Development of film materials has been limited by the hardness-fatigue resistance trade-off. The purpose of the present study was to obtain films with a combination of both high hardness and strong ...fatigue resistance. To achieve this, CoCrFeMnNi high entropy alloy films (HEAFs) were fabricated with three different structures: amorphous, high-density nanotwinned crystal structure with twin spacings of 2.2–5.6 nm, and ultrahigh-density nanotwinned columnar grains with twin spacings of 1.2–2.5 nm. Nanoindentation with dynamic mechanical analysis was used to measure the hardness and perform the fatigue tests. While higher twin densities could dissipate more energy by detwinning during fatigue loading to enhance the fatigue resistance, twin spacings larger than and small than 2 nm could, respectively, result in hardening and softening. Our results showed a high hardness of ~9 GPa and fair fatigue resistance (~104 cycles) for both amorphous and high-density nanotwinned crystalline layers. For the ultrahigh-density nanotwinned columnar grain structure, a high hardness of ~8.5 GPa and an excellent fatigue resistance (~106 cycles) were obtained. The outstanding fatigue resistance and high hardness were attributed to the synergistic effect of strain hardening and detwinning of ultrahigh-density nanotwins. The results not only enable CoCrFeMnNi HEAFs with a predominant combination of hardness and fatigue resistance, but also shed light on a new perspective for overcoming the conflict between hardness and fatigue resistance in film materials for microelectromechanical applications.
•We fabricated high entropy alloy films with different structures containing nanotwins.•We used dynamic mechanical analyses to measure hardness and perform fatigue tests.•Nanotwins dissipate energy by detwinning under loading to enhance fatigue resistance.•Twin spacings larger and small than 2 nm could, respectively, yield hardening and softening.•Films with twin spacings spanning across 2 nm showed excellent hardness-fatigue resistance.
Abstract
Many energy absorption applications utilize flexible polymeric foams for their viscoelastic properties. It is desired that the material will perform consistently across repeated compression ...cycles. This study examines the effect of fatigue at low strain rates on the viscoelasticity of open‐cell polyurethane foam. Six polyurethanes of the same base composition with two porosities (70% and 80%) and three chemical indexes (79i, 100i, and 121i) are tested. Large deformation cyclic compression of the foams is conducted on a universal testing system (UTS). These data are then post‐processed leveraging dynamic mechanical analysis Fourier transform rheology to characterize changes in the viscoelasticity of the materials over fatigue cycles. Results show that foams can increase or decrease in stiffness up to 10% over 10
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cycles. Specifically, higher chemical index, higher excitation frequency, and larger excitation amplitude correlate with a more pronounced decrease in stiffness. Damping can also change by 15% and correlates with chemical index and excitation frequency. Consequently, the findings suggest that internal foam structure and bulk material properties as well as applied loading parameters affect the viscoelastic fatigue response of flexible polymeric foams.
The study aims to compare the way modern resin‐based composites (RBCs) respond to mechanical stress related to the tooth structure they are designed to replace. Eight representative light‐cured RBCs, ...including ormocers, giomers, RBCs with nano and agglomerated nanoparticles, prepolymerized, or compact fillers, were selected. Flexural strength, FS and modulus/E, were measured in a three‐point bending test. A fractographic analysis determined the origin of fracture. The quasi‐static (indentation hardness/HIT, indentation modulus/EIT) and viscoelastic (storage modulus/E′, loss modulus/E″, loss factor/tan δ) behavior was assessed by a depth‐sensing indentation test equipped with a dynamic‐mechanical analysis module. One and multiple‐way analysis of variance (ANOVA), Tukey honestly significant difference (HSD) post‐hoc tests (α = 0.05), and Weibull statistics were applied. Parameter material exhibited the highest effect on E (p < .001, ηP2 = .857), followed by FS (ηP2 = .729), and the strain (ηP2 = .553). Highest material reliability was identified in the RBCs with nano and agglomerated nanoparticles. The most frequent type of failure originated from volume (81.3%), followed by edge (10.6%), and corner (8.1%) flaws. Enamel evidenced three times higher HIT, EIT, and E′ values as RBCs and dentin, and the smallest deviation from ideal elasticity. Ormocers exhibited the highest damping capacity, followed by the RBCs with prepolymerized fillers. Damping capacity and static mechanical properties are mutually exclusive. Analyzed RBCs and the tooth structure are better adapted to the relevant frequency for chewing than for higher frequencies. RBCs are comparable to dentin in terms of their mechanical performance, but apart from the damping behavior, they are far inferior to enamel. Damping ability of analyzed material could be exploited for correlation with the clinical behavior.
