http://hdl.handle.net/10016/7174 Wed, 22 May 2013 04:39:31 GMT 2013-05-22T04:39:31Z http://e-archivo.uc3m.es:80/retrieve/29783/dptomcte copia.jpg http://hdl.handle.net/10016/7174 http://hdl.handle.net/10016/16718 Title: Influence of shear plugging in the energy absorbed by thin carbon-fibre laminates subjected to high-velocity impacts Author(s): Buitrago, Brenda L.; García-Castillo, Shirley K.; Barbero, Enrique Abstract: This work examines the energy-absorption process in thin woven laminates made from carbon fibres, with the aim of analysing the energy employed in the formation of a shear plug. This study was conducted with a simplified model which considered five energy-absorption mechanisms. The model was validated with experimental tests and numerical simulations, with regard to the residual velocity of the projectile and perforation velocity. The model makes it possible to evaluate the influence of the shear plugging in laminates of different thickness. It has been demonstrated that this energy-absorption mechanism needs to be considered in the analysis. The main energy-absorption mechanisms for impact at low velocity (i.e. below the perforation velocity) are related to the elastic deformation of fibres and shear plugging, whereas when a higher impact velocity is considered (i.e. above the perforation velocity) such mechanisms are related to the acceleration field of the laminate and the shear plugging. Mon, 31 Dec 2012 23:00:00 GMT http://hdl.handle.net/10016/16718 2012-12-31T23:00:00Z http://hdl.handle.net/10016/15849 Title: A dislocation-based constitutive description for modeling the behavior of FCC metals within wide ranges of strain rate and temperature Author(s): Rodríguez-Martínez, José Antonio; Rodríguez-Millán, Marcos; Rusinek, Alexis; Arias, Ángel Abstract: In this work a dislocation based constitutive description for modeling the thermo visco plastic behavior of FCC metals has been developed. The constitutive description, which is founded on the concepts of thermal activation analysis and dislocation dynamics, assumes the plastic flow additively decomposed into internal stress and effective stress. The internal stress represents the applied stress required for the transmission of plastic flow between the polycrystal grains and it is defined by the Hall Petch relationship. The effective stress formulation, which is the main innovative feature of this work, represents the thermally activated deformation behavior. This is defined taking into account the interrelationship between strain rate and temperature, and gathers structural evolution dependence. This structural evolution is described as a function of dislocations density, which acts as internal state variable in the material deformation behavior. A systematic procedure for identifica tion of the material parameters is developed and the model is applied to define the behav ior of annealed OFHC copper. The analytical predictions of the constitutive description are compared with the experimental data reported by Nemat Nasser and Li (Nemat Nasser, S., Li, Y., (1998). Flow stress of FCC polycrystals with application to OFHC Copper. Acta Mater. 46, 565 577). Good correlation between experiments and analytical predictions is found within wide ranges of strain rate and temperature. Wed, 30 Nov 2011 23:00:00 GMT http://hdl.handle.net/10016/15849 2011-11-30T23:00:00Z http://hdl.handle.net/10016/15847 Title: Dynamic fracture-initation toughness determination of AI 7075-T651 aluminum alloy Author(s): Loya, José Antonio; Fernández-Sáez, José Abstract: We present values of the static and dynamic fracture-initiation toughness at different loading rates of the aluminum alloy Al 7075-T651 obtained on three-point bend specimens with different thicknesses and initial crack lengths. In static conditions, the critical stress intensity factor was measured according to well known procedures. The methodology of dynamic fracture initiation toughness is not yet standardized, and the dynamic tests were done with a modified Hopkinson pressure bar coupled to high-speed cameras to measure the crack mouth opening displacement CMOD of the specimens. The critical stress intensity value was obtained from the CMOD at the time that crack starts to grow. This instant was detected by means of crack gauges at the crack tip. Sun, 31 Dec 2006 23:00:00 GMT http://hdl.handle.net/10016/15847 2006-12-31T23:00:00Z http://hdl.handle.net/10016/15845 Title: Delamination prediction in orthogonal machining of carbon long fiber-reinforced polymer composites Author(s): Santuiste, Carlos; Olmedo, Álvaro; Soldani, Xavier; Miguélez, Henar Abstract: Machining processes of composites are common operations in industry involving elevated risk of damage generation in the workpiece. Long fiber reinforced polymer composites used in high-responsibility applications require safety machining operations guaranteeing workpiece integrity. Modeling techniques would help in the improvement of machining processes definition; however, they are still poorly developed for composites. The aim of this paper is advancing in the prediction of damage mechanisms involved during cutting, including out-of-plane failure causing delamination. Only few works have focused on three-dimensional simulation of cutting; however, this approach is required for accurate reproduction of the complex geometries of tool and workpiece during cutting processes. On the other hand, cohesive interactions have proved its ability to simulate out-of-plane failure of composites under dynamic loads, as impact events. However, this interlaminar interaction has not been used up to date to model out-of-plane failure induced during chip removal. In this paper, both a classical damage model and cohesive interactions are implemented in a three-dimensional model based on finite elements, in order to analyze intralaminar and interlaminar damage generation in the simplified case of orthogonal cutting of carbon LFRP composite. More realistic damage predictions using cohesive interactions were observed. The strong influence of the stacking sequence on interlaminar damage has been demonstrated. Sat, 30 Jun 2012 22:00:00 GMT http://hdl.handle.net/10016/15845 2012-06-30T22:00:00Z