Strain-induced crystallisation (SIC) significantly enhances the mechanical performance of natural rubber. However, the presence of reinforcing fillers such as carbon black or silica complicates the identification of the crystallisation onset with hysteresis measurements due to overlapping of chain orientation and viscoelastic effects. This study proposes a novel, indirect approach to identification of the SIC onset by analysing overstress evolution during multi-step relaxation tests (MSRT) in both filled and unfilled natural rubber compounds. A custom clamp system was designed to enable large, consistent deformations without specimen slippage. Unfilled specimens exhibited minimal overstress until stretches above λ = 4 at room temperature, where a sharp increase in relative overstress indicated crystallite formation. This result was validated by hysteresis measurements at slow deformation rates, which showed a plateau in the stress response consistent with crystallisation. For filled materials, viscoelastic contributions were, as expected, observed from the very beginning of the test, and SIC onset was observed at lower stretches of λ≈ 2 . The crystallite growth appeared more gradual due to filler interference with the material matrix. Finally, it was confirmed that the SIC onsets determined directly by X-ray diffraction exactly coincide with those determined by the mechanical analysis. These findings suggest that overstress analysis is a valuable tool for identifying SIC onset in filled elastomer compounds, offering an effective alternative to less accessible measurement methods.

The Poynting effect, characterized by the emergence of normal stresses or strains during simple shear deformation, is a well-documented but often overlooked phenomenon in material testing and modeling. In classical linear elasticity, it is often assumed that simple shear deformations result solely in shear stresses. Experimental studies have, however, repeatedly shown that this ideal stress state is difficult to obtain in practice. This study revisits the Poynting effect through a simplified, two-dimensional linear elastic model that conceptualizes the buildup of forces along the diagonals of a sheared cuboid. The model is further employed to study the influence of sample geometry and material (represented through the ratio of bulk and Young’s modulus for linear elastic materials). The results indicate, that both factors play a significant role in the development of the Poynting effect in simple shear. With tall geometries and material characteristics representative of nearly incompressible materials exhibiting strong Poynting effect, while wide samples reduce the Poynting effect.

In comparison with metals, the characteristic temperatures at which polymers change their behaviour are significantly smaller. Temperature-related or temperature-driven phenomena in meltable thermoplastics, weakly crosslinked elastomers or highly crosslinked thermosets have their origin in physical or chemical changes on the microscale. On the macroscopic scale, the mechanical, thermal and caloric properties of polymers change. Some of these phenomena are reversible, others are irreversible. They take place when the temperature is changing due to heat supply from outside or energy dissipation caused by inelasticity and dynamic mechanical loads. As we know, growing temperature increases the mobility of the polymer molecules and changes the rates of chemical reactions. This review article addresses selected phenomena relevant for technical applications. As a reversible phenomenon, the process-dependent stiffening and softening of polymers around the glass transition is treated. Crystallisation, driven by deformation or temperature, is also a reversible phenomenon discussed in this article. Adhesives are applied in everyday life and change their material properties during curing. A phenomenon of high technical importance is ageing. Irreversible chemical ageing increases with the temperature or the environmental oxygen concentration, results from the generation of new crosslinks in combination with chain scission and modifies the mechanical material behaviour. Another characteristic, especially of thermoplastics, is physical ageing. It occurs below the glass transition, corresponds to a decrease in the free volume and leads to an increase in the relaxation times. If polymer parts are dynamically deformed over long times, dissipative heating takes place and leads to an increase in temperature. The focus of this review article is material modelling. Experimental investigations support the argumentation.

Laser powder bed fusion of metals (PBF-LB/M) has emerged as a leading additive manufacturing (AM) method for fabricating geometrically complex, high-performance metallic components, particularly those made from Ti-6Al-4V alloy. This contribution presents a comprehensive overview of the PBF-LB/M process, emphasizing its current research landscape and the persistent challenges in process design, particularly concerning the application of support structures and thermal management. Drawing on methods from welding science, a physically motivated framework is proposed to systematically analyze the thermal, mechanical, and metallurgical interactions that occur during fabrication. Special attention is given to the microstructural evolution of Ti-6Al-4V under PBF-LB/M conditions, highlighting the formation of acicular martensite and its behavior during the manufacturing process. The insights provided form a foundation for developing more efficient and reliable process strategies with practical relevance in industrial applications.

