Small-sized Specimens Research Articles

Sedimentation-affected engineering performances and microstructures of a hybrid Portland-sulfate aluminate cement grout cast in long tubes

Material sedimentation may have non-negligible impacts on engineering properties of flowable cement grouts, and this issue cannot be addressed by in-lab tests on small size specimens. Herein, sedimentation tests were conducted to a high-strength hybrid Portland-sulfate aluminate cement (P-SAC) grout cast in 6-m-long tubes. Compressive strength and density of the P-SAC specimens at different depths were measured, and microstructures were assessed by X-ray computed tomography (XCT), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results showed that the hybrid P-SAC grout possessed the superior indices of flowability, expansion and compressive strength. The increasing rates of density and compressive strength to depth were 9.3 kg/m4 and 0.5 MPa/m, respectively. The shallow sites possessed a porous structure with 14.5 % more big pores (>1 mm). The pore structure followed fractal patterns, and the fractal dimensions increased slightly with depth. Our findings not only deepen the understandings in slurry sedimentation and the consequences of engineering properties, but also narrow the knowledge gaps between in-lab tests and in-situ applications for grouting construction.

Influence of dimensional deviation and thickness non-uniformity on the small-size specimen tensile results of CLF-1 steel

Tensile testing of small-size specimens has been widely used to evaluate the influence of neutron irradiation on the mechanical properties for structural materials of fusion reactors. In recent years, researchers have been trying to standardize small-size specimen tensile test method. In the present paper, we have investigated the influence of dimensional deviation and thickness non-uniformity on the tensile results of small-size specimen by both experiments and finite element simulations, based on one of the candidate structural materials of fusion reactor, i.e. CLF-1 steel. It was found that under the conditions of small grain size, small metallurgical defect size and suitable specimen preparation, the tensile results of SS-J3 specimen could be close to the results of large-size specimen. Slightly higher yield and ultimate strengths for small specimens may be caused by the surface treatment of the wheel grinding. The repeatability of ultimate strength was better than that of yield strength, and the repeatability of elongation was worse than that of strength. For tensile tests on eight SS-J3 specimens, the maximum difference in total elongation was about 3 %. With ±0.1 mm deviation of thickness and parallel width, the maximum variation in total elongation was about 1.8 %. The ductility properties were sensitive to specimen's thickness non-uniformity, the measured uniform and total elongations would obviously decrease even with 0.01 mm thickness non-uniformity.

Mechanically Adjustable 4-Channel RF Transceiver Coil Array for Rat Brain Imaging in a Whole-Body 7 T MR Scanner.

Investigations of human brain disorders are frequently conducted in rodent models using magnetic resonance imaging. Due to the small specimen size and the increase in signal-to-noise ratio with the static magnetic field strength, dedicated small-bore animal scanners can be used to acquire high-resolution data. Ultra-high-field (≥7 T) whole-body human scanners are increasingly available, and they can also be used for animal investigations. Dedicated sensors, in this case, radiofrequency coils, are required to achieve sufficient sensitivity for the high spatial resolution needed for imaging small anatomical structures. In this work, a four-channel transceiver coil array for rat brain imaging at 7 T is presented, which can be adjusted for use on a wide range of differently sized rats, from infants to large adults. Three suitable array designs (with two to four elements covering the whole rat brain) were compared using full-wave 3D electromagnetic simulation. An optimized static B1+ shim was derived to maximize B1+ in the rat brain for both small and big rats. The design, together with a 3D-printed adjustable coil housing, was tested and validated in ex vivo rat bench and MRI measurements.

Clinical significance of transjugular liver biopsy in acute liver failure – a real-world analysis

