Multiscale damage analysis of the tension‐tension fatigue behavior of a low‐density sheet molding compound

This article presents the experimental findings of tension-tension stress-controlled fatigue tests performed on low-density sheet molding compound (LD-SMC). LD-SMC composite is a type of SMC including a polyester resin reinforced with chopped glass fibers bundles and hollow glass spheres. The coupled frequency-amplitude affects the nature of the overall fatigue response, which can be controlled by the damage mechanisms accumulation and/or by the self-heating. In fact, the self-heating produced a material softening and decreased the fatigue lifetime. For fatigue loading at 80 Hz, self-heating has been observed and yielded to a temperature rise to 65°C, which is more than a glass transition temperature of polyester. Thus, the polyester matrix is subjected to remarkable thermally activated modifications of its physical state. Multiscale damage analysis of the randomly-oriented sample in fatigue showed that the first observed damage phenomenon corresponds to the debonding of the hollow glass microspheres occurring in the fiber depleted zones

Processing and Quality Control of Masks: A Review

It is clear that viruses, especially COVID-19, can cause infection and injure the human body. These viruses can transfer in different ways, such as in air transfer, which face masks can prevent and reduce. Face masks can protect humans through their filtration function. They include different types and mechanisms of filtration whose performance depends on the texture of the fabric, the latter of which is strongly related to the manufacturing method. Thus, scientists should enrich the information on mask production and quality control by applying a wide variety of tests, such as leakage, dynamic respiratory resistance (DBR), etc. In addition, the primary manufacturing methods (meltblown, spunlaid, drylaid, wetlaid and airlaid) and new additive manufacturing (AM) methods (such as FDM) should be considered. These methods are covered in this study

Some New Concepts of Shape Memory Effect of Polymers

In this study some new concepts regarding certain aspects related to shape memory polymers are presented. A blend of polylactic acid (PLA) (80%) and polybutylene succinate (PBS) (20%) was prepared first by extrusion, then by injection molding to obtain the samples. Tensile, stress-relaxation and recovery tests were performed on these samples at 70 °C. The results indicated that the blend can only regain 24% of its initial shape. It was shown that, this partial shape memory effect could be improved by successive cycles of shape memory tests. After a fourth cycle, the blend is able to regain 82% of its shape. These original results indicated that a polymer without (or with partial) shape memory effect may be transformed into a shape memory polymer without any chemical modification. In this work, we have also shown the relationship between shape memory and property memory effect. Mono and multi-frequency DMA (dynamic mechanical analyzer) tests on virgin and 100% recovered samples of polyurethane (PU) revealed that the polymer at the end of the shape memory tests regains 100% of its initial form without regaining some of its physical properties like glass transition temperature, tensile modulus, heat expansion coefficient and free volume fraction. Shape memory (with and without stress-relaxation) tests were performed on the samples in order to show the role of residual stresses during recovery tests. On the basis of the results we have tried to show the origin of the driving force responsible for shape memory effect

Micro and macroscopic characterization of A-SMC under high speed tensile test

Advanced 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 test are achieved using servo-hydraulic test equipment in order to get required high strain rates up to 100 s -1 . 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 optimised 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 fibers (RO) and Highly Oriented fibers (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 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 -1 ) to 100 s -1

In vitro study of drug release from various loaded polyurethane samples and subjected to different non-pulsed flow rates

Drug-eluting implants with a polymeric matrix are currently widely used and the interest of modeling their behavior is increasing. This article aims to present preliminary results of an in vitro under steady flow, study the behavior of drug-loaded polyurethane samples used as drug delivery matrices. Polyisocyanate and polyol synthesis supplied the polyurethane studied in this work. A molding and heat at 50 °C for about 30 min make it possible to prepare films from these components. The prepared samples are placed in the impermeable Plexiglas tube and they are in contact with the medium (distilled water). Tests have been performed without flow and three other cases with steady flow, at a temperature of 37 °C. The substance active incorporated in these films, as the drug, for carrying out the release tests is the C20H24C12N2O3. This drug supplied in granular form is composed of a mixture in the following proportions, 15 mg of diclofenac epolamine and 50 mg of diclofenac-sodium. Four sample variants were carefully prepared: pure-PU and PU loaded in a mass ratio of 10, 20 or 30%. Weighing, DSC, FT-IR, and DMTA are the methods used to analyze the samples. In addition, SEM micrographs are used to explore qualitatively the microstructure during the release tests. The kinetics in vitro of the drug release and water absorption by the polyurethane films are discussed in detail. The results show that these two quantities depend on the initial drug loading and the flow rate value, as a function of the in vitro incubation time

High strain rate visco-damageable behavior of Advanced Sheet Molding Compound (A-SMC) under tension

Advanced 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−1. 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−1) to 100 s−1. 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

Effect of process parameters on thermal and mechanical properties of polymer‐based composites using fused filament fabrication

