Ultra-high Modulus Carbon Fibre Research Articles

Fatigue Repair of Cracked Steel Plates Using Small-Patch Ultrahigh-Modulus CFRP Governed by Bond Failure

This study evaluates the effectiveness of externally bonded small-patch ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) plates of 460 GPa modulus in extending fatigue life and slowing crack propagation in steel plates with simulated fatigue cracks. The study investigates a range of very short bond lengths for applications where bonding space may be limited or accessibility restricted, together with the effect of single- versus double-sided application, on fatigue performance. It also compares short UHM CFRP plates with similar length normal modulus (NM) (165 GPa) CFRP plates with regard to extending fatigue life and reducing stress concentration at the crack tip. Distributed fiber-optic sensors (DFOS) and digital-image correlation (DIC) are used to capture the full strain field and track crack growth. Results showed that fatigue life was increased by up to 2.0 and 2.34 times for single- and double-sided UHM CFRP repairs. As bond length increased from 25 to 100 mm, fatigue life increased from 1.36 to 2.0. UHM CFRP more effectively reduced stress concentration at the crack tip, by 60% compared with 37% for NM CFRP, indicating that it has the potential for superior fatigue life gains, relative to NM CFRP if the necessary bond length to prevent or delay debonding is provided. As debonding failure governed in this study, NM CFRP plates achieved comparable fatigue life extension. DIC tracking of crack growth matched the traditional “beach marking” technique with less than 6% difference.

Outstanding electromagnetic wave absorption performance of polyacrylonitrile-based ultrahigh modulus carbon fibers decorated with CoZn-bimetallic ZIFs

PAN-based carbon fibers have been widely used in aerospace materials due to high specific strength, high specific modulus and many other outstanding features. As one kind of carbon-based electromagnetic wave (EMW) absorption material, carbon fibers are expected to absorb more EMW due to multiple polarization losses and large specific surface area in which EMW can be reflected many times. However, they also have certain disadvantages when used as EMW absorption material due to their high dielectric constant, low permeability and low reflection loss strength. Herein, a facile hydrothermal synthesis method was used to construct the three-dimensional (3D) bimetal-organic framework compound onto the surfaces of polyacrylonitrile(PAN)-based ultrahigh modulus carbon fibers (UHMCFs). Through the control of key parameters in the synthesis process, 3D bimetallic ZIF particles with different morphologies were assembled on the fiber surfaces, and a further high temperature heat treatment resulted in significantly improved EMW absorption properties. The results showed that three fibrous structures including rod-shaped, threadlike and flower-like morphologies had been formed with the introduction of CoZn-ZIFs. Among them, the uniform structure of rod-shaped sample could be preserved after carbonization and it also showed optimal EMW absorption performance, e.g. its minimum reflection loss (RLmin) and effective absorption bandwidth (EAB) values were − 67.67 dB (EMW loss above 99.9 %) and 4.28 GHz, respectively, with the thickness of 2.00 mm. In the final, the EMW absorption mechanism of CoZn-bimetallic ZIF decorated UHMCFs including interfacial loss, conductive loss, polarization loss, multiple scattering and excellent impedance matching was discussed in detail.

Evaluation of Spliced UHM CFRP Strip Panels for Strengthening Steel Beams

Short ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) strip panels connected through a finger joint configuration offer a convenient modular method for strengthening steel girders. Three-dimensional nonlinear finite-element (FE) analysis was conducted to characterize the interfacial and flexural behavior of strip panels. The calibrated FE model provides an efficient and economical method of evaluating different parameters related to the material properties and strengthening configuration of the UHM CFRP strip panels, for which experimental data are not available. Analysis implemented robust features, including debonding of CFRP using a mixed-mode bond–slip model, CFRP rupture, steel yielding, and concrete slab crushing. Predictions were calibrated and validated against experimental results from double lap shear tests and flexural tests of steel beams and steel–concrete composite beams. The FE model was used to investigate the effects of finger joint location, joint length, and laminate thickness. Strip panels with 300-mm-long finger joints and thicknesses of up to 2 mm equaled the strength of a continuous laminate with the same CFRP area. Both failed by CFRP rupture. At greater thicknesses, debonding occurred at lower ultimate loads than for a continuous laminate. The finger joint splice was also compared to the traditional splice plate method. The splice plate length required to achieve the same level of load transfer was longer than the finger joint length when the connection was in the maximum moment region. For a given CFRP thickness and splice plate length (or finger joint length), strip panels with finger joints provide greater load-carrying capacity.

