The thermal behavior of hemp-poly lactic acid composites with both untreated and chemically surface modified hemp fiber was characterized by means of activation energy of thermal degradation. Three ...chemical surface modification employed were; alkali, silane and acetic anhydride. Model-free isoconversion Flynn–Wall–Ozawa method was chosen to evaluate the activation energy of composites. The results indicated that composites prepared with acetic anhydride modified hemp had 10–13% higher activation energy compared to other composites. Further, among the three surface modifications, acetic anhydride resulted in higher activation energy (159–163kJ/mol). Fourier transform infrared spectroscopy supported the findings of thermogravimetric analysis results, wherein surface functionalization changes were observed as a result of surface modification of hemp fiber. It was concluded that, higher bond energy results in higher activation energy, which improves thermal stability. The activation energy data can aid in better understanding of the thermal degradation behavior of composites as a function of composite processing.
Medical personal protective equipment (PPE) made from nonwoven thermoplastic fibers has been intensively used, resulting in a large amount of biohazardous waste. Sterilization is indispensable before ...recycling medical waste. The aim of this work is to evaluate the effects of the decontamination treatments and help properly recycle the PPE materials. The study investigated the effects of three disinfection treatments (NaClO, H
2
O
2
, and autoclave) on chemical composition, molecular weight, thermal properties, crystallinity, crystallization kinetics, and mechanical tension of three types of PPE (Gown #1, Gown #2, and Wrap) made of isotactic polypropylene fibers. The chemical compositions of the materials were not evidently affected by any of the treatments. However, the M
w
of the polymers decreased about 2–7% after the treatments, although the changes were not statistically significant. The treatments barely affected the melting and crystallization temperatures and the maximum force at break, but they tended to elevate the thermal degradation temperatures. Although the treatments did not notably influence the crystallinities, crystallization rates and crystal growths were altered based on the Avrami model regression. Since the detected changes would not significantly affect polymer processing, the treated materials were suitable for recycling. Meanwhile, evident differences in the three types of raw materials were recorded. Their initial properties fluctuated notably, and they often behaved differently during the treatments, which could affect recycling operation. Recyclers should test and sort the raw materials to assure product quality. The results in this study provide fundamental data for recycling medical PPE to reduce its environmental footprint.
Durability and dynamic failure properties are critical parameters for naval composite ships in seawater. However, previous measurements have significantly underestimated the intrinsic durability of ...composite structures. In this study, a simple composite seawater tank approach is developed to accurately simulate the material/mechanics conditions of composite structures in seawater. Only one surface of each composite specimen is exposed to seawater and this exposed surface is subjected to drop-weight impact testing followed by characterization of residual compressive strength. A series of experiments on dry and wet composite specimens were conducted to characterize the impact damage, and the residual compressive strength. Results from seawater exposure indicate that the compression-after-impact strengths of the wet specimens reduced by around 10% compared to the baseline dry specimens over 29-month seawater exposure. Therefore, durability of current marine composite is better than the previously measured properties. Our simple seawater tank durability experiment is expected to provide accurate justification for the required maintenance period of new composite ship structures.
Weight savings in vehicles enhances fuel efficiency and decreases maintenance costs, especially in mass transit systems. Lightweight composite materials, such as glass fiber reinforced polymers, have ...been used to replace traditional steel and aluminum components. In this paper, a mass transit bus side body panel was designed, analyzed, and manufactured using thermoplastic composite materials. The design featured a sandwich composite with E-glass fiber/polypropylene (glass/PP) face sheets and PP honeycomb core as constituents that provide low weight, high strength and energy absorption benefits. The panel was designed and analyzed using Pro/Engineer 2001 (Pro/E), Altair
® Hypermesh
® 6.0 (Hypermesh) and ANSYS 7.0 (ANSYS). A single diaphragm forming process was used to manufacture the glass/PP face sheets. This process provides excellent consolidation, which was confirmed by microstructural analysis of the face sheets. The face sheets and core material were adhesively bonded and tested to validate the model. The failure of the body panel occurred by adhesive failure when the load reached 11.7
kN. The static loading requirements of the American Public Transportation Association (APTA) for the body panel were met. The thermoplastic composite body panel exhibited excellent weight saving of more than 55% compared to a conventional bus with aluminum skin and supporting steel bars.
Natural fiber reinforced thermoplastic matrix composites have been increasingly used in semi-structural applications in automotive applications because of their good specific strength and modulus, ...low carbon footprint and recyclability. This research work studies the effects of material treatment(s) on the mechanical behaviors of hemp fiber reinforced polypropylene (PP) composites. The material treatment(s) are realized by chemically treating the hemp fiber with different concentration NaOH and/or adding maleic anhydride grafted polypropylene (MAPP) to the PP matrix. The purpose of the material treatment(s) is to enhance the bonding between the hemp fibers and the polypropylene matrix which otherwise has low surface energy and limited bonding. The mechanical behaviors are investigated with different combinations of material treatment(s) such as 5 wt% MAPP, 5% NaOH treated hemp fiber, 10% NaOH treated hemp fiber, and 5% NaOH + 5 wt% MAPP. 15 wt% and 30 wt% hemp fiber loadings are used in the composites with these material treatments. It is found that the material treatment(s) result(s) in composites with better mechanical properties compared to the composites without any treatment(s). The composites with 5 wt% MAPP addition show the best mechanical properties.
