# Experimental Comparison of Fastener Implementation Approaches in Fused Deposition Modeling
## 3 Results and Discussion
A significant increase is observed between 10% and 20% infill samples, but the change is very small when the infill ratio is increased to 40%. The average tensile strength of 20% infill parts is 779 N with a standard deviation of 11%; for 40% infill parts, the strength is 957 N, and there is a standard deviation of 4%. Comparing the three types of samples with 10% infill, we can see an obvious alignment as type III is, on average, 26% stronger than type II, which is 45% stronger than type Ia. As seen in Figure 10, the differences are approximately 125 N. While type Ib and type II samples are in the middle in terms of tensile strength, blank samples are at the weak end in terms of flexural strength. Type III samples are the strongest in both results for 10% infill. Three-point flexural tests were carried out according to the ISO 178 standards. In order to compare and better evaluate the results, blank samples were also tested in the three-point flexural test. The three-point flexural test results of one of each design and infill are presented in Figure 11. The flexural modulus of the samples is almost the same up to 1.2 mm displacement. The reason for that is the samples have the same wall thickness and top and bottom thickness. After that point of flex, infill and other elements have effects on strength. Between samples with 40% infill, there is a small difference, but 10% and 20% infill parts show different plot and different values of maximum strength. The ultimate strength results of all the samples are given in Figure 8.0 The average strength of the blank samples with 10% infill is 510 N, with 20% infill it is 569 N, and with 40% infill it is 810 N. For 10% infill samples, the standard deviation is 4%. The consistency in the results increases with the infill ratio. The standard deviation is 2% for 20% infill parts and 1% for 40% infill parts. Figure 8.1 The load/displacement results of flexural test samples. The flexural test results for type Ia samples present a significant difference between 40% and the others. The average strength is 543 N for 10% samples and 583 N for 20% samples. Parts with 40% infill have an average strength of 803 N, which is 35% more than the 20% infill parts. Type I.b samples present the weakest samples for the flexural tests. Samples with 10% infill have 473 N strength, 20% samples have 559 N strength, and samples with 40% infill have 738 N strength. Type I.b is the only design in which five of the samples were broken into two pieces in the flexural tests. Results of the three-point flexural test of the type II samples: the average strength of the 10% infill parts is 520 N, that of the 20% infill parts is 634 N, and that of the 40% infill parts is 824 N.  
The type III flexural test results reveal that type III is the most durable design among the others. The three-point flexural strength of the 10% infill samples is 602 N, 661 N for 20% infill, and 833 N for 40% infill samples. The results for the 40% infill are very close to each other. When designing any part with 40% infill, flexural strength is not an important factor if longer inserts are not used, such as in type I.b. The infill ratio might be lower when weight is a concern in design, like in an aerial vehicle; the 27% difference between the highest value and the lowest value is worth considering for the 10% infill. Even though type I.b has better values in other tests, other design variables should be taken into account because of the lower strength in flexural tests. Torque tests were conducted to determine the maximum torque each design can handle in the case of tightening screws, and the results are presented in Figure 8.2 The ultimate torque strength of type I.a samples with 10% infill is 3.2 Nm, for samples with 20% infill it is 3.66 Nm, and for samples with 40% infill it is 4.04 Nm, with an average of 12 samples each. Type I.b samples with 40% infill show the best results in terms of the torque test, with an average strength of 5.05 Nm.