Dynamic Flexural Properties Research Articles

Artificial caries and dynamic flexural properties of bioactive materials

Artificial caries and dynamic flexural properties of bioactive materials

A scientific view on composite inlays in running shoes: The influence of epoxy crosslink density on bending and fatigue properties

This study highlights the need for a deeper understanding of the structure-property relationships of carbon fiber reinforced thermosets applications, whenever considered as a functional part for running footwear. This is done, investigating the static and dynamic flexural properties of three different epoxy resins in prepreg-based carbon fiber composite laminates, varying the glass transition temperature (Tg). In this way, the inherent morphology of the resin was correlated with the fatigue properties of the laminate, which is crucial for the design of composite stiffening inlays for running shoes. First, it was shown that the crosslink density and aromatic content of the resin, which correlates with Tg, drastically affect the compressive strength of the matrix and are therefore crucial for the static and dynamic flexural properties of CFRP. Increasing the Tg from 147 °C to 269 °C leads to stiffening of the resin and thus increased resistance to fiber buckling, resulting in improved bending stiffness, flexural strength, bending angle, overall fatigue strength and thus durability of CFRP plates for running shoes. Moreover, the percentage of fibers in the loading direction can be considered as the main factor affecting the flexural properties of the laminate. Here, a quasi-isotropic stacking order leads to an increased bending angle but to a decrease in bending stiffness, flexural strength and fatigue strength compared to a unidirectionally reinforced composite due to a high load bearing capacity of the 0° fibers. This knowledge creates a basis to bridging the gap between composite material and biomechanical sports science for future work.

Effect of layer thickness of prepreg on static and dynamic flexural properties of continuous carbon fiber reinforced polyamide 6

Effect of layer thickness of prepreg on static and dynamic flexural properties of continuous carbon fiber reinforced polyamide 6

Effect of thermal shock cycling on the quasi‐static and dynamic flexural properties of flax fabric‐epoxy matrix laminates

ABSTRACTThe aim of the present work is to investigate the influence of thermal shock cycling on the quasi‐static and dynamic flexural properties of epoxy matrix composites reinforced with natural flax fibers fabric. Polymer composite laminates reinforced with four plies of natural flax fiber fabric have been manufactured. The samples have been exposed to different number of thermal shock cycles (0, 50, 100, 200, 300, 400), at a temperature range from −40 °C to +28 °C. Dynamic mechanical analysis (DMA) tests were performed on both pristine and thermally shocked specimens in order to determine their viscoelastic response. Due to the thermal shock cycling and after 100 thermal shock cycles, a maximum decrease in storage and loss modulus on the order of 50% was observed. After 100 thermal shock cycles, no further degradation of dynamic properties was observed. On the contrary, damping factor and glass transition temperature values showed a minor variation as number of thermal shock cycles increased. In addition, the time–temperature superposition principle (TTSP) was successfully applied, confirming the fact that the flax fiber fabric‐epoxy laminate is a thermo‐rheologically simple material. Likewise, quasi‐static three‐point bending tests were executed and a maximum decrease of 20% in flexural strength was observed after 400 thermal shock cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48529.

Experimental study on the effect of strain rates on the dynamic flexural properties of rubber concrete

Static and dynamic flexural tests were carried out with a 100-mm-diameter split Hopkinson pressure bar (SHPB) apparatus on rubber concrete for which the fine aggregate was replaced with rubber particles made from waste tires at various volume ratios (0%, 10%, 20%, 30%, 40%, and 50%). The incident and transmission bars of the SHPB apparatus were each sleeved on a modified pad for a three-point flexural test. Experimental results showed that the flexural strength and mid-span displacement of the rubber concrete had a strain-rate effect. The rubber concrete had a more sensitive strain rate than the normal concrete when the replacement ratio of rubber particles was below 30%. However, excessive rubber content (40% and 50%) decreased the sensitivity of strain rate. The strain-rate effect of the rubber concrete was due to a short test duration, which caused more aggregates to be broken, and compressive behavior during the tests. Rubber concrete with a replacement ratio of 30% demonstrated the greatest deformability and had a lower cracking speed than the normal concrete. These results demonstrated that, under a dynamic flexural load, rubber particles can reduce the brittleness of concrete without excessive mixing.

