Shear Strength Of Matrix Research Articles

Effect of synergistic action of anodising and graphene on the mechanical properties of fibre-reinforced metal laminates

Fibre reinforced metal laminates (FMLs) are widely used in various fields due to their excellent properties. However, the weak interlayer properties of FMLs limit their applications. In this paper, the interlayer properties of FMLs are enhanced by anodising the 2024-T3 aluminium alloy layer in FMLs or by epoxy matrix modification of graphene nanoplatelets (GNPs). The effect of both synergistic impacts on the interlayer properties of most FMLs is investigated. The FMLs were manufactured using the wet lay-up technique using 2024-T3 aluminium alloy, E51 epoxy and EW100 glass fibre. The results showed that the type I fracture toughness, tensile strength, flexural strength, interlayer shear strength and single layer shear strength of FMLs after anodic oxidation treatment were increased by 406.4%, 10.3%, 18.3%, 42.6% and 28.3%, respectively, compared with those of pure FMLs. The type I fracture toughness, tensile strength, flexural strength, interlayer shear strength and single layer shear strength of the GNPs-modified FMLs matrix were increased by 280.4%, 3.7%, 6.8%, 34.5% and 19.1%, respectively, compared with those of pure FMLs. Moreover, the synergistic effect of FMLs indicates that the simultaneous anodic oxidation and GNPs modification of FMLs can lead to the best mechanical properties of FMLs. Microscopic images and schematics illustrate the toughening mechanism of anodising and GNPs, including the enhancement of aluminium/resin interface and fibre/resin interface and the enhancement of resin matrix properties.

The role of constitutive properties on the longitudinal compressive strength of composites

The longitudinal compressive strength of fibre-reinforced composites is often a limiting factor for structural design. This paper uses micromechanical finite-element analyses to examine how the constitutive properties of the matrix, fibres, and interface affect the composite’s strength. For a typical carbon/epoxy composite, the matrix shear strength has a larger effect than the modulus; a linear-elastic perfectly-plastic approximation of the matrix shear curve may overestimate the composite’s strength by over 15%. A pressure-dependent and dilatant matrix plasticity response may strengthen the composite by 30%, considering current uncertainties in friction and dilation angles of epoxy matrices. The finite shear modulus of carbon fibres may weaken the composite by more than 10%. Considering a cohesive interface using traction–separation laws significantly affects the predicted response of the composite, even for interfaces stronger than the matrix. Opportunities for improving the characterisation, modelling and performance of the constituents in terms of matrix plasticity, fibre shear modulus, and interface response are discussed.

Microstructure and Mechanical Properties of a Three‐Dimensional Oxide/Oxide Composite after Long‐Term Thermal Exposure

Herein, a three‐dimensional (3D) oxide fiber reinforced oxide matrix (oxide/oxide) composite is fabricated via slurry infiltration and sintering process. Subsequently, the effects of thermal aging on the microstructure and mechanical properties of the 3D oxide/oxide composite at 900 and 1100 °C are investigated. Experimental results indicate that the thermal aging affects the matrix microstructures and fiber/matrix interface. The elastic modulus of the matrix and interfacial shear strength increases with aging temperature and time. Aging treatment at 900 °C for 100 and 300 h results in a moderate decrease in the flexural strength and fracture toughness but improves the delamination resistance, whereas that at 1100 °C for 100 h lead to a significant decrease in the flexural strength and fracture toughness. The changes in mechanical properties might be attributed to matrix densification and enhanced interfacial bonding.

