Structural Strength Research Articles

A core-shell microneedle system for stable fibroblast delivery in cell-based therapies.

Human cells, such as fibroblasts and particularly human mesenchymal stem cells (hMSCs), represent a promising and effective therapeutic tool for a range of cell-based therapies used to treat various diseases. The effective delivery of therapeutic cells remains a challenge due to limitations in targeting, invasiveness, and cell viability. To address these challenges, we developed a microneedle (MN) system for minimally invasive cell delivery with high cellular stability. The MN system comprises a core of gelatin methacryloyl (GelMA) hydrogel embedded with fibroblasts, encased in a polylactic-co-glycolic acid (PLGA) shell that enhances structural integrity for efficient skin penetration. The fabrication process involves UV-crosslinking of the GelMA hydrogel with cells, optimizing both cell encapsulation and structural strength. This MN system achieves over 80% cell viability after seven days in vitro, with the conventional GelMA formulation providing superior stability and cellular outcomes. This platform's ability to ensure sustained cell viability presents promising implications for future applications in regenerative medicine, wound healing, and localized treatments for skin conditions. This MN system opens new avenues for cell-based therapies, offering a versatile and scalable solution for therapeutic cell delivery.

Detection of Stress Corrosion Cracking in SS304 under Calcium Silicate Thermal Insulation Using Acoustic Emission Technique

Despite its remarkable structural strength, austenitic stainless steels such as SS304 are susceptible to stress corrosion cracking (SCC) under thermal insulation due to the synergism of cyclic loading and chloride-containing environments. This study aims to detect SCC for insulated SS304 samples using the acoustic emission technique (AET) as monitoring tool to characterize the various stages of SCC damage mechanism. As-received (AR) and sensitized (SEN) SS304 samples were prepared as per ASTM G30 and experimented with soluble chloride drip test under calcium silicate thermal insulation following ASTM C692. Both AR and SEN samples revealed SCC behavior correlated with measured acoustic signals. AR samples exhibited a single crack with low energetic signals, whereas SEN showed multiple cracks with higher energetic signal events. The difference can be attributed to microstructure change by heat sensitization and the enhancement of the corrosion environment under calcium silicate insulation when wetted by salt solution. The acoustic emission (AE) parameters were characterized and correlated with different stages of SCC phenomena, showing that AET is useful for predicting SCC to avoid catastrophic failures in industries.

Inflammatory immune response and its key roles in the process of bone fractures healing

Bone fractures, which represent 2% - 5% of adults annually, are considered a significant health concern, particularly as their incidence has recently increased. Bones are composed of minerals such as calcium and phosphate, and organic components like type I collagen, provide structural integrity and strength. The periosteum plays a vital role in bone healing, with children's thicker periosteum contributing to faster recovery compared to adults. This review emphasizes the critical role of the immune system in bone fracture healing, highlighting the inflammatory response as a key factor in bone healing. Immediately after the occurrence of a fracture, immune cells are recruited to the site of the fracture, initiating a cascade of healing processes that include angiogenesis and tissue repair scenarios. The healing process is classified into primary and secondary healing, each with distinct mechanisms. Factors influencing healing include fracture location, patient age, physical activity levels, medical conditions, medication use, smoking, and the biomechanical environment. The healing phases—inflammatory, repair, and remodeling—are regulated by the immune cells, particularly macrophages and T-cells, which can either facilitate or hinder recovery. Understanding the immune response is essential to developing effective therapeutic strategies for the healing of the bone structures.

Threshold for oscillatory-flow ripple initiation on cohesive and non-cohesive mixtures of sand and mud

ABSTRACT The threshold hydraulic condition of wave ripple initiation has been essential in a wide range of disciplines, including coastal engineering and geology, but remains unclear for the case of sand-mud mixtures as substrates. Scale experiments were conducted using an oscillating-bed to study wave ripple initiation in sand-mud mixtures, considering bed material, wave period and maximum orbital velocity. Four kinds of sand-mud mixtures were employed as bed material with different muds (cohesive kaolin and non-cohesive silt) and mixing ratios. Ripple initiation in the cases with sand-mud mixtures tended to require larger orbital velocity than pure sand, indicating that mud mixed in bed material hinders ripple formation and spreading of the ripple field. The results of the threshold for pure sand and 10% kaolin mixture show that cohesive mixed sand-mud hindered ripple formation and spreading. In contrast, in the case of the non-cohesive sand-silt mixture beds, the results differed depending on the proportion of sand and silt, which implied the effect of the strength of network structure. The inhibition of ripple initiation due to mud mixing observed in the present experiments is considered to have a significant effect, particularly in environments with limited wave action duration, such as intertidal zone.

