Experimental Study of Upsetting and Die Forging with Controlled Impact
The results from experimental research of deformation by upsetting and die forging of lead specimens wit controlled impact are presented. Laboratory setup for conducting the investigations, which uses cold rocket engine operated with compressed air, is described. The results show that when using controlled impact is achieving greater plastic deformation and consumes less impact energy than at ordinary impact deformation process. Keywords—Rocket Engine, Forging Hammer, Sticking Impact, Plastic Deformation.
KINEMATIC INVARIANTS WITH INFINITESIMALLY CLOSE POSITIONS OF MECHANISMS WITH TWO DEGREES OF FREEDOM
The last 2-3 decades are characterized by the widespread use of robots in the micro world for molecular and nano technological operations. There is a dynamic development in the area of micro and nano actuators. Macro and micro movements are consecutive and to a great extent independent of each other. The structures of the manipulation mechanisms (??) change according to the activation of macro motors or micro actuators. In both cases micro operations are performed by short-range movements. In this sense, the synthesis of ?? through the methods of infinitesimally close positions (ICP) is particularly appropriate. With the mechanisms having two degrees of freedom (DoF) two substantially different problems for the synthesis with ICP can be formulated: a direct problem – one for a given configuration of the mechanism and a given transmission ratio of the velocities at the two inputs where the point of Boll is to be found, and a reverse problem where with a given point of Boll and the normal to its trajectory the kinematic parameters of the mechanism are sought. In the present paper a methodology was created for the synthesis with ICP, adopted for five-link mechanisms with two DoF. The said methodology may also be used with slight amendments to it for the synthesis of mechanisms with open kinematic chains. Actually, ICP are the end sections of the trajectory. They can be used with precise finishing operations. The input velocities may be constant, whereby the impact of the inertia forces, and of the deformations, respectively, becomes insignificant.
A model for predicting heat transfer through gypsum‐board/wood‐stud walls exposed to fire
To facilitate the development of cost-effective and flexible design options there is a need to develop models to predict the fire resistance of wood-frame building assemblies. Such assemblies often derive much of their fire resistance from a protective membrane composed of gypsum board. A simple two-dimensional computer model is presented to predict heat transfer through gypsum-board/wood-stud walls exposed to fire. Input data for the thermophysical properties of gypsum board were measured exploying standard bench-scale tests. Input data for wood were selected from the literature. Small-and full-scale fire resistance tests were conducted on gypsum-board/wood-stud wall assemblies to provide data for the validation of the model. The model is shown to predict heat transfer through these walls rather well.