Increase In Shear Strength Research Articles

Shear strength of steel-concrete composite walls (aspect ratio 2.0) with steel U-SECTION boundary element

A steel-concrete composite wall with steel U-section boundary elements was developed for enhanced structural performance and constructability. In the present study, cyclic lateral loading tests were performed to investigate the shear strength of the proposed walls. Test parameters were the type of boundary reinforcement (rebars or steel U-sections), sectional area of steel U-sections, and type (horizontal rebars, steel plate beams, or steel faceplates) and spacing of web reinforcement. The test results showed that the boundary steel U-sections restrained diagonal tension cracking and shear sliding in the web. Further, the steel U-sections restrained cracking and crushing of the boundary concrete, confining the boundary zone. For this reason, the shear strength of the composite wall was 35 % greater than that of the counterpart reinforced concrete wall with conventional boundary reinforcement. The use of steel plate beams and steel faceplates further increased shear strength. Existing reinforced concrete design methods underestimated the shear strength of the composite walls, neglecting the contribution of steel U-sections. The tested shear strengths exceeded the web crushing strengths of ACI 318, even though the horizontal web reinforcement ratio was less than the code-based maximum ratio.

Mechanical responses and fracturing behaviors of coal under complex normal and shear stresses, Part I: Experimental results

This work presents experimental tests based on coal collected from a coal mine based underground water reservoir (CMUWR). The mechanical responses of dry and water-soaked coal samples under the complex normal and shear stresses under multi-amplitude and variable frequency is investigated. The experimental results reveal the effects of stress path, water soaking and frequency on deformation, energy dissipation, secant modulus and shear failure surface roughness. The experimental results show that when normal and shear stresses are applied simultaneously, there is a significant competitive relationship between them. On the dominant side, the strain rate will be significantly increased. The sample under a loading frequency of 0.2 Hz exhibits a longer fatigue life. During the cyclic shear test, the shear strain of the water-soaked sample is higher than that of the dry samples. The average roughness coefficient of failure surface exhibits an increasing pattern with increase in shear strength, the elevated roughness of a shear surface is advantageous in constraining shear displacements of specimens, thereby lowering the energy dissipation. This study can provide theoretical and practical implications for a long-term safety evaluation of CMUWR.

Micro- and macro- mechanical properties of an Al2O3/Al2O3 ceramic matrix composite after thermal aging at 1400 °C

The evolution mechanism of mechanical properties at elevated temperature is particularly crucial to the oxide/oxide composites. In this work, an Al2O3/Al2O3 ceramic matrix composite was prepared by laminating with high solid content slurry. The microstructure, micro- and macro- mechanical properties of the composites before and after thermal aging at 1400 °C were examined. The density and porosity of the original composite were ∼2.60 g/cm3 and ∼27.2 %, respectively. The sintering phenomenon of matrix in the composite after thermal aging was clearly visible, resulting in the matrix modulus increased by 83.5 % and the interfacial shear strength increased by 154.9 % compared with those of the original composite. The fundamental mechanics theory of composites stated that the significant increase of interfacial shear strength was the main reason that the flexural strength retention ratio of the composite decreased to ∼55 % after thermal aging.

Investigation of the Shear and Pore Structure Characteristics of Rubber Fiber-Reinforced Expansive Soil

In recent years, many researchers have evaluated the sustainable use of waste tire rubber as an aggregate in soil. Its effectiveness has been widely acknowledged. The main objective of this work is to study the influence of rubber fibers on shear strength and pore structure characteristics in relation to expansive soil. In this context, we conducted a series of experiments that were carried out on reinforced expansive soil with rubber fiber contents of 0, 5, 10, 15, and 20%. The results show that the shear strength and maximum dilatation angle increase gradually with rubber fiber content. Due to the pore water pressure and creep effects, the deviator stress and effective cohesion of the samples under the consolidated drained conditions were higher than those under the undrained conditions. The converse was true for the internal angle. The addition of an appropriate amount of (5–10%) rubber fiber can effectively inhibit the development of soil cracks and reduce the porosity of the samples. The results obtained can highlight the beneficial effects of rubber fiber, which is highly desirable in many backfill applications.

