Significant Loss Of Strength Research Articles

Enhancing magnesium oxalate cements with copper slag and silica fume

Magnesium oxalate cement is an alternative binder made by reacting dead-burned magnesia and oxalic acid salts. Dead-burned magnesia, which has a high carbon footprint, was replaced at different levels (25–100 %) with copper slag, as a source of iron and thus a reactive component, or silica fume, as an inert or low-reactivity component. The powder mixtures contained ∼25–35 % oxalate, by mass. Physical and mechanical properties were investigated as well as changes in the mineralogy and morphology of paste and mortar specimens. Replacement of up to 50 % of dead-burned magnesia yielded strong (> 30 MPa) and water-resistant mortars with extended setting times, for mixtures with lower oxalate content. Mixtures with higher oxalate content and those without any dead-burned magnesia suffered significant strength loss in water. When copper slag was used, humboldtine, an iron oxalate, formed instead of or in addition to glushinskite, the main reaction product of magnesium and oxalate ions. Silica fume did not yield any crystalline reaction products.

Influence of dislocation cells on hydrogen embrittlement in wrought and additively manufactured Inconel 718

Hydrogen embrittlement (HE) is a major issue for the mechanical integrity of high-strength alloys exposed to hydrogen-rich environments, with diffusion and trapping of hydrogen being critical phenomena. Here, the role of microstructure on hydrogen diffusion, trapping and embrittlement in additively manufactured (AM) and wrought Inconel 718 is compared, revealing the key role played by dislocation cells. Trapping behaviour in hydrogen-saturated alloys is analysed by thermal desorption spectroscopy and numerical simulations. A high density of hydrogen traps in cell walls, attributed to dense dislocations and Laves phases, are responsible for the local accumulation of hydrogen, causing significant loss in strength, and triggering cracking along dislocation cell walls. The influential role of dislocation cells alters fracture behaviour from intergranular in the wrought alloy to intragranular for the AM alloy, due to the large proportion of dislocation cells in AM alloys. In addition, the cellular network of dislocations accelerates hydrogen diffusion, enabling faster and deeper penetration of hydrogen in the AM alloy. These results indicate that the higher HE susceptibility of nickel superalloys is intrinsically associated with the interaction of hydrogen with dislocation walls.

Enhancing mechanical properties of dissimilar steel A-TIG weld joint by in-situ induction post-heating

An approach is proposed to enhance the mechanical properties (ductility and impact toughness) of dissimilar martensitic steel-austenitic stainless steel joint by ‘A-TIG welding with induction post-heating (A-TIG(I) welding)’. The A-TIG(I) welding mitigates the martensite formation and promotes the ferrite formation within the weld zone (WZ) by retarding the cooling rate (from 9.83 °C/s to 0.8 °C/s). Microstructural transformations enabled in achieving the improved ductility (44.9 %) without significant loss of strength (665.75 MPa). Overmatched impact toughness (103 ± 2) J of WZ was also obtained.

Effects of liquid accelerators on long-term mechanical strength development and microstructural changes of wet-mixed shotcrete

The significant long-term strength loss of shotcrete can greatly affect the safety and stability of underground shotcrete structures. Developing high-quality liquid accelerators remains an indispensable research direction and a viable approach to mitigate challenge. This study synthesizes three distinct kinds of liquid accelerators - alkali-free fluorine-free (GJ), alkali-free fluorine-containing (MJ), and low-alkaline (JJ) and investigates their effects on the long-term mechanical strength of wet-mixed shotcrete. Moreover, changes in the phase composition and microstructure of accelerated shotcrete were explored utilizing X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopy techniques to reveal underlying mechanisms. Results indicate that accelerated cement paste and mortar with a 6 wt% fixed dosage of liquid accelerators exceeded the prescribed basic performance indices (setting time and 28-day compressive strength ratio) for shotcrete applications. Among the accelerators, the alkali-free fluorine-containing type exhibited the most beneficial effect on long-term strength, attributed to increased C-(A)-S-H formation from added Al and Si into the system. Morphological and crystal composition changes in hydrate phases, notably the transformation of ettringite to AFm and additional formation of monosulfate and hemicarbonate, increased the solid volume, refined pore structure and reduced total porosity, thus enhancing long-term strength. This study offers valuable insights into the synthesis and optimization of main accelerator components to mitigate long-term strength loss in shotcrete for practical engineering applications.