Modelling and Analysis of CNC Milling Machine Bed with UHM CFRP composite Material

Abstract: Structural materials are used in a machine tool have a key role in defining the productivity, accuracy and Size proportions of the part manufactured by machine tool. The conventional structural materials like cast iron and Stainless or carbon steel at high operating speeds but used in precision machine tools grow positional errors due to the vibrations transferred into the Machine tool structure. Faster cutting speeds can be achieve only by structure which has good damping characteristics and high stiffness. Clearly the life of a machine tool is proportional to the levels of vibration Produce by machine. The further Work is carried out to Study the deformation and natural frequency using Static analysis and Modal analysis respectively. The bed in machine tool Took Major role in the precision in components. It is one of the greatest vital tool structures which is absorb the vibrations resultant from the cutting operation. To analyse the bed for possible material changes and Structure changes that could increase stiffness, decrease weight, expand damping characteristics and segregate natural frequency at the operating range. So main enthusiasm behind the impression to go for a composite Material in model involving ultra-High Modulus Carbon Fibre Reinforced Polymer Composite Material (UHM CFRP). In a carbon has good stiffness and strength properties but its absences in damping requirements. On the other hand, polymers, though its deficiencies in strength but, good damping in characteristics and it is easily holding the carbon fibres. So, this is makes greatest combination of materials in an appropriate manner. In this work, a machine tool’s bed is selected for the analysis static loads. Then study is carried out to decrease the weight of the machine tool’s bed without affecting its structural rigidity. The 3D CAD model of the bed has been created by using commercial 3D modelling software and analyses were carried out using ANSYS 2021 R2. Keywords: Composite material, hybrid structures, Milling machine bed, UHM CFRP.

CFRP strengthening of butt-welded ultra-high strength steels under quasi-static tensile loading

Due to the softening at the heat-affected zone (HAZ) in ultra-high strength steels (UHSS), the mechanical properties can deteriorate depending on the steels’ grade, welding heat input, and its associated cooling rate. Hence, a design based on the properties of the base material (BM) may not be appropriate, and there is a need to retain the lost properties of the weldment. This study presents an effort to strengthen butt-welded UHSSs using ultra-high modulus (UHM) carbon fiber reinforced polymer (CFRP) plates. Although the rehabilitation and strengthening of steel structures using CFRPs have been available during the last two decades, they have not been used to strengthen higher grades of steel such as UHSSs. For this aim, a series of tensile tests were carried out on butt-welded UHSSs strengthened with adhesively bonded UHM CFRP plates on both sides of the weldment. Two welding processes, i.e. the gas metal arc welding (GMAW) and laser welding, were implemented separately to join the plates. Microhardness measurements and tensile tests were carried out for the experimental part, as well as finite element (FE) analysis of the joints. The results were also compared with other available methods, i.e. high-frequency mechanical impact (HFMI) treatment and TIG-dressing (tungsten inert gas) of the weld toe that are commonly used to increase the fatigue life of UHSS joints. It was found that CFRP strengthening can not only retain the lost properties of the weldment but can also increase the joint strength up to 32% compared to the BM, and a considerable 50% higher stiffness. In contrast, the other methods (HFMI and TIG-dressing) had no impact on the tensile characteristics of the weldments.

Prestressing low clinker structural concrete elements by ultra-high modulus carbon fibre reinforced polymer tendons

The combination of low clinker high-performance concrete (LCHPC) and ultra-high modulus (UHM) carbon fibre reinforced polymer (CFRP) tendons was recently proposed for prestressed structural elements. The 70% reduction in cement content resulting in limited creep and shrinkage of the LCHPC in comparison to a conventional high-performance concrete (HPC) and the very high UHM-CFRP tendon stiffness (> 509 GPa) were expected to impact the mechanical behaviour of such structures. This study focuses on the behaviour of 3 m-long beam specimens during prestressing, concrete hardening and in 4 point-bending experiments. Fibre optic sensors were implemented inside the CFRP tendons to measure strain during those stages and a digital image correlation system was employed to monitor the 4-point-bending tests. After 28 days, the LCHPC recipe, despite a 70% cement reduction and much smaller environmental footprint, did not show measurable differences in the prestress loss behaviour in comparison to a conventional HPC. The UHM-CFRP prestressing tendons, because of their stiffness, showed both higher prestress losses of around 40% and on average a nearly doubled prestress transfer length. However, they increased the beam`s maximum load-bearing capacity by 21% and showed 47% less deflection at failure in comparison to beams prestressed with the standard modulus (UTS)-CFRP tendons.

