Papers by Author: Ewald Macha

Abstract: The paper presents strength machine control system for characterization of fatigue properties of materials based on recently defined energy fatigue damage parameter under polyharmonic bending and torsion.

Abstract: The paper contains the results of fatigue tests under cyclic bending of C45 steel with amplitude of energy parameter control. The tests were performed on the smooth specimens. Based on these tests, energy fatigue characteristic of the tested material was elaborated.

Abstract: In this paper the results of fatigue tests under cyclic bending of 2024 aluminium alloy with amplitude of strain energy density parameter control are presented. Based on these tests, energy fatigue characteristic of the tested material was elaborated.

Abstract: The paper presents strength machine control system for characterization of fatigue properties of materials based on a new, recently defined, energy fatigue damage parameter. It is used in new procedure for precise determination of the fatigue characteristics of materials with the controlled strain energy density parameter. The new parameter distinguishes positive and negative values strain energy density histories during variable loading. In case of modern, cyclically unstable materials the new closed-loop control system of strength machine allows to univocally establish the relevant stress-strain based fatigue characteristic under bending and torsion. This control system has been implemented with the use of National Instruments LabVIEW software. The mechatronic stand based on fatigue machine for material testing under bending moment and torsion moment has been described and preliminarily material tests have been done.

Abstract: The paper presents structure and principles of operation of the fatigue test stand for specimens subjected to polyharmonic proportional bending and torsion. The stand is equipped with a digital control system based on data acquisition board Daqboard/2000 and LabVIEW environment. The history of polyharmonic loading is a sum of four harmonic components of various amplitudes, frequencies and phases adjusted by means of four rotating disks with unbalanced masses of the inertial vibrator. Application of a computer with the software elaborated by the authors and the control system enables determination of fatigue characteristics of the material under constant or variable amplitude bending, torsion and any combination of bending with torsion.

Abstract: The paper presents a definition of a new energy based parameter which allows to better describe fatigue proprieties of materials, especially cyclically unstable materials in comparison with the Lagoda-Macha parameter. The proposed parameter distinguishes positive and negative work of external force and depends on the sign of the stresses in paths of strain in materials. It is used in laboratory tests for control of a fatigue process on hydraulic stand. A close-loop control system has been equipped with computer program based on MATLAB/Simulink module.

Abstract: The paper contains results of investigations of the crack growth in plane specimens made of Ti-6Al-4V titanium alloy and AlCu4Mg1 aluminium alloy under cyclic bending. The tests were done on specimens with the stress concentrators being one-sided sharp notch. On the fractures there have been observed first of all transcrystalline cracks through the α phase grains for both materials.

Abstract: Unreliable and inflexible analog control systems of fatigue test stands applied in laboratories are being replaced by systems enabling easy development and implementation of new test ideas. This paper presents a digital control system applied in the fatigue test stand SHM 250b. It is based on a new electronic system and the I/O board RT-DAQ4/PCI with the software Matlab/Simulink used for communication with the board. The control system for the fatigue test stand SHM 250b gives the possibility of performing fatigue tests under controlled strain ε(t), stress σ(t) and energy parameter W(t) which is calculated from the stress and strain signals. The applied control system is now used, depending on the performed fatigue tests, and can be developed for specific needs of material strength analysis.

Abstract: This paper presents a two-channel digital control system for the hydraulic stand MZPK 100 designed for fatigue tests of cruciform specimens under biaxial tension-compression. In the past, the fatigue test stand MZPK 100 was provided with unreliable analog control power cubicles. Application of the computer with an analog and digital input-output signal path board, Matlab/Simulink software and a new control box equipped with the necessary electronic subassemblies (responsible for proper switching of the hydraulic supplier, command electrovalves, conditioning of signals from sensors and so on) enables replacement of the old analog system by a new two-channel digital control system. Nowadays, it is easy to modify the control system to different requirements of material tests because the hardware (electronic) solutions have been simplified, and the software has a friendly Simulink interface. Such an approach allows for the implementation of different control algorithms, e.g. PID, adaptive, and fuzzy logic etc. Moreover, this paper presents a description of how to keep the center of the specimen static under a controlled force that is being applied by four independent actuators.

Abstract: The paper includes a review of literature on the multiaxial fatigue failure criteria based on the critical plane concept. The criteria were divided into three groups according to the distinguished fatigue damage parameter used in the criterion, i.e. (i) stress, (ii) strain and (iii) strain energy density criteria. Each criterion was described mainly by the applied the critical plane position. The multiaxial fatigue criteria based on two critical planes seem to be the most promising. These two critical planes are determined by different fatigue damage mechanisms (shear and tensile mechanisms).