Specimen Size Research Articles

Anisotropic Tensile Properties of a 14YWT Nanostructured Ferritic Alloy: On the Role of Cleavage Fracture

Two plates of nanostructured ferritic alloy NFA-1 were processed by ball milling atomized Fe-14Cr-3W-0.4Ti-0.2Y (wt.%) with FeO powders, canning, and hot-extrusion at 850 °C, followed by annealing and multipass cross-rolling at 1000 °C. This produces a severe (001) brittle cleavage texture on planes running parallel to the plate faces. In the first plate (P1), pre-existing microcracks (MCs) formed on the cleavage planes during cross-rolling. The second plate (P2) contained far fewer, if any, MCs. Here, we compare the tensile data for out-of-plane (S) and in-plane (L) tensile axis orientations, at temperatures from −196 °C to 800 °C. We also assess the tensile property differences between P1 and P2, and the effect of specimen size. The L-orientation strength and ductility were excellent; for example, the room temperature (RT) yield stress, σy ≈ 1042 ± 102 MPa, and the total elongation, εt ≈ 12.9 ± 1.5%. In contrast, the S-orientation RT σy ≈ 708 ± 57 MPa, and εt ≤ 0.2%. These differences were due to cleavage on the brittle (001) planes. Cleavage leads to beneficial delamination toughening, but is deleterious to deformation processing and through-wall heat transfer. Therefore, it is important to quantitatively characterize the pronounced NFA-1 strength anisotropy due to severe crystallographic texturing and cleavage fracture.

Analyzing the effects of size and density on the ultimate compressive strength of structural laminated bamboo parallel to the grain

Considering the influence of natural flaws of raw materials and procedures, the size effect is an inherent characteristic that is critical when applying most construction materials. This study focuses primarily on the compressive properties of laminated bamboo, which has become increasingly popular in construction due to its durability and strength. Two specimen sizes (25 × 25 × 100 mm and 50 × 50 × 200 mm) and three densities (0.60, 0.67, and 0.69 g/cm3) were evaluated under uniaxial compression. As a result of this study, the size effect is examined in terms of failure mode, mechanical property, data distribution, and description model, as well as introducing the size effect model with density in an innovative manner. To investigate the effect of specimen size on compressive strength along the grain direction, data analyses were performed. These analyses included failure mechanism analysis, distribution testing, and descriptive model development. According to the results, the compressive strength decreases with increasing dimensions, averaging 62.29 MPa–56.93 MPa, with a decrease rate of 8.60 %, although the failure modes are seldom different. In accordance with the increase in density, the rate of strength reduction also increases, and shows an approximate linear relationship with density. With the change in size, the distribution of the data changes, resulting in a reduction of up to 13.34 % in the standard value. The weakness-link model is better suited for describing data than fracture energy models and fractal theory models, based on which reduction ratios are predicted. By adding density to the size effect model, a more accurate prediction model can be derived between size, density, and compressive strength. As a result of these investigations, we will gain a better understanding of the gap between small clear specimens and large members, as well as those key influences necessary to optimize the use of laminated bamboo in structural applications.

Comparative skull osteology of Amphisbaena arda and Amphisbaena vermicularis (Squamata: Amphisbaenidae).

The skull anatomy of amphisbaenians directly influences their capacity to burrow and is crucial for the study of their systematics, which ultimately contributes to our comprehension of their evolution and ecology. In this study, we employed three-dimensional X-ray computed tomography to provide a detailed description and comprehensive comparison of the skull anatomy of two amphisbaenian species with similar external morphology, Amphisbaena arda and Amphisbaena vermicularis. Our findings revealed some differences between the species, especially in the sagittal crest of the parietal bone, the ascendant process, and the transverse occipital crest of the occipital complex. We also found intraspecific variation within A. vermicularis, with some specimens displaying morphology that differed from their conspecifics but not from A. arda. The observed intraspecific variation within A. vermicularis cannot be attributed to soil features because all specimens came from the same locality. Specimen size and soil type may play a role in the observed differences between A. arda and A. vermicularis, as the single A. arda specimen is the largest of our sample and soil type and texture differ between the collection sites of the two species.

