## The idea

CoDeAn was born from the idea to create a tool for students to quickly familiarize themselves with basic theories in the field of structural mechanics of composite laminates. The majority of composite structures used in engineering applications are laminated plates. These plates are made by stacking different material layers, or plies, on top of one another. In structural mechanics many theories have been developed to allow the analysis of such non-isotropic laminated plates. One well-known theory is called 'classical laminated plate theory' with which the stiffness (ABD) and compliance (abd) matrix of the laminate are calculated as well as the equivalent stiffness properties (Young's modulus, shear modulus, Poisson's ratio). Other theories focus on defining failure criteria with first-ply failure generally referred to as maximum stress failure, maximum strain failure, Tsai-Hill, Tsai-Wu and Hashin-Rotem failure theory. Finally, a third crucial aspect when designing composite plates is the buckling behavior of the plate under different boundary conditions and applied loads. The aim of CoDeAn is to allow you to quickly perform the calculations done in aforementioned theories and thereby assist students or structural engineers in grasping these theories and use the results for designing composite structures.

## Theoretical background

The theories used in the calculations of CoDeAn are not described in the app, however, all calculations are based on the theories described in the book 'Design and Analysis of Composite Structures' by dr. Christos Kassapoglou. The different sections in the app have references to the associated sections where elaborate explanations in the book can be found.

## The app

CoDeAn was developed with support from the chair of Aerospace Structures and Materials at TU Delft and the app consists of two libraries and four analysis modules. The first library is the material library. In this library the user can define the different materials, or plies, that are stacked in the laminated plates by storing their stiffness and strength properties thereby creating a database of ply materials. The second library is the laminate library and in this library different laminated plates can be defined by combining the plies from the material library in any specific order thereby creating a database of laminated plates. Subsequently, the laminates in this database can be used in the analysis modules.

The first analysis module is called 'Laminated-plate theory' and it allows you to quickly see the results of calculations performed in classical laminated-plate theory. All analysis modules can be used in two ways: either you can inspect a complete and detailed results overview for individual laminates or you can compare specific values for a set of laminates in interactive bar plots. So in the laminated-plate theory module you could either inspect the complete ABD-matrix, compliance matrix and equivalent stiffness properties of a single laminate or you can create bar plots to compare, for example, the A(1,1) values of different laminates.

The second and third analysis modules are called 'Strength check' and 'Strength determination' and these modules focus on the calculation of first-ply failure criteria. With the strength check module you can define the loads exerted on the laminate and quickly see whether the laminate fails according to the different failure criteria. In the strength determination module you only have to define the ratio between the different loads on the laminate and the module will determine the strength of the laminate according to the different failure theories. For example, you could define a load ratio where you have tension in x-direction plus twice that load for compression in y-direction and the module will provide you with the load combination at which the laminate fails. Just like the laminated-plate theory module you can either inspect the results for different laminates or create bar plots to compare the strengths of different laminates.

The fourth and last analysis module in CoDeAn is the 'Plate buckling' module. In this module you can define a plate and choose from a list of eleven combinations of boundary conditions and applied loads and let the app determine the critical buckling load for you. Again you either inspect detailed buckling analysis results for individual laminates, including the amount of half waves associated with the critical buckling load, or you can compare the buckling loads of different laminates in interactive bar plots.

A final feature of CoDeAn is the incorporated help section in every screen of the app. You can hide/unhide the help section by swiping from below the navigation bar (similar to the navigation centre) and the section will have both tips on how to use the section you are currently in as well as references to relevant sections in the book for more theoretical background.

The first analysis module is called 'Laminated-plate theory' and it allows you to quickly see the results of calculations performed in classical laminated-plate theory. All analysis modules can be used in two ways: either you can inspect a complete and detailed results overview for individual laminates or you can compare specific values for a set of laminates in interactive bar plots. So in the laminated-plate theory module you could either inspect the complete ABD-matrix, compliance matrix and equivalent stiffness properties of a single laminate or you can create bar plots to compare, for example, the A(1,1) values of different laminates.

The second and third analysis modules are called 'Strength check' and 'Strength determination' and these modules focus on the calculation of first-ply failure criteria. With the strength check module you can define the loads exerted on the laminate and quickly see whether the laminate fails according to the different failure criteria. In the strength determination module you only have to define the ratio between the different loads on the laminate and the module will determine the strength of the laminate according to the different failure theories. For example, you could define a load ratio where you have tension in x-direction plus twice that load for compression in y-direction and the module will provide you with the load combination at which the laminate fails. Just like the laminated-plate theory module you can either inspect the results for different laminates or create bar plots to compare the strengths of different laminates.

The fourth and last analysis module in CoDeAn is the 'Plate buckling' module. In this module you can define a plate and choose from a list of eleven combinations of boundary conditions and applied loads and let the app determine the critical buckling load for you. Again you either inspect detailed buckling analysis results for individual laminates, including the amount of half waves associated with the critical buckling load, or you can compare the buckling loads of different laminates in interactive bar plots.

A final feature of CoDeAn is the incorporated help section in every screen of the app. You can hide/unhide the help section by swiping from below the navigation bar (similar to the navigation centre) and the section will have both tips on how to use the section you are currently in as well as references to relevant sections in the book for more theoretical background.