Measurement Of Interfacial Shear Strength Research Articles

A scalable fiber bundle pullout manufacturing method for data-driven interfacial shear strength measurements of micro and nanomaterials

Adhesive and surface treatment technologies are crucial for the structural integrity of the composite parts. The interfacial shear strength (IFSS) reflects the load transfer efficiency between reinforcement and matrix. However, no current test can be performed quickly with statistically significant replications. As a solution, this paper presents a horizontal mold and geometry matched testing fixture for manufacturing samples for the pullout test in large quantity batches. The open-face mold design can accommodate matrices with a wide range of viscosity and solves the problem of testing nanomaterial and micromaterial bundle interfaces using the same pattern. The effectiveness of sample manufacturing made of carbon nanotube (CNT) yarns and IM7 carbon fiber (CF) with three different polymer matrices was demonstrated in this work. The IFSS of each sample were recorded using a conventional tensile machine, and their surface morphology was evaluated with SEM images. Analysis of Variance (ANOVA) and Tukey's pairwise comparison tests demonstrated a significant difference in IFSS means when changing matrices on CNT yarn specimens but no statistically significant difference on IM7-CF specimens for the three matrices in this study. This mold is expected to help researchers obtain faster results and study matrices that have not been thoroughly tested.

Characterization of interfacial strength in natural fibre – polyolefin composites at different temperatures

ABSTRACT It is often suggested that optimization of the fibre-matrix interfacial adhesion is essential to improve the mechanical performance of natural fibre reinforced thermoplastic compounds. The use of such composites in many applications often requires characterisation of performance over a range of temperatures. This paper presents a study on the measurements of the interfacial adhesion of coir fibre with various polyolefin matrices at room temperature. We then present a novel adaptation of a dynamical mechanical analyser to enable the measurement of interfacial shear strength over the temperature range of −40°C to 120°C. Results from these measurements are presented and discussed in terms of the relationship of apparent IFSS to residual thermal stresses in such thermoplastic composites.

Quantitative analysis based on atomic force microscopy characterization of interfacial properties between carbon fibers and epoxy resin subjected to hygrothermal and thermal treatments

It has been proved the interface between fibers and resin matrix suffers from severe service conditions, but it was rarely explored how to directly and quantitatively evaluate those negative effects. In this work, a novelly-designed quantitative analysis method was established via atomic force microscopy (AFM) based on shrinkage degree of resin matrix, and was further applied to assess the effects of hygrothermal and thermal treatment on the interfacial adhesion property of carbon fibers/epoxy composites (CFRPs). This method presented that the shrinkage extent of resin around carbon fibers after treatment could in a certain extent reflect the interfacial properties at the stability and linear constraint region. Furthermore, interlaminar shear strength and interfacial shear strength measurements demonstrated the validity of this novel method for interfacial properties, and revealed that the interface was more susceptible to hygrothermal than thermal treatment. This method is believed promising for studies on the interface of fibers/resin composites.

Piezoelectric Stack Actuator for Measurement of Interfacial Shear Strength at High Strain Rates

Limited methods exist for the characterization of interfacial properties in fiber reinforced composites under dynamic loading conditions since conventional techniques are designed for the measurement of a composite’s bulk properties rather than that of the fiber-matrix interface. Here, a novel experimental method is reported for the measurement of interfacial strength across various loading rates using a single fiber. The experimental apparatus uses a single fiber pullout approach along with a piezoelectric stack actuator to enable a single fixture to generate a wide range of controlled loading rates. The voltage-strain relationship is measured and the applied strain rate is controlled using resistors with varying magnitudes within a properly designed discharge circuit. The piezoelectric actuator is protected against backflow current surges using a silicon controlled rectifier, and against parasitic inductance through a toggle switch. It is shown that the proposed method accommodates single fiber specimens while providing similar performance to a Split-Hopkinson bar by reaching strain rates of up to 104 s−1, however with greater flexibility of loading rate. Single aramid fibers are tested at various strain rates and show expected interfacial shear strength independent of the embedded fiber length. The results indicate the potential of the proposed experimental method as a simple and fast technique to measure the fiber matrix interfacial properties through direct pullout at high strain rates.

