Abstract
Tensile fatigue specimen of G20Mn5 and G22NiMoCr5-6 were tested to quantify the influence of internal defects on the fatigue resistance of cast steel components. Defects with varying sizes, geometric shapes and distribution were enforced by influencing the solidification and recorded by computer tomography (CT). Besides the characteristics of the detected cavities, the surrounding fungoid microstructure is classified and evaluated. Later the specimens were tested under cyclic tension and S/N-curves are derived. These data form the basis for extensive numerical simulations of the damage process and the crack growth of every individual specimen. Both processes are affected by the local multiaxial stress states and have their origin in the inside of the specimen. For validation, knowledge of the crack initiation time and propagation properties are essential. Therefore, all specimens respectively the properties of the internal defects are monitored during testing with three different state-of-the-art non-destructive testing (NDT) methods. Background and application of these NDT techniques are described within this paper. Finally, fracture surface analyses show different failure modes and provide further information for model validation.
Highlights
Cast steel components are used in several industrial sectors such as construction industry, transportation or mechanical engineering
Former research [1,2,3] has shown a reduction in lifetime as these defects cause multiaxial stress fields and act as notches which could have the shape of sharp cracks
During the last decades foundry research mostly focused on the prediction and avoidance of casting defects
Summary
Cast steel components are used in several industrial sectors such as construction industry, transportation or mechanical engineering. During the last decades foundry research mostly focused on the prediction and avoidance of casting defects This results in higher expenses in the casting process causing uneconomic and oversized components. The scope of the present article is the description of fatigue tests on tensile specimen with internal defects These tests form the basis for numerical simulations and the improvement of design guidelines. Special evaluation techniques such as state-of-the-art NDT methods are required due to the variety and location of the casting imperfections. Besides the investigations presented within this paper, material characterization is done based on monotonous tensile tests, low-cycle fatigue tests, incremental step tests, crack growth tests and high-cycle fatigue tests For these investigations, blocks of material without imperfections have been casted. After depicting the relevant influences numerically, parameter studies and worst-case scenarios are investigated to deduce design procedures
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