The influence of the nozzle geometry on pressure losses and energy efficiency in industrial cooling and drying systems was experimentally investigated. Three circular nozzles with different outlet geometries were analysed. Two POM-C nozzles with 8 and 12 mm diameters, and one aluminium nozzle with a diameter of 8 mm were evaluated through pressure and volume flow measurements. Loss coefficients were calculated to quantify the energy dissipation associated with each design. Results indicate that the POM-C nozzles exhibit substantially lower loss coefficients ( ≈1.0 ) compared to the aluminium nozzle ( ≈2.5 ), demonstrating superior energy efficiency and minimal pressure loss. Measurement deviations at very low pressures were attributed to sensor limitations. These findings confirm that optimised nozzle geometry significantly enhances energy performance, providing both environmental and economic advantages.

The Fused Filament Fabrication (FFF) process has established itself as a key technology in prototyping and development and has garnered increasing interest in academic research. A substantial body of research on the FFF process has focused on the influence of process parameters on the resultant material/part properties. The thermal history of the printed part has proven itself as one of the most important factors in the printing process. It influences warping behavior, dimensional accuracy, build plate adhesion, as well as the mechanical properties of the finished part. A key requirement for understanding the influence of thermal history is the knowledge of the thermal properties of the considered material. In this study, the temperature-dependent thermal properties (isobaric heat capacity, thermal conductivity and density) of an unfilled polyamide 6 material for 3D printing are provided. Special attention is given to discussing the challenges associated with measuring these properties, particularly regarding how well the measured values represent the actual conditions during the printing process.

In this study, the embrittlement behavior of as-built Ti–6Al–4V manufactured by Laser Powder Bed Fusion (PBF-LB/M) was investigated with a focus on effects caused by in-process heat accumulation. The microstructural evolution was analyzed through systematic heat treatment of Ti–6Al–4V samples, Vickers hardness testing, and differential scanning calorimetry (DSC) analysis. A distinct hardness peak was observed at around 500 $$\mathrm {^\circ C}$$ , coinciding with an irreversible exothermic event seen in DSC measurements, suggesting a distinctive transformation specific to the $$\alpha ^{\prime }$$ microstructure. Tensile tests on embrittled samples showed an increased yield strength ( $$1197\, \pm \, 34$$ MPa) and an ultimate tensile strength ( $$1252\, \pm \, 19$$ MPa) but a significantly reduced ductility ( $$0.7\, \pm \, 0.6$$ % elongation). Compression testing confirmed high strength and low ductility, while Charpy impact energy dropped by 45.9 % compared to the as-built condition. Fractographic analysis indicated a transition to mixed trans- and intercrystalline fracture modes. Although direct evidence of $$\mathrm {Ti_{3}Al}$$ precipitation remains inconclusive, the literature suggests that vanadium segregation and $$\beta$$ phase stabilization could provide favorable conditions for its formation. These results highlight the critical impact of local reheating on mechanical performance and emphasize the need to consider embrittlement phenomena in process parameter optimization and the design of support structures. The study contributes to a fundamental understanding of microstructural sensitivity in PBF-LB/M Ti–6Al–4V and supports the development of more robust and certifiable additive manufacturing strategies.

Sustainability in product development emphasizes the need for extended product lifetimes to minimize replacements and reduce resource consumption and environmental impact. This study investigates the impact of different thread manufacturing processes, cutting, rolling, and deep rolling, on the fatigue resistance of M12 threads fabricated from quenched and tempered chromium‐molybdenum alloy steel. Fatigue tests conducted under cyclic tensile loading revealed that rolled threads exhibited superior performance, enduring higher stress levels without failure. Deep rolling significantly increased the fatigue strength compared to cutting, demonstrating its efficiency as a post‐processing technique for enhancing durability. These findings highlight the sustainability and reliability of rolling as well as deep rolling processes and show that deep rolling is an effective post‐processing technique for improving the durability of cut threads.

