Mechanical Tests Research Articles

Strength Retention of Carbon Fiber/Epoxy Vitrimer Composite Material for Primary Structures: Towards Recyclable and Reusable Carbon Fiber Composites

Recently, the growth of the recyclability of carbon fiber reinforced polymer (CFRP) composites has been driven by environmental and circular economic aspects. The main aim of this research work is to investigate the strength retention of a bio-based vitrimer composite reinforced with carbon fibers, which offers both recyclability and material reusability. The composite formulation consisted of an epoxy resin composed of diglycidyl ether of bioshpenol A (DGEBA) combined with tricarboxylic acid (citric acid, CA) and cardanol, which was then reinforced with carbon fibers to enhance its performance. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were performed to analyze the chemical composition and curing behavior of the vitrimer. Mechanical testing under tensile loading at room temperature was carried out on epoxy, vitrimer, and associated carbon fiber reinforced composite materials. The results demonstrated that the DGEBA/CA/cardanol vitrimer exhibited thermomechanical properties comparable to those of an epoxy cured with petroleum-based curing agents. It was observed that the maximum tensile strength of vitrimer is about 50 MPa, which is very close to the range of epoxy resins cured with petroleum-based curing agents. Notably, the ability of the vitrimer composite to be effectively dissolved in a dimethylformamide (DMF) solvent is a significant advantage, as it enables the recovery of the fibers. The recovered carbon fiber retained comparable tensile strength to that of the fresh carbon composites. More than 95% strength was retained after the first recovery, which confirms the use of fibers for primary and secondary applications. These research results open up new avenues for efficient recycling and contribute to the overall sustainability of the composite material at an economic level.

Does Ovariectomy Affect the Mechanics of the Mandibular Alveolar Bone Structure of Wistar Rats Subjected to Tooth Loss and Modified Diet?—A FEA Study

The aim of this study was to evaluate the mechanical effect of ovariectomy, diet, and tooth extraction on the bone structure of the mandible of Wistar rats. Mandibles from 40 female Wistar rats were used, divided into rats with ovariectomy surgery or surgical simulation. Half of the rats had the right upper incisor extracted and a soft diet was introduced for half of the animals for 30 days. After euthanasia, microtomography of the mandibles was performed for bone segmentation to construct three-dimensional models. Each mandible was subjected to a three-point bending test. The simulation by finite element method was configured according to the protocol for positioning the part on the support and force action by the load cell defined in the mechanical tests. Stress dissipation was described qualitatively on a color scale distributed in ranges of stress values. All models showed a higher concentration of stresses in the regions of force action and in the support regions, with differences in stress values and locations. Diet and dental condition interfered in the distribution of stresses, with the lateral surface of the mandible being more influenced by diet and the medial surface of the mandible by diet and dental condition.

Strengthening by {110} and {112} edge dislocations in BCC high entropy alloys

Abstract Mechanical tests and microscopy studies on body-centered cubic (BCC) high entropy alloys reveal transitions from screw to edge dislocation slip and from {110} to {112} slip plane activity. Here, a strengthening theory for BCC edge dislocation slip on {112} planes is thus developed that parallels a recent theory for {110} slip. Using the atomistic dislocation pressure fields for four BCC elements (Nb, Ta, Mo, W) as proxies to span the range of likely alloy cores, theory predicts that the zero temperature yield strength for {112} slip is slightly lower (0%–20%) than that for {110} slip but that the associated energy barrier is slightly (0%–20%) higher. This leads to cancelling effects, and hence very similar strengths, at finite temperatures and strain rates. Full atomistic results on selected dilute binary alloys show some shifts in these trends, but with similar magnitudes and cancelling effects. The close strengths of {110} and {112} slip modes indicate that subtle aspects beyond the scope of the theory will determine which slip system controls the observed strengthening. This closeness in strength cements the use of the {110} edge theory for guiding alloy design independent of actual slip system.

