**4. Conclusion**

176 Mechanical Engineering

In analyzing the feasibility of fused deposition modeling to fully evolve into a rapid manufacturing tool, it is important to assess the fatigue properties of FDM specimens and their dependence upon raster orientation. A comprehensive fatigue study is warranted and is currently underway by the authors. At this time, however, a pilot fatigue study utilizing a tension-tension loading configuration has been completed. The fatigue tests utilized specimens originally with natural undamaged surfaces. The maximum load of the fatigue cycles was set to 70% of the mean failure load as determined in the static tensile tests for each specific raster orientation. The minimum cycle load was set as 1/10 of the maximum load, and the resulting stress ratio R for the fatigue tests was 0.1. The value of 70% of the mean failure load was selected following a preliminary study focused on determining a reasonable compromise between the occurrences of excessively long fatigue lives and being

All fatigue tests were performed at room temperature. To eliminate any heating effects due to considerable strains, the fatigue loading was applied at a low frequency, 0.25 Hz. The specimen surface was observed during testing and the number of cycles to final failure was determined. The test results appear in Table 11. The 45º raster orientation fractured with the smallest mean number of cycles to failure (1312), representing only 26.7% of that of the

Cycles to Failure

A one-way ANOVA was completed in order to consider the equivalence of the mean number of cycles to failure for the four raster orientations. The results, appearing in Table 12, provide a calculated F-test statistic of F(3,16) = 124.95 and a *p*-value of 0.0001, indicating a significant difference between some or all of the mean cycle values associated with the four raster orientations at a level of significance of = 0.05. The resulting coefficient of

Source DF SS MS F P Raster Angle 3 54093034 18031011 124.95 0.0001

Tukey post hoc comparisons indicated that the difference between the mean number of cycles to failure was not significant for the pairwise comparisons of 0° with +45°/-45°, or 45° with 90° raster specimens. All other pairwise comparisons were significantly different.

 Longitudinal (0º) 4557 694 Diagonal (45º) 1312 211 Transverse (90º) 1616 195 Default (+45º/-45º) 4916 150

Standard Deviation

**3.5 Tension-tension fatigue testing** 

too close to the static strength.

+45º/-45º raster orientation (4916).

Raster Orientation Mean No.

determination associated with this analysis was R2 = 0.9591.

Total 19 56401993

Error 16 2308959 144310

Table 12. One-way ANOVA results for tension-tension fatigue testing

Table 11. Tension-tension fatigue test results

The mechanical properties of ABS specimens fabricated by fused deposition modelling display anisotropic behaviour and are significantly influenced by the orientation of the layered rasters and the resulting directionality of the polymer molecules. The presence of air

Anisotropic Mechanical Properties of ABS Parts Fabricated by Fused Deposition Modelling 179

ASTM Standard D3039/D3039M – 08. (2008). Standard Test Method for Tensile Properties of

ASTM Standard D3479. (2007). Standard Test Method for Tension-Tension Fatigue of

Chua, C., Feng, C., Lee, C. & Ang G. (2005). Rapid investment casting: direct and indirect

Es Said, O., Foyos, J., Noorani, R., Mendelson, M., Marloth, R. & Pregger, B. (2000). Effect of

Lee, C., Kim, S., Kim, H. & Ahn, S. (2007). Measurement of anisotropic compressive strength

Montgomery, D. (2009). *Design and Analysis of Experiments* (7th Edition), John Wiley & Sons,

Odian, G. (2004). *Principles of Polymerization*(4th Edition), John Wiley & Sons, ISBN 978-0-

Riley, W., Sturges, L. & Morris, D. (2006). *Mechanics of Materials* (6th Edition), John Wiley &

Rodriguez, J., Thomas, J. & Renaud, J. (2001). Mechanical Behavior of Acrylonitrile

Rodriguez, J., Thomas, J. & Renaud, J. (2003). Mechanical behavior of acrylonitrile butadiene

Sood A., Ohdar R. & Mahapatra, S. (2010). Parametric appraisal of mechanical property of

Sood, A., Ohdar, R. & Mahapatra, S. (2011). Experimental investigation and empirical

Sun, Q., Rizvi, G., Bellehumeur, C. & Gu, P. (2008). Effect of processing conditions on the

*Advanced Research*, DOI:10.1016/j.jare.2011.05.001, ISSN 2090-1232

*Rapid Prototyping Journal*, Vol. 7, No. 3, pp. 148-158, ISSN 1355-2546

Butadiene Styrene (ABS) Fused Deposition Materials. Experimental Investigation.

styrene fused deposition materials modeling. *Rapid Prototyping Journal*, Vol. 9, No.

fused deposition modelling processed parts. *Materials & Design*, Vol. 31, No. 1, pp.

modeling of FDM process for compressive strength improvement. *Journal of* 

bonding quality of FDM polymer filaments. *Rapid Prototyping Journal*, Vol. 14, No.