Surface oxidation of PAN-based ultrahigh modulus carbon fibers (UHMCFs) and its effect on the properties of UHMCF/EP composites

In this study, nitric acid oxidation with varied treatment temperature and time was conducted on the surfaces of polyacrylonitrile-based ultrahigh modulus carbon fibers. Scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and surface tension/dynamic contact angle instruments were used to investigate changes in surface topography and chemical functionality before and after surface treatment. Results showed that the nitric acid oxidation of ultrahigh modulus carbon fibers resulted in decreases in the values of the crystallite thickness Lc and graphitization degree. Meanwhile, increased treating temperature and time made the decreases more obviously. The surfaces of ultrahigh modulus carbon fibers became much more activity and functionality after surface oxidation, e.g., the total surface energy of oxidized samples at 80 °C for 1 h increased by 27.7% compared with untreated fibers. Effects of surface nitric acid oxidation on the mechanical properties of ultrahigh modulus carbon fibers and its reinforced epoxy composites were also researched. Significant decreases happened to the tensile modulus of fibers due to decreased Lc value after the nitric acid oxidation. However, surface treatment had little effect on the tensile strength even as the treating temperature and processing time increased. The highest interfacial shear strength of ultrahigh modulus carbon fibers/epoxy composites increased by 25.7% after the nitric acid oxidation. In the final, surface oxidative mechanism of ultrahigh modulus carbon fibers in the nitric acid oxidation was studied. Different trends of the tensile strength and tensile modulus of fibers in the nitric acid oxidation resulted from the typical skin–core structure.

Chemical prestressing of high-performance concrete reinforced with CFRP tendons

Chemical prestress (self-prestress) is a process, in which expansion of concrete with special additives can be used to generate tension in the reinforcement and prestress in the concrete. Until now, the prestress levels that could be reached with this technique were usually lower than with traditional (external) prestressing. With the new family of expansive high-performance concretes (HPC) developed by us, very high levels of residual expansion can be achieved without compromising the durability and still reaching very good mechanical properties of the concrete. In this paper, we combine the expansive HPC with tendons made of ultra-high modulus (>400 GPa) carbon fiber reinforced polymers (CFRP). Through the expansion of the concrete and its bond with the sand-coated tendons, we could introduce tensile stresses of more than 600 MPa in the tendons (for 1% reinforcement ratio), corresponding to more than 4 MPa compressive stress (prestress) in the concrete. 4-Point bending tests show that the chemical prestress increased the cracking moment of slender concrete beams more than three times compared to the reference concrete. Our long-term tests of the strains of the tendons show that the losses of prestress due to shrinkage and compressive creep are very low.

Effect of fiber microstructure studied by Raman spectroscopy upon the mechanical properties of carbon fibers

AbstractThe microstructure of polyacrylonitrile (PAN)‐based high‐performance carbon fibers, including high‐strength carbon fibers (HSCFs), high‐modulus carbon fibers (HMCFs), and ultrahigh‐modulus carbon fibers (UHMCFs), was systematically characterized by the Raman spectroscopy. Two characteristic bands, D‐line and G‐line, showed up in the Raman spectra of HSCFs, HMCFs, and UHMCFs. However, the wavenumber of the G‐line peak of HSCFs shifted to higher wavenumber (about 1,595 cm−1) and that of the D‐line peak of HMCFs and UHMCFs shifted to lower wavenumber (about 1,350 cm−1). The relationship between the microstructure and mechanical properties of carbon fibers was also studied in detail. It was of significant relevance between surface disordered structure and the mechanical properties of HSCFs, and decreases in the full width at half maximum values of the disorder‐induced D‐line and A‐line could result in higher tensile strength and tensile modulus of HSCFs. As for HMCFs and UHMCFs, the disorder‐induced D′‐line more easily affected the tensile strength. A higher tensile modulus of HMCF and UHMCF was obtained as a result of decreases in the disordered structure and increases in the graphite structure. An increase of the intensity ratio ID/IG together with IA/IG (HSCFs) or ID′/IG (HMCFs and UHMCFs) could result in increases in the tensile strength and tensile modulus of carbon fibers.

