Dynamic Tensile Properties of CFRP Manufactured by PCM and WCM: Effect of Strain Rate and Configurations

Carbon fiber-reinforced plastic (CFRP) is a promising material to achieve lightweight automotive components. The effects of the strain rate and configurations of CFRP on dynamic tensile properties have not yet been fully explored; thus, its lightweight benefits cannot be maximized. In this paper, the dynamic tensile properties of CFRPs, tested using two different processes with two different resins and four different configurations, were studied with a strain rate from 0.001 to 500 s−1. The tensile strength, modulus, failure strain, and fracture mechanism were analyzed. It was found that the dynamic performance enhances the strength and modulus, whereas it decreases the failure strain. The two processes demonstrated the same level of tensile strength but via different fracture mechanisms. Fiber orientation also significantly affects the fracture mode of CFRP. Resins and configurations both have an influence on strain rate sensitivity. An analytic model was proposed to examine the strain rate sensitivity of CFRPs with different processes and configurations. The proposed model agreed well with the experimental data, and it can be used in simulations to maximize the lightweight properties of CFRP.

Enhanced Acceptance Specification of Asphalt Binder to Drive Sustainability in the Paving Industry

Testing small amounts of extracted and recovered asphalt binder as used in construction allows for the acceptance of materials in accordance with traffic and climate requirements. This approach facilitates the sustainable use of resources and thus prepares the paving industry for the true circular economy. Oscillatory, creep, and failure tests in a rheometer are compared for the performance grading of 32 asphalt binders extracted and recovered from real-world contract samples. Films 8 mm in diameter and 0.5 mm thick were tested from 35 to −5 °C in dynamic shear, followed by shear creep at 0 and 5 °C, and finally in tertiary tensile creep at 15 °C. The enhanced protocol uses a very small amount of material in contrast to current methods, yet it provides comparable results. Phase angle measurements appear to be optimal for performance grading, but further field study is required to determine if additional binder properties such as stiffness and/or failure strain would be required for the control of cracking.

The effect of fibre surface treatment and coupling agents to improve the performance of natural fibres in PLA composites

This paper describes work carried out to assess the effect of fibre treatments and coupling agent on the mechanical performance of PLA composites reinforced with 20 wt% fibre. The chemically-treated harakeke and hemp fibres used to produce fibre mats. Maleic anhydride (MA) grafted PLA (MA-g-PLA) was used as a coupling agent. Composites with fibre treated with silane and dicumyl peroxide (DCP) and composites using MA-g-PLA were characterised by swelling testing, scanning electron microscopy (SEM), tensile testing, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). It was found that the interfacial bonding for composites with fibres treated using silane and peroxide and composites coupled with MA-g-PLA noticeably improved supported by lower swelling indices, higher tensile strengths and lower tan δ compared to those composites with fibres treated using alkali only, with the highest tensile strength of about 11% higher obtained from composites treated with MA-g-PLA followed by silane and then peroxide. However, using silane, peroxide and MA-g-PLA as additional composite treatments increased significantly the composite failure strain by up 11, 19 and 30%, respectively for harakeke composites and by 13, 24 and 30%, respectively for hemp composites.

Strain Range Dependence of Young’s Modulus and Size Effects of Mechanical Properties for Chiral Graphene by Molecular Dynamics Simulations

The stress-strain response of pristine monolayer graphene under uniaxial loading/unloading over a larger size range (100nm×100nm) is studied by molecular dynamics (MD) simulations, which proves that graphene is perfectly elastic prior to the failure strain. Young’s modulus of graphene is calculated by selecting different strain ranges in the elastic region. It is found that Young’s modulus is strongly dependent on the strain range. When the selected strain ranges are increased from 0.5% to 8%, Young’s modulus of the armchair and zigzag graphene is reduced by approximately 60 Gpa and 150 Gpa, respectively. Based on the Pearson correlation coefficient method, the linearity of the stress-strain curve during graphene stretching is studied. The elastic region of the tensile curve is divided into the linear elastic region and non-linear elastic region. simultaneously, the linear elastic limit strains for the armchair and zigzag graphene are defined to be about 2.5% and 1.5%, respectively, and they are independent of the size of graphene. On this basis, the chirality dependence and size effects of Young’s modulus, failure strain, and fracture strength of pristine monolayer graphene are investigated. The results show that Young’s modulus is dependent on the chiral angle but insensitive to size. The failure strain and fracture strength depend on the chiral angle and have obvious size effects, which decrease with the increase of size range and size ratio.

