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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 paper proposes the analysis of strain and stress state, through experimental and numerical means, of a circular hole type concentrator. The strain state is analyzed through the microscopic Digital Image Correlation technique, due to the small scale of the samples, whose calibrated region is 10x8 mm. The numerical analysis is conducted using the Finite Element Method, through a static structural analysis, using a linear-elastic material model. The results from the two procedures are compared by means of strain field distribution around the stress concentrator and stress variation at the concentrator peak cross section. For validation, the analytical gross stress concentrator of the problem is used as baseline, Ktg. The results show that accurate reading can be achieved on this small scale. Additionally, the experimental method has also successfully identified crack initiations and propagations on the tested samples, significantly smaller than 1 mm, which can reveal future fracture mechanics analysis and supply data to models adapted to microscopic scale phenomena. [ABSTRACT FROM AUTHOR]

Flax fiber-reinforced plastics have an innate eco-friendly nature due to the fiber reinforcement and reduced energy requirements in fabrication when compared to current fiber reinforced composite materials. They possess a complex time-dependent material behavior, which is investigated in the present paper. A composite material with flax fiber reinforcement on the load direction, embedded in an epoxy resin matrix, was studied. The procedures used were tensile tests, repeated loading-recovery, and creep-recovery tests, which were meant to expose the components of the response with respect to stress level and load duration. The results showed an elastic bi-linear behavior, a yield point at approximately 20% of the ultimate tensile stress, and tensile moduli of 35.9 GPa and 26.3 GPa, before and after yield. This is coupled with significant non-linear viscoelastic and, after yield, viscoplastic components, accounting for up to 14% of the strain response. The behavior is inherited from both the matrix and the fiber reinforcement and is attributed to the amorphous nature of the matrix combined with the microstructural re-organization of the fiber under load, which are partially reversible. [ABSTRACT FROM AUTHOR]

In this research, the mechanical properties of 3D-printed polycaprolactone (PCL), a biocompatible and biodegradable semi-crystalline polyester, available as feedstock for additive manufacturing technology based on the material extrusion process, were determined. The influence of the infill pattern (zig-zag vs. gyroid) and ultraviolet (UV-B) exposure over the specimens' mechanical performances were also investigated to gather relevant data on the process parameter settings for different applications. Specimens and samples of 3D-printed PCL were analyzed through tensile and flexural tests. The experimental data showed the good repeatability of the manufacturing process, as well as a mechanical behavior independent of the specimens' infill pattern at full density. No differences between the failure patterns of the tensile specimens were recorded. UV-B exposure proved to have a significant negative impact on the specimens' tensile strength. The 3D printing of PCL and PCL blends is reported mainly for use in scaffold manufacturing or drug delivery applications. As another novelty, the suitability of commercial PCL filaments for producing patient-customized wrist–hand orthoses was also assessed in this study. Semi-cylindrical PCL samples mimicking the forearm part of a wrist–hand orthosis with hexagonal open pockets were 3D-printed and mechanically tested. The results were discussed in comparison to samples with a similar design, made of polylactic acid. The experiments revealed the need to carefully calibrate the manufacturing parameters to generate defect-free, good quality prints. Once settings were established, promising results were obtained when producing orthoses in a ready-to-use form. On the other hand, the attempts to thermoform flat 3D-printed PCL orthoses proved unsuccessful. [ABSTRACT FROM AUTHOR]

The present paper analyses the possibility of using the digital image correlation technique to study the mechanical behavior of small scale components. A microscope is supplemented to the equipment for magnification, together with a miniature tensile testing machine. Several samples with already studied stress concentrators were analyzed. For comparison purposes, a finite element model of the geometry, with appropriate loading conditions, is created and the strain field is compared, in orderv to be validated to the experimental one. Results show that an accurate reading can be made by using this technique. Furthermore, crack initiation and its propagation path can be determined, by the appearance of high strains in the region. [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]

Featured Application: Fabricated structures can be used as substrates for the SERS technique of Raman spectroscopy. Bimetallic nanostructures have the potential to become the new generation candidates for applications in catalysis, electronics, optoelectronics, biosensors and also for surface-enhanced Raman Spectroscopy (SERS). The bimetallic nanocrystals offer additional properties over the single metal components such as improved electromagnetic properties and corrosion protection. This work presents a simple and inexpensive method to fabricate large area biplasmonic (bimetallic) substrates, employing DC magnetron sputtering, picosecond laser pulses and a digital galvanometric scanner. The aim of this study was to achieve large area homogeneous substrates while having a good and predictable signal amplification by SERS effect. Gold thin films with 200 nm thickness were deposited on optical polished substrates and then irradiated in atmospheric air with λ = 1064 nm wavelength laser pulses with 8 ps pulse duration and 500 kHz fixed repetition rate. Various laser fluences and laser irradiation speeds were employed in order to optimize the Laser-Induced Periodic Surface Structures (LIPSS) formed on the substrate. The results are presented comparatively for the standalone Cu substrates and for the Cu-Au substrates using Raman spectral analysis on a single signal peak of a Rhodamine 6G solution. [ABSTRACT FROM AUTHOR]

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