Search Results (145)

Bisphenol A (BPA) has been listed as a substance of very high concern (SVHC) due to its endocrine-disrupting properties according to REACH in 2017. European competent authorities have prepared a REACH restriction proposal to reduce BPA levels in the environment. The proposed limit for the concentration of free BPA and other bisphenols in articles is 10 mg kg⁻¹. If exceeded, migration testing can demonstrate that no more than 0.04 mg L⁻¹ is released from the product or material over its lifetime. German authorities are drafting a new restriction proposal after the original was temporarily withdrawn. The residual and migration limits mentioned above were key requirements from the previous restriction proposal. Numerous national and international standards exist for assessing how environmental factors affect the physical and chemical properties of products and materials—such as notch impact strength and tensile strength—but these standards do not cover the release of pollutants. A standardised procedure that covers all aspects of artificial weathering and monitors the subsequent release of pollutants is necessary, especially in the context of the regulation of these substances. An accelerated weathering procedure was established for non-protected samples. This material was not intended for outdoor applications. The testing procedure applied a typical weathering scenario that represents Central European climate conditions. The procedure was validated and applied to samples under distinct quality assurance aspects. Released BPA is quantified via an organic isotope dilution LC-MS/MS method. In parallel, identical samples were weathered outdoors on a weathering rack. Haze and yellowness index are measured to compare outdoor and weathering chamber results. Full article

The anisotropic mechanical properties of selective laser melting (SLM)-processed Ti-6Al-4V (TC4) alloy hinder its deployment in polar marine equipment. This study systematically probes the relationships between laser scanning strategies (unidirectional vs. 67°-rotated scanning between layers), notch orientation (governing loading direction), and cryogenic impact energy of SLM-TC4. Charpy impact tests from −60 °C to 20 °C were performed on V-notched specimens fabricated with distinct scanning strategies and notch orientations (top/side surfaces). The analysis of impact energy data and macro/micro-fractography demonstrates that impact energy declines markedly with decreasing temperature, showing a 25–35% reduction at −60 °C versus 20 °C while exhibiting enhanced data consistency under cryogenic conditions. Notably, specimens fabricated with 67°-rotated scanning between layers achieve higher impact toughness than unidirectionally scanned equivalents. Moreover, for identical scanning strategies, side-notched specimens consistently outperform top-notched specimens, evidencing superior interfacial bonding strength between deposited layers relative to bonding within individual layers. Within individual layers, toughness normal to the laser scan path exceeds that parallel to the path. However, controlling ductile-to-brittle transition behavior and precluding brittle failure are imperative for SLM-TC4 components in polar cryogenic service. This work delivers essential quantitative benchmarks and experimental validation for optimizing SLM processing in critical polar vessel components. Full article

The mechanical and structural design of railway vehicles is heavily influenced by their lifetime. Because fatigue is a significant factor that impacts the longevity of railway components, it is imperative that the fatigue resistance properties of crucial components, like leaf springs, be thoroughly investigated. This research investigates the fatigue resistance of 51CrV4 steel under bending and axial tension, considering different stress ratios across low-cycle fatigue (LCF), high-cycle fatigue (HCF), and very-high-cycle fatigue (VHCF) regimes, using experimental data collected from this work and prior research. Data included fractographic analyses aiming to help in understanding some of failures for different loads. The presence of geometric discontinuities, such as notches, amplifies stress concentrations, requiring a probabilistic approach to fatigue assessment. To address notch effects, the theory of critical distances (TCD) was employed to evaluate fatigue strength. TCD model was integrated in fatigue statistical models, such as the Walker model (WSN) and the Castillo–Fernández-Cantelli model adapted for mean stress effects (ACFC). Extending the application of the TCD theory, this research provides an improved probabilistic fatigue model that integrates notch sensitivity, mean stress effects, and fatigue regimes, contributing to more reliable design approaches of railway leaf springs or other components produced in 51CrV4 steel. Full article