BackgroundHistopathological characterization obtained by transjugular liver biopsy (TJLB) may theoretically contribute to clarification of the exact aetiology of acute liver failure (ALF). It's unclear whether the histopathological information from TJLB, due to the small specimen size, significantly contributes to diagnosing ALF causes, guiding therapy decisions, or predicting overall prognosis. This retrospective study aimed to analyse safety and clinical significance of TJLB in patients with ALF.MethodsThis retrospective, monocentric study investigated safety and efficacy of TJLB in patients with ALF over a ten-year period at a tertiary care transplant-center. The predictive value of various clinical and laboratory characteristics as well as histopathological findings obtained by TJLB on 28-day liver-transplant-free survival were evaluated by calculating uni- and multivariate Cox-proportional hazard regression models. Additional univariate logistic regression analyses were performed to explore the influence of degree of intrahepatic necrosis on the secondary endpoints intensive-care-unit (ICU) admission, need for endotracheal intubation, renal replacement therapy and high-urgency listing for LTX.ResultsA total of 43 patients with ALF receiving TJLB were included into the study. In most cases (n = 39/43 cases) TJLB confirmed the initially already clinically presumed ALF aetiology and the therapeutic approach was unchanged by additional histological examination in the majority of patients (36/43 cases). However, in patients with a high suspicion for aetiologies potentially treatable by medical immunosuppression (e.g. AIH, GvHD), TJLB significantly influenced further treatment planning and/or adjustment. While the degree of intrahepatic necrosis showed significance in the univariate analysis (p = 0.04), it did not demonstrate a significant predictive effect on liver transplant-free survival in the multivariate analysis (p = 0.1). Only consecutive ICU admission was more likely with higher extent of intrahepatic necrosis (Odds ratio (OR) 1.04 (95% CI 1–1.08), p = 0.046).ConclusionsPerformance of TJLB in ALF led to a change in suspected diagnosis and to a significant change in therapeutic measures only in those patients with a presumed high risk for aetiologies potentially responsive to immunosuppressive therapy. Clinical assessment alone was accurate enough, with additional histopathological examination adding no significant value, to predict overall prognosis of patients with ALF.

Measuring fatigue crack growth using microscale specimens: Si-modified Inconel 939 alloy processed by laser powder bed fusion additive manufacturing

Quantitative assessment of fatigue crack growth (FCG) in a Si-modified Inconel 939 alloy, processed by laser powder bed fusion additive manufacturing (L-PBF AM), was conducted through cyclic bending of pre-notched cantilevers with a characteristic cross-sectional dimension of 25 μm × 25 μm. To the best of our knowledge, this work is the first to show that cyclic bending of such pre-notched microscale cantilevers can sense both the threshold regime and the Paris-law regime of FCG quantitatively, despite the small specimen size. The deliberate fabrication of such microscale test specimens enables control of the direction of fatigue crack propagation with respect to a given microstructure, while avoiding the inclusion of volumetric defects within the test volume. Significant differences in FCG behavior were observed when the direction of crack propagation was switched from being parallel to the AM build direction to being perpendicular to it. The present work demonstrates the efficacy of FCG assessment using microscale specimens, which can enhance our understanding of the influence of a given microstructure on crack growth behavior.

Non-destructive evaluation of residual strength distribution of recycled aggregate concrete and bond strength between recycled aggregate concrete and deformed bar with different cover thicknesses after freeze-thaw cycles

The thickness of a cover significantly influences both the bonding performance and the durability of materials against frost resistance. This research investigates the degradation and damage distribution of fundamental mechanical properties in two specimens of recycled aggregate concrete (RAC), each with varying sizes, following freeze-thaw cycles (FTCs). This comparison is facilitated through non-destructive and damage tests. Subsequently, the influence of freeze-thaw damage (FTD) on the bond strength of specimens with differing cover thicknesses is examined via pull-out tests on 14 groups of center pull-out specimens. Lastly, the bond strength is theoretically analyzed. The test results reveal that FTCs diminish the material strength of RAC, and the FTD distribution within RAC specimens is not uniform. The surface concrete sustains a higher degree of damage compared to the internal concrete, resulting in an average FTD of small-size specimens that surpasses that of large-size specimens. The residual strength of RAC can be assessed using a non-destructive test, specifically the ultrasonic wave velocity test. For center pull-out specimens, FTD not only decreases the material strength but also increases the wedge splitting angle while reducing the critical protective layer thickness. This paper proposes a soft sleeve correction theory that comprehensively accounts for the effects of FTD. When combined with non-destructive test results—namely those from the ultrasonic wave velocity test—this theory can effectively evaluate the bond strength of RAC post-FTD. This approach offers valuable insights for the design and assessment of recycled concrete in cold climates.

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.

Fracture Behavior of Crop Circle Ceramic Tiles: Experimental and Numerical Study

This research investigates the effect of three-dimensional (3D) bee-crop-circle tiles on load deformation, initial cracking and propagation, and stress redistribution. Experimental tests provide limited data due to the small specimen size and brittle nature of the material. A finite element (FE) model is constructed and validated by laboratory data to analyze the stress-strain responses and failure mode. The model enables a detailed description of stress patterns, stress propagation, and redistribution of layers beneath the bee design. The study concludes that a 3D crop circle-inspired design significantly influences the ultimate load-carrying capacity and stress-related behavior. The load-deformation response is nonlinear, and the coloring influences the thickness of coatings, further affecting the ultimate load and initial stiffness. Furthermore, designs with convex details result in an arc action, deviating the stress concentrations away from the line of loading. The FE model slightly overestimates the initial stiffness but represents the ultimate load and load-displacement response with high accuracy.