Casting of nickel powder based MMC using microwave energy

In this paper, an experimental setup is developed to cast a metal matrix composite (MMC) specimen, by using microwave energy as a heat source. A MMC (Nickel and 15 % of SiC by weight percentage) specimen of size 140 × 30 × 2 mm3 is in-situ cast by using a domestic microwave applicator at 2.45 GHz frequency, and 900 W, power output. As per selected process parameters, the exposure time to cast MMC specimen, inside an electromagnetic environment is optimized as 33 min. A COMSOL Multiphysics software tool is also used to model the in-situ microwave-assisted casting setup. Numerical simulations are performed to visualize the microwave heating effects within the applicator cavity. Microwave heating effects are analyzed in terms of electric field distribution, resistive heating and temperature profile. As per the simulation study results, maximum electric field intensity (4.46 × 104 (V/m)) is observed around the mold. Resistive heating losses are maximum (4 .9× 109 W/m3) in the susceptor zone. It is observed from the simulation study, that uniform heating of the specimen is observed throughout the cross-section and the melting temperature of the specimen is achieved in 38 min. A good correlation is observed between experimental and simulation study results in terms of exposure time of cast specimen and microwave heating effects within the applicator cavity

The microscopic fracture model for determining the fracture behavior of self-compacting lightweight concrete

The fracture toughness (KIC) and tensile strength (ft) of concrete are critical parameters governing crack resistance. Concrete usually exhibits brittleness under flexure and tension, so this brittle fracture first occurs at the micro level. Many researchers have studied its fracture properties at the micro level. However, the theoretical model and calculation formulae do not reflect the influence of micro-material parameters on the corresponding fracture properties. In this paper, the microscopic fracture model of self-compacting lightweight aggregate concrete (SCLC) was developed, considering the parameters of micro-nano silica materials. First, the characteristic parameters, such as particle size, specific surface area, and unit weight of micro silica (MS) and colloidal nano-silica (CNS), were considered, and the calculation equation for fictitious crack growth length was proposed. Then, the micro-fracture model was developed, which was further used to calculate the fracture parameters KIC and ft of SCLC incorporated with micro-nano silica. The results are found to be consistent with the fracture parameters determined by the size effect model. In addition, the failure curves of different structural fracture modes of SCLC were established through the fracture parameters KIC and ft obtained from the microscopic fracture model, and the fracture modes of SCLC incorporated with MS and CNS were identified. The peak load of the minimum specimen size satisfying linear elastic fracture was also predicted. This research provides a new perspective for evaluating concrete fracture parameters, realizes the progressive prediction of concrete fracture performance from macro to micro, and fills in the research gaps in the existing knowledge base on the synergistic effect of MS and CNS to enhance the fracture performance of SCLC.

Size effect of compressive performance of concrete under elevated temperatures: Tests and meso-scale analysis

This study investigates the size effect of concrete under ambient and elevated temperatures through tests and numerical simulations. Compressive performance of prismatic and cylindrical concrete specimens with varying dimensions were tested at temperatures ranging from ambient temperature to 600°C. Meso-scale finite element analysis (FEA), assuming that the mechanical properties of matrix and interfacial transition zones (ITZ) followed Weibull distribution, was employed to simulate the tested specimens and to conduct parametric analysis on specimens with larger or smaller sizes and under temperatures up to 800°C. Both experimental and numerical results showed that the cracks on the specimen surface became finer and denser as an increase of specimen sizes under elevated temperatures. A noticeable decrease in concrete compressive strength with increasing specimen dimensions was observed below 600°C, but peak strain and elastic modulus did not exhibit significant size effect. Size effect on strength diminished at temperatures exceeding 800°C. Classic Size Effect Laws (SEL), such as Weibull's and Bažant's SEL, were applicable to characterize the size effect on strength of specimens within common lab test dimensions under elevated temperatures. Based on the results from experiments, FEA and Bažant's SEL, a stress-strain model under elevated temperatures considering size effect was proposed. The predicted results from this model showed good agreement with test results.

