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The purpose of this study is to investigate the mechanical feasibility of a hybrid Glass/Flax/Epoxy composite material for bone fracture fixation such as fracture plates. These hybrid composite plates have a sandwich structure in which the outer layers are made of Glass/Epoxy and the core from Flax/Epoxy. This configuration resulted in a unique structure compared to prior composites proposed for similar clinical applications. In order to evaluate the mechanical properties of this hybrid composite, uniaxial tension, compression, three-point bending and Rockwell Hardness tests were conducted. In addition, water absorption tests were performed to investigate the rate of water absorption for the specimens. This study confirms that the proposed hybrid composite plates are significantly more flexible axially compared to conventional metallic plates. Furthermore, they have considerably higher ultimate strength in tension, compression and flexion. Such high strength will ensure good stability of bone-implant construct at the fracture site, immobilize adjacent bone fragments and carry clinical-type forces experienced during daily normal activities. Moreover, this sandwich structure with stronger and stiffer face sheets and more flexible core can result in a higher stiffness and strength in bending compared to tension and compression. These qualities make the proposed hybrid composite an ideal candidate for the design of an optimized fracture fixation system with much closer mechanical properties to human cortical bone. [ABSTRACT FROM AUTHOR]

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]

Bone fracture plates are used to stabilize fractures while allowing for adequate compressive force on the fracture ends. Yet the high stiffness of conventional bone plates significantly reduces compression at the fracture site, and can lead to subsequent bone loss upon healing. Fibre-reinforced composite bone plates have been introduced to address this drawback. However, no studies have optimized their configurations to fulfill the requirements of proper healing. In the present study, classical laminate theory and the finite element method were employed for optimization of a composite bone plate. A hybrid composite made of carbon fibre/epoxy with a flax/epoxy core, which was introduced previously, was optimized by varying the laminate stacking sequence and the contribution of each material, in order to minimize the axial stiffness and maximize the torsional stiffness for a given range of bending stiffness. The initial 14×4 14 possible configurations were reduced to 13 after applying various design criteria. A comprehensive finite element model, validated against a previous experimental study, was used to evaluate the mechanical performance of each composite configuration in terms of its fracture stability, load sharing, and strength in transverse and oblique Vancouver B1 fracture configurations at immediately post-operative, post-operative, and healed bone stages. It was found that a carbon fibre/epoxy plate with an axial stiffness of 4.6 MN, and bending and torsional stiffness of 13 and 14 N·m 2 , respectively, showed an overall superiority compared with other laminate configurations. It increased the compressive force at the fracture site up to 14% when compared to a conventional metallic plate, and maintained fracture stability by ensuring the fracture fragments’ relative motions were comparable to those found during metallic plate fixation. The healed stage results revealed that implantation of the titanium plate caused a 40.3% reduction in bone stiffness, while the composite plate lowered the stiffness by 32.9% as compared to the intact femur. This study proposed a number of guidelines for the design of composite bone plates. The findings suggest that a composite bone plate could be customized to allow for moderate compressive force on the fracture ends, while remaining relatively rigid in bending and torsion and strong enough to withstand external loads when a fracture gap is present. The results indicate that the proposed composite bone plate could be a potential candidate for bone fracture plate applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experimental investigation on a unique braided polyimide composite material. [•] Tensile static and fatigue tests at both room temperature and elevated temperature. [•] Tests reveal that elevated temperature causes a reduction in microscopic damage. [•] Temperature-dependent damage development caused a reduction in fatigue life. [•] A fundamental understanding of the novel material behavior was achieved. [ABSTRACT FROM AUTHOR]

Abstract: A study is conducted to characterize and subsequently model the elevated temperature fatigue behavior of a triaxially braided carbon fiber reinforced polymer matrix composite. An experimental investigation reveals that the elevated temperature environment significantly alters the microscopic fatigue damage evolution and the corresponding stiffness degradation response of the material. The developed fatigue damage model, which is based on quantified parameters of observed damage mechanisms, predicts with a high degree of precision the response of the material for all applied stresses and at both temperatures considered. The predictive model captures the unique characteristics of fatigue damage evolution in the braided composite, and is a viable design tool. Overall, this study yielded a fundamental understanding of microscopic fatigue damage evolution and local deformation behavior of the braided composite. [Copyright &y& Elsevier]