The influence of variations in salinity levels on the biocementing process on soil improvement of liquefaction potential

Abstract This article presents an innovative method of soil improvement cementing to increase the shearing strength of very loose sand with 10% relative density (Dr) in saline conditions. Salt in saline soils destroys the stability of stable soils. In contrast, the salt content reduces the level of homogenization of unstable soils, causes technical problems in calcareous soils, and affects their stability, especially if the salt content is more than 3.0%. The variations in salinity levels can determine the optimal percentage of salt levels in the stabilized soil. The application of biocementation to saline soil can drastically increase the shear strength of soil in soil with potential liquefaction in coastal areas due to earthquakes. Calcium carbonate deposition (MICP) in the microbial-induced biocementing process is a new method that utilizes the metabolic processes of microorganisms in this study using Bacillus sp. In the MICP process, microbes need Ca2+ ions obtained from fly ash, which can produce SiO2 and CaO to produce CaCO3 for binding between particles. Soil improvement was carried out by combining initial soil, fly ash, mycobacteria, and variations in salinity obtained from NaCl with varying percentages of 0%, 1%, 2%, and 3,4% after testing at curing times 7, 14, 21, and 28 days. The research samples from the UCS and direct shear tests showed that the shear and UC strength that were treated increased. The highest increase in shear strength was at 3,4% salinity at 28 days of 80.9°. CaCO3 production resulting from the binding between particles in the biocementing reaction can be seen from the results of SEM tests. Soil improvement using biocementing in this study resulted in an effective increase in the strength of loose sand soil in salinity condition.

Shear strengthening of damaged reinforced concrete beams with iron-based shape memory alloy (Fe-SMA) strips: numerical and parametric analysis

Shape memory alloys (SMAs) are metallic materials that are characterized by their ability to restore their original shape after large deformation when activated by heating. This unique property renders SMAs appealing for various civil engineering applications. Iron-based SMAs (Fe-SMAs), including alloys like Fe–Mn–Si, stand out due to their cost-effectiveness and high strength. The primary focus of this research lies in the computational modeling of Fe-SMA strips utilized to reinforce damaged concrete structures. To achieve this, details from an experimental test are leveraged for the computational simulation of real-scale reinforced concrete beams that were first loaded to some level of damage, then released and strengthened, and subsequently retested. The strengthening approach involves the application of external Fe-SMA strips wrapping around the beams. This paper presents an original computational modeling setup that incorporates a switch option for the Fe-SMA material. This feature enables one to use a single simulation platform for the whole process. The significance of this method originates from its capacity to ensure a robust analysis that includes all simulation steps-testing unstrengthened beams, installing and heating Fe-SMA strips, and testing both damaged and strengthened beams—in a single, multi-step analysis. The computational simulation results were compared with the outcomes of the experimental test, revealing an acceptable level of agreement. The findings indicate a substantial increase in both shear strength and ductility as a result of the application of Fe-SMA strips. Additionally, parametric and mesh sensitivity studies were conducted. These aimed to investigate the mesh dependency of the model and to identify the optimal mesh size. Furthermore, variations in the details of the Fe-SMA strips, including thickness, width, quantity, and effect of applied temperature were explored to compare the outcomes of different applications of these strips.

Experimental Study on the Shear Strength of Different Interfaces of Fine-Grained-Tailing-Filled Geotextile Tubes

As damming material, fine-grained tailings present challenges such as low dam strength and poor stability. To address these issues, this study employs geotextile tube technology to mix water with fine-grained tailings, forming a tailing slurry with a concentration of 60%, which is filled into a geotextile bag to form a geotextile tube, so as to improve the stability of fine-grained tailings. The shear strength characteristics of each interface under different consolidation times and different filling degrees were studied via an indoor shear experiment, including the shear strength of tailing particles, that between tailings and geotextiles, and that within geotextile tubes themselves. The results show that the shear strength of each interface conforms to the Mohr–Coulomb strength criterion, and that the interface cohesion is greatly affected by the consolidation time, while the interface friction angle is mainly affected by the filling degree. Moreover, the shear strength comparison, based on the comprehensive friction angle concept, indicates a substantial increase in shear strength at the interfaces between geotextile tubes compared to both that of the tailings themselves and the interface between tailings and geotextiles, highlighting the reinforcing effect of the geotextile tube filling technology on tailings’ shear strength.