Capsule-based self-healing technologies offer a promising solution to extend pavement service life without requiring external activation. The effect of the capsule content on the mechanical behaviour of self-healing asphalt mixtures still needs to be understood. This study presents a numerical evaluation of the isolated effect of incorporating capsules containing encapsulated rejuvenators, at different volume contents, on the stiffness and strength of asphalt mixtures through a three-dimensional discrete-based programme (VirtualPM3DLab), which has been shown to predict well the experimental behaviour of asphalt mixtures. Uniaxial tension–compression cyclic and monotonic tensile tests on notched specimens are carried out for three capsule contents commonly adopted in experimental investigations (0.30, 0.75, and 1.25 wt.%). The results show that the effect on the stiffness modulus progressively increases as the capsule content grows in the asphalt mixture, with a reduction ranging from 4.3% to 12.3%. At the same time, the phase angle is marginally affected. The capsule continuum equivalent Young’s modulus has minimum influence on the overall rheological response, suggesting that the most critical parameter affecting asphalt mixture stiffness is the capsule content. Finally, while the peak tensile strength shows a maximum reduction of 12.4% at the highest capsule content, the stress–strain behaviour and damage evolution of the specimens remain largely unaffected. Most damaged contacts, which mainly include aggregate–mastic and mastic–mastic contacts, are highly localised around the notch tips. Contacts involving capsules remained intact during early and intermediate loading stages and only fractured during the final damage stage, suggesting a delayed activation consistent with the design of healing systems. The findings suggest that capsules within the studied contents may have a moderate impact on the mechanical properties of asphalt mixtures, especially for high-volume contents. For this reason, contents higher than 0.75 wt.% should be applied with caution. Full article

S355NL structural steel is extensively employed in bridges, ships, and power station equipment owing to its excellent tensile strength, weldability, and low-temperature toughness. However, pronounced fluctuations in its Charpy impact energy at low temperatures significantly compromise the reliability and service life of critical components. In this study, vacuum-induction-melted ingots of S355NL steel containing 0–0.086 wt.% rare earth cerium were prepared. The effects of Ce on microstructures, inclusions, and impact toughness were systematically investigated using optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and Charpy V-notch testing. The results indicate that appropriate Ce additions (0.0011–0.0049 wt.%) refine the average grain size from 5.27 μm to 4.88 μm, reduce the pearlite interlamellar spacing from 204 nm to 169 nm, and promote the transformation of large-size Al₂O₃-MnS composite inclusions into fine, spherical, Ce-rich oxysulfides. Charpy V-notch tests at –50 °C reveal that 0.0011 wt.% Ce enhances both longitudinal (269.7 J) and transverse (257.4 J) absorbed energies while minimizing anisotropy (E_t/E_l  =  1.01). Conversely, excessive Ce addition (0.086 wt.%) leads to coarse inclusions and deteriorates impact performance. These findings establish an optimal Ce window (0.0011–0.0049 wt.%) for microstructural and inclusion engineering to enhance the low-temperature impact toughness of S355NL steel. Full article

This study investigates the fracture toughness of adhesive joints between carbon fiber-reinforced polymer composites (CFRP) and boron-alloyed high-strength steel under Mode I and II loading, based on linear elastic fracture mechanics (LEFM). Two adhesive types were examined: the excess resin from the prepreg composite, forming a thin layer, and a toughened structural epoxy (Sika Power-533), designed for the automotive industry, forming a thick layer. Modified double cantilever beam (DCB) and end-notched flexure (ENF) specimens were used for testing. The results show that using Sika Power-533 increases the critical energy release rate by up to 30 times compared to the prepreg resin, highlighting the impact of adhesive layer thickness. Joints with the thick Sika adhesive performed similarly regardless of whether uncoated or Al–Si-coated steel was used, indicating the composite/Sika interface as the failure point. In contrast, the thin resin adhesive layer exhibited poor bonding with uncoated steel, which detached during sample preparation. This suggests that, for thin layers, the resin/steel interface is the weakest link. These findings underline the importance of adhesive selection and layer thickness for optimizing joint performance in composite–metal hybrid structures. Full article

Food contact polymers require thermochromic pigments to provide temperature-sensitive visual cues for consumer safety and product integrity. However, their susceptibility to ultraviolet (UV) degradation limits long-term application. This study investigates the UV resistance of food-grade thermochromic polypropylene blends under simulated indoor and outdoor UV exposure for 500 and 1000 h. Visual properties, colorimetric (CIE L*a*b*) measurements, mechanical testing (tensile and impact), and mass variation analysis were performed to assess photostability and material integrity. Exposure to UV led to progressive discoloration (ΔE*_ab up to 34.07) and significant mechanical deterioration. Tensile strain at break decreased by 48.67%, and notched impact strength dropped by 44.15% after 1000 h of UV exposure. No measurable mass loss occurred, indicating degradation was confined to surface-level oxidation rather than bulk material erosion or leaching. These findings highlight the need for optimal pigment loading and UV stabilization to extend the shelf life of thermochromic food packaging materials in light-exposed storage and retail environments. The study offers a framework for improving the long-term reliability of smart packaging in the food industry. This work uniquely integrates optical, mechanical, and mass loss analyses to evaluate thermochromic packaging degradation under extended UVA exposure. Full article