Abstract: Thermography was used to investigate the fatigue behavior of a braided carbon fiber polymeric composite plate. A thermographic approach, originally developed in an earlier study for metallic alloys, was employed to rapidly determine the composite high cycle fatigue strength. The method yielded a fatigue threshold value that was in excellent agreement with that obtained through a conventional experimental test program. The damage mechanisms responsible for the increased heat dissipation and ultimately failure were identified, which provides support for the existence of a fatigue threshold for this material. An extension of the thermographic technique to rapidly determine the entire fatigue stress-life curve for the composite plate provided a direct correlation to the stress-life curve determined through a conventional test program. Energy dissipation was also used as an indicator to determine the high cycle fatigue strength, providing support for the thermographic approach. A relationship between the dissipated heat, the intrinsic energy dissipation and the number of cycles to failure has been clearly established. [Copyright &y& Elsevier]

Abstract: The angled crack problem has been given special attention in the recent years by fracture mechanics investigators due to its close proximity to realistic conditions in engineering structures. In this paper, an investigation of fatigue crack propagation in rectangular steel plates containing an inclined surface crack is presented. The inclined angle of the crack with respect to the axis of loading varied between 0° and 90°. During the fatigue tests, the growth of the fatigue crack was monitored using the AC potential drop technique. A series of modification factors, which allow accurate sizing of such defects, is recommended. Paris power law is normalized and adopted for data analysis. Subsequently, this concept is applied to predict crack growth due to fatigue loads. The results obtained are compared with those obtained using the commonly employed fracture criterion and the experimental data. [Copyright &y& Elsevier]

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]

Abstract: This paper presents an effective methodology for the optimum design of two-component armours using Florence’s model and a new hybrid evolutionary solving technique. The proposed methodology provides a practical platform for the design of composite armours while accounting for various design criteria. The simulated design results are compared with those obtained from analytical design models. Comparison with the published experimental data shows that the present methodology, by taking into account all the design considerations, can produce more accurate results than analytical design methods. Moreover, unlike the conventional analytical design models, the present methodology allows the determination of optimal designs whereby both the armour materials and their thickness ratios are taken as integral design parameters. [Copyright &y& Elsevier]

• Fractographic analysis finds airfoil fracture surface to be characteristic of HCF. • Numerical method is developed to capture combined LCF HCF stress field. • Predicted crack growth trajectory and shape correlate well with fractured airfoils. • LCF accelerates crack growth by imposing positive mean stress to HCF load. • Propagation life of 255,000 cycles is estimated from Forman-Newman-de Koning model. This paper presents a 3D crack growth simulation of an aircraft engine high pressure compressor blade which fractured in service. Using FRANC3D, an initial crack is inserted and grown using the max tensile stress theory. A numerical method was developed to capture the stress field under low cycle fatigue (LCF) and high cycle fatigue (HCF) loading by superimposing test measured dynamic loading with steady stresses. In doing so, the predicted crack trajectory, aspect ratio, and shape more closely agreed with the fractured airfoils compared to performing the simulation under LCF loads alone. This supports findings from fractographic investigation that the crack exhibits HCF rather than LCF characteristics. [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]

Background Intramedullary nails are the primary choice for treating long bone fractures. However, complications following nail surgery including non-union, delayed union, and fracture of the bone or the implant still exist. Reducing nail stiffness while still maintaining sufficient stability seems to be the ideal solution to overcome the abovementioned complications. Methods In this study, a new hybrid concept for nails made of carbon fibers/flax/epoxy was developed in order to reduce stress shielding. The mechanical performance of this new implant in terms of fracture stability and load sharing was assessed using a comprehensive non-linear FE model. This model considers several mechanical factors in nine fracture configurations at immediately post-operative, and in the healed bone stages. Results Post-operative results showed that the hybrid composite nail increases the average normal force at the fracture site by 319.23 N ( P < 0.05), and the mean stress in the vicinity of fracture by 2.11 MPa ( P < 0.05) at 45% gait cycle, while only 0.33 mm and 0.39 mm ( P < 0.05) increases in the fracture opening and the fragments' shear movement were observed. The healed bone results revealed that implantation of the titanium nail caused 20.2% reduction in bone stiffness, while the composite nail lowered the stiffness by 11.8% as compared to an intact femur. Interpretation Our results suggest that the composite nail can provide a preferred mechanical environment for healing, particularly in transverse shaft fractures. This may help bioengineers better understand the biomechanics of fracture healing, and aid in the design of effective implants. [ABSTRACT FROM AUTHOR]