In order to achieve process stability in the industrial thermoforming of fiber reinforced polymers (FRPs), typically, cost- and time-intensive trial-and-error-processes are required. The experimental boundary conditions, as well as the material composition and component design optimization, are highly dependent on material phenomena related to various material scales and constituents. It is therefore necessary to develop finite element constitutive models that are validated against experimental results and incorporate various material phenomena in order to reduce the experimental effort and evaluate the composite’s performance with reliable predictions. In this work, an existing thermo-mechanically coupled constitutive model for polyamide 6 is extended in a thermodynamically consistent manner to represent the anisotropic composite behavior, including anisotropic conduction, thermal expansion as well as internal heat generation associated with irreversible processes. Furthermore, the crystallization process is incorporated using experimental standard (S-DSC) and flash (F-DSC) differential scanning calorimetry results. The thermal and mechanical model parameters of the homogenized macroscopic material formulation are identified and the model response is successfully validated with a data base comprising both experimental and virtual results. Finally, the model capabilities are assessed in several thermo-mechanical structural computations, including a 3D thermoforming example in comparison with experimental results. In particular, the influence of the anisotropy on material self-heating, thermal expansion and the resulting crystalline state is investigated, demonstrating the potential of this new approach to efficiently and accurately predict FRPs in the future. Our source code, data, and exemplary input files are available under https://doi.org/10.5281/zenodo.15052983.

The increasing importance of sustainability in engineering demands the development of long-lasting, high-performance components that reduce material and energy consumption over time. This study investigates how different thread manufacturing processes, i.e., cutting, rolling, and deep rolling, affect the fatigue strength of bolts made from 42CrMo4+QT steel. Cylindrical specimens with M12 threads were subjected to cyclic tensile loading with constant mean stress. Fatigue strength was evaluated using the staircase method, and supporting analyses included X-ray diffraction for residual stress, and full width half maximum examination and Vickers microhardness measurements. Results show that thread rolling significantly improves fatigue strength, achieving 113.8 MPa compared to 45.1 MPa for cut threads. Deep rolling also enhanced fatigue strength to 71.1 MPa, offering a practical alternative for low volume production. Residual stress and hardness distributions confirmed the mechanical benefits of both rolling methods.

The mechanical performance of semicrystalline thermoplastics like polyamide 6 (PA6) is strongly influenced by crystallinity, which poses challenges for consistent viscoelastic characterization, especially at elevated temperatures. This study addresses this issue by exploring immiscible blends of PA6 and amorphous cyclic olefin copolymer (COC) as a novel approach to systematically tailor crystallinity without relying on thermal annealing, thereby avoiding cold crystallization during mechanical testing. Blends with varying crystallinity were prepared via melt blending and characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) across wide temperature and frequency ranges. To extend the measured data and identify relaxation spectra, time-temperature superposition (TTS) was applied and master curves were constructed. Shift factors were modeled using both the Williams-Landel-Ferry (WLF) equation and a custom polynomial fit, enabling reliable extrapolation across the entire experimental temperature spectrum. The viscoelastic behavior was quantitatively described using a Generalized Maxwell Model (GMM) with parameters fitted via nonlinear optimization. The resulting model accurately captures the viscoelastic behavior of the blends over several frequency decades. This work establishes a comprehensive experimental and modeling framework to describe the thermomechanical performance of PA6 as a function of crystallinity; thereby supporting its application in temperature- and frequency-sensitive environments.

This study investigates the fluid mechanical behaviour of outgoing free jets from circular nozzles, focusing on jet angle and velocity profile analysis. Two nozzles with outlet diameters of 8 and 12 mm were examined using schlieren photography and Pitot tube measurements. Schlieren imaging revealed a consistent jet angle of approximately 22 ^∘ unaffected by variations in pressure or nozzle diameter. Additionally, the schlieren method revealed that turbulence within the jet boundary increased at lower pressures due to greater mixing with the ambient air. The velocity profiles, obtained through dynamic pressure measurements, followed a Gaussian distribution within the core and transition regions, with the larger 12 mm nozzle producing a more stable and extended core region compared to the 8 mm nozzle. Deviations were observed near the jet boundaries, particularly at lower velocities, highlighting the challenges in measuring low dynamic pressures. The study’s findings contribute to the understanding of free jet dynamics, offering insights for optimising industrial cooling and drying systems.