Smart Concrete Using Optical Sensors Based on Bragg Gratings Embedded in a Cementitious Mixture: Cure Monitoring and Beam Test

Smart concrete is a structural element that can combine both sensing and structural capabilities. In addition, smart concrete can monitor the curing of concrete, positively impacting design and construction approaches. In concrete, if the curing process is not well developed, the structural element may develop cracks in this early stage due to shrinkage, decreasing structural mechanical strength. In this paper, a system of measurement using fiber Bragg grating (FBG) sensors for monitoring the curing of concrete was developed to evaluate autogenous shrinkage strain, temperature, and relative humidity (RH) in a single system. Furthermore, K-type thermocouples were used as reference temperature sensors. The results presented maximum autogenous shrinkage strains of 213.64 με, 125.44 με, and 173.33 με for FBG4, FBG5, and FBG6, respectively. Regarding humidity, the measured maximum relative humidity was 98.20 %RH, which was reached before 10 h. In this case, the recorded maximum temperature was 63.65 °C and 61.85 °C by FBG2 and the thermocouple, respectively. Subsequently, the concrete specimen with the FBG strain sensor embedded underwent a bend test simulating beam behavior. The measurement system can transform a simple structure like a beam into a smart concrete structure, in which the FBG sensors’ signal was maintained by the entire applied load cycles and compared with FBG strain sensors superficially positioned. In this test, the maximum strain measurements were 85.65 με, 123.71 με, and 56.38 με on FBG7, FBG8, and FBG3, respectively, with FBG3 also monitoring autogenous shrinkage strain. Therefore, the results confirm that the proposed system of measurement can monitor the cited parameters throughout the entire process of curing concrete.

Chemically Crosslinked Alginate Hydrogel with Polyaziridine: Effects on Physicochemical Properties and Promising Applications.

Alginate biopolymer is widely employed in many industrial fields thanks to its pleasing features of biodegradability, biocompatibility, low toxicity, and relatively low cost. The gelling process of alginate with divalent cations is fairly simple and thus it is used as a versatile biomaterial to tailor the desired mechanical and moisture properties. This study focused on developing new gel formulations to enhance the properties of calcium-alginate hydrogel (CA). The newly synthesized hydrogels, referred to as CA-CHEM gels, were chemically cross-linked with different ratios of pentaerythritol tris[3-(1-aziridinyl)propionate] (PTAP) through the reaction between the carboxylic groups of alginate and aziridines of PTAP. The reaction was successfully monitored by NMR. The new CA-CHEM gels were chemically characterized using FTIR-ATR, while SEM analysis confirmed the changes in the porosity and homogeneity of the network. Additionally, thermogravimetric analyses and mechanical properties showed improvement in degradation stability and in structural strength, compared to plain CA, with an increasing PTAP content up to 1% w/w. Finally, the new CA-CHEM gels effectively controlled water absorption and release. In particular, CA-CHEM-1 performed as the most controlled system, making it promising for delivering aqueous cleaning solutions on water-sensitive surfaces such as a wooden historical musical instrument.

