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The initial fracture propagation within a full-scale stiffened quasi-isotropic composite panel and coupons with stringer feet under tensile loads was investigated. The specimens were made from Non-Crimp Fabric through Vacuum assisted Resin Transfer Moulding. The failure loads of all configurations were successfully related using the same value of trans-laminar fracture energy. The method involved independent tests of scaled-down Over-height Compact Tension specimens and the Virtual Crack Closure Technique. It was found to be crucial to include the fully developed damage process zone in the crack length and to interpret the results carefully in order to identify the failure loads consistently. [ABSTRACT FROM AUTHOR]

Rock mass behavior is controlled mainly by weak planes in sedimentary rocks. Geomechanical model tests were conducted for simulating tunnel excavations in horizontal, the 45° and vertical inclined rock strata. Infrared thermography was employed for detecting rock responses during the excavations. Infrared temperature (IRT) curve obtained by averaging the matrices of the infrared sequence can be viewed as temporal observation of the overall energy release from the rock under excavation. The IRT curve characterizes the horizontal and vertical strata as linear behavior and the 45° inclined strata as piecewise linear behavior over the full-face excavation and the three strata as plastic-like behavior over the staged excavation, respectively. The constitutive heterogeneity can be represented by the Weibull modus obtained by curve-fitting to the Weibull model using the probability distribution of the IRT temporal observations. The vertical strata has the smallest Weibull modulus values corresponding to the higher heterogeneity compared with the else two strata models. The structural response of the rock under excavation was characterized by the IRT distribution of the infrared image. IRT distribution of the horizontal strata evolved from scattering distribution to localized high-temperature zone around the face. In contrast, IRT distribution for the 45° and vertical strata distributed as belt-like IRT parallel to the weak surface; indicating the frictional sliding damage mechanism. Most intense friction was observed in the excavation in the 45° inclined rock strata. [ABSTRACT FROM AUTHOR]

This paper presents prediction of the high velocity, oblique impact response and quasi-static residual tensile strength of thin [45/90/−45/0] 2s carbon/epoxy laminates using finite element (FE) models. A High-Fidelity Finite Element Method (Hi-FEM) with an automated unit cell meshing technique was employed. The predicted impact damage, characterised by the extent of fibre failure and delamination area, was validated against results from gas-gun tests for a range of impact velocities. The numerical results captured the trend of increasing impact damage with impact energy as observed from the tests. Changes in projectile orientation before impact were shown to increase the extent of fibre failure at high impact energies, up by 38% in edge impact cases. The residual tensile strength of the impacted laminates was then investigated, where the numerical results for edge-impacted laminates agreed with the test data within 8%. On the other hand, the residual strength modelling results of centre-impacted laminates were found to be unconservative, mainly due to the extent of fibre failure predicted during impact. Machined notches were also studied for their residual tensile strength in comparison to impact induced damage. The predicted strength of edge-notched laminates was found to be in close agreement with the experimental results for edge-impacted laminates, differing by an average of 9%. [ABSTRACT FROM AUTHOR]

Defects such as out-of-plane wrinkles are known to strongly affect in-plane strength but there has been very little research on their effect on out-of-plane properties. Experimental and numerical studies of multi-directional curved-beam laminates were thus carried out to understand the effects of out-of-plane wrinkles on through-thickness tensile strength. The initially selected layup saw free-edge delamination interacting with transverse cracking, which is undesirable. After suppressing the free-edge delamination by dispersing the plies near the specimen surfaces, through-thickness tensile failure was observed near the mid-plane. The effects of out-of-plane wrinkles could be studied with this appropriate layup, showing a 16% reduction in strength. A High-fidelity Finite Element Method (Hi-FEM) has been used to distinguish between the different failure modes and to understand the effects of wrinkles. Good agreement was achieved between the numerical and experimental results in terms of through-thickness tensile strengths and delamination locations. Image 1 [ABSTRACT FROM AUTHOR]

The creation of high-performance polylactic acid (PLA) materials combining excellent mechanical robustness and flame-retardant performances are essential to meet demanding performances requirements for their practical applications in industry. Despite encouraging advances, current strategies by introducing toughening agents and flame retardants usually show compromised mechanical strength/ductility because of the irrational interphase reaction design of multi-component polymer blends. To date it remains challenging to robust and flame-retardant PLA via controlling interphase reactions. We, herein, report the rational design of mechanically robust and flame-retardant PLA by in situ manipulating interphase reactions between PLA, epoxidized soybean oil (ESO), a biobased and inexpensive toughening agent, and ammonia polyphosphate (APP), an effective eco-friendly flame retardant. We show that in addition to a high tensile strength of 42.0 MPa, as-designed PLA/ESO/APP ternary blend exhibits a high extensibility of 165% and a fracture toughness as high as 46 MJ/m3, which are respectively 21 and 14 folds of that of the bulk PLA. Meanwhile, a desired V-0 rating and a high limited oxygen index of 30.2% are achieved. Such outstanding performance portfolios are enabled by the rational manipulation of interphase reactions, leading to the in situ formation of favorable phase structures. This work offers an innovative methodology for facilely and massively creating high-performance multi-component polymer blends by tailoring interphase reactions, and contributes to expanding the extensive applications of PLA. Image 1 • Advanced PLA/ESO/APP ternary blends have been rationally designed via manipulating interphase reactions. • As-designed PLA/ESO/APP blend exhibits a large extensibility of 165% and a fracture toughness as high as 46 MJ/m3. • The PLA/ESO/APP ternary blend retains a high tensile strength of 42.0 MPa. • The PLA/ESO/APP blend can pass a V-0 rating in addition to showing a high LOI of 30.2%. [ABSTRACT FROM AUTHOR]