Slurry infiltration and sintering cycle‐dependent mechanical properties of 3D oxide/oxide ceramic matrix composites

AbstractIn this study, oxide/oxide ceramic matrix composites reinforced with three‐dimensional fiber preform were fabricated by a slurry infiltration and sintering (SIS) process. The influence of the SIS cycle on microstructures and mechanical properties of the 3D oxide/oxide composite was investigated. Results showed that the porous matrix was densified due to the SIS effect. The elastic modulus of the weak matrix and interfacial shear strength increased with the increasing SIS cycle. This led to an obvious improvement in flexural strength and interlaminar shear strength of the composite. The fracture toughness and work of fracture of the composite slightly decreased. A good balance between fracture strength and damage tolerance was achieved on the sixth SIS fabricated oxide/oxide composite, which had a high flexural strength of 295.1 ± 14.9 MPa, a high interlaminar shear strength of 18.2 ± .5 MPa, and a high fracture 11.5 ± .8 MPa m1/2. The SIS process is a promising way to fabricate the 3D oxide/oxide composite.

Water Resistance of Super Adhesive Emulsified Asphalt Based on Dynamic Water Scouring

This study aimed to address the issue of inadequate water resistance in asphalt pavement tack coat materials by preparing super adhesive emulsified asphalt (SAE). Due to the lack of consideration of dynamic water scouring in previous studies on the water resistance analysis of tack coat materials, this research employed self-designed inclined shear, pullout, and dynamic water scouring devices to examine the shear and tensile strength of matrix emulsified asphalt, styrene block copolymer (SBS)-modified emulsified asphalt, and SAE under various conditions of sprinkling volumes, temperatures, and scouring times. The findings indicate that, in the dynamic water scouring test conducted under the optimal sprinkling amount of tack coat material and the most unfavorable temperature conditions between layers, SAE exhibited residual shear and tensile strengths that were higher than SBS-modified emulsified asphalt and matrix emulsified asphalt. Combining polymerized styrene butadiene rubber (SBR) and polyurethane (PU) as two modifiers in the mix exhibits a synergistic effect, enhancing the bonding performance, scouring resistance, and water resistance of SAE as the tack coat material.

Frictional Damage Mechanism for Matrix Failure in Cutting Unidirectional CFRP

Abstract In machining carbon fiber–reinforced polymer (CFRP) materials of different fiber orientations, the uncut material fracture occurs at different chip formation angles owing to either the fiber-dominated failure or matrix failure. For the matrix failure mode, it is found that the cracks in the damaged material can still affect the chip formation by providing additional Coulomb friction on the closed crack surfaces. To investigate the effect of the damage state of the matrix on the chip formation mechanism, this paper proposes a new cutting mechanics model for CFRP, by attributing the increase of the matrix shear strength to the Coulomb friction on the closed fracture surface. The frictional damage of matrix material, including damage initiation, propagation, and complete failure, is considered to provide a physical explanation for the increase of matrix shear strength and prove that the damaged matrix still influences the chip formation after complete failure. The proposed model determines the transition of chip formation mode, the variation of chip formation angle, and the cutting forces with the fiber orientation, considering the friction in the damaged area and the elastic stress in the undamaged area. According to the comparison with the models which do not consider the material damage state and attribute the increase of shear strength to the “internal friction” without a physical explanation, it is found that the proposed frictional damage model is able to capture the matrix failure in chip formation in the fiber orientation of [0deg,66deg] and [90deg,180deg] and explains the change of chip formation mechanism from matrix compression failure to fiber tension failure in the fiber orientation range of [67deg,89deg]. The necessity of considering the friction on the fractured surfaces in the machining process of CFRP is experimentally validated by cutting experiments at various fiber orientations.