Polyamide 12 (PA12) is a semi-crystalline thermoplastic used in the automotive and aerospace industries due to its high resistance to chemicals and abrasion and its good thermal stability. The material can be processed with various manufacturing technologies, including selective laser sintering (SLS), which offers great potential for industrial production due to its excellent and reproducible mechanical properties and thus motivates a detailed understanding of the mechanical behavior. This paper presents an approach for modeling the mechanical behavior of selectively laser-sintered polyamide 12. A continuum mechanical model is developed based on a comprehensive temperature and velocity-controlled experimental program, and its parameters are identified. After presenting the test specimens developed in-house, which utilized the geometric freedom of the SLS process, the kinematic description of the test specimens and the digital image correlation technique used for this purpose are discussed. The experimental test results are then presented, which consist of relaxation tests and experiments with a constant strain rate at various temperatures. After the two material-theoretical approaches of linear viscoelasticity and endochronic plasticity have been presented, the material model is derived in three dimensions, and the parameters are identified.

This study investigates the swelling and diffusion behavior of additively manufactured thermoplastic polyurethane elastomers with aviation fuels. It aims to demonstrate that replacement parts can be additively manufactured and can be used in contact with fuels in the near future. Thermoplastic polyurethane is studied as a function of the printing parameter "form factor" (FF), which defines the distance between individual polymer droplets used in the Arburg Plastic Freeforming (APF) process. The samples were chemically characterized and mechanically tested before and after immersion in jet fuel. Sorption experiments show that the chemical composition of the polymer is primarily responsible for compatibility with the fuel and, thus, mainly for equilibrium absorption. Samples with a higher FF exhibit higher diffusion rates due to a larger free volume than the ones with a lower FF. As swelling progressed, an increase in mass and volume was accompanied by a decrease in residual stress at break. In addition to the chemical composition, the "form factor" offers a variety of possibilities to influence not only the mechanical material properties but also the swelling behavior.

Antibacterial properties of components are increasingly becoming an important challenge in material development especially in polymer technology. A well-known additive with which an antibacterial effect can be achieved is the metal oxide titanium dioxide. The aim of this research work was to investigate possible influences on the flexural properties of additively manufactured components resulting from the addition of titanium dioxide as an antimicrobial additive. Compounds with 5 %, 10 % and 15 % titanium dioxide and polyamide 12 as matrix material were produced. Three-point bending test specimens were fabricated out of these compounds, anaylsed and the results were compared with specimens made of virgin polyamide 12. The investigations show a general loss in ductility compared to the virgin polyamide 12. A comparison of the different titanium dioxide contents shows no clear change in the flexural stress at conventional bending. The flexural strain at break seems to decrease for higher titanium dioxide contents. Antibakterielle Eigenschaften von Bauteilen werden zunehmend zu einem wichtigen Bestandteil in der Werkstoffentwicklung, insbesondere in der Polymertechnologie. Ein bekannter Zusatzstoff, mit dem eine antibakterielle Wirkung erzielt werden kann, ist das Metalloxid Titandioxid. Ziel der vorliegenden Forschungsarbeit war die Untersuchung m & ouml;glicher Einfl & uuml;sse auf die Biegeeigenschaften von additiv gefertigten Bauteilen durch die Zugabe von Titandioxid als antimikrobielles Additiv. Hierf & uuml;r wurden Compounds mit 5 %, 10 % und 15 % Titandioxid und Polyamid 12 als Matrixmaterial hergestellt. Aus diesen Compounds wurden Biegeproben gefertigt, untersucht und die Ergebnisse mit Proben aus reinem Polyamid 12 verglichen. Die Untersuchungen zeigen einen Verlust an Duktilit & auml;t durch Zugabe des Titandioxids gegen & uuml;ber den Proben aus reinem Polyamid 12. Werden die verschiedenen Titandioxidgehalte miteinander verglichen, so konnte keine deutliche Ver & auml;nderung der maximalen Biegespannung bei konventioneller Biegung festgestellt werden. Die Bruchdehnung scheint bei h & ouml;heren Titandioxidgehalten erneut abzunehmen. Decrease of the ductility when using titanium dioxide compounds in selective laser sintering. This paper determines the effects on the flexural properties when using titanium dioxide as an antimicrobial additive with polyamide 12 powder as matrix material. image