Stabilizacja zboczy podatnych na osuwiska za pomocą kotew rurowych

This paper presents an anchor of a new design, whose properties have been selected to retain the advantages of a tubular anchor over the other anchor types and at the same time, ensure its adaptation to specific conditions associated with slope stabilization. The proposed anchor consists of a steel tube filled with expanding cement mortar. The outer diameter of the tube is 2-3 mm less than the diameter of the borehole, a groove is cut on the outer surface of the tube. A metal rod is placed in the center of the tube at the outer end of which a support plate is installed, and a tie wrench is fixed. The length of the metal rod is equal to the depth of the bore hole, while the length of the steel tube is at least half the length of the borehole. In the process of solidification and expansion of the solution, pressure is created on the walls of the bore hole. Under the influence of pressure, the pipe is opened around the groove and close contact is achieved between the pipe and the borehole surfaces. As soon as the solution hardens, the steel tube is firmly embedded in the concrete, after which the anchor reaches operational capacity. Preliminary tests of the proposed anchor showed that it has a high clamping force (for hard rock conditions - 46-75 kN/m and for soft rock conditions 32-36 kN/m). He has other advantages, namely it does not require special equipment for installation, the inside of a tube is filled with hard concrete-like mass, which hampers the process of corrosion and increases shear strength.

Hierarchical Polyimide‐Covalent Organic Frameworks Carbon Fiber Structures Enhancing Physical and Electrochemical Properties

The multifunctionality of carbon fiber (CF) is being extensively explored. Herein, polyimide covalent organic frameworks (PI‐COFs) are grafted bound to CF to enhance their mechanical and electrochemical properties. Here, a range of COF scaffolds are grafted to the surface of CFs via a two‐step functionalization. First, melamine is tethered to the fiber surface to provide an anchoring point for the COFs followed by a “graft from” approach to grow three different sized PI‐COFs utilizing three differently sized dianhydride, PMDA to form MA‐PMDA, NTCDA to form MA‐NTCDA, and PTCDA to form MA‐PTCDA COFs. These COFs increase the capacitance of CF by a maximum of 2.9 F g−1 (480% increase) for the MA‐PTCDA, this coincides with an increase in interfacial shear strength by 67.5% and 52% for MA‐NTCDA and MA‐PTCDA, respectively. This data represents that the first‐time CF has been modified with PI‐COFs and allows access to COF properties including their porosity and CO2 capture ability while being attached to a substrate. This may lead to additional high‐value recyclability and second‐life applications for CFs.

Performance of optimized composition of epoxy resin adhesive used in High Friction Surface Treatment

The High Friction Surface Treatment (HFST) paving technique is widely employed in engineering practices globally, serving to enhance the long-term anti-skid performance of pavements. However, there still exist significant gaps in research regarding the modified and optimized composition and corresponding content of the polymer binding materials used in HFST, as well as the performance of the pavements laid with modified and optimized blended aggregates during service. To address these issues, this research first modified and optimized the composition ratio of traditional epoxy resin materials. Subsequently, a toughened, high-flow epoxy bonding system suitable for the maintenance of concrete pavements was prepared. Additionally, the study explored the bonding performance of this system with both the cement base surface and aggregates. The results established that the optimal ratio range for the modified epoxy adhesive system is E51 epoxy resin to curing agent to toughening agent to diluent in the proportions of 100: 30–35: 20–30: 5. The experimental group used a high-flow epoxy resin adhesive ratio of E51 epoxy resin: curing agent: toughener: diluent = 100:30:20:5. For control group 1, the ratio of epoxy resin adhesive was E51 epoxy resin: curing agent = 100:30, and for control group 2, the ratio was E44 epoxy resin: curing agent = 1:1. Compared with control groups 1 and 2, the modified epoxy system with the cement base demonstrated a 149 % increase in average pull-off strength and an 18 % increase in average shear strength. Similarly, in comparison with control groups 1 and 2, the modified epoxy system with aggregates exhibited a 174 % increase in average pull-off strength and a 541 % increase in average shear strength. Based on the pull-off and shear test results, it was ultimately determined that the dosage of modified epoxy binder for HFST mixtures should be controlled at 1.0–1.2 kg/m2, and the dosage of aggregate should be controlled at 3.3–4.3 kg/m2. These findings provide valuable insights into optimizing HFST pavement compositions for improved performance and longevity.