The effect of epoxidized soybean oil on the operational, technological, and physical and mechanical properties of composites based on high-density recycled polyethylene filled with wood floor was investigated. It has been shown that the introduction of epoxidized soybean oil in the amount of 0.5 wt.% into the wood-polymer composite (WPC) improves the physical, mechanical, and operational properties of the material: the Charpy impact strength (on notched samples) increases from 7.5 kJ/m² to 20.0 kJ/m², the bending strength increases from 31.6 MPa to 50.8 MPa, and the coefficient of linear thermal expansion decreases by 15%. With a further increase in the content of epoxidized soybean oil in the composite, its water absorption and technological shrinkage decrease, but its physical and mechanical properties deteriorate. Full article

With the increasing demands for mechanical properties of ultra–high–strength steels (UHSSs), enhancing their strength and obtaining an excellent strength–toughness matching have received widespread attention. In this paper, the influence of microstructure and primary carbides on the mechanical properties of 2200 MPa ultra–high–strength steel was studied by treating it at different solid–solution temperatures. The mechanical properties of the experimental steel following aging demonstrated a non–monotonic dependence on solid–solution temperature, manifested as an initial increase followed by a gradual decline in both strength and toughness. Microstructural evolution analysis reveals that elevated solid–solution temperatures induce coarsening of prior austenite and martensite grains in the steel, thereby promoting toughness enhancement. Concurrently, primary carbides progressively dissolve into the matrix with increasing solid–solution temperature, generating a supersaturated solid–solution that facilitates M₂C carbide precipitation during aging, ultimately leading to strength improvement in the experimental steel. An exceptional combination of strength, ductility, and toughness with an ultimate tensile strength of 2142 MPa, yield strength of 1830 MPa, elongation of 12.5%, and Charpy U–notch impact energy of 60.5 J was obtained when the experimental steel was solid–solution treated at 910 °C. Full article

In modern surgery, the internal fixation plates fabricated from hydroxyapatite/poly(L-lactide) (HA/PLLA) composites encounter clinical limitations in fracture treatment due to their inadequate mechanical properties. In this work, pressure-induced flow (PIF) technique is employed to address this limitation. Under optimal processing conditions (140 °C and 250 MPa), the HA/PLLA composites exhibit an impressive flexural strength of 199.2 MPa, which is comparable to that of human cortical bone, the strongest bone tissue in the body. The tensile strength and the notched Izod impact strength are close to 84.2 MPa and 16.7 kJ/m², respectively. Meanwhile, the HA/PLLA composites develop multi-level stacked crystal layers during PIF processing, accompanied by increases in crystallinity (53.1%), crystal orientation (81.6%) and glass transition temperature (78.8 °C). After 2 months of in vitro degradation, the HA/PLLA composites processed by the PIF technique still maintain considerable flexural strength (135.3 MPa). The excellent mechanical properties of HA/PLLA composites processed by PIF technique expand their potential as an internal fixation plate. Full article

Concerns have been raised regarding the mechanical recycling rates of automotive parts, which appear to be low in comparison to those of other sectors. Addressing this issue demands the promotion of the mechanical recycling of waste automobile bumpers. This study investigates primer treatment effects on the mechanical properties of injection-molded waste bumpers. The primer treatment effects vary depending on the bumper coating. The flexural strength of coated bumpers is greater: 27.6 MPa vs. 29.2 MPa. The flexural modulus is also greater: 1667 MPa vs. 1761 MPa. By contrast, the notched Charpy impact strength is less: 25.4 kJ/m² vs. 23.4 kJ/m². The flexural strength and flexural modulus of the bumpers lacking a coating are also lower, respectively, at 25.0 MPa vs. 22.9 MPa and 1523 MPa vs. 1314 MPa. However, the notched Charpy impact strength is greater: 40.0 kJ/m² vs. 73.6 kJ/m². These findings suggest that primer treatment can control the mechanical properties of injection-molded parts produced from waste automobile bumpers, which is an important achievement for promoting the mechanical recycling of waste automobile bumpers. Full article

