New anatomical reference systems for the bones of the foot and ankle complex: definitions and exploitation on clinical conditions

Background A complete definition of anatomical reference systems (ARS) for all bones of the foot and ankle complex is lacking. Using a morphological approach, we propose new ARS for these bones with the aim of being highly repeatable, consistent among individuals, clinically interpretable, and also suited for a sound kinematic description. Methods Three specimens from healthy donors and three patients with flat feet were scanned in weight-bearing CT. The foot bones were segmented and ARS defined according to the proposed approach. To assess repeatability, intra class coefficients (ICC) were computed both intra- and inter-operator. Consistency was evaluated as the mean of the standard deviations of the ARS position and orientation, both within normal and flat feet. Clinical interpretability was evaluated by providing a quantification of the curvature variation in the medial-longitudinal and transverse arches and computing the Djiann-Annonier angle for normal and flat feet from these new ARS axes. To test the capability to also provide a sound description of the foot kinematics, the alignment between mean helical axes (MHA) and ARS axes was quantified. Results ICC was 0.99 both inter- and intra-operator. Rotational consistency was 4.7 ± 3.5 ° and 6.2 ± 4.4° for the normal and flat feet, respectively; translational consistency was 4.4 ± 4.0 mm and 5.4 ± 2.9 mm for the normal and flat feet, respectively. In both these cases, the consistency was better than what was achieved by using principal axes of inertia. Curvature variation in the arches were well described and the measurements of the Djiann-Annoier angles from both normal and flat feet matched corresponding clinical observations. The angle between tibio-talar MHA and ARS mediolateral axis in the talus was 12.3 ± 6.0, while the angle between talo-calcaneal MHA and ARS anteroposterior axis in the calcaneus was 17.2 ± 5.6, suggesting good capability to represent joint kinematics. Conclusions The proposed ARS definitions are robust and provide a solid base for the 3-dimensional description of posture and motion of the foot and ankle complex from medical imaging.

Damage Detection and Localization on Real Structures Subjected to Strong Motion Earthquakes Using the Curvature Evolution Method: The Navelli (Italy) Case Study

In recent years, structural health monitoring (SHM) has received increasing interest from both research and professional engineering communities. This is due to the limitations related to the use of traditional methods based on visual inspection for a rapid and effective assessment of structures and infrastructures when compared with the great potential offered by newly developed automatic systems. Most of these kinds of systems allow the continuous estimation of structural modal properties that are strictly correlated to the mechanical characteristics of the monitored structure. These can change as a result of material deterioration and structural damage related to earthquake shaking. Furthermore, a suitable configuration of a dense sensor network in a real-time monitoring system can allow to detect and localize structural and non-structural damage by comparing the initial and a final state of the structure after a critical event, such as a relevant earthquake. In this paper, the modal curvature evaluation method, used for damage detection and localization on framed structures, considering the mode curvature variation due to strong earthquake shaking, is further developed. The modified approach is validated by numerical and experimental case studies. The extended procedure, named “Curvature Evolution Method” (CEM), reduces the required computing time and the uncertainties in the results. Furthermore, in this work, an empirical relationship between curvature variation and damage index has been defined for both bare and infilled frames.

Using Fuzzy Control for Feed Rate Scheduling of Computer Numerical Control Machine Tools

In industrial processing, workpiece quality and processing time have recently become important issues. To improve the machining accuracy and reduce the cutting time, the cutting feed rate will have a significant impact. Therefore, how to plan a dynamic cutting feed rate is very important. In this study, a fuzzy control system for feed rate scheduling based on the curvature and curvature variation is proposed. The proposed system is implemented in actual cutting, and to verify the data an optical three-dimensional scanner is used to measure the cutting trajectory of the workpiece. Experimental results prove that the proposed fuzzy control system for dynamic cutting feed rate scheduling increases the cutting accuracy by 41.8% under the same cutting time; moreover, it decreases the cutting time by 50.8% under approximately the same cutting accuracy.

Residual stresses developed in thermoplastic composites during laser-assisted tape laying

The main focus of the study is the determination of residual stresses developed in thermoplastic composites during tape placement. An experimental characterization of the residual stresses is carried out and based on the measurement of the curvature variation with temperature for unsymmetrical laminates. The tested plates are made of APC-2 and processed on the SPIDE-TP, a filament winding machine based in Cetim, France. A thermo-mechanical model based on the modified laminate theory is used in this work. Heat transfer and crystallization are taken into account in the model, allowing the description of the evolution of the mechanical properties of the composite during the whole process. The model is able to predict the residual stresses present at the end of the process. The results showed stress gradients through the thickness of the laminates where the transverse residual stresses can reach up to 20 MPa. In addition, the results showed that increasing the mandrel temperature reduces the crystallization and thermal gradients in the laminate thickness.