Electrochemical surface modification of polyacrylonitrile-based ultrahigh modulus carbon fibers and its effect on the interfacial properties of UHMCF/EP composites

The surfaces of polyacrylonitrile(PAN)-based ultrahigh modulus carbon fibers (UHMCFs) were electrochemically oxidized in NH4HCO3 electrolyte solution, with increasing current density. The microphysical topography, functionalization composition and chemical structure were characterized in detail. Longitudinal ridges on UHMCF surfaces became much more well-defined and a large number of oxygen-containing functional groups were introduced onto the UHMCF surfaces after electrochemical surface modification. However, a significant decrease followed by a certain extent of increase happened to the tensile strength of UHMCF with increasing current density. The corresponding step-wise oxidation mechanism of UHMCFs in the electrochemical modification was revealed. In the first stage, the chemical etching and oxidation happened to the fiber surfaces which resulted in an obvious increase in the ID/IG ratio and significant decreases in the tensile strength of UHMCFs. As the electrochemical oxidation progressed, the outermost layer of UHMCF surfaces could possibly be broken or peeled off and thus the inside ordered graphite structure exposed, which led to a further decrease in the ID/IG ratio. Meantime, the chemical crosslinks between the unfolded graphite layers of UHMCF surfaces showed up which could give longitudinal or lateral cohesion to the fiber. Therefore, the tensile strength of oxidized UHMCFs increased as the electrochemical oxidation progressed. Effect of electrochemical surface modification of UHMCFs on the interfacial properties of UHMCF reinforced epoxy resin (EP) composites was also researched. Increased wettability and functionality of UHMCFs due to electrochemical surface oxidation resulted in increases in interfacial chemical bonding between UHMCF and EP. Therefore, the interlaminar shear strength (ILSS) of UHMCFs reinforced composites continued rising in electrochemical surface modification with increasing current density.

Evolution of microstructure and electrical property in the conversion of high strength carbon fiber to high modulus and ultrahigh modulus carbon fiber

Evolution of microstructure and electrical property in the conversion of high strength carbon fiber (HSCF) to high modulus carbon fiber (HMCF) and ultrahigh modulus carbon fiber (UHMCF) was investigated. Longitudinal grooves on fiber surfaces became less well-defined during high temperature graphitization. The tensile modulus of carbon fibers was affected by fiber crystalline structure and it increased with decreases in the value of interlayer spacing and improvements in the value of crystallite thickness. Increases in the crystallite size almost had little effect on the tensile strength. However, a lower interlayer spacing and a higher preferred orientation could result in a higher tensile strength. The crystal structure of carbon fibers became much more ordered during high temperature graphitization. It was found that the electrical resistivity gradually decreased from 14.69 × 10−4 Ω·cm to 9.70 × 10−4 Ω·cm and 8.80 × 10−4 Ω·cm, respectively, in the conversion of HSCF to HMCF and UHMCF.

Compressive strength determined for ultrahigh modulus fiber reinforced composites by [90/0]ns laminates

Traditional ASTM D6641 standard is not suitable for ultrahigh modulus carbon fiber reinforced polymer (CFRP) composites under longitudinal compression due to the unacceptable failure mode of end crushing. Experiments and micro-mechanical finite element simulations are conducted for [90/0]ns laminates under compression to check if it is acceptable using results of [90/0]ns laminates to calculate longitudinal compressive strength. Experimental results show that failure modes in [90/0]ns laminates are acceptable. Fiber splitting, fiber breakage and kink band are found clearly in 0-degree lamina under SEM. Failure index distributions before peak load in simulation show that it is fiber failure in 0-degree lamina that causes the final failure which indicates that [90/0]ns laminates can be used to calculate compressive strength. Four different types of fibers with different modulus and [0/90]ns micro-mechanical model for ultrahigh modulus CFRP are also built for comparison. Results show that this method is also applicable for T800H CFRP composites, but not for T300 and T700 CFRP composites.

Bond Performance of Sand Coated UHM CFRP Tendons in High Performance Concrete.

The bond behaviour of novel, sand-coated ultra-high modulus (UHM) carbon fibre reinforced polymers (CFRP) tendons to high performance concrete (HPC) was studied by a combined numerical and experimental approach. A series of pull-out tests revealed that the failure type can vary between sudden and continuous pull-out depending on the chosen sand coating grain size. Measuring the same shear stress vs. tendon draw-in (τ-δ) curves in the same test set-up, for sand coated CFRP tendons with a longitudinal stiffness of 137 and 509 GPa, respectively, indicated that the absolute bond strength in both cases was not influenced by the tendon’s stiffness. However, the τ-δ curves significantly differed in terms of the draw-in rate, showing higher draw-in rate for the UHM CFRP tendon. With the aid of X-ray computed tomography (CT), scanning electron microscopy (SEM) and visual analysis methods, the bond failure interface was located between the CFRP tendon and the surrounding sand-epoxy layer. For further investigation, a simplified finite element analysis (FEA) of the tendon pull-out was performed using a cohesive surface interaction model and the software Abaqus 6.14. A parametric study, varying the tendon-related material properties, revealed the tendon’s longitudinal stiffness to be the only contributor to the difference in the τ-δ curves found in the experiments, thus to the shear stress transfer behaviour between the CFRP tendon and the concrete. In conclusion, the excellent bond of the sand-coated UHM CFRP tendons to HPC as well as the deeper insight in the bond failure mechanism encourages the application of UHM CFRP tendons for prestressing applications.

