Low Interfacial Shear Strength Research Articles

Room and Elevated Temperature Sliding Friction and Wear Behavior of Al0.3CoFeCrNi and Al0.3CuFeCrNi2 High Entropy Alloys

In this study, processing–structure–property relations were systematically investigated at room and elevated temperatures for two FCC Al0.3CoFeCrNi and Al0.3CuFeCrNi2 high-entropy alloys (HEAs), also known as complex concentrated alloys (CCAs), prepared by conventional arc-melting. It was determined that both alloys exhibit FCC single-phase solid solution structure. Micro-indentation and sliding wear tests were performed to study the hardness and tribological behavior and mechanisms at room and elevated temperatures. During room-temperature sliding, both alloys exhibit similar friction behavior, with an average steady-state coefficient of friction (COF) of ~0.8. Upon increasing sliding temperatures to 300 °C, the average COF decreased to a lowest value of ~0.3 for Al0.3CuFeCrNi2. Mechanistic wear studies showed this was due to the low interfacial shear strength tribofilms formed inside the wear tracks. Raman spectroscopy and energy dispersive spectroscopy determined the tribofilms were predominantly composed of binary oxides and multi-element solid solution oxides. While the tribofilms at elevated temperatures lowered the COF values, the respective wear rates in both alloys were higher compared to room-temperature sliding, due to thermal softening during 300 °C sliding. Thus, these single FCC-phase HEAs provide no further benefit in wear resistance at elevated temperatures, and likely will have similar implications for other single FCC-phase HEAs.

Hybrid green composites using rice straw and jute fabric as reinforcement for soy protein-based resin

In this research, high amounts of the world's most wasted agricultural residue (rice straws) were utilized to produce hybrid green composites. Rice straws (RS) were needle-punched into jute fabric to form hybrid reinforcement mats which were impregnated with a soy protein isolate resin (SPR). Thermoset hybrid composites were produced at three different fiber contents of 40, 50, and 60% by wt. They were characterized for their tensile, flexural, interfacial, fractural, and hygroscopic properties. The hybrid composites with 40% fiber content enhanced Young's modulus (Ey) and ultimate tensile strength (TS) of the pure resin by 200% and 47%, respectively, compared to pure resin. With increasing fiber content, mechanical properties such as Ey, TS, flexural modulus, and flexural strength decreased, indicating insufficient resin volume. Interfacial shear strength values of RS/SPR and Jute/SPR were measured at 2.68 and 4.25 MPa, respectively. The high volumes of low-density RS and higher viscosity of the resin used in the hybrid composites seemed to overwhelm the resin's capacity to effectively wet the fibers. Insufficient wetting and low interfacial shear strength (IFSS) resulted in fiber pull-outs at fracture surfaces. Furthermore, as fiber content increased from 40 to 50 to 60%, moisture absorption increased from 10.4 to 12.9 to 22.6%, respectively. This is in spite of the fact that SPR was the most hydrophilic component of the three constituents. These results suggest that the high volumes of low-density fibers induce structural defects and exhaust the resin's wettability. Overall, the hybrid biodegradable composites had good tensile properties for use in packaging, transportation, housing, and furniture.

Bio-tribological studies of Structalit/UHMWPE composites as an alternative to UHMWPE for hip joint application

In this study, epoxy based composites are evaluated for their mechanical and bio-tribological properties to find an alternative to UHMWPE liner material for hip joints. Structalit/UHMWPE composites were successfully developed with excellent filler-matrix bonding. Lower friction and wear of the composite (with 24 wt% of UHMWPE) against CoCrMo are attributed to the higher bulk mechanical strength and lower interfacial shear strength. Additionally, lubrication was supported by heterogeneity driven lubricant flow at the composite pin surface. Burnishing, abrasion, and protuberances were main surface damage mechanisms of UHMWPE whereas composite had few micro-cracks on its surface when filler loading was less.

Experimental investigation on interlaminar and in-plane shear damage evolution of 2D C/SiC composites using acoustic emission and X-ray computed microtomography

Carbon fiber-reinforced silicon carbide composites (C/SiC) are widely used in lightweight aerospace structures for thermal protection due to its excellent mechanical properties. The low interfacial shear strength of the composites decreases its performance and limits its application. To investigate the shearing performance of C/SiC composite, interlaminar shear and in-plane shear tests were conducted. Real-time X-ray micro-computed tomography (XCT) non-destructive testing technology is an effective method for damage analysis of composite materials. The damage mechanisms of 2D plain weave C/SiC composites prepared by chemical vapor infiltration process under interlaminar shear loading are investigated using the combination of XCT and acoustic emission detection system. The in-situ XCT results reveal the damage visualization mechanisms of the composites and the damage evolution process including matrix damage, interfacial debonding and fiber fracture. The failure mechanisms and morphology of the shear effect for 2D plain weave C/SiC were analysed.