Single fibre model composite: Interfacial shear strength measurements between reactive polyamide-6 and cellulosic or glass fibres by microdroplet pullout test

This work aims to study the effect of reactive molding on polyamide-6 (PA6) based micro composites with either glass or high tenacity viscose as fibre reinforcements. For this purpose, microdroplet pullout test was found to be well suited to determine the interfacial shear strength. For pull-out testing, samples are prepared with a common method implying melting polyamide-6 and an innovative method which allows the microdroplets formation by direct wetting in the reactive mixture. Conditions to obtain microdroplet in this new method are close to those of real size composite molding. First, this work focus on the verification of the new sample preparation method using 1H and 13C NMR to determine conversion rate and verify the presence of polyamide-6 on wetted fibres bundles. Contact angle are calculated to confirm the NMR analysis conclusions. Both of these analyses confirm that PA6 is effectively formed on fibres when wetting with the reactive mixture. Finally, interfacial shear strength is compared for both glass and high tenacity viscose with these two types of preparation procedures. Obtained values for glass fibres are τ = 25 ± 6 MPa with PA6-melting and τ = 20 ± 3 MPa with reactive mixture wetting. Reactive mixture wetting also allows to avoid high tenacity viscose degradation during PA6 formation, leading to the determination of the interfacial shear strength τ = 12 ± 3 MPa.

Novel Flexible Composites Reinforced with CNT-Grafted Carbon Fibers

ABSTRACTNovel flexible composites were received by modification of polyurethane-carbon fiber interface. The modification was done by carbon nanotube grafting onto a surface of the fiber. The almost inevitable grafting-induced deterioration of the fiber properties was avoided due to sophisticated grafting technique, which includes introduction of a protective aluminium oxide layer. Re-enforced composites were fabricated with polyurethane as a matrix. The measurement of interfacial shear strength (IFSS) was used for estimation of polymer-fiber interface properties. It was shown that IFSS increased more than twice due to nanotube grafting. Thermal conductivity and mechanical properties enhancement was registered for composites with modified interface. Significant improvement of delamination resistance was proven for composites with modified polymer-fiber interface.

The Effect of Pores in Dual Nano Hydroxyapatite Coating on Thermally Oxidized Commercial Pure Titanium : Mechanical and Histological Evaluation

Background:In this study,TiO2 layer was thermally grown as a diffusion barrier on CP Ti substrate prior to electrophoretic deposition of HA coatings, to improve the coating’s compatibility also macro and micro pores in nano Hydroxyapatite dual coatings were created and their effect on the bond strength between the bone and implant was evaluated. Materials and methods: Electrophoretic Deposition technique (EPD) was used to obtain coatings for each one of four types of Hydroxyapatite(HA)on CP Ti screws (micro HA, nano HA, dual nano HA with micro pores, dual nano HA with macro pores) where carbon particles used as fugitive material to be removed by thermal treatment to create porosity.For examination of the changes occurred on the substrate, SEM, SPM and XRD used, coatings characterized by XRD, SEM and interfacial shear strength measurements. Results:The results mentioned the formation of rutilenano TiO2 with, SEM showed that the size of pores in HA coatings corresponded to the size of carbon particles. Statistical analysis of the removal torque tests showed highest means of the single nano HA coating at 2 and 4 weeks implantation intervals. Histological analysisrevealed a faster reaction of bone and higher osteoblasts activity towards thermally oxidized CP Ti implants coated with single nano HA coating. Conclusion:Carbon particles as a fugitive material within nano HA coat produced porosity.Presence of pores ˃ 1µ in nano HA coats did not achieve highest removal torque values nor highest osteoblasts activity in 2 and 4 weeks implantation intervals. Keywords:Titanium, Thermal oxidization, Nano Hydroxyapatite, Coatings, porosity.

Modification of carbon fiber–polyurethane interface with carbon nanotubes

Modification of polyurethane–carbon fibre (CF) interface by grafting carbon nanotubes onto a surface of the fibre is reported. The grafting technique allows avoiding the fibre mechanical properties deterioration. The technique includes desizing of CFs, introduction of a protective aluminium oxide coating, deposition of Fe catalyst and then chemical vapour deposition for nanotube growth. Re-enforced composites were fabricated with polyurethane as a matrix. Polymer–fiber interface properties were estimated through the measurement of interfacial shear strength (IFSS). It was shown that IFSS increased more than twice due to nanotube grafting. The enhancement of both thermal conductivity and mechanical properties of composites with modified interface was observed. Significant improvement of delamination resistance was proven for composites with modified polymer–fibre interface.

