Víctor Chaves

A constitutive formulation based on a metric in stress space is presented to describe the nonlinear behaviour of UD composites under multiaxial loading. Plastic yielding is interpreted geometrically as the attainment of a critical distance in stress space, measured through a material-dependent metric tensor. This metric induces an equivalent stress that generalizes classical yield measures and provides a unified framework to account for anisotropy and pressure sensitivity. An associated flow rule follows directly from the metric-induced geometry.The formulation is applied to off-axis tension/compression tests on AS4/PEEK composites and to multiaxial transverse compression–shear experiments reported in the literature. The predicted stress–strain responses show good agreement with experimental data under both uniaxial and multiaxial loading paths, capturing the coupling between normal and shear components as well as the pressure-sensitive behaviour of the material. The results suggest that the proposed metric-based formulation provides a consistent and physically transparent description of anisotropic plasticity, without requiring Drucker–Prager-type extensions or non-associated flow rules.

El Método de las Deformaciones Locales es habitualmente utilizado en la industria para calcular la vida de componentes sometidos a cargas de fatiga de bajo número de ciclos. Sin embargo, su aplicación está limitada a cargas uniaxiales. La extensión del método al caso general de cargas multiaxiales, requiere la generalización de las ecuaciones de flujo plástico al caso multiaxial. Este trabajo se basa en un modelo de plasticidad que reproduce el comportamiento plástico estabilizado de metales sometidos a cargas multiaxiales, incorporando todos los ingredientes del Método de las Deformaciones Locales, como curvas cíclicas, ciclos de histéresis o efecto memoria. El modelo está basado en la idea de distancia en el espacio de tensiones, que se calcula a través un tensor métrico. Este tensor está caracterizado por dos constantes para materiales isótropos. Para un material ortótropo, las constantes independientes a determinar son 6. La creciente importancia de materiales no metálicos fabricados por impresión 3D, hace necesaria la reformulación de algunos aspectos importantes de las ecuaciones. En este trabajo se aborda la adaptación del modelo para que sea capaz de recoger el comportamiento de estos materiales, característicamente anisótropo y se propone una metodología que permita su aplicación para materiales no metálicos.

Knowledge of the forces applied to the pedals during cycling is of great importance both from the point of view of improving sporting performance and medical analysis of injuries. The most common equipment for measuring pedal forces is usually limited to the study of forces in the sagittal plane. Equipment that measures three-dimensional forces tends to be bulky and to be incorporated into bicycles that are modified to accommodate it, which can cause the measurements taken to differ from those obtained in real pedalling conditions. This work presents a device for measuring the 3D forces applied to the pedal, attachable to a conventional bicycle and pedals, which does not alter the natural pedalling of cyclists. The equipment consists of four gauges located on the pedal axis and two on the crank, controlled by a microcontroller. Pedal forces measurements were made for six cyclists, with results similar to those shown in the literature. The correct estimation of the lateral-medial direction force is of great interest when evaluating a possible overload at the joints; it will also allow a comparison of the effectiveness index during pedalling, showing the role of this component in this index from a mechanical standpoint.