Contents of the Journal of Mechanical Engineering 51, 3 (2000)

J. REMENEC, L. STAREK: Updating mathematical model 
of vibrating mechanical systems (in Slovak)                               133

J. KOSUT:  Analysis of hypothesis of cumulative fatigue damage based
on the damage factors in repeated block loading case                      161

P. MUCKA: The influence of quarter-car model parameters
on the quality of active suspension (in Slovak)                           174

K. KALNA: Design of  brittle-failure-resistent steel structures
 by different European standards (in Slovak)                              187 

The most widespread approach for numerical modeling in engineering design is the finite element method. Modern computers, which are capable of processing large matrix problems at high speed, have enabled the construction of large and sophisticated numerical models and the rapid processing of digitized data obtained from analogue measurements. For various reasons, to be elaborated upon in the paper, the experimental results and numerical predictions often conspire to disagree. This work addresses the problem of updating a numerical model by using data acquired from physical vibration test.

The cumulative fatigue damage hypothesis, based on immediate and history damage factors is analysed in repeated block loading case. The derived expression for a number of loading blocks to fracture substantially reduces the amount of computation, compared with the general expression. The simple approximate expressions proposed on the basis of analysis are suitable for engineering use. The influence of loading sequence in loading block on endurance is negligible in the case when loading block is repeated many times before fracture. In this case, the analysed hypothesis gives always shorter fatigue lives than the linear one.

In this paper four active suspension concepts for heavy vehicles are analysed. For modeling of heavy vehicle dynamic behaviour the quarter car model is used. The performance of active suspension concepts with respect to variation of vehicle model parameters (stiffness and mass values) is evaluated. The vehicle model is kinematically excited by a random signal corresponding to road unevenness and by a deterministic obstacle. Specially the influence of active suspension concepts on the road surface dynamic load due to variation of vehicle model parameters is analysed. Also capacity of active suspension concepts to provide improved ride comfort, small workspace of suspension, and low energy consumption are taken into account.

Designing of brittle-failure-resistent steel structures, in principle two approaches can be used: according to transition temperature or according to fracture toughness K_IC of materials. Design approaches according to impact toughness KCV are based on practical experience. Pseudo-fracture mechanical approaches are based on correlation of KCV data with K_IC, but they are insufficiently precise. Maximum permissible thicknesses of structure details h_max, specified by various standards, show great differences. Different h_max data are due to different dimensions of fictitious crack a_F and inconvenient correlation of KCV-K_IC data.