Efficient fabrication of PLA/PHB composites with enhanced mechanical properties, excellent thermal stability, fast crystallization ability, and degradation rate via the synergistic of weak shear field and melt quenching technique

Polylactic acid (PLA)/polybutylene adipate terephthalate (PBAT) blend is a fully degradable polymer blend with balanced strength and toughness. However, the performance of PLA/PBAT blends deteriorates significantly after undergoing physical aging. In this work, dicumyl peroxide (DCP) and methyl methacrylate-glycidyl methacrylate copolymer (P(MMA-co-GMA)) were used respectively for reactive compatibilization by dynamic vulcanization. The effects of dynamic vulcanization on the interfacial compatibility and thus on the mechanical properties of PLA/PBAT blends were evaluated using nanomechanical mapping. Results show that the degree of interfacial compatibilization can be determined by the interface length of microscopic Young's moduli distribution between PLA and PBAT. A longer interfacial length indicates an enhanced interfacial interaction between the components in the blend, which leads to improved macroscopic mechanical properties. Moreover, the improvement of interfacial compatibility allows the PLA/PBAT blends to maintain higher mechanical properties after physical aging, which provides an experimental basis for the design of PLA-based blends with both high mechanical properties and resistance to physical aging. 

Unveiling the effect of enhanced interfacial compatibility on the mechanical properties of PLA/PBAT blends

This paper presents the residual flexural capacity of reinforced concrete beams under combined actions of corrosion and elevated temperatures. 17 concrete beams were manufactured and accelerated corrosion tests were conducted to obtain corrode concrete beams. After fire tests according to ISO 834 standard fire, each specimen was subjected to a four-point bending test. The results showed that corrosion led to premature failure of concrete beams. During fire tests, corrosion-induced cracks accelerated heat transfer in the concrete. Slight corrosion had little effect on the yield and ultimate load of concrete beams. One hour fire exposure had little effect on the load bearing capacities of slightly corroded or uncorroded beams. But when the corrosion degree exceeded 0.1, the load bearing capacities decreased by up to 31%. Increasing the concrete cover thickness significantly improved the load bearing capacity of corroded concrete beams. When the degree of corrosion of tension bars exceeded 0.069, energy dissipation capacities decreased significantly as much as 21%. The longer the fire exposure time was, the greater the decrease in energy dissipation. The conclusions obtained in this paper can provide a theoretical basis for the evaluation of residual performance of corroded concrete structures after exposure to fire. 

Residual flexural capacity of corroded reinforced concrete beams after exposure to fire

Cemented tailings backfill (CTB) is continually practiced in a large number of metallic mines for re-filling underground ore extraction areas. Re-filling these areas can boost the security of mining teams during construction. Hence, CTB’s durability/ductility is extremely vital to ensure the safety of the entire mine. In this study, layered-fiber-reinforced CTB (LFR-CTB) was manufactured using polypropylene fiber (PPF) to increase the strength and flexibility of backfilling. The strength and bending features of CTB and LFR-CTB specimens were explored through a three-point bending test and SEM microanalysis. Test findings pointed out that the flexural strength of 14-day-cured CTB specimens without fiber delamination and with cement showed that a tailings ratio of 1:4 was the largest among others. Residual flexural strength of LFR-CTB was greater than those of CTB without fiber delamination. Accumulating fiber delamination effectively improved CTB’s flexural features. CTBs without fiber delamination presented the largest average flexural modulus values. LFR-CTBs presented greater average toughness index values than ordinary CTB specimens. Adding fiber facilitated the progress of CTB’s post-peak rigidity. LFR-CTBs containing high-fiber delamination dimensional height have excellent bending properties. The damage mode of all backfill specimens is chiefly tensile damage. The overall bonding of LFR-CTB specimens in the presence of interlayer interfaces is outstanding, not affecting their bending performance. Ettringite and CSH gels were found to be key hydration materials. The addition of fiber to the filling has an inhibitory impact on the extension of the cracks occurring within specimens. Finally, this study’s key consequence is to deliver a technical guideline and reference in order to reveal LFR-CTB’s enhancement and delamination mechanism for industrial applications. 

