Characterization of the translaminar cohesive law

Characterization of the translaminar cohesive law

Last April 20th, the AMADE’s researcher Adrián Ortega got his PhD in Technology for the research work titled:

Characterization of the translaminar cohesive law

Advisors: Dr. Pere Maimí and Dr. Emilio V. González

Description

The outstanding stiffness and strength properties, with respect to their weight, of fibre-reinforced polymers have led to an increase of their usage in structures that needed a weight reduction. This has been specially the case of the aerospace industry, where the use of light materials has a significant effect on the fuel consumption of aircraft structures, resulting in two direct benefits: first reducing the economic costs of flights, and second, reducing the gas emission that causes the greenhouse effect.

When a fibre-reinforced composite laminate is subjected to traction or compression, they develop a relatively large Fracture Process Zone where material toughening mechanisms such as matrix cracking, fibre-bridging and fibre pull-outs take place. The damage onset and damage propagation are well defined from a cohesive model point of view, although no standard procedure has been yet developed to characterize the translaminar Cohesive Law. The present Ph.D. thesis proposes an objective inverse method for obtaining the Cohesive Law from a single Compact Tension test.

Firstly, a semi-analytic model has been developed for a Compact Tension specimen subjected to a controlled displacement and corresponding load within a cohesive model framework. The model is able to capture the material response while the Fracture Process Zone is being developed, obtaining the evolution of multiple variables such as the crack opening and the cohesive stresses, for any given arbitrary Cohesive Law shape.

Secondly, with the aid of the aforementioned model, an algorithm has been developed capable of obtaining the translaminar Cohesive Law from a single Compact Tension test. The methodology to solve the inverse problem consists on defining a piecewise unknown Cohesive Law. The segments widths and slopes are found in order to best fit the experimental curve.

Lastly, the proposed inverse problem method has been used to perform an in-depth discussion of the Cohesive model. First, the Cohesive Law has been measured for several interplay hybrid laminates, in order to study the influence of the stacking sequence on the resulting curve. Secondly, the method has been applied to show the invariability of the obtained Cohesive Law for different geometries and specimen sizes.

Members of the panel

  • Professor Lars Berglund, KTH Royal Institute of Technology, Sweden (President).
  • Dr Xiaodong Xu, University of Bristol, United Kingdom (Vocal).
  • Professor Josep Costa Balanzat, University of Girona, Spain (Secretary).

 

Publications

  • A. Ortega, P. Maimí, E.V. González, J.R. Sainz de Aja, F. de la Escalera, P. Cruz,Translaminar fracture toughness of interply hybrid laminates under tensile and compressiveloads, Composites Science and Technology, Volume 143, 2016, Pages 1-12.
  • A. Ortega, P. Maimí, E.V. González, D. Trias, Specimen geometry and specimen sizedependence of the R-curve and the Size Effect Law from a Cohesive Model point of view,International Journal of Fracture, Volume 205 (2), 2016, Pages 239-254.
  • A. Ortega, P. Maimí, E.V. González, D. Trias, Characterization of the translaminarfracture Cohesive Law, Composites Part A: Applied Science and Manufacturing, Volume 91,2016, Pages 501-509.
  • A. Ortega, P. Maimí, E.V. González, Ll. Ripoll, Compact   tension   specimen   fororthotropic materials, Composites Part A: Applied Science and Manufacturing, Volume 63,2014, Pages 85-93.