Flexural Behavior of Polyurethane Concrete Reinforced by Carbon Fiber Grid

In view of the problems of traditional repair materials for anchorage concrete of expansion joints, such as ease of damage and long maintenance cycles, the design of polyurethane concrete was optimized in this article, which could be used for rapid repair of concrete in anchorage zone of expansion joints. A new type of carbon fiber grid–polyurethane concrete system was designed, which makes the carbon fiber grid have an excellent synergistic effect with the quick-hardening and high-strength polyurethane concrete, and improved the flexural bearing capacity of the polyurethane concrete. Through the four-point bending test, the influence of the parameters such as the number of grid layers, grid width, and grid density on the flexural bearing capacity of polyurethane concrete beams was tested. The optimum preparation process parameters of carbon fiber grid were obtained to improve the flexural performance of polyurethane concrete. Compared with the Normal specimen, C-80-1’s average flexural strength increased by 47.7%, the failure strain along the beam height increased by 431.1%, and the failure strain at the bottom of the beam increased by 68.9%. The best width of the carbon fiber grid was 80 mm, and the best number of reinforcement layers was one layer. The test results show that the carbon fiber grid could improve the flexural bearing capacity of polyurethane concrete. The carbon fiber grid–polyurethane concrete system provides a new idea for rapid repair of the anchorage zone of bridge expansion joints, and solves the problems such as ease of damage and long maintenance cycles of traditional repair materials, which can be widely used in the future.

Investigation of Mechanical and Physical Properties of Big Sheep Horn as an Alternative Biomaterial for Structural Applications

This paper investigates the physical and mechanical properties of bighorns of Deccani breed sheep native from Karnataka, India. The exhaustive work comprises two cases. First, rehydrated (wet) and ambient (dry) conditions, and second, the horn coupons were selected for longitudinal and lateral (transverse) directions. More than seventy-two samples were subjected to a test for physical and mechanical property extraction. Further, twenty-four samples were subjected to physical property testing, which included density and moisture absorption tests. At the same time, mechanical testing included analysis of the stress state dependence with the horn keratin tested under tension, compression, and flexural loading. The mechanical properties include the elastic modulus, yield strength, ultimate strength, failure strain, compressive strength, flexural strength, flexural modulus, and hardness. The results showed anisotropy and depended highly on the presence of water content more than coupon orientation. Wet conditioned specimens had a significant loss in mechanical properties compared with dry specimens. The observed outcomes were shown at par with results for yield strength of 53.5 ± 6.5 MPa (which is better than its peers) and a maximum compressive stress of 557.7 ± 5 MPa (highest among peers). Young’s modulus 6.5 ± 0.5 GPa and a density equivalent to a biopolymer of 1.2 g/cc are expected to be the lightest among its peers; flexural strength 168.75 MPa, with lowest failure strain percentage of 6.5 ± 0.5 and Rockwell hardness value of 60 HRB, seem best in the class of this category. Simulation study identified a suitable application area based on impact and fatigue analysis. Overall, the exhaustive experimental work provided many opportunities to use this new material in various diversified applications in the future.

Evaluation of Monkman–Grant strain as a key parameter in ductility exhaustion damage model to predict creep rupture of grade 92 steel

Conventional strain-based numerical prediction assumes that failure occurs when ductility is exhausted or accumulation of creep strain reaches the critical failure strain. Due to instability at the onset of rupture, the failure strain value appears to be scattered and leads to the erroneousness in prediction. In this paper, a new local constraint-based damage model incorporating the Monkman–Grant ductility, as a measure of strain during uniform creep deformation stage, was implemented into a Finite Element (FE) model to predict the creep damage and rupture of Grade 92 steel under uniaxial and multiaxial stress states. The prediction was applied on plain and notched bar specimens with various notch acuities. The uniaxial stress-dependent Monkman–Grant (MG) failure strain was adopted in the FE to simulate the influence of the constraints which were induced by the creep damage. The implication of reduced failure strain in long-term creep time on the rupture prediction is discussed. The multiaxial MG failure strain of the notched bar, which has a lower value than uniaxial failure strain due to the geometrical constraint, was estimated based on the linear inverse relationship between normalised MG failure strain and normalised triaxiality factor. It was found that the results obtained from the proposed technique were in good agreement with the experimental data within the scatter band of ± factor of 2. It was shown that MG failure strain can be used as an alternative to strain at fracture. MG strain outweighed strain at fracture because the determination of its value only required short-term testing to be performed. In most cases considered in the present investigation, the rupture-type fracture was predicted, however, there was evidence that under high constraint and low stress, stable crack propagation occurred before fracture. The location of the maximum creep damage was found to be dependent on the creep time, geometry or acuity level of the specimen. For sharp notch specimen, the failure was initiated near the notch root, however, as the notch radius increased, the initiation location moved further away towards the specimen centre.

Calibration of Failure Criteria for Additively Manufactured Metallic Materials

A new version of failure criterion for additively manufactured materials, together with simple and accurate calibration procedures, is proposed and experimentally verified in this paper. The proposition is based on void growth-based ductile failure models. The failure criterion for ductile materials proposed by Hancock–Mackenzie was calibrated using simple methods and accessories. The calibration procedure allows the determination of failure strain under pure shear. The method is accurate and simple due to the fact that it prevents strain localization disturbing stress distribution at the failure zone. The original criterion was modified to better suit the deformation behavior of additively manufactured materials. Examples of calibration of the original and modified failure criteria for additively manufactured 316L alloy steel is also given in this paper, along with analyses of the obtained results.