Utilization of marine waste enteromorpha prolifera powder to prepare sustainable lightweight cementitious materials

This study innovatively used enteromorpha prolifera powder (EPP) to prepare lightweight cementitious materials. The effect of EPP on the physical properties, mechanical strengths, and microstructure of mortar was tested and discussed. The results indicated that the density and thermal conductivity of mortar were significantly reduced after adding EPP, but the water absorption and porosity were increased accordingly, resulting in a significant loss of mechanical strength. Surprisingly, the density and thermal conductivity of mortar incorporated with 8 % EPP was only 855.00 kg/m3 and 0.28 W/m•K (reduced by 57 % and 83 % respectively compared with plain mortar), and the 28 d compressive strength was still as high as 1.90 MPa. The results of thermogravimetric analysis and X-ray diffraction showed that as the EPP content increases, the Ca(OH)2 content decreases, and the CaCO3 content increases. This was due to the increase in porosity causing CO2 in the environment to enter the interior of the matrix. This study not only proposed new material for preparing sustainable lightweight cement mortar but also found a new way to utilize large amounts of waste enteromorpha prolifera resources.

Radiofrequency Echographic Multi Spectrometry (REMS) Technology for Bone Health Status Evaluation in Kidney Transplant Recipients.

Background: A significant loss in bone density and strength occurs during the post-renal-transplant period with higher susceptibility to fracture. The study aims to compare the performance of the Radiofrequency Echographic Multi Spectrometry (REMS) in the bone mineral density assessment with the conventional dual-energy X-ray absorptiometry (DXA) in a cohort of kidney transplant recipients (KTR). Methods: A cohort of 40 patients underwent both DXA and REMS examinations on the lumbar spine and/or proximal femur. The paired t-test was used to compare DXA and REMS measurements; the chi-square test was used to compare the prevalence of osteoporosis/osteopenia. The agreement between the two techniques was assessed through Spearman's correlation. Results: As expected, most KTR patients were osteopenic or osteoporotic with both REMS and DXA (86.5% and 81% for the femur; 88% and 65% for the lumbar spine p < 0.05). A modest correlation (r = 0.4, p < 0.01) was observed at the lumbar spine between the T-score measured by REMS and DXA. A strong correlation was defined between REMS and DXA in the femoral region (r = 0.7, p < 0.0001). Conclusions: The study demonstrates the exchangeability of the two techniques on the proximal femur in KTR and a higher diagnostic accuracy of REMS at the spine level than DXA.

Enhancing rubber concrete with supercritical fluid-assisted Nano-SiO2 embedding and high-temperature stirred waste rubber

Using waste rubber particles(WRP) to replace fine aggregates in producing rubber concrete promotes recycling and reduces natural sand consumption, which is crucial for sustainable resource use. Unfortunately, rubber's low rigidity and poor interface bonding with the concrete matrix cause a significant strength loss. Many have done surface treatments on the particles, yet these often result in low efficiency and insignificant strength increases. This paper introduces a novel approach: employing supercritical fluid (CO2) assisted shearing to embed nano-silica and high-temperature stirring for pre-treating rubber particles. This improves the rigidity, removes impurities, and enhances surface smoothness. Thermal Gravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy(FT-IR), Scanning Electron Microscope(SEM), and Energy-Dispersive X-ray Spectroscopy(EDS) tests on treated particles show SiO2 embedded inside, clean surfaces, and hard oxide film formation. Rubber concrete prepared using this shows obvious improvement in mechanical properties compared to untreated rubber particles, with 7-day and 28-day cubic compressive strengths increasing by 74.9 % and 54.8 %, respectively. These increases outperform most reported in the literature.