Transient Thermal Tensile Behaviour of Novel Pitch-Based Ultra-High Modulus CFRP Tendons.

A novel ultra-high modulus carbon fibre reinforced polymer (CFRP) prestressing tendon made from coal tar pitch-based carbon fibres was characterized in terms of high temperature tensile strength (up to 570 °C) with a series of transient thermal and steady state temperature tensile tests. Digital image correlation was used to capture the high temperature strain development during thermal and mechanical loading. Complementary thermogravimetric (TGA) and dynamic mechanical thermal (DMTA) experiments were performed on the tendons to elucidate their high temperature thermal and mechanical behaviour. The novel CFRP tendons investigated in the present study showed an ambient temperature design tensile strength of 1400 MPa. Their failure temperature at a sustained prestress level of 50% of the design tensile strength was 409 °C, which is higher than the failure temperature of most fibre reinforced polymer rebars used in civil engineering applications at similar utilisation levels. This high-temperature tensile strength shows that there is potential to use the novel high modulus CFRP tendons in CFRP pretensioned concrete elements for building applications that fulfill the fire resistance criteria typically applied within the construction industry.

High Precision Coulometry of Commercial PAN-Based Carbon Fibers as Electrodes in Structural Batteries

Carbon fibers have the combined mechanical and electrochemical properties needed to make them particularly well suited for usage as electrodes in a structural lithium-ion battery, a material that simultaneously works as a battery and a structural composite. Presented in this paper is an evaluation of commercial polyacrylonitrile-based carbon fibers in terms of capacity and coulombic efficiency, as well as a microstructural and surface evaluation. Some polyacrylonitrile based carbon fibers intercalate lithium ions, resulting in a similar capacity as state-of-the-art graphite based electrodes, presently the most commonly used negative electrode material. Using high precision coulometry, we found a capacity of around 250–350 mAh/g and a very high coulombic efficiency of over 99.9% after ten cycles, which is even higher than a commercial state-of-the art graphitic electrode evaluated as reference. The high coulombic efficiency is attributed to the very low surface area of the carbon fibers, resulting in a small and stable solid-electrolyte interface layer. A highly graphitized ultra high modulus carbon fiber was evaluated as well and, compared to the other fibers, less lithium was inserted (corresponding to approximately 150 mAh/g). We show that the use of carbon fibers as an electrode material in a structural composite battery is indeed viable.

Modulus Effect of Bonded CFRP Laminates Used for Repairing Preyield and Postyield Cracked Concrete Beams

AbstractTwo different prerepair loading histories were simulated in 3,000×300×150 mm reinforced concrete beams, namely cracking within the elastic range, and overloading in the plastic range. After unloading, the beams were repaired with either high or ultrahigh modulus (210 or 400 GPa) carbon fiber–reinforced polymer (CFRP) plates, or a hybrid system, and then reloaded to failure. It was shown that the level of preexisting damage has insignificant effect on strengthening effectiveness and failure mode at ultimate. The 210 and 400 GPa CFRP of reinforcement ratio ρf=0.17% increased the yielding load by 33 and 60%, respectively, whereas the ultimate strength was increased by up to 29 and 51%, respectively. Doubling ρf of the 400 GPa CFRP to 0.34% resulted in a 63% overall gain in flexural strength, which is only an 8% increase over ρf=0.17%, because of change in failure mode from rupture to concrete cover delamination. The beam retrofitted by hybrid CFRP showed remarkable pseudoductility and warning signs....