A New Approach for the Control and Reduction of Warpage and Residual Stresses in Bonded Wafer

A geometrical modification on silicon wafers before the bonding process, aimed to decrease (1) the residual stress caused by glass frit bonding, is proposed. Finite element modeling showed that (2) by introducing this modification, the wafer out-of-plane deflection was decreased by 34%. Moreover, (3) fabricated wafers with the proposed geometrical feature demonstrated an improvement for the (4) warpage with respect to the plain wafers. A benefit for curvature variation and overall shape of the (5) bonded wafers was also observed.

Using Fuzzy Control for Feedrate Scheduling of Computer Numerical Control Machine Tools

In industrial processing, workpiece quality and processing time have become important issues lately. Fortunately, dynamic cutting feedrate scheduling has been proposed to improve machining accuracy and decrease cutting time. Studies have shown that the curvature and cutting feedrate significantly influence the machining accuracy. Therefore, the present study proposes a fuzzy control system for feedrate scheduling based on the curvature and curvature variation. The proposed system is implemented in actual cutting, and an optical three-dimensional scanner is performed as a verification to measure the cutting trajectory of the workpiece. Experimental results prove that the proposed fuzzy control system for dynamic cutting feedrate scheduling increases the cutting accuracy by 43% under the same cutting time; moreover, it decreases the cutting time by 49% under the same cutting accuracy.

Structural Damage Identification Based on Principal Curvatures of Mode Shape

This paper presents a procedure for damage identification and characterization on plates, based on the principal curvatures of their first mode shape. Each mode shape represents the displacement of the structure at its corresponding natural frequency. Since, variations in the geometry due to cracks or material property degradation, make changes in the mode shapes of the structure, such changes can be used for damage identification methods. The presented procedure only requires the first mode shape of the intact and damaged structure. It is shown that the principal curvatures of the surface defined by the first mode shape of the structure, are sensitive to damage and the maximum principal curvature can be used to highlight damages on the structure. The performance of the developed method is firstly evaluated using finite element analysis. To this aim, the procedure is applied to highlight both single and multi-damages in different locations of the plate with different boundary conditions. It is shown that the location of the maximum curvature variation coincides well with the location of damages and the amount of the maximum curvature change can be used as a parameter to describe damage severity. The accuracy of the proposed method is also experimentally verified by test on an aluminum plate and it is demonstrated that the proposed method remains effective even in experimental condition when only a limited number of measurements are available.

Parametric Blending of Hole Patches Based on Shape Difference

A triangular mesh obtained by scanning 3D models typically contains holes. We present an effective technique for filling a hole in a triangular mesh in geometric modeling. Simple triangulation of a hole is refined and remeshed iteratively to generate an initial patch. The generated patch is then enhanced to become a target patch by minimizing the variation of principal curvatures. In discrete approximation, this produces a third-order Laplacian system of sparse symmetric positive definite matrix, and the symmetry can efficiently be used to find the robust solutions to the given Laplacian system. Laplacian smoothing of the target patch is defined as a source patch. The shape difference between two corresponding vertices of the source and the target patches is measured in terms of Euclidean distance and curvature variation. On the basis of the shape difference and a user-specified control parameter, different blending weights are determined for each vertex, and the final patch is generated by blending two patches. We demonstrate the effectiveness of our technique by discussing several examples. The experimental results show that our technique can effectively restore salient geometric features of the original shape.

Finite Beam Element for Curved Steel–Concrete Composite Box Beams Considering Time-Dependent Effect

Curved steel–concrete composite box beams are widely used in urban overpasses and ramp bridges. In contrast to straight composite beams, curved composite box beams exhibit complex mechanical behavior with bending–torsion coupling, including constrained torsion, distortion, and interfacial biaxial slip. The shear-lag effect and curvature variation in the radial direction should be taken into account when the beam is sufficiently wide. Additionally, long-term deflection has been observed in curved composite box beams due to the shrinkage and creep effects of the concrete slab. In this paper, an equilibrium equation for a theoretical model of curved composite box beams is proposed according to the virtual work principle. The finite element method is adopted to obtain the element stiffness matrix and nodal load matrix. The age-adjusted effective modulus method is introduced to address the concrete creep effects. This 26-DOF finite beam element model is able to simulate the constrained torsion, distortion, interfacial biaxial slip, shear lag, and time-dependent effects of curved composite box beams and account for curvature variation in the radial direction. An elaborate finite element model of a typical curved composite box beam is established. The correctness and applicability of the proposed finite beam element model is verified by comparing the results from the proposed beam element model to those from the elaborate finite element model. The proposed beam element model is used to analyze the long-term behavior of curved composite box beams. The analysis shows that significant changes in the displacement, stress and shear-lag coefficient occur in the curved composite beams within the first year of loading, after which the variation tendency becomes gradual. Moreover, increases in the central angle and shear connection stiffness both reduce the change rates of displacement and stress with respect to time.