*and Manufacturing Processes*, Vol. 15, No. 1, pp. 107–22, ISSN 1532-2475. Lee, B., Abdullah, J. & Khan, Z. (2005). Optimization of rapid prototyping parameters for

*Processing Technology*, Vol. 182, pp. 477–488, ISSN 0924-0136

from: <www.astm.org>

*Technology*, Vol. 25, pp. 11–25, ISSN

pp.54–61, ISSN 0924-0136

pp. 627–630, ISSN 0924-0136

471-27400-1, Hoboken, New Jersey

4, pp. 219-230, ISSN1355-2546

2, pp. 72 – 80, ISSN 1355-2546

287–95, ISSN 0261-3069

ISBN 978-0-470-12866-4, Hoboken, New Jersey

Sons, ISBN 978-0-471-70511-6, Hoboken, New Jersey

*International*, West Conshohocken, Pennsylvania, DOI: 10.1520/D0790-10, Available

Polymer Matrix Composite Materials. *ASTM International*, West Conshohocken, Pennsylvania, DOI: 10.1520/D3039\_D3039M-08, Available from: <www.astm.org>

Polymer Matrix Composite Materials. *ASTM International*, West Conshohocken, Pennsylvania, DOI: 10.1520/D3479M-96R07, Available from: <www.astm.org> Caulfield, B., McHugh, P. & Lohfeld, S. (2007). Dependence of mechanical properties of

polyamide components on build parameters in the SLS process. *Journal of Materials* 

approaches via model maker II. *International Journal of Advanced Manufacturing* 

layer orientation on mechanical properties of rapid prototyped samples. *Materials* 

production of flexible ABS object. *Journal of Materials Processing Technology*, Vol. 169,

of rapid prototyping parts. *Journal of Materials Processing Technology*, Vol. 187–188,

gaps and the quantity of air voids between the rasters or fibers additionally influences the strength and effective moduli in regard to all of the tests completed in this study.


The results of this project are useful in defining the most appropriate raster orientation for FDM components on the basis of their expected in-service loading. Results are also useful to benchmark future analytical or computational models of FDM strength or stiffness as a function of void density. Additional research currently in progress includes a thorough fatigue analysis of FDM specimens with varying raster orientations.

### **5. References**


gaps and the quantity of air voids between the rasters or fibers additionally influences the

a. Tension tests indicate that the ultimate and yield strengths are the largest for the 0° raster orientation, followed by the +45°/-45°, 45°, and 90° orientations in descending order. The differences between mean ultimate tensile strengths are significant for all pairwise comparisons of different raster orientations. Fracture paths are affected by the directionality of the polymer molecules and the strength of individual layers. The longitudinal specimens benefit from the alignment of molecules along the stress axis. b. The compression test data indicates that the 45º raster specimens are significantly weaker in compression than the other raster orientations, and they distort prior to failure as a result of shearing along the raster axes. The other three raster orientations have mean yield strengths that are significantly larger than that of the 45º raster specimens, and that

c. The results of both three-point bend and impact tests correlate well with tension test results, again indicating that the yield strengths are the largest for the 0° raster orientation, followed by the +45°/-45°, 45°, and 90° orientations in descending order. The 0° rasters offer the most resistance to bending due to the largest effective raster lengths. As raster angle increases, the effective length and associated flexural and impact strengths decrease. Mean flexural and impact strengths are significantly affected by raster orientations, with the pairwise comparison of 45º and 90º rasters as the only

d. Preliminary tension-tension fatigue tests indicate anisotropic behaviour on the basis of raster orientations. The difference between the mean number of cycles to failure was statistically significant for all pairwise comparisons other than 0° with +45°/-45°, and 45° with 90° raster specimens. Failure modes are similar to those seen in static tension tests. The results of this project are useful in defining the most appropriate raster orientation for FDM components on the basis of their expected in-service loading. Results are also useful to benchmark future analytical or computational models of FDM strength or stiffness as a function of void density. Additional research currently in progress includes a thorough