The friction and thermal conductivity are two vital factors affecting braking components in manned aircraft. It is imperative to find a rational design basis for high-performance lightweight polymeric materials with excellent toughness, coefficient of friction, and thermal conductivity. In light of the outstanding mechanical strength, stiffness, and good dimensional stability of polyamide 6 (PA6), herein, we have demonstrated the fabrication of high-performance PA6 composites by adding one-dimensional SiC whiskers (SCWS) as both a reinforcement agent and anti-abrasion agent. The results show that addition of 2 wt% SiC whiskers (SCWS) increases the tensile strength of PA6 by 37.6% (reaching 58.2 MPa). Meanwhile, the elongation at break is over five times (around 280%) of that of the PA6 matrix, which means that the fracture toughness is increased around seven-fold. Moreover, the addition of 30 wt% SCWS reduces the coefficient of friction from 0.31 for the PA6 to 0.15, indicating improved anti-abrasion performance. Such significant improvements in both mechanical and anti-wear properties are primarily due to the high stiffness of SCWS and the strong interfacial interactions with the PA6 matrix. This work provides a facile approach to the design of mechanically robust, wear-resistant polymer composites which hold significant promise for producing advanced gears and bearing parts in aerospace and automobile applications. • High-performance PA6 composites by adding various loading levels of SiC whiskers (SCWS) were prepared. • The addition of 2wt% SCWS increases the tensile strength of PA6 by 37.6%. • Adding 2wt% of SCWS increases the elongation at break of PA6 over 5 times and the fracture toughness by around 7 times. • The addition of 30 wt% SCWS reduces the friction coefficient from 0.31 for the PA6 to 0.15. [ABSTRACT FROM AUTHOR]

Composite components are required to be resilient against Foreign Object Damage (FOD) induced by localised high velocity impact events. Here an experimental investigation into high velocity oblique impacts and residual tensile strength of thin quasi-isotropic carbon/epoxy laminates is reported. Oblique (45°) impacts between 100 m/s and 350 m/s were carried out using 3 mm steel cubes on the edge and the centre of the laminates, mounted as a cantilever beam. Impact induced damage was characterised using X-ray Computed Tomography (CT) and the residual strength of impacted laminates was determined through quasi-static tensile tests. The residual strength shows a strong dependence on the impact damage size, characterised in terms of fibre fracture width and delamination area. Machined notches were then investigated and compared to impacted laminates in terms of residual strength. [ABSTRACT FROM AUTHOR]

[Display omitted] • A multifunctional small molecule (HCPA) has been prepared. • The presence of HCPA endowed PVA with a nanostructure within the continuous matrix. • 5 wt% of HCPA endows PVA with a self-extinguishing behavior. • 5 wt% of HCPA increases tensile strength of PVA by 47% and toughness by 370%. • The PVA/HCPA composites exhibit a water-trigged healing efficiency over 90%. The combination of high fire retardancy, high strength, and great toughness as well as good healability is essential for successful real-world applications of polymeric materials in the fields of packaging, electronics & electrics, and optical devices. To date, there have been few successes in achieving such performance portfolios in polymers due to their different and even mutually exclusive governing mechanisms. Inspired by the nanoconfinement effect that governs the unique mechanical properties of spider silk, we, herein, rationally design a multifunctional small molecule, HCPA, that can serve as a fire retardant and hydrogen-bond crosslinker for poly(vinyl alcohol) (PVA). Benefiting from the dual-phase fire-retardancy effect and the dynamic cross-linking effect, the addition of 5.0 wt% of HCPA enables PVA to achieve a desired self-extinguishment in combination with a high tensile strength of 133 MPa and a toughness of 112 MJ/m3. In addition, the as-prepared polymer material exhibits a high healing efficiency of over 90% (based on strength) if triggered by water. This proof-of-concept opens numerous opportunities for the creation of self-extinguishing, strong, tough, and self-healing polymers for many high-end applications in the above-mentioned industries. [ABSTRACT FROM AUTHOR]

[Display omitted] • A multifunctional MXene-based hybrid (Zr-MXene) has been prepared. • 1 wt% of Zr-MXene increases ductility and toughness of TPU by 33% and 88%, respectively. • 1 wt% of Zr-MXene increases the tensile strength and fatigue resistance of TPU. • The addition of Zr-MXene significantly reduce the flammability of TPU. • The peak heat release rate and peak smoke production rate are respectively reduced by 63% and 56%. Thermoplastic polyurethane (TPU) features many important industrial applications, but intrinsic flammability extremely impedes its practical applications. Current fire-retardant strategies often lead to improved flame retardancy but reduced mechanical properties (strength, ductility, and toughness). Hence, to date it has been unsuccessful to design advanced TPU materials that are strong, stretchable, tough, fatigue-and fire-resistant to meet increasing performance portfolio requirements. Here, we report a hybridized fire retardant (Zr-MXene) by in situ facilely loading zirconium amino-tris-(methylenephosphonate) (Zr-AMP) onto the titanium carbide (MXene) surface. Our results show that with 1 wt% of Zr-MXene, the resultant TPU nanocomposites demonstrate a record break strain (2060%) and toughness (316 MJ/m3) to date, in addition to increased tensile strength by 43.4% and improved fatigue resistance relative to the TPU matrix, because of favorable interfacial hydrogen-bonding. Moreover, the resultant TPU material exhibit significantly reduced flammability as a result of the combined physical barrier, catalytical carbonization and diluting effects of Zr-MXene. This work provides a promising strategy for the creation of multifunctional MXene and its polymeric nanocomposites, which hold great promise for many industrial applications. [ABSTRACT FROM AUTHOR]