Innovative composite materials as reinforcing interlayer systems for asphalt pavements: an experimental study

Interlayers for asphalt reinforcement are considered an effective option to enhance pavement service life. In this regard, innovative factory-made composite materials can be designed as interlayer systems able to combine reinforcing and stress-relieving properties. This can be accomplished by embedding grids or fabrics in bituminous membranes. Given this background, this study considered dynamic flexural properties and interface shear strength of asphalt systems reinforced with different composite membranes obtained by changing the embedded reinforcement and/or the bituminous compound. Results clearly rank the studied materials showing enhanced fatigue response of reinforced asphalt layers. However, interface shear properties strongly suggest proper design and adequate selection of the installation depth.

Mechanical Properties of Alkali-Activated Concrete Subjected to Impact Load

AbstractDrop-weight tests are conducted to study the dynamic flexural properties of alkali-activated concrete (AAC) under four different impact velocities, corresponding to strain rates of 15, 35, ...

Dynamic Mechanical Properties of EVA Polymer-Modified Cement Paste at Early Age

Abstract The polymer-modified cementitious materials are widely used as functional building materials since the expanding of the application of polymer in construction industry. The dynamic mechanical properties of EVA polymer-modified cement pastes at early age were investigated by dynamic mechanical analysis at 0.49Hz-100 Hz (loading frequency). Experimental results show that the dynamic flexural properties, as expressed by the storage modulus and loss tangent, ascended linearly with a logarithmic frequency. The storage modulus increased with the increase of the hydration time. On the contrary, the loss tangent of 3% and 5%P/C decreased according to increase of the hydration time at 7dyas.

2-D analytical model for characterizing flexural damping responses of composite laminates

Abstract The flexural damping behaviors of composite laminates were characterized analytically in this study. A 2-D analytical model was developed based on the extension of Ni–Adams model [Ni RG, Adams RD. The damping and dynamic moduli of symmetric laminated composite beams—theoretical and experimental results. J Compos Mater 1984;18(2):104–21] accounting for the energy dissipation contributed by the laminar stresses of σxy and σyy. The specific damping capacity (SDC) of the composite was determined in accordance with the energy dissipation concept, which was defined as the ratio of the dissipated energy to the stored energy for per circle of vibration. The 2-D analytical model was validated by comparing the SDC of [0/−60/60]s and [0/90/45/−45]s laminates with the experimental data and the finite element (FEM) results. In addition, the effects of interlaminar stress on the flexural damping responses of laminated plates were also characterized in the 3-D FEM analysis. Results indicated that the interlaminar stress effect may not be so significant that the current 2-D model is adequate for the evaluation of the damping responses of the composite laminates. Furthermore, the present predictions, as compared to the Ni–Adams [Ni RG, Adams RD. The damping and dynamic moduli of symmetric laminated composite beams—theoretical and experimental results. J Compos Mater 1984;18(2):104–21] and Adams–Maheri [Adams RD, Maheri MR. Dynamic flexural properties of anisotropic fibrous composite beams. Compos Sci Technol 1994;50(4):497–514] models, generally demonstrate good agreements with the experimental data and the FEM results.