PENERAPAN TEKNOLOGI DRYING DENGAN GREEN HOUSE EFFECT UNTUK PENINGKATAN EFISIENSI PRODUKSI DAUR ULANG PLASTIK PADA DR PLASTIK GUNUNGKIDUL

DR Plastik is a creative industry in the field of plastic recycling located in Putat Village, Patuk District, Gunungkidul. The number of employees at DR Plastik is 25 people, both as waste sorters, shredding machine operators, washers and administrators. The production capacity of recycled plastic waste is ± 2 tons/day. The plastic waste is processed in the form of dry plastic shreds and resold. Current conditions, the drying process at DR Plastik still takes 2-3 days manually (during the rainy season). This condition makes production run ineffectively and causes product quality to decrease due to uneven drying. The aim of the program is to create drying room technology with a green house effect. This program involves several stages such as coordination with DR Plastik partners regarding the drying room area, procurement of materials and tools, manufacturing a drying room with green house effect, training, and monitoring and evaluation. The result of implementing the program is a drying room with a green house effect measuring 6x10 m2 with a transparent galvalum roof. Galvalum has advantages in terms of resistance to impact, high structural strength, and has good heat absorption capacity, so that the temperature in the building remains comfortable. Apart from that, the production of rainwater channels is centralized in the production process, so that the dried plastic is safe from rainwater. This program shows a significant increase in employee knowledge and skills regarding the use of drying rooms. Apart from that, the drying process has become more effective and efficient from 2-3 days (during the rainy season) to 1 day (during the rainy season) and the production of dry plastic shreds ready for sale has increased by 75%.

Expandable Microspheres Transform 2D Electrospun Mats Into 3D Composite Scaffolds.

Electrospun nanofibers have proven versatile across numerous fields, including environmental, energy, and biomedical applications. Typically, however, electrospun nanofiber materials are fabricated as two-dimensionalsheets, membranes, or mats. In this study, a straightforward and adaptable foaming method is presented to create three-dimensionalmicrosphere-nanofiber composite structures. This approach involves incorporating expandable microspheres within the nanofiber mats during electrospinning, followed by thermal treatment to achieve the 3D morphology. The expansion ratio and compressive strength increase with higher concentrations of expandable microspheres. In addition, the compressive strength of the 3D composite structures significantly surpasses that of 3D nanofiber scaffolds expanded with subcritical CO2 fluids. This approach presents a promising pathway for fabricating 3D microsphere-nanofiber composite scaffolds with broad potential applications.

Quantitative characterization of damage and the cross-scale evolution mechanism of soft rock under dry-wet cycles

Soft rock undergoes internal structural redistribution and random damage under the action of dry–wet cycles, with these processes ultimately affecting its mechanical properties. In order to analyze the evolution mechanism of mineral composition inside soft rocks, an effective method for the characterization of the nonlinear damage of soft rock using a multifractal spectrum is presented. Moreover, a cross-scale correlation model of internal structural changes and strength degradation is established. Based on scanning electron microscopy (SEM) images of soft rock subjected to a varying number of dry–wet cycles, the damage propagation path was tracked via a rock-like compression failure test. The study results indicate that soft rock exhibits a random fractal damage effect under the action of dry–wet cycles. As the number of cycles increases, the multifractal spectrum becomes more asymmetric and the discretization degree becomes more uneven. The soft rock exhibits cross-scale evolution characteristics from mesostructural to macroscopic damage after encountering water. After a series of reactions between water and soft rock, the bonding between particles weakens and recombines, ultimately affecting the mechanical properties of the soft rock. The research results have enriched the research framework of soft rock failure mechanisms, and provided an effective method for quantitatively characterizing the correlation analysis between soft rock damage and damage at different scales.

Research on alloying the Cu-Ni-Sn system equivalent to grade C72500 in vacuum induction furnace

In this article, research on smelting technology of elastomeric copper alloy of Cu-Ni-Sn system grade C72500 in vacuum induction furnace and some results of studying the structure and mechanical properties of C72500 alloy were shown. The C72500 alloy was smelted in a vacuum medium frequency furnace with a small burning rate and high cleanliness. Some methods to evaluate by determining structure, mechanical properties as: EDX spectroscopy analyzes element content, Optical microscope equipment to determine microscopic structure, ultrasonic equipment to evaluate defects and equipment to test mechanical properties. The after-casting alloy has a chemical composition and mechanical properties equivalent to imported copper alloys according to ASTM B122/B122M-20 standards, single α phase structure, good ductility but low strength, elongation 62.2%, tensile limit 301.43 MPa, yield limit 171 MPa and hardness distributed along the sample, high on the outside (82.4 HV) and low in the center (73.4 HV), is used in manufacturing elastic, abrasion and corrosion resistant parts.

