Zur Entwicklung der Steifigkeitsmatrizen für dünnwandige Stäbe

On the development of stiffness matrices for thin‐walled members. A glance into the early development of element stiffness matrices for thin‐walled members is given in the present paper and their most mature shapes are shown. Those shapes, the most general and later reduced to two particular forms, refer to the specifics of the classical Vlasov theory of thin‐walled bars [1] as well as to the Bornscheuer systematics of the cross‐sectional properties involved [2]. Appropriate modifications of the relevant matrices are performed and their coordinate system dependence is demonstrated.     

Experimental results and fatigue life evaluation of magnesium laserbeam‐welded joints under proportional and non‐proportional multiaxial fatigue loading with variable amplitudes

Fatigue life of magnesium laserbeam‐welds (AZ31 and AZ61 alloys) was assessed experimentally under variable amplitude loadings. The specimens were subjected to load‐controlled cyclic loadings. The tests were carried out using a Gauss‐distributed amplitude sequence of length L_S = 5 · 10⁴ cycles and loading ratio R = –1 under pure axial, pure torsion as well as in‐phase and out‐of‐phase combined loadings. The notch stresses were obtained from a linear‐elastic FE‐model using the reference radius approach with r_ref  = 0.05 mm. The stress‐based hypotheses were applied: Effective equivalent stress hypothesis (EESH), shear stress intensity hypothesis (SIH), Findley, and modified Gough‐Pollard. A non‐proportionality factor is introduced and steps required for computing are presented in order to improve fatigue life assessment under non‐proportional loadings.     

Effect of cut-outs shape and position on the axial compression behavior of aluminum thin-walled structures

The effect of cut-outs positions and shapes on deformation behaviors and energy absorption of automobile thin-walled structures is researched by quasi-static axial compression, using MTS machine and digital image correlation method. The accuracy of finite element modeling is verified by axial compression test. The relationship between variation characteristics of different time and sections and deformation of the sample is analyzed. The results show that the number of surface deformation concentrated areas is affected by position of circular cut-outs. Peak load of sample could be effectively reduced by slotted-shaped cut-outs. The energy absorption of slotted-shaped cut-outs with different aspect ratios and directions is different, horizontally-long-slotted cut-outs is increased by 5.13 %. The position of deformation concentration region is affected by compression half-wavelength. Deformation concentration region of sample less than half-wavelength is below cut-outs. By digital image correlation method, strain of horizontally-long-slotted cut-outs is more concentrated. Peak load is effectively reduced. The results of finite element analysis show that when the thin-walled structure is bulking, the section of sample is deformed from top to bottom. The initial area of cross-section at center of cut-outs is linear with peak load. These achievements may serve as guideline for enhancing compression performance of thin-walled structures.     

Experimental Analysis of the folding force in thin wall extruded cells under quasi‐static in‐plane loading

In most of the engineering structures, specially moving ones and generally in structures under dynamic and static loadings, energy absorber systems are implemented for preventing or reducing damages. These systems are employed in all on‐road vehicles, train wagons, airplanes and ships. Energy absorbers are subjected to two forms of in‐plane and out‐of‐plane loadings. In this paper, the effects of geometrical parameters such as thickness and height of structure and mechanical parameters such as yield stress in the cell structure are investigated. The effect of changing boundary conditions on the folding force is also investigated. According to the results, the energy absorbed by the cell, directly relates to the increase in the number of rows; the main reason of this increase is the increase in shared walls. Moreover, doubling the wall thickness has resulted in a 4.7 times higher energy absorption. In addition, the accuracy of different analytical models is compared, and the model with most precise predictions is introduced.