Measuring of Fiber/Matrix Adhesion in Thermoplastic Polymer Composites: A Preliminary Study

The possibilities of the application of microbond test and cylinder tests for determining the interfacial shear strength at the fiber-matrix interface in thermoplastic matrix polymer composites were investigated. Possibilities of test specimen preparation were also investigated. Finally the applicability of the method to make high precision measurement of interfacial shear strength was evaluated.

Pull-out method for direct measuring the interfacial shear strength between short plant fibers and thermoplastic polymer composites (TPC)

Abstract Thermoplastic polymer composites reinforced with short plant fiber are worldwide in focus of research activities. Interfacial shear strength (IFSS) is an important indicator for evaluating the bonding quality between the fiber and the matrix polymer. However, the direct measurement of IFSS is especially difficult in the case of short fibers. In the present article, a method is proposed to this purpose, which is related to the known “fiber pulling out” methodology. In the case of single bamboo fibers, the IFSS in a polypropylene (PP) matrix was on, an average, of 5 MPa, which can be considered as weak. Scanning electron microscopy images revealed a rough inner surface in PP cavities left after fiber pulling out. This is direct evidence that a mechanical interlocking mechanism is active in the interphase between the hydrophilic fibers and the hydrophobic matrix.

Effect of flax fibres individualisation on tensile failure of flax/epoxy unidirectional composite

The study of plant fibres composites is a widespread research topic; nevertheless, the reinforcement mechanism understanding of these materials must be still improved. The paper presents a study of the effect of the mechanical properties, the dispersion and the fibre/matrix interface property of elementary fibres on the tensile properties of unidirectional composites. Our work shows that the mechanical performances of unidirectional composites could be linked to those of the elementary fibres as well as to the composites microstructure. Flax fibres individualisation, linked to the homogeneity of the microstructure, is highly dependent on the fibre extraction process. The importance of the composites homogeneity has been confirmed by the Rosen model, which could be used thanks to interfacial shear strength measurements.

Analysis of a modified microbond test for the measurement of interfacial shear strength of an aqueous-based adhesive and a polyamide fibre

The microbond test was used to measure the interfacial shear strength (IFSS) between a polyamide fibre and a water-based polyurethane. Due to the low viscosity of the water based polyurethane, the droplet could not be formed using a conventional preparation method. A disc shaped microbond droplet forms when an aqueous-based colloidal polymer adhesive was deposited onto the pin hole in a mounting card with a vertical polyamide fibre in the middle after drying and curing at an elevated temperature. Since the droplets were formed with a disc shape, which differs from the conventional ellipsoid, a finite element analysis of the stress distribution at the interface for these contrastingly shaped droplets were calculated and compared. The stress analysis showed that the interfacial shear stress profiles were well matched for both providing confidence that the disc-shaped droplets could be used for interfacial analysis. The microbond test using a disc-shaped droplet was used to study the influences of silane treatment and plasma treatment on the interfacial shear strength between a polyamide fibre and an aqueous deposited polyurethane. The interfacial shear strength of the fibre after plasma treatment was 10.3 MPa, much higher than that of the control and the silanised fibres, 5.2 MPa and 5.4 MPa respectively. The results showed that the microbond test could be used to investigate the interfacial properties of the polyamide fibre and water-based polymer adhesive.

Measurement of interfacial shear strength in single wall carbon nanotubes reinforced composite using Raman spectroscopy

A novel method of measuring interfacial shear strength using Raman peak shift is reported. Carbon nanotubes (CNT) functionalized with biomolecules have been used to form a composite with polyvinyl alcohol. Type I collagen has proven to improve the load transfer from the matrix to the tubes leading to improvement of interfacial shear strength. Collagen interacts with single wall CNTs and probably wraps around it. When a composite structure is formed with the collagen, load transfer takes place through the collagen molecule. The interfacial strength of the nanotubes-matrix interface was found to be larger than 160 MPa, which is significantly higher than that observed before. A similar shear strength is estimated using a simple analytical calculation.