Effect of Sintering Temperature on Mechanical Behaviors of an Oxide Fiber‐Reinforced Oxide Matrix Composite

Sintering temperature can significantly affect the mechanical behaviors of ceramic matrix composites. Herein, the effect of sintering temperature (900–1200 °C) on micro‐ and macromechanical properties of an oxide fiber‐reinforced oxide matrix (oxide/oxide) composite is investigated. The crack propagation path is predicted by the He–Hutchinson model. Results show that the elastic modulus of matrix and interfacial shear strength increase with sintering temperature. The propagating crack converts from deflection along the interface to direct penetration into the matrix at 1200 °C. With increase of the sintering temperature, the flexural strength and interlaminar shear strength monotonically increase, while the fracture toughness increases and then decreases at 1200 °C. A good balance between the fracture strength and fracture toughness is achieved on the 1100 °C sintered composite, which possesses a high flexural strength of ≈276.7 MPa, a high interlaminar shear strength of ≈17.2 MPa, and a high fracture toughness of ≈13.9 MPa m1/2. The study offers a new sight in deep understand of the preparation and applicability of oxide/oxide composite at high temperatures.

Influence of Polymer Matrices on the Tensile and Impact Properties of Long Fiber-Reinforced Thermoplastic Composites

To investigate the influence of polymer matrices on the tensile and impact properties of long fiber-reinforced thermoplastic (LFT) composites, composites of long basalt fiber-reinforced thermoplastic were developed in this work. Two types of polyethylene, namely 8008 and 100S, and two types of polyethylene, namely C4220 and K8303, were chosen as the matrices. The fiber volume fractions were set as 2.8%, 5.9%, 8.1%, and 10.6%. The melt flow index (MFI), crystallinity, tensile properties, impact strength, and fracture morphology of the neat polymers and the corresponding composites were tested. The composites of 8008 showed the highest tensile strength since neat 8008 showed a much higher MFI value and crystallinity. The composites of 8008 and K8303 showed a much higher tensile modulus since the neat thermoplastic showed a higher tensile modulus than the other two composites. The polymer toughness was the factor that determined whether the polymer could be toughened by fibers. Moreover, the interfacial shear strength was calculated and compared with the matrix shear strength, based on which fracture modes of the LFT were predicted. Effective methods were proposed for further improvement of the mechanical properties. The results of this paper were essential for attaining the anticipated properties when designing LFT composites.

Integrative tensile prediction and parametric analysis of unidirectional carbon/basalt hybrid fiber reinforced polymer composites by bundle-based modeling

In this study, the previous bundle-based concept, in which the impregnated fiber bundle is considered as a basic element, was adopted to model unidirectional hybrid fiber-reinforced polymer (FRP) composites in a full-scale manner. Hybrid composites with carbon and basalt fibers were modeled and validated using previous experimental data. A comprehensive parametric study of the constituent properties was performed to determine their sensitivities to overall behaviors. On this basis, an optimization framework was developed to reflect the integrative performance and cost-performance of hybrids. The simulation obtained a saturation point of the matrix shear strength of approximately 70 MPa, beyond which the overall behavior rarely changed. A dispersed arrangement of the fiber bundles could significantly delay the damage propagation and enhance the overall behavior only at low contents of high-elongation fibers. In the present case, the mean ultimate strength can be improved from 1063 MPa to 1315 MPa. The sensitivity analysis indicated that for the elastic moduli of fibers, carbon fiber strength, and Weibull shape parameter of basalt fibers, trade-offs must be considered to balance the overall ultimate strain, strength, ductility, and hybrid effect. The bundle-based modeling concept provides a fast and convenient approach to evaluate the global behavior of hybrids.

Micromechanical Tests on Natural Fibre Composites with Enzymatically Enhanced Fibre–Matrix Adhesion

Natural fibre–reinforced composites are more sustainable than other composites with respect to the raw materials. Their properties are attractive due to high specific properties, and especially so wherever high damping is valued. As the interphase between fibre and matrix is the region of highest stresses, a strong bond between fibre and matrix is essential for any composites’ properties. The present study compares two methods of determining the interfacial shear stress in natural fibre–reinforced composites: the single fibre fragmentation test and the single fibre pullout test. The studied composites are flax fibre reinforced epoxy. For a variety of fibre–matrix interaction, the fibres are treated with a laccase enzyme and dopamine, which is known to improve the fibre–matrix shear strength. In the observed samples, single fibre fragmentation test data, i.e. of fracture mode and fragment length, scatter when compared to pullout data. In single fibre pullout tests, the local interfacial shear strength showed a 30% increase in the laccase-treated samples, compared to the control samples. The method also permitted an evaluation of the frictional stress occurring after surface failure.

