Several reduced-activation ferritic-martensitic (RAFM) steel grades have been proposed for structural applications in fusion reactors since the 1990s by several countries. The European reference RAFM ...steel EUROFER97 has been produced in four batches since 1998. It is intended for fabrication of Test Blanket Modules (TBM) for ITER as well as the blanket first wall and divertor cassettes of DEMO.
RCC-MRx is the design code developed for high-temperature, research and fusion reactors by AFCEN. Its latest edition contains a provisional section dedicated to EUROFER97, aggregating properties of the first two batches, whereas a full qualification and final inclusion of a material requires three batches minimum. The completion of the code is required for the design assessment of TBM units in the frame of the nuclear licensing process.
The EUROfusion project coordinates efforts to broaden the knowledge of EUROFER97 properties, which will be used for closing the database gaps in RCC-MRx. Low cycle fatigue (LCF) tests are a significant part of the EUROfusion test programme, since the material fatigue properties are indispensable for the component assessment owing to the cyclic nature of a tokamak operation.
In this work we report the results of interlaboratory LCF tests on EUROFER97 batch 3 performed in a temperature range relevant for its application in ITER (RT–550 °C), wide selection of total strain ranges (0.3–1.5 %) and two values of strain ratio Rε (0 and –1). Along with the estimated fatigue life and cyclic behaviour, a fractographic analysis done with scanning electron microscopy (SEM) is presented.
Epoxy nanocomposites are crucial in aerospace, enhancing structural performance, reducing weight, and improving fuel efficiency across various applications. They ensure safety, reliability, and ...optimal performance in critical aerospace systems. Optimizing fracture properties like crack growth resistance (KIC), critical stress intensity factor (GIC), and critical crack tip opening displacement (CTODc), is vital for safety, durability, and innovation, especially in epoxy nanocomposites under extreme conditions. This study examines how random Graphene Nanoplatelets (GNP) and aligned Fe3O4-GNP nanoplatelets impact the fracture resistance of epoxy nanocomposites. It analyzes various fracture properties and crack propagation mechanisms following ASTM D5045-99 standards for CT specimen toughness tests using a COD gauge, focusing on nanoparticle alignment and wt% loading effects. Neat epoxy has a KIC of 0.94 MPa m1/2, increasing to 1.20 with 0.600 wt% GNP. Aligned Fe3O4-GNP peaks at 1.49. the baseline GIC starts at 209 J/m2 and rises to 301 J/m2 with 0.600 wt% GNP, and notably to 419J/m2 with aligned Fe3O4-GNP. Aligned Fe3O4-GNP significantly enhances fracture properties by modifying stress distribution at primary crack fronts through mechanisms such as deflection, branching, and twisting. These findings offer crucial insights for improving epoxy nanocomposites in aerospace, ensuring increased safety, reliability, and performance in critical components.
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•Two-stage data augmentation method is developed, improves deep learning models' performance.•Semantic segmentation in SEM fractographic analysis marks new phase in this ...field.•SegFormer accurately segments complex fracture patterns, outperforming UNet, DeepLabV3+.
Fractographic analysis poses a significant challenge for field researchers without specialized training in fractography. To address this issue, this study introduces a comprehensive integrated workflow that encapsulates the entire process from dataset preparation and data enhancement to leveraging the SegFormer model for deep learning-driven semantic segmentation. An extensive collection of fractography images is formulated and augmented to train the SegFormer model, enabling precise semantic segmentation of morphological fracture regions including cleavage, ductile, dimple, fatigue striations, and others. To accommodate the demanding SEM imaging conditions which frequently include distortions, noise, and aberrations, we developed a two-stage method with diverse data augmentation strategies. This method resulted in a robust model demonstrating exceptional performance, as evidenced by a high mean Intersection over Union (mIOU) score of 59.7 and other metrics. The findings validate the potential of deep learning techniques, particularly the SegFormer model's efficacy in morphological fractography image segmentation for the first time. Our work offers a cost-effective, and efficient alternative deep learning approach to traditional experimental fracture analysis, thereby expanding opportunities for a broader range of professionals in the engineering domain.