High temperature sliding wear behavior and mechanisms of cold-sprayed Ti and Ti–TiC composite coatings

Ti and Ti-based alloys are used in many aerospace and automotive components due to their high strength-to-weight ratio and corrosion resistance. However, room and elevated temperature wear resistance remain an issue, thus requiring some form of secondary hard phase, e.g., refractory carbides, as well as solid lubrication to mitigate wear. In this study, cold spray Ti-xTiC (x = 14, 24 and 35 vol%) composite coatings were deposited on mild steel substrates with comparisons made to a baseline cold-sprayed Ti coating. The dry sliding friction and wear behavior were studied from 25 °C to 575 °C and during thermal cycling in this temperature range. While the room temperature friction coefficient of all the coatings remained relatively constant at ~0.5, the wear rate continually decreased from ~1 × 10−3 to ~2 × 10−5 mm3/N·m with increasing TiC loading. Raman spectroscopy measurements determined that the same TiO2 tribochemical phases (rutile and anatase) were present on the room temperature sliding wear surfaces, thus responsible for similar friction coefficients. With increasing sliding temperatures to 575 °C, the Ti–35%TiC composite coating exhibited the best overall tribological behavior, i.e., the friction coefficient decreased to ~0.3 along with a negative wear rate of −6.6 × 10−5 mm3/N·m (material gain on the wear track was recorded due to oxidation and transfer from the counterface). These friction and wear reductions were determined to be due to the formation of stable, low interfacial shear strength oxide glaze layers on the wear surfaces, composed of TiO2, WO3, and CoWO4 (transfer from WC-Co counterface). In addition, self-adaptive friction behavior was observed during thermal cycling as a result of the microstructural and tribochemical differences in the tribolayers.

A machine learning framework for predicting the shear strength of carbon nanotube-polymer interfaces based on molecular dynamics simulation data

Modern aerospace applications require lightweight materials with exceptionally high strength and stiffness. Carbon nanotube (CNT)-reinforced composites have great potential in addressing these requirements. However, one critical factor limiting the potential of CNT-reinforced composites is the limited load transfer capability between CNTs through a polymer matrix, which arises due to low CNT-polymer interfacial shear strength at a molecular scale. While molecular dynamics (MD) simulations can be employed to investigate the CNT-polymer interface, such simulations are computationally expensive. It is thus intractable to explore a sufficiently large design space for interface modifications and optimization using MD simulations alone, motivating the use of surrogate models to efficiently map CNT-polymer interfacial configurations to interfacial strength. In this paper, we develop a surrogate machine learning model trained with MD models of functionalized CNT-epoxy and the corresponding interfacial shear strength. The proposed ML model consists of (i) a feature representation of CNT-epoxy based on radial distribution functions; (ii) a convolutional neural network model to map feature representations to a metric of interfacial shear strength; and (iii) a data augmentation method to maximize the use of limited training data. The proposed ML model can predict the CNT pullout force quite well despite a large variation associated with the pullout force.

Effects of critical interfacial shear strength between polymer and nanoclay on the Pukanszky's “B” interphase factor and tensile strength of polymer nanocomposites

This paper aims to develop the “B” interphase parameter and Pukanszky model for tensile strength of polymer clay nanocomposites assuming critical interfacial shear strength (τc) providing the stress transferring between polymer and nanoparticles. The clay properties express the “τc” and both “τc” and interfacial shear strength (τ) develop the effective thickness, strength and volume fraction of interphase region as well as the effective volume fraction of clay in nanocomposites. The effective terms are applied to expand the “B” interphase parameter and Pukanszky equation. The experimental data of tensile strength for some samples and the parametric investigations validate the developed equations for “B” and tensile strength of nanocomposites. All parameters consistently control the “B” and tensile strength. Low critical interfacial shear strength, high interfacial strength, thick interphase, high interfacial shear strength, high aspect ratio (length per thickness) of clay and a small number of clay in the stacks produce a high “B” and improve the tensile strength of nanocomposites. The absence of interphase section in nanocomposites largely decreases the “B” and very thin interphase deteriorates the strengthening efficiency of nanoclay in nanocomposites.