The fused filament fabrication (FFF) process of polymer-based composites has been developed due to its capability to make complex geometries and shapes with reasonable mechanical properties. However, the improvement of mechanical properties of the obtained parts and products are still under study and are interesting for designers. There are several strategies to enhance these desired properties of produced pieces, for example optimizing the process parameters and/or using different architecting designs. This paper presents the effect of some overriding process parameters (liquefier temperature, print speed, layer height, and platform temperature) on the temperature evolution and mechanical behavior of PA6 reinforced with chopped carbon fibers produced by FFF. Due to deposition of multilayers, there is a cyclic profile of temperature in the FFF process, which is a considerable note related to fabrication and consequently the strength of the manufactured parts. In parallel with the study of process parameters effect, this cyclic temperature profile has been measured. The preliminary results related to physicochemical and mechanical properties revealed that differences in crystallinity percentage exist and failure stress/strain can be considered as an indicator to evaluate the mechanical properties of FFF manufactured products. Moreover, measuring the temperature profile of the deposited filaments revealed that process parameters have a considerable influence on the cooling process of deposited filaments which itself affects the bonding of adjacent filaments. The higher temperatures led to slower cooling rate. Finally, the results confirm the impact of mentioned parameters roles on the bonding formation in the FFF process and also the subsequent obtained mechanical properties of the printed parts. Therefore, selection of the optimized and suitable process parameters is an important design consideration

Mathematical Modeling and Optimization of Fused Filament Fabrication (FFF) Process Parameters for Shape Deviation Control of Polyamide 6 Using Taguchi Method

Fused filament fabrication (FFF) is a layer-by-layer additive manufacturing (AM) process for producing parts. For industries to gain a competitive advantage, reducing product development cycle time is a basic goal. As a result, industries’ attention has turned away from traditional product development processes toward rapid prototyping techniques. Because different process parameters employed in this method significantly impact the quality of FFF manufactured parts, it is essential to optimize FFF process parameters to enhance component quality. The paper presents optimization of fused filament fabrication process parameters to improve the shape deviation such as cylindricity and circularity of 3D printed parts with the Taguchi optimization method. The effect of thickness, infill pattern, number of walls, and layer height was investigated as variable parameters for experiments on cylindricity and circularity. The MarkForged® used Nylon White (PA6) to create the parts. ANOVA and the S/N ratio are also used to evaluate and optimize the influence of chosen factors. As a result, it was concluded that the hexagonal infill pattern, the thickness of 5 mm, wall layer of 2, and a layer height of 1.125 mm were known to be the optimal process parameters for circularity and cylindricity in experiments. Then a linear regression model was created to observe the relationship between the control variables with cylindricity and circularity. The results were confirmed by a confirmation test

Thermal aging effects on overall mechanical behavior of short glass fiber-reinforced polyphenylene sulfide composites

In this article, the overall mechanical properties of a short glass fiber-reinforced polyphenylene sulfide (PPS) composite were tested after oxidation at different temperatures (140, 160, 180, and 200°C), with a maximum oxidation time of approximately 5,300 h. In aspect of thermal aging process, the oxidation rates in 200 and 180°C are considerably harsher and faster than the case in 160 and 140°C, according to the concentration evolution of [C=O]. In aspect of mechanical properties, for virgin samples, due to an excellent fiber–matrix adhesion, no progressive damage is developed. Moreover, the fatigue results of aged samples show that the fatigue lifetime of PPS composites decreases more and more obviously with the oxidation time increasing while no significant loss of stiffness is observed. In addition, both monotonic and cyclic loadings are basically driven by the PPS matrix deformation. In the end, the relationship between fatigue lifetime and concentration of [CO] is built and discussed

An Investigation to Study the Effect of Process Parameters on the Strength and Fatigue Behavior of 3D-Printed PLA-Graphene

3D printing, an additive manufacturing process, draws particular attention due to its ability to produce components directly from a 3D model; however, the mechanical properties of the produced pieces are limited. In this paper, we present, from the experimental aspect, the fatigue behavior and damage analysis of polylactic acid (PLA)-Graphene manufactured using 3D printing. The main purpose of this paper is to analyze the combined effect of process parameters, loading amplitude, and frequency on fatigue behavior of the 3D-printed PLA-Graphene specimens. Firstly, a specific case study (single printed filament) was analyzed and compared with spool material for understanding the nature of 3D printing of the material. Specific experiments of quasi-static tensile tests are performed. A strong variation of fatigue strength as a function of the loading amplitude, frequency, and process parameters is also presented. The obtained experimental results highlight that fatigue lifetime clearly depends on the process parameters as well as the loading amplitude and frequency. Moreover, when the frequency is 80 Hz, the coupling effect of thermal and mechanical fatigue causes self-heating, which decreases the fatigue lifetime. This paper comprises useful data regarding the mechanical behavior and fatigue lifetime of 3D-printed PLA-Graphene specimens. In fact, it evaluates the effect of process parameters based on the nature of this process, which is classified as a thermally-driven process