Ballistic Performance of Polycarbonate Plate Subjected to Truncated Cone Projectile

In the present study, a quasi-static compression test and impact test are carried out on a Polycarbonate plate with thickness of 2.66 mm and an effective diameter of 205 mm. The impact test is carried out on a pneumatic gun using a hardened truncated cone projectile of mass 25.8 g at different velocities. On the other hand, a servo mechanical universal testing machine with a 50 kN capacity is used to carry out the quasi-static compression test at a speed of 2 mm/min adopting an indenter of truncated nose shape. The Dynamic Enhancement Factor, or DEF, is computed as the ratio of quasi-static perforation energy to impact perforation energy. The measured DEF in the present study is compared with previously published results for metal and polycarbonate. Also local deformation of the plate after perforation is compared for both quasi-static test and dynamic test.

Mechanical Properties Test and Failure Analysis of Composite Foam Sandwich Structure in Ramp-Down Zone

Mechanical Properties Test and Failure Analysis of Composite Foam Sandwich Structure in Ramp-Down Zone

Optimizing sustainable concrete mixes with recycled aggregate and Portland slag cement for reducing environmental impact

Concrete is the world’s most extensively manufactured material, with the integration of recycled materials becoming crucial for sustainable construction. This study investigates the mechanical properties of concrete mixes containing Recycled Aggregates (RA) and Portland Slag Cement (PSC) to understand their suitability for sustainable construction applications. Utilizing normal-strength concrete with a compressive strength of 35 MPa and a 0.45 water-to-cement ratio, fifteen mix designs were tested, varying RA and PSC replacement levels from 0 to 100% and 0% to 50%, respectively. Comprehensive mechanical testing, including compressive and tensile strength assessments at 7 and 28 days, alongside modulus of elasticity and stress–strain curve evaluations, was conducted. The results reveal that full replacement of Natural Aggregate (NA) with RA decreased compressive strength by 10% and modulus of elasticity by 20%. However, a partial replacement of 25% of Ordinary Portland Cement (OPC) with PSC, in the presence of RA, moderated the reduction of compressive strength to 0.92% and increased the modulus of elasticity by 3.7%. The optimum mix, consisting of 75% OPC, 25% PSC, and 50% RA, significantly enhances concrete’s mechanical properties, recommending it for reinforced concrete applications due to its potential environmental and structural benefits.

Digital finance, capital-biased and labor-biased technical progress: Important grips for mitigating carbon emission inequality

As an innovative financial model in the era of the digital economy, digital finance, with its inclusive characteristics, provides effective financial support for the realization of the carbon peak and carbon neutrality. To realize the “double carbon” goal, it is necessary not only to control the total amount and intensity of carbon emissions but also to consider the coordination and fairness of carbon emission reduction between regions. The existing literature has discussed the carbon reduction effect of digital finance, but few studies have focused on the impact and mechanism of digital finance on regional carbon emission inequality. On the basis of data from 287 prefecture-level cities in China from 2011 to 2021, this paper empirically examines the effect of digital finance on carbon emission inequality via a fixed effects model and convergence model. Digital finance not only reduces the Theil index of carbon emissions but also promotes the convergence of carbon emissions, which mitigates regional carbon emission inequality. The mechanism test shows that digital finance reduces the level of regional carbon emission inequality by promoting capital- and labor-biased technical progress in high-carbon emission regions. Heterogeneity analysis proves that digital finance can better exert its inhibitory effect on carbon emission inequality in regions with low financial agglomeration levels, weak industrial bases and small digital business scales. Further analysis indicates that digital finance can effectively reduce carbon emission inequality between regions, but the effect on carbon emission inequality within regions is not significant. The above findings provide a realistic reference for the formulation of differentiated digital finance policies to support carbon emission reduction.