Ahn, S., Montero, M., Odell, D., Roundy, S. & Wright, P. (2002), Anisotropic Material

ASTM Standard D256. (2010). Standard Test Methods for Determining the Izod Pendulum

Pennsylvania, DOI: 10.1520/D0256-10, Available from: <www.astm.org> ASTM Standard D695. (1996). Standard Test Method for Compressive Properties of Rigid

ASTM Standard D790. (2010). Standard Test Methods for Flexural Properties of

Properties of Fused Deposition Modeling ABS. *Rapid Prototyping Journal*, Vol. 8, No.

Impact Resistance of Plastics. *ASTM International*, West Conshohocken,

Plastics. *ASTM International*, West Conshohocken, Pennsylvania, DOI:

Unreinforced and Reinforced Plastics and Electrical Insulating Materials. *ASTM* 

strength and effective moduli in regard to all of the tests completed in this study.

are statistically equal to each other at a level of significance of = 0.05.

fatigue analysis of FDM specimens with varying raster orientations.

10.1520/D0695-10, Available from: <www.astm.org>

one with no statistical difference.

4, pp. 248 –257, ISSN 1355-2546

**5. References** 

*International*, West Conshohocken, Pennsylvania, DOI: 10.1520/D0790-10, Available from: <www.astm.org>


**Design and Evaluation of Self-Expanding Stents** 

Atherosclerosis is one of the most prominent diseases that induce dysfunction of circulation, and it is a disease of large and medium size arteries. If cholesterol presenting at high concentration in a blood injures an intima, a white corpuscle, i.e. a monocyte, goes into the intima and mutates into a foam cell. Then, smooth muscle cells migrate from the media to the intima, and they grow proliferously there. Based on these phenomena, cholesterol and other lipid materials accumulate in the intima. Atherosclerosis has become a serious problem in the developed countries that are aging. Therefore, countermeasures to the atherosclerosis have become important. Although there are various medical treatments for the atherosclerosis, a stent placement has received much attention as a minimally invasive procedure for vascular stenotic lesion based on the coronary atherosclerosis, the arteriosclerosis obliterans, etc. A stent is a cylindrical tube-shaped medical device that can expand the stenotic lesion in a blood vessel continuously. When considering the expansion method of a stent, two types are available. One is a self-expanding type that can expand by itself when released from the sheath of a catheter. Another is a balloon-expandable type that must be expanded forcibly using a balloon catheter. Because the self-expanding stent continues to expand to the memorized diameter at the stenotic lesion, it has the long-term patency of a vascular wall. In the present study, the main target is the self-expanding type. Recently, the severe problem of in-stent restenosis has arisen in a blood vessel with a stent placed and left in it. In-stent restenosis results from the neointimal thickening in the blood vessel based on the hyperplasia of smooth muscle cells. The hyperplasia of smooth muscle cells is caused by a mechanical stimulus from the stent to the vascular wall. The drugeluting stent (DES) containing immunosuppressive agents is already in clinical use to resolve this problem (Morice et al., 2002). It can be said that the DES is more effective in preventing the development of restenosis than a bare metal stent (BMS). However, it can be said that the DES does not help to improve the life prognosis or to prevent myocardial infarction (Babapulle et al., 2004; Kastrati et al., 2007; Lagerqvist et al., 2007). It is also reported that the DES might cause deterioration in the life prognosis, although the BMS does not (Nordmann et al., 2006). Depletion of immunosuppressive agents has been pointed

**1. Introduction**

**Suitable for Diverse Clinical Manifestation** 

**Based on Mechanical Engineering** 

*Department of Biomedical Engineering, Graduate School of Biomedical* 

Daisuke Yoshino and Masaaki Sato

*Engineering,Tohoku University,* 

*Japan* 

Upcraft, S. & Fletcher, R. (2003). The rapid prototyping technologies. *Assembly Automation*, Vol.23, No.4, pp. 318–330, ISSN 0144-5154 **8** 