Energy harvesting of a metamaterial beam with acoustic black holes

Abstract This paper proposed an improved metamaterial piezoelectric beam with the acoustic black holes (ABHs) for low-frequency energy harvesting. The ABHs are embedded in the local resonant beams distributed on both sides of the primary beam. Piezoelectric plates are attached to the ABHs, leveraging the energy-focusing effect to enhance the energy harvesting performance. Finite element simulation results indicate that the energy harvesting electrical energy has improved by 6.92 times compared to the traditional metamaterial resonant beam without ABHs. Parameter analysis indicates that increasing the number of local resonators and extending the length of the piezoelectric patches can further enhance energy harvesting performance. However, reducing the truncation thickness of the ABH boosts energy harvesting but compromises structural strength. Extending the ABH length and increasing load resistance within the appropriate range are conducive to energy harvesting. Besides, the optimal load resistance varies with frequency. These findings provide useful guidance for future applications of improved metamaterial beam.

Investigating the Compressive Strength of Clay Brick Masonry: A Case Study of Nangarhar, Afghanistan

In Afghanistan, masonry structures using burnt clay bricks have long been used for public and private buildings. However, still, there is no standard for masonry structural design based on local material properties. This study investigated the compressive strength of clay brick masonry prisms in Nangarhar, Afghanistan, through experimental testing and finite element modeling (FEM). Three brick classes, with compressive strengths between 8 and 14 MPa, were used to construct prism specimens. The research aimed to propose specific values for masonry compressive strength using local materials and examine the effects of brick strength (fb), mortar strength (fj), joint thickness (tj), and slenderness ratio (h/t) on masonry compressive strength (fm). Test results showed fm values of 17.2 MPa for first-class, 10.0 MPa for second-class, and 7.6 MPa for third-class brick masonry, indicating the influence of the brick’s quality. Key findings showed that an increase in fb causes an equal increase in fm, a 5% increase in fj leads to a 1% increase in fm, a 5 mm increase in tj gives an 8% fm increase, and a 5.5% increase in h/t results in a 1% decrease in fm. The research provides valuable information for evaluating the compressive strength of masonry structures based on the quality of local materials, which can be used to revise Chapter 7 of the Afghanistan Building Code, 2012.

Shear Failure Assessment of a G+3 RC Framed Building via Nonlinear Static Pushover Analysis using SAP2000

Accurately modelling shear behaviour in reinforced concrete (RC) structures is essential for seismic evaluation, as shear failure can lead to catastrophic outcomes. Current industry practices often emphasize nonlinear flexural analysis while underestimating the critical role of shear behaviour. This study aims to develop a nonlinear force-deformation model specifically for shear in RC sections to bridge the gap in existing literature. Standards like IS-456:2000 and ACI-318:2008 provide ultimate strength estimates but may inadequately consider the contribution of concrete under seismic loads. Insights from models by Priestley et al. (1996) and Park and Pauley (1975) are integrated to improve the calculation of shear hinge properties. A comparative nonlinear static (pushover) analysis of an RC framed building, with and without shear hinges, demonstrates the impact of shear modelling. Results show that neglecting shear hinges overestimates base shear and roof displacement capacity, masking non-ductile failure modes. Incorporating shear hinges provides a more realistic assessment of structural strength and ductility, emphasizing their necessity in seismic analysis and design. Keywords: Shear behaviour, Reinforced concrete (RC) structures, Seismic evaluation, Shear failure, Nonlinear analysis, Force-deformation model, Shear hinge.

