Specimen Shape Research Articles

Very high cycle fatigue properties of short glass fiber reinforced polyetheretherketone (PEEK)

The fatigue properties of 14 wt-% short glass fiber reinforced polyetheretherketone (PEEK–GF14) have been investigated in the high and very high cycle fatigue (VHCF) regime. Experiments were performed at a load ratio of –1 with servohydraulic and electrodynamic equipment at cycling frequency 10–20 Hz, and with ultrasonic equipment at 19 kHz. A new specimen geometry has been developed that allows ultrasonic tests up to high stress amplitudes. The same specimen shape was used in both testing series to exclude size effects, which enabled to focus on the influence of cycling frequency and testing technique. Ultrasonic fatigue testing with intermittent loading served to avoid heating of specimens. The S-N curves measured at 10–20 Hz and 19 kHz show a similar slope exponent (i.e., 10 % deviation). Mean S-N curve determined with ultrasonic equipment is shifted to slightly lower stress amplitudes, which may be attributed to statistical scatter. PEEK–GF14 does not show a fatigue limit and failures still occurred above 109 cycles. The VHCF strength of PEEK-GF14 is approximately two times higher compared with unreinforced PEEK. Fractographic investigations revealed fiber fracture and, less frequently, fiber pull-out.

Development of a novel approach to correlate small punch fatigue with uniaxial ratcheting fatigue

The miniaturization of fatigue specimens has seen significant advancements, realized either by scaling down conventional specimens while preserving their geometry or by experimenting with novel specimen shapes and loading configurations. In this study, the small punch test (SPT) technique, which is well-established for estimating tensile, creep, and ductile-to-brittle transition temperature (DBTT), is employed to predict the cyclic deformation behaviour of SS 316LN and modified 9Cr-1Mo (P91) steels. The small punch fatigue (SPF) experiments demonstrated continuous displacement accumulation, similar to strain accumulation in ratcheting. The study evaluates the influence of various load parameters, such as amplitude and mean load, on SPF outcomes and compares these to the effects of stress amplitude and mean stress on ratcheting results. The differences in deformation behaviour between ratcheting and small punch fatigue and the effect of biaxiality in SP configuration life is analysed. Finally, to establish a correlation between SPF and ratcheting results, the three life prediction models (Gerber, Goodman, and Smith-Watson-Topper) are examined and a new correlation is proposed by introducing a novel damage parameter.

Effect of speed sintering process on the microstructure, flexural strength and translucency of zirconia

ObjectivesTo determine the impact of the speed sintering program on the microstructure, flexural strength and translucency of zirconia in comparison with those of the conventional sintering program. Materials and methodsrectangular shape specimens (12.5 × 15.5 × 1.2 mm) were prepared from four commercial pre-sintered zirconia ceramics (KATANA HTML, KATANA STML, InCoris TZI and InCoris ZI) that were sintered with conventional and speed sintering programs according to the manufacturer's instructions. The phase composition of the sintered specimens was determined by X-ray diffraction (XRD). The grain size was evaluated using scanning electron microscopy (SEM), while the three-point flexural strength was assessed based on the ISO 6872: 2015 standard. Translucency was assessed using a spectrophotometer. The data were analyzed using independent t tests (α = 0.05) and one-way ANOVA. ResultsThe XRD patterns were similar for all the groups, indicating that there was no phase transformation. SEM revealed that the average grain size was lower than 1 μm. The grain size, flexural strength and translucency results showed increasing trends when speed sintering is compared with the conventional one but the differences were not significant (P > 0.05). ConclusionsThe results of this research indicate that the speed sintering program had no significant impact on the microstructure, flexural strength and translucency of the examined zirconia, a speed-sintering program can process the ceramic material within a short time with slightly increase their flexural strength and translucency Therefore, a speed-sintering program is appropriate for zirconia (Y-TZP).

