The masks have always been mentioned as an effective tool against environmental threats. They are considered as protective equipment to preserve the respiratory system against the non-desirable air droplets and aerosols such as the viral or pollution particles. The aerosols can be pollution existence in the air, or the infectious airborne viruses initiated from the sneezing, coughing of the infected people. The filtration efficiency of the different masks against these aerosols are not the same, as the particles have different sizes, shapes, and properties. Therefore, the challenge is to fabricate the filtration masks with higher efficiency to decrease the penetration percentage at the nastiest conditions. To achieve this concept, knowledge about the mechanisms of the penetration of the aerosols through the masks at different effective environmental conditions is necessary. In this paper, the literature about the different kinds of face masks and respiratory masks, common cases of their application, and the advantages and disadvantages of them in this regard have been reviewed. Moreover, the related mechanisms of the penetration of the aerosols through the masks are discussed. The environmental conditions affecting the penetration as well as the quality of the fabrication are studied. Finally, special attention was given to the numerical simulation related to the different existing mechanisms.

Untreated and acid-treated multi-walled carbon nanotubes (MWNT) were used to fabricate MWNT/ epoxy composite samples by sonication technique. The effect of MWNT addition and their surface modification on the mechanical properties were investigated. Modified Halpin-Tasi equation was used to evaluate the Young's modulus and tensile strength of the MWNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. There was a good correlation between the experimentally obtained Young's modulus and tensile strength values and the modified Halpin-Tsai theory. The fracture surfaces of MWNT/epoxy composite samples were analyzed by scanning electron microscope.

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a b s t r a c tAdvanced Sheet Molding Compound (A-SMC) is a serious composite material candidate for structural automotive parts. It has a thermoset matrix and consists of high weight content of glass fibers (50% in mass) compared to standard SMC with less than 30% weight fiber content. During crash events, structural parts are heavily exposed to high rates of loading and straining. This work is concerned with the development of an advanced experimental approach devoted to the micro and macroscopic characterization of A-SMC mechanical behavior under high-speed tension. High speed tensile tests are achieved using servo-hydraulic test equipment in order to get required high strain rates up to 100 s À1 . Local deformation is measured through a contactless technique using a high speed camera. Numerical computations have led to an optimal design of the specimen geometry and the experimental damping systems have been optimized in terms of thickness and material properties. These simulations were achieved using ABAQUS explicit finite element code. The developed experimental methodology is applied for two types of A-SMC: Randomly Oriented (RO) and Highly Oriented (HO) plates. In the case of HO samples, two tensile directions were chosen: HO-0 (parallel to the Mold Flow Direction (MFD)) and HO-90 (perpendicular to the MFD). High speed tensile tests results show that A-SMC behavior is strongly strain-rate dependent although the Young's modulus remains constant with increasing strain rate. In the case of HO-0 , the stress damage threshold is shown an increase of 63%, when the strain rate varies from quasi-static (0.001 s À1 ) to 100 s À1 . The experimental methodology was coupled to microscopic observations using SEM. Damage mechanisms investigation of HO and RO specimens showed a competition between two mechanisms: fiber-matrix interface debonding and pseudo-delamination between neighboring bundles of fibers. It is shown that pseudo-delamination cannot be neglected. In fact, this mechanism can greatly participate to energy absorption during crash. Moreover, the influence of fiber orientation and imposed velocity is studied. It is shown that high strain rate and oriented fiber in the tensile direction favor the pseudo-delamination.

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SYNOPSISMechanistic schemes of radical oxidation of hydrocarbon polymers in which initiation is only due to unimolecular or bimolecular hydroperoxide decomposition have been studied. The results of their kinetic analysis have been compared with literature data relative to the thermal oxidation of polypropylene in solid state (60-160°C). These data are in remarkably good agreement with the "unimolecular" scheme whose main characteristics are:( 1 ) the quasi-independence of the kinetic behavior with initial conditions (for low initial content of thermolabile structures), and ( 2 ) the fact that an arbitrarily defined induction period depends only on the rate constant of unimolecular hydroperoxide decomposition. 0 1995 John Wiley & Sons, Inc.

Poly (phenylene sulfide) (PPS) is one kind of high‐performance polymer with high thermal stability that can be used widely in different industrial domains. However, according to an investigation of the literature, few reviews have comprehensively focused on the continuous development of PPS applications in the past decade. To meet this demand, this paper provides an overall investigation of PPS polymer and PPS‐based composites from synthesis and process to applications. Briefly, this paper introduces PPS materials according to the following topics. First, the molecular weight distribution and morphology of PPS, as well as their reinforced parts, are introduced. Afterward, the topic is focused on the synthesis, process, and blending of PPS. In the next part, this paper investigates the key points regarding PPS as a high‐performance polymer, focusing on the aspect of thermal behavior and mechanical properties. Finally, PPS composite applications are emphasized and overviewed from a wide range of aspects.

This paper presents the experimental results of tension-tension stress-controlled fatigue tests performed on advanced sheet molding compound (A-SMC). It aims at analyzing the effect of fiber orientation, loading amplitude, and frequency on the fatigue response and the related temperature evolution due to the self-heating phenomenon. Two types of A-SMC have been analyzed: randomly oriented (RO) and highly oriented (HO). The coupled effect of the loading amplitude and the frequency has been studied. It has been shown that the couple frequency-amplitude affects the nature of the fatigue overall response which can be governed by the damage mechanisms accumulation (mechanical fatigue) and/or by the self-heating (induced thermal fatigue). For fatigue loading at 100 Hz, self-heating has been observed and yielded to a temperature rise up to 70 C. The latter causes a decrease of the storage modulus related to the b-transition of the vinylester. It has been demonstrated that the self-heating produced a material softening and decreased the fatigue life. SEM observations revealed that the samples tested at 100 Hz, exhibit smooth debonding surfaces due to the induced thermal softening of the matrix whereas more brittle fracture of the matrix surrounding fibers is observed during the fatigue tests achieved at 10 Hz.