Structural Performance of Sisal Fiber Mat Retrofits for Post-Fire Damaged Reinforced Concrete Beams

Concrete experiences degradation in mechanical properties when exposed to high temperatures, leading to spalling, disintegration, and surface damage. Research shows a 26-40% reduction in structure strength under fire. While strengthening and restoring existing structures is a practical solution, a more sustainable approach is needed. This study evaluated the performance of sisal fiber mat retrofits for post-fire damaged beams and investigated natural fiber retrofits as a sustainable solution for fire-damaged structures, addressing challenges like elevated temperatures and moisture sensitivity to restore safety, stability, and functionality. The physical, chemical, and mechanical properties of the constituent materials used to fabricate the reinforced concrete beams and retrofitted material were characterized. The mechanical properties of 150×225×650 mm reinforced concrete beams exposed to 800 °C for 1 hour were assessed. The load-carrying capacity of the concrete beam was determined after it had been repaired with one or two layers of sisal fiber mat. The results indicated that the load-carrying capacity of concrete reinforced beams exposed to fire was reduced by 13.03%. However, the use of two layers of sisal fiber mat retrofits in the beams restored the load-carrying capacity by 33.86% and improved ductility by 43.56%. These findings demonstrate the feasibility of using sisal fiber mat retrofits to repair fire-damaged reinforced concrete beams, as the fiber mat enhances the load-carrying capacity by providing additional tensile strength to the structure.

Enhancing the Mechanical and Fire-Resistant Properties of GFRP Composite using Boric Acid and Sodium Silicate Fillers

This study investigates the effects of Boric Acid (BA) , H3BO3, and Sodium Silicate (SS), Na2SiO3, as single fillers on the mechanical and fire-resistant properties of Glass Fiber Reinforced Polymer (GFRP) composites. Various compositions of BA and SS were incorporated into the GFRP matrix, and the resulting composites were analyzed using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo-Gravimetric Analysis (TGA), and Differential Thermal Analysis (DTA). The results demonstrate that BA significantly enhances the amorphous structure and mechanical strength of GFRP composites, with optimal performance at 10% BA content. In contrast, SS improves thermal stability but reduces mechanical strength at higher concentrations due to agglomeration. Fire resistance testing revealed that both fillers increase the ignition time and decrease the burning rate, with BA exhibiting superior performance. These findings suggest that BA is a more effective filler for improving the mechanical and fire-resistant properties of GFRP composites, while SS can serve as a complementary additive to enhance thermal stability.

Effect of double-layer formwork curing on the early temperature field and properties of precast concrete components in environments with large diurnal temperature variations

An efficient double-layer formwork curing method using an “inner supporting formwork + outer insulation formwork” was proposed in this study to address the early cracking of precast concrete components in high altitude regions. Steel and plywood formwork were designed as inner support formwork, while polystyrene (PS) and polyurethane (PU) were used as outer insulation formwork. Indoor experiments and two finite element methods (The complete simulation method focuses on computational accuracy, and the equivalent simulation method emphasizes computational efficiency) were employed to analyze the evolution of the concrete temperature field under different double-layer formwork curing methods throughout the curing period, combined with compressive strength and pore structures testing. The results show that steel + 5-mm-thick PU insulation formwork curing method can significantly mitigate the impact of large diurnal temperature variations on the internal temperature of concrete. Unlike traditional steam-curing, this method does not deteriorate the pore structure or compressive strength of the concrete. This study is of great significance in addressing the problem of early cracking of precast concrete components exposed to large diurnal temperature vriations in high altitude regions.

The Characteristics of Resin Waste (RW)/Recycled High-Density Polyethylene (R-HDPE) Blends to Enhanced Pavement

Permeable pavement is characterized by open cell structures that enable the drainage of rainfall and snowmelt, as opposed to the runoff observed on impervious pavements. The structural strength of commercial permeable pavement materials is lower than that of conventional pavements due to inherent permeability and structural distinctions. This research focuses on the fabrication of samples using a combination of Resin Waste (RW) and reinforced Recycled High-Density Polyethylene (R-HDPE) in varying ratios of RW (30%, 40%, 50%, 60% and 70% wt/wt). The fabrication process involves a 3-hour heating process at 200°C in a furnace, followed by a 24-hour cure at room temperature. Physical and mechanical properties of the RW/R-HDPE Blends were examined, revealing that the 60% R-HDPE ratio resulted in the lowest density (4.523 g/cm3) and porosity (0.246%). SEM images displayed fewer voids, indicating effective filler dispersion and resin matrix interaction at the 60% resin waste ratio. Tensile strength and stiffness elasticity were maximized at 60% wt/wt of R-HDPE, reaching 3.36 MPa, while the bending strength peaked at 1.1 MPa at the same ratio. The 60% RW/R-HDPE ratio recorded the highest impact strength (26.25 kJ/m2) and energy absorption (1.69 J), showcasing the sample's ability to absorb impact energy through controlled failure mechanisms. In conclusion, the 60% wt/wt RW/R-HDPE Blends exhibit promising potential for enhancing the properties of permeable pavement, particularly in road applications, due to its superior bending and tensile strength.