Achieving process stability in the thermoforming of fiber reinforced polymer materials (FRPs) for aerospace or automotive manufacturing is usually associated with a costly trial-and-error process, where experimental boundary conditions and other influencing factorsRWTHblau such as, for example, material composition RWTHblau need to be adjusted over time. This is especially true when material phenomena on the microlevel, such as the crystallization kinetics of the polymer matrix or resulting stresses from temperature gradients, are the cause of the process instability. To reduce the experimental effort and reliably predict the material behavior during thermoforming, finite element simulation tools on multiple scales are a useful solution. RWTHblauHereby, incorporating micromechanical phenomena into the model approaches is crucial for an accurate prediction by further reducing the deviation between simulation and experiment, in particular with regard to the underlying nonlinear material behavior. In this work, unit cell simulations on the microscale of a unidirectional glass fiber reinforced polymer (UD GFRP) are conducted to predict effective thermomechanical properties of a single material ply and ascertain the effect of individual ply constituents on the homogenized material behavior. The polymeric matrix material model used was identified in a prior publication with experimental data at various temperatures for polyamide 6 blends with varying degrees of crystallinities. Various randomization methods are tested to generate the unit cells and replicate the composites’ random fiber distributionRWTHblau with a focus on process automation. The simulative results are successfully compared to an experimental study on glass fiber reinforced polyamide 6 tested at various temperatures, demonstrating the potential of the approach to reduce RWTHblauboth time and cost required for material characterization. Finally, the unit cells are used to generate a RWTHblaudatabase RWTHblauto predict untested load cases that will be used in future work to characterize a homogenized macroscopic material model.

Laser powder bed fusion (LPBF) is an additive manufacturing process for metallic components, typically used to fabricate structures out of high-strength materials like Ti–6Al–4V. Due to the laser-based melting process, knowledge about heat conduction is essential. Here, the influence of process heat can be classified into a local effect with melting and re-melting and a global impact with complex heating and cooling cycles. This contribution investigates the capability of measurements with thermocouples to analyze the global temperature effect. With the provided setup, the evolution of interlayer temperature changes was studied under LPBF process conditions. It is shown that the complex thermal history in the samples is highly dynamic in the time domain with rapid temperature increases and cooling rates up to 172 $$\mathrm {\frac{^\circ C}{s}}$$ . During the printing process, it transforms into a quasi-static temperature profile characterized by a global temperature with small temporal variations as the number of layers proceeds. The thermocouple measurement is evaluated as a reliable method that provides repeatable experimental data. This tool should be further used to gain necessary knowledge about the LPBF process, especially the process-determining thermal evolution within components.

Pipes and hoses in automotive and aircraft design engineering represent the central application area for polyamide 12 (PA12). This is due to its exceptionally high abrasion resistance, high fatigue resistance, and good chemical resistance. The manufacturing process of selective laser sintering (SLS) brings a unique design freedom that allows the manufacturing of tube specimens in geometries (with cavities) that would not be possible to produce using conventional manufacturing processes. Here we present a remarkable tube specimen for torsion and tension/compression experiments, which has been specially adapted to the SLS manufacturing process. The novel specimen geometry manufactured with the SLS process provides reproducible torsion test results. The torsion experiments provide information on the shear behavior of the polyamide 12, considering its viscoelastic properties. The contribution finishes with a first modeling approach that predicts the viscoelastic properties of the PA12 material.