Nanostructured ZnO Interphase for Carbon Fiber Reinforced Composites with Strain Rate Tailored Interfacial Strength

AbstractComposite materials designed for ballistic applications typically require fiber–matrix interfacial properties which are considerably different than those used in more common structural applications. Ballistic composites are usually benefited through the use of a weaker interface that allows the high tenacity of the fiber to be utilized for energy absorption, whereas structural composites require strong interfaces to ensure materials which do not easily delaminate or experience cracking. Here, the multifunctionality of a zinc oxide (ZnO) interphase through a tailored interfacial shear strength (IFSS) as a function of strain rate is demonstrated. Both ZnO nanowires (NWs) and nanoparticles (NPs) are shown through variable strain rate pullout to enable tailored behavior with the NWs producing an 87% increase in IFSS over untreated fibers under quasi‐static loading, and 53% lower interfacial shear strength than untreated fibers at 2200 s−1. The reduced interfacial strength under dynamic loading conditions is attributed to the polymer's viscoelasticity, as matrix stiffening effects reduce the NWs' functional gradient, causing brittle failure of the ceramic interphase. The results demonstrate the potential for ZnO NWs and NPs to enable the tailored design of interfaces and to realize multifunctional materials with optimal behavior under both static and dynamic loading conditions.

Microstructure and interfacial strength of SiC fiber-reinforced Ti17 alloy composites with different consolidation temperatures

The interfacial reaction and titanium matrix microstructure in continuous SiC fiber-reinforced titanium matrix composite were investigated. By comparison of two samples actuated by 800 °C (in α + β dual-phase field) and 920 °C (in β single-phase field) consolidation, it can be concluded that tri-layer interfacial reaction regions consisting of fine TiCx/transition TiCx/coarse TiCx are formed in both two samples. In addition, the total thickness of reaction layer for composites prepared at 920 °C is thicker than that consolidated at 800 °C, while fine TiCx layer of 920 °C sample is thinner than that of 800 °C sample, which may be ascribed to the quick growth of PVD-Ti17 grain manufactured at 920 °C. In addition, lower interfacial shear strength is obtained in 920 °C sample, which can be ascribed to the formation of too thick brittle TiC layer. The research in the work is expected to motivate further exploration for interface adjustment of titanium matrix composites.

Synthesis and Tribological Performance of Carbon Nanostructures Formed on AISI 316 Stainless Steel Substrates

Carbon nanostructures were directly grown onto standard AISI 316 stainless steel by spray pyrolysis of α-pinene, a biorenewable material. Two different nanostructures were formed: (1) multi-walled carbon nanotubes when using ferrocene as an external catalyst mixed with α-pinene and (2) ribbon carbon nanofibers when using only α-pinene. In both cases, homogeneous layers of carbon nanostructures randomly distributed and completely covering the metal substrate were observed. Carbon nanotube films were thicker (~230 μm) than carbon nanofiber films (~180 μm). A significant friction reduction was observed for both structures; however, carbon nanofibers displayed a lower friction coefficient (~0.15) than carbon nanotubes (~0.20) at 5 N of load for 200 and 2000 cycles. Scanning electron microscopy and Raman spectroscopy analyses of the wear tracks reveal that, upon rubbing, both carbon nanostructures experienced the removal of stacking faults developing large, parallel and smooth graphene layers with low interfacial shear strength which may account for the friction reduction and wear protection observed.

Solid/Self-Lubrication Mechanisms of an Additively Manufactured Ni–Ti–C Metal Matrix Composite

A Ni–TiC–C metal matrix composite (MMC) has been processed using laser engineered net shaping. This additive manufacturing technique produced a Ni–3Ti–20C (at.%) composition with in situ formation of homogeneously distributed eutectic and primary TiC and graphite precipitates throughout the Ni matrix. The MMC exhibits a low steady-state friction coefficient of ~0.1 in dry sliding conditions. Novel insights into solid/self-lubrication mechanisms, with implications to other metal matrix-graphite particle composites, were revealed with focused ion beam serial sectioning inside worn surfaces. It was determined that lowering of the friction coefficient was a result of the formation of a low interfacial shear strength disordered carbon tribofilm that extruded to the surface through refined Ni grain boundaries. This was supported by finite element analysis that showed the evolution of subsurface stress states and precipitate motion during repeated sliding frictional contact.