Bond shear performances and constitutive model of interfaces between vertical and horizontal filaments of 3D printed concrete

To determine the bond shear performance and shear load-deformation curve of the interfaces between vertical and horizontal filaments of 3D printed concrete (3DPC), a double-shear test was conducted. An advanced XCT scanning technique was used to detect the distribution of defects and porosity in the matrix and interfaces. Based on the elastic brittle damage theory, shear constitutive models of interfaces between layers, strips, and matrices were proposed. Note that the shear strengths between the layers and the strips are 5.16 MPa and 4.84 MPa, accounting for 85.7% and 80.3% of the matrix shear strength, respectively. The porosity of the matrix, interface between layers, and porosity of the interface between the strips were 2.22%, 3.82%, and 4.09%, respectively, which had a linear relationship with the shear strength. Moreover, the obtained shear constitutive model of the interface can accurately reflect the mechanical response of the interface of the 3DPC under shear stress, which fits well with the test results. This provides a foundation for the theoretical and numerical analysis of 3DPC.

Influence of vetiver grass (Chrysopogon zizanioides) on infiltration and erosion control of hill slopes under simulated extreme rainfall condition in Bangladesh

Rainfall events on hill slopes can cause both soil erosion and slope failures. With global climate change, the frequency of these events is increasing with greater consequences. Rainfall-induced erosion need to be studied in an integrated way to understand hill slope sediment yields. Among different methods for controlling erosion and slope stabilization, vegetation is widely used nowadays all over the world. Vetiver (Chrysopogon zizanioides) is a tropical grass which offers a practical and cost-effective way to prevent soil erosion. This deeply rooted and long-lived perennial grass has restrained erodible soils for decades. In this study, the effectiveness of vetiver grass in reducing soil erosion has been studied with a small-scale model study. Performance of slope against erosion was studied under rainfall for both bare slope and vetiver-rooted slope. A small-scale 1G physical model with a 40% slope was used to model bare and vegetated slope. Direct shear tests were conducted to evaluate the effect of vetiver roots on the shear strength of soil-root matrix. Rainfall was simulated using an artificial rainfall simulator with a rainfall intensity of 188 mm/h and Christiansen’s uniformity (CU) coefficient of 86.3%. The vegetated system reduced the surface runoff 18–71% for all vertical intervals compared to the control run. The infiltration capacity of the vegetated slope was evaluated with respect to different infiltration models. The results of the present study were found in close agreement with Kostiakov’s infiltration model.

Structural analysis across length scales of the scorpion pincer cuticle

Biological structures such as bone, nacre and exoskeletons are organized hierarchically, with the degree of isotropy correlating with the length-scale. In these structures, the basic components are nanofibers or nanoplatelets, which are strong and stiff but anisotropic, whereas at the macrolevel, isotropy is preferred because the direction and magnitude of loads is unpredictable. The structural features and mechanisms, which drive the transition from anisotropy to isotropy across length scales, raise fundamental questions and are therefore the subject of the current study. Focusing on the tibia (fixed finger) of the scorpion pincer, bending tests of cuticle samples confirm the macroscale isotropy of the strength, stiffness, and toughness. Imaging analysis of the cuticle reveals an intricate multilayer laminated structure, with varying chitin–protein fiber orientations, arranged in eight hierarchical levels. We show that the cuticle flexural stiffness is increased by the existence of a thick intermediate layer, not seen before in the claws of crustaceans. Using laminate analysis to model the cuticle structure, we were able to correlate the nanostructure to the macro-mechanical properties, uncovering shear enhancing mechanisms at different length scales. These mechanisms, together with the hierarchical structure, are essential for achieving macro-scale isotropy. Interlaminar failure (ILF) analysis of the cuticle leads to an estimation of the protein matrix shear strength, previously not measured. A similar structural approach can be adopted to the design of future synthetic composites with balanced strength, stiffness, toughness, and isotropy.