Interfacial improvements in poly(3-hydroxybutyrate)-flax fibre composites with hydrogen bonding additives

Improvement of the interfacial properties of composites consisting of poly(3-hydroxybutyrate) and flax fibres was provided by addition of 4,4 ′-thiodiphenol (TDP) at various concentrations up to 10% v/v. The additive TDP is known to form hydrogen bonds with many functional groups. The flax fibres were initially treated with TDP before being used to prepare the composites. The effects of the TDP on the functional groups of the fibres and the matrix were monitored using Fourier transform infrared spectroscopy and it was confirmed that hydrogen bonding occurred in the composites, which consequently brought about advantageous changes in the dynamic flexural properties. The thermal stability determined by thermogravimetry showed a favourable shift of degradation temperatures to higher values and the thermal properties of the matrix determined from differential scanning calorimetry were also affected. With the aid of scanning electron microscopy and polarised optical microscopy, the composites were shown to exhibit improvement in the fibre–matrix bonding and the dynamic mechanical properties of the matrix changed from brittle to ductile as the TDP content increased.

Effect of Hybridization on the Creep and Stress Relaxation Characteristics of Pultruded Composites

Pultrusion manufacturing process is a well established technique for the cost-effective production of high-modulus and lightweight composite materials having constant cross-sectional profiles. The pultruded composites are widely used as structural members viz., beams, trusses and stiffeners, owing to the presence of high proportion of axial fibers necessary to sustain large tractive forces. These structural members are subjected to a combination of static and dynamic loading conditions at wide temperature ranges and over longer periods. Since polymeric composites exhibit viscoelastic behavior, the effectiveness of these materials as structural members must be thoroughly evaluated to ensure long-term stability. In previous research, the dynamic performance characteristics of pultruded glass-graphite/epoxy hybrids were evaluated at room temperature. The effects of temperature, frequency, post-curing, along with the type and placement of fibers on the dynamic flexural properties of glass/epoxy and hybrid glass-graphite/epoxy were also investigated. This paper focuses on the evaluation of creep and stress relaxation performance characteristics of pultruded glass-graphite/epoxy hybrid composites. Dynamic mechanical analysis technique was adopted for the accelerated creep and stress relaxation testing. Time-temperature superposition principle, which greatly reduced the experimental time, was effectively utilized for predicting the creep and stress relaxation properties of the hybrid composites. Results indicate that the type and amount of fibers as well as their lay-up sequence plays a significant role in determining the flow and load bearing characteristics.

Experimental and Finite Element Analysis of Pultruded Glass-Graphite/Epoxy Hybrids in Axial and Flexural Modes of Vibration

The effects of hybridization on the extensional and flexural dynamic properties of pultruded composite materials are reported in this paper. The composite materials considered were made up of unidirectional glass, graphite fibers in an epoxy matrix, and hybrids of glass-graphite/epoxy produced by the pultrusion manufacturing process. The dynamic storage modulus and loss factor of the rectangular and circular cross-section samples were first evaluated using the nondestructive impulse-frequency response vibration technique. The long and slender flat specimens were analyzed in both extensional and flexural modes of vibration in a free-free test configuration, whereas the thicker round specimens were analyzed only in the axial mode of vibration. The properties of the monofiber type glass/epoxy and graphite/epoxy composites were used as input to the finite element model for predicting and experimental validation of various pultruded (and hypothetical) glass-graphite/epoxy hybrid combinations. The modal strain energy method was used for computing the structural loss factors of the hybrid specimens based on the element stiffness matrices and estimated mode shapes in the fundamental mode of vibration. Results of this investigation showed excellent agreement between experimental data and numerical predictions for the dynamic extensional properties of both flat and round specimens. The numerical results for dynamic flexural properties of flat specimens were found to have a similar trend as that obtained from the experimental technique. Small variations in flexural properties could be attributed to the irregular shapes (which were not taken into account in the finite element model) of layers in the hybrid combinations formed during the pultrusion manufacturing process. Results also demonstrated that while the extensional properties were independent of the fiber location and fiber packing geometry, the flexural properties were highly dependent upon these two factors. Previously reported data (which was obtained by testing these flat hybrid specimens in the flexural mode of vibration in a clamped-free boundary condition) were re-analyzed using the free-free configuration and modal strain energy method, yielding more reasonable results.