Search

This study examines the mechanical properties, specifically strength and stiffness, of technical hemp and flax fibers grown in Romania. Tensile testing was employed to determine stress–strain curves and the Young's modulus and to assess the failure strength of both fiber types. Although samples of various lengths were tested, no significant length-dependent variations were observed. However, a strong dependence on fiber diameter was noted, with the smallest diameters approaching the documented strength of elementary fibers. Due to the considerable variability in the experimental results pertaining to the characteristics of the reinforced fibers, a statistical analysis using a two-parameter Weibull distribution was employed. The analysis revealed three distinct stress–strain curve profiles, i.e., linear, bi-linear, and tri-linear patterns, with the average ultimate stress ranging from 412 to 566 MPa for hemp and 502 to 598 MPa for flax. [ABSTRACT FROM AUTHOR]

This paper examined the mechanical properties of wrist–hand orthoses made from polylactic acid (PLA) and polyethylene terephthalate glycol (PETG), produced through material extrusion with infill densities of 55% and 80%. These orthoses, commonly prescribed for wrist injuries, were 3D-printed flat and subsequently thermoformed to fit the user's hand. Experimental and numerical analyses assessed their mechanical resistance to flexion after typical wear conditions, including moisture and long-term aging, as well as their moldability. Digital Imaging Correlation investigations were performed on PLA and PETG specimens for determining the characteristics required for running numerical analysis of the mechanical behavior of the orthoses. The results indicated that even the orthoses with the lower infill density maintained suitable rigidity for wrist immobilization, despite a decrease in their mechanical properties after over one year of shelf life. PLA orthoses with 55% infill density failed at a mean load of 336 N (before aging) and 215 N (after aging), while PETG orthoses did not break during tests. Interestingly, PLA and PETG orthoses with 55% infill density were less influenced by aging compared to their 80% density counterparts. Additionally, moisture and aging affected the PLA orthoses more, with thermoforming, ongoing curing, and stress relaxation as possible explanations related to PETG behavior. Both materials proved viable for daily use, with PETG offering better flexural resistance but posing greater thermoforming challenges. [ABSTRACT FROM AUTHOR]

A hybrid mold is developed, with its structure including some components made of polymer, as a variant to a classical structure. This hybrid mold is destinated to manufacturing, by cold plastic deformation, of stainless steel thin parts, in particular of certain 0.1 mm thickness stainless steel bipolar plates (BPPs) from proton exchange membrane fuel cell stacks. The mold conceptual and designed main data are revealed. Numerical simulation and analysis by a structural FEA method is applied. A general evaluation is unrolled, with the results referring to the technical – economic use of the developed hybrid mold. [ABSTRACT FROM AUTHOR]

The paper presents a study on the dimensional and weight characterization of 3D printed polyethylene terephthalate specimens designed specifically for compliant mechanisms. Compliant mechanisms find applications in various industries, including medical, consumer goods, education, and research and development. Ensuring these mechanisms meet the required functional needs is crucial, particularly when customizing medical devices. The research focuses on material selection, a critical aspect for 3D printed compliant mechanisms. To investigate the influence of the material deposition angle on the quality and precision of 3D printing, the study considers traction and bending specimens. For each specimen type, three sets of five specimens are manufactured, incorporating different deposition angles: 0°, ±45°, and 90°. In total, 30 specimens are produced, labeled, weighted, and measured. The results reveal that specimens printed at a deposition angle of 45° exhibit the smallest dimensional and mass deviations, indicating higher precision and accuracy. Those printed at 0° follow closely in terms of deviation, while specimens printed at 90° display larger deviations. [ABSTRACT FROM AUTHOR]

The present paper is aimed at studying the in-plane shear response of a flax fiber - epoxy resin composite laminate. Rectangular specimens, with ±45° laminate orientation with respect to loading direction were used for the experimental procedure. Tensile testing up to failure allowed to extract the shear strain-shear stress curve, which have shown a linear domain, up to approximately 25 MPa, where a shear modulus was calculated, of 1.67 GPa and a Poisson ratio of 0.7, value which is typical for off axis laminates. Strain measurement during these tests, using Digital Image Correlation, have shown that, at high stress levels, concentrators occur in the specimen in the region of failure. Repeated loading tests have shown that the material stiffens approximately 9% when increasing loading speed, leading to conclude that a viscoelastic component of the deformation is present during loading. Repeated creeprecovery tests showed that, for longer periods of time, viscoplastic deformations appear as well, with an exponential evolution with respect to the creep duration. [ABSTRACT FROM AUTHOR]

Copyright of Industria Textila is the property of Institutul National de Cercetare-Dezvoltare pentru Textile si Pielarie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)