Research on compression properties of unidirectional carbon fiber reinforced epoxy resin composite (UCFREP)

To research the axial compression properties of unidirectional carbon fiber reinforced epoxy resin composite (UCFREP), the compression experiments at different strain rates were carried out by using the MTS universal electronic testing machine and the equipment of split Hopkinson pressure bar (SHPB). Furthermore, the finite element analysis (FEA) was also used to study the compression properties of UCFREP with different conditions. The true stress-strain curves in quasi-static and dynamic compression were obtained, and the relationship between yield limit and strain rate was coupled. The microstructure of the failure area was observed by scanning electron microscope (SEM). A formula for predicting compression strength of combined buckling under the quasi-static condition was presented. The application range of Chang-Chang failure criterion was discussed by FEA, and the compression failure of UCFREP with different fiber directions was predicted. The results show that UCFREP has the obvious strain rate effect, the mechanical properties at dynamic compression are nonlinear. Shear is the main compression failure mode, which includes the shear cracking of matrix between fibers and the shear buckling of fiber. The direction of the fiber is the main factor that causes the shear cracking, such as the shear cracking shows the feature of 45° when the direction of the fiber is 45°. As a conclusion, increasing the shear strength of matrix and fiber will be a way to increase the compression strength of UCFREP. This paper could be used as a reference to develop the new constitutive model, especially considering the nonlinear effect.

A shear hardening model for cohesive element method and its application in modeling shear hydraulic fractures in fractured reservoirs

Although the cohesive element method has been widely used for modeling hydraulic fracturing, the hardening properties of shear strength and shear fracture energy of rock matrix and natural fracture with the increasing of confining pressure have not been applied to the constitutive law of cohesive element for a long time. In this study, a shear hardening model and the corresponding user subroutine USDFLD are proposed and verified. Numerical results show that the shear hardening model has an excellent performance in modeling initial geo-stress state and shear hydraulic fracture (SHF) propagation in fractured reservoirs. The distribution and proportion of SHF affected by natural fracture asperity, azimuth of natural fracture network, and stress field are analyzed and discussed. The results suggest that SHF is a significant part of the hydraulic fracture network in fractured reservoirs with a proportion of 18%–61%, and plays a vital role in enhancing the complexity of hydraulic fracture network. The SHF has the potential to become the main type of the fracture network, indicating that its contribution in enhancing the conductivity of fractured reservoirs cannot be ignored. The macro width of the hydraulic fracture network and the tortuosity of the main hydraulic fracture decreases as asperity increases. High stress difference is a favorable stress environment for the development of SHF. As the absolute confining pressure of fractured reservoir increases, the possibility of shear hydraulic fractures becoming the primary fracture increases significantly.

A bundle-based shear-lag model for tensile failure prediction of unidirectional fiber-reinforced polymer composites

In this study, a novel shear-lag model based on impregnated fiber bundle (IFB) element is developed to predict the tensile behavior of unidirectional fiber-reinforced polymer (FRP) composites. Rather than using a fiber element, the new model enables a full-field failure simulation due to its finite number of elements. Based on the micromechanical difference equation, we validated the effectiveness of the model and identified the damage evolution pattern by applying it to a basic model of 6 mm FRP tendon. Then, the effect of varied constituent properties, hybrid fibers and initial defects were investigated using the Monte Carlo (MC) method. Several interesting results were found and compared with the findings of earlier studies. For instance, it was found that a more stable IFB strength and higher matrix shear strength reduced variations in composite strength. A moderate hybrid ratio and careful packing of high- and low-elongation fibers helped to achieve optimum composite properties. In the thin-ply composite, transverse initial defects were more detrimental to composite strength than longitudinal defects. These findings prove the value of the bundle-based model, which can be used in future studies as an effective tool for evaluating the strength of various composites.