Experimental Investigation of Tensile, Shear, and Compression Behavior of Additional Plate Damping Structures with Entangled Metallic Wire Material

To fulfill the vibration damping requirements of plate structures under complex conditions, additional damping structures with entangled metallic wire material (EMWM) are proposed based on the excellent physical properties of EMWM. A batch of specimens with different filament diameters, densities, and thicknesses are prepared. The stiffness and loss factors are taken as the evaluation indexes, and orthogonal tests are conducted to obtain the tensile, shear, and compression properties. The results show that the optimal parameter combinations can be obtained through orthogonal tests. For the specimens with optimal parameter combinations, the mechanical tests under different loading rates and loading displacements are carried out. With the increase in loading rate, the tensile and shear forces appear to display fracture failure in advance, and the compression performance is stable without significant changes. The change rule under each mechanical test is explored using the stiffness and loss factor evaluation index. It provides a reference for the analysis of the preparation parameters of subsequent additional damping structures with EMWM.

New Materials from the Integral Milk Kefir Grain Biomass and the Purified Kefiran: The Role of Glycerol Content on the Film’s Properties

Microbial exopolymers are gaining attention as sources for the development of biodegradable materials. Milk kefir, a fermented dairy product produced by a symbiotic community of microorganisms, generates milk kefir grains as a by-product, consisting of the polysaccharide kefiran and proteins. This study develops two materials, one from whole milk kefir grains and another from purified kefiran. Film-forming dispersions were subjected to ultrasonic homogenisation and thermal treatment, yielding homogeneous dispersions. Kefiran dispersion exhibited lower pseudoplastic behaviour and higher viscous consistency, with minimal effects from glycerol. Both films exhibited continuous and homogeneous microstructures, with kefiran films being transparent and milk kefir films displaying a yellowish tint. Analysis revealed that milk kefir films comprised approximately 30% proteins and 70% kefiran. Kefiran films demonstrated stronger interpolymeric interactions, as evidenced using thermogravimetric and mechanical tests. Glycerol increased hydration while decreasing thermal stability, glass transition temperature, elastic modulus, and tensile strength in both films. However, in kefiran films, elongation at the break and water vapour permeability decreased at low glycerol content, followed by an increase at higher plasticiser contents. This suggests an unusual interaction between glycerol and kefiran in the absence of proteins. These findings underscore differences between materials derived from the whole by-product and purified kefiran, offering insights into their potential applications.

Analysis of aging effects on the mechanical and vibration properties of quasi-isotropic basalt fiber-reinforced polymer composites

Eco-friendly natural fiber composites, such as basalt fiber composites, are gaining traction in material science but remain vulnerable to environmental degradation. This study investigates the mechanical and vibrational properties of quasi-isotropic basalt fiber composites subjected to aging in two different environments: ambient (30 ºC) and subzero (-10 ºC), both in distilled water until moisture saturation. Aged specimens absorbed 8.66% and 5.44% moisture in ambient and subzero conditions, respectively. Mechanical testing revealed significant strength reductions in tensile, flexural, impact, and short beam shear tests, with ambient-aged specimens showing the largest decline (up to 31.7% in flexural strength). Vibrational analysis showed reduced natural frequencies, particularly under ambient conditions (27.27%). Sound absorption tests showed that pristine specimens had the highest transmission loss, while moisture-rich ambient-aged specimens had the lowest. SEM analysis confirmed surface degradation, with fiber pull-out and matrix debonding contributing to property loss. This research provides valuable insights into the environmental limitations of basalt fiber composites, emphasizing the need for enhanced durability in eco-friendly materials.

