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1. Interlaminar fracture toughness of hybrid carbon fiber‐carbon nanotubes‐reinforced polymer composites

   https://doi.org/10.1002/pc.25054  

   Boroujeni, Ayoub Yari ; Al‐Haik, Marwan S. ( September 2018 , Polymer Composites)

   In this study, a relatively low temperature synthesis technique; graphitic structure by design (GSD), was employed to grow multi‐walled carbon nanotubes (MWCNTs) over carbon fiber fabrics. The MWCNTs forests were grown into two different morphologies, uniform and patterned. Hybrid carbon fiber‐reinforced polymer composites (CFRPs) were fabricated based on the hybrid reinforcement. Double cantilever beam tests were performed to investigate the effect of the surface grown nano‐reinforcements on the Mode I interlaminar fracture toughness (G_Ic) of the hybrid CFRPs. Results revealed that the surface grown MWCNTs enhanced the G_Icof the CFRPs by 22 and 32%, via uniform and checkerboard‐patterned growth morphologies, respectively. Fractography was also employed to reveal the MWCNTs’ role in interlaminar crack stoppage and deflection resulting in improving G_Icof the hybrid CFRPs. POLYM. COMPOS., 40:E1470–E1478, 2019. © 2018 Society of Plastics Engineers

    

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2. Electro-mechanical behavior of multi-functional glass fiber composites under dynamic Mode-I fracture loading

   https://doi.org/10.1177/00219983231201697  

   Sousa, Richard ; Chalivendra, Vijaya ( September 2023 , Journal of Composite Materials)

   An experimental study was performed to investigate damage sensing and fracture toughness of multifunctional conductive glass fiber composites under dynamic mode-I fracture loading. Carbon nanotubes (CNTs) were dispersed within the epoxy matrix using a shear mixing and sonicating process. An electrostatic wet flocking process was used to reinforce milled short PAN-based carbon fibers onto each of the layers of glass fiber fabric along the thickness direction in the composites. These layers of flocked fabric were stacked, and a vacuum infusion process was employed to fabricate the composites. The parametric study consisted of two carbon fiber lengths (80 μm and 150 μm) and two fiber densities (1000 fibers/mm²and 2000 fibers/mm²) and was performed to investigate the damage sensing capabilities of a three-dimensional conductive network generated through CNTs and carbon fibers. A double cantilever beam (DCB) configuration was considered, and a modified Hopkinson pressure bar setup along with a high-speed camera was used to investigate dynamic fracture toughness of the composites. The piezo-resistance response of the composites during dynamic fracture was measured using a modified system of four probes. For comparison, composites were also characterized for fracture toughness and piezo-resistance under quasi-static fracture loading conditions. The addition of short, milled PAN-based carbon fibers significantly increased the fracture toughness of glass/epoxy composites. The piezo-resistance response of the composites was easily correlated with instances of sudden crack growth during static fracture loading.

    

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3. Structural fatigue and fracture of shape memory alloy actuators: Current status and perspectives

   https://doi.org/10.1177/1045389X211057216  

   Hasan, Md Mehedi ; Baxevanis, Theocharis ( July 2022 , Journal of Intelligent Material Systems and Structures)

   Shape Memory Alloy (SMA)-actuators are efficient, simple, and robust alternatives to conventional actuators when a small volume and/or large force and stroke are required. The analysis of their failure response is critical for their design in order to achieve optimum functionality and performance. Here, (i) the existing knowledge base on the fatigue and overload fracture response of SMAs under actuation loading is reviewed regarding the failure micromechanisms, empirical relations for actuation fatigue life prediction, experimental measurements of fracture toughness and fatigue crack growth rates, and numerical investigations of toughness properties and (ii) future developments required to expand the acquired knowledge, enhance the current understanding, and ultimately enable commercial applications of SMA-actuators are discussed. 

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4. Laser induced graphene for in-situ ballistic impact damage and delamination detection in aramid fiber reinforced composites

   https://doi.org/https://doi.org/10.1016/j.compscitech.2020.108551  

   Steinke, Kelsey ; Groo, Lori Anne ; Sodano, Henry ( January 2021 , Composites science and technology)

   null (Ed.)

   Aramid fiber reinforced polymer composites have been shown to exhibit impressive mechanical properties, including high strength-to-weight ratio, excellent abrasion resistance, and exceptional ballistic performance. For these reasons, aramid composites have been heavily used in high impact loading environments where ballistic properties are vital. In-situ damage monitoring of aramid composites under dynamic loading conditions typically requires externally bonded sensors, which add bulk and are limited by size and space constraints. To overcome these limitations, this work presents a piezoresistive laser induced graphene (LIG) interface for embedded impact sensing in aramid fiber reinforced composites. Through the monitoring of electrical impedance during ballistic impact, information regarding time and severity of the impact is obtained. The impact velocity correlates with the impedance change of the composites, due to delamination between aramid plies and damage to the LIG interface. The delamination length in Mode I specimens also correlates to changes in electrical impedance of the composite. The interlaminar fracture toughness and areal-density-specific V50 of the LIG aramid composites increased relative to untreated aramid composites. This work demonstrates a methodology to form multifunctional aramid-based composites with a LIG interface that provides both improved toughness and imbedded sensing of impact and damage severity during ballistic impact. 

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5. Fracture toughness and fatigue crack growth resistance of precipitate-free and precipitation hardened NiTiHf shape memory alloys

   https://doi.org/10.1016/j.msea.2024.146443  

   Young, Benjamin ; Orrostieta, Roberto ; Haghgouyan, Behrouz ; Lagoudas, Dimitris C ; Baxevanis, T ; Karaman, Ibrahim ( May 2024 , Materials Science and Engineering: A)

   The present work investigates fracture toughness, and actuation and mechanical fatigue crack growth responses of Ni50.3Ti29.7Hf20 HTSMAs across martensitic transformation with two different microstructures, one with H-phase nanoprecipitates and one without. H-phase precipitation is known to stabilize the actuation cycling response of NiTiHf HTSMAs and notably impacts transformation-induced plasticity. The fracture toughness tests performed reveal that precipitate-free NiTiHf has a higher fracture toughness and undergoes significantly more inelastic deformation than the one with the precipitates resulting in toughness enhancement, i.e., stable crack advance during fracture toughness experiments, which is not observed in the precipitated NiTiHf for the crack configuration and loading conditions tested. Furthermore, the precipitate free NiTiHf has higher actuation and mechanical fatigue crack growth resistance than the precipitation-hardened microstructure. This is attributed to plasticity buildup, which exacerbates the manifestation of retained martensite upon repeated transformations. The fatigue crack growth rates obtained from both actuation and mechanical fatigue experiments align to a single Paris Law Curve for the precipitation-hardened NiTiHf. This work aims to determine if unified Paris Law curves can be generated from mechanical and actuation fatigue experiments, irrespective of composition and microstructure, to estimate actuation fatigue crack growth rates, laborious and challenging to measure, from easier to detect mechanical fatigue crack growth rates. 

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