Micromechanical analysis of transversal strength of composite laminae

The paper presents analysis of several micromechanical models for estimating transversal strength of composite laminae and comparing theoretical results with the available experimental data. The tensile, compressive and shear transversal strengths are analyzed. For a load transversal to the fiber direction, micromechanical analysis becomes complicated due to stress concentration. In order to deal with it, an elasticity-based solution is used to obtain stress around single inclusion in infinite matrix. In addition, the finite element simulations are carried out to derive approximation functions for actual values of fiber volume fraction. For tensile transversal strength, the density of dilatational energy is assumed to be the dominant failure mechanism, while for the compressive transversal strength, the interface failure is modeled. Since the critical dilatational energy and interface strength are commonly unavailable in literature, average values are obtained based on the experimental data. Alternatively, a semi-empirical modification of Chamis model is also proposed. For transversal shear strength, the results indicate that the matrix shear strength provides a good approximation. It should be noted that closed-form expressions are obtained, resulting in simple and efficient implementation for engineering applications and design optimization. Results are compared with other micromechanical models and with 58 experimental data from the literature. In general, elasticity-based models and modified Chamis model present a considerable advancement in transversal strength estimation with the small average errors.

Simplified Compression Field Theory-Based Model for Shear Strength of Fabric-Reinforced Cementitious Matrix- Strengthened Reinforced Concrete Beams

Simplified Compression Field Theory-Based Model for Shear Strength of Fabric-Reinforced Cementitious Matrix- Strengthened Reinforced Concrete Beams

Investigating the influence of bonded and non-bonded interactions on the interfacial bonding between carbon nanotube and polymer

CNT-polymer interaction plays a crucial role in defining the efficiency of CNT for reinforcing polymer. So, it is in high demand to investigate the influence of interfacial interactions on the load transferring issue from matrix to CNT. In this research, pull-out simulations are carried out numerically on both normal and functionalized CNTs to examine the influence of non-bonded and also bonded interactions at the interface between CNT and polymer. A multi-scale finite element modeling is performed in the context of semi-continuum modeling to simulate the pull-out process of CNT from matrix and experienced interfacial shear strength is analyzed. Firstly, a CNT interacting with polymer through the pure non-bonded interaction is investigated and then the influence of bonded cross-links between CNT and polymer in conjunction with non-bonded interaction is simulated. Comparing the obtained results with available experimental data and also reported results with molecular dynamics simulation in literature, a good agreement is observed which implies on the proper performance of semi-continuum modeling as a compromise to atomistic modeling techniques.

Investigating the effects of liquid-plasma treatment on tensile strength of coir fibers and interfacial fiber-matrix adhesion of composites

The liquid-plasma treatment based on microwave plasma in the liquid was used to treat coir fiber in this study. The effects of such treatment on tensile properties of coir fiber and its compatibility with the epoxy matrix were investigated. Water and sodium bicarbonate (NaHCO3) solution was used as a medium in this treatment. Tensile properties and interfacial shear strength (IFSS) between coir fiber and epoxy resin were determined with single fiber tensile and pull-out tests respectively. Fourier transform infrared spectroscopy, scanning electron microscope and X-ray diffraction were used to characterize the alteration of treated coir fibers. The results show that tensile strength of coir fibers slightly reduce after liquid-plasma treatment with both water and sodium bicarbonate medium except on 12 wt% sodium bicarbonate solution medium for 5 min exposure time. Meanwhile, the interfacial shear strength of coir fiber-epoxy matrix is obtained improvement after water and sodium bicarbonate medium treatment due to good interfacial adhesion between fiber and matrix which could be influenced by micropores on fiber surfaces leading to interlocking adhesion.