Experimental investigation of size effect on unreinforced concrete brick masonry walls under in-plane shear loading

The size effect is one of the primary structural characteristics exhibited in reinforced concrete (RC) members in shear. Even though numerous studies have been conducted on masonry walls under shear, very few studies have been conducted that definitively answer whether a size effect exists for masonry walls. Diagonal compression tests on two groups of masonry walls with different dimensions were conducted to investigate the size effect on concrete brick masonry walls. A total of sixty masonry wall panels were tested. Five bed-joint mortar mix properties were used for each specimen. Test results showed that four failure modes were observed: diagonal tension failure, combined failure, sliding failure, and toe-crushing failure. In particular, the diagonal tension strength was significantly related to the specimen size. The larger specimen size led to a lower shear strength. Also, the shear modulus was highly dependent on the specimen size. Through experimentation, this study demonstrated that masonry walls exhibit a size effect. Moreover, the size effect is valid only in cases of diagonal tension failure. Based on the test results, this study revealed a correlation between diagonal tension strength and wall size. Lastly, the adequacy of the predictions was compared to the existing masonry codes.

Experimental research on mechanical behavior of UHPCFST under repeated axial compression

This paper investigates the mechanical behavior of ultra-high performance concrete-filled steel tubes (UHPCFST) subjected to repeated axial compression. A total of 34 specimens of UHPCFST were systematically designed, constructed, and evaluated experimentally. The design parameters encompassed steel tube wall thickness, UHPC type, specimen size (varying diameters while preserving a consistent diameter-to-thickness ratio), and loading scheme. The failure patterns, stress-strain relationships, axial load-bearing capacity, and stiffness were meticulously examined. Predominantly, shear failure and drum-shaped upsetting failure were identified as the primary failure mechanisms in the specimens. The axial load-bearing capacity was found to increase notably with the use of thicker steel tubes and higher-grade UHPC. Under repeated loading, a reduction in stiffness was noted, which was dependent on factors such as the steel content, tube diameter, and the volume of coarse aggregate of UHPC. Current predictive equations for the axial load-bearing capacity of CFST were assessed using the experimental results of UHPCFST and were determined to over-predict the axial load-bearing capacity of UHPCFST. Consequently, a refined equation is proposed to yield a more precise estimation of the axial load-bearing capacity for UHPCFST. Furthermore, an empirical model was developed to characterize the stress-strain behavior of UHPCFST under repeated axial compression, offering a tool for practical engineering design and analysis.

Influence of Specimen Size on the Compressive Strength of Wood

Influence of Specimen Size on the Compressive Strength of Wood

Enhancing Fish Auction with Deep Learning and Computer Vision: Automated Caliber and Species Classification

The accurate labeling of species and size of specimens plays a pivotal role in fish auctions conducted at fishing ports. These labels, among other relevant information, serve as determinants of the objectivity of the auction preparation process, underscoring the indispensable nature of a reliable labeling system. Historically, this task has relied on manual processes, rendering it vulnerable to subjective interpretations by the involved personnel, therefore compromising the value of the merchandise. Consequently, the digitization and implementation of an automated labeling system are proposed as a viable solution to this ongoing challenge. This study presents an automatic system for labeling species and size, leveraging pre-trained convolutional neural networks. Specifically, the performance of VGG16, EfficientNetV2L, Xception, and ResNet152V2 networks is thoroughly examined, incorporating data augmentation techniques and fine-tuning strategies. The experimental findings demonstrate that for species classification, the EfficientNetV2L network excels as the most proficient model, achieving an average F-Score of 0.932 in its automatic mode and an average F-Score of 0.976 in its semi-automatic mode. Concerning size classification, a semi-automatic model is introduced, where the Xception network emerges as the superior model, achieving an average F-Score of 0.949.

