Laser shock peening treatment to control and moderate fatigue crack growth in aircraft structure based on residual stress engineering approach

Laser Shock Peening (LSP) is a surface enhancement treatment which induces a significant layer of beneficial compressive residual stresses of up to several mm underneath the surface of metal components in order to improve the detrimental effects of the crack growth behavior rate in it. The aim of this thesis is to predict the crack growth behavior in metallic specimens with one or more stripes which define the compressive residual stress area induced by the Laser Shock Peening treatment. The process was applied as crack retardation stripes perpendicular to the crack propagation direction with the object of slowing down the crack when approaching the peened stripes. The finite element method has been applied to simulate the redistribution of stresses in a cracked model when it is subjected to a tension load and to a compressive residual stress field, and to evaluate the Stress Intensity Factor (SIF) in this condition. Finally, the Afgrow software is used to predict the crack growth behavior of the component following the Laser Shock Peening treatment and to detect the improvement in the fatigue life comparing it to the baseline specimen. An educational internship at the “Research & Technologies Germany – Hamburg” department of AIRBUS helped to achieve knowledge and experience to write this thesis. The main tasks of the thesis are the following: •To up to date Literature Survey related to “Laser Shock Peening in Metallic Structures” •To validate the FE model developed against experimental measurements at coupon level •To develop design of crack growth slowdown in Centered Cracked Tension specimens based on residual stress engineering approach using laser peened strip transversal to the crack path •To evaluate the Stress Intensity Factor values for Centered Cracked Tension specimens after the Laser Shock Peening treatment via Finite Element Analysis •To predict the crack growth behavior in Centered Cracked Tension specimens using as input the SIF values evaluated with the FE simulations •To validate the results by means of experimental tests

Effects of the inclusion of microalgae spirulina (Spirulina platensis) in the diet of Gilthead Sea bream (Sparus aurata) on growth and metabolism

In gilthead seabream aquaculture, the feed supplies in the market is very expensive due to its high content of animal protein. In this respect, spiruline appears to be a valuable substitute to animal and vegetable protein. In this study we performed two experiments. The scope of the first one was to determine the effect of the inclusion of Spirulina platensis hydrolyzed on the physiological state and growth in juveniles of Sparus aurata. A total of 180 individuals were fed for 128 days with three different feeds: control diet, diet with 2% of hydrolyzed microalgae (Sp2), and diet with 4% of hydrolyzed microalgae (Sp4).The experimental groups were tested in triplicate (except control group that was in duplicate). Biometric parameters were registered every two or three weeks. At the end of the experiment blood samples were collected to analyze plasma metabolites. After this we tried to evaluate the anti-oxidant response in animals remained from the first experiment using a toxicological assay with sodium nitrite lasting three days. Fish were divided into control, Spi 2% and Spi 4%, all them with and without NaNO2. Even then, the plasma metabolites data were collected after 24h and 72h. At the end of the first experiment the administration of S. platensis appeared to have a negative impact on growth of S. aurata respect the control feed. Furthermore, the lactate content registered showed a significant difference between the control and the spiruline administration. In the second experiment the spiruline feed showed a glucose and a lactate content with significant differences after 72h of exposition to nitrites respect the control group due to the interaction between nitrites and treatment. S. platensis hydrolyzed 2% and 4% do not seems a good substitution for S. aurata both as a growth enhancer and improver of health metabolic pathways. Its role as a good antioxidant has not been confirmed in these experiments.