Mechanical properties of poly(ethylene succinate) thin films incorporated with chemical synthesis copper oxide nanoparticles

This study investigates the synthesis and characterization of poly(ethylene succinate) (PES) thin films and their composites with copper oxide (CuO) nanoparticles. CuO nanoparticles were synthesized using a chemical synthesis method, achieving an average size of 20 nm. PES/CuO composites were prepared by incorporating CuO at various concentrations of 0, 1, 3, and 5 wt%. The thin films were produced through solution polymerization followed by casting. Mechanical testing revealed that the tensile strength of pure PES was 25 MPa, while incorporating 1 wt% CuO increased the tensile strength to 30 MPa. At 3 wt%, the tensile strength reached 35 MPa, and at 5 wt%, it peaked at 40 MPa, demonstrating a significant enhancement in mechanical properties. The elongation at break also improved, increasing from 200% for pure PES to 250% for the 5 wt% CuO composite. Characterization of the materials was performed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to analyze structural and morphological properties. The results confirm that the PES/CuO composites exhibit enhanced mechanical properties, indicating their potential for diverse applications in sustainable materials and biomedical fields.

Annealing Temperature-Dependent Microstructure, Mechanical, and Tribological Properties of Intercritically Heat-Treated Dual-Phase Steel

Abstract This study investigates the role of intercritical annealing temperature on microstructural characteristics, mechanical performance, and wear resistance of DP1000 steel. As-received DP1000 steel samples in cold-rolled conditions were subjected to intercritical annealing between 730 and 880 °C with an interval of 30 °C, followed by water quenching. After heat treatment, the specimens were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), mechanical tests consisting of hardness, impact, and tensile tests, and dry sliding wear tests. The findings revealed that equiaxed ferrite grains replaced elongated ones, and the martensite ratio increased from 21% up to 64% with increasing annealing temperature. Due to the formation of equiaxed grains, the impact strength was at least doubled for each specimen by heat treatment, reaching a peak value (9.55 J/cm2) at 760 °C. The hardness (311 HB) and tensile strength (1007 MPa) of the as-received sample were higher than that of the annealed steels up to 820 °C. The mechanical strength of the samples improved at 850 and 880 °C by approximately 10%, and accordingly, the lowest wear rate was obtained at the specimen annealed at 850 °C. The increase in temperature up to 880 °C caused a decrease in wear resistance due to excessive brittleness.

Determining the Relationship Between Corneal Stiffening and Tissue Dehydration After Corneal Cross-Linking.

To quantify corneal cross-linking (CXL)-induced stiffening via mechanical testing to estimate the impact of changes in hydration levels (H) and evaluate depth-dependent tissue hydration after CXL. Eighty-three porcine corneal buttons were divided into three groups: Standard protocol CXL (S-CXL), accelerated CXL (A-CXL), and untreated (nonirradiated riboflavin-only) controls. Samples were hydrated or dehydrated to modulate H and dynamic mechanical analyzer compression tests were performed to measure Young's modulus (E). To extract the solid tissue network modulus, the cornea was modeled as a biphasic material after measuring E at different H. Corneal hydration was correlated with depth-dependent tissue thickness characterized by confocal reflection microscopy (CRM). Young's modulus increased fourfold after S-CXL (0.72 ± 0.1 MPa) and threefold after A-CXL E (0.53 ± 0.12 MPa) versus controls (0.17 ± 0.045 MPa). However, H decreased from 4.07 ± 0.35 in controls to 2.06 ± 0.2 after S-CXL and 2.79 ± 0.12 after A-CXL. After H modulation and biphasic mechanical modeling, Young's modulus for corneal solid tissue network showed only a 1.8-fold increase after S-CXL (2.25 MPa) and 1.5-fold increase after A-CXL (1.85 MPa) versus controls (1.22 MPa). With CRM, the overall thickness of the corneal tissue was found to linearly correlate to hydration H as expected. No appreciable depth dependence of hydration-induced thickness changes throughout the corneal buttons were observed. Corneal tissue hydration changes significantly impact measured corneal stiffness after CXL using mechanical testing. Not considering H leads to major overestimation of the stiffening effect of the CXL procedure. Depth-dependence of corneal thickness because of changing hydration is strongly dependent on the integrity of the tissue.