Effect of Cr content on thermally activated deformation in single-crystal micropillars of Fe–Cr binary alloys

This study identifies the role of solute Cr in the thermal activation process in the plastic deformation of α-(Fe, Cr) ferrite (BCC solid solutions) using micropillar compression tests for micron-sized single-crystals fabricated on various Fe–Cr binary alloys that were solution-treated at 1573 K. Fe–18%Cr single-crystal micropillars with a mean diameter d of ∼2 μm exhibited a relatively higher strain rate sensitivity (m) of 0.12 for the stress required for slip initiation. Larger Fe–18%Cr micropillars (d = 5 μm) exhibited a lower m value of 0.04. The corresponding activation volume of 50 b3 was equivalent to the millimeter-sized pure Fe and Fe–18%Cr alloy specimens (60–70 b3), indicating the prevalence of a general mechanism involving dislocation motion (kink-pair nucleation of screw dislocations). This mechanism controls the thermal activation process of plastic deformation in the Fe–18%Cr alloy, which has sufficient sources for dislocation multiplication. In the Fe–25%Cr and Fe–40%Cr single crystal micropillars, a less pronounced size-dependent m value (0.01–0.03) was determined, almost independent of specimen size. The corresponding activation volumes of large micropillars (74–77 b3) were similar to those of millimeter-sized specimens, which indicates a mild effect of solute Cr atoms on the thermal activation process of dislocation motion in Fe–Cr binary alloys at ambient temperature. Initial dislocations, rather than Cr content in Fe–Cr binary alloys, led to the low changes in size-dependent activation volume of Fe–Cr alloys with higher Cr content. Planar faults (Cr-enriched regions) were observed in Fe–40%Cr alloys, which may become sufficient sources for dislocation nucleation. However, the influence of Cr-enriched regions on dislocation motion remains unclear.

Deformation Responses and Fracture Behaviors of AA6061 under Different Stress Triaxialities

This study investigates the deformation responses and fracture behaviors of AA6061 under different stress triaxiality. Specimens of specific shapes and sizes are designed to achieve different stress triaxialities. Mechanical experiments and scanning electron microscopy analyses are performed to capture the mechanical behaviors and failure features of each specimen. Results show that thicker specimens deform more evenly in thickness than thinner specimens but exhibit slightly more brittleness, while the opposite is true for the notch radius of the specimens. Therefore, these two factors can be applied to the design of specimens for specific testing requirements. The failure mechanism is sensitive to the geometrical factors of the specimen. In addition, the distribution of failure features on the fracture surface is found to play a dominant role in the change in mechanism.

Strain rate and size effects on dynamic tensile behaviour of standard and high-strength concrete: An experimental study

The strain rate and specimen size are the main dominant factors affecting the splitting tensile behaviour of concrete. The static size effect is well-known for concrete behaviour, but it needs more knowledge about the dynamic size effect. The present study investigated the strain rate sensitivity and size effect dependency of dynamic tensile behaviour of two different grades of concretes (M35 and M60) using the Split Hopkinson Pressure Bar (SHPB) setup. From the outcomes of the experimental analysis, it was noted that the quasi-static tensile strength underwent a reduction of 8.96% and 11.39% in standard and high-strength concrete, respectively. This decrease occurred as the diameter increased from 29.5 mm to 45 mm, aligning notably with the principles outlined in the "Bazant Size Effect Law," as proposed by Bazant et al. [52]. Whereas, the dynamic tensile strength and DIF increased with increased specimen diameter, which is opposite to the quasi-static size effect. The maximum split tensile strength observed was 18.56 and 19.86 MPa, corresponding to 13.30 and 12.13 s−1 strain rates with 3.69 and 3.51 dynamic increase factor (DIF) for standard (M35) and high-strength concrete (M60), respectively. The dynamic results also demonstrated a size-effect dependency, where larger diameter specimens exhibited higher strain rate sensitivity, leading to increased strength and DIF due to lateral inertial and crack propagation effects. The modified DIF model of CEB-FIP proposed by the Malvar et al. [17] considering the strain rate and size effect simultaneously strongly supported the experimentally obtained DIF values with an ± 13% deviations. In addition, the strain rate significantly influenced the concrete failure pattern, but no size effect was observed. At a low strain rate, the initiated crack propagated towards the loading ends and split the specimen into two semi-cylindrical halves with penetration cracks. While at higher strain rates, additional wedge-shaped crushed regions formed at the loading end due to tensile and shear damage generated due to stress concentration and local crushing. The crack width becomes wider, and the triangular-shaped local crushing zone continuously moves toward the centre of the specimen from both loading ends and generates the crushed strap.

