PSI - Issue 72

P.M.M. da Silva et al. / Procedia Structural Integrity 72 (2025) 69–76

72

2.2.3. DCB test specimens The specimens for the DCB test were machined to the dimensions specified in the ASTM D5528-01 standard. The initial crack was cut on a Minitom precision cutting machine from Struers. A diamond cutting disc from Metkon with a thickness of 0.4 mm and Ø127 mm was used at 400 rpm. The final dimensions are shown in Fig. 2.

Fig. 2. DCB specimen size based on the ASTM D5528-01 standard.

Hinges were attached to the specimens for fixation to the machine. All contact surfaces were sanded, cleaned, and degreased with acetone. After bonding, the adhesive cured for one week. One specimen side was prepared to measure crack propagation, by applying brittle paint and glueing a millimeter scale to measure the crack length ( a ). 2.2.4. ENF test specimens The manufacturing process for the ENF test specimens is identical to the DCB specimens. However, the ENF test does not require any fixing system to the test machine. Fig. 3 shows the specimen dimensions. A fragile paint was applied to the side face and a millimeter scale has been glued on to make it easier to measure a .

Fig. 3. ENF specimen dimensions.

3. Results 3.1. Tensile mechanical tests

The DIN EN ISO 527-04: 1997 standard was chosen for this test. The test at room temperature was run at 5 mm/min. A mechanical extensometer was applied to measure the strains. After processing the data, the mechanical properties were calculated. A more detailed analysis shows that  f follows a proportional linearity for SMC 15%, SMC 20% and SMC 45% (Fig. 4 a). However, the values for SMC 30% do not follow the same tendency. The E values experience a gradual increase, i.e., the higher the FVF, the higher is E (Fig. 4 b). This trend confirms that the stiffness of the material is strongly influenced by the % of fiber. However, there is a limit to the admissible FVF. Beyond a certain percentage, the molding reliability is compromised. There is a major FVF influence on the measured properties, especially  f , which experiences a major improvement from FVF 20 to 30%. From Table 2, with average and deviation of  f and E ,  f increases 229.7% between limit FVF, while increasing 123.1% between 20 and 40% FVF. The relative E improvement between limit conditions was 18.5%. In this test, the reinforcement type has a clear effect on the part response.