Equivalent in-plane elastic modulus of honeycomb sandwich in the direction of cell vertical wall

The equivalent in-plane elastic modulus [Formula: see text] of a honeycomb sandwich in the direction of cell vertical wall can be assessed by the law of mixture from the modulus of face sheet [Formula: see text] and the equivalent modulus of honeycomb core [Formula: see text]. However, significant errors as large as 40% can be made depending on material and geometry parameters, when the used [Formula: see text] is obtained from a cellular model of core alone without considering the skin effect of face sheet. The main reason of the error is that the rigidity to deformation of y-direction is different greatly between the vertical cell wall of core and inclined cell wall of core. In the present paper, an analytical model is proposed to assess [Formula: see text] of honeycomb sandwich with considering the interference effect of the core with the face sheet. In the proposed model, the influence of the face sheet rigidity on [Formula: see text] is taken into account. The results demonstrate that the contribution of the core to [Formula: see text] is also dependent on the face sheet rigidity significantly. The validity of presented model is verified by comparing the results with numerical results of FEA.

Effect of dislocation and layer height on the compression performance of tandem honeycombs

In this study, the compression mechanical response of tandem honeycomb cores was investigated to determine the effect of dislocation length and layer height on the compression resistance of tandem honeycomb. A series of flatwise compressive tests were carried out on single-layer and double-layer honeycombs, which showed that tandem honeycomb obtains higher equivalent elastic modulus and collapse stress, and the core assembled with dislocation can achieve almost the same collapse stress with the aligned assembled honeycombs. In addition, a mesoscale finite element modeling method was developed and used to evaluate the effect of dislocation length and layer height on the mechanical response of tandem honeycomb through parametric simulation. Overall, our results suggest that dislocation length is proportional to the collapse stress, and the layer height decides the equivalent modulus and collapse stress of tandem honeycomb, specifically, dislocation length helps achieve higher collapse stress in the tandem honeycomb of varying layer heights.

The equivalent modulus of elasticity of soil mediums for designing shallow foundations

As known, in a Winkler type of analysis the soil medium underneath the foundation is violently replaced by a row of parallel springs having constant ks. For the effective calculation of the latter, which is called the modulus of subgrade reaction, the two elastic constants of the soil (the elastic modulus, E and the Poisson’s ratio, ν) must be known. Although for homogenous soils this generally seems not to be a problem, the same does not stand for stratified mediums or mediums with linearly increasing modulus with depth. In such an analysis, the proper pair of elastic constant values of soil should be selected. This refers to a Poisson’s ratio value equal to zero corresponding to the deformation pattern of springs (compression with no lateral expansion) and the respective modulus. In the present paper a method for calculating the equivalent elastic constants for the above mentioned mediums is proposed based on the theory of elasticity combining the principle of superposition. Various cases are considered, since the equivalent modulus, Eeq, depends on the rigidity and the shape of the footing. As shown, the derived Eeq values not only return reliable settlement results, but also settlement profiles that are similar to those corresponding to the original soil mediums.

A Kind of Filling Lattice Structure Based on DFAM for Mechanical Parts: The Diamond Lattice Structure

Thanks to the geometric and material complexity of additive manufacturing, the design space of mechanical parts has been developed, in which lattice filling structure customization can be applied to the solid filling of mechanical parts to achieve the goal of mechanical structure lightweight. A kind of diamond lattice structure unit is designed by imitating the natural method based on Design for Additive Manufacturing of mechanical parts. The mathematical model of the relative density and mechanical properties of the unit are established, and the relationship between the two is obtained, which is verified by simulations; then the relatively uniform results are obtained. The variable density hypothesis of diamond lattice structure is proposed, the methods of simulations and compression tests are used to verify the hypothesis, and the results show that the variable density structure with the density of the filling element decreasing gradually with the stress point as the center has better compression performance and concurrently verify the correctness and applicability of the equivalent modulus of elasticity mathematical model. The results of this study can be applied to the solid sandwich filling of pressure mechanical parts, and the stress density matching relationship can be carried out to further specific design.

Stability Analysis of Composite Shafts Considering Internal Damping and Coupling Effect

A mathematical model is proposed to analyze the stability of composite shafts, considering the internal damping, transverse shear deformation and Poisson’s coupling effect at the same time. The strain–displacement relations are described using the Timoshenko beam theory, and the strain energy and kinetic energy are expressed using the weak form quadrature element method (QEM), for which each nodal point has 4 degrees of freedom. Then, the motion equation of the system is established using the Lagrange equation. The instability thresholds of the composite shaft are determined using the proposed model. The results were compared with those calculated by the equivalent modulus beam theory (EMBT), equivalent single layer theory (ESLT) and simplified homogenized beam theory (SHBT). Good agreement has been achieved. Therefore, the proposed model can be effectively used for the dynamic analysis of composite shafts.

Thermal Actuation Analysis of Twisted and Coiled Polymer Actuators

Twisted and coiled polymer actuators (TCPAs), an emerging class of artificial muscles, exhibit the advantages of large stroke, low hysteresis, low cost, etc. The effect of design parameters on thermal actuation is important for the effective design of TCPAs. In this study, a new model has been developed to describe the effect of geometrical parameters on thermal actuation based on Castigliano’s second theorem. In this model, an equivalent modulus based on its radial bias angle has been introduced from the twisted polymer actuator (TPA)’s equivalent model. The proposed model provides a simple and accurate expression to describe the TCPA’s thermal actuation by using its fundamental characteristic. The proposed model was validated with respect to the experimental data from the literature and subsequently used in the parametric analysis of TCPA. The numerical results show that the amplitude of actuation increases linearly with pitch angle and nonlinearly with spring index.