Synthesis, characterisations and applications of boron nitride based hybrid metal matrix composites

ABSTRACT This study focuses on how reinforcements impact the base material (specifically AA 6082) regarding its microstructure, mechanical behaviour& corrosion behaviour. Boron nitride (BN) & molybdenum disulphide (MoS2) employed as reinforcing materials ranged from 1% to 3% of BN & 1% to Constant MoS2. The composite materials were produced utilising the stir casting technique. X-ray diffraction (XRD), scanning electron microscope (SEM) with Energy Dispersive spectroscopy (EDAX) & an optical microscope (OM) were used to examine microstructural phase identification analysis. Tensile, compressive, impact, density& porosity fracture mechanisms were investigated by mechanical testing. BN & MoS2 reinforced particles’ presence in the samples is confirmed by XRD and microstructural pictures showing consistent matrix reinforcement distribution. According to the findings, incorporating BN & MoS2 reinforcements improved the mechanical & corrosion properties but slightly reduced the impact strength. The fractured samples revealed micro cuts, micro ploughing, cracks, trans-granular cleavage facets, dimples in the tensile & impact tests. Reduction in Corrosion rate was achieved gradually by adding reinforcement particles for the composites.AA6082, 3 wt: % BN, & 1 wt.% MoS2 composites have shown a decrease in corrosion current density by 1.901 mA/cm2 & an increase in charge transfer resistance by 99.934 Ω cm-2, attributed to passivation.

The Perception of Policy Uncertainty and the Labor Income Share of Firms: Empirical Research Based on Double Machine Learning

ABSTRACTBased on the double machine learning model, this study examines the impact of perception of policy uncertainty (PPU) on labor income share (LIS). We find that PPU negatively influences LIS. Mechanism test indicates that PPU not only results in a reduction in fixed asset investment, distorting human capital structure, but leads to a financing dilemma for firms, ultimately exerting a detrimental effect on LIS. Additionally, PPU primarily diminishes LIS of ordinary employees rather than executives. Furthermore, the inhibitory effect of PPU on LIS is significantly more pronounced in firms characterized by smaller union scales and those operating within monopolistic industries.

Directors from related industries and corporate diversification

ABSTRACT This paper aims to examine the impact of directors from related industries on corporate diversification. Director social networks, as a form of informal institution, have significant effects on firms’ production, operation, and strategic decision-making. However, few studies have focused on the economic effects of directors from related industries. We select Chinese A-share listed companies from 2012 to 2021 as our research sample and empirically examine the impact of directors from related industries on corporate diversification. The study finds that directors from related industries can promote corporate diversification. Mechanism tests that they can influence corporate diversification through the information channel. Heterogeneity analysis shows that the impact of directors from related industries on corporate diversification is more pronounced in firms with strong absorptive capacity, non-state-owned enterprises, and in regions with poor institutional environments. Additionally, directors from related industries can strengthen the positive correlation between diversification and corporate investment efficiency.

Artificial Intelligence and the Development of “Specialized, Refined, Unique, and Innovative” Small‐ and Medium‐Sized Enterprises

ABSTRACT“Specialized, Refined, Unique, and Innovative” (SRUI) enterprises are a crucial part of the national innovation system and play a significant role in enhancing national core competitiveness by leveraging strengths and addressing weaknesses. Given the limited quantitative analysis on the productivity of SRUI enterprises in the academic field, this paper constructs an enterprise‐level artificial intelligence index based on text analysis and machine learning. Using panel data from 2018 to 2022, we investigate the impact of artificial intelligence on the productivity of SRUI small‐ and medium‐sized enterprises (SMEs). The research findings indicate that (1) artificial intelligence significantly enhances the productivity of SRUI SMEs, and for each one standard deviation increase in artificial intelligence, the productivity level of SRUI enterprises will increase by 6.82%. (2) Mechanism tests reveal that artificial intelligence improves productivity by optimizing labor structure, improving labor resource allocation, stimulating endogenous motivation and innovation vitality within enterprises, and enhancing management level and investment efficiency. (3) Heterogeneity analysis indicates that at the regional level, artificial intelligence significantly boosts the productivity of enterprises with well‐developed network infrastructure and robust intellectual property protection systems. At the industry level, AI has a more pronounced effect on the productivity of technology‐intensive and competitive industries. Additionally, we also find that the impact of AI on productivity is more significant in enterprises with younger executive teams and executives with digital and intelligent education backgrounds. This study expands the research scope of productivity and provides valuable insights for the government to optimize digital economy policies and for enterprises to formulate digital innovation strategies.