The length of fracture process zone deciphers variations of rock tensile strength

Tensile strength is one of the most critical design factors in many rock engineering projects. However, despite many available testing techniques, an accurate estimation of the true tensile strength of quasi-brittle rock-like materials is yet a controversial problem since it can vary by the shape and size of a test specimen, the adopted test method, and applied loading conditions. Different studies have tried to address this issue by providing (mainly empirical) laws for determining variations of rock tensile strength as a function of a particular test parameter such as specimen size. In this study, however, a new general approach is presented that can decipher the tensile strength variations of rock under various testing conditions. Using coupled Finite Fracture Mechanics (FFM), it is first proved that the length of the Fracture Process Zone (FPZ) can be determined with accuracy and ease using the energy criterion of coupled FFM. Then, the length of FPZ is used in the stress criterion of coupled FFM to determine rock tensile strength. The failure stress of a material is then proved to be mainly a function of the FPZ length following a power law originated from the Linear Elastic Fracture Mechanics (LEFM). The results assist in deciphering variations of rock tensile strength related to the sample size and test method.

Dimensional changes over time in stereolithographic models fabricated with a 3D printer.

This study aimed to ascertain the effects of the shape of stereolithographic models fabricated with a three-dimensional (3D) printer and the use of different types of liquid resin on the dimensional changes of these models over time, to obtain valuable information for determining the period for which such models can be used following fabrication. Stereolithography models with the shape of a large truncated cone or a small truncated cone were fabricated using liquid resin as surgical guides (Group G) or master casts (Group M). (four groups in total, each n = 11). The shapes of all experimental specimens were measured immediately after fabrication and 1day, 1week, 2weeks, 3weeks, 4weeks, 2months, 3months, 6months, 1year, and 1.5years later. The shape data collected immediately after fabrication were taken as baseline data, and the dimensional changes over time at each timepoint were calculated. No significant change from 1day to 1year after fabrication was observed in any of the groups, but the change after 1.5years was significantly larger than the changes at the other timepoints (p < 0.001). Significantly larger changes were evident in Group M than in Group G at all timepoints (p < 0.001). These results suggested that, from the viewpoint of dimensional stability over time, stereolithographic models should be used within 1year of fabrication, and that the type of liquid resin used for stereolithographic model fabrication may affect how its dimensions change over time.

Effect of specimen size and shape on the compressive performance of high strength engineered cementitious composites at elevated temperatures

This study provides detailed insights into the effect of specimen size on the residual compressive strength of hybrid polyethylene-steel fibre reinforced high strength engineered cementitious composite after exposure to elevated temperatures. A mix design with high residual performance was selected and a total of 120 specimens with different cross-section shape (square and circular), aspect ratio (1 and 2) and sizes (cylinders of 40 mm, 75 mm, 100 mm, 150 mm diameter with height to diameter ratio of 2:1, cubes of 50 mm, 75 mm, 100 mm side and prism of size 75 × 75 × 150 mm) were cast. These specimens were subjected to temperatures ranging from 200 to 800 °C and the residual compressive strength and change in microstructure was then analysed after air cooling. Experimental results indicated that cubic specimens experienced less strength loss compared to prism specimens with the same cross-sectional area and the damage was found to decrease with increase in the volume to surface area ratio of the specimens. Furthermore, no spalling occurred in any of the specimens despite the change in specimen size or cross-section. Unlike previous studies that did not present any clear influence of specimen size, the present work established that the residual strength is dependent on aspect ratio and volume to surface area ratio of the specimen. As a result, these findings are valuable for selecting appropriate specimen size in elevated temperature studies and for the development of suitable guidelines to facilitate meaningful comparisons with the existing data.