Effect of interface laser texture on the bonding property of co-extruded laminate with dissimilar DP600/AA1060 alloys

Steel-aluminum laminates show promise in industrial manufacturing, yet their utilization is limited by unstable interface bonding. This study investigates the influence of laser texturing on the interface bonding properties of DP600/AA1060 obtained through co-extrusion. White-light interference profilometry (WLIP) and MATLAB algorithms are used to quantify different surfaces. A model is established to predict the shear load with different process angles. Furthermore, energy dispersive spectroscopy (EDS), scanning electron microscope (SEM) and X-ray diffraction (XRD) are utilized to examine the microstructure of interface fractures and DP600/AA1060 alloys. Notably, the laser texturing process (LTP) significantly enhances the interface bonding strength of the DP600/AA1060, yielding a 37% increase in maximum shear strength compared to the original sample. The prediction holds true for the process angle in the range of 0°–45° but failed between 45° and 90° due to the occurrence of tensile/compressive stress in the laser-textured area, leading to unstable bonding caused by oxides and alloy particles. However, the laser-textured surface of DP600 enhances mechanical interlocking and increases the number of micro-protrusions, thereby strengthening the interface bonding and improving the mechanical properties of co-extruded laminates.

Nano-engineered hierarchical natural fibre composites with localised cellulose nanocrystals and tailored interphase for improved mechanical properties

Natural fibre composites have been utilised in many applications such as automotive and buildings, thanks to their high specific properties and environmentally friendly nature. However, the incompatibility between hydrophilic natural fibres and hydrophobic polymer resins remains a longstanding issue in natural fibre composites. Inspired by nature's hierarchical structures and tailored functionalities, a nano-engineered hierarchical natural fibre composite has been developed in this study, utilising cellulose nanocrystals (CNCs) as localised nano-reinforcements at flax surfaces in a flax/bio-epoxy system. A simple and versatile spray coating technique was used to deposit CNCs on unmodified flax fibres, without using any chemical solvents. With the increased surface roughness and hence improved epoxy wetting on nano-engineered flax surfaces (3 wt% CNC loading), mechanical properties of the hierarchical composites have been significantly improved, with a 60 % increase in interlaminar shear strength, indicating an enhanced interfacial load transfer between flax and epoxy, alongside improved flexural modulus (14 %) and strength (23 %). This green approach without using any chemicals provides a scalable and sustainable way to develop tailored interfaces for natural fibre composites with enhanced resin wetting and mechanical properties.

Counter-intuitive mechanical performance variation in aged low-temperature interconnections in electronic packaging

Different from the conventional aging induced continuous mechanical performance deterioration in solder joints, a counter-intuitive “decrease-increase-decrease” variation in shear strength with a peak value 12 MPa higher than the initial state was captured in aged low-temperature BGA structure Cu/Sn–58Bi/Cu solder joints. The first decrease in shear strength was dominated by the coarsening of Sn and Bi phases. The following increase in shear strength was rooted in the concurrent Bi subgrain strengthening, solid solution strengthening of Bi element in Sn-rich phase and precipitation strengthening induced by the Bi-rich phase particles. The eventual decrease in shear strength was ascribed to severely deteriorated interface between the solder matrix and intermetallic compound layer being the weaker site in the long time aged solder joint. This aging induced strengthening phenomenon is inspiring in mechanical performance optimization and reliability elevation of SnBi-based solder joints for the coming chiplet and heterogeneous integration packaging.

Exploring engineering properties of sustainable multi‐grade concrete: Materials, structural, and environmental aspects

AbstractThrough experimental and theoretical studies, this research explores the materials, structural, and environmental aspects of multi‐grade concrete (MGC), a potentially sustainable structural concrete. The experimental part investigates the compressive, split cylinder, flexural, and shear strengths of MGC, essential parameters for the design of structural members composed of MGC. It also provides the relationships between various strengths. The compressive behavior is correlated with the cracking pattern and the confinement effect caused by the end platens. The theoretical study involves determining the carbon emissions (CEs) and modifying ASTM/ACI expressions for the flexural tensile strength (FTS) and shear capacity applicable to MGC. Three uni‐grade concretes (UGCs) with distinct materials, properties, and grades: grade 17 (G17), grade 25 (G25), and grade 30 (G30), were poured in layers of varied thicknesses to make two variants of MGC. Experimental investigations showed that the higher‐strength concrete (HSC) confined the lower‐strength concrete (LSC) part thus increasing the compressive strength. Replacing 50% of LSC with HSC led to an increase in compressive and shear strengths by 21% and 40%, respectively. The shear strength values of reinforced MGC beams observed experimentally are aligned with those obtained through the modified expressions developed by the authors. A trade‐off analysis among the strengths, CEs, and costs of UGC and MGC can aid in selecting MGC customized to specific requirements, thereby contributing to the development of sustainable structural concrete.

