Ultra-high Modulus Research Articles

A new family of carbon materials with exceptional mechanical properties

A new family of carbon materials with ultrahigh-strength and nano-onion grains has been successfully produced from nano-diamond particles by spark plasma sintering. It is believed that the spark plasma and applied pressure help overcome the difficulties in densification. Also diamond has a much greater density than that of graphite, leading to the volume expansion when nano-diamond particles transform to graphite onions during heating, facilitating the consolidation. The as-prepared bulk graphite with a density of 1.84 g/cm3 has ultrahigh bending strength, modulus and microhardness, 150 MPa, 31.3 GPa and 2.6 GPa, respectively, due to the unique microstructure of nano-graphite onions.

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.

Two-dimensional stoichiometric boron carbides with unexpected chemical bonding and promising electronic properties

We identify two B–C bonding patterns: pyramidal-geometry tetra-coordinated and hexa-coordinated sp2carbon moiety; B4C3has an ultrahigh Young's modulus that can even outperform graphene; the B2C sheet is metallic with a relatively high superconducting transition temperature (Tc≈ 21.20 K).

Pseudo-ductility and reduced notch sensitivity in multi-directional all-carbon/epoxy thin-ply hybrid composites

Un-notched and notched tensile response and damage accumulation of quasi-isotropic carbon/epoxy hybrid laminates made of ultra-high modulus and intermediate modulus carbon fibre/epoxy thin-ply prepregs were studied. It was confirmed that the ply fragmentation demonstrated previously in unidirectional hybrids as a successful pseudo-ductility mechanism can be transferred to multi-directional laminates. Furthermore, reduced notch sensitivity was demonstrated in quasi-isotropic specimens for both open holes and sharp notches as a result of local ply fragmentation around the notch.

Ultrahigh Elastic Strain Energy Storage in Metal-Oxide-Infiltrated Patterned Hybrid Polymer Nanocomposites.

Modulus of resilience, the measure of a material's ability to store and release elastic strain energy, is critical for realizing advanced mechanical actuation technologies in micro/nanoelectromechanical systems. In general, engineering the modulus of resilience is difficult because it requires asymmetrically increasing yield strength and Young's modulus against their mutual scaling behavior. This task becomes further challenging if it needs to be carried out at the nanometer scale. Here, we demonstrate organic-inorganic hybrid composite nanopillars with one of the highest modulus of resilience per density by utilizing vapor-phase aluminum oxide infiltration in lithographically patterned negative photoresist SU-8. In situ nanomechanical measurements reveal a metal-like high yield strength (∼500 MPa) with an unusually low, foam-like Young's modulus (∼7 GPa), a unique pairing that yields ultrahigh modulus of resilience, reaching up to ∼24 MJ/m3 as well as exceptional modulus of resilience per density of ∼13.4 kJ/kg, surpassing those of most engineering materials. The hybrid polymer nanocomposite features lightweight, ultrahigh tunable modulus of resilience and versatile nanoscale lithographic patternability with potential for application as nanomechanical components which require ultrahigh mechanical resilience and strength.

Tuning Phase Composition of Polymer Nanocomposites toward High Energy Density and High Discharge Efficiency by Nonequilibrium Processing.

Polymer nanocomposite dielectrics with high energy density and low loss are major enablers for a number of applications in modern electronic and electrical industry. Conventional fabrication of nanocomposites by solution routes involves equilibrium process, which is slow and results in structural imperfections, hence high leakage current and compromised reliability of the nanocomposites. We propose and demonstrate that a nonequilibrium process, which synergistically integrates electrospinning, hot-pressing and thermal quenching, is capable of yielding nanocomposites of very high quality. In the nonequilibrium nanocomposites of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and BaTiO3 nanoparticles (BTO_nps), an ultrahigh Weibull modulus β of ∼30 is achieved, which is comparable to the quality of the bench-mark biaxially oriented polypropylene (BOPP) fabricated with melt-extrusion process by much more sophisticated and expensive industrial apparatus. Favorable phase composition and small crystalline size are also induced by the nonequilibrium process, which leads to concomitant enhancement of electric displacement and breakdown strength of the nanocomposite hence a high energy density of ∼21 J/cm3. Study on the polarization behavior and phase transformation at high electric field indicates that BTO_nps could facilitate the phase transformation from α- to β-polymorph at low electric field.