Experimental investigation and numerical modeling of effect of specimen size on microwave-induced fracturing of diorite

The effect of specimen size on microwave-induced fracturing of rocks has not been well understood. In this study, the experimental tests using open-ended microwave and numerical simulations coupling COMSOL Multiphysics and four-dimensional lattice spring model (4D-LSM) were carried out to investigate the evolution process of microwave-induced cracks, and to elucidate the mechanisms responsible for size-dependent microwave-induced fracturing. The experiments show that with the increase of the specimen dimension, the number of microwave-induced cracks is almost constant, and the total crack length first increases and then decreases, while the maximum crack width and maximum crack depth decrease gradually. A comparison of the experimental and numerical temperature characteristics as well as cracking characteristics indicates that the models established in this study are reasonable in the simulation of the rock fracturing behaviours. The numerical results show that the crack initiation time increases logarithmically with the increase of the specimen dimension. For the small-sized specimens, the microwave-induced cracks started from the outer boundary of the specimen and propagated toward to specimen center and into the depth. For the medium-sized and large-sized specimens, the microwave-induced cracks initiated near the outer boundary of the antenna aperture, and then propagated toward to the center of the specimen and the outer boundary of the specimen. The main reason for the size-dependent of fracturing behavior is that the local fracture energy will dramatically decrease when the crack is approaching the specimen boundary.

Experimental investigation on the size-dependent CFRP shear contribution in CFRP-strengthened RC shear wall

Most of the current methods for estimating the shear contribution of CFRP are based on laboratory testing of small-sized specimens. The applicability of the current codes on large-sized FRP-strengthened shear walls remains debatable. The present study addresses the problem by investigating the combined effects of structural sizes and CFRP ratios on the shear contribution of CFRP. Through experiments, a series of geometrically similar CFRP-strengthened RC shear walls were designed and subjected to a cyclic horizontal loading. From the experiments, the following results can be obtained. The application of the externally bonded CFRP strips alters the failure mode and enhances remarkably the seismic resistance by suppressing crack propagation and increasing the energy dissipation. The increasing specimen size reduces the enhancement effects of CFRP on the nominal shear strength, ductility, and energy dissipation. These findings indicate that without considering the size effect, the effective strain that reflects the shear contribution of CFRP strips are greatly overestimated by the current codes. Therefore, the present study proposed and validated an effective strain factor capturing the combined effects of the structural size and the CFRP ratio on the shear contribution of CFRP strips, serving in assessing the shear strengthening effect of CFRP on shear walls.

Closed-form fracture model for evaluating crack resistance of 3D printed fiber-reinforced alkali-activated slag/fly ash recycled sand concrete

To reduce resource consumption and greenhouse gas emissions, 3D printed alkali-activated slag/fly ash recycled sand (RS) concrete (3DP AARSC) was developed in this paper. The reasonable evaluation of its crack resistance is crucial to structural safety and stability since steel bars are still difficult to embed in 3DP samples automatically so far. The realistic fracture parameters can be responsible for the reasonable evaluation and are extremely difficult to predict accurately based on traditional methods unless the specimen sizes are large enough. Therefore, the purpose of this study is to determine the size-independent tensile strength (ft) and fracture toughness (KIC) through a predictive fracture model incorporating the heterogeneity and discontinuity of 3DP AARSC. First, fracture tests of small-sized specimens were conducted to clarify the fracture mechanisms of 3DP AARSC in different loading directions. Subsequently, based on the boundary effect model, the size-independent ft and KIC were explicitly correlated to the maximum fracture load (Fmax) in different loading directions and directly obtained if Fmax was measured from the tests. The results displayed that the predicted ft and KIC of 3DP AARSC loaded perpendicular to the printing direction were significantly higher than the counterparts of concrete loaded parallel to the printing direction by 108.7% at most. The greatest cracking resistance was demonstrated in the specimens with the RS replacement rate of 60% for natural river sand (NS), resulting in the maximum increase of 19.9% in ft and KIC compared with the 3DP concrete with 100% NS. The fiber addition and partial RS replacement increased the difference in the crack resistance along various loading directions. Moreover, the fiber incorporation had no significant improvement in the crack resistance of 3DP AARSC loaded parallel to the printing direction and apparently increased its ft and KIC along other loading directions.