Electrochemical properties and corrosion induced mechanical degradation of biomedical Zn–Cu–Li alloy in simulated body fluid

The electrochemical behavior and corrosion induced mechanical degradation of biodegradable Zn–2Cu–0.03Li alloy were in detail investigated. The results indicated that the corrosion product film presented an increasing corrosion resistance, while the localized corrosion induced by microgalvanic effect was intensified. Corrosion pits, as the typical defect, acted as the crack initiation sites and accelerated the fracture process of the Zn–2Cu–0.03Li alloy. Accordingly, the fracture mode transformed from ductile to brittle failure. Significant loss in ultimate tensile strength and elongation of the alloys occurred due to strong stress concentration at corrosion pit, threatening the mechanical reliability after implantation.

Acid resistance of alkali-activated binders based on clays from phosphate mining by-products

This paper outlines the results of studying the resistance of alkali-activated materials (AAM), based on calcined yellow clay from phosphate mine by-products as a precursor, to an acid attack (with sulfuric and phosphoric acids, 5 %, pH ≈ 0,8–2). Calcined yellow clay (YC850) is used as the source of aluminosilicates, containing montmorillonite, dolomite, and quartz. The alkali-activation of such materials allows the determination of an adequate valorization way and evaluating their durability leads to defining the range of application. The residual compressive strengths were measured after 1, 2, and 4 weeks of immersion in those acids. The deterioration suffered by the paste specimens was examined using different techniques.The degree of deterioration differs from one acid to another; in sulfuric acid, the strengths decrease from 47 MPa to 10.6 MPa presenting 77.4 %. While in phosphoric acid, the decrease was about 36.2 % (30 MPa) after 28 days of attack. This detriment in the strengths is associated with changes not only in the microstructure but also with the alteration of the reaction products, mainly the binding gels C-A-S-H and (C,N)-A-S-H, which undergoes dealumination and decalcification. What is more, the chemical attack involves several reactions; calcium coming from the precursor reacts with the sulfates (in the H2SO4 attack) inducing the precipitation of gypsum, which is responsible for the significant strength loss. In addition, the dissolution of crystalline minerals, such as periclase and gehlenite (present in the precursor) generates higher porosity explaining the obtained results.

Assessment of function and muscle strength after endoscopic iliopsoas tenotomy to treat iliopsoas impingement after total hip arthroplasty.

The objective of this study was to evaluate the functional outcome during follow-up (FU) after endoscopic tenotomy for iliopsoas (IP)-cup impingement and to quantitatively analyze the hip flexion strength. This was a monocentric, retrospective cohort study of a single surgeon series. Functional assessment was based on the modified Harris score, the Oxford score and the visual analog scale score. Strength was measured with a handheld dynamometer in the sitting and lying position. Thirty-six IP tenotomies for cup impingement were performed between May 2013 and November 2021. Seven (19%) patients were lost to FU. At the time of tenotomy, the mean (standard deviation) age was 62,6 (12,2) and BMI was 26,5 (4,1). The mean FU time after tenotomy to the last FU was 3,6 (0,8) years. All three outcome scores improved from preoperatively to six months postoperatively (p < 0.001). There were no significant change from six months to last FU. The minimal clinically important difference (MCID) of the modified Harris score was set at 25. 20 (69%) patients had values that exceeded the threshold at one month and six months and neutral 19 (65.5%) had values that exceeded the threshold at the last FU. The limp symmetry index concerning hip flexion strength was 63% at 90° and 40% at 30° at the last FU. Most patients significantly improved their outcome scores after endoscopic iliopsoas tenotomy, with results remaining consistently stable over time. Despite a significant loss in hip flexion strength, the majority of patients did not report any impairment of their quality of life. Level III, Retrospective cohort study.

Erosion mechanism of low-alloy steel at simulated conditions for artillery firing environment

To investigate erosion mechanism as exposed to extreme interior ballistic environment within artillery barrels, a specially designed testing apparatus has been utilised to perform simulated erosion testing at stress-temperature regimes close to practical working conditions. Detailed metallographic examination after testing at 600°C with a contact force of 9000 N has identified erosion mechanisms involved with adhesive and oxidative wear with the formation of an ultra-fined grain layer in subsurface regions. The erosion mechanism during testing at 1000°C is associated with a significant loss of strength for the matrix due to austenitisation and rapid formation of porous oxides. The approach utilised in the present study has facilitated an evaluation of erosion resistance of barrel materials with high efficiency and low cost.

