Linear damage accumulation of self-pierce riveted joints (#107)
L. Masendorf1, M. Wächter1, S. Horstmann2, M. Otroshi2, A. Esderts1, G. Meschut2
1 Clausthal University of Technology, Institut für Maschinelle Anlagentechnik und Betriebsfestigket, Clausthal-Zellerfeld, Lower Saxony, Germany
Joining technology is regarded as a key technology for reducing energy consumption and CO2 imitation as well as the use of innovative materials and development of new, resource-saving products. Punch riveting is a widely used and established joining process in many sectors. The white and brown goods, electrical engineering, construction and, in particular, the automotive industry are some of the sectors mentioned here.
Since the design and assessment of punch rivet components with regard to structural durability can only be carried out experimentally using prototypes due to a lack of experience and calculation concepts, the improvement of this uneconomical and time-consuming procedure is the goal of this contribution.
Therefore, a numerical simulation and design method for cyclically loads punched riveted joints shall be introduced. This concept shall be based on the notch strain concept.
The following steps are necessary to achieve the goal shown above:
In order to verify the simulation and calculation method, service life investigations have been carried out on punched riveted components under constant and variable amplitude load.
The test results, as well as the workflow through the fatigue assessment and its accuracy in estimation the fatigue life will be shown in this contribution.
Keywords: punch rivet, notch strain conept, structural durability
Application of an Integral Treatment of Butt Joints for the Fatigue Life Assessment under Variable Amplitude Loading (#68)
1 Fraunhofer Institute for Structural Durability and System Reliability LBF, Materials and Components, Darmstadt, Hesse, Germany
The fatigue assessment of welded joints according to recommendations and standards is based on fatigue (FAT) classes. These FAT classes were derived from experimental results of specimens and components, but do not include the low cycle fatigue regime and, hence, an elastic-plastic description of the material behaviour. The typical fatigue life of structures within the design of truck cranes is related to the low cycle fatigue (LCF) regime and often focuses on critical details of welded joints. Butt joints are essential load-carrying welds. An example of highly stressed structures is the telescopic boom of truck cranes.
The analysis of existing service measurements already showed that service loading of highly loaded crane structures can be approximated by Gaussian-like load spectra with loads related to the low cycle fatigue regime.
For a fatigue life assessment in the transition from the low cycle to the high cycle fatigue regime, an integral treatment of butt joints has been introduced. This integral treatment is based on the cyclic material behaviour, but characterises butt welds by cyclic stress-strain curves and strain-life curves using representative volume elements to describe a material integral considering the range from base material across the weld to the base material with the help of strain-controlled fatigue testing. A strain-based approach using damage parameters to assess modelled stress-strain paths is used for the fatigue life estimation. This approach, using the integral treatment of the butt joint, is not just applied for the verification under constant amplitude loading, but also for the fatigue life estimation under variable amplitude loading of the Gaussian-like load spectra.
Keywords: integral treatment, strain-based fatigue life assessment, high-strength fine-grained steels, welded butt joints, gaussian load spectrum
Analysis of the notch effect components of weld joint (#85)
V. Chmelko1, M. Harakaľ2, P. Zlabek3
1 Slovak University of Technology, Applied Mechanics and Mechatronics, Bratislava, Slovakia
In general, the welded joints are multifactorial notches. This study presents the methodology of experimental separation of total notch factor into two basic components: geometrical influence (when the weld can be seen on the surface) and technological factors like (internal defects of the weld joint, structural changes of the material and residual stress). Proposed methodology of this separation comes out from the cyclic test of three specimens – group with an existing weld joint, group without any weld joint (base material) and another group where the outer geometry of the weld joint was removed (see figure).
In the article, there will be shown the effect of weld geometry on the weld joint fatigue life-time which will be obtained by FEM methods as well as there will be presented the methodology and discussion of practical usage for obtained results.
Keywords: weld joint, notch factor, life time
Extremely low cycle fatigue assessment model for structural steel and its application to welded joints (#122)
T. Hanji1, K. Tateishi1
1 Nagoya University, Department of Civil and Environmental Engineering, Nagoya, Japan
Low cycle fatigue damage was observed in steel bridge members, for instance, in the 1995 Southern Hyogo Prefecture Earthquake and the 2011 off the Pacific coast of Tohoku Earthquake. In a strong seismic event, steel members may undergo repetitive inelastic deformation. Simultaneously, extremely large cyclic strains are locally introduced to welded joints, which can cause low cycle fatigue cracks. In order to establish a design method against low cycle fatigue, fatigue strength of steel members, particularly that of welded joints, should be assessed as precisely as possible.
 K. Tateishi and T. Hanji (2004) Low cycle fatigue strength of butt-welded steel joint by means of new testing system with image technique, International Journal of Fatigue, Vol.26(12), pp.1349-1356.
Keywords: Extremely low cycle fatigue strength, Welded joint, Damage mechanics, Miner’s rule