Investigation on the biaxial tensile testing method for metal foil using cruciform specimen

The assessment of mechanical properties of metal foil under complicated stress states poses a considerable challenge, requiring the development of new testing methods and the optimization of new specimen geometry. In this research, the biaxial tensile method and specimen shape were designed and optimized by using simulation and experiment. It is determined that the strain measurement area can be suggested as the central area of 0.6 to 0.8 times the arm width. The influence of different parameters on the tensile results of cruciform specimens was comprehensively evaluated by finite element method and multi-factor analysis. The results indicate that the number of slits markedly impacts the stress–strain uniformity and shear stress in the central region, followed by the slit length. The effect of the arm width and the slit width is comparable, more influential than the corner radius. According to the analyzed results and application requirements, a four-axis independently driven biaxial tensile test machine for small scale samples was fabricated. During the biaxial tension, the center point offset of the specimen remains within ±0.01 mm. The displacement and load synchronization errors do not exceed 0.01 mm and 50 N, respectively, facilitating the precise control of four-axis synchronization. Conclusively, cruciform specimens featuring diverse geometric characteristics were designed for industrial pure titanium, 304 stainless steel, and Inconel 718 superalloy with thickness of less than 0.3 mm. The biaxial tensile tests were performed to delineate the yield loci, revealing notable anisotropy and size effect. The validation confirms the suitability of the testing method and optimized cruciform specimens for conducting biaxial tensile mechanical properties testing on metal foils characterized by diverse types and thicknesses.

Determination of residual stress field in laser cladding using finite element updating method driven by contour deformation

Laser cladding is a cutting-edge technology widely used in additive manufacturing and surface modification. This process entails rapid melting and solidification driven by laser heating, which induces residual stress within the material. This study presents a data-driven approach to refine the numerical model of laser cladding, simultaneously emphasizing both the temperature characteristics and residual stress distribution within the thermomechanical coupling process. After integrating the residual stress distribution data obtained through the contour method with the molten pool morphology shaped by the thermal effects of laser cladding, a Levenberg-Marquardt optimization algorithm based finite element model updating scheme is proposed to efficiently identify the parameters of double ellipsoid heat source model, which employs parallel computing to reduce the computational time for iterations. The effectiveness of the proposed method is validated using experimental data. Moreover, this approach is adaptable, unaffected by the specimen size and shape, and can accurately predict the residual stress distribution characteristics. Therefore, it offers a robust framework for simulating the mechanisms of residual stress generation in titanium alloy laser cladding.

Investigating specimen size and shape effects on compressive mechanical behaviors of recycled aggregate concrete using discrete element mesoscale modeling

In comparison to natural aggregate concrete (NAC), recycled aggregate concrete (RAC) typically exhibits a more diverse composition of materials, heightened variability and greater inherent weaknesses. These characteristics may result in varying effects of specimen size and shape on compressive responses. Within this framework, the present study endeavors to comprehensively investigate these influences on RAC's compressive properties and their underlying mechanisms utilizing discrete element simulation technology. At the mesoscale, RAC is depicted by several components, encompassing both new and old aggregates, mortar and interfacial transition zones. Through integrating contacts for each phase, elucidating mesoscale mechanical responses with a parallel bond model and introducing Weibull random fields to delineate variations in phase properties, this study effectively simulates these mechanical responses. Subsequent extensive calculations scrutinize the repercussions of specimen size and shape on the compressive strength, elastic modulus, peak strain and failure modes of RAC across varying water-to-binder ratios. The study concludes that RAC manifests a size effect, albeit less pronounced than in NAC with an equivalent water-to-cement ratio, yet more significant than in mortar. Moreover, owing to end plate constraints, the reduction in RAC's cubic compressive strength is notably less than its prismatic compressive strength. Based on these findings, it is recommended to establish the strength size reduction coefficient and cube-to-cylinder shape coefficient for RAC at 0.86 and 0.72, respectively. Notably, these values diverge significantly from the respective 0.81 and 0.78 coefficients for NAC.

Evaluation of Fatigue Behavior of Asphalt Field Cores Using Discrete Element Modeling.