Strength-Plasticity Relationship and Intragranular Nanophase Distribution of Hybrid (GNS + SiCnp)/Al Composites Based on Heat Treatment.

The distribution of reinforcements and interfacial bonding state with the metal matrix are crucial factors in achieving excellent comprehensive mechanical properties for aluminum (Al) matrix composites. Normally, after heat treatment, graphene nanosheets (GNSs)/Al composites experience a significant loss of strength. Here, better performance of GNS/Al was explored with a hybrid strategy by introducing 0.9 vol.% silicon carbide nanoparticles (SiCnp) into the composite. Pre-ball milling of Al powders and 0.9 vol.% SiCnp gained Al flakes that provided a large dispersion area for 3.0 vol.% GNS during the shift speed ball milling process, leading to uniformly dispersed GNS for both as-sintered and as-extruded (0.9 vol.% SiCnp + 3.0 vol.% GNS)/Al. High-temperature heat treatment at 600 °C for 60 min was performed on the as-extruded composite, giving rise to intragranular distribution of SiCnp due to recrystallization and grain growth of the Al matrix. Meanwhile, nanoscale Al4C3, which can act as an additional reinforcing nanoparticle, was generated because of an appropriate interfacial reaction between GNS and Al. The intragranular distribution of both nanoparticles improves the Al matrix continuity of composites and plays a key role in ensuring the plasticity of composites. As a result, the work hardening ability of the heat-treated hybrid (0.9 vol.% SiCnp + 3.0 vol.% GNS)/Al composite was well improved, and the tensile elongation increased by 42.7% with little loss of the strength. The present work provides a new strategy in achieving coordination on strength-plasticity of Al matrix composites.

High-Performance Dopamine-Based Supramolecular Bio-Adhesives.

The need for wound closure or surgical procedures has been commonly met by the application of sutures. Unfortunately, these are often invasive or subject to contamination. Alternative solutions are offered by surgical adhesives that can be applied and set without major disruption; a new class of supramolecular-based adhesives provides potential solutions to some of these challenges. In this study, a series of polymers utilizing dopamine as a self-assembling unit are synthesized. It is found that these motifs act as extremely effective adhesives, with control over the mechanical strength of the adhesion and materials' tensile properties enabled by changing monomer feed ratios and levels of cross-linking. These materials significantly outperform commercially available bio-adhesives, showing yield strengths after adhesion at least two times higher than that of BioGlue and Tisseel, as well as the ability to re-adhere with significant recovery of adhesion strength. Promisingly, the materials are shown to be non-cytotoxic, with cell viability > 90%, and able to perform in aqueous environments without significant loss in strength. Finally, the removal of the materials, is possible using benign organic solvents such as ethanol. These properties all demonstrate the effectiveness of the materials as potential bio-adhesives, with potential advantages for use in surgery.

Acidification in cement paste in which clinker is partially replaced with limestone or silica

This paper examines the acid resistance of cement pastes where a portion of the cement clinker is replaced with limestone (LS or calcium carbonate, CaCO3) or ground silica (GS). Specifically, the work is intended to better understand the acid resistance of ASTM C595 IL cement as compared with ASTM C150 cement. The performance of OPC, OPC + GS, and OPC + LS systems were tested in sulfuric acid baths where the pH was held constant at 2.0 and 3.0 using an automated setup that uses titration to add acid. The degradation of the cement paste was measured as a function of time. Thermogravimetric analysis (TGA) was used to quantify changes in the calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3) contents of the paste. In addition, the flexural strength of the cement paste specimens was measured. Results indicate that the dissolved sulfate and calcium concentrations due to acidification were not noticeably different for the OPC + GS and OPC + LS mixtures exposed to the same pH. However, as expected, differences were observed between the samples immersed in the solution of pH∼2 and pH∼3 sulfuric acid with the lower pH corresponding to more severe deterioration. TGA results showed that Ca(OH)2 is more susceptible to acid attack than limestone as evidenced by the larger Ca(OH)2 and sulfuric acid consumption in samples immersed at pH∼2. The additional acid consumption that is beyond the consumption of Ca(OH)2 can be explained by the acid attack of other hydration products such as CSH and unreacted cement phases. This results in a significant B3B flexural strength loss for the samples immersed in a pH∼2 as compared to those in the pH∼3 solution. The results demonstrated that the performance of ASTM C595 IL cements was promising and comparable with ASTM C150 cements.

