Carbon Fiber Rods Research Articles

Magnetic resonance elastography: a method for the noninvasive and spatially resolved observation of phase transitions in gels.

Dynamic magnetic resonance elastography (MRE) is a new imaging technique 1 recently developed for the noninvasive determination of biomechanical properties of biological tissue. 2 Compared to traditional medical palpation techniques, MRE is characterized by a high spatial resolution and a high sensitivity to the varying stiffness between healthy and pathologic tissues even in nonaccessible body regions. 3 Moreover, MRE also provides new information for other research fields. We report the spatially and temporally resolved observation of the sol/gel phase transition in a thermo-reversible gel. Observed wave patterns were reproduced using a model calculation based on temperature-dependent biomechanical properties of the sample. Dynamic MRE is based on the visualization of propagating shear waves in harmonically excited samples. The shear waves are usually generated mechanically with excitation frequencies between 50 and 600 Hz. 1 Minimum amplitudes for particle displacement are in the order of 0.1 Im. This enables the transmission of shear waves with low damping into the sample. The wave patterns, which depend on the local biomechanical properties of the sample, are visualized by using motion-sensitive MRI techniques. 1 Maps of local shear stiffness or shear moduli (elastograms) can be reconstructed from the wave images. 4 The gel phantom was prepared by dissolving 22.5 g of agar (1.5%) in 1.5 L of water heated to 90 °C. The fluid gel was examined in a double-walled container open at the top. The cooling of the sample (total cooling time 5 h), monitored with a thermometer between 60 and 25 °C, showed an exponential time dependence. Shear waves with a frequency of 200 Hz were induced parallel to the B0-field direction (z) by a copper coil fixed to a pivoting carbon fiber rod connected with the surface of the gel. The excitation device was fixed to the standard head coil of a clinical scanner (1.5 T, Siemens, Erlangen, Germany). Data were

Impact Response of Unidirectional Carbon Fibre Rod Elements with and without an Impact Protection Layer

Rods of unidirectional CFRP offer outstanding performance in terms of strength to weight ratio. Their performance is, however, expected to be limited by their resistance to in-service impact threats, especially with regard to compressive loadings. The work reported here has verified that damage is done to unprotected rods at relatively minor impact levels and that a substantial reduction in compressive strength is experienced after impact. Identical rods have been overwound with high modulus aramid fibre under tension to act as a protective layer and subsequently impacted. These rods are much more resistant to impact than the unprotected rods; the best case studied to date being more than three times as strong after impact as the unprotected rods and more than twice as strong when taking the mass of aramid fibre into account. The longitudinal splitting seen in the impacted, unprotected rods has been completely suppressed by the tensioned overwind. This novel approach to reducing the influence of impact on the post-impact properties of composite rods has been validated by these tests.

Compression testing of pultruded carbon fibre-epoxy cylindrical rods

The fibre waviness inherent in conventional prepreg laminatessignificantly reduces their compressive strength. This waviness canbe reduced through the use of unidirectional fibre rods. In thiswork, the development of a new test procedure and specimen design isreported that was used to determine the compressive properties ofpultruted T300/828 and IM7/828 carbon fibre-epoxy unidirectionalrods at room temperature. The IM7/828 system demonstrates a highercompressive strength than the T300/828 composite due to strongerfibres used and fewer manufacturing defects. Since the fibres as intension primarily carry the compressive load, the final fracture ofthe rods occurs when the fibres fail. Post-failure examinationreveals that failure of the fibres is microbuckling-induced. This isa bending failure as a consequence of buckling. Other events such asfibre-matrix debonding (splitting) and matrix yielding do not bythemselves cause the final failure, but they facilitate fibrebuckling by reducing the lateral support for the fibres.Microbuckling failure models are used to predict the compressivestrength of the carbon fibre rods; agreement between theory andexperiment is acceptable.

The histology of regenerated tissue after failed carbon fibre matrix implants

The histology of fibrocartilage regenerated by the use of carbon fibre rods and pads for treatment of articular cartilage defects is reported. On macroscopic examination the regenerated tissue appeared to be a thin translucent membrane which peeled easily from the underlying carbon fibre pad and rods. Microscopically, the regenerated tissue is similar to any other repair tissue without any definitive organisation, unlike articular cartilage which consists of predominantly Type II collagen arranged in a definite pattern of organisation, and hence may be unable to withstand the stresses and strain (up to 18 500 psi) it may be constantly subjected to during everyday activities. It is therefore clear that although such attempts of stimulation of repair tissue for articular cartilage may provide short-term relief of symptoms, these benefits are not long lasting as the regenerated tissue breaks down.

The use of Fabry Perot fiber optic sensors to monitor residual strains during pultrusion of FRP composites

This paper describes the use of an embedded optical sensor to measure the process induced strain in pultruded carbon fiber reinforced composite rods. The survivability of Fabry Perot optical sensors in the pultrusion process, real time strain monitoring during the pultrusion process and residual strain measurements within the composite rods, were the three objectives of the research. Strain profiles were recorded for individual experiments as the sensors traveled through the pultrusion die, and for the cool down period after the sensor had exited the die. For the total pultrusion process, the residual strain after cooling was found to present somewhat of a problem. For several experiments, the residual strain after exiting the pultrusion die was in the range of +200 to 400 microstrain, after which the sensors ceased to function. Calculations indicated that the radial shrinkage of the carbon fiber rods was sufficient to cause failure of the glass capillary portion of the Fabry Perot sensors. A novel method of reinforcing the Fabry Perot sensors before being pultruded was successful in allowing the sensors to survive the total process with only a slightly negative residual strain.

