The effect of honeycomb relative density on its effective in-plane elastic moduli: An experimental study

2008 ◽  
Vol 84 (4) ◽  
pp. 293-299 ◽  
Author(s):  
S. Balawi ◽  
J.L. Abot
Keyword(s):  
Experimental Study ◽  
Relative Density ◽  
Elastic Moduli

Fountains impinging on a density interface

2008 ◽  
Vol 595 ◽  
pp. 115-139 ◽  
Author(s):  
JOSEPH K. ANSONG ◽  
PATRICK J. KYBA ◽  
BRUCE R. SUTHERLAND
Keyword(s):  
Experimental Study ◽  
Relative Density ◽  
Constant Velocity ◽  
Gravity Current ◽  
Return Flow ◽  
Experimental Measurements ◽  
Ambient Fluid ◽  
Initial Momentum ◽  
Front Position ◽  
Homogeneous Environment

We present an experimental study of an axisymmetric turbulent fountain in a two-layer stratified environment. Interacting with the interface, the fountain is observed to exhibit three regimes of flow. It may penetrate the interface, but nonetheless return to the source where it spreads as a radially propagating gravity current; the return flow may be trapped at the interface where it spreads as a radially propagating intrusion or it may do both. These regimes have been classified using empirically determined regime parameters which govern the relative initial momentum of the fountain and the relative density difference of the fountain and the ambient fluid. The maximum vertical distance travelled by the fountain in a two-layer fluid has been theoretically determined by extending the theory developed for fountains in a homogeneous environment. The theory compares favourably with experimental measurements. We have also developed a theory to analyse the initial speeds of the resulting radial currents. The spreading currents exhibited two different flow regimes: a constant-velocity regime and an inertia-buoyancy regime in which the front position, R, scales with time, t, as R ∼ t3/4. These regimes were classified using a critical Froude number which characterized the competing effects of momentum and buoyancy in the currents.

In-Situ Sensing of the Expansion of Low Density Core (LDC) Ti-6Al-4V Sandwich Structures

1998 ◽  
Vol 521 ◽  
Author(s):  
D. T. Queheillalt ◽  
B. W. Choi ◽  
H. N. G. Wadley ◽  
D. S. Schwartz
Keyword(s):  
Relative Density ◽  
Eddy Current ◽  
Elastic Moduli ◽  
Sandwich Structures ◽  
Ultrasonic Sensor ◽  
Low Density ◽  
Laser Ultrasonic ◽  
Simple Method ◽  
Aerospace Applications ◽  
In Situ Sensing

ABSTRACTA combination multifrequency eddy current and laser ultrasonic sensors have been used to measure the pore expansion kinetics and elastic moduli evolution during the annealing of low density core (LDC) Ti-6Al-4V sandwich structures. The LDC samples were heated to 920°C and held there for up to 12 hr. The eddy current sensor measured the sample thickness (i.e. relative density) and revealed that the samples began to expand early during heating and was nearly complete after 4 hr at 920°C. The laser ultrasonic sensor measurements indicated a concomitant decrease in the elastic moduli with the reduction in relative density. The combination of an eddy current and laser ultrasonic sensor is therefore able to measure both the density and the elastic moduli independently during the annealing stage of LDC Ti-6Al-4V sandwich structure processing providing a simple method for directly controlling the parameters most critical to aerospace applications of these new materials.

Multiobjective optimization of a newly developed additively manufactured functionally graded anisotropic porous lattice structure

2020 ◽  
Vol 234 (11) ◽  
pp. 2233-2255
Author(s):  
Mahshid Mahbod ◽  
Masoud Asgari
Keyword(s):  
Elastic Modulus ◽  
Analytical Solution ◽  
Multiobjective Optimization ◽  
Relative Density ◽  
Elastic Moduli ◽  
Lattice Structure ◽  
Functionally Graded ◽  
Elastic Behavior ◽  
Average Error ◽  
Lattice Structures

