Simulation of Cross Set in Frame Structures

Experimental study of the influence of preliminary complex mechanical loads on the deformation and strength properties of polymer composites

This paper introduces a methodology to predict the non-linear stiffness–suction and shear strength–suction relationships for unsaturated soils within the lower suction range from the non-linearity of the soil-water characteristic curve (SWCC), using a normalised function formulated with ‘suction times exponential degree of saturation’. The information required in this methodology includes (a) measurements of the shear strength or stiffness properties at saturation condition and one unsaturated condition and (b) the SWCC. Published experimental data on the stiffness and shear strength properties and the SWCC obtained from 25 different soils varying from coarse-grained sands to expansive clays are used to validate the proposed normalised function and to calibrate the exponent value. It is found that the normalised function, using exponent values of 1·0 and 2·0, respectively, for cohesionless and cohesive soils, provides reasonable predictions of the stiffness–suction and shear strength–suction relationships for all the soils used in this study, taking account of various influencing factors including external stress, soil structure, anisotropy, hydraulic hysteresis and testing technique.

유한요소법을 적용하여 고형, 박벽 및 혼합형 단면을 갖는 복합재료 블레이드의 2차원 단면 해석 프로그램을 개발하였다. 이종 적층 복합재료에 대한 물성치는 가중 계수법을 도입하여 결정하였다. 전단 중심치와 비틀림 강성 계수는 St. Venant 비틀림 이론 및 Trefftz 의 정의를 토대로 구하였다. 해석 과정에서 발생하는 단면 강성 행렬의 특이치 문제는 고유치 해석으로부터 강체 모드를 제거함으로써 해결하였다. 다양한 단면 형상에 대한 강성치, 중심치 및 관성치에 대한 수치계산을 수행하였다. 기존의 상용해석 소프트웨어 및 여타 문헌에 제시된 단면 해석 결과와 폭 넓은 비교, 검증 연구를 수행하였으며, 이를 토대로 본 해석 프로그램의 타당성을 보였다. A two-dimensional cross-section analysis program based on the finite element method has been developed for composite blades with solid, thin-walled and compound cross-sections. The weighted-modulus method is introduced to determine the laminated composite material properties. The shear center and the torsion constant for any given section are calculated according to the Trefftz' definition and the St. Venant torsion theory, respectively. The singular value problem of cross-section stiffness properties faced during the section analysis has been solved by performing an eigenvalue analysis to remove the rigid body mode. Numerical results showing the accuracy of the program obtained for stiffness, offset and inertia properties are compared in this analysis. The current analysis results are validated with those obtained by commercial software and published data available in the literature and a good correlation has generally been achieved through a series of validation study.

Three-dimensional tow inclination model for calculating elastic constants of three-dimensional triaxial braided composites

Finite element analysis of single-walled carbon nanotubes based on a rod model including in-plane cross-sectional deformation

<p>In this study specimens cut from intermediate timber floor beams that have been in service for more than 120 years were tested. The objective of this paper is to determine the strength characteristics and stiffness modulus of old wood and examine relationships between different properties. Experimental tests for determining the mechanical properties in bending have been carried out in short-term static loading. Also shear strength and compression strength perpendicular to the fiber direction was determined by tests. It is concluded that the modulus of elasticity of wood during long-term service under load decreases faster than the strength properties. When evaluating the relationship between wood strength and stiffness properties, a weak correlation was found between bending strength and modulus of elasticity. As well as other properties (density, moisture content etc.) didn’t show any remarkable correlation significance.</p>

A macro level finite element-based model has been developed to simulate the mechanical and impact response of triaxially-braided polymer matrix composites. In the analytical model, the triaxial braid architecture is simulated by using four parallel shell elements, each of which is modeled as a laminated composite. For the current analytical approach, each shell element is considered to be a smeared homogeneous material. The commercial transient dynamic finite element code LS-DYNA is used to conduct the simulations, and a continuum damage mechanics model internal to LS-DYNA is used as the material constitutive model. The constitutive model requires stiffness and strength properties of an equivalent unidirectional composite. Simplified micromechanics methods are used to determine the equivalent stiffness properties, and results from coupon level tests on the braided composite are utilized to back out the required strength properties. Simulations of quasi-static coupon tests of several representative braided composites are conducted to demonstrate the correlation of the model. Impact simulations of a represented braided composites are conducted to demonstrate the capability of the model to predict the penetration velocity and damage patterns obtained experimentally.