Abstract: The focus of this study is to assess, using infrared thermography, the fatigue behavior and the corresponding damage states of a textile polymeric composite plate, as a prerequisite step in the development of damage based life prediction models for such advanced composite materials. Monotonic (quasi-static) loading test results confirmed that the dominant damage mechanism is cracking in the braider yarns, which was monitored using thermographic images and confirmed by edge replication microscopic observations. Fatigue results confirmed that the saturation of braider yarn cracks during cyclic loading corresponded to changes in the stiffness degradation rate as well as the surface temperature profile. This was confirmed by edge replication and scanning electron microscopic analysis. The reported results and observations provide an important step in the validation of thermography as a powerful non-destructive evaluation tool for monitoring the development of fatigue damage as well as predicting the damage states of laminated composite materials in general, and braided polymeric composite materials in particular. [Copyright &y& Elsevier]

The nonsteady internal ballistics of a star-grain solid-propellant rocket motor are investigated through a numerical simulation model that incorporates both the internal flow and surrounding structure. The effects of structural vibration on burning rate augmentation and wave development in nonsteady operation are demonstrated. The amount of damping plays a role in influencing the predicted axial combustion instability symptoms of the motor. The variation in oscillation frequencies about a given star grain section periphery, and along the grain with different levels of burnback, also influences the means by which the local acceleration drives the combustion and flow behaviour. [Copyright &y& Elsevier]

A genetic algorithm (GA) based finite element analysis (FEA) procedure was developed for size and shape optimization of planar and space trusses. The purposed procedure interfaces a binary GA within a FEA software package in order to initially test the applicability and viability of such integration. In addition, special features of the GA were included to dynamically alter the population size, and the crossover and mutation rate in order to facilitate faster convergence and hence reduce the computational effort required. In other words, the GA adapted itself as search and optimization process progressed. The paper also brings a focus on the applicability of integrating a GA as an optimization tool within a FEA software. It was shown by way of many examples––solved by numerous mathematical, as well as other heuristic approaches in the literature––that the purposed methodology is quite efficient and capable of finding lighter and reasonable structural designs than that reported in the literature. Moreover, it is shown that the purposed method removes the immense effort required in coding ones own finite element codes by utilizing already existing finite element software. Nonetheless, it was found that even with a GA, optimization for very large problems was computationally extensive. [Copyright &y& Elsevier]

• Evolved coefficient of friction obtained through calibration of 3D crack growth simulations. • Predicted crack growth trajectory and shape correlate well with fractured fan hubs. • Propagation life estimated from FNK model matches well with test data. • Modified SWT parameter accurately predicts fretting nucleation location and life. The fretting fatigue and crack propagation of an aircraft engine fan dovetail attachment made of Ti-6Al-4V alloy has been numerically modeled and compared with controlled spin test results. The study suggests the fretting-specific modified SWT parameter predicts the nucleation location of the crack more accurately compared to the plain fatigue SWT parameter. The fretting model uses a prescribed coefficient of friction value of 0.7, obtained through calibration of 3D crack growth simulations with the fractured components in regards to crack trajectory, aspect ratio, shape, and propagation life. [ABSTRACT FROM AUTHOR]

A study is conducted with the aim of developing and implementing a fatigue prediction model for assessing the damage tolerance capabilities of polymer matrix composite structures. The damage mechanics based model uses empirical material parameters to represent orthotropic damage evolution. The model accounts for local multiaxial stresses as well as variable amplitude cyclic loading, which may result from local stress redistributions caused by damage evolution. The numerical results show the capability of the developed model to predict the variation of damage evolution and material property degradation in a triaxially braided carbon fiber polymer matrix component. The predictions are validated by independent experiments on composite components using digital image correlation, which shows a strong correlation between the measured and predicted strain contours at various cyclic intervals. This is a key contribution and a step forward in developing a viable design tool for assessing the integrity and durability of composite structures. [ABSTRACT FROM AUTHOR]