Haversian canal structures can be associated with size effects in cortical bone

Prediction of periprosthetic failure may be improved by an improved model of bone elasticity which includes microstructural information. Micropolar theory facilitates such information to be included in a continuum model. We assessed the extent of bone’s micropolar behaviour in bending both numerically and experimentally. The numerical model was consistent with micropolar behaviour, and experimental results exhibited size effects that may have been confounded by surface roughness effects, as predicted numerically

Analysis of a typical railway turnout sleeper system using grillage beam analogy

A simplified grillage beam analogy was performed to investigate the behaviour of railway turnout sleeper system with a low value of elastic modulus on different support moduli. This study aimed at determining an optimum modulus of elasticity for an emerging technology for railway turnout application - fibre composites sleeper. The finite element simulation suggests that the changes in modulus of elasticity of sleeper, Esleeper and the sleeper support modulus, Us have a significant influence on the behaviour of turnout sleepers. The increase in Us from 10 to 40 MPa resulted in a 15% reduction in the bending moment while the increase in Esleeper from 1 GPa to 10 GPa has resulted in almost 75% increase in the bending moment. The shear forces in turnout sleepers is not sensitive to both the changes of the Esleeper and Us while the sleeper with low Esleeper tend to undergo greater settlement into the ballast. An Esleeper of 4 GPa was found optimal for an alternative fibre composite turnout sleeper provided that the Us is at least 20 MPa from the consideration of sleeper ballast pressure and maximum vertical deflection. It was established that the turnout sleeper has a maximum bending moment of 19 kN-m and a shear force of 158 kN under service conditions

Mechanical Characterization of Fourth Generation Composite Humerus

Mechanical data on upper extremity surrogate bones, supporting use as biomechanical tools, is limited. The objective of this study was to characterize the structural behaviour of the fourth-generation composite humerus under simulated physiologic bending, specifically, stiffness, rigidity, and mid-diaphysial surface strains. Three humeri were tested in four-point bending, in anatomically defined anteroposterior (AP) and mediolateral (ML) planes. Stiffness and rigidity were derived using load–displacement data. Principal strains were determined at the anterior, posterior, medial, and lateral surfaces in the humeral mid-diaphysial transverse plane of one specimen using stacked rosettes. Linear structural behaviour was observed within the test range. Average stiffness and rigidity were greater in the ML (918 ± 18 N/mm; 98.4 ± 1.9 Nm2) than the AP plane (833 ± 16 N/mm; 89.3 ± 1.6 Nm2), with little inter-specimen variability. The ML/AP rigidity ratio was 1.1. Surface principal strains were similar at the anterior (5.41 µε/N) and posterior (5.43 µε/N) gauges for AP bending, and comparatively less for ML bending, i.e. 5.1 and 4.5 µε/N, at the medial and lateral gauges, respectively. This study provides novel strain and stiffness data for the fourth-generation composite humerus and also adds to published construct rigidity data. The presented results support the use of this composite bone as a tool for modelling and experimentation

The design, kinematics and torque analysis of the self-bending soft contraction actuator

This article presents the development of a self-bending contraction actuator (SBCA) through analysis of its structure, kinematics, and torque formulas, and then explores its applications. The proposed actuator has been fabricated by two methods to prove the efficiency of the human body inspiration, which represents the covering of human bones by soft tissues to protect the bone and give the soft texture. The SBCA provides bending behaviour along with a high force to-weight ratio. As with the simple pneumatic muscle actuator (PMA), the SBCA is soft and easy to implement. Both the kinematics and the torque formula presented for the SBCA are scalable and can be used with different actuator sizes. The bending actuator has been tested under an air pressure up to 500 kPa, and the behaviour of its bending angle, parameters, dimensions, and the bending torques have been illustrated. On the other hand, the experiments showed the efficient performances of the actuator and validate the proposed kinematics. Therefore, the actuator can be used in many different applications, such as soft grippers and continuum arms

On the spectrum of a bent chain graph

We study Schr\"odinger operators on an infinite quantum graph of a chain form which consists of identical rings connected at the touching points by $\delta$-couplings with a parameter $\alpha\in\R$. If the graph is "straight", i.e. periodic with respect to ring shifts, its Hamiltonian has a band spectrum with all the gaps open whenever $\alpha\ne 0$. We consider a "bending" deformation of the chain consisting of changing one position at a single ring and show that it gives rise to eigenvalues in the open spectral gaps. We analyze dependence of these eigenvalues on the coupling $\alpha$ and the "bending angle" as well as resonances of the system coming from the bending. We also discuss the behaviour of the eigenvalues and resonances at the edges of the spectral bands.Comment: LaTeX, 23 pages with 7 figures; minor changes, references added; to appear in J. Phys. A: Math. Theo

Computational modelling and experimental characterisation of heterogeneous materials

Heterogeneous materials can exhibit behaviour under load that cannot be described by classical continuum elasticity. Beams in bending can show a relative stiffening as the beam depth tends to zero, a size effect. Size effects are recognised in higher order continuum elastic theories such as micropolar elasticity. The drawback of higher order theories is the requirement of addition constitutive relations and associated properties that are often difficult to establish experimentally. Furthermore the finite element method, of great benefit in classical elasticity, has shown limitations when applied to micropolar elasticity. The determination of additional constitutive properties and the computational modelling of micropolar elasticity will be discussed in the context of a model heterogeneous material loaded in simple 3 point bending. The model material was created by drilling holes in aluminium bar in a regular pattern, with the hole axis normal to the plane of bending. The bending tests show that a size effect is present. These results are compared against modelling the detailed beam geometries in the finite element package ANSYS, which again shows the size effect. These two bending test are used to extract the additional micropolar elastic material properties. A comparison is then made against analytical solutions,numerical solutions using a micropolar beam finite element and a micropolar plane stress control volume method.It will be shown that the need for extensive experimental testing to determine the additional constitutive properties may not be necessary with the appropriate use of numerical methods

Modelling of SFRC using inverse finite element analysis

A method of inverse finite element analysis is used to determine the constitutive relationship of SFRC in tension, using primary experimental data. Based on beam bending test results and results from pull-out tests, an attempt is made to explain the physical processes taking place during the cracking stage. Basic models predicting the behaviour of SFRC in tension are proposed. © RILEM 2006