Applied Mechanics and Materials Vol. 104

Abstract: The recent emphasis on car styling caused tolerance requirements for sheet metal parts in the automotive industry to increase. In addition, the new materials (steel and alloy) have a different deviation behavior around the springback after the deep-drawing process. In the early design phases a product can be optimized to fulfill tight tolerance specifications. This work shows the simulation background and the resulting optimization methodology.

Abstract: Uncertainty during production processes has an important influence on the product quality as well as production costs. For multilevel process chains with serially connected processes, additional uncertainty can be caused by the previous step. The manufacturing of precision holes by drilling and reaming is an important multilevel process chain. The interactions between machine, tool and pre-drilled hole cause process errors during the quality determinant final reaming process. In this paper, a systematic approach for the identification and control of uncertainty during the reaming process is presented. Thus, the influence of key aspects like skewness of pre-drilled hole or the influences of material strength gradients are analyzed. Further, simulation models for the consideration of these uncertainties are presented.

Abstract: Today, the components of smart structures consisting of structural and smart materials are generally produced separately and assembled in additional processes afterwards. An alternative approach, which combines the forming of metallic parts and the assembly of the structures in one process step, is proposed in this paper. Incremental forming processes are applied for this operation. Significant joining mechanisms will be analyzed and some applications of this combined forming and assembly process are shown. As sensors, smart components allow a monitoring of appearing loads, as actuators they allow an active influencing on appearing disturbances. The research contains numerical analyses and experimental tests.

Abstract: The paper presents an algorithm of fatigue life determination for materials with no parallel fatigue characteristics under pure bending and pure torsion. The presented model uses the iteration method, and the applied fatigue criterion is function of the ratio of normal and shear stresses coming from bending and torsion, respectively. Three materials were applied for analysis: CuZn40Pb2 brass, 30CrNiMo8 medium-alloy steel and 35NCD16 high-alloy steel.

Abstract: Uncertainty in load carrying systems e.g. may result from geometric and material deviations in production and assembly of its parts. In usage, this uncertainty may lead to not completely known loads and strength which may lead to severe failure of parts or the entire system. Therefore, an analysis of uncertainty is recommended. In this paper, uncertainty is assumed to occur in processes and an approach is presented to describe uncertainty consistently within processes and process chains. This description is then applied to an example which considers uncertainty in the production and assembly processes of a simple tripod system and its effect on the resulting load distribution in its legs. The consistent description allows the detection of uncertainties and, furthermore, to display uncertainty propagation in process chains for load carrying systems.

Abstract: Nowadays, mechanical industries operate in a highly competitive environment, therefore the process of developing a component from concept through detailed Computer-Aided Engineering (CAE) and performance validation is optimized for reduced development time and increased product performance. To continuously improve the product design and performance and reduce the costs and time to market, the design and performance engineering is shifted more and more towards virtual modeling and simulation processes from the expensive test-based design evaluations. Secondly, the booming introduction of active and adaptive systems in mechanical structures leads to a ‘mechatronics systems’ revolution, which further improves the product performance at the expense of increased system complexity. It is noted that the potential of structural dynamics test and analysis methods for addressing a structural dynamics design assessment or design optimization depends largely on the confidence that one can have in the results. That is, the results must be accurate, characteristic for the actual problem (and not be the result of testing artifacts) and representative for the actual behavior of the investigated structure. In this context, a key aspect is to be aware of the key sources of uncertainty in the designed product, and the impact thereof on the product performance in terms of structural dynamics, crashworthiness and/or acoustics. This paper reviews the main elements of test data and modal modeling uncertainty and assesses the impact of the uncertainty on some typical modeling problems taken from automotive and aerospace industry.

Abstract: The content of this work is the presentation of the prototype of a new active suspension system with an active air spring. As being part of the Collaborative Research Unit SFB805 “Control of Uncertainties in Load-Carrying Structures in Mechanical Engineering”, founded by the Deutsche Forschungsgemeinschaft DFG, the presented active air suspension strut is the first result of the attempt to implement the following requirements to an active suspension system: Harshness and wear: Reduced coulomb friction, i.e. no dynamic seal. Plug and drive solution: Connected to the electrical power infrastructure of the vehicle. Vehicle and customer application by software and not by hardware adaption. These requirements were defined at the very beginning of the project to address uncertainties in the life cycle of the product and the market needs. The basic concept of the active air spring is the dynamic alteration of the so-called effective area. This effective area is the load carrying area A of a roller bellow and defined by A:=F/(p-pa). F denotes the resulting force of the strut, p the absolute gas pressure and pa the ambient pressure. The alteration of this effective area is realized by a mechanical power transmission, from a rotational movement to four radial translated piston segments. Due to the radial movement of the piston segments, the effective area A increases and so does finally the axial compression force F. The prototype presented in this paper serves as a demonstrator to proof the concept of the shiftable piston segments. This prototype is designed to gather information about the static and dynamic behavior of the roller bellows. Measurements show the feasibility of the concept and the interrelationship between the piston diameter and the resulting spring force.

Abstract: The paper describes a study carried out by Dipartimento di Meccanica Politecnico di Milano, aimed at investigating how uncertainty in railway vehicle suspension components can be treated in the framework of vehicle design and performance assessment in respect to vehicle dynamics. In railway vehicle suspensions, sources of parameter uncertainty may arise from inaccuracy in the modelling of a vehicle component or from a scatter in the behaviour of nominally identical components, on account of the variability implied by the component manufacturing process. The approach proposed in this paper, completely new to the railway field, is to use statistical methods having different complexity (and entailing a proportional computational effort), to analyse the propagation of uncertainty from the parameters input in the vehicle mathematical model to the results of running dynamics, in terms of the assessment quantities used for verification and evaluation of train performances. The problem is treated by numerical means, being the dependency of simulation outputs from the input parameters typically non-linear, and not defined in an analytical form.

Abstract: Uncertainty in usage of load-carrying systems mainly results from not fully knownloads and strength. This article discusses basic approaches to control uncertainty in usage ofload-carrying systems by passive and active means. An active low damped column system critical to buckling is presented in which a slender column can be stabilised actively by piezo stackactuators at one of its ends only. Uncertainty may be controlled in the active column systemby temporarily enhancing the bearable axial load theoretically up to three times compared to the passive column system in case of critical loading. However, in the implementation of theseapproaches, system-speci c uncertainty may also occur. In numerical examinations it is shown, that small deviations in measured axial loading may increase the active force signi cantly to achieve stabilisation. The increase of applied active force might affect lifetime of the piezo stackactuators and thus the stabilising capability of the active column system.

Abstract: The algorithm of fatigue life determination for machine elements subjected to random loading uses fatigue characteristics of the material determined under constant-amplitude loading. They are usually stress or strain characteristics as well as characteristics using the energy parameter. Their correct selection influences correctness of the obtained results related to the experimental data. The paper presents analysis of convergence of the calculated fatigue lives of some constructional materials subjected to random loading under uniaxial loading state. For calculations concerning one material the same loading state was assumed and fatigue characteristics were determined on the basis of one data set obtained under constant strain amplitude tests. Calculated fatigue lives based on different fatigue characteristics were compared and their convergences were tested. It has been proved that convergences are different depending on the material. The comparison results were presented in form of graphs.