Research on low‐velocity impact damage of composites based on improved Chang–Chang criterion

AbstractConsidering the nonlinearity of shear in the mechanics of composite materials, the increase of shear strength when the substrate interface is compressed, and the shear of the matrix itself, the Chang–Chang criterion is improved. The improved Chang–Chang criterion was used to establish a progressive damage model of low‐velocity impact of composites. The low‐velocity impact process of T700/EM134 composite laminates in the energy range from 5 to 10 J was compared by physical tests and finite element simulations, and the calculated impact response curves and material damage were in good agreement with the test results, which proved that the model of the improved criterion was suitable for the damage prediction of low‐velocity impact of composite laminates.Highlight Consider various situations in composite material shearing. Improved based on the Chang–Chang criterion. Establishing a progressive damage model for low‐speed impacts. Comparison through physical experiments and finite element simulation. Prove that the improved criterion model is suitable for damage prediction.

Investigation of the mechanical and thermal properties of epoxy adhesives reinforced by carbon nanotubes and silicon dioxide nanoparticles in single-lap joints

In this study, the shear strength and thermal properties of the adhesively bonded joints were investigated of adhesives reinforced with nanoparticles using carbon fiber-reinforced composite materials. The diglycidyl ether bisphenol A (DGEBA) was used as the epoxy resin. Single lap joint tests of 1% wt. Multi-walled carbon nanotubes (MWCNT) and 3, 5, and 7% wt. silicon dioxide (SiO2) nanoparticle-reinforced mixed adhesives were performed according to ASTM D5868 standards. The shear strengths of the mixed adhesives obtained by mixing at different ratios were compared with the epoxy resin. Upon conducting an analysis of the shear strengths of nanomaterials, results indicate that the incorporation of 1CNT + 3SiO2 in the nanomaterials showed the greatest improvement, with a 46% increase in shear strength. 1CNT + 5SiO2, 1CNT, and 1CNT + 7SiO2 showed increases of 32%, 14%, and 5%, respectively. The results of a tensile test indicate that pure epoxy exhibited a tensile strength of 5953 N, 1CNT, and 3SiO2, while the epoxy composite demonstrated a significantly higher tensile strength of 8738 N, along with an elongation of 0.72 mm. In addition, the morphology of fractured surfaces was examined by scanning electron microscopy (SEM). To investigate damage mechanisms, such as bridging, crack blunting, and branching of nanoparticles were observed. Characterization of epoxy resin and mixed MWCNT + SiO2 nanoparticles reinforced adhesives were also performed using Fourier infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). Nanoparticles are settled between polymer chains, improving polymer chains’ motion and thermal properties.

Effects of amount and geometrical properties of steel fiber on shear behavior of high-strength concrete beams without shear reinforcement

This study aims to investigate the effects of the geometrical properties and volume content of steel fibers on the shear resistance of reinforced high-strength concrete (HSC) beams without stirrups. Hooked-end and twisted steel fibers with different aspect ratios ranging from 60 to 100 were used at volume fractions of 0.5%–1.0%. The shear strength of HSC beams without stirrups significantly increased due to the addition of steel fibers and by increasing their volume fraction by up to 1.0%, resulting in approximately 1.7 times higher shear resistance. A higher fiber aspect ratio was effective in improving the resistance to shear failure of HSC beams without stirrups and in enhancing beam deformability relative to the increase in shear strength. Using twisted steel fibers led to better shear resistance than hooked-end steel fibers, resulting in 1.11- and 3.34-times higher shear strength and ductility at the same fiber volume fraction on average. The shear strength of steel fiber-reinforced concrete (SFRC) beams was also predicted using eight different models. Narayanan's model most precisely predicted the shear strengths of reinforced SFRC beams without shear reinforcement, with an average vu,exp/vu,pred ratio of 1.16. The shear strength increased with the decrease in shear span-to-depth (a/d) ratio and the increase in the fiber factor. The contribution of steel fibers to shear strength was greater for deep beams than slender beams. The predicted shear strengths of deep beams and high-strength SFRC showed a significant deviation from the actual value and required careful consideration.