Systematically varied interfaces of continuously reinforced glass fibre/polypropylene composites: Comparative evaluation of relevant interfacial aspects

Interface related mechanical properties of unidirectional continuous glass fibre (GF)/polypropylene (PP) com- posites made of commingled yarns have been systematically studied according to a three level, three-factor factorial design. The three systematically varied factors comprised different silane coupling agent and film former contents in GF sizings as well as a varying GF diameter. Besides the statistical evaluation of those main effects on the transverse tensile and com- pression shear strengths of the composites, interfacial shear strength measurements on model composites have been per- formed. The latter ones as well as the results of the dynamic mechanical thermal analysis support the statistical significance of sizing components, the sizing content on the GF, and GF diameter for the mechanical properties of the composites. This highlights the interplay of proper sizing formulation and reproducible GF-spinning conditions, as both affect the interfacial bonding of continuously reinforced GF/PP composites.

Effect of the Interfacial Stress Distribution on the Material Interfacial Shear Strength Measurement

An integrated experimental and numerical analysis is carried out to study the interfacial shear strength of bonded materials. Two types of shear tests, namely the Iosipescu shear test, and the short-beam shear test are employed to understand the effect of interfacial stress on the interfacial shear strength measurements. The measured average shear strengths are very close, even though the interfacial shear stress distributions of these two kinds of specimens are very different. Therefore, we conclude that the interfacial stress distribution has the least effect on the interfacial strength measurement if the interfacial shear stress is non-singular.

Thermodynamics and Kinetics of Oxidation of Pure Indium Solders

ABSTRACTMicroElectroMechanical System (MEMS) devices often require low-temperature, fluxless soldering techniques due to their high temperature sensitivity and performance requirements of the components. While seeking the development of a soldering technology using pure indium, the major focus of this study is to assess the thermodynamics and kinetics of indium oxidation at various solder reflow environments that will ultimately provide a processing window for solder reflow and surface oxide cleaning. With a glove box employed to generate reducing environments, oxygen, moisture, and hydrogen contents were varied to examine their effects on oxidation and reduction behavior of indium. We also explored oxidation mechanisms at different regimes of temperature and time. In particular, electron transport from indium to indium oxide is shown to be the rate controlling mechanism under specific oxidizing conditions. For accurate thickness measurements, a spectroscopic ellipsometer was employed. In addition, the effect of indium oxidation on solder joint reliability was observed via wetting angle and interfacial shear strength measurements.

Mechanical properties of TiN thin film coatings on 304 stainless steel substrates

Titanium nitride (TiN) film was deposited on 304 stainless steel using a hollow cathode discharge ion-plating (HCD-IP) technique. Film thickness and N/Ti ratio were controlled. The depth profile of the composition was determined by secondary ion spectroscopy (SIMS). The results showed that the compositions of the films were uniform for the films deposited at the same deposition conditions. The purpose of this study is to investigate the variation of structure and mechanical properties of the TiN films with different film thickness. The preferred orientations of TiN films were determined using X-ray diffraction (XRD). The dominant preferred orientation of the TiN coatings for the deposition conditions was (111), especially for the films thicker than 1 μm. The residual stress of the TiN films was also measured by XRD using sin 2 Ψ method. The residual stress was ranging from −5.93 to −2.70 GPa, varying with film thickness. Hardness of the films was measured by nanoindentation. The hardness values were ranging from 14.9 to 33.6 GPa, increasing with the film thickness. The ultimate interfacial shear stress between TiN/304SS was determined by in-situ strip tension of the TiN-coated specimens in a scanning electron microscope (SEM) chamber. The limiting thickness for the effective measurement of interfacial shear strength by the in-situ strip tension method is close to 0.5 μm. N/Ti ratios of the thin films were all at 0.8 measured using both X-ray photoelectron spectrometer (XPS) and Rutherford backscattering spectrometer (RBS). The packing factors of TiN films, calculated from the results of RBS, were 0.62–0.99, increasing with film thickness and leveling off at a thickness above 1.2 μm.