The Fracture Resistance Of The Endodontically Treated Molar Teeth With MOD Preparations Restored With Different Types Of Composit Material

Compared to teeth with healthy pulps, root filled teeth are considered more susceptible to fracture. The present study was directed toward improving the effect of using flowable composite with or without polyethylene fiber reinforcement on fracture resistance of the endodontically treated mandibular molars with MOD preparations. Thirty sound extracted human mandibular molars were randomly assigned to three groups (n=10). All teeth were root filled and MOD cavity preparation were created.Group (1) was restored with a dentine bonding system(DBS: SE Bond) and composite resin( CR). In group (2), flowable composite resin ( Protect liner F) was used before restoring teeth with CR. In group (3) leno woven ultra high modulus polyethylene ribbon fiber ( Ribbond, Seattle, WA. USA) was inserted into the cavities in a buccal to lingual direction and teeth were then restored with DBS and CR. After finishing and polishing the specimens were stored in 100% humidity at 37C° for 1 day. Compressive loading of the teeth was performed using a universal testing machine at a crosshead speed of 0.5 mm min "' . the mean load necessary to fracture the samples were recorded in newtons (N) and were subjected to analysis of variance (ANOVA) and Tukey test. The results showed that the used of flowable composite resin under composite restorations had no effect on fracture resistance of root filled molars teeth with MOD preparation . while the used of polyethylene fjtffer under composite restorations in root filled teeth with MOD preparations significantly, increased fracture strength .
 Aim
 To evaluate the effect of using flowable composite with or without ultra high modulus polyethylene fiber reinforcement on fracture resistance of root filled mandibular molars with mesio - occluso-distal(MOD) preparations.

Engineering properties of CFRP laminate under high strain rates

This paper presents the results of experimental investigations of the tensile properties of different types of CFRP plates. Coupon specimens of low, normal and ultra-high modulus CFRP plates were prepared and tested under tensile loading. Four different strain rates were used, including one low strain rate and three high strain rates. Two methods of capturing strain were used: image correlation photogrammetry and foil strain gauges. The results showed a significant increase in the tensile strength, ultimate strain and elastic modulus for coupons under high strain rates. The CFRP coupons were prepared and tested in accordance with the ASTM3039-08 standards. Finite element analysis was performed and the results agreed very well with the experimental results.

Mode I fatigue crack arrest in tensile steel members using prestressed CFRP plates

Numerous studies in the literature have shown that the strengthening of steel members using carbon fiber reinforced polymer (CFRP) composites can significantly extend the fatigue life of these structures. However, not enough attention has been focused on the potential of prestressed CFRP reinforcements for fatigue crack arrest in such members. In the current study, a simple analytical model is proposed to calculate the required prestressing level in the CFRP reinforcements in order to arrest the propagation of an existing fatigue crack in tensile steel members. Furthermore, a novel mechanical unbonded system is developed to anchor the high prestressing forces in CFRP reinforcements to the steel substrate using friction. A set of fatigue tests are performed on unstrengthened and strengthened precracked steel plates to verify the proposed model. The experimental results of the current study showed that the application of nonprestressed ultra-high modulus CFRP plates as externally bonded reinforcements can increase the fatigue life of precracked steel plates by a factor of 4.3. However, fatigue crack arrest is only possible when prestressed CFRPs of a certain prestressing level are used. Based on the analytical, numerical, and experimental results of the current study, it can be concluded that existing fatigue cracks in tensile steel members can be arrested using the proposed prestressed unbonded reinforcement system with the initial prestressing level calculated using the proposed model. In addition, some design recommendations are provided for fatigue crack arrest in practical cases.

