An Investigation Into Low Velocity Impact Of 3D Printed Thermoplastic Plates

<div>PolyLactic Acid (PLA) is the most widely used material for 3D printing, especially in industrial applications. PLA is an environment-friendly material as it is biodegradable and has high stiffness and low cost. But PLA shows brittle nature when subjected to out-of-plane loading, i.e. impact. Hence, in this paper, a pendulum impact test apparatus was used to perform impact tests and understand the impact damage characteristics of 3D printed PLA coupons. A high-speed and an infra-red camera were used to investigate the impact damage characteristics of the coupons and understand the failure mechanisms. 24 coupons were printed on a Prusa i3 MK2S 3D printer with a 0° raster angle and different layer thickness. The layer thickness was varied from 0.10 mm to 0.18 mm and the coupons were impacted with 3 J impact energy at two different impact locations, which were, at the center and near the upper clamped edge. For impact at the center of the specimen, the absorbed energy first increased and then decreased and the coupons with higher absorbed energy showed more damage. The absorbed energy was always higher for the coupons impacted at the second location, i.e. near the clamped edge with an only exception in the case of 0.16 mm layer thickness. Coupons with 0.16 mm layer thickness had the highest absorbed energy percentage for the impact to the plate center, however for the impact near the clamped edge, 0.12 mm layer thickness had the highest absorbed energy percentage. Specimens with cracks in the direction perpendicular to the orientation absorb more energy than the specimens with cracks in the direction of extrudates. And specimens with only horizontal or vertical cracks absorb less energy than the coupons with cracks in multiple directions.</div>

An Investigation Into Low Velocity Impact Of 3D Printed Thermoplastic Plates

<div>PolyLactic Acid (PLA) is the most widely used material for 3D printing, especially in industrial applications. PLA is an environment-friendly material as it is biodegradable and has high stiffness and low cost. But PLA shows brittle nature when subjected to out-of-plane loading, i.e. impact. Hence, in this paper, a pendulum impact test apparatus was used to perform impact tests and understand the impact damage characteristics of 3D printed PLA coupons. A high-speed and an infra-red camera were used to investigate the impact damage characteristics of the coupons and understand the failure mechanisms. 24 coupons were printed on a Prusa i3 MK2S 3D printer with a 0° raster angle and different layer thickness. The layer thickness was varied from 0.10 mm to 0.18 mm and the coupons were impacted with 3 J impact energy at two different impact locations, which were, at the center and near the upper clamped edge. For impact at the center of the specimen, the absorbed energy first increased and then decreased and the coupons with higher absorbed energy showed more damage. The absorbed energy was always higher for the coupons impacted at the second location, i.e. near the clamped edge with an only exception in the case of 0.16 mm layer thickness. Coupons with 0.16 mm layer thickness had the highest absorbed energy percentage for the impact to the plate center, however for the impact near the clamped edge, 0.12 mm layer thickness had the highest absorbed energy percentage. Specimens with cracks in the direction perpendicular to the orientation absorb more energy than the specimens with cracks in the direction of extrudates. And specimens with only horizontal or vertical cracks absorb less energy than the coupons with cracks in multiple directions.</div>

Extperimental Characterization of 3D Printed Thermoplastic Plates Subjected To Low Velocity Impact

Poly Lactic Acid (PLA) is a biodegradable material which is being extensively used in industrial applications. Due to its low glass transition temperature and cost, PLA is ideal as a feed stock in 3D printing applications. However, it has a brittle nature which makes it vulnerable to impact loads. In this paper, PLA is used to make 3D printed plates that are impact tested using an in-house low velocity impact test apparatus. A high-speed camera and an infrared thermography system are used to investigate the impact damage properties of the material. The plates manufactured with 0° orientation are used to conduct two different experiments; one with varying energies and the other with varying thickness at two different impact locations, namely at plate’s centre and close to a clamped edge. At 1 J impact energy, the plates showed a tensile crack behaviour (cracks between extrudates) and for 3 J energy it showed a mixed crack behaviour of tensile and shear (cracks along and across extrudates) with more energy dissipations than the 1 J impact. For the 1 J impact, more energy is dissipated at the centre of the plate (42.3%) than the impact close to a clamped edge (32.8%), whereas for the 3 J impact more energy is dissipated near clamped edges (97.1%) compared to the centre of the plate (54.9%). Subsequently, the 3 J impact is used for the second experiment due to the higher energy dissipation. Finally, an experimental study is conducted on plates with varied layer thickness from 0.10 mm to 0.18 mm. Results show that the increase in layer thickness (decrease in number of layers) increases the impact absorption for plates impacted at their centre. For plates impacted near their clamped edge, a zig-zag impact damage pattern of increasing and decreasing magnitudes is observed, but the energy dissipation values are higher than the centre impacted plates.

Extperimental Characterization of 3D Printed Thermoplastic Plates Subjected To Low Velocity Impact

Poly Lactic Acid (PLA) is a biodegradable material which is being extensively used in industrial applications. Due to its low glass transition temperature and cost, PLA is ideal as a feed stock in 3D printing applications. However, it has a brittle nature which makes it vulnerable to impact loads. In this paper, PLA is used to make 3D printed plates that are impact tested using an in-house low velocity impact test apparatus. A high-speed camera and an infrared thermography system are used to investigate the impact damage properties of the material. The plates manufactured with 0° orientation are used to conduct two different experiments; one with varying energies and the other with varying thickness at two different impact locations, namely at plate’s centre and close to a clamped edge. At 1 J impact energy, the plates showed a tensile crack behaviour (cracks between extrudates) and for 3 J energy it showed a mixed crack behaviour of tensile and shear (cracks along and across extrudates) with more energy dissipations than the 1 J impact. For the 1 J impact, more energy is dissipated at the centre of the plate (42.3%) than the impact close to a clamped edge (32.8%), whereas for the 3 J impact more energy is dissipated near clamped edges (97.1%) compared to the centre of the plate (54.9%). Subsequently, the 3 J impact is used for the second experiment due to the higher energy dissipation. Finally, an experimental study is conducted on plates with varied layer thickness from 0.10 mm to 0.18 mm. Results show that the increase in layer thickness (decrease in number of layers) increases the impact absorption for plates impacted at their centre. For plates impacted near their clamped edge, a zig-zag impact damage pattern of increasing and decreasing magnitudes is observed, but the energy dissipation values are higher than the centre impacted plates.

