Fatigue behavior of 316L steel structural lattice beams under four-points-bending symmetric cyclic loading

FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING ICCS27 27th International Conference on Composite Structures Ravenna 3-6 September 2024 Antonio Coluccia* Giorgio De Pasquale Dept. of Mechanical and Aerospace Engineering Politecnico di Torino –Italy *[email protected] Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING PoliTo –Smart Structures and System Lab Topics Structures/Microstructures and Systems characterized by: •Lightweight •Multi-functionality •Integration •Innovative materials and processes Skills •Design and analytic modelling •Numerical simulation •Experimental characterization Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING Objectives •Development of an efficient method for the fatigue failure analysis of lattice component •Application of the method to the investigated case study: the 4-points-bending test •Experimental validation tests Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING Lattice structures Lattice structures have been gaining much attention in the last decades due to their good mechanical properties and their functionality From Ying et al., Aerosp. Sci. Technol. (2019) From De Pasquale et al., P. I. Mech. Eng. C-J Mec. (2019) Application fields for lattice structures: •Lightweight (panels, energy absorbers) •Biomedical (osseointegration) •Thermal insulation, heat management From Zargarian et al., Theor. Appl. Fract. Mech. (2019) Fatigue failure analysis of lattices also highly investigated: •Development of computational models •Adaptation of fracture mechanics models to lattices •Fatigue experimental campaigns aimed at evaluating performances Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING Method The method for the fatigue failure analysis of lattice structures here presented is composed of different steps: 1. Homogenization of the lattice RVE 2. Simulation of the component with the medium material in place of the actual lattice employing loads coincident with the alternate force the component is subject to during the fatigue tests 3. Most critical lattice cell identification through a strain-based criterion 4. De-homogenization of the critical RVE and retrieving of the original stress configuration of the critical lattice cell Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING Case study: 4-points-bending test The method is applied to the case study of the 4-points-bending fatigue test •The sample is designed for fully reversed fatigue: 𝑅 = Τ 𝜎𝑚𝑖𝑛 𝜎𝑚𝑎𝑥 = −1 •Lattice is only present in the middle section of the sample, where the momentum is maximum •Side supports are only necessary in order to let the momentum grow from zero to its max •A certain number of lattice cell is present in the vertical direction of the sample in order to study the effects of the momentum along the thickness and an eventual grading application in the future Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING 1. Homogenization First step of the method is the application of the homogenization to the lattice RVE involved in the analysis x/y/z xy/yz/xz Equivalent orthotropic properties 𝐸𝑋 𝐸𝑌 𝐸𝑍 𝐺𝑋𝑌 𝐺𝑌𝑍 𝐺𝑋𝑍 𝜈𝑋𝑌 𝜈𝑌𝑍 𝜈𝑋𝑍 •A finite element model of the single lattice RVE is defined •A routine for the cell geometry parametrization has been used •Six static simulations with unitary strain are performed on the RVE •Necessary for the definition of the equivalent mechanical property in one direction/plane •Equivalent mechanical properties extracted through an output routine •To be used for the definition of an orthotropic material medium Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING 2. Simulation of the component Once the medium material is defined, it is possible to perform the static simulation on which is based the method: The load applied is equal to the alternate force FA FA F t Boundary conditions and geometry of the model are in line with the sample manufactured for the experimental tests The middle section of the sample, where the lattice is placed, now presents the medium material with the properties achieved through homogenization Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING 3. Definition of the most critical element / RVE Itis now possible to identify the most critical lattice cell through a strain-based criterion (element = cell) For every element of the lattice medium material part, the norm of the strain tensor is evaluated: The element presenting the maximum 𝜀is recognized as the critical one For the case study considered in this investigation, the critical element is placed at almost 1/3 of the lattice section Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING Conclusions •Acomputationally advantageous method for the fatigue failure analysis of lattice structures has been successfully applied to a 4-points bending test case study •The method offers a simple way to recognize the point from where the fracture defining the failure is going to generate •According to the fatigue failure criterion later employed, different information can be extracted from the de-homogenized RVE analysis Future work: •In order to predict the fatigue life of a lattice component based on fatigue tests performed on bulk material, correcting coefficients need to be furtherly investigated THANK YOU FOR YOUR ATTENTION ICCS27 27th International Conference on Composite Structures Ravenna 3-6 September 2024 Antonio Coluccia Giorgio De Pasquale Dept. of Mechanical and Aerospace Engineering Politecnico di Torino –Italy Antonio Coluccia - FATIGUE BEHAVIOR OF 316L STEEL STRUCTURAL LATTICE BEAMS UNDER FOUR-POINTS-BENDING SYMMETRIC CYCIC LOADING Contact 18 Smart Structures and Systems Lab Politecnico di Torino www.s3laboratory.com [email protected] Antonio Coluccia