Anisotropic pH-Responsive Hydrogels Containing Soft or Hard Rod-Like Particles Assembled Using Low Shear

A simple and versatile low-shear approach for assembling hydrogels containing aligned rod-like particles (RLPs) that are birefringent and exhibit pH-triggered anisotropic swelling is developed. Anisotropic composite hydrogels are prepared by applying low shear (0.1 s–1) to mixtures of pH-responsive nanogels (NGs) and RLPs. The NGs, which contained high methacrylic acid contents, acted as both shear transfer vehicles and macro-cross-linkers for anisotropic gel formation. Three model RLP systems are investigated: (i) soft triblock copolymer worms, (ii) stiff self-assembled β-sheet peptide fibers, and (iii) ultrahigh modulus nanocrystalline cellulose fibers. RLP alignment was confirmed using polarized light imaging, atomic force microscopy, and small-angle X-ray scattering as well as modulus and anisotropic swelling experiments. Unexpectedly, the composite gel containing the soft copolymer worms showed the most pronounced anisotropy swelling. The copolymer worms enabled higher RLP loadings than was possible ...

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 Stiffness Concrete for Tall Buildings under Severe Conditions: Mix Design and Structural Member Test

A new type of concrete, which contains volcanic aggregate and well-graded river sand, having both high strength and ultra-high modulus of elasticity has been developed for tall buildings under severe conditions, and its properties were characterized. The structural deformation of high-rise buildings can be substantially reduced by using this type of concrete, thereby decreasing the cross-section area of the structural members and increasing the economic benefits, not to mention alleviating shrinkage and creep problems of concrete. Uniaxial compression test, static elastic modulus test and scanning electron microscope test were conducted to characterize the properties of concrete specimens with different mix proportions. The experimental results showed that volcanic rock as coarse aggregate, well-graded river sand as fine aggregate, sand ratio around 43%, silica fume content about 10% as well as some mineral admixtures such as metakaolin and nanosilica led to higher modulus of elasticity of concrete. A particular type of concrete with the compressive strength of 146 MPa and modulus of elasticity of 53.5 GPa was developed, which is much stiffer than normal concrete in the code of practice. Four concrete mixtures including C45, C80, high modulus and ultra-high modulus concrete were applied in producing structural members, verifying the advantages of utilization of high stiffness concrete.

A Retrofit Theory to Prevent Fatigue Crack Initiation in Aging Riveted Bridges Using Carbon Fiber-Reinforced Polymer Materials.

Most research on fatigue strengthening of steel has focused on carbon fiber-reinforced polymer (CFRP) strengthening of steel members with existing cracks. However, in many practical cases, aging steel members do not yet have existing cracks but rather are nearing the end of their designed fatigue life. Therefore, there is a need to develop a “proactive” retrofit solution that can prevent fatigue crack initiation in aging bridge members. Such a proactive retrofit approach can be applied to bridge members that have been identified to be deficient, based on structural standards, to enhance their safety margins by extending the design service life. This paper explains a proactive retrofit design approach based on constant life diagram (CLD) methodology. The CLD approach is a method that can take into account the combined effect of alternating and mean stress magnitudes to predict the high-cycle fatigue life of a material. To validate the retrofit model, a series of new fatigue tests on steel I-beams retrofitted by the non-prestressed un-bonded CFRP plates have been conducted. Furthermore, this paper attempts to provide a better understanding of the behavior of un-bonded retrofit (UR) and bonded retrofit (BR) systems. Retrofitting the steel beams using the UR system took less than half of the time that was needed for strengthening with the BR system. The results show that the non-prestressed un-bonded ultra-high modulus (UHM) CFRP plates can be effective in preventing fatigue crack initiation in steel members.

Hybrid specimens eliminating stress concentrations in tensile and compressive testing of unidirectional composites

Two novel approaches are proposed for elimination of stress concentrations in tensile and compressive testing of unidirectional carbon/epoxy composites. An interlayer hybrid specimen type is proposed for tensile testing. The presented finite element study indicated that the outer continuous glass/epoxy plies suppress the stress concentrations at the grips and protect the central carbon/epoxy plies from premature failure, eliminating the need for end-tabs. The test results confirmed the benefits of the hybrid specimens by generating consistent gauge-section failures in tension. The developed hybrid four point bending specimen type and strain evaluation method were verified and applied successfully to determine the compressive failure strain of three different grade carbon/epoxy composite prepregs. Stable failure and fragmentation of the high and ultra-high modulus unidirectional carbon/epoxy plies were reported. The high strength carbon/epoxy plies exhibited catastrophic failure at a significantly higher compressive strain than normally observed.