Fatigue cracking is one of the primary distresses of asphalt pavements, which significantly affects the asphalt pavement performance. The fatigue behavior of the asphalt mixture observed in the laboratory test can vary depending on the type of fatigue test and the dimension and shape of the test specimen. The variations can make it difficult to accurately evaluate the fatigue properties of the field asphalt concrete. Accordingly, this study proposed a reliable method to evaluate the fatigue behavior of the asphalt field cores based on discrete element modeling (DEM). The mesoscopic geometric model was built using discrete element software PFC (Particle Flow Code) and CT scan images of the asphalt field cores. The virtual fatigue test was simulated in accordance with the semi-circular bending (SCB) test. The mesoscopic parameters of the contacting model in the virtual test were determined through the uniaxial compression dynamic modulus test and SCB test. Based on the virtual SCB test, the displacement, contact forces, and crack growth were analyzed. The test results show that the fatigue life simulated in the virtual test was consistent with that of the SCB fatigue test. The fatigue cracks in the asphalt mixture were observed in three stages, i.e., crack initiation, crack propagation, and failure. It was found that the crack propagation stage consumes a significant portion of the fatigue life since the tensile contact forces mainly increase in this stage.

Plastic-sleeve test method to measure autogenous and drying shrinkage in paste, mortar, and concrete: Test Results

The Plastic-Sleeve Test (PST) method of molding cylindrical specimens in plastic sleeves enables the measurement of autogenous and total shrinkage of pastes, mortars, and concretes. Photogrammetric tests confirmed that the linear support of the specimens with a temporary bottom support mold does not restrain deformation. Tests were performed to compare the PST versus corrugated tube methods and similar relative humidity and autogenous shrinkage results were obtained. The PST shows comparable CoV values to those of the corrugated tube test. The method presented provides solid circular cross-section samples, enabling control over entrapped air content, specimen shape, and bleeding effects, thereby ensuring the measurement method’s high repeatability. The PST showed a tighter seal than prismatic samples molded for total shrinkage testing according to EN 1367-4. Results indicate that the PST can effectively be used for molding samples intended for total shrinkage measurement. It is concluded that the PST method is an effective method to measure autogenous shrinkage and total shrinkage of cementitious materials.

The optimal design of double-edge wedge-splitting tensile test for ultra high performance concrete

The double-edge wedge-splitting (DEWS) test is a new indirectly tensile test, those of stress distribution similar with the uniaxial tension state. However, there are no standard rules regarding the splitting specimen and groove dimensions suitable for the UHPC tensile properties. In this paper, DEWS test, conventional splitting test, and direct tensile test were performed to measure the tensile strength and tensile stress vs. crack opening response of UHPC. The digital image correlation (DIC) technique was utilized to detect the crack propagation paths and fracture modes. Two specimen shapes, three groove angles and three fiber types are utilized to this investigation. The experimental results of 18 DEWSs under tensile loading, including peak strength, tensile stress-COD curves, fracture modes and properties, and the crack paths, are presented. The results show that the UHPC tensile performance used with cubic specimen is less sensitive to groove angle than in the cylinder. An important finding is that DEWS test used with 45° grooved cube specimen presents the lowest variation in peak strength and stress-COD curve for UHPC tensile behaviors. After comparison, the tensile strengths using DEWS test and direct tension test are essential equal in first-cracking and peak strength. The crack paths and fracture mode are basically the same inside the DEWS and direct tension specimens. Accordingly, the DEWS test used with 45° grooved cubic specimen is suggested for measuring the UHPC tensile property.

Green sol-gel auto-combustion synthesis of CeO2/MnCr2O4 nanocomposite using banana juice and its potential application for enhanced degradation of methyl orange under visible light

Despite the introduction of different semiconductor photocatalysts for removing a variety of colors and contaminants, the development of novel multi-component substances with strong light-harvesting capacity remains a challenge. The purpose of this paper is to rationally design binary CeO2/MnCr2O4 heterostructure nanocomposites through the green sol-gel self-combustion route and use them as visible light-active nano-photocatalysts in wastewater treatment. Several physicochemical instruments, including powder X-ray diffraction (XRD), Energy Dispersive X-Ray Spectroscopy (EDS), and Field Emission Scanning Electron Microscopy (FESEM), were used to examine the effects of banana juice volume on crystal structure, purity, and shape of as-formed specimens. Optical results demonstrate that binary CeO2/MnCr2O4 nanocomposites have high photocatalytic activity due to their 2.9 eV band gap. As a result of using 10 mL of banana juice, the best performing product removed almost 84 % and 93 % of methyl orange (MO) in 90 minutes and 120 minutes, respectively, under visible and UV light. CeO2/MnCr2O4 nanocomposite is a promising candidate for photocatalysis according to these findings.