A computational approach to identify the material parameters of the relaxed micromorphic model

We determine the material parameters in the relaxed micromorphic generalized continuum model for a given periodic microstructure in this work. This is achieved through a least squares fitting of the total energy of the relaxed micromorphic homogeneous continuum to the total energy of the fully-resolved heterogeneous microstructure, governed by classical linear elasticity. We avoid establishing exact micro–macro transition relations, as in classical homogenization theory, because defining a representative volume element is not feasible in the absence of scale separation, as such an element does not exist. The relaxed micromorphic model is a generalized continuum that utilizes the Curl of a micro-distortion field instead of its full gradient as in the classical micromorphic theory, leading to several advantages and differences. The most crucial advantage is that it operates between two well-defined scales. These scales are determined by linear elasticity with microscopic and macroscopic elasticity tensors, which respectively bound the stiffness of the relaxed micromorphic continuum from above and below. While the macroscopic elasticity tensor is established a priori through standard periodic first-order homogenization, the microscopic elasticity tensor remains to be determined. Additionally, the characteristic length parameter, associated with curvature measurement, controls the transition between the micro- and macro-scales. Both the microscopic elasticity tensor and the characteristic length parameter are here determined using a computational approach based on the least squares fitting of energies. This process involves the consideration of an adequate number of quadratic deformation modes and different specimen sizes. We conduct a comparative analysis between the least square fitting results of the relaxed micromorphic model, the fitting of a skew-symmetric micro-distortion field (Cosserat-micropolar model), and the fitting of the classical micromorphic model with two different formulations for the curvature; one simplified formulation involving only one single characteristic length and a simplified isotropic curvature with three parameters. The relaxed micromorphic model demonstrates good agreement with the fully-resolved heterogeneous solution after optimizing only four parameters. The “simplified” full micromorphic model, which includes isotropic curvature and involves the optimization of seven parameters, does not achieve superior results, while the Cosserat model exhibits the poorest fitting.

Influence of prior austenite grain size on martensite-austenite islands morphology and decomposition characteristics during two-step tempering in Mn-Ni-Mo steel

Martensite-austenite (M/A) islands are typical in the quenched microstructure of Mn-Ni-Mo steel, frequently utilized for fabricating reactor pressure vessels (RPV). These islands can decompose into harmful long rod-shaped Fe3C carbides during tempering above 600°C, quantifying the negative effect of M/A island decomposition on mechanical properties and indicating a potential issue in RPV fabrication. To address this issue, the present study investigates a two-step tempering process on three different prior austenite grain size (PAGS) specimens (5 µm, 47 µm, and 119 µm). The effect of PAGS on M/A island decomposition characteristics during sub-600°C tempering and their impact on precipitated carbide morphology is investigated. A preliminary pre-tempering treatment at 200°C, 350°C, and 500°C for 2 hours was followed by a 3-hour final tempering step at 650°C. The findings revealed unique temperature-dependent decomposition characteristics of M/A islands. For example, at 200°C, partial M/A island decomposition took place, resulting in long rod-shaped carbides during final tempering. Meanwhile, the 350°C pre-tempering specimen revealed aggregated carbide precipitates of varying sizes in former M/A island locations. In contrast, the 500°C pre-tempering specimen showed coarse globular carbides and the absence of carbide precipitate clustering. This result can be attributed to the decrease in surface energy associated with the carbide-matrix interface as size increases. After tempering, all specimens produced three types of precipitates: rod-shaped Fe3C carbides, rhombus-shaped Mn7C3, and globular-shaped Mn23C6 carbides. The formation of long rod-shaped carbides during M/A island decomposition reduces the critical cleavage stress for micro-crack initiation, jeopardizing steel mechanical properties. Aggregated carbides cause the simultaneous formation of numerous micro-voids in close proximity, which eventually merge to form a large crack, resulting in material failure. When compared to other pre-tempered and directly tempered specimens, pre-tempering at 500°C produced the most favorable microstructure in terms of impact properties.