Ultrahigh strength and modulus copolyamide films with uniaxially cold-drawing induced molecular orientation

The tensile strength of polymer films is generally lower than 200 MPa. Copolyamide (CPA) films with ultrahigh strength (approximately 317–865 MPa) and high modulus (approximately 3.96–11.76 GPa) were obtained by uniaxial cold-drawing and heat treatment. The relationship between structures and properties in the orientation state was also investigated. The results of Fourier transform infrared (FTIR) spectroscopy indicate that hydrogen bonding interactions change a little with drawing. Wide-angle X-ray diffraction patterns show orientational stretch induces π–π ordered packing after drawing 100%. The tensile strength and modulus of the drawn CPA films are improved approximately 41%–173% and 9%–197% compared to undrawn films. Dichroic ratios obtained under polarized FTIR spectroscopy represent overall orientation factors. The decrease of dichroic ratios at about 3300 cm−1 and 1650 cm−1 and the increase of dichroic ratios at 1515 cm−1 prove that the orientation of macromolecular chains is improved along stretch direction. What’s more, the degree of orientation is further increased after heat treatment, which is the phenomenon of spontaneous orientation. The degree of spontaneous orientation increases with the increase of cold-drawing ratio. Thus, the initial orientation in cold-drawing and spontaneous orientation during heat treatment leads to ultrahigh modulus and high strength.

Effect of crack orientation on fatigue behavior of CFRP-strengthened steel plates

The introduction of carbon fiber reinforced polymer (CFRP) with higher Young’s modulus has broadened its application to the strengthening of steel structures, especially under fatigue loading. Most research on CFRP strengthening of steel under fatigue loading has focused on tension fatigue testing, assuming that cracks or crack-like defects propagate in pure tension mode. However, the complex details and welded connections in aging metallic structures may contain cracks orientated randomly with respect to the loading direction. This paper aims to extend the current knowledge of CFRP strengthening of steel elements in tensile fatigue loading to the case of mixed tension and shear loading. Steel plates were artificially cracked from a central hole at six different angles (10°–90°) with respect to the loading axis. Each crack angle represents a certain degree of mode mixity. Ultra-high modulus CFRP was used for strengthening in this study. Twelve specimens were strengthened with two CFRP patching configurations. Six unrepaired specimens were tested to act as control specimens. A shifting phenomenon was identified to describe the influence of mixed mode in terms of crack propagation. A mixed mode modification factor was developed to estimate the fatigue life of CFRP-strengthened steel plates with inclined initial cracks.

Experimental and Numerical Study on Strengthening of Steel Members Subjected to Impact Loading Using Ultrahigh Modulus CFRP

AbstractCarbon fiber–reinforced polymers (CFRPs) are commonly used for strengthening steel and concrete structures, with different types of CFRP used for strengthening different structural elements. A number of studies have focused on strengthening of steel members using low and normal-modulus CFRP. However, there is a lack of understanding on the use of ultrahigh modulus (UHM) CFRP for strengthening steel structures under impact loading. This paper presents experimental and numerical investigations on the effect of high load rates on the ultimate joint capacity, failure mode, effective bond length, and strain distribution along the bond interface between CFRP and steel plates in double-strap joints. Two methods of capturing strain were used in this program: (1) Image correlation photogrammetry was used for specimens tested under quasi-static tensile load, and (2) foil strain gauges were used for specimens tested under impact tensile loading. UHM CFRP was used to strengthen the joints using epoxy. The res...

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.

High-Performance Polyethylene Fibers “Al Dente”: Improved Gel-Spinning of Ultrahigh Molecular Weight Polyethylene Using Vegetable Oils

We demonstrate that the major drawbacks of so-called gel spinning and solid-state processing of “virgin”, i.e. never molten or fully dissolved, ultrahigh molecular weight polyethylene (UHMW PE) to produce ultrahigh modulus and ultrahigh strength fibers and films, which are the unfavorably low polymer concentrations in highly flammable solvents typically employed in the former process and low production rates in the latter, can be largely avoided by employing relatively poor—as opposed to good—solvents, including, among others, fatty acids and natural oils omnipresent in, for example, fruits, nuts, and seeds, which have additional major recovery and environmental advantages.