Fractional Lengthening of Forearm Flexor Tendons: A Cadaveric Biomechanical Analysis

Multiple procedures have been described for wrist and finger flexion contractures and spasticity. Fractional lengthening of forearm flexor tendons involves making parallel transverse tenotomies at the musculotendinous junction to elongate the muscle. Currently, there is limited literature to define the biomechanical consequences of this lengthening technique. Forty-eight flexor tendons were harvested from eight paired upper limbs including flexor carpi radialis, flexor carpi ulnaris, flexor pollicis longus, and flexor digitorum superficialis tendons. Each tendon that was lengthened was paired with the contralateral tendon as a control. A pair of transverse tenotomies were completed for the fractional lengthening. The first tenotomy was performed at the musculotendinous junction where the tendon narrowed to 75% of its maximal width. The second tenotomy was made 1 cm distal to the first. Tendon length was measured before and after fractional lengthening at a constant resting tension of 1 N. The maximum load at failure of each tendon and the mechanism of failure were each measured and compared with the contralateral side. After fractional lengthening, the mean increase in resting tendon length was 4 mm. When loaded to failure, the mean maximum load of fractionally lengthened tendons was 42% of the mean maximum load of intact tendons. All lengthened tendons failed at the distal tenotomy site. Fractional lengthening resulted in an increase of 3-6 mm (mean: 4 mm) in tendon length at resting tension. There was a significant loss in tensile strength and load to failure following fractional lengthening compared with an intact musculotendinous unit. The reduction in tensile strength following fractional lengthening results in loads at failure that are, in some cases, lower than the estimated forces required to perform basic tasks. Caution during the healing and rehabilitation period is warranted.

Mitigating autogenous shrinkage of cement with carbon nanotube sponge

Autogenous shrinkage can be mitigated by the addition of superabsorbent polymer (SAP), however, typically at the cost of a significant strength loss. To overcome such dilemma, hydrophilic carbon nanotube sponge (H-CNTSP) was proposed in this study as a novel internal curing agent. Due to the high porosity and enriched hydrophilic functional groups, H-CNTSP can absorb pore solution at 72 g/g driven by the capillary force, which is 176%–620 % higher than the commercial SAPs. The autogenous shrinkage of cement can be reduced or mitigated with the addition of 0.05–0.2 wt% H-CNTSP due to the continuous water release after final setting. Interestingly, the compressive strength loss resulting from the addition of H-CNTSP can be greatly diminished and even be overcompensated by the formation of CNT/hydrate nanocomposite shell with a higher modulus. This study illustrates the great potential to optimize concrete performance through proper design of assembly structures with chemically functionalized nanomaterials.

The long-term leaching behavior of heavy metals in geopolymers and Portland cement bricks containing MSWI fly ash: A comparative study

