PSI - Issue 37

Mohammed Zwawi et al. / Procedia Structural Integrity 37 (2022) 1057–1064 Mohammed Zwawi/ Structural Integrity Procedia 00 (2019) 000 – 000

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3.2 Discussion A number of interesting observations were made in this study. Model “OR”— weighing 50 grams — withstood 2595 N, whereas the “AS” model (42 grams) only reached 2546 N before failure. Hence, the cylindrical holes within the “AS” model had a minimal effect on the loading capacity. The weight reduction in model “AS” compared to model “OR” was 16% ( Table 3). Based on the purchasing calculations, one gram of PLA filament costs 4 cents. Therefore, model “OR” cost USD$2, whereas the cost of model “AS” was reduced by 16%. The experimental results, along with the cost calculations, showed that model “AS” had excellent performance under loading with a weight reduction of 28%. Models “TK” and “FS” showed highly similar behavior, with the weight reduction and hole design affecting the loading capacity by 23 –25%. Model “TK” had a weight reduction of 23%, whereas model “FS” was 20% lower in w eight. Therefore, the loading capacity performance of model “TK” was better than the “FS” model. However, both models behaved poorly compared to model “OR”. Finally, model “AD” behaved the worst among all models, with its load capacity being reduced by 43% compared to model “OR”. The load capacity for each model vs. the models’ weights is displayed in Figure 6.

Table 3: Eye grab hook model data.

Eye grab hook model

Weight reduction

Load capacity reduction

Cost ($)

OR TK AD FS AS

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$2.00 $1.44 $1.44 $1.60 $1.68

28% 28% 20% 16%

23% 43% 25%

2%

Figure 6: Force applied vs. hook mass for each eye grab hook model.

All eye grab hook model failures were analysed to investigate the effect of the holes on each failure pattern. First, the models were modelled in SolidWorks® simulations using linear FEA. The hook in the simulation imitates the eye grab hook’s real -life mechanical behaviour and predicts the failure points at which the crack initiates and propagates. The displacements of the eye grab hooks in the simulations were compared to the displacements in the experimental results at the load required to produce a failure. A comparison study is presented in Table 4. Furthermore, the simulation results well predicted the crack initiation, where the red arrow points, for each eye grab hook model, as shown in Figure 7 . Model “OR” in Figure 7(a) had a crack initiation point as expected in the simulation. The red colour shows where the maximum stress was accumulated due to the combined load concentration. Models “TK” and “AD” fractured at the minimum area, as expected by the simulation in Figure 7(b) and Figure 7(c), respectively. Model “FS” had the crack initiation point at which the stresses were at their maxima, as illustrated in Figure 7(d). In contrast to the other models, model “AS” did not fail as expected by the FEA simulation (Figure 7(e)), yet its failure prediction point was very close.

Table 4: Comparison of experimental and FEA displacements.

FEA

Eye grab hook model

Max. experimental load (N)

Experimental displ. (mm)

Disp. (mm)

Disp. error %

Strain

Stress (MPa)

OR

2595

5.66

6.08

7.42%

4.06%

7.95