PSI - Issue 3

G.M. Domínguez Almaraz et al. / Procedia Structural Integrity 3 (2017) 562–570 Author name / Structural Integrity Procedia 00 (2017) 000–000

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Figure 8 shows that the stress intensity factor range thresold (  K TH ), is close to 3.7 MPa m 0.5 , under ultrasonic fatigue loading, with low displacement, low applied load and immersion in water with pH = 7. Values for the fractures toughness in function of stress intensity factor rate have been obtained in the past 12 years (Weerasooriya et al., 2006), which indicate that fracture toughness is close to 4 MPa m 0.5 for loading rates near to 40,000 MPa m 0.5 /s; this indicates values of same order for both mechanical properties when PMMA is loaded under the described conditions. 4. Conclusions The following conclusions can be drawn from the present work:  Ultrasonic fatigue tests have been carried out on self-fabricated PMMA under low displacements, low applied stress and immersion in water (pH = 7).  The polymerization process of heat curing was used to self-fabricate the PMMA ultrasonic fatigue testing specimen.  The Higher testing temperature was keeping low (65° C, corresponding to 59% of glass transition temperature of this polymer), assuming predominant mechanical domain over thermal domain.  The Von Mises stress range applied on this polymeric material was from  6 to  9 MPa, which cover the upper range of human bite: 5 – 8 MPa (Koc et al., 2010).  Ultrasonic fatigue endurance of PMMA with immersion in water was close to 75,000 cycles when the applied load was 9 MPa; this mechanical property was near to 270,000 cycles with 6 MPa of applied load.  At the ultrasonic fatigue frequency, moderate effect of frequency is expected on the FCG rate with low applied strain and stress.  The strain rate under ultrasonic fatigue testing of PMMA was maintained without variation; therefore, no strain rate sensitivity was considered under this modality of fatigue tests.  Dynamic fracture was observed on the PMMA under ultrasonic fatigue testing with crack tip speed surpassing 10 -1 m/s, leading to expect no important effect of surrounding water on the crack initiation and propagation.  Stress waves have been observed on the fracture surfaces of testing specimen, indicating a predominant dynamic fracture.  Experimental results show that the stress intensity factor range threshold (  K TH ), was close to 3.7 MPa m 0.5 under this modality of fatigue tests, with low displacement and applied load and immersion in water. Acknowledgements The authors express their gratitude to the University of Michoacan in Mexico for the support received in the development of this work. A special mention of gratitude to CONACYT (The National Council for Science and Technology, Mexico), for the financial support destined to this study by the program grant: CB- 241117-2014. Ali U., Abd Karim K.J. Bt., Buang N.A., 2015. A Review of the properties and applications of poly (Methyl Methacrylate) (PMMA). Journal Polymer Reviews 55(4), 678-705. Ali Moussa A.R., Ibrahim Zaki D.Y., El Gabry H.S., Ahmed T.M., 2012. Comparative adaptation Accuracy of heat cured and injection molded resin denture base materials. Journal of Applied Sciences Research 8(8), 4691-4696. ASM International, 2003. Characterization and Failure Analysis of Plastics, Materials Park, OH 44073-0002, pp. 485. Baloš S., Milutinović M., Potran M., Vuletić J., Puškar T., Pepelnjak T., 2015. The mechanical properties of moulded and thermoformed denture resins. Journal of Mechanical Engineering 61(2015)2, 138-145. Bhola R., Bhola S.M., Liang H., Mishra B., 2010. Biocompatible denture polymers – A Review. Trends in Biomaterials & Artificial Organs 23(3), 129-136. Cheng W.M., Miller G.A., Manson J.A., Hertzberg R.W., Sperling L.H., Mechanical behaviour of poly (methyl methacrylate)—part 2: the temperature and frequency effects on the fatigue crack propagation behavior. Journal of Materials Science 25(4), 1924–1930. References