Characterization of the interfacial shear strength of glass-fiber reinforced polymers made from novel RTM processes

In this study, three different glass fiber reinforced polymers have been investigated with respect to the interfacial shear strength. Conventional resin transfer molding (RTM) and the compression RTM (CRTM) process for the production of reinforced samples with an epoxy matrix were chosen. The third process was a thermoplastic RTM (TRTM) process for producing composites with a thermoplastic polyamide 6 matrix. Fiber type and coupling agent were not varied. The interfacial shear strengths reached by the different processing routes were determined by push-out tests. It is shown that the RTM interface shear strength is very high and comparable to that generated by the CRTM process, despite increased fiber fracture for the RTM samples. The TRTM process yielded significantly lower interfacial shear strength values. Plastographic analysis of the material systems showed the formation of an interfacial layer between the fibers and the thermoset matrix. For the thermoplastic matrix a significant lower formation of crystalline spherulites at the interface and no interfacial layer could be observed.

Study of Maleic Anhydride Grafted Polypropylene Effect on Resin Impregnated Bamboo Fiber Polypropylene Composit

Previously, Polyvinyl Alcohol (PVA) and phenolic resin were used for resin impregnated bamboo fiber reinforced PP composites which was manufactures for resin impregnated bamboo fiber with polypropylene (PP). Resin impregnation method can show improvement on tensile strength of fiber. However, to reduce the contact surface area and low inter-facial shear strength (IFSS) between impregnated resin and matrix, using 40% weight fraction of bamboo fiber in PP matrix, PVA impregnated composites with mean flexural and tensile strength 10% higher than untreated composites were produced butphenolic resin impregnated fiber reinforced composition’s mechanical properties were decreased. In this study maleic anhydride grafted polypropylene (MAPP) was used to increase interfacial shear strength between resin impregnated fiber and PP. With 10% MAPP, IFSS between resin impregnated fiber and PP increased more than 100% and reinforced composites. MAPP with untreated, phenolic resin and PVA impregnated cases showed similar mechanical properties. Yet in water absorption test, the PVA treatment with bamboo/PP composites increased water absorption ratio. But with 10% MAPP, matrix PP water absorption ratio decreased like phenolic resin impregnated fiber reinforced composites. 10% MAPP with resin impregnated bamboo fiber reinforced PP composites can improve IFSS, mechanical properties of composite and can decrease water absorption PVA resin impregnated bamboo fiber reinforced composites.

Study of fiber length and fiber-matrix adhesion in carbon-fiber-reinforced polypropylenes

Carbon-fiber-reinforced polypropylenes often exhibit insufficient mechanical properties because of low affinity between the carbon fibers (CFs) and the matrix resins. From the viewpoint of designing materials with better properties, it is important to control the interfacial properties. In this study, the interfacial properties are quantified in terms of the interfacial shear strength (IFSS), and the relationships among the IFSS, composite strength, and impact resistance are evaluated. When the fiber length is sufficiently short (as in injection-molded materials), the composite strength and impact resistance improve with increasing IFSS. On the other hand, when the fiber length is longer, the impact resistance improves with decreasing IFSS. Longer CFs with low IFSS require higher energy to pull out from the matrix resin than that required for interfacial debonding.

An improved microbond test method for determination of the interfacial shear strength between carbon fibers and epoxy resin

An improved microbond method, with a corresponding testing device, was developed to measure the interfacial shear strength (IFSS) between carbon fibers and epoxy resin. Compared to other methods, this proposed approach is both highly efficient and easy to operate. As a case study for this new method, we measured the IFSS between carbon fibers and epoxy resin. Although the average IFSS obtained was only 7.08 MPa, which is much lower than values documented in several previous studies, the displacement-load curves demonstrate the strong reliability of this method. The lower IFSS could be explained by the highly inert surface of the carbon fibers, which was highly graphitized and had no sizing treatment. Therefore, this method has high potential in applications for screening the sizing agents of carbon fibers or optimizing the surface sizing processes.