Ductility Variation and Improvement of Strain-Hardening Cementitious Composites in Structural Utilization.

Strain-hardening cementitious composite (SHCC) has the obvious advantages of excellent material properties such as its high tensile and compressive strengths, high tensile strain capacity, and excellent durability against multi-cracking performance with very fine crack widths. In particular, the multi-cracking performance of SHCC during structural utilization is obviously reduced compared to that of SHCC in uniaxial tension tests using dumbbell-shaped specimens of small size. The corresponding tensile strain capacity of SHCC during structural utilization is, thus, significantly decreased compared to that of SHCC in uniaxial tension tests. However, the reduction in the ductility of SHCC during structural utilization has not been sufficiently understood, and further study is required. This paper presents an experimental investigation into the ductility variation of flexural-failed and shear-failed SHCC members as well as the ductility improvement of SHCC members with steel reinforcement compared with that of SHCC in uniaxial tension tests using small-sized specimens. This study focuses on not only the decrease in the crack elongation performance of the SHCC material during structural utilization but also the increase in the crack elongation performance of SHCC members with steel reinforcement. The results demonstrate that the crack elongation performance of flexural-failed and shear-failed SHCC members is significantly reduced compared to that of SHCC in the uniaxial tension tests. Moreover, it was confirmed that steel reinforcement can effectively improve the SHCC member, increasing the strain-hardening capacity and multi-cracking performance. The load-carrying capacity of the flexural-failed SHCC member with steel reinforcement seemed to increase linearly with an increase in the reinforcement ratio, accompanied by an increase in the distribution of multiple fine cracks in the flexural-failed SHCC member with steel reinforcement.

Assessing the master curve reference temperature T0 estimated from the Charpy impact transition curve and consequences on the correlation between Charpy DBTT- and fracture toughness T0-shifts

Integrity assessment of reactor pressure vessels of light water reactors follows well established procedures relying on the surveillance program and defined by codes, standards and nuclear regulatory requirements. These procedures were developed in times where scientific knowledge was limited increasing therefore conservative safety margins to overcome the scientific shortcomings.Taking profit from the development of a number of test techniques and evaluation, it is possible nowadays to propose an alternative interpretation of the test results that provides a complementary information to the standard regulatory approach. In this work, the focus is on the Charpy impact test as it plays a critical role in surveillance programs monitoring reactor vessel degradation induced by neutron irradiation. The development of methodologies allowing experimental determination of fracture toughness from small size specimens triggered alternative approaches of extracting fracture toughness from the Charpy impact test. One of those approaches was recently successfully developed using the instrumented Charpy impact test from which the dynamic and static fracture toughness can be estimated with a reasonably good accuracy. This paper aims to provide an equally performant but simplified procedure allowing estimation of the master curve reference temperature, T0, from the Charpy impact transition curve applied to a large variety of reactor materials and irradiated conditions.

Size effect on fatigue performance of SLM-ed AlSi10Mg alloy: Role of defect size distribution

The size effect on high-cycle fatigue performance of SLM-ed AlSi10Mg alloy was studied with three different highly stressed areas. It shows clear that small size specimens present higher S-N data and small fatigue initiator sizes compared to large specimens. Fatigue cracks were initiated from either lack of fusion (LOF) pores or gas pores. The sizes of fatigue initiators were analyzed based on Gumbel distribution and Frechet distribution, respectively. The LOF defects were equivalent to small cracks and Paris equation was used to reveal the relationship between the fatigue life, applied stress and fatigue initiator size. P-S-N curves were obtained by combining the fatigue initiator size distributions with crack propagation formula. According to the weak-link theory, P-S-N curves of other sizes could be predicted and it was found that Frechet approach could give a better prediction.

Comparative Study on Complete Characterisation of Elastic–Ductile Compressive Behaviour of Aged and New Norway Spruce Timber

ABSTRACT Material properties of historical timber structures may change over time due to decay, change of chemical composition of material, biological agents, climatic conditions, etc. Adequate bending performance requires stiffness and strength both in tension and compression, as well as sufficient ductility in compression. While the focus of most research is on the former quantities, the latter one is generally disregarded. This study gives a comparative analysis on complete characterization of compressive behaviour of recent and 60-years-old aged spruce timber (Picea abies). Parallel-to-grain compressive tests on small-sized specimens were conducted to obtain stress – strain diagrams and to determine failure modes. All material properties of stiffness, strength, and ductility were calculated for each specimen. It was concluded that elastic stiffness, elastic limit stress, and compression strength are virtually invariable after sixty years of service while the ductility decreased and the post-peak behaviour became more brittle. It is also found that end-rolling failure mode can yield the same elastic and stiffness properties as the standard kinkband failure. Climatic changes increase the risk of material deterioration prompting for more thorough monitoring and study of historical timber structures.