The study examines impact of bondline thickness and overlap length on the performance of single-lap bonded joints by analyzing the dynamic strain distribution using mechanoluminescence (ML) sensing. ...As the bondline thickness increased from 0.1 to 1.0 mm, the pattern of crack propagation from the top and bottom edges of the bonded region exhibited a marked transition toward rupture. Specifically, the differences in crack propagation behavior were visually identified near one or both bonding interfaces. Additionally, the impact of overlap length on failure modes in lap shear tests, including crack propagation and shear forces, was visually differentiated through ML. Despite its simplicity as a spray-on sensor, ML sensing demonstrated effectiveness in indicating mechanical behavior related to bonding design, such as bondline thickness and overlap length.
In the present review, the recent progress in describing the intricacies of mechanical and thermal properties of all types of graphene- and modified graphene-based polymer nanocomposites has been ...comprehensively examined. The effectiveness of microscopy bouquet for the intrinsic characterization of graphene family and their composites was clearly demonstrated in this research. Furthermore, the utility of the dynamic mechanical analysis and thermo-gravimetric analysis employed for thermal characterization that has been reported by various researchers was exhaustively analyzed in this paper. This research primarily focused on the analyses of several good articles concerned with hybrid graphene composites and the synergetic effect of graphene with other nanofiller to assess its effect on the mechanical properties of its corresponding composites. Such systematic analysis of previous literatures imparted a direction to the researchers about the solution of improved interfacial properties as well as the enhanced dispersion into the vicinity of the matrix. This current research has suggested that the presence of the graphene filler even at very low loadings has shown considerable improvement in the overall mechanical properties of graphene. Further studies to optimize the value of the filler need to be addressed in order to gain complete understanding of the properties of graphene. The potential applications, current challenges, and future perspectives pertaining to these nanocomposites were elaborately discussed in the current study with regard to the multi-scale capabilities and promising developments of the graphene-family-based nanocomposites materials.
Polypropylene composites find widespread application in industries, including packaging, plastic parts, automotive, textiles, and specialized devices like living hinges known for their remarkable ...flexibility. This study focuses on the manufacturing of polypropylene composite specimens by incorporating varying weight percentages of fly ash particles with polypropylene using a twin-screw extruder and injection molding machine. The composites were comprehensively tested, evaluating tensile, compressive, and flexural strength, solid-state and polymer melt properties, modulus, damping, and thermal response. The findings reveal that the compressive strength of polypropylene increases up to 2 wt% of added fly ash particles and subsequently exhibits a slight decline. Tensile strength demonstrates an increase up to 1 wt% of fly ash, followed by a decrease with a 2 wt% addition, and then a subsequent increase. Flexural strength shows improvement up to 3 wt% fly ash addition before declining. The storage modulus curve is categorized into three regions: the glassy region (up to 0 °C), the glass transition region (0–50 °C), and the glass transition region of polypropylene (>50 °C), each corresponding to different molecular motions. Weight loss curves exhibit similar trends, indicating uniform pyrolysis behavior attributed to consistent chemical bonds. Plastic degradation commences around 440 °C and concludes near 550 °C. Additionally, elemental mapping of fly ash composition identified various elements such as O, Si, K, Mg, Ca, Cl, Na, P, Al, Fe, S, Cu, Ti, and Ni. These findings offer valuable insights into the mechanical and thermal properties of polypropylene composites reinforced with fly ash, rendering them suitable for a wide range of industrial applications necessitating strength and durability across temperature variations.
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•Plastic composites made from Polypropylene (PP) and waste flying ash are prepared.•Waste utilization for the development of automotive composite plastics, considering the circular economy.•The resulting plastic composites were subjected to various strength assessments.•Fly ash addition increased the compressive, tensile, and flexural strength of PP plastic.
