Dynamic earth pressures against a retaining wall caused by Rayleigh waves

An approximate procedure for studying harmonic soil-structure interaction problems is presented. The presence of Rayleigh waves is considered and the resulting governing equations of the dynamic soil-structure system are solved in the time domain. With this method the transient and steady states of a vibratory motion and also the nonlinear behaviour of the soil can be studied. As an example, the dynamic earth pressure against a rigid retaining wall is investigated. The loads are assumed to be harmonic Rayleigh waves with both static and dynamic surface surcharges. The dependence of the results on the excitation frequency is shown

Seismic earth thrust against massive building walls

The problem of earth thrust for a massive building in a seismic environment is analysed. Intertial and kinematic soil-structure interactions are considered by modelling the soil and the structure together. The problem is solved in the frequency domain by using the computer code FLUSH. Results show that the horizontal component of the seismic earth thrust is much greater than that obtained when applying the Mononobe-Okabe theory. This study establishes a set of conclusicns and recommendations for both design and practical purposes, and proposes future lines of investigation

Los efectos de borde en problemas geotécnicos estáticos analizados por el M.E.F

En el presente artículo se plantea el problema de las condiciones de borde que deben ser consideradas, para los límites laterales de un modelo de elementos finitos, en el caso de que se pretenda analizar un problema geotécnico en condiciones estáticas. Partiendo de las soluciones existentes para el caso de problemas dinámicos de interacción suelo-estructura, los autores demuestran que puede deducirse un nuevo borde aplicable a las condiciones estáticas. Dicho borde se materializa en una matriz de rigidez que interrelaciona entre sí todos los nudos del lado que se considera. La bondad de la solución propuesta, así como la correspondiente a otras condiciones de borde, es estudiada en un problema concreto que dispone de una solución, estableciéndose unas conclusiones particulares respecto al comportamiento de las diferentes condiciones de borde analizadas

Analytical modelling of metallic circular plates subjected to impulsive loads

14 pages, 15 figures.This paper presents an analytical approach to the dynamic response of metallic circular plates subjected to impulsive loads. It is based on the plate energy balance equation and assumes that the plate material behaves viscoplastically. The proposed method permits a consideration of the influence of the different terms of the kinetic energy and the plastic work of the plate. A yield criterion is proposed, which involves the coupled effect of the radial and circumferential internal force resultants. By applying the normality rule, the distribution of the bending moments and membrane forces inside the plate are computed. For model validation, its analytical predictions are compared with experimental results.The authors are indebted to the Comunidad Autónoma de Madrid for the financial support of this work (project 07N/0004/1998).Publicad

An engineering model on penetration of eroding rods into ceramic/polymer composite

6 pages, 3 figures.-- Issue title: "EURODYMAT 2003 - 7th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading" (Porto, Portugal, Sep 8-10, 2003).A new material composed of a polymer matrix loaded with ceramic partiales, at low cost and of higher ballistic efficiency than that of the metallic materials used for armouring applications, is proposed as an alternative to the ceramic tiles traditionally adopted for mixed panels. An engineering model was developed to simulate normal impacts of projectiles against this particulate composite backed by a metallic plate. The equation governing the erosion of projectile and ceramic is that proposed by Tate and Alekseevskii, modifie to consider a moving target. For the volume of particulate composite between the projectile and the metallic plate, an equation was derived to include a momentum balance. For the metallic plate, an energy balance equation was used. When the projectile has eliminated the ceramic/polymer composite and meets the plate, the model of Awerbuch & Bodner is adopted, again modifie to consider a moving target. ln this way, the impact process is described by a set of non-linear differential equations, to be integrated in time. The model was validated with experimental results and with full numerical simulations and showed agreement with both of them.The authors are indebted to the Comunidad Autónoma de Madrid (Project 07N/0004/1998) for the financial support of this work.Publicad

An analytical model for high velocity impacts on thin CFRPs woven laminated plates