(Invited) Mechanical Property Design of Multilayered Ti/Au Microcomponents by Electrodeposition Toward High-Sensitive MEMS Accelerometers

Recently, MEMS accelerometers employing Au components prepared by electrodeposition are reported to have a small size whiling retaining a high sensitivity [1], which is mainly contribute by Au’s high mass density, as shown in Fig. 1. Detections of body tremors and muscular sounds are realized using this highly sensitive MEMS accelerometer [2]. However, low mechanical strength of Au, when compared to Si-based materials commonly used in conventional MEMS accelerometers, leads to insufficient structure stability for the long-term use of the device. To enhance the mechanical strength of Au-based materials, several approaches have been reported; for example, multi-layered metal technology [3], and alloying Au with Cu [4]. On the other hand, effects of such approaches on the long-term structure stability of the Au-based materials with dimensions in micro-scale remain uncleared. Considering the relationship between mechanical properties of metallic materials and size of the specimens evaluated, evaluation of the long-term structure stability of Au-based materials in micro-scare is essential for commercial uses of the Au-based MEMS device.Cantilever-like structures are commonly used in movable components in MEMS devices [1, 3]. Repeatedly electrodeposition of gold following by deposition of a material with a high mechanical strength to realize a multi-layered structure is an effective strategy to enhance the structural stability [5]. From the Euler-Bernoulli beam theory, the structural stability of a cantilever-like structure is improved by using materials having high Young's modulus (as noted E). Although, the E is an intrinsic property of materials, which should be constant as the specimen size changes, but the E of small-sized specimens is reported to differ as the size changes. The E of a small-sized specimen with a specific geometry is called the effective Young’s modulus (E eff). The E eff of a micro-cantilever could be determined from the resonance frequency of the micro-cantilever, and the resonance frequency could be measured by a laser doppler vibrometer [4].In this report, various Ti/Au multi-layered structures, as shown in Fig. 2, were prepared. Firstly, the E eff of complex three dimensional (3D) multi-layered Ti/Au structures was determined from the resonance frequency obtained with a laser doppler vibrometer, as shown in Fig. 3. Next, we studied the effects of these various Ti/Au multi-layered structures on the long-term structure stability by vibration tests. Lastly, we discuss the relationship between the Ti/Au multi-layered structures with characteristic E eff values and long-term structure stability. The discussion could contribute to the material design for highly sensitive and stable MEMS accelerometers.Reference: Yamane, et al., Appl. Phys. Lett., 104, 074102 (2014).Onishi, et al., Jpn. J.Appl.Phys., 61, SD1028 (2022)Machida, et al., ECS Trans., 61, 21 (2014).Nitta, et al., J.Electrochem.Soc., 167, 082503 (2020)Teranishi et al., Microelectro. Eng. 187–188 , 105–109 (2018) Figure 1

Determination of tensile strength and fracture toughness of nuclear graphite and prediction of its structural failures

The fracture properties of nuclear graphite and their effects on the structural failure process threaten the integrity and safety of High Temperature Gas-cooled Reactor structures. This study aims to develop close-form solutions to determine the size-independent tensile strength and fracture toughness of graphite from small-sized specimens, and thus to predict its structural failure behaviors. Firstly, the scale coefficient and dispersion coefficient are introduced to reflect the heterogeneity of graphite; these are estimated to be 21.0 and 16.8, respectively, in accordance with the meso-structural characteristics and macro-mechanical responses of the graphite. The fracture parameters of geometrically non-similar IG-11 graphite specimens are statistically analyzed with a normal distribution to determine the true fracture toughness and tensile strength, in the form of analytical solutions. Thus, a complete fracture failure curve is constructed to evaluate its fracture behavior. Then, the proposed method is employed to obtain the fracture responses of geometrically similar IG-11 graphite specimens. Good consistency in the calculation results of two types of specimens are observed, verifying the accuracy and size-independence (including absolute and relative sizes) of the proposed method for determining the fracture parameters of graphite. Finally, the structural failure loads of IG-11 and IG-110U graphite specimens with different sizes are predicted within an error margin of 15%. The minimum size requirements of graphite specimens satisfying the condition of linear elastic fracture mechanics are discussed, and the relationship between the fracture behavior of small-sized graphite specimens in the laboratory and the structural failure of actual large-sized graphite members is established.