This study aimed to extract the thermomechanical fatigue behavior of a CF/PEKK composite under low and ultrasonic frequency fatigue tests (LFFTs and UFFTs) in the presence of the self-heating effect. ...Preliminary increasing amplitude tests (IATs) were performed to obtain the minimum load level at which the self-heating is observable. Extracting the fatigue strength from T-σ curves for three mean stress levels resulted in constructing S-N curves for the LFFT regime at different load levels using a shift procedure. However, combining LFFT and UFFT results via S-N curve was impractical, while joining such results through the heat dissipation rate (q̇) was feasible for various constant amplitude tests and IATs. The derived σ-q̇ curves from combining LFFT and UFFT results and comparing the fracture mechanisms of CF/PEKK composite using fractography would make a step for bridging the transition zone between LFFTs and UFFTs and making the results transferable. The microscopy images obtained from fractography also confirmed the similarities of fatigue fracture mechanisms between LFFTs and UFFTs.
•LFFT and UFFT results are transferable using the heat dissipation rate concept.•Mean stress effect in S-N curves is derived through the application of thermography.•S-N curves obtained from combining LFFT and UFFT results showed a transition zone.•Combining LCF and VHCF regimes using S-N curve for CF/PEKK composite is unfeasible.
•Dynamic initiation and propagation of an internal crack in brittle material were observed.•The circumferential stress field at the pre-crack tip was obtained.•The effects of non-singular T stress ...and the friction were discussed.•The mode III fracture characteristics were observed in fracture morphology.
Different defects are widely distributed inside natural rock masses, and the development of these defects poses a potentially severe threat to the entire structural stability and safety. Most studies at present are concentrated on the propagation of two-dimensional (2D) penetrated cracks under static loads. In this paper, a series of tests were carried out on cubic glass specimens containing a closed pre-crack using a split Hopkinson pressure bar (SHPB) system, aiming to investigate the internal three-dimensional (3D) crack growth under dynamic compression. The results indicate that the dynamic compressive strength of the cubic specimen is influenced by the inclination direction of the 3D pre-crack. Theoretical analysis of the circumferential stress field at the pre-crack tip reveals the mechanism behind dominant crack initiation and favorable direction, which are also affected by non-singular T stress along and perpendicular to the pre-crack plane, as well as friction between crack planes. Through the post-mortem examination, the mode III fracture characteristics, crack bifurcation and Wallner lines are observed in fracture morphology. The terminal length of wrapped wing cracks subjected to dynamic loads is sensitive to pre-crack inclination angle, while it is approximately 1–1.5 times the pre-crack radius under static compression.
This paper presents a comprehensive experimental investigation on the fatigue response of glass-filled epoxy composites when subjected to cyclic loading. Rod-shaped particulate glass fibers in a ...volume fraction of 0%, 5%, 10% and 15% are reinforced in the epoxy matrix. The mechanical behavior of the resulting composite is studied under monotonic tensile loading and tension–tension cyclic fatigue loading. The undergoing damage mechanisms leading to the crack initiation and its propagation are studied using the in-situ low cycle fatigue testing. The crack initiation behavior and the crack initiation life are found to be affected by different crack initiation sites such as the epoxy-fiber interface, the matrix and the fiber itself. Fractography reveals that the crack coalescence, crack propagation and the failure are largely affected by the varying volume fraction of glass fibers. The specimen with 10% volume fraction is found to exhibit the maximum fatigue life under the applied cyclic loading.
•Rod-shaped glass fibers in varying volume fraction are used in the epoxy matrix.•Composites are subjected to monotonic and cyclic tension–tension loading.•Epoxy, the fiber and their interface are identified as the crack initiation sites.•Fibers act as crack nucleation sites resulting in coalescing the microcracks at the interface.•The specimen with 10% volume fraction exhibited the maximum fatigue life.
The tensile mechanical properties and fracture behavior of three tungsten heavy alloys (fine-grained 93W–4.9Ni–2.1Fe–0.03Y; coarse-grained 93W–4.9Ni–2.1Fe; coarse-grained 95W–3.5Fe–1.5Ni, wt%) have ...been investigated in the temperature range from 25 to 1100°C. The results show that ultimate tensile strength, yield strength, fracture strength and nominal total elongation of the three tungsten heavy alloys are strongly temperature-dependent and in most cases decrease with increasing temperature. Fractographic observations using scanning electron microscopy (SEM) show that the fracture modes of the three alloys evolve from a mixture of W cleavage and matrix phase ductile rupture at low temperatures to a mixture of tungsten/matrix and tungsten/tungsten interfacial debonding failure at elevated temperatures.
