DYNAMIC FACTURE OF HYDROTHERMALLY DEGRADED CARBON-EPOXY COMPOSITES

2021 ◽  
Author(s):  
EMILY PITTMAN ◽  
STYLIANOS KOUMLIS ◽  
LESLIE LAMBERSON
Keyword(s):  
Elevated Temperature ◽  
Dynamic Fracture ◽  
Fracture Behavior ◽  
Salt Water ◽  
Ambient Condition ◽  
Image Correlation ◽  
Epoxy Composites ◽  
Mode I ◽  
Significant Difference

Structures used in naval applications are often subjected to marine or other aqueous environments during their work-life. It has been observed that many composites absorb moisture when exposed to such environments, which can lead to material damage and degradation of mechanical properties. The addition of salt to the water solution may have additional impacts on the material degradation over time. Furthermore, many of these applications require that the material be subject to stresswave loading environments like impact that may cause dynamic fracture. In this experimental study, the effect of water absorption on the Mode-I dynamic fracture behavior of carbon-epoxy composites is investigated. Specifically, the effects of moisture uptake and the role of saline on the critical dynamic SIF are investigated. Samples were hygrothermally soaked in an elevated temperature bath (70 °C) of either ASTM standard sea water or distilled water. The elevated temperature accelerates mass absorption, making experimental observation possible on a more reasonable timeline than natural aging. Soaking durations varied between 3.5 hours to excess of 4 months to explore the role of soak time on dynamic fracture behavior. Pre-cracked specimens were impacted using a unique long-bar striker device at 4 m/s, and the resulting Mode-I (opening mode) fracture behavior investigated. Digital image correlation (DIC) was used in conjunction with ultra-high-speed imaging to track the crack tip surface displacements, and an elastodynamic solution was leveraged to extract the stress intensity factors (SIF) at fracture initiation. The dynamic fracture toughness of the soaked samples was compared with results from a group of unsoaked, ambient condition samples. The results indicated that the ambient condition samples had a consistently higher Mode-I SIF than any of the soaked conditions. The difference between the ambient condition SIF and the soaked conditions was observed to be approximately 60% for the 3.5 hour soaks, 40% for the 2 day soaks, 50% for the 2 week soaks, and 80% for the samples soaked for longer than 4 months. The SIF reduction is thought to be due primarily to matrix and interface degradation. No statistically significant difference in the SIF was observed between samples soaked in DI water versus salt water.

FRACTURE ANALYSIS OF RUBBER TOUGHENED ADDITIVELY MANUFACTURED THERMOSETS

2021 ◽  
Author(s):  
MEGAN SHEPHERD ◽  
KAMRAN MAKARIAN ◽  
GIUSEPPE PALMESE ◽  
NICHOLAS BRUNSTAD ◽  
LESLIE LAMBERSON
Keyword(s):  
Dynamic Fracture ◽  
Fracture Behavior ◽  
Agile Manufacturing ◽  
Image Correlation ◽  
Dynamic Mode ◽  
Rubber Toughening ◽  
Least Squares Fit ◽  
Rubber Toughened ◽  
Part Complexity

This study explores the role of rubber toughening on the dynamic fracture behavior of additively manufactured (AM) high-performance thermosetting polymers formed through digital light processing (DLP). Using DLP to create these polymers allows for rapid, agile manufacturing of prototypes meeting the lightweight and building speed requirements of relevance to military mission applications. This method also provides flexibility in part complexity while maintaining relatively high isotropy compared to traditional AM techniques. Previous work has demonstrated a dependence of these DLP specimens on print layer orientation and loading rate, prompting further investigation into other manufacturing parameters to improve toughness [1]. This study examines the role of rubber toughening on the quasi-static and dynamic fracture behavior of bis-GMA thermosets. Current literature largely reports on quasi-static behavior of DLP specimens, although dynamic conditions are more applicable to many realistic loading scenarios and extreme environments often seen in defense applications. Dynamic experiments leverage a unique long bar striker device that impacts a specimen opposite a pre-crack, sending a stress-wave driven load to initiate a dynamic Mode-I (opening) fracture event. Full-field displacement data ahead of the propagating crack is obtained using ultra high-speed imaging combined with 2D digital image correlation (DIC). An elastodynamic solution following the principles of dynamic fracture mechanics extracts the stress intensity factor (SIF) using a least squares fit at crack initiation and a Newton-Raphson scheme for crack propagation. The rubber toughened thermosets in this study exhibited a rate dependence in fracture toughness with the quasi-static SIF being 1.20 MPa and the dynamic SIF being 0.41 MPa .

scholarly journals Investigation by Digital Image Correlation of Mixed Mode I and II Fracture Behavior of Metallic IASCB Specimens with Additive Manufactured Crack-Like Notch

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 400 ◽  
Author(s):  
Ivo Campione ◽  
Tommaso Maria Brugo ◽  
Giangiacomo Minak ◽  
Jelena Janković Tomić ◽  
Nebojša Bogojević ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Mixed Mode ◽  
Fracture Behavior ◽  
Selective Laser Sintering ◽  
Local Stress ◽  
Fatigue Loading ◽  
Image Correlation ◽  
Mode I ◽  
Displacement Fields

This work investigates the fracture behavior of maraging steel specimens manufactured by the selective laser sintering (SLS) technology, in which a crack-like notch (sharp notch) was directly produced during the additive manufacturing (AM) process. For the evaluation of the fracture toughness, the inclined asymmetrical semi-circular specimen subjected to three points loading (IASCB) was used, allowing to cover a wide variety of Mode I and II combinations. The effectiveness of manufacturing crack-like notches via the SLS technique in metals was evaluated by comparing the obtained experimental results with the ones obtained with pre-cracks induced by fatigue loading. The investigation was carried out by using the digital image correlation (DIC) technique, that allowed the evaluation of the full displacement fields around the crack tip. The displacement field was then used to compute the stress intensity factors (SIFs) for various combinations of Mode I and II, via a fitting technique which relies on the Williams’ model for the displacement. The SIFs obtained in this way were compared to the results obtained with the conventional critical load method. The results showed that the discrepancy between the two methods reduces by ranging from Mode I to Mode II loading condition. Finally, the experimental SIFs obtained by the two methods were described by the mixed mode local stress criterium.