Geopolymers was considered as an ideal alternative to cement solidification/stabilization for municipal solid waste incineration fly ash (MSWI FA). However, the long-term leaching behavior of heavy metals in geopolymers had attracted less attention. In this study, the long-term leaching behavior of heavy metals in geopolymers containing MSWI FA was investigated and compared with Portland cement bricks under various corrosion scenarios. The findings revealed a consistent trend of "slowly increasing - slowly decreasing - gradually stabilizing" in the pH changes in the effluent of all samples and the absence of corrosive risk in the utilization of geopolymers. The maximum pH values of the effluent were G2 (12.00) > G1 (11.90) > G3 (10.83) > C1 (9.67), suggesting that geopolymers were not corrosive in resource utilization. The long-term leaching behavior of heavy metals under different corrosion conditions could be divided into two stages, which included quick release in stage Ⅰ and gradual stabilization in stage Ⅱ. Compared with Portland cement bricks, the cumulative leaching concentration of heavy metals in geopolymers was lower, indicating less environmental risk. Due to the strongest corrosiveness from simulated acid rain (SAR), C2 and G2 exhibited significant compressive strength loss rates of 20.2% and 9.25%, respectively. In the leaching of CO2-saturated water (CSW), the leaching behavior of heavy metals was mainly regulated by the nucleation-dissolution trade-off of carbonates, however the dissolution mechanism of heavy metals in SAR could be summarized as follows: (1) corrosion/replacement of H+, and (2) counter-ion effect. this study will promote the resource utilization of MSWI FA. In a word, this work systematically studied the long-term environmental risk of geopolymers, which was beneficial to the resource utilization of MSWI FA.

Shear Strength and Durability of Expansive Soil Treated with Recycled Gypsum and Rice Husk Ash

Expansive soil underlying structures pose a significant risk to the integrity of superstructures. Chemical soil stabilization can be used to strengthen soils due to the cost and impracticality of mechanical approaches. Waste materials such as recycled gypsum and rice husk ash have been considered alternatives because of their sustainable and economic advantages. A combination of these additives was used to address the high absorption of gypsum and the lack of cohesion of the pozzolan. The study assessed the short-term and long-term performance of expansive soil treated with recycled gypsum and rice husk ash under normal and fluctuating moisture conditions. Direct shear tests indicated ductile and compressive soil behavior with improved shear strength. A good approximation of stress–strain response was made with a modified hyperbolic model for treated soils that exhibited strain hardening and compressive volumetric strain. Durability and water immersion tests were performed for samples after varying curing periods and cycles of capillary soaking to assess the behavior when exposed to varied environmental conditions. Samples under the modified durability test experienced significant strength loss, with decreasing compressive strength as curing durations increased. Specimens in the modified water immersion test experienced significant strength loss; however, it was determined that curing durations did not contribute to the change in the strength of the sample. Expansion index tests also determined that the treatment effectively mitigated expansivity and collapsibility in all samples. Despite improvement in shear strength and expansion potential, further investigation is needed to enhance the durability of soil treated with gypsum and rice husk ash.

Degradation of molecular structure and residual strength of polycarbonate under cyclic loading: Insights from coarse-grained molecular dynamics simulation

Coarse-grained molecular dynamics simulations have been employed to provide insights into the molecular behavior and degradation of monodisperse polycarbonate subjected to cyclic loading with varying molecular structures characterized by two distinct parameters: radius of gyration and molecular entanglement. The fatigued polycarbonate structures were subjected to monotonic deformation in order to assess their residual strength. Our findings reveal that structures characterized by a higher degree of molecular entanglement exhibit a more significant loss of residual strength, attributable to the disentanglement induced by cyclic deformation. Furthermore, an increase in the radius of gyration contributes to greater resilience against cyclic loading, resulting in a higher level of residual strength compared to the impact of molecular entanglement.

Form Check: Exercise Posture Correction Application

Weightlifting is a popular sport and a hobby of millions; however, the risk of injury is high, primarily when performed with incorrect form/posture due to voluntary or involuntary reasons. It results in a significant loss of strength and hinders progress. The gradual strain on tendons and ligaments causes wear and tear. This paper aims to develop a deep learning model that detects incorrect posture and provides insight into remedial steps that need to be taken to correct the same, thereby providing increased safety and efficiency. Our Form Check model detects a user's form, vector geometry of posture is evaluated and corrected. A graphical representation of the exercise is provided as feedback to the user. Object detection, pose estimation, and action recognition algorithms infer the human skeleton and recognize the exercise. The inconsistency in the exercise performed is determined and mapped to specific imperfections in the stance of users during the exercise through Graph