In this paper, the elastic behavior of uniform and functionally graded porous lattice structures made by a double pyramid dodecahedron unit cell is investigated. Analytical solutions are derived in order to estimate the elastic moduli of the proposed structures in two directions. The analytical solution is validated by finite element simulations and experimental tests while the results show good agreement in general. The average difference between the numerical and analytical values of elastic modulus is under 14.44%, while the average error of experimental test and analytical solution is 15.69%. A comprehensive optimization is performed by considering elastic moduli in two different directions as objective functions. Various uniform lattice structures with different relative densities are optimized using NSGA-II algorithm as well as lattice structures with graded distribution of porosity. A variety of optimal designs are achieved by multiobjective optimization algorithm and the best point of the Pareto front is selected by the TOPSIS method. Furthermore, the functionally graded lattice structures are optimized by considering desirable relative densities in each layer and applying constructive constraints. Different distribution patterns of relative density are considered in layers in order to present the flexible design capability of the developed structure. The obtained results show that the elastic modulus is significantly dependent on the relative density of each layer as well as cell configuration. Also, different lattice structures could be achieved by applying desirable prescribed distribution of properties. A comparison between optimized and base model indicated that elastic moduli was considerably improved in optimized models. In optimization of uniform models, [Formula: see text] was increased by 115%, 89%, and 69% in optimized structures for relative densities of 10%, 30%, and 50%, respectively. Moreover, [Formula: see text] was improved in optimized models by 27%, 24%, and 18% for relative densities of 10%, 30%, and 50%, respectively.

Impact of the Lattice Angle on the Effective Properties of the Octet-Truss Lattice Structure

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Mohamed Abdelhamid ◽  
Aleksander Czekanski
Keyword(s):  
Mechanical Properties ◽  
Relative Density ◽  
Elastic Moduli ◽  
Effective Properties ◽  
Lattice Structure ◽  
Cellular Materials ◽  
Cubic Symmetry ◽  
Shear Moduli ◽  
Octet Truss ◽  
The Impact

Cellular materials are found extensively in nature, such as wood, honeycomb, butterfly wings, and foam-like structures like trabecular bone and sponge. This class of materials proves to be structurally efficient by combining low weight with superior mechanical properties. Recent studies have shown that there are coupling relations between the mechanical properties of cellular materials and their relative density. Due to its favorable stretching‐dominated behavior, continuum models of the octet‐truss were developed to describe its effective mechanical properties. However, previous studies were only performed for the cubic symmetry case, where the lattice angle θ=45 deg. In this work, we study the impact of the lattice angle on the effective properties of the octet-truss: namely, the relative density, effective stiffness, and effective strength. The relative density formula is extended to account for different lattice angles up to a higher-order of approximation. Tensor transformations are utilized to obtain relations of the effective elastic and shear moduli, and Poisson's ratio at different lattice angles. Analytical formulas are developed to obtain the loading direction and value of the maximum and minimum specific elastic moduli at different lattice angles. In addition, tridimensional polar representations of the macroscopic strength of the octet‐truss are analyzed for different lattice angles. Finally, collapse surfaces for plastic yielding and elastic buckling are investigated for different loading combinations at different lattice angles. It has been found that lattice angles lower than 45 deg result in higher maximum values of specific effective elastic moduli, shear moduli, and strength.

Numerical Evaluation of the Size-Dependent Elastic Properties of Cellular Polymers

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Gurudutt Chandrashekar ◽  
Chung-Souk Han
Keyword(s):  
Relative Density ◽  
Cell Size ◽  
Elastic Properties ◽  
Numerical Evaluation ◽  
Elastic Moduli ◽  
Size Dependence ◽  
Experimental Studies ◽  
Length Scale ◽  
Cellular Solid ◽  
Size Dependent

Several experimental studies have revealed that the size-dependent deformation in polymers at nano- to micro-meter length scales is significantly associated with elastic deformation. Such size-dependent deformation in polymers is expected to affect the in-plane macroscopic elastic properties of cellular polymers with micrometer-sized cells. A finite element (FE) formulation of a higher-order elasticity theory is applied to evaluate the in-plane macroscopic elastic properties of different polymer cellular geometries by varying the cell size from the macroscopic to micron length scale. For a given relative density of the cellular solid, a reduction in the cell size from the macroscopic to micron length scale resulted in geometry-specific variations in the in-plane macroscopic elastic moduli and Poisson's ratios. Furthermore, an increase in the relative density for a given cell size revealed variations in the size dependence of the elastic properties. The size dependence of elastic properties is interpreted based on the influence of rotation gradients with varying cell size of the cellular solid. Also, the evaluated size-dependent elastic properties are compared with the available analytical solutions from the literature.

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