The equine hoof wall has outstanding impact resistance, which enables high-velocity gallop over hard terrain with minimum damage. To better understand its viscoelastic behavior, complex moduli were ...determined using two complementary techniques: conventional (∼5 mm length scale) and nano (∼1 µm length scale) dynamic mechanical analysis (DMA). The evolution of their magnitudes was measured for two hydration conditions: fully hydrated and ambient. The storage modulus of the ambient hoof wall was approximately 400 MPa in macro-scale experiments, decreasing to ∼250 MPa with hydration. In contrast, the loss tangent decreased for both hydrated (∼0.1–0.07) and ambient (∼0.04–0.01) conditions, over the frequency range of 1–10 Hz. Nano-DMA indentation tests conducted up to 200 Hz showed little frequency dependence beyond 10 Hz. The loss tangent of tubular regions showed more hydration sensitivity than in intertubular regions, but no significant difference in storage modulus was observed. Loss tangent and effective stiffness were higher in indentations for both hydration levels. This behavior is attributed to the hoof wall's hierarchical structure, which has porosity, functionally graded aspects, and material interfaces that are not captured at the scale of indentation. The hoof wall's viscoelasticity characterized in this work has implications for the design of bioinspired impact-resistant materials and structures.
The outer wall of horse hooves evolved to withstand heavy impacts during gallop. While previous studies have measured the properties of the hoof wall in slowly changing conditions, we wanted to quantify its behavior using experiments that replicate the quickly changing forces of impact. Since the hoof wall's structure is complex and contributes to its overall performance, smaller scale experiments were also performed. The behavior of the hoof wall was within the range of other biological materials and polymers. When hydrated, it becomes softer and can dissipate more energy. This work improves our understanding of the hoof's function and allows for more accurate simulations that can account for different impact speeds.
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The advancement in composite additive manufacturing allows the design of fiber placement to tailor the performance (stiffness and strength) of the structure and reduce its weight. However, the design ...process requires an understanding of various mechanical properties of the materials as well as the effective properties of the laminate. The present work focuses on obtaining the mechanical characteristic of a thermoplastic matrix composite, Onyx, with two different continuous fiber infill patterns. The interlaminar shear and tensile tests are performed to study the interlaminar strength and failure of additively manufactured composites. The experimental failure characteristics of the printed composites are compared with finite element analysis (FEA) using classical composite failure criteria. In addition, the current research utilizes dynamic mechanical analysis (DMA) for temperature/frequency sweeps to probe the viscoelastic performance and thermophysical properties (glass transition, creep strain rate and activation energy) of additively manufactured fiber-reinforced composites. It is shown in both failure and dynamic mechanical analyses that the fiber layout affects the strength, glass transition temperature and activation energy of printed composites. The DMA results also revealed the high temperature-dependency and unexpectedly low frequency-dependency of the storage modulus and damping parameter indicating that the materials are predominantly elastic with moderate viscoelastic behavior.
Fungal mycelia are versatile, highly productive and sustainable sources for biocomposites to replace conventional plastics. However, with only very few fungal strains that have been characterized, ...numerous strains still remain unexplored as potential competitors against traditional non-biodegradable materials. Moreover, the functionality of mycelium composites at commonly occurring, challenging ambient conditions such as changing humidity and temperature is not well characterized. Here we evaluated the properties of the fungal composite material produced by novel fungal strains, including Trichoderma asperellum and Agaricus bisporus, grown on oat husk and rapeseed cake after oil pressing. The results showed that the mycelium composites were hydrophobic and strong, particularly when grown on rapeseed cake. A. bisporus grown on rapeseed cake exhibited increased stiffness after humidity was successively increased and decreased. The moisture-resistance of these novel mycelium composites is encouraging for novel sustainable material solutions.
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•The dynamic mechanical properties of mycelium composites were studied for the first time at a broad moisture gradient.•Novel mycelium composites from Agaricus bisporus gave high moisture-resistance.•The dense structure and rich chemical composition of rapeseed cake made it a potent feeding substrate for mycelia.
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