adding G-DOPO into the composite. Moreover, the mechanical properties results showed that the comprehensive effects of G-DOPO on the interface enhancement and matrix toughness were found.

Development and Characterization of Polypropylene/Polyethylene Vinyl Acetate/Micro Cellulose Trays as a Prototype for Chilled Food Packaging Application

Cellulose and polypropylene (PP) were successfully designed as a composite material. To obtain higher efficiency, ethylene vinyl acetate (EVA) with vinyl acetate (VA) content 28 % was integrated as a coupling agent. The presence of EVA improved the composite compatibility and polypropylene matrix toughness under low temperatures. The composite was compounded by twin screw extrusion (TSE) with 30 part of EVA per hundred parts of resin (phr) and varying ratios of cellulose 5, 10, 20 and 30 phr, respectively. The effects of cellulose and EVA on properties of the composite were investigated. Thermal degradation temperature of PP/cellulose composites with and without EVA was higher than pure PP. The impact strength of the composite with EVA was increased compared to composite without EVA. PP/EVA/cellulose-10 phr is the best condition which showed a very high elongation at break and tan δ. In conclusion, the role of cellulose and EVA could improve the thermal stability and flexibility of thermoplastic composites and would be useful in packaging chilled food.