Push-Out Analysis on the Shear Performance of a New Type of Bellow-Sleeved Stud

For continuous steel–concrete composite girder bridges based on the post-combined method, the conventional rectangular group studs contribute to the isolation of the steel girder and the concrete slab before prestressing, leading to the majority of prestress forces being introduced to the concrete slab. However, rectangular-group stud holes cause the prestress forces to be unevenly distributed. In this study, a new type of bellow-sleeved stud (BSS) was developed to mitigate the weakening effects of rectangular group stud holes on the slab. A steel corrugated sleeve with a diameter of 60 mm was employed to cover the stud, which served as an internal formwork to prevent the concrete from bonding with the root of the stud. After prestressing was complete, the steel sleeve was filled with ultra-high-performance concrete (UHPC) to create a reliable combination between the concrete slab and the steel girder. To investigate the shear performance of this new type of connection, eight push-out test specimens were designed, and finite-element models were built. This study drew a comparison between the BSS and the ordinary headed stud (OHS). The research findings suggested that the BSS is subjected to less bending–shear coupling and offers a 4.5% increase in shear strength and a 31.9% increase in shear stiffness compared with the OHS. The study also analyzed the structural parameters influencing the shear performance of the BSS. It is found that the steel sleeve of the BSS has a negative effect on shear performance, but this can be mitigated by infusing high-strength material into the sleeve. Furthermore, the study examined the effect of construction quality on shear performance and suggested that sleeve deviation and grout leakage considerably reduced the shear performance of the BSS. Accordingly, strict control over the construction quality of the BSS is necessary.

Enhancing solid-liquid separation performance of copper tailings by regulating settling floc properties

The effective improvement of dewatering performance of fine tailings slurry is a common challenge in tailings disposal and mining environmental protection worldwide. Flocculation is a commonly used method for solid-liquid separation of tailings, and the properties and structure of tailings flocs play a key role in sedimentation and filtration performance. This study proposed to improve the dewatering efficiency of tailings by regulating the floc properties and structure through polycarboxylate ether/ester (PCE). It simultaneously enhanced dewatering speed and reduced filter cake moisture. Dewatering experiments results showed that the assistance of PCE increased the initial filtration rate (IFR) of tailings by approximately 60 % and reduced filter cake moisture by 4.16 %. Moreover, the increase of shear strength in the slurry had a detrimental effect on dewatering performance. The dynamic evolution process of flocs was studied using focused beam reflectance measurement (FBRM) technology. The results showed that the addition of PCE caused a significant increase in floc size and counts, while the structural strength and regrowth ability of flocs also improved. Floc density calculations and scanning electron microscope (SEM) observations revealed that PCE caused densification of flocs, with particles aggregating more compactly. Contact angle analysis indicated that the adsorption of PCE on particles surface weakened their hydrophilicity. This study could conduce to understand the mechanism of dewatering performance enhancement in solid-liquid separation.

Encapsulation of SiC/SiC cladding tubes with excellent mechanical performance and air tightness using a CaO-modified Y2O3–Al2O3–SiO2 glass

Currently, the encapsulation of SiC/SiC has been a key technical challenge limiting further application, and YAS-based glass offered a possible solution. In this paper, different CaO-doped Y2O3–Al2O3–SiO2 (YAS) glass solders were prepared and employed to join SiC/SiC. The joints were all structurally dense with the room temperature shear strengths higher than or equal to ∼51.7 MPa. Notably, joints containing 3.0 wt% CaO exhibited increased shear strength of ∼57.1 MPa, and the shear strength at 1200 °C was about 15.8 MPa in an air environment, meeting the requirements of the LOCA conditions. Optimal performance was achieved by using 3.0 % CaO-doped YAS glass to encapsulate SiC/SiC cladding, yielding a continuous, dense encapsulation region with predominantly small closed pores (≤1.0 mm3). Glass infiltration was found in both the end plug and cladding wall. The joints did not leak after 72h of holding pressure at 15 MPa, indicating their excellent air tightness.