Recycled Carbon Fibres: Contact Angles and Interfacial Bonding with Thermoset Resins

Recycled T800S carbon fibre from a polymer composite using a pyrolysis process was compared with virgin T800S fibre and the contact angle and interfacial shear strength with epoxy and vinyl ester resins were measured. The contact angles were measured using drop length-height method, and the interfacial shear strengths were measured using micro-bond method. For the same type of resin, the recycled T800S carbon fibre had a greater contact angle and lower interfacial shear strength than those of the virgin fibre.

Study on longitudinal tensile properties of SiCf/Ti–6Al–4V composites with different interfacial shear strength

Abstract Effect of interfacial shear strength on longitudinal tensile properties for SiC f /Ti–6Al–4V composites is investigated by Monte Carlo finite element method. A two-parameter Weibull function is employed to describe random distribution of fiber strength. Fiber breakage, matrix cracking and interfacial debonding are simulated by killing the element when stress applied to element exceeds corresponding strength and releasing coupled nodes when shear stress exceeds shear strength at interfaces. The results show that tensile strength of SiC f /Ti–6Al–4V composites keeps unchanged for various interfacial shear strengths, but low interfacial shear strength is advantageous to reduce catastrophic failure. Moreover, with low interfacial shear strength, fiber breakage in the composites is more inclined to be non-coplanar. In addition, tensile strength obtained from finite element method is compared with those predicted by global load-sharing model (GLS), local load-sharing model (LLS) and conventional rule of mixtures (ROM) and is identical with that obtained from LLS.

Adhesion of thermoplastic polyurethane elastomer to galvanized steel

When a thermoplastic polyurethane elastomer (TPU) is co-molded with galvanized steel, the subsequent adhesion and its durability are very sensitive to the chemical bonds created at the interface. Silane coupling primers are known for enhancing adhesion between inorganic substrates and several polymers and this study addresses their efficiency at the TPU–metal interface. γ-APS aminosilane was deposited with different parameters, including pH and solvents. Several other surface treatments were studied for comparison: degreasing, corona discharge, acidic etching, gas flame, and a zinc phosphate conversion coating. The adhesion was characterized with a single wire pull-out test derived from the microbond test geometry, after different aging conditions. Results confirmed that γ-APS worked as a coupling agent in between TPU and the inorganic substrate, outperforming all other surface treatments tested in term of strength and durability, but the silane required the appropriate deposition parameters to be really efficient. In parallel, a finite element approach was proposed for the modeling of fiber reinforced thermoplastic elastomer composites accounting for the non-linear viscoelastic material properties and its results compared to an analytical elastic shear-lag interpretation of the single filament pull-out test. The analytic interpretation was found to be sufficiently accurate for stress analysis but not for fracture mechanics. The FEM analysis offered an evaluation of the internal stresses developed within the entire system, which helped the interpretation of results. The model, compared to experimental results, also revealed that it is important to account for internal stresses, mostly for treatments leading to low intrinsic interfacial shear strength values.

Mechanism for shear banding in nanolayered composites

Recent studies have shown that two-phase nanocomposite materials with semicoherent interfaces exhibit enhanced strength, deformability, and radiation damage resistance. The remarkable behavior exhibited by these materials has been attributed to the atomistic structure of the bimetal interface that results in interfaces with low shear strength and hence, strong barriers for slip transmission due to dislocation core spreading along the weak interfaces. In this work, the low interfacial shear strength of Cu/Nb nanoscale multilayers dictates a new mechanism for shear banding and strain softening during micropillar compression. Our findings, supported by molecular dynamics simulations, provide insight on the design of nanocomposites with tailored interface structures and geometry to obtain a combination of high strength and deformability. High strength is derived from the ability of the interfaces to trap dislocations through relative ease of interfacial shear, while deformability can be maximized by controlling the effects of loading geometry on shear band formation.

Self-lubricating carbon nanotube reinforced nickel matrix composites

Nickel (Ni)—multiwalled carbon nanotube (CNT) composites have been processed in a monolithic form using the laser-engineered net shape (LENS™) processing technique. Auger electron spectroscopy maps determined that the nanotubes were well dispersed and bonded in the nickel matrix and no interfacial chemical reaction products were determined in the as-synthesized composites. Mechanisms of solid lubrication have been investigated by micro-Raman spectroscopy spatial mapping of the worn surfaces to determine the formation of tribochemical products. The Ni-CNT composites exhibit a self-lubricating behavior, forming an in situ, low interfacial shear strength graphitic film during sliding, resulting in a decrease in friction coefficient compared to pure Ni.