Lightweight carbon fibre rods and truss structures

Lightweight carbon fibre rods and truss structures are of growing importance for modern transportation technologies. The struts of such frameworks are commonly designed as fibre-wound CFRP tubes. Here CFRP sandwich rods are an advantageous alternative. They have a lightweight foam core covered by a relative thin layer of composite material. In many real applications, however, the superior mechanical properties of such struts can only be utilized with appropriate load transfer elements. Two types of load transfer elements designed for high tensile and compressive loads with a simple screw connection will be described. The framework structures discussed in this paper refer to framework beams which have, in their simple version, cross-sections of an equilateral triangle. To realise a single point support at the ends of the beam-like truss, the rail struts must converge into a conical structure. The presented structures are connection designs without any metallic elements. An outstanding application of CFRP-trusses, rod connectors, and the mentioned formlocking load transfer elements can be found in the advanced lightweight structure of a recently developed semi-rigid airship, the Zeppelin NT.

Transfer Length of Carbon Fiber Rods in Precast Pretensioned Concrete Beams

This paper presents the results of an experimental study to determine the transfer length of carbon fiber reinforced polymer (CFRP) rods in prestressed concrete beams. Five large-scale concrete T-beams were pretensioned with four 5/16 in. (8 mm) diameter CFRP Leadline rods. In addition, four rectangular beams were pretensioned using a single Leadline rod. Three levels of prestressing, 50, 60 and 70 percent of the guaranteed strength of the rod, were considered. The strain profile along the length of the beam was determined by measuring the strain in both the prestressing rods and the concrete. The results of the experiment were used to determine the instantaneous and long-term transfer length of CFRP rods and to examine the applicability of existing equations available for steel. The measured transfer length for these CFRP rods was 80 to 90 times the bar diameter, and existing models for steel may give unconservative transfer lengths for the CFRP rod.

Mechanical Properties of CFRC Additionally Reinforced with CFRP Rods

Potential of using pitch-based high modulus carbon fiber was investigated as a reinforcement in cementitious composites for structural reinforced concrete (RC) members. For this purpose, effects of carbon fiber mechanical properties on the mechanical properties of CFRC reinforced with CFRP rods were studied through the three-point flexural test by using several pitch-based high modulus carbon fiber rods of varying fiber moduli and strengths. For the specimens with a fiber volume fraction larger than the critical volume fraction, the flexural strength is found to exceed the CFRC matrix strength and is linearly proportional to the sum of all rod strengths, and the flexural modulus after matrix cracking is found to also be linearly proportional to the sum of all rod stiffnesses.

The chondrogenic potential of carbon fiber and carbon fiber periosteum implants: an ultrastructural study in the rabbit

The articular tissue generated on carbon fiber rods in rabbit knee joints after 75 days of intermittent active motion was compared with tissue generated on carbon fiber rods whose articular surfaces were covered with a free reversed periosteal graft. Both methods were effective in generating articular tissue; however, tissue with ultrastructural characteristics similar to those of hyaline cartilage was noted more frequently on the composite implants. If such composite implants were clinically effective then they might be useful in treating symptomatic osteochondral defects.

Intramedullary nailing of the tibia without a fracture table: the transfixion pin distractor technique.

A series of 44 fractures of the tibia requiring operative stabilization were treated using an intraoperative external transfixion pin frame to correct angular deformity and maintain length in preparation for intramedullary (IM) nailing, eliminating the need for a fracture table. The technique requires a radiolucent operating room table; the injured extremity is draped free. A transfixion pin is inserted in the os calcis. Rotational deformity is manually corrected. Using fluoroscopic control, a second transfixion pin is inserted at a location just distal and parallel to the proximal tibial articular surface, paralleling the horizontal plane of the first pin. The transfixion pins are connected with carbon fiber rods, creating a rectangular frame. Manual fracture reduction is followed by "fine tuning" with compressor/distractor clamps as needed. Alternatively, for added reduction force, the carbon fiber rod on the concave side of the angular deformity may be replaced with the AO/ASIF universal distractor. IM nailing is then performed in the usual fashion. In this series, an acceptable reduction was obtained in all cases. This technique shortens setup time, provides complete access to the distal part of the tibia, and allows free manipulation of the limb, thereby facilitating nail insertion and placement of distal locking screws. Use of medial and lateral bars prevents the angular deformity often created or exacerbated with the use of the universal distractor alone. This technique is recommended for IM nailing of all fractures of the tibia that would otherwise require use of the fracture table or universal distractor.

External fixation of the pelvis: Application of the resuscitation frame

The authors describe the application and use of an emergency frame for pelvic fracture stabilization. This “resuscitation frame” can be placed rapidly, even in the emergency department setting, and provides the patient with an effective means of tamponade. Because carbon fiber rods are used, radiograph will show the reduction. Later, definitive fixation of the pelvis may be performed with the frame in place, or if a stable fracture is present, the frame may be used to treat the fracture definitively