Endoscopic submucosal dissection and endoscopic mucosal resection for esophageal and gastric lesions: A comparison of procedures

ObjectiveEsophageal and gastric lesions are effectively managed with minimally invasive upper endoscopic procedures such as endoscopic mucosa resection (EMR) and endoscopic submucosal dissection (ESD), offering patients alternatives to invasive interventions. While ESD is well established in Eastern Asia, its adoption in Denmark for superficial esophageal cancer is recent. This study presents real-world data on the feasibility, safety, and hospitalization duration associated with ESD and EMR for esophageal and gastric lesions. MethodsA retrospective analysis was conducted on patients who underwent ESD or EMR at a specialized center in Denmark from October 2016 to June 2022. Data on treatment, indication, lesion location, hospitalization duration, procedure duration, specimen size, complications, recurrence, and one-year overall survival were collected. Statistical comparisons utilized the Mann–Whitney U test, independent sample median test, and chi-squared test. ResultsThe study included 130 patients (144 procedures): 72 underwent ESD and 58 underwent EMR. Compared with EMR, ESD resulted in greater percentages of en bloc and R0 resections (98.8% vs. 64.1%, p < 0.001; and 83.9% vs. 23.8%, p < 0.001), greater complication rates (28.7% vs. 3.1%, p < 0.001) and longer procedure times (119.5 min vs. 37.0 min, p < 0.001). The ESD procedure time significantly decreased over time (p = 0.01). The local recurrence rates were 14.5% for ESD and 23.8% for EMR (p = 0.767). The one-year overall survival rates were similar between the groups (95.8% vs. 94.8%, p = 0.553). ConclusionBoth ESD and EMR are safe and viable for treating esophageal and gastric lesions. ESD offers advantages but requires more time and skill. These findings support the literature, emphasizing the importance of considering patient-specific factors and surgeon proficiency in selecting the appropriate procedure.

Defining Optimal Settings for Lung Cryobiopsy in End-Stage Pulmonary Disease. A Human, Ex Vivo, Diseased Lung Clinical Trial.

To evaluate optimal settings of probe size, freezing time, and distance to the pleura that influence the size and quality of biopsy specimens during transbronchial lung cryobiopsies in ESPD. We prospectively recruited 17 patients undergoing lung transplantation. We created a nonperfused ex vivo bronchoscopy setting to perform multiple cryobiopsies with different probe sizes (1.7, 1.9, and 2.4mm), freezing times (3, 5, 7, 10, 20, 30 seconds), and probe distance from pleura (5, 10, and 20mm). Alveolated pulmonary parenchyma area≥50% in histology was considered a good quality biopsy, with a minimum procedural artifact. We used logistic regression to identify independent parameters as risk factors for histologic adequacy. A total of 545 cryobiopsies were obtained from 34 explanted lungs after pneumonectomy for lung transplantation. The mean maximum diameter of the specimen achieved with the 1.7 probe was larger (13.5mm) than those obtained with 1.9 and 2.4mm probes (11.3 and 10.7mm, P= 0.07). More pleural macroscopic damage and pleural tissue in histology occurred with the 2.4mm probe ( P <0.001). There was no difference in the quality of specimens between the different freezing times and the distance from the pleura. Freezing time and distance from the pleura did not affect the histologic quality for diagnosing ESPD in severely damaged lungs. Smaller cryoprobe size did not negatively affect sample adequacy.