Static and dynamic tensile behaviour of polycarbonate connected to the deforming specimen shape

Like other structural thermoplastic polymers, polycarbonate (PC) exhibits a typical two-stage plastic deformation mode, including a first phase of strain localization and a second phase of strain propagation. At the same time, the stress-strain curves at the local scale undergo two distinct loading phases connected by a softening-instability decreasing phase. This mechanical response is not yet fully recognized and the reproduction of the peculiar phenomena in numerical simulations is not yet commonly standardized. In this work, the relationship between the straining/loading macroscopic response and the material flow curve at the local scale is investigated in detail, aiming at the two-way relationships enabling to infer the latter curve from the former data. Experimental tests at static and dynamic rates are carried out to verify how the special features of the PC are affected by the strain rate and to estimate its rate sensitivity.

Evaluation of tensile failure behavior of ultra high performance concrete under double-edge wedge splitting and direct tension loadings

UHPC tensile strength is often measured indirectly through splitting tests and flexural tests substituted for direct tensile tests. However, the tensile strain-hardening and multiple cracking performance of UHPC is highly sensitive to the testing techniques and the specimen shape used. In this paper, the double-edge wedge splitting (DEWS) test and direct tensile test were performed to evaluate the tensile strain-hardening properties and damage evolution of UHPC. The digital image correlation (DIC) technique was utilized to detect the cracking opening displacement (COD) and evaluate the damage evolution in the tensile stress vs. crack opening response. The results show that the tensile strength between DEWS and direct tensile tests in UHPC strain-hardening and strain-softening stages had a high correlation value of 0.98. Moreover, the difference in cracking strengths in the DEWS and direct tensile tests was less than 5 %, and those of peak strengths were fewer than 5.23 MPa. An improvement in relative COD increment was observed in DEWS and direct tensile tests before 90 % of the peak load at the post-peak branch. Results indicate that the DEWS testing is an efficient way to evaluate the UHPC tensile failure properties.

Polyhydroxy-3-Butyrate (PHB)-Based Composite Materials Reinforced with Cellulosic Fibers, Obtained from Barley Waste Straw, to Produce Pieces for Agriculture Applications: Production, Characterization and Scale-Up Analysis.

Cellulosic fibers obtained from Barley straw were utilized to reinforce PHB. Four different processed fibers were employed as reinforcing material: sawdust (SW), defibered (DFBF), delignified (DBF), and bleached (BBF) fibers. The composite was processed from two different perspectives: a discontinuous (bach) and an intensification process (extrusion). Once processed and transformed into final shape specimens, the materials were characterized by mechanical testing (tensile mode), scanning electron microscopy, and theoretical simulations by finite elements analysis (FEA). In terms of mechanical properties, only the elastic moduli (Et) exhibited results ranging from 37% to 170%, depending on the reinforcement composition. Conversely, strengths at break, under both tensile and bending tests, tended to decrease, indicating poor affinity between the components. Due to the mechanical treatment applied on the fiber, DFBF emerged as the most promising filler, with mechanical properties closest to those of neat PHB. DFBF-based composites were subsequently produced through process intensification using a twin-screw extruder, and molded into flowerpots. Mechanical results showed almost identical properties between the discontinuous and intensification processes. The suitability of the material for agriculture flowerpots was demonstrated through finite analysis simulation (FEA), which revealed that the maximum von Mises stresses (5.38 × 105 N/m2) and deformations (0.048 mm) were well below the limits of the composite materials.