Study on dynamic fracture behavior of mode I crack under blasting loads

2019 ◽  
Vol 117 ◽  
pp. 47-57 ◽  
Author(s):  
Ruifeng Liu ◽  
Zheming Zhu ◽  
Meng Li ◽  
Bang Liu ◽  
Duanying Wan
Keyword(s):  
Dynamic Fracture ◽  
Fracture Behavior ◽  
Mode I ◽  
Mode I Crack

Performance of promising rice varieties under ambient and elevated temperature regimes

2019 ◽  
Vol 4 (01) ◽  
pp. 10-17
Author(s):  
Shubhechhya Regmi ◽  
Binayak P. Rajbhandari
Keyword(s):  
Elevated Temperature ◽  
Open Field ◽  
Ambient Condition ◽  
P Value ◽  
Research Station ◽  
Chamber System ◽  
Open Top Chamber ◽  
Rice Varieties ◽  
Plastic Sheet ◽  
Significant Difference

Open top chamber system was designed for undertaking research into rice crop response to increased temperature during rainy season at Regional Agricultural Research Station (RARS), Khajura, Banke in 2018. With the objective of determining the efficacy of the chamber system and to generate possible differences in climate which could alter plant response between ambient and chamber system, 5 different rice varieties (Radha-4, Sukhkhadhan-3, Sukhkhadhan-2, IR83383-G-B-141-1 and IR87751-20-4-4-2) with three temperature conditions were used: ambient condition, open top chamber with 1.2m height enclosed from base with plastic sheet and open top chamber with 1.5m height enclosed from base with plastic sheet. With 3.1°c higher temperature Sukhkhadhan-2 significantly (p value= 0.0199) produced higher grain yield 4.33 t/ha under chamber condition in contrast to open field (2.93 t/ha) as well as significantly (p value=0.0175) higher biomass yield 13.62 t/ha under elevated temperature. Also, Sukhkhadhan-2 significantly (p value=0.0012) attained maximum height (86.99 cm) under chamber condition compared to open field (73.06 cm) during harvest. Statistical analysis showed no significant difference for number of tillers per hill during maturity stage. Significantly sukhkhadhan-3 (p value=0.02994) showed longer panicle length 25.7cm under chamber than normal field condition (23.74 cm). In addition, Radha- 4 significantly (p value=0.03823) produced more filled grains per panicle (169) under chamber conditions than ambient condition (112). The consideration of crop variety is a good adoption measure to minimize incidence of elevated temperature in farming system.

scholarly journals Determination of mode I dynamic fracture toughness of IM7-8552 composites by digital image correlation and machine learning

2019 ◽  
Vol 210 ◽  
pp. 707-714 ◽  
Author(s):  
Rafael A. Cidade ◽  
Daniel S.V. Castro ◽  
Enrique M. Castrodeza ◽  
Peter Kuhn ◽  
Giuseppe Catalanotti ◽  
...  
Keyword(s):  
Machine Learning ◽  
Fracture Toughness ◽  
Digital Image Correlation ◽  
Dynamic Fracture ◽  
Digital Image ◽  
Dynamic Fracture Toughness ◽  
Image Correlation ◽  
Mode I

Tensile and Fracture Characterization of PETI-5 and IM7/PETI-5 Graphite/Epoxy Composites Under Quasi-Static and Dynamic Loading Conditions

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Dongyeon Lee ◽  
Hareesh V. Tippur ◽  
Brian J. Jensen ◽  
Philip B. Bogert
Keyword(s):  
Dynamic Loading ◽  
Dynamic Fracture ◽  
Fracture Behavior ◽  
Matrix Material ◽  
Image Correlation ◽  
Dynamic Crack ◽  
Loading Conditions ◽  
Fiber Reinforced ◽  
Dynamic Loading Conditions ◽  
Static And Dynamic Loading

Tensile and fracture responses of the phenylethynyl terminated imide oligomer (PETI-5) are studied. Since this polymer is a candidate aerospace structural adhesive as well as a matrix material in composite systems, neat as well as fiber reinforced forms of PETI-5 are studied under static and dynamic loading conditions. A split-Hopkinson tension bar apparatus is used for performing tensile tests on dogbone specimens. The dynamic fracture tests are carried out using a drop tower in conjunction with 2D image correlation method and high-speed digital photography on edge cracked specimens in three-point bend configuration. A toughened neat epoxy system, Hexcel 3900, is also studied to provide a baseline comparison for neat PETI-5 system. The tensile stress-strain responses show PETI-5 to have excellent mechanical characteristics under quasi-static and dynamic loading conditions when compared with 3900. Fracture behavior of PETI-5 under quasi-static and impact loading conditions also shows superiority relative to 3900. The dynamic fracture behavior of a PETI-5 based graphite fiber reinforced composite, IM7/PETI-5, is also studied and the results are comparatively evaluated relative to the ones corresponding to a more common aerospace composite system, T800/3900-2 graphite/epoxy. Once again, the IM7/PETI-5 system shows excellent fracture performance in terms of dynamic crack initiation and growth behaviors.

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