The influence of stiffness and road profile on stress proportionality of axle trailers (#84)
V. Chmelko1, M. Margetin1, E. Schäfer1
1 Slovak University of Technology, Applied Mechanics and Mechatronics, Bratislava, Slovakia
The time-depending relationship for normal and shear stresses is analyzed on the basis of direct measurements in practice of trailers with a load capacity of up to 3.5 tons. In the critical weld joint of the car axle were deployed the sensors in order to separate the effect of normal and shear stresses. During analysis were performed many tests where there was analyzed the influence of road relief like (block pavement road, resonance bumps, panel road,...) and influence of three different suspension types of systems on proportionality of time-depending signals of s and t. The proportionality of these stresses is one of the key questions for choosing and applying the multiaxial fatigue approaches of evaluation the fatigue lifetime.
Keywords: proportionlity, multiaxial loading, axle
Load assumption for structural components of agricultural machines (#106)
S. Stellmach1, L. Braun1, M. Wächter1, A. Esderts1, S. Diekhaus2
1 TU Clausthal, Insititut für Maschinelle Anlagentechnik und Betriebsfestigkeit, Clausthal-Zellerfeld, Lower Saxony, Germany
On the one hand, durability and strength is an essential argument for commercial vehicle customers to purchase new products. On the other hand, the topics of efficient use of resources and lightweight design are getting more important for manufacturers of agricultural machines. The foundation to achieve these targets during the development process of the machines are appropriate load assumptions. The challenges for manufacturers are the different operating conditions regarding the regional characteristics and the possible use cases of the machines in the agricultural environment.
Load data acquisition for all components and variants of machines requires high measurement equipment effort. Additionally there is only a short timeframe to test the complete machine with all functions during the harvest. It is the task to reduce this effort to a minimum without losing information. Building and improving knowledge of the dependency between components of the machine is essential to describe the complete machine behaviour. It is important to define constraints and influencing parameters in this system. These information can be used to develop an efficient and application oriented method for load data acquisition. Measured data and the benefits of multi body simulation will be considered for this approach. The aim of this article is to report about how to get load data for structural components of an agricultural machine and how to use it for fatigue design.
Keywords: load assumption, agricultural machine, load data
Review of practical experiences from development of buses: service stresses, laboratory fatigue tests and fatigue life calculations (#71)
M. Kepka1, M. Kepka junior1
1 University of West Bohemia, Regional Technological Institute - research center of Faculty od Mechanical Engineering, Pilsen, Czech Republic
Over the last twenty years, Research and Testing Institute Plzen has been developing a methodology of computational and experimental investigation of strength and fatigue life of bodies of road vehicles for mass passenger transport. A summary of this methodology – which was used for designing many SKODA trolleybuses and buses – has already been presented to the public (Kepka, 2009). The SKODA methodology is very complex. The development of a new bus structure contains both computational and experimental activities: CAD - MBS - FEM - stand test - measurement with bus prototypes - fatigue life assessment.
It continues to be developed in cooperation with the Regional Technological Institute, which is a research center of the Faculty of Mechanical Engineering of University of West Bohemia. For example the challange is increasing electro-mobility and battery-powered electric buses opens a new field of research (Kepka-Spirk, 2015). Heavy battery packs significantly change vehicle dynamics and stress response in the chassis and bodywork of the vehicle.
The practical experiences form stress mesurements, laboratory fatigue tests and fatigue life calculations of SKODA buses will be reviewed in the firs part of the contribution (Kepka-Kepka Jr., 2016). The second part of the contribution will present new university research activities. For example, design stress spectra are validated by stress measurements on real city roads and testing grounds. The effort is focused on probability dimensioning, taking into account an existing scatter of fatigue properties of materials and random loads of assessed components. The parametric studies were carried out which used the knowledge about stress spectra in the bus constructions and the recommendations of the International Institute of Welding for improving the fatigue strength of welded joints with HFMI treatment.
The contribution will be prepared under project LO1502 ‘Development of the Regional Technological Institute‘ under the auspices of the National Sustainability Programme I of the Ministry of Education of the Czech Republic aimed to support research, experimental development and innovation.
Kepka M. Durability and Fatigue Life Investigation of Bus and Trolleybus Structures: Review of SKODA VYZKUM Methodology. In: 2nd International Conference on Material and Component Performance under Variable Amplitude Loading, DVM, Darmstadt, Germany, March 23 – 26, 2009, pp.1231-1240, ISBN 978-3-00-027049-9.
Kepka M., Spirk S. Tests and computer simulations of electric buses. In: the 6th International Conference on Mechanics and Materials in Design: Recent advances in mechanics and materials. J. V. Silva Gomes and Sheker A. Meguid (Editors), Ponta Delgada, Portugal, 211-212, 2015.
Kepka M., Kepka M Jr.: Parametric Calculations of Allowable Operating Stresses in Vehicle Components under Fatigue Loading, In: IRF 2016 - New Trends on Integrity, Reliability and Failure, Paper ref. 6300, Porto, 2016
Keywords: servise stresses, laboratory fatigue tests, fatigue life calculations
Load Spectra for the Design of Railway Car-Bodies (#77)
1 IMA Materialforschung und Anwendungstechnik GmbH, Dresden, Saxony, Germany
This approach shows several important disadvantages:
The further use of the endurance limit approach in railway industry increases the danger of the use of non-valid design loads and the danger of a failed fatigue strength assessment after the obligatory on-track measurements for some types of railway vehicles.
In this paper, a new approach for the definition of design loads for car-bodies of railway vehicles will be described. It bases on the established normative load cases. These load cases will be combined to a synthetic operational load sequence, which shall be similar to measured operational loads. The first part of the paper describes the algorithm for the generation of synthetic operational load sequences. The second part of the paper describes the comparison of measured load spectra on different types of railway vehicles with the actual normative load cases for the endurance limit approach. At least, the parameters of the algorithms for the generation of synthetic operational load sequences will be adjusted to come to save design loads similar to the real operational loads.
2. Algorithm for the generation of synthetic operational load sequences
An example of such a synthetic load sequence is depicted in Figure 1.
3. Comparison of normative load cases with measured load spectra
The design loads for the fatigue strength assessment in railway applications are given as constant acceleration amplitudes with an assigned number of load cycles at N = 107. The measured load spectra were calculated from the measured load histories by rain-flow counting and mean stress correction, here as mean stress elimination by use of a mean stress sensitivity equal to Zero.
An example of such a comparison is depicted in Figure 2.
4. Adjustment of the parameters for the generation of synthetic operational load sequences
Finally, the validated algorithm for the generation of synthetic operational load sequences enables the fatigue strength assessment based on cumulative damage approach also in the design phase of railway vehicles. It is independent from the used materials and allows the consideration of new design concepts and of application-typical influences on the operational loads.
Keywords: Railway Car-Bodies, Spectra, Design