No abstract

Anisotropic mechanical behavior is an inherent characteristic o f parts produced using additive manufacturing (AM) techniques in which parts are built layer by layer. It is expected that in-plane and out-of-plane properties be different in these parts. E-beam fabrication is not an exception to this. It is, however, desirable to keep this degree o f ani sotropy to a minimum level and be able to produce parts with comparable mechanical strength in both in-plane and out-of-plane directions. In this manuscript, this degree o f anisotropy is investigated fo r Ti6Al4V parts produced using this technique through ten sile testing o f parts built in different orientations. Mechanical characteristics such as Young's modulus, yield strength (YS), ultimate tensile strength (UTS), and ductility are evaluated. The strain rate effect on mechanical behavior, namely, strength and ductility, is also investigated by testing the material at a range o f strain rates from 10~2 to 10~4 s~*. Local mechanical properties were extracted using nanoindentation technique and com pared against global values (average values obtained by tensile tests). Although the prop erties obtained in this experiment were comparable with literature findings, test results showed that in-plane properties, elastic modulus, YS, and UTS are significantly higher than out-of-plane properties. This could be an indication o f defects in between layers or imperfect bonding o f the layers. Strong positive strain rate sensitivity was observed in out-of-plane direction. The strain rate sensitivity evaluation did not show strain rate dependency fo r in-plane directions. Local mechanical properties obtained through nano indentation confirmed the findings o f tensile test and also showed variation o f properties caused by geometry.

In this study, the degree of mechanical anisotropy was investigated through tensile testing of specimens built in different orientations and designed according to the ASTM D638 standard. The mechanical properties that were evaluated include Young’s modulus, ultimate tensile strength (UTS), and percentage elongation. Additionally, physical properties, such as mean surface roughness (Ra), density and dimension of the cross-sectional area, were also measured. These properties were then compared with the available standard data to see how SLA performs comparing to the traditional manufacturing methods. The obtained modulus of elasticity and UTS values of the printed samples were 2481 ± 50 MPa and 51.9 ± 1.3 MPa respectively, which were very similar to the standard data (2550 and 52 MPa, respectively) as provided by the material suppliers. The percentage elongation values (4.8% ± 0.4%) were a bit lower than the expected value of 6%. However, the surfaces of all the printed samples were quite smooth, with a surface roughness range of 2.28 ± 0.59 µm. A design of experiments was created to study the influence of the independent variables such as build orientation and angular orientation on the mechanical properties. Extensive statistical analysis, using the Taguchi method and analysis of variance (ANOVA), was performed to examine the effect of these independent variables on the mechanical properties. The SLA printed parts can be classified as isotropic since the build orientation and the angular orientation did not have a statistically significant impact on the mechanical properties. The effect of aging on the mechanical properties was also evaluated and it shows that the specimens that had been aged for a longer time resulted in superior mechanical properties. For example, the UTS increased from 24 to 54 MPa when the sample aligned parallel to the XY plane was aged from 1 week to 6 months, respectively. This significant increase implies that aging has a substantial effect on the mechanical properties of the parts fabricated by stereolithography. The resin used for this study, Visijet Sl Clear, produced very consistent mechanical properties in different directions.

No abstract

No abstract