Modal damping ratio of symmetric laminate composite under the effect of attached mass using experimental design

Nowadays, the use of composite materials has taken a large place in civilian industries as well as in military and aerospace industries. Therefore, significant investigations about their mechanical and physical properties are needed. The present study addresses the effect of attached mass on damping ratio of symmetric angle ply laminate composite. Furthermore, factor influencing the effect of attached mass on damping ratio of laminate composite are studied using Taguchi method. The considered factors parameters are: attached mass locations from the clamped edge, stacking sequences and boundary conditions. The results of this study indicate that the damping ratio of the laminate composite plates is sensitive to the attached mass, where the damping ratio is found to be proportional to the locations of the attached mass. The findings of this study indicate that the attached mass decreases frequency parameter and increase the damping ratio of the composite plate, if it is inserted at a point other than a nodal line. In addition, the paper presents a good correlation between the numerical results of the fundamental frequency obtained by the ANSYS software and those obtained experimentally.

A New Analytical Method for Spherical Thin Shells’ Axisymmetric Vibrations

In order to improve the spherical thin shells’ vibrations analysis, we introduce a new analytical method. In this method, we take into consideration the terms of the inertial couples in the stress couples’ differential equations of motion. These inertial couples are omitted in the theories provided by Naghdi–Kalnins and Kunieda. The results show that the current method can solve the axisymmetric vibrations’ equations of elastic thin spherical shells. In this paper, we focus on verifying the current method, particularly for free vibrations with free edge and clamped edge boundary conditions. To check the validity and accuracy of the current analytical method, the natural frequencies determined by this method are compared with those available in the literature and those obtained by a finite element calculation.

An Experimental Investigation of Combined Symmetric-Asymmetric Composite Laminates

It has been found that certain asymmetric composite laminates exhibit bistability, where the composite laminate exhibits multiple stable static equilibrium states. If the bistable composite is actuated, it will snap to its secondary equilibrium state and then remain there without further actuation. This study investigates how the amount of symmetry in a combined symmetric asymmetric rectangular laminate under an imposed clamped edge boundary condition affects the bistability and the curvature of the laminate. Laminates with varying amounts of asymmetry were fabricated and then measured using a profilometer to capture the curvatures of the equilibrium shapes. The results showed that up to 20% symmetry can be introduced in the laminate without a substantial loss in snap through curvature, and that up to 83% symmetry can be introduced in the laminate before bistability is lost. Finite element simulations were conducted in Abaqus and showed good correlation with the experimental results.

A Semianalytical Vibration Analysis of Partially Wet Square Cantilever Plate With Numerical and Experimental Verification: Partially Wet Modeshapes

A semianalytical study of a uniform homogenous partially submerged square cantilever plate vibration is presented. The structure is assumed to be a Kirchhoff's plate, clamped on one edge and free on the other edges. The lengthwise section of the plate is a cantilever clamped-free (CF) beam, while the widthwise section is a free-free (FF) beam. The plate modeshape is a weighted superposition of the product of the beam modeshapes, with unknown weights. The CF beam has only flexural modes. The FF beam has two rigid-body modes, i.e., translational and rotational modes. Rayleigh–Ritz method (RRM) is used to set up the free vibration eigenvalue problem. The eigenvector gives the unknown weights. The modeshapes generated are further used in the boundary element method (BEM) to calculate the fluid inertia, which participates in the vibration and leads to a consistent drop in frequencies. The dependence of this reduction on the submergence level is studied for the first six frequencies of the plate. The frequencies are also experimentally generated by the impact hammer test, both in the dry state, and under three distinct levels of submergence: 25%, 50%, and 75% from the free edge opposite to the clamped edge. The frequencies and modeshapes are also verified through numerical analysis using the commercial code ansys 16.0. Conclusions are drawn regarding the influence of fluid inertia distribution on the final plate modeshape, leading to insights into sound structural designs.

Comparative Study of Post-Buckling Load Redistribution in Stiffened Aircraft Panel With and Without Material Nonlinearity

In this article, a comparative study is presented on the post-buckling load redistribution in stiffened aircraft panels modeled with and without material nonlinearity. In the first part of the study, a baseline stiffened panel is generated for further investigation of the material nonlinearity on the post-buckling behavior and on the effective width of the stiffened panel. In this respect, a stiffener section which provides classical clamped edge condition is designed by matching the compression buckling coefficient determined by the finite element analysis closely with the analytically determined buckling coefficient of the clamped edge panel. Post-buckling analysis of the stiffened panel is then performed utilizing linear and nonlinear material models in the finite element analysis and the effect of material plasticity on the post-buckling behavior of the panel is ascertained. The load distribution in the stiffened panel is investigated just before the buckling of the panel and before the collapse of the panel in the post-buckled stage. The effective widths of the panel are calculated before the collapse of the panel using the load distributions determined by the finite element analyses of the panel models with and without material nonlinearity and comparisons are made with the effective width calculated by the classical effective width formulation. It is shown that material nonlinearity accounts for higher effective width and in general the classical empirical approach gives the smallest effective width.