Importance of local microstructure for damage tolerant light weight design of Ti–6Al–4V forgings

Effect of microstructure on the fatigue properties of Ti–6Al–4V titanium alloys

“…), titanium components (particularly Ti-6Al-4V) are often used for manufacturing critical systems such as airfoils, undercarriage components, and airframes [1][2][3][4] instead of heavy steel components. During these applications titanium structures are often exposed to fatigue loading [1].…”

“…Depending on the thermomechanical treatment or heat treatment of the (α + β) titanium alloy, such as Ti-6Al-4V, the microstructure and mechanical properties can vary in a wide range [3,6]. Such influences have been documented in numerous reports in the literature [4,[7][8][9][10][11].…”

Topology and Shape Optimization of a Mount Link Considering Local Microstructure-Dependent Fatigue Properties Obtained From Forming Simulations

“…The fatigue model used for Ti-6-4 does not only take into account the local microstructure resulting from the forging process and heat treatment, but also the beneficial effects of surface treatments such as shot peening, the stress gradient, the mean and amplitude stress and the operating temperature [4], as depicted in Figure 14. This model is implemented into the fatigue postprocessor BoFaP [2] (Boehler Fatigue Postprocessor), which accesses directly the results of the Abaqus TM stress analysis and the microstructural data of a Deform TM forging simulation; damage and critical crack sizes are estimated from the calculated local stresses, local microstructural parameters, and the given load spectrum, as detailed below.…”

“…All components of the stress tensors A, B and C, which result from the maximum force for each direction, are multiplied with the amplitude factors f a*k and the mean stress factors f m*k (equation (1) - (3) and equation (6) - (8); * denotes A, B, or C, respectively). In the next step, a total mean stress S mk and a total amplitude stress S ak as resulting stress from all loading directions is calculated as shown by equation (9) and equation (4). Since it has been found that the equivalent von Mises stress proves to be very suitable for the material Ti-6-4 with respect to fatigue loading, now an equivalent mean stress |S mk | and an equivalent amplitude stress |S ak | are calculated (equation (10) and equation (5)).…”

“…Rather, we are concerned with optimizing the geometrical design of the engine mount by means of topology and shape optimization in a way that weight and/or fatigue lifetime are optimized. The fatigue lifetime calculation consists of a finite element stress analysis followed by post-processing by a special purpose software [2] in which a complex fatigue model [4] for Ti-6-4 has been implemented; the model allows an assessment of cumulative fatigue damage following the Miner rule as well as the computation of admissible flaw sizes, i.e., a damage tolerance assessment, under a given load spectrum. In order to verify the entire simulation chain, several topology-optimized components have been manufactured and tested at different loads; the numerical predictions are in good accordance with the experiments.…”