Thin-walled composite sub-elements possess excellent properties, including high specific strength, lightweight, internal torque and moment resistance which offer opportunities for applications in ...mass transit and ground transportation. In the present work, an open section thin-walled thermoplastic composite frame segment (sub-element) of a mass transit bus was designed, analyzed and manufactured to replace a conventional metal-based design. Three cross-section configurations, rectangular, V-shape and rounded C-shape, were considered, and different lamina stacking sequences, (0/90)
6, ±45/(0/90)
2
s
, and ±45/(0/90)
3 were compared. Carbon fiber/polyphenylene sulphide (carbon/PPS) was the material choice, and single diaphragm forming (SDF) process was adopted to manufacture the frame segment. In-plane compression testing was conducted on the manufactured carbon/PPS composite frame to validate the finite element analysis results. A successful design concept to manufacture strategy of the open thin-walled carbon/PPS thermoplastic composite frame segment was demonstrated.
This review summarizes the recent research progress on the post-processing techniques to improve the as-built metallic structure fabricated by additive manufacturing. The comprehensive comparison ...reveals that hot isostatic pressing (HIP) is the only one of few that can eliminate the internal porosity (< 0.01%) with high efficiency and availability. Traditional heat treatments (HTs) are still the best approach to improve or alter the microstructure for the overall bulk properties. Various surface post-processes are presented that are more flexible and cost-effective than common machining and polishing. Laser-based techniques are the most popular treatment for surface modification to induce compressive stress, remove the surface pores, reduce the surface roughness, or apply coatings for functionality. Other mechanical methods like shot peening (SP), laser shock peening (LSP), ultrasonic nanocrystal surface modification (UNSM), and abrasive-based treatments facilitate plastic deformation to impact surface beneficially for hardness, fatigue, or corrosion resistance. In addition, impact-type surface treatments (SP, LSP, and UNSM) are more effective on enhancing the mechanical properties due to greater energy imparted to the surface than abrasive-type treatments. Electrochemical polishing is capable to achieve the best surface smoothness (
R
a
< 0.1
μ
m
), while friction stir processing shows the best effectiveness on homogenize the structure without significant grain growth at nanoscale. Advanced but costly surface techniques are only suitable to satisfy specific requirement and application of high value metallic component. By optimizing the process parameters and adopting in situ tools, the as-built structure can be enhanced with minimized necessity for post-processing. Overall, a complete solution of post-treatment includes HIP, HTs, surface modification, and/or special process.
Hybrid carbon fiber and glass fiber reinforced thermoset composites are commonly used in structural applications throughout the energy, aerospace, automotive, and marine industries. The differing ...fiber types can be combined into a hybrid composite with the intent to efficiently utilize the beneficial properties of each type of reinforcement. The fiber fraction of each individual fiber type influences the mechanical properties of the overall composite. Measurement of the fiber fraction of each individual fiber type allows understanding and prediction of the mechanical properties as well as a method of quality control in manufacturing. A combination of a carbonization in nitrogen method for the measurement of fiber content in carbon fiber reinforced composites and an oxidation method to measure the glass fiber content are used for the first time. It has been demonstrated that the approach is effective at measuring the carbon fiber and glass fiber contents in hybrid glass and carbon fiber thermoset composites in both epoxy and vinyl ester resin systems.
Applying specific amount of fiber pretension during the manufacturing process of the composite rebars would potentially enhance their performance and durability. In this study, five sets of lab-scale ...prestressed glass fiber/vinyl-ester composite rebars were fabricated. Each set was manufactured using unique amount of fiber pretension. A set of unprestressed composite rebar was prepared as well. The effect of fiber pretension on the microstructure, tensile properties and long-term durability of rebars was investigated. In addition, the performance of the prestressed composite rebars was compared to composite rebars currently available in the market. An improvement in fiber alignment and a reduction in void content were observed within the pretensioned rebars. The composite rebars fabricated with pretension of 30 MPa showed the maximum increase in tensile properties. The guaranteed tensile strength and average tensile modulus were improved by 7.5% and 2.6%, respectively, compared to the unprestressed counterpart. The prestressed rebars showed relatively less surface degradation and lower moisture absorption after conditioning in alkaline solution at 60°C for 90 days. After conditioning, the tensile properties of the prestressed composite rebars showed superiority over the unprestressed rebar. Comparing to composite rebars available in the market, the prestressed composite rebars prepared in this study showed high performance in both short-term and long-term use.
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