Polypropylene Fiber Effect on Flexural Strength, Toughness, Deflection, Failure Mode and Microanalysis of Cementitious Backfills under Three-Point Bending Conditions

Effect of 3D printed skeleton shapes on strength behavior, stress evolution and microstructural response of cement-based tailings backfills

The influence of long-term thermal exposure on microstructure evolution and tensile behavior of a new wrought γ′-hardened Ni-base superalloy at different temperatures are investigated. The experimental superalloys are thermal exposure at 650 °C for different times up to 2300 h and tensile tests are performed in both heat treatment and thermal exposure conditions. The results show that some discontinuous carbides precipitate at the grain boundaries and spherical γ′ precipitates homogeneously disperse within the γ matrix after heat treatment. During thermal exposure, the γ′ precipitates remain spherical morphology, and the coarsening behavior of γ′ conforms to the LSW model. The tensile strength of the experimental superalloy after heat treatment generally shows a downward trend with the increase of tensile temperature while the elongation reaches a maximum at 650 °C. After thermal exposure, the tensile strength of the experimental superalloy has improved while the elongation slightly decreases. 

Influence of thermal exposure on microstructural stability and tensile properties of a new Ni-base superalloy

Thin-ply composite failure modes also significantly differ from conventional ply composite failure modes, with the final failure mechanism switching from irregular progressive failure to direct fracture characterized by a uniform fracture with the reduction of the ply thickness. When open holes and bolt joints are involved, thin-ply-laminated composites exhibit more complex stress states, damage evolution, and failure modes. Compared to the experimental study of thin-ply-laminated composite-bolted joints, there are few reports about numerical analysis. In order to understand the damage evolution and failure mechanism of thin-ply-laminated composites jointed by single-lap bolt, a progressive damage model based on three-dimensional (3D) LaRC failure criterion combined with cohesive element is constructed. Through an energy-based damage evolution method, this model can capture some significant mechanical characteristics in thin-ply-laminated structures, such as the in situ effect, delamination inhibition, and fiber compressive kinking failure. The comparisons between the numerical predictions and experimental observations are made to verify the accuracy of the proposed model. It is found that the predicted stress-displacement curves, failure modes, damage morphologies, etc., are consistent with the experimental results, indicating that the presented progressive damage analysis method displays excellent accuracy. The predicted stress at the onset of delamination is 50% higher than that of the conventional thick materials, which is also consistent with experimental results. Moreover, the numerical model provides evidence that the microstructure of thin-ply-laminated composite performs better in uniformity, which is more conducive to inhibiting the intra-layer damage and the expansion of delamination damage between layers. This study on the damage inhibition mechanism of thin-ply provides a potential analytical tool for evaluating damage tolerance and bearing capabilities in thin-ply-laminated composite-bolted joints.

/pdf/modeling-progressive-damage-and-failure-of-single-lap-thin-1wr9ha4y.pdf

Modeling Progressive Damage and Failure of Single-Lap Thin-Ply-Laminated Composite-Bolted Joint Using LaRC Failure Criterion

Physical aging-induced embrittlement of PLA/PBAT blends probed by tensile test and AFM nanomechanical mapping

Revealing the microstructural evolution and its influence on mechanical properties of heterostructured steel fabricated by laser melting deposition

Understanding the mechanical properties and failure process of cemented paste backfill with recycled rubber (RCPB) is the foundation of backfill design in underground mining. In this study, physical and mechanical tests were conducted on RCPB to obtain its mechanical property parameters, such as its uniaxial compressive strength (UCS), toughness, and peak strain. The influence of the rubber dosage on the mechanical properties of RCPB was also analyzed. In addition, the deformation behavior, fracture development, and failure process of RCPB with different rubber contents were observed using the digital image correlation (DIC) technique. The experimental results suggested that, although the UCS of RCPB is reduced as more rubber is added, its toughness and ability to absorb energy is increased. Moreover, the impact resistance of RCPB is improved by this increased toughness. With the increase in the rubber content, the deformation corresponding to the plastic yield stage of RCPB increased, which resulted in better ductility and improved impact resistance. The failure of the RCPB specimens mainly showed an “X” shape. The results of this study help us to better understand the mechanical behavior of RCPB after backfilling underground.

/pdf/the-failure-mechanical-properties-of-cemented-paste-backfill-3ibgx0ny.pdf

The Failure Mechanical Properties of Cemented Paste Backfill with Recycled Rubber

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