Highly toughened bio-based polylactic acid (PLA)/Eucommia ulmoides gum (EUG) blends were prepared using organic montmorillonite (OMMT) as a compatibilizer through melt-blending. Both the theoretically predicted values and the experimental results confirm that the majority of the OMMT’s nanolayers are selectively localized at the PLA/EUG interface. This localization leads to improved interfacial properties and a more refined morphology of the dispersed EUG phase. By increasing the OMMT content from 0 phr to 2 phr, the notched Izod impact strength of the PLA/EUG/OMMT (85/15/2) blend increases to a maximum value of 44.6 kJ/m². This is significantly higher than the values observed for neat PLA at 3.8 kJ/m² and the PLA/EUG (85/15) blend at 4.7 kJ/m². Moreover, compared to neat PLA and the PLA/EUG (85/15) blend, which exhibit poor tensile ductility, as indicated by their low elongation at break, the PLA/EUG/OMMT blend demonstrates a substantial improvement in its tensile ductility when an appropriate amount of OMMT is added. It is believed that the enhanced toughness of the PLA/EUG/OMMT blends can primarily be attributed to the refinement and more uniform dispersion of the EUG domains, which is caused by the incorporation of OMMT. In addition, the crystalline properties, thermal degradation behavior, and extrudate swell behavior of the PLA/EUG blends with and without OMMT were also evaluated in detail. Finally, the experimental results prove that the PLA/EUG (85/15) blend containing 2 phr of OMMT exhibits the highest impact toughness and tensile ductility, accompanied by improved thermal stability and extrusion stability. Full article

To investigate the influence of varying concentrations and types of carbon fiber (CF) on the mechanical properties of polyamide 6 (PA6) composites, this study explores the mechanical properties of PA6 composites with various CF types and quantities. The micro-morphology of the composites and the CF length distribution were characterized. The results indicate that the inclusion of carbon fibers significantly enhances the tensile, flexural, and notched impact strengths of PA6. Specifically, when about 30 wt% of CF T300 was added, the tensile and flexural strength of the composite reached a maximum of 166 MPa and 224 MPa, respectively, representing increases of 236.6% and 229.6%, respectively, compared to pure PA6. The maximum flexural modulus achieved 14.6 GPa, which was six times as large as that of pure PA6. Moreover, the CF length in the PA6 matrix follows a near-Gaussian distribution. A proper CF length and orientation, along with strong interfacial bonding between CF and the PA6 matrix, contribute to improved mechanical properties. The overall performance of T700-reinforced composites is better than that of T300-reinforced ones due to T700’s higher precursor strength and better fiber-length retention. This study provides guidance for fabricating high-performance PA6 composites. Full article

The hybridization of additive manufacturing (AM) with conventional manufacturing processes in tooling applications allows the customization of the tool. Examples include weight reduction, improving the vibration-dampening properties, or directing the coolant to the critical zones through intricate conformal cooling channels aimed at extending the tool life. In this regard, metallurgical challenges like the need for a post-processing heat treatment in the AM segment to meet the thermal and mechanical properties requirements persist. Heat treatment can destroy the dimensional accuracy of the pre-manufactured heat-treated wrought segment, on which the AM part is built. In the case of dissimilar joints, heat treatment may further impact the interface properties through the ease of diffusional reactions at elevated temperatures or buildup of residual stresses at the interface due to coefficient of thermal expansion (CTE) mismatch. In this communication, we report on the laser powder bed fusion (L-PBF) processing of MAR 60, a weldable carbon-free maraging powder, to manufacture a hybrid tool holder for general turning applications, comprising a wrought segment in 25CrMo4 low-alloy carbon-bearing tool steel. After L-PBF process optimization and manipulation, as-built (AB) MAR 60 steel was characterized with a hardness and tensile strength of ~450 HV (44–45 HRC) and >1400 MPa, respectively, matching those of pre-manufactured wrought 25CrMo4 (i.e., 42–45 HRC and 1400 MPa). The interface was defect-free with strong metallurgical bonding, showing slight microstructural and hardness variations, with a thickness of less than 400 µm. The matching strength and high Charpy V-notch impact energy (i.e., >40 J) of AB MAR 60 eliminate the necessity of any post-manufacturing heat treatment in the hybrid tool. Full article