Tobias Wille

Prediction of Process-Induce Distortions and Residual Stresses of Ancomposite Suspension Blade

This paper deals with a universal simulation strategy for the calculation of process-induceddistortions and residual stresses of a composite part. The mechanical material behavior is describedby a viscoelastic material model depending on temperature and degree of cure . The required materialparameters are derived by dynamic mechanical analyses. For the description of the reaction kinetic aphenomenological based model considering chemical and diffusion-controlled reactions is introduced.The reaction model parameters are fitted to isothermal and dynamic DSC measurements via globaland local optimization. The thermal expansion and chemical shrinkage are characterized by thermalmechanical analysis and using the contact angle measurement method. The simulation strategy isdemonstrated for a GFRP suspension blade for the automobile industry. Based on a sequential coupledtemperature-displacement analysis thermal hot spots, temperature and degree of cure distributions aswell as the final corresponding process-induced distortions and residual stresses are calculated andanalyzed. The development of the stiffness and the correlated stress during the curing process arediscussed in more detail. Furthermore, the effect of a degree of cure dependent stiffness on the stressesis investigated.

A robustness-based design strategy for composite structures

Purpose – This paper aims to present a new robustness-based design strategy for thin-walled composite structures under compressive loading, which combines strength requirements in terms of the limit and ultimate load with robustness requirements evaluated from the structural energy until collapse. Design/methodology/approach – In order to assess the structural energy, the area under the load-shortening curve between several characteristic points such as local buckling, global buckling, onset of degradation and collapse load is calculated. In this context, a geometrically nonlinear finite element analysis is carried out, in which the ply properties are selectively degraded by progressive failure. Findings – The advantage of the proposed methodology is observed by analyzing unstiffened composite plates under compressive loading, wherein the lightest plate that satisfies both strength and robustness requirements can be attained. Practical implications – As a practical implication, this methodology gives a ne...

Composite Process Chain Towards As-Built Design

The relation between design and manufacture is of particular importance within the composite structure development process. Therefore, a continuous composite process chain beyond state-of-the-art is described in this section. Such an all-embracing process chain realizes a concurrent engineering, where iteration loops are enabled and, thus, product improvements and higher process efficiency are achieved. Concurrent engineering comprises the various interdisciplinary working phases and provides the necessary connectivity. In contrast to the traditional one-way relation from design to manufacture, the improved process chain also deals with the feedback from manufacture to design, based on numerical simulations. This is demonstrated by the example of composite parts made by Tailored Fiber Placement (TFP), including effects of the feedback on load bearing capacity.

A robustness-based design strategy for composite structures – probabilistic approach

Purpose – The purpose of this paper is to present the probabilistic approach to a new robustness-based design strategy for thin-walled composite structures in post-buckling. Design/methodology/approach – Because inherent uncertainties in geometry, material properties, ply orientation and thickness affect the structural performance and robustness, these variations are taken into account. Findings – The methodology is demonstrated for the sake of simplicity with an unstiffened composite plate under compressive loading, and the probabilistic and deterministic results are compared. In this context, the structural energy and uncertainties are employed to investigate the robustness and reliability of thin-walled composite structures in post-buckling. Practical implications – As practical implication, the methodology can be extended to stiffened shells, widely used in aerospace design with the aim to satisfy weight, strength and robustness requirements. Moreover, a new argument is strengthened to accept the coll...