The paper contains the tatigue tests results for specimens made of three cast irons under proportional and non-proportional variable amplitude tension with torsion. The experimental data for long fatigue life have been compared with those calculated according to the algorithm with use of the modified criterion of the maximum normal stress in the critical plane. In the considered algorithm the Palmgren-Miner hypothesis of damage cumulation seems to he useless whereas the Serensen-Kcgaycv hypothesis gives satisfactory results. Applying the method of fatigue damage cumulation we obtain the critical plane direction which agrees with the experimental fracture plane very well.

In the present paper, an analysis uf lower bound estimation of the load carrying capacity of structures with intermediate stiffeners is undertaken. Thin-walled structures with intermediate stiffeners in the elastic range, being under axial compression and a bending moment, are examined on the basis of the Byskov and Hutchinson's method [4] and the co-operation between all the walls of the considered structures is shown. The structures are assumed to be simply supported at the ends. The study is based on the numerical method 01· the transition matrix using Godunov's orthogonalization [2]. Instead of the finite strip method, the exact transition matrix method is used in this case. In the presented method for lower bound estimation uf the load carrying capacity of structures, it is postulated that the reduced local critical load should be determined taking into account the global pre-critical bending within the first order non-linear approximation to the theory of the interactive buckling of the structure. The results are compared to those obtained from the design code and the data reported by other authors. The present paper is a continuation of papers [9], [ 11], [ 19], where the interactive buckling of thin-walled beam-columns with central intermediate stiffeners in the first and the second order approximation was considered. The most important advantage of this method is that it enables us to describe a complete range of behaviour ot· thin-walled structures from all global (flexural. flexural-torsional, lateral, distortional and their combinations) to local stability. In the solution obtained, the effects of interaction of modes, the transformation of buckling modes with an increase in load, the shear lag phenomenon and also the effect of cross-sectional distortions arc included.

The paper contains a review of energy-based multiaxial fatigue failure criteria for cyclic and random loading. The criteria for cyclic loading have been divided into three groups, depending on the kind of strain energy density per cycle which is assumed as a damage parameter. They are: a) criteria based on elastic strain energy for high-cycle fatigue, b) criteria based on plastic strain energy for low-cycle fatigue. and c) criteria based on the sum of plastic and elastic strain energies for both low- and high-cycle fatigue. The criterion for random loading is based on the new definition of energy parameter which distinguishes plus and minus signs in history or specific work of stress on strain along chosen directions in the critical fracture plane. The criteria which rake into account strain energy density in the critical plane dominate in the energy description or multiaxial fatigue. Parameters dependent on loading and factors dependent on a kind or marcrial and inlluencing selection of the critical plane have been given. The author presented the mathematical models or the criteria and next distinguished those including influence of mean stresses and stress gradients as well as proportional and non-proportional loading. It has been emphasised that the generalized criterion of maximum shear and normal strain energy density in the critical plane seems to be the most efficient in practice and it should be developed and verified in a future.

Application or a hydropneumaiic boom support system with controlled stiffness and dissipation parameters in a crane in its ready-for-transport position allows for modification of dynamic properties or the crane and for vibration mode control during the ride. Adjusting the support system llexibility to disturbances being the result of uneven terrain may heir to reduce the loading of the bearing structure and to increase speed still maintaining the required safety and comfort standards. That improves the functional quality of mobile machines. The results of this study may be used as the basis for evaluation 01· vibration control methods in mobile cranes in which the boom acts as a dynamic absorber.

The paper is devoted to development of the evaluation methods tor limiting condition of metal alloys and steels under uniaxial and biaxial proportional and non-proportional low-cycle fatigue. To investigate the fatigue behavior of Type 08X 18H I OT stainless steels and titanium alloys BT9 strain controlled tests under 12 proportional and nonproportional loading ar room temperature were carried out. A strain parameter. namely, a nonproportional strain range. is proposed to obtain a correlative dependence with lifetime. For the majority or the materials this dependence can be derived from uniaxial tests and described by a linear function. It made it possible to propose simple engineering method for lifetime prediction.