This paper presents the effect of infill patterns (IPs) on the mechanical response of 3D printed specimens by conducting the low-velocity impact test (LVI) and compression test. The poly-lactic acid ...(PLA, purity 98 wt% >) material has selected and printed using fused deposition modeling (FDM, speed 20 mm/s, layer height 0.2 mm, no of layers 30, extruded at 200 °C) with four different IPs: triangle, grid, quarter cubic, and tri-hexagon. The LVI test on velocity-time, energy-time and force-displacement, and the compression responses have examined and presented in this study. The LVI test was carried out to determine the penetration energy level, energy absorption capacity (toughness), stiffness, and strength of PLA porous parts (60% infill density) for implant/tissue/recyclable product applications. The results have shown that the triangular pattern has produced the highest absorbed energy in LVI test (penetration energy 7.5 J, and stiffness 668.82 N/mm) due to more sheared/contact layers’ perpendicular to impactor (hemispherical insert); while the grid pattern exhibited the highest compressive strength (72 MPa) due to more layers aligned along the compressive loading direction The SEM fracture surface image of Triangular IP has produced effective raster and layer bonding, less number of voids, more amount of circular beach markings, and absence of ratchet lines leading to possess improved mechanical properties.
•Four infill patterns of triangle, grid, quarter cubic, and tri-hexagon were printed by FDM.•Triangular IP exhibited highest penetration limit velocity (0.28 m/s).•Triangular IP produced maximum stiffness (669 N/mm).•Grid IP displayed more compressive strength (72 MPa).•SEM surface topography and fractography were examined.
The aim of the study was to evaluate the influence of surface finishing in three polymer-based composits (composits) on the result of a 3-point bending test using quantitative and qualitative ...fractography as well as microstructural characteristics.
270 rectangular specimens (n = 30) of three composits were prepared, stored and tested according to NIST No. 4877. Prior testing, the samples were subjected to three surface treatments: 1) no treatment, to preserve the oxygen inhibition layer, 2) with FEPA P1200 (ANSI equivalent grit 600) SiC paper abraded surface, and 3) polished surface. A three-point bending testing was employed, followed by quantitative (assessment of reason for failure and fracture pattern) and qualitative (fracture mirror measurements) fractography, 3D and 2D surface imaging, surface roughness, reliability and Fe-SEM analysis. The mirror radius that runs in the direction of constant stress was used to calculate the mirror constant (A) using Orr's equation. Uni- and multifactorial ANOVA, Tukey's post hoc test, and Weibull analysis was performed for statistical analysis.
Surface finishing has less influence on the fracture pattern, reliability and mechanical parameters and has no influence on the mirror constant. The amount of inorganic filler has a direct impact on flexural strength and modulus, while the ranking of materials was independent of surface treatment. Failures initiated by volume defects were the most common failure mode (77.0%) with surface defects accounting for 14.9% (edge) and 7.7% (corner). Polishing resulted in lower peak-to valley height compared to no treatment, both 3–4 times lower compared to the 600 grit treatment. The increase in roughness within the analyzed range did not lead to an increase in surface-related failures.
The clear dominance of volume defects in all examined materials as a cause of material fracture reduces the impact of roughness on the measured properties. This insight was only possible using qualitative and quantitative research fractography.
Strength of additive manufactured alumina Schlacher, J.; Lube, T.; Harrer, W. ...
Journal of the European Ceramic Society,
November 2020, 2020-11-00, Volume:
40, Issue:
14
Journal Article
Peer reviewed
Open access
The strength of 3D-printed alumina parts fabricated using the Lithography-based Ceramic Manufacturing (LCM) technology is investigated. The influence of the sintering parameters, printing direction, ...surface condition (i.e. machined or as-printed), and/or geometry on the strength distribution is studied under uniaxial and biaxial bending tests. Weibull parameters, i.e. characteristic strength and Weibull modulus, are determined and compared between the different samples. Experimental findings show that samples sintered at higher temperatures yield higher Weibull modulus, associated with a more homogeneous microstructure. Fractographic analyses reveal the influence of surface finish (as-printed or machined) on strength and show the importance of reporting testing configuration along with printing direction to assess the mechanical response of 3D-printed parts. Based on these results, manufacturing recommendations are given which shall advance the progress in optimization of alumina ceramics fabricated using the LCM technology.
