Search

Intramedullary nails are the golden treatment option for diaphyseal fractures. However, their high stiffness can shield the surrounding bone from the natural physiologic load resulting in subsequent bone loss. Their stiff structure can also delay union by reducing compressive loads at the fracture site, thereby inhibiting secondary bone healing. Composite intramedullary nails have recently been introduced to address these drawbacks. The purpose of this study is to evaluate the mechanical properties of a previously developed composite IM nail made of carbon-fibre/epoxy whose structure was optimized based on fracture healing requirements using the selective stress shielding approach. Following manufacturing, the cross-section of the composite nail was examined under an optical microscope to find the porosity of the structure. Mechanical properties of the proposed composite intramedullary nail were determined using standard tension, compression, bending, and torsion tests. The failed specimens were then examined to obtain the modes of failure. The material showed high strength in tension ( 403.9 ± 7.8 MPa), compression ( 316.9 ± 10.9 MPa), bending ( 405.3 ± 8.1 MPa), and torsion ( 328.5 ± 7.3 MPa). Comparing the flexural modulus ( 41.1 ± 0.9 GPa) with the compressive modulus ( 10.0 ± 0.2 GPa) yielded that the material was significantly more flexible in compression than in bending. This customized flexibility along with the high torsional stiffness of the nail ( 70.7 ± 2.0 N m 2 ) has made it ideal as a fracture fixation device since this unique structure can stabilize the fracture while allowing for compression of fracture ends. Negligible moisture absorption ( ~ 0.5 % ) and low porosity of the laminate structure (< 3%) are other advantages of the proposed structure. The findings suggested that the carbon-fibre/epoxy intramedullary nail is flexible axially while being relatively rigid in bending and torsion and is strong enough in all types of physiologic loading, making it a potential candidate for use as an alternative to the conventional titanium-alloy intramedullary nails. [ABSTRACT FROM AUTHOR]

Abstract: The ultimate objective of this study is to provide further understanding of the behaviour of laminated composites of varying lamina orientations and stacking sequences, when under high-velocity impact. Emphasis is placed on the determination of ballistic limits of these composites. To this end, an experimental program is carried out and a computational model, with progressive damage modeling capabilities, is developed using LS-DYNA. Experiments are performed whereby striking velocities are measured, via high-speed photography, to determine the ballistic limits of carbon fiber-reinforced polymer (CFRP) laminates of various stacking sequences. The results are reproduced closely by a numerical simulation, indicating that the numerical analysis conducted, including the choice of material model and contact definition, is an accurate means for modeling the high-speed impact characteristics of CFRP laminates. It is found that the use of static elastic and strength properties to describe the material is reasonable, since strain rate effects are found to be negligible. The kinetic energy of the projectile, plotted over the simulated impact duration, is used as the prime parameter to compare the experimental and numerical results. The numerical results accurately predict the experimental ballistic limit for six of the seven tested laminate stacking sequences. Failure due to delamination is found to play a vital role with respect to the energy absorbing ability and lamina stacking sequence of CFRP laminates. [Copyright &y& Elsevier]

Laminated structures are normally designed using a set of strength values that are determined experimentally. Such values are determined by carrying out experiments on unidirectional test coupons. In this paper it is argued that the predicting the failure of multidirectional laminates based on the lamina to laminate approach cannot be accurately done using lamina properties obtained from unidirectional coupon test. Instead, one needs to obtain the effective properties of laminae as deduced from multidirectional laminate test. A method is therefore proposed to determine the effective tensile properties of a composite laminate. In particular, two types of composite materials were examined, namely carbon fiber-reinforced epoxy and glass fiber-reinforced epoxy. The failure behavior of laminates made from these materials is explained and the effect of multiple cracking in strength reduction is outlined. The experimental results confirm that the failure of multidirectional laminates cannot be accurately predicted using unidirectional laminae properties. Instead, the paper describes how to obtain the effective properties and shows that these are quite different from those obtained using unidirectional configurations. [ABSTRACT FROM AUTHOR]

The influence of conventional drilling (CD) and abrasive water jet (AWJ) cutting on the fatigue performance of carbon fabric/epoxy plates was investigated. Observations of machined hole regions revealed more severe damage on the CD hole surfaces with larger damage regions penetrating into the material. For both material systems investigated, the surface roughness for AWJ holes was in fact higher in comparison to CD holes. Nonetheless, static properties, short-term fatigue properties and endurance limits of the plates were not affected by the machining technique. Observed damage, stiffness and temperature evolutions during short-duration cyclic tests showed no significant changes in fatigue response for CD and AWJ plates, suggesting that surface roughness is not a good indicator of hole quality. However, long-duration cyclic tests revealed that CD plates exhibited greater stiffness degradation and advanced damage after a cyclic threshold, beyond which machining-induced delamination cracks began to propagate. This was not observed for the AWJ plates, where instead cyclic loading-induced delamination cracks initiated and propagated much later. These key findings are critical for assessing the unique performance characteristics of fabric/epoxy plates with holes. Since these materials are increasingly used for primary fatigue-critical structures, the presented outcomes are vital for designing corresponding structure joining methods. [ABSTRACT FROM AUTHOR]

The high stiffness of conventional intramedullary (IM) nails may result in stress shielding and subsequent bone loss following healing in long bone fractures. It can also delay union by reducing compressive loads at the fracture site, thereby inhibiting secondary bone healing. This paper introduces a new approach for the optimization of a fiberreinforced composite nail made of carbon fiber (CF)Iepoxy based on a combination of the classical laminate theory, beam theory, finite-element (FE) method, and bone remodeling model using irreversible thermodynamics. The optimization began by altering the composite stacking sequence and thickness to minimize axial stiffness, while maximizing torsional stiffness for a given range of bending stiffnesses. The selected candidates for the seven intervals of bending stiffness were then examined in an experimentally validated FE model to evaluate their mechanical performance in transverse and oblique femoral shaft fractures. It was found that the composite nail having an axial stiffness of 3.70 MN and bending and torsional stiffnesses of 70.3 and 70.9 N ∙ m2, respectively, showed an overall superiority compared to the other configurations. It increased compression at the fracture site by 344.9 N (31%) on average, while maintaining fracture stability through an average increase of only 0.6 mm (49%) in fracture shear movement in transverse and oblique fractures when compared to a conventional titanium-alloy nail. The long-term results obtained from the bone remodeling model suggest that the proposed composite IM nail reduces bone loss in the femoral shaft from 7.9% to 3.5% when compared to a conventional titanium-alloy nail. This study proposes a number of practical guidelines for the design of composite IM nails. [ABSTRACT FROM AUTHOR]