Fatigue tests on steel plates with longitudinal weld attachment strengthened by ultra high modulus carbon fibre reinforced polymer plate

ABSTRACTWelded steel connections of infrastructures are susceptible to fatigue failure. Advanced carbon fibre reinforced polymer (CFRP) has been demonstrated promising for fatigue strengthening of steel structures. Limited research was conducted on CFRP strengthening of welded connections. This paper focuses on the application of ultra high modulus (UHM) CFRP plates with a modulus of 460 GPa to strengthen steel plates with longitudinal fillet weld attachment using five CFRP strengthening configurations. A series of fatigue tension tests were carried out with constant amplitude fatigue loading. Beach marking technique was adopted to record the crack propagation process. Effects of CFRP bond length, bond width and bond locations on fatigue performance of welded steel joints were investigated. The experimental results showed that UHM CFRP plates could generally increase the fatigue life of the welded steel joints. It seems better to apply CFRP on the welding side of the specimen to achieve longer fatigue life. Then, the effects of weld and weld attachment on the CFRP strengthening efficiency was further studied by comparing experimental results of non‐welded steel plates with single side UHM CFRP plate strengthening. Finally, the classification method was adopted to assess the strengthening efficiency of the UHM CFRP plate to the steel plates with longitudinal weld attachment.

The Effect of Abrasion Surface Treatment on the Bonding Behavior of Various Carbon Fiber-Reinforced Composites

In this paper we show that current abrasion surface preparation practices do not perform equally on all composite surfaces. The effect of abrasion on the adhesive bond strength of various carbon fiber (CF) composites was investigated. Cyanate ester composites were fabricated using a low, a high and an ultra high modulus carbon fiber (T300, M55J, K13C2U). XPS and contact angle measurements showed that the surface energy of all three composites increased due to the removal of contaminants as well as increased in surface roughness. However, the lap shear strength degraded sharply for a number of cases, irrespective of roughness, depending on the fiber used. Composites utilizing lower modulus carbon fibers increased in adhesive bond strength following abrasion in comparison to composites with higher modulus fibers. As the modulus of the fiber and the abrasive grit size increased, the degree of degradation caused by abrasion was shown to increase significantly. Scanning electron microscopy (SEM) and profilometry measurements showed the development of an abrasion-affected zone that was especially prevalent for higher stiffness composites. The failures for the higher modulus specimens were caused by subsurface damage located a few fiber diameters below the abraded surface. However, an alternate technique using atmospheric plasma surface treatment exhibited efficient removal of contaminants while showing no degradation of bond quality when treating these ultra high modulus composites.

Thermal expansion behaviour of ultra-high modulus carbon fibre reinforced magnesium composite during thermal cycling

The thermally induced strain response of unidirectional P100S/AZ91D carbon fibre-reinforced magnesium composite was studied over five cycles in the ±100 °C temperature range. A temperature-dependent one-dimensional model was employed to predict the anticipated response to the cycling thermal environment. Strain hysteresis was observed during cycling and attributed to matrix yielding. First cycle residual plastic strains were modelled with reasonable agreement. Experimental results deviated from predictions during subsequent cycles with continued thermal ratcheting shifting the hysteresis loops to higher strains with increasing cycles. This was thought to be associated with interfacial debonding and frictional sliding at fibre/matrix interfaces. The effect of thermal treatment on composite expansion behaviour was investigated and the results discussed in terms of minimising thermally induced deformations during anticipated service conditions. Treatments were found to affect the first cycle behaviour, reducing in particular residual plastic strain generation. Matrix yield strength was exceeded over the thermal cycle due to a lack of sufficient hardening, and since interfacial conditions were unaltered, interfacial sliding and thermal ratcheting could not be eliminated. The potential for improvement of C/Mg composite thermal strain response was explored in the light of the current findings.

The effect of thermal cycling on the properties of a carbon fibre reinforced magnesium composite

Effects of thermal cycling on mechanical properties of two unidirectional ultra-high modulus carbon fibre reinforced magnesium composites (P100S/AZ91D) have been investigated. Composite specimens reinforced with ∼50% or 60% fibre volume fraction were thermally cycled between the temperatures of 100 °C and −100 °C, in a vacuum, for up to 100 cycles. Mechanical testing showed there was no change in the bending strength of samples or the associated failure mode during cycling. Composites did, however, exhibit a moderate reduction in bending modulus and interlaminar shear strength during the first few thermal cycles. Little further degradation was observed thereafter. Modifications to the matrix microstructure were examined and related to a change in matrix properties measured via microhardness testing. Composite property degradation was attributed to the formation of microvoids and interfacial sliding in the early stages of cycling. The implications these processes may have on composite application are discussed and it is concluded that based on the limited dependence of mechanical properties to thermal cycling carbon fibre reinforced magnesium shows potential for space applications operating under transient thermal conditions.