A review of extensible continuum robots: mechanical structure, actuation methods, stiffness variability, and control methods

Abstract Extensible continuum robots (ECRs) offer distinct advantages over conventional continuum robots due to their ability to enhance workspace adaptability through length adjustments. This makes ECRs particularly promising for applications that require variable lengths involving the manipulation of objects in challenging environments, such as risky, cluttered, or confined. The development of ECRs necessitates careful consideration of mechanical structures, actuation methods, methods of stiffness variability, and control methods. The selection of papers is based on their relevance to ECRs within the period of 2010 to 2023 in the databases of Scopus and Web of Science. Distinguishing itself from other review papers, this paper aims to deliver a comprehensive and critical discussion about the advantages and disadvantages of ECRs concerning their mechanical structures, actuation methods, stiffness variability, and control methods. It is a beneficial resource for researchers and engineers interested in ECRs, providing essential insights to guide future developments in this field. Based on the literature, existing ECRs exhibit an inherent trade-off between flexibility and structural strength due to the absence of systematic design methods. Additionally, there is a lack of intelligent and effective controllers for achieving complex control performance and autonomous stiffness variability.

Study on flexural resilience of composite foam sandwich structures under hygrothermal environment

Under hygrothermal environments, the structural stability and strength of all-fiber composite aircraft are significantly affected during long-term flight use. The wing skin, as a critical structural component, plays a vital role in bearing and transmitting aerodynamic loads. Therefore, it is crucial to investigate the structural compressive stability and strength of the wing skin throughout the aircraft's entire life cycle under these conditions. This study employs a real wing carbon fiber foam sandwich structure to investigate the compressive stability and strength of the wing skin structure of a new energy aircraft under actual flight conditions, specifically during the entire process of the room temperature dry state (RTD) and elevated temperature wet state (ETW). Initially, three-point bending tests were conducted on carbon fiber reinforced polymer (CFRP) laminates, foam cores, and CFRP reinforced foam sandwich structures. The CFRP laminates fully rebounded after bending damage in both the RTD and ETW environments. While CFRP reinforced foam sandwich structures also rebounded fully in the RTD environment, their rebound performance diminished in hygrothermal conditions due to the thermoplastic mobility of the foam cores, resulting in only weak rebound capabilities. In hygrothermal environments, the thermoplastic mobility of the foam core leads to diminished resilience after bending damage, resulting in only weak rebound capabilities. Subsequently, compressive instability tests were conducted on the wing skin foam sandwich structure. The results indicated that the basic test study effectively predicted the structural test outcomes. Structural components in the RTD environment exhibited overall flexural instability under compressive load, with damage morphology resembling a circular curve; the damaged specimens fully rebounded after unloading. Conversely, specimens in the ETW environment displayed localized instability, characterized by a wrinkled damage profile, resulting in only weak rebound capabilities after unloading.

Parametric assessment of new O-ring bracing performance under progressive collapse using nonlinear analysis

Progressive collapse poses a significant threat to the structural integrity of buildings under extreme loading conditions, necessitating robust design strategies to mitigate its effects. This paper extends prior research by the same authors on the performance of O-ring bracing during progressive collapse in comparison with other bracing systems. The primary objective is to investigate various design parameters and configurations that optimize the performance of O-ring bracing systems under progressive collapse scenarios through a comprehensive parametric assessment. Nonlinear finite element analysis is employed to evaluate different design parameters, including the size, shape, orientation, and strength of O-ring braced sections, and connection detailing. These factors are assessed for their influence on structural strength, stiffness, and ductility. The parametric study identifies configurations that significantly enhance structural resilience, providing recommendations for future designs aimed at preventing progressive collapse in O-ring braced frames. Data AvailabilityAll data is available from the Authors upon reasonable request.