MODARES TECHNICAL AND ENGINEERING
Year:2004 | Volume:- | Issue:17|Papers Count:10

This paper introduce a theoretical model to determine mean crushing loads for the quasi - static loading on the Honeycomb, when behavior of honeycomb material assumesto be Rigid- Strainhardening.The above assumption gives this opportunity to modify theoretical model by substitution of flow stress, which its amount is variable between yield and ultimate stress with ultimate stress.Introduced theoretical solution compares with experimental and theoretical results of other authors. This solution can replaces the less accurate earlier analysis of the same problem due to Wierzbicki.

Recent usage of shock waves in industry necessitates a large effort to increase the accuracy and ability of the numerical simulations of shock dynamics. To fulfill this requirement, many models to predict the behavior of materials under dynamic loading have been presented by researchers. There have been many efforts to construct a model, which can explain this behavior accurately for a wide range of problems. Unfortunately such attempts have failed because of the nonlinear nature of the underlay processes. However, there are plenty of models to express the behavior of materials in a specific range. In this paper we compare two widely used models, namelg Johnson-Cook and Steinberg models. The results of numerical simulations show that both models provide good results for a wide range of shock loading. However, Steinberg model is superior in problems, which encounter large strain rates.

The drag force imposed on a convex body in a free molecule regime flow together with corrections of the atmosphere model is investigated in the present study. Convex simple bodies such as a sphere and a cone and bodies with combination of these are modeled using the software's Solidworks and ANSYS. The drag force of the mentioned bodies are obtained and compared with the data reported in literature. The HSN model for gassurface interaction modeling is introduced as well. A computer code for drag force calculations is written. The results obtained using this program are in good agreement with the experimental results of other investigators. This indicates that variation of R-value of the air cannot be neglected. The drag force results obtained by HSN model have lower values in comparison to the standard Nocilla model.

In order to reduce the energy consumption in buildings and reduction of thermal losses, it is necessary to use thermal insulation in .building envelopes. Thickness of thermal insulation and its position in the building envelope are important, because they vary in different climates.In this study the above-mentioned parameters are investigated for three different cities in Iran.Including: Tehran with moderate climate, Tabrii with cold climate and Ahvaz with hot climate. The Opaque software was used for calculating annual thermal building loads.Based on the obtained results, in Tehran city, insertion of 5 to 7.5 cm insulation as two slice in wall envelope have greatest reduction in yearly thermal loads. Also, in Tabriz city insertion of 5 to 7.5 cm insulation as a whole (1 piece) in internal layer of wall have greatest reduction in yearly thermal loads, in Ahvaz city insertion of 5 to 7.5 cm insulation as a whole (1 piece) in external layer of wall have greatest reduction in yearly thermal loads.

In this paper, free vibration analysis of simply supported cylindrical shells with longitudinal stiffeners i.e. stringer, using Ritz method and stiffeners treated as discrete elements, is presented. In strain energy formulation, adopting sanders theorem, stretching and bending characteristic of shell and also stretching, bending and wrapping effects of stiffeners are considered. However the translational inertia in three directions for shell and stiffeners and also rotary- inertia for stiffeners are considered. The polynomial functions are used for Ritz functions Natural frequency results for stringers with uniform spacing and constant eccentricity have been compared with. referenced analytical and experimental results, and good agreements between these have been seen. With constant stiffeners mass, the effects of non-uniform eccentricity for three types of distribution, i.e. linear form, quadratic form, and third order form were considered and natural frequencies variations, specially fundamental frequency was determined.

The main objective of this study is to demonstrate the use of bonded composite patches in strengthening or repair of damaged structural elements. The high strength, light weight, formability and relative ease of application, make composite materials an excellent option for use as external reinforcing systems for structures.A square aluminum plate with a central circular cutout is considered as a damaged structural element. The change in vibration response of damaged metallic plates reinforced with fiber reinforced polymer composite materials (composite patch) are presented in this study.Numerical studies using commercial finite element software were conducted to investigate the effects of variation in patch geometries and fiber orientation on free vibration responses of repaired plates. A quantitative measure for the effectiveness of the composite patches is taken to be the relative change in natural frequencies of the repaired plates compare to those of the damaged one. The results presented herein indicated that, for vibration response of a repaired aluminum plate with central cutout, a set of composite patches with different shapes and fiber angles can be found which change and improve vibration frequency of damaged plates.

Pipes with square cross sections are used as structural elements in buildings and automotive industries. These pipes can be produced from the round pipes by the reshaping process. In actual production, the design of process variables such as diameter of round pipe, profile of rolls and number of necessary stands are carried out experimentally.In this paper, a computer aided simulation code has been developed based on the 2-D elasticplastic finite difference method. The shear deformation is considered in the analysis of the reshaping process. By using this program, the effect of various parameters such as initial round pipe diameter and mechanical properties of metal on product dimension and quality can be investigated. Moreover, design of reshaping process including the peripheral shrinkage, the necessary number of stands, the radius of rolls and the height of pipe at each stand, can be performed.This simulation can reduce trial and errors and costs and help to manufacture the square pipes with high dimensional accuracy and good quality. Comparisons between the obtained results and experimental results are made and the applicability of obtained results is confirmed.

A drawback of convensional ADI method in solving heat conduction problem is that for stability, a small time step is required. In this paper, a new method is introduced in which the time step can be increased by a factor of 1/f (0<1/f <1) so that solutions remain stable, and high accuracy is retained. This new method is compared heat flux, and a constant surface temperature. The new method is compared with the conventional ADI method and the well – known Brain and Douglas methods. The results show that the improved ADI method is more accurate and requires less computer storage.