24 - The finite element method

Additive technologies have made it possible to create medical devices with inhomogeneous structure. The structures of such products, called metamaterials, allow not only to reduce the weight of the product, but also to control the effective physical and mechanical properties by varying the geometry of their microarchitecture. Controlling physical-mechanical properties helps prevent post-operative complications associated with implantation. This study focuses on determining the stiffness and strength properties of different types of the lattice metamaterials, which are subsequently used to develop a numerical model and design endoprostheses, as well as to investigate antibiotic elution from bone cement. The work presents an experimental testing of three metamaterial types with two variations of cross-sectional angle, both with and without embedded cement. The cross-sectional angles of the specimens were selected based on the results of numerical simulations. The studied specimens were fabricated using laser stereolithography on a photopolymer printer, followed by post-polymerization. Stiffness properties were determined through using in situ four-point bending tests. As a result, the stiffness and maximum load values were obtained. These values were normalized to those of solid specimens. The specimens with embedded cement were at least 28 % stiffer than those without cement. A comparison of numerical and in situ experiments revealed qualitative agreement in the results for the first and third types of specimens when the cross-section rotation was varied. However, the maximum load observed of the in situ experiments for the strongest specimens, according to the numerical model, showed little difference compared to the maximum loads of other specimens types. The authors attribute this result to the dependence of changes in physical and mechanical properties on geometry during polymerization.

The handling and control of towed cable and body systems onboard surface ships and submarines presents a significant technical challenge to design engineers in the defense and ocean industries. The current approaches rely heavily on the empirical methods and the time-consuming and costly prototype testing. Computer simulation provides a cost effective way to reduce the high risks associated with the towed cable/body system. However, the current dynamic analysis of towed cables is mostly done by the finite difference (FD) method in stead of the finite element (FE) method that is widely used in almost all engineering fields. This paper presents an alternative FE method to simulate the dynamics of towed cable and body system, in which the large rigid body motion is coupled with small elastic deformation. The newly derived FE method is formulated in terms of element nodal positions, which is different from the existing FE methods that use displacements. The alternative FE method solves for the cable position directly in order to eliminate accumulated numerical errors arising from existing FE methods that solve for displacements first in order to obtain the cable position over very long period of time. The alternative FE formulation is implemented and applied to real applications to demonstrate its robustness by comparing simulation results with the experimental and sea trial data.

This paper provides a simple numerical method to determine the optimal parameters of tuned mass damper (TMD) and viscoelastic dampers (VEDs) in frame structure for wind vibration control considering the soil-structure interation (SSI) effect in frequency domain. Firstly, the numerical model of frame structure equipped with TMD and VEDs considering SSI effect is established in frequency domain. Then, the genetic algorithm (GA) is applied to obtain the optimal parameters of VEDs and TMD. The optimization process is demonstrated by a 20-storey frame structure supported by pile group for different soil conditions. Two wind resistant systems are considered in the analysis, the Structure-TMD system and the Structure-TMD-VEDs system. The example proves that this method can quickly determine the optimal parameters of energy dissipation devices compared with the traditional finite element method, thus is practically valuable.

Cross-laminated timber panels offer an effective option for timber structures; they allow biaxial load transfer and have good dimensional stability. However, practical transportation and handling limits size of the panel and a stiff connection between the panels is required to effectively utilise biaxial properties. In this paper, a dovetail splice joint for timber panels is presented using cross-banded LVL with cast concrete grout interlayer. The interlayer allows a tight fit, which is important for stiffness, but also avoiding installation problems due to manufacturing tolerances and moisture-induced dimensional changes. The mechanical behaviour of the dovetail joint was investigated experimentally for various geometries. Furthermore, a numerical model was developed that shows a wide agreement with the experiments, especially in the cases with governing failure in the LVL. Using the numerical model, a parameter study was performed where the influence of the connection length (number of dovetails) and the joint geometry on the strength and stiffness properties was investigated. Besides the optimal geometrical configurations of the dovetail joint, also a significant increase of the strength and stiffness properties with increasing connection length was identified.

The aim of present study was to create a theoretical model that allowed, with security and reliability, to obtain values of strength and stiffness to which the structural element will be submitted throughout its useful life. The effect was studied for strength and stiffness properties, and the modulus of elasticity (EM) and bending strength (fM) on static bending test were evaluated according to the increasing number of cycles of the fatigue test for the five classes of hardwoods, recommended by NBR 7190 Standard Code. A reduction in strength and stiffness properties was observed with increasing loading Ncycles applied at two frequency levels. From the multivariate regression models and the respective determination coefficients, a generic model was obtained for the set involving the five wood species, emphasizing the insertion of the apparent density as an independent variable, which allowed a greater generalization of the use of the adjustments in the estimation of the EM and fM properties, presenting significant determination coefficients, ranging between 67.89% and 70.58%.

Using finite element method, models of different element mesh density for the center hole in flat plate were established according to one actual steel plate with central circular hole. The stress concentration coefficients of these models were calculated by means of numerical method. Then the calculated results were compared with the theoretical solution results of Elastic Mechanics. And it was analyzed subsequently that the influences which were caused by different element mesh density on the stress concentration coefficients around the hole in flat plate. The relationship between the element mesh density and the stress concentration coefficients around the hole in flat plate was proposed finally. Results show that the element mesh density for calculation affects the stress concentration coefficients around the hole in flat plate significantly, but the influence is few when the mesh density increases to a certain extent.

Analysis of framed tube structures of arbitrary sections