Laboratory stand for impact action tests | TECHNICAL UNIVERSITY - SOFIA
 


Project


Developing of laboratory stand for experimental investigation of “combined impact” effect.


Challenge


The “combined impact” effect is achieved when additional force action is applied on moving body before, during or after the impact. The determination of the energy value, time and moment of inclusion of the additional force action for achieving of “adhesion impact”, i.e. “combined impact” without rebound is extremely important for the forging-press production, brick production and pile driving. The absence of rebound increases the operational life of the technological equipment and assists for the optimal running of the plastic deformation process.

Special requirements:

The additional force action should be realized through a jet nozzle and compressed air source.


Solution


 


The project is developed on the basis of original mechanical structure characterized by:

1. Specific design solutions:
  • A system for linear guiding of the mobile parts with minimal frictional factor /rolling friction/ is applied;

  • The bearing of the mobile parts allows the realization of zero clearance between the guide roller and the guiding rails;

  • Minimum necessary number of rolling elements are used;

  • The chosen linear guiding system provides for compensation of the error due to non-paralellism and allows mounting distance between the two guides within the framework of the complete running;

  • The mobile parts are statically balanced against two mutually perpendicular axes crossing the sphere moving axis;

  • Position feedback by a noncontact method within the limits of the complete run of the mobile parts is realized;

  • Possibility for fixing of different attachments in the zone of the force action is provided depending on the type of the test;

  • The stand is provided with a 10 l air receiver at maximum nominal pressure of 10bar;

  • The stand has a self-locking mechanical positioning lock with possibility for infinite adjustment of the falling height within the limits of the complete run of the mobile parts.

2. Functional possibilities:
  • Possibility for individual change of each separate parameter of the test process;
  • Possibility for precise repetition of the parameters during multiple tests;
  • The stand is completed with the relevant control and recording apparatuses;
  • Specialized software for recording and statistical processing of results is developed;
  • The stand is completed with a measuring system for reading the static force action during operation of the jet engine;
  • Possibility to determine the electro-mechanical time constant from the moment of switch-on of the electromagnet valve till achieving maximum jet force at set-up pressure in the accumulator;
  • Possibility for infinite change of the jet engine nozzle cross-section aimed at achieving maximum jet force;
  • Precise control on the operation of the jet engine in regards to switch-on moment and duration of the force action.


Principle scheme of positioning noncontact feedback system

A positioning noncontact feedback system is shown on the figure. It is characteristic that displacements with resolution less than 0.2 mm may be read by a noncontact method in real time. The main advantage of this type of measuring system is that its components /emitter 1 and receiver 2/ are protected from force actions by mounting on fixed elements of the structure. 

From the geometric dependence shown on the figure the transmission coefficient for given angle of inclination /α/ of the optical system may be defined, where the value of the vertical displacement /S/ is expressed by means of the crosswise displacement /δ/.

S= δ /(sin α . tn α)

Where the transmission coefficient

К=1 / (sin α . tn α)



Result

Thanks to the original positioning noncontact feedback realized by optical sensors the recording of precise data (up to 350 points per test) at excellent result repetition becomes possible.