15 pages, 12 figures.-- MSC2000 codes: Primary: 74R15; Secondary: 74M20, 74E30, 74K20, 74-05.Zbl#: Zbl 1178.74147An analytical model to study the impact process of a spherical projectile penetrating at high velocity into a carbon/epoxy plain woven laminate is developed in this work. The model is based on an energy balance, where the kinetic energy of the projectile is absorbed by the laminate by three different mechanisms: laminate crushing, linear momentum transfer and tensile fiber failure. A non-homogeneous differential equation is obtained. A subsequent simplification using regular perturbation analysis gives a closed-form solution that allows the approximative calculation of the residual velocity and hence the ballistic limit. The model is validated with the results of experimental tests in which the residual velocity is measured by means of high speed cameras.The authors are indebted to the Comisión Interministerial de Ciencia y Tecnología of Spain for the financial support of this work (Project MAT98-0273).Publicad

Statistical distribution of the estimator of Weibull modulus

3 pages, 3 figures.The Weibull statistic has been widely used to study the inherent scatter existing in the strength properties of many advanced materials, as well as in the fracture toughness of steels in the ductile-brittle transition region.The authors are indebted to the Fundación Ramón Areces (Área de Materiales, IX Concurso Nacional) for its financial support of this research.Publicad

Statistical analysis of the mechanical properties of composite materials

7 pages, 6 figures.The Weibull statistic is currently used in designing mechanical components made of composite materials. This work presents useful formulae to describe the behaviour of the Weibull modulus estimator, which in turn may be described by means of a three-parameter Weibull distribution. Expressions for the parameters of this latter distribution, dependent on the sample size, are also given in the paper, so, the percentage points, published until now in tabular form, may be directly calculated. Empirical expressions are derived for determining the A-basis and the B-basis material properties as a function of the sample size.The authors are indebted to the Fundación Ramón Areces (Área de Materiales, IX Concurso Nacional) for the financial support of this research.Publicad

Compressive residual strength at low temperatures of composite laminates subjected to low-velocity impacts

7 pages, 8 figures.Compression after impact behaviour of different carbon fibre reinforced composite laminates (tape and woven) was studied at low temperatures. Low-velocity impact tests on thin plates at room temperature were made, followed by compression after impact tests at −60°C and −150°C. The results of these tests were compared with those of non-impacted specimens to study the variation of the residual strength at different impact energies. In tape laminates, the lower temperature decreased compression after impact strength, although no influence was detected regarding temperature in the variation of the compressive-strength-retention factor. However, at low temperatures, the woven laminate showed greater strength and a less loss of the retention factor than at room temperature.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT-98/0273) for the financial support of this work.Publicad

Simulación numérica tridimensional de ensayos de fractura dinámica en dispositivos de barra Hopkinson modificada

6 pages, 10 figures.-- Contributed to: "XXI Encuentro del Grupo Español de Fractura" (Punta Umbría, Huelva, Spain, Mar 24-26, 2004).[EN] This work presents a three-dimensional Finite Element analysis of Dynamic three point bending fracture tests performed in a modified Split Hopkinson Pressure Bar, including the projectile, the incident bar, the specimen and the supporting device. The influence of different parameters, such as the specimen thickness, crack length and impact velocity of the projectile on the critical stress intensity factor is analyzed. To obtain the instant at which the crack starts to grow, a local fracture criteria is applied, considering that crack begins its propagation when a critical stress at a characteristic distance of the crack tip is reached. Numerical results show that critical stress intensity factor decreases with specimen thickness, projectile impact velocity and initial crack length.[ES] En este trabajo se presenta un análisis numérico tridimensional, por el método de los Elementos Finitos, de los ensayos de flexión dinámica que se pueden realizar en dispositivos experimentales basados en modificaciones de la barra Hopkinson, incluyendo la modelización del proyectil, la barra incidente, la probeta y su sistema de apoyo. Se analiza la influencia de diferentes parámetros como son el espesor de la probeta, la longitud de la fisura con relación al canto de la probeta y la velocidad de impacto en el valor crítico del factor de intensidad de tensiones. Para obtener dicho valor crítico, se ha utilizado un criterio local de fractura que considera que la fisura progresa de manera inestable cuando se alcanza una tensión crítica a una distancia característica del extremo de la fisura. Los resultados numéricos ponen de manifiesto que el citado valor crítico disminuye a medida que aumenta el espesor de la probeta, la velocidad de impacto del proyectil, y el tamaño de la fisura inicial.Publicad