Abstract
Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.
Highlights
IntroductionInstead of removing material from an existing block of material, additive manufacturing (AM)
Instead of removing material from an existing block of material, additive manufacturing (AM)technologies form a component by fusing material in a layerwise manner
Specimens without integrated eSHM system were subjected to the loading until the deformation of the specimen exceeded pre-set limits corresponding to the complete rupture of the specimen
Summary
Instead of removing material from an existing block of material, additive manufacturing (AM). Technologies form a component by fusing material in a layerwise manner. The three-dimensional design is split into different layers, each layer containing two-dimensional cross sectional information of the component at a particular height in the component. Starting from the base plate, material is selectively added according to the two-dimensional shape defined in the layer. Once a layer is completed, the layer is added on top of the previous one until the build is completed. AM was initially introduced as being a prototyping technology. Recently has AM been considered a promising technique for functional part production [1]. The design freedom offered by AM is a key Materials 2017, 10, 993; doi:10.3390/ma10090993 www.mdpi.com/journal/materials
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