Normal statistical fracture analysis of Roller-compacted concrete on the basis of non-linear elastic fracture mechanics

Roller-compacted concrete (RCC) is widely used in dam structures; the fracture properties of RCC directly affect the cracking resistance of RCC dams. Solving the discrete problem of the RCC fracture properties and obtaining real material parameters is important for the healthy and stable operation of RCC structures. The tensile strength (ft) and fracture toughness (KIC) are two critical parameters that have a direct impact on the fracture properties of RCC structures. In this study, the relative ligament depth [(W − a0)/di] is associated with the fictitious crack growth length (Δafic). A normal statistical fracture model is developed to describe the dispersion of the RCC ft and KIC to obtain the real material parameters of RCC with different cement-to-aggregate (C/A) ratios. For an increase in the C/A ratio from 12 % to 17 %, the ft and KIC for each group of RCC structures are 4.05–6.35 MPa and 0.90–1.41 MPa·m1/2, respectively. Based on the results of the normal statistical analysis, fracture failure curves are constructed with 95 % reliability, revealing that the fracture behavior of RCC is quasi-brittle fracture. Additionally, a relationship between the peak load (Pmax) and the material parameters is proposed, this confirms the correctness of the proposed model. Finally, the relationship between indoor small-size specimens and actual engineering-scale RCC dams regarding fracture failure is discussed based on the fracture failure curve.

Development and performance study on low strength and high rockburst tendency similar simulation material of coal

The current similar simulation materials (SSM) are featured with the contradiction between low strength and high rockburst tendency (RT), thus being unable to simultaneously realize the qualitative rockburst of small size specimen and the impact damage restoration of large size model. In this case, this study developed a new SSM of low strength and high RT by using water glass (WG) as cement, talcum powder (TP) as aggregate and adding curing agent sodium silicofluoride (SSF). Under the requirements of initial set volume shrinkage rate (IVSR), long-term volume decay rate (LVDR), uniaxial compressive strength (UCS) and modulus index (MI), the optimal ratios of SSF and TP were obtained 20% and 70% by orthogonal experiment and multiple linear regression method, respectively. Micro-macroscopic experiments such as uniaxial compression, scanning electron microscope (SEM), acoustic emission (AE) and Infrared thermal imager were utilized to monitor in real time the energy-temperature-strength synergistic change characteristics and similarities between this material and the coal with a strong RT. The experimental results show that: the UCS value of this material is 6.11 MPa and its MI is 11.57, which meets the requirements for low strength and high RT. Meanwhile it satisfies a certain similar proportionality between its physical parameters and those of coal. In the whole process of uniaxial compression, there are energy and temperature homologous changes in the characteristics of consistency, and both materials conform to the stress–strain phase law. The infrared radiation temperature displays a trend of “slowly decreasing-gradually warming-continuously cooling-suddenly warming-sharply cooling”. The AE energy count rate shows a trend of “calm transition and sudden increase before and after the stress peak”. All are characterized by strong RT. There is still some difference between the two specimens during energy and temperature changes, due to their different molding characteristics and load-bearing capacity. The feasibility of the material was confirmed in terms of physical parameters, degree of rockburst and homologous energy and temperature characteristics. Meanwhile, this study revealed the multi-parameter precursor characteristics of rockburst damage in the specimen, which can lay a foundation for the prevention and study of impact ground pressure disaster.

Time-of-flight polarization contrast neutron imaging for enhanced characterization of ferritic phase fractions in Fe-Mn-Si shape memory alloys

The determination of the amount and distribution of different phase fractions in additively manufactured shape memory alloys processed with laser powder bed fusion is crucial for understanding the correlation between processing parameters, microstructure, and mechanical properties. Neutron imaging techniques, such as Bragg edge imaging and polarization contrast neutron imaging (PNI), have been introduced to complement and overcome the limitations of traditional characterization methods, which are often destructive and limited to surface analyses and small-sized specimens. Bragg edge imaging can distinguish and quantify crystallographic phase fractions with spatial resolutions of a few tens of micrometers, while PNI is highly sensitive to crystallographic phases and is particularly suited for sub-percent phase fractions and in-situ, time-resolved, and tomographic analyses. In this work, we present a time-of-flight PNI method that enables simultaneous measurements of phase fractions.