Page - 53 - in 3D Printing of Metals

Metals 2017,7, 91 onmechanicalproperties.Othermethods, inparticular, electronbeammelting (EBM),arewidelyused inadditiontoselective lasermelting(SLM).Their suitability for themanufactureofcomponents for applicationswithabio-medicalbackgroundhas inmanycasesbeenconfirmed[1–3]. Besidespure titaniumandtitaniumalloys [4,5],pure tantalum[6,7] isalsousedasamaterial for theproductionofsufficientlyresilientmechanical load-bearingelements. Additivemanufacturingand the three-dimensionaldesignof componentsor structuresusing Ti6Al4Vpowderofferawiderangeofunprecedentedapplications inmedical technologythanks to theirmultifariousproperties (biomedical compatibility, corrosionresistance,mechanicalproperties). Themechanicalpropertiesessentiallydefine thesuitabilityandsuccessfulapplicationofmechanically optimizedstructures, suchasbonesubstitutes, inbiomedicalfields [8–10]. Thegeometrical shapeaswell as theproperties of the structuresproducedcanbe influenced directly throughthemanufacturingparameters [11–13]andthroughheat treatment [14,15]. In thedevelopmentofopenporous load-bearingstructures, theorientationof the load-bearing rodsandthe loadangle [16–19]aswellas therelationshipbetweenelasticmodulusandporosityplay an important role [20,21]. Open porous load-bearing lattice structures consist of a regularly or irregularly composed form of geometrically describable individual elements. Here, simple lattice structures [22] play just as great a role as geometrically complicated forms (gyroid) [23]. Efforts to characterize the widespread latticestructures [24] range fromstudiesof themechanicalproperties tomacroscopicand microscopic investigations. The largenumberof researchprojects showsthehighrelevanceofgridstructures inengineering applications. The intentionhere is to create specificqualities byproducing structureswith ahigh degreeof freedom, as for example inmedical applications. Themechanical qualities againare the central consideration. The characterization of the relevant properties is carried out primarily on complete latticestructures [25], standardspecimens[26,27]oronapplicationmodelswithabiomedical background[28–30]. Theeffortsofmanyresearchgroupsfocusontheestimationof themechanicalpropertiesusing numericmethods. Labes et al. [31] developed amethod for studying the structural response and failureprocessofopenstainless steel316L latticestructuresmanufacturedusingSLM.Theypredicted theelasticmodulusofseveral latticestructureswithvariousstrut ratios. Topredict thequasi-static responseandfailureofdifferentcore latticestructuresheusedlinearstaticandnon-linearelasto-plastic analysis. Ahmadi et al. [32] present a new analytical solution and closed-form relationship for predictingmechanicalproperties, suchas theelasticmodulusandcriticalbuckling load. Toestimate themechanical properties of the diamond lattice, they used an analytical solution based on the Euler–Bernoulli theoryandananalytical solutionbasedontheTimoshenkobeamtheory. Inadditionto theestimationof themechanicalproperties,work is focusedonobtainingresults andcomparing themtopredictions. Ushijimaetal. [33] comparedanalytical andFEpredictionsof latticestructureswithexperimental results. Topredict the initial stiffnessandplastic collapsestrength of latticestructures,heusedbeamelementsaswellasaBCC(body-centeredcubic)unit cell topology. Suardetal. [34]presentedastandardizedmethodforpredicting themechanical responseof lattice structuresmanufacturedusingEBM.Twoequivalentdiametersweredefinedtosimulatetheproperties of the latticestructurewhile takingthemanufacturingconstraints intoaccount.Deshpandeetal. [35] discussedthemechanismofbendingandstretchingdominatedarchitectures fromcellularsolidsusing experimental and theoretical techniques. Mazuret al. [36] theoreticallypredicted thedeformation behaviorof latticestructures indifferentcell topologies,cellsizesandcellnumbers,andexperimentally validatedtheresults. Lastly, the mechanical properties are experimentally determined, evaluated and compared between the test partners and relationships.McKown et al. [37] tested a range ofmetallic lattice structures to investigate theircollapsebehavior, failuremechanismsandstrain-ratesensitivity. 53