Effect of Cyclic Load Frequency on the Fatigue Crack Nucleation and Growth of Annealed and Prestrained Austenitic SS 304

ABSTRACTThe austenitic stainless steels are widely used in several engineering fields due to their high ductility, corrosion and high temperature performance. Despite its noble properties, components manufactured in austenitic stainless steel are subject to fatigue failure. Studies indicate that loading frequency can impact the austenitic stainless steel fatigue performance. In this scenario, the present study aims to evaluate the effect of frequencies of 3 and 30 Hz on the fatigue behavior of SS 304 alloy under load control in order to identify in which fatigue stage the effect is outstanding. Therefore, fatigue and fracture mechanics tests were evaluated on the alloy annealed at 1000°C. Furthermore, fatigue tests were also applied to the alloy after previous tensile plastic strain of 0.5. The analyses denoted a significant reduction in fatigue strength with increasing frequency, especially for the strained alloy. Fatigue crack nucleation is encouraged with greater load frequency. This behavior may be attributed to strain‐induced martensite and other strain mechanisms such as twinning and slip bands that are encouraged by lower strain rates but are relieved by auto‐heating achieved in higher frequencies, as mentioned in the literature, which decrease the strength to fatigue nucleation.

Local Government Debt and Corporate Fraud: Evidence from China

ABSTRACT Local government debt acts as a double-edged sword for economic development. While it has effectively stimulated local economic growth, it has also led to crowding-out consequences of crowding out corporate financing and investment. This study analyzes data of Chinese listed firms from 2007 to 2020, revealing the detrimental effects of local government debt on firms’ misconduct. We find that local government debt is positively related to corporate fraud, and the results remain robust to a series of sensitivity tests. The mechanism tests demonstrate that an increase in local government debt exerts pressure on firms’ financing and performance. Moreover, we observe that the adverse effects are more pronounced in private firms, and firms with poor governance systems.

Investigating the Impact of Long-Term Use on Mattress Firmness and Sleep Quality—Preliminary Results

Mattress comfort, often associated with firmness, is a complex construct influenced by factors such as material composition, construction, and personal preference. In this short communication paper, we indirectly investigated the effects of long-term mattress use on its hardness and sleep quality by observing the changes in the mattress. A mechanical durability test was performed on two structurally different mattress samples (with polyurethane core and pocket spring core) using a modified method based on the EN 1957 standard, aiming to understand the long-term effects of mattress characteristics on sleep quality. Preliminary results confirm that the mattress samples can maintain firmness and support during long-term use. The polyurethane foam mattress experienced initial compression but quickly stabilized, while the pocket spring mattress showed slight softening, maintaining overall firmness. For the polyurethane mattress, after the initial drop, the hardness value stabilized, varying between 7.53 and 9.03 N/mm, and at the end of the test, it stopped at 8.60 N/mm. The firmness rating stabilized at 4.3, showing minimal fluctuation between 4.0 and 4.6 throughout the process, while the total height loss was 3.79 mm. The hardness value of pocket spring mattresses generally decreased with increasing test cycles (it started at 5.86 N/mm and ended at 5.21 N/mm). The firmness remained relatively stable, varying between 7.3 and 7.1, and the total height loss was only 2.86 mm. The findings suggest that the firmness of a mattress can be changed with its use, highlighting the need for further research on a larger number of samples in the direction of the long-term implications of these changes on sleep comfort.