Micromechanical behavior of ultraviolet-exposed polyurea

Shaik, Atif Mohammed; Huynh, Nha Uyen; Youssef, George

doi:10.1016/j.mechmat.2019.103244

Cited by 19 publications

(3 citation statements)

References 24 publications

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“…Composite interfaces with α (α − 2β) > 0 are characterized by compression of the interface layer due to an elastic mismatch. In this configuration, as was the case for both interfaces under consideration herein, an increase in the shear stresses was predicted, leading to the increased likelihood of interfacial crack formation [31][32][33]. Since β was nonzero, this suggested minor crack kinking in the crack tips, which was observed in some locations around the outer diameter of the Terfenol-D cylinder.…”

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confidence: 84%

“…In an effort to mechanistically explain the predominance of the interface debonding at the silver epoxy/Terfenol-D interface with the lack of kinking, the framework of Dundurs' parameters from linear elastic fracture mechanics of multilayered structures was brought into consideration. Dundurs' parameters describe the strain distributions and, therefore, crack-branching behavior in a discrete composite as a function of the relative properties of each material phase [31][32][33]:…”

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confidence: 99%

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Long-Term Converse Magnetoelectric Response of Actuated 1-3 Multiferroic Composite Structures

2021

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Multiferroic composite materials operating under the principle of strain mediation across the interfaces separating different material boundaries address many limitations of single-phase magnetoelectric materials. Although significant research has been conducted to explore their responses relating to the topography and directionality of material polarization and magnetic loading, there remain unanswered questions regarding the long-term performance of these multiferroic structures. In this study, a multiferroic composite structure consisting of an inner Terfenol-D magnetostrictive cylinder and an outer lead zirconate titanate (PZT) piezoelectric cylinder was investigated. The composite was loaded over a 45-day period with an AC electric field (20 kV/m) at a near-resonant frequency (32.5 kHz) and a simultaneously applied DC magnetic field of 500 Oe. The long-term magnetoelectric and thermal responses were continuously monitored, and an extensive micrographic analysis of pretest and post-test states was performed using scanning electron microscopy (SEM). The extended characterization revealed a significant degradation of ≈30–50% of the magnetoelectric response, whereas SEM micrographs indicated a reduction in the bonding interface quality. The increase in temperature at the onset of loading was associated with the induced oscillatory piezoelectric strain and accounted for 28% of the strain energy loss over nearly one hour.

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confidence: 84%

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confidence: 99%

Long-Term Converse Magnetoelectric Response of Actuated 1-3 Multiferroic Composite Structures

2021

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“…In the current state-of-the-art, the mechanical properties of polymers undergoing ultrahigh strain rate dynamic response are extracted using postmortem, i.e., after failure, characterization techniques. [27,28] Despite the valuable information the current state-of-the-art can provide, there lacks an experimental technique to elucidate the intrinsic mechanical behavior of impact mitigating polymers, such as polyurea. Here, terahertz spectroscopy is introduced as a possible bulk spectroscopic technique for the characterization of polymeric material systems.…”

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confidence: 99%

Spectro‐Microscopic Characterization of Elastomers Subjected to Laser‐Induced Shock Waves

Huynh

Gámez

Youssef

2021

Macro Materials & Eng

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The core of this research is separated into three domains, the ultrahigh strain rate response of elastomeric polymers, laser-induced shock waves , and terahertz time-domain spectroscopy (THz-TDS). Elastomers, e.g., polyurea, constitute an advance class of materials suitable for many applications, specifically in high impact loading scenarios, thus, a laser-induced shock wave (LSW) experimental technique is used to investigate the mechanical response of shock-loaded polyurea. LSW can submit samples to a strain rate exceeding 10 6 s −1 at low strains, enabling determination of material intrinsic failure modes. The large deformation induced during shock loading may alter the macromolecule structure, which can only be detected spectroscopically. Therefore, this research incorporated terahertz bulk spectroscopy to detect and report molecular conformational changes. Microscopy techniques were also used to elucidate changes in the microscale properties, morphology, and topography. The interpretation of the results explicated brittle failure in terms of partial and total spallation and, remarkably, ductile failure leading to plastic deformation, including plastic bulging and adiabatic shearing, not previously associated with LSW technique. Furthermore, spectral changes found in the terahertz regime substantiated the validity of terahertz spectroscopy in elucidating the underlying mechanism associated with the impact mitigating properties of dynamically loaded polyurea.

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Coexistence of Hardening and Softening Phenomena in Elastomeric Polymers under Nano‐Impact Loading

Kumar,

Youssef

2024

Macro Materials & Eng

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This article reports the coexistence of hardening and softening phenomena when polyurea is submitted to repeated nano‐impacts with various impact forces while controlling the strain rate. The manifestation of these phenomena is further elucidated by interrogating ultraviolet irradiated samples under ambient and nitrogen atmospheres, wherein artificial weathering accelerates hardening by reducing the nano‐impact depths as a function of exposure duration while increasing the impact load, nano‐impact repetitions and strain rate sensitivity favored softening. A 21% and 48% increase in indentation depth are recorded after 100 repetitions at a relatively higher force (10 mN) at a low strain rate and low force (2.5 mN) at a relatively higher rate for pristine and weathered polyurea, respectively. Electron microscopy evidences the induced, progressive damage at the nanoscale based on the agglomeration of hard segments, reduced free volume, and weathering‐induced surface embrittlement.

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Micromechanical behavior of ultraviolet-exposed polyurea

Cited by 19 publications

References 24 publications

Long-Term Converse Magnetoelectric Response of Actuated 1-3 Multiferroic Composite Structures

Long-Term Converse Magnetoelectric Response of Actuated 1-3 Multiferroic Composite Structures

Spectro‐Microscopic Characterization of Elastomers Subjected to Laser‐Induced Shock Waves

Coexistence of Hardening and Softening Phenomena in Elastomeric Polymers under Nano‐Impact Loading

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