Shell asymmetry in Cretaceous Cyclothyrididae (Brachiopoda): variability, ontogeny and terminology

The asymmetry observed in rhynchonellid brachiopod shells has been discussed for decades and continues to attract attention. This noteworthy modification of the anterior margin morphology during the ontogeny has evolved several times in rhynchonellids, and seems to reflect a genetic basis. First, we try to clarify the terminology regarding asymmetrical, dissymmetrical and symmetrical shells that has existed since the beginning of the 20th century. The Cretaceous populations observed clearly exhibit antisymmetry (also called random asymmetry). During the Cretaceous, some populations of Cyclothyris McKoy, 1844 include a mixture of truly asymmetrical specimens and others that exhibit an intermediate degree of asymmetry, herein called atypical morphologies. Shapes of specimens coming from two different locations in France were captured using geometric morphometrics. We used the range of different morphologies: 1) to test alternative hypotheses about the ontogeny of asymmetry; 2) to test for the possibility of several morphogroups; and 3) to discuss the determinism of the asymmetry.

Influence of the Emitter Shape on the Field-of-View in Atom Probe Tomography.

Atom probe tomography (APT) is a unique analytical technique that offers three-dimensional elemental mapping with a spatial resolution down to the sub-nanometer. When APT is applied on complex heterogenous systems and/or under certain experimental conditions, that is, laser illumination, the specimen shape can deviate from an ideal hemisphere. Insufficient consideration of this aspect can introduce artifacts in the reconstructed dataset, ultimately degrading its spatial accuracy. So far, there has been limited investigation into the detailed evolution of emitter shape and its impact on the field-of-view (FOV). In this study, we numerically and experimentally investigated the FOV for asymmetric emitters and its evolution throughout the analysis depth. Our analysis revealed that, for asymmetric emitters, the ions evaporated from the topmost region of the specimen (summit) project approximately to the detector center. Furthermore, we demonstrated the implications of this finding on the FOV location for asymmetric emitters. Based on our findings, the location of the center of the FOV can deviate from the specimen central axis with an evolution depending on the evolution of the emitter shape. This study highlights the importance of accounting for the specimen shape when developing advanced data reconstruction schemes to enhance spatial resolution and accuracy.

The influence of soil specimens shape and dimensions on consolidation parameters used in foundation settlement prediction

The theory of elasticity is used in geotechnical engineering for the calculation of foundation settlement. The equation used in the evaluation of consolidation settlement uses the soil compressibility parameters which usually are determined on cylindrical soil specimens with ϕ 71.4 mm. Laboratory tests performed on soil specimens showed that the parameters that are used in foundation settlement analysis are influenced by the dimensions of the tested soil specimens and the shape of that specimen. The paper presents the influence of specimen size, shape and method used for the coefficient of consolidation evaluation on the final value of the foundation settlement. The analysis was performed using the Settle3 software from Rocsience, considering the case of an elastic foundation flexible square foundation (1.5 m × 1.5 m) which transmits to the ground a pressure of 100 kPa.

Prediction of ductile cracking in the titanium alloy forging process

Abstract The control of surface cracking in the forming of titanium alloy forgings is a significant problem in the forging industry. For titanium alloys, the formation of surface cracks is related to temperature, strain rate, and stress state. This study selected the widely used medium to high strength titanium alloy Ti-6Al-4V in the field of forging as the research material, and designed six different shapes of specimens for high-temperature tensile and compression tests. The mechanisms underlying crack formation were analyzed at the microscopic level, and the critical fracture displacement of these tests was extracted. Moreover, their critical fracture strains were obtained through simulations, and a High-temperature damage model was established based on the DF2016 model. The research results showed that cracks through void at grain boundaries propagate and aggregate to form, leading to a fracture mechanism characterized by ductile fracture through micro-pore aggregation. Simulation results demonstrate that the established model accurately predicts the crack of forgings.