On the Characterization of Wetting and Adhesion in Glass Fiber-PA12 Composites

A variety of glass fibers (GF) and Polyamide 12 (PA 12) resins were selected to study fiber-matrix wetting and adhesion in thermoplastic composites. The fibers differed in the nature of their surface treatment, the PA 12 resins in their content of amine terminal groups and melt viscosity. The wetting behavior and the interfacial adhesion were investigated by conducting contact angle and interfacial shear strength measurements on fiber-droplet specimens. Depending on the fiber surface finish, variations in contact angle of up to 600 and differences in interfacial shear strength of up to 7 M Pa were obtained. Slight variations in contact angle and interfacial shear strength were also observed as a function of the resin viscosity and the chain termination chemistry. These results are of practical relevance for tailoring the fiber-matrix interface, to minimize the fiber impregnation time during processing and optimize the mechanical performance of the composite during service. The results also allow a correlation to be established between the contact angle and the interfacial shear strength, in agreement with an existing model. The validity of the experimental methods suggested for the determination of contact angle and interfacial shear strength in thermoplastic composites is thus confirmed.

On the Characterization of Wetting and Adhesion in Glass Fiber-PA12 Composites

A variety of glass fibers (GF) and Polyamide 12 (PA 12) resins were selected to study fiber-matrix wetting and adhesion in thermoplastic composites. The fibers differed in the nature of their surface treatment, the PA 12 resins in their content of amine terminal groups and melt viscosity. The wetting behavior and the interfacial adhesion were investigated by conducting contact angle and interfacial shear strength measurements on fiber-droplet specimens. Depending on the fiber surface finish, variations in contact angle of up to 600 and differences in interfacial shear strength of up to 7 M Pa were obtained. Slight variations in contact angle and interfacial shear strength were also observed as a function of the resin viscosity and the chain termination chemistry. These results are of practical relevance for tailoring the fiber-matrix interface, to minimize the fiber impregnation time during processing and optimize the mechanical performance of the composite during service. The results also allow a correlation to be established between the contact angle and the interfacial shear strength, in agreement with an existing model. The validity of the experimental methods suggested for the determination of contact angle and interfacial shear strength in thermoplastic composites is thus confirmed.

E‐Glass/DGEBA/m‐PDA single fiber composites: The effect of strain rate on interfacial shear strength measurements

AbstractPrecise measurements of fiber break regions have been made during the single fiber fragmentation test (SFFT) procedure on E‐glass/diglycidyl ether of bisphenol‐A (DGEBA)/meta‐phenylenediamine (m‐PDA) test specimens. From these measurements, the location and size of each fiber fragment was determined, and the resulting information was used to construct fragmentation maps of the tested fiber. By comparing these maps, the fragmentation process supports random fragmentation along the length of the fiber. Since the interfacial shear strength (IFSS) or the interfacial shear stress transfer coefficient (I‐STC) is obtained from the fragment length data at the end of the test (saturation), frequency histograms of the fragment length data were constructed to determine the repeatability of the fragmentation process. Since the SFFT is performed by sequential step‐strains of the test specimen, test protocols were developed by controlling the step size of each strain increment and the time between each step‐strain (dwell time). For the testing protocols used in this research, the E‐glass/DGEBA/m‐PDA frequency histograms of the fragment lengths were found to be generally repeatable. However, when the effective strain rate of the test was altered by changing the dwell time between strain increments, the fragment distribution at saturation of the E‐glass/DGEBA/m‐PDA SFFT specimens changed. The direction of the change was found to be inconsistent with the effect one might expect when only the nonlinear viscoelastic behavior of the matrix is considered. However, the magnitude of the change observed in the E‐glass/DGEBA/m‐PDA SFFT specimens is not universal. Fragmentation data obtained on E‐glass/polyisocyanurate SFFT specimens revealed a much smaller change in fragment length distributions with the same change in testing protocols. Consistent with the results obtained on the E‐glass/DGEBA/m‐PDA, fiber fragmentation occurs when the polyisocyanurate matrix exhibits nonlinear viscoelastic behavior. The implication of these results for interfacial shear strength measurements is discussed.