Enhancing upper tract urothelial carcinoma diagnosis: Utility of cytokeratin 17 and CK20/CD44/p53 immunohistochemical panel

Upper tract urothelial carcinoma (UTUC) presents diagnostic challenges due to small biopsy specimen size, poor orientation, and technical obstacles that can yield equivocal diagnoses. This uncertainty often mandates repeated biopsies to evaluate the necessity of nephroureterectomy. Prior studies have suggested cytokeratin 17 (CK17) immunostain as an adjunctive tool for diagnosing bladder urothelial neoplasia in both urine cytology and tissue biopsy specimens. We evaluated the utility of CK17 in differentiating UTUC from benign urothelium and its ability to stratify low-grade from high-grade neoplasia. Our study involved a cohort of previously diagnosed cytology (n = 29) and tissue specimens from biopsies and resections (n = 85). We evaluated CK17 staining percentage in cytology and tissue samples and localization patterns in biopsy/resection samples. Our findings showed a statistically significant distinction (p < 0.05) between UTUC and benign tissue specimens based on full thickness localization pattern (odds ratio 8.8 [95% CI 1.53–67.4]). The percentage of CK17 staining failed to significantly differentiate neoplastic from non-neoplastic cases in cytology or tissue samples. Additionally, based on prior research showing the efficacy of CK20/CD44/p53 triple panel in bladder urothelial neoplasia, we utilized tissue microarrays to evaluate if these markers could distinguish UTUC from benign urothelium. We found that CK20/CD44/p53, individually or in combination, could not distinguish urothelial neoplasia from non-neoplasia. Full thickness CK17 urothelial localization by immunohistochemistry was highly reproducible with excellent interobserver agreement and may play a supplementary role in distinguishing upper tract urothelial neoplasia from benign urothelium.

Size Dependent Compressive Strength of FIB Machined Single Crystal Manganese Pillars

The deformation behavior of single crystals of manganese pillars generated by focused ion beam (FIB), with diameters ranging from ~1 m to ~4.5 m, has been studied as a function of specimen size using micropillar compression at ambient temperature. The manganese pillars were machined from randomly chosen larger grains of polycrystalline metal. At ambient temperature, single crystals of manganese display chaotic slip planes emerging on the sample surface and brittle plastic deformation when the sample size is decreased to the micrometer scale. The manganese pillars reached very high flow stresses in the range of 4-5.6 GPa. The stress-strain curves of all tested manganese pillars demonstrated significant work hardening and smooth flow behavior, with strains up to 8-10%. After 10% strain, however, the flow stresses remained constant with no work hardening. As previously reported, the manganese pillars with undetermined orientation demonstrated a less pronounced size effect (-0.14) by the size effect exponent of BCC pillars.

Water loss and shrinkage prediction in 3D printed concrete with varying w/c and specimen sizes

In 3D printed concrete (3DPC), the absence of formwork leads to increased shrinkage compared to traditional cast concrete which uses formwork. This increase in shrinkage is primarily due to the rapid evaporation of moisture during the early stages. Therefore, our research focused on how the initial water content and the exposed surface area affect the total shrinkage by varying water-to-cement ratio (w/c) and the surface-to-volume ratio (s/v). For 3DPC with high w/c, we used calcium formate (CaF) to improve its printability by increasing static yield stress. Dry environment makes the evaporation the predominant mode of water loss, significantly decelerating the hydration process in samples with fully exposed surfaces. At 28 d, the evaporated moisture in 3DPC is 2.8 times higher than the moisture consumed by hydration. A predictive model for the shrinkage properties of 3DPC has been developed by considering that 3DPC experiences both hydration and evaporation simultaneously from early stages on the basis of the water mass conservation principle. The predictions were found to align with actual shrinkage test results, as evidenced by quantitative analysis of parameters like internal RH, mass loss, degree of hydration, and porosity, thus validating the accuracy of the model.