J.A. Loya

Torsion of cracked nanorods using a nonlocal elasticity model

This paper presents a nonlocal cracked-rod model from which we have analysed the torsional vibrations of a carbon nanotube with a circumferential crack. Several types of boundary conditions, including the consideration of a buckyball at the end of the nanotube, have been studied. The nonlocal Eringen elasticity theory is used to formulate the problem. The cracked rod is modelled by dividing the cracked element into two segments connected by a torsional linear spring whose stiffness is related to the crack severity. The effect of the nonlocal small-scale parameter, crack severity, cracked section position, different boundary conditions and attached mass are examined in this work.

First order solutions for the buckling loads of weakened Timoshenko columns

In this work, closed-form expressions for the buckling loads of weakened Timoshenko columns with different boundary conditions and shear force approaches (proportional to the bending rotation or to the total slope) are presented. The crack model used promotes discontinuities in both transversal displacements and rotation due to bending. To solve the buckling problem, the perturbation method is used, considering that the solutions for both the cracked and the uncracked columns are slightly different. This procedure leads to first-order closed-form expressions for the buckling loads of the Timoshenko cracked column, which were compared with those found by directly solving the corresponding eigenvalue problem, establishing validity limits for these solutions.

First-Order Solutions for the Buckling Loads of Euler-Bernoulli Weakened Columns

In this work, closed-form expressions for the buckling loads of a weakened column with different boundary conditions are presented. The cracked-column model is based on the well-known method consisting of dividing the column into two segments connected by a rotational linear spring whose flexibility is related to the crack size and the geometry of the cross section. For the formulation of closed-form expressions, the perturbation method is used and the results are compared with those found by directly solving the eigenvalue problem.

Analysis of high-speed impact problems in the aircraft industry

The high cost of the energy needed to propel aircraft and ground vehicles has meant that reducing the weight in these systems is vital in order to reduce operational costs. This factor has a significant influence on the design of structures in the aeronautical industry and more recently in others such as high-speed rail networks and road haulage. This is a particularly sensitive issue for the civil aviation industry, given that the cost of fuel is one of the main expenses incurred by passenger airlines. Bearing in mind that fuel represents up to 40% of the total weight of an aircraft, a reduction of its weight results in a concurrent reduction in the amount of fuel needed as well as a significant reduction of the gross weight taken into account.

Numerical analysis of the brittle-ductile transition in the failure-mode in polymeric materials

In this paper we analyze, using the Finite Element Method, the process of brittle-ductile transition in the failure mode observed in polycarbonate notched specimens under impact loads. In order to analyze this transition we have implemented, through a user subroutine, a damage model which combines a tensional fracture criterion and an energetic, acting simultaneously. The competition between both criteria predicts the difference in material behavior from a critical impact velocity, and how this transition is produced on different planes through the thickness of the specimen. These results show the necessity of employing three-dimensional models for its study.

Numerical analysis for design of bioinspired ceramic modular armors for ballistic protections

The exigent requirements for personal protections in terms of energy absorption and ergonomics have led to increasing interest in bioinspired protections. This work focuses on the numerical analysis of ballistic behavior of different bioinspired geometries under impact loadings. Ceramic armors based on ganoid fish scales (the type exhibited by gars, bichirs and reedfishes), placoid fish scales (characterizing sharks and rays) and armadillo natural protection have been considered. Different impact conditions are studied, including perpendicular and oblique impacts to surface protection, different yaw angle, and multiple impacts. Main conclusion is related to the improved efficiency of modular armors against multiple shots exhibiting more localized damage and crack arrest properties. Moreover, its potential ergonomic is a promising characteristic justifying a deeper study.

Numerical Modeling of Post-Processing of Composite Materials

This paper focuses on learning about post-processing of composite materials in the current context of Manufacturing Engineering education in Spain. The use of composites has been significantly increased in different sectors in industry during the last decades. The students,taking manufacturing courses in engineering study plans, need basic formation concerning post-processing of composites. Due to the complexity of the process, powerful numerical tools are needed to develop practical models focused on damage prediction. Learning skills include modeling of anisotropic materials and specific concepts of composite such as machining induced damage.