Flexural Impact Research Articles

Specimen Size Effects and Dynamic Fracture Toughness of Cement-Based Foams

AbstractThis paper presents the effect of geometrically similar specimen size on the mechanical properties of cement-based foams. The experimental study also investigates fracture-mechanical parameters under flexural impact. A preformed foam was employed to prepare the specimens using a synthetic foaming agent that was known to achieve a stable bubble structure. The cement-based foams were prepared to a cast density of 475 kg/m3 and were examined under compression and flexure. Along with a plain unreinforced mix, polypropylene fiber at a volumetric fraction of 0.2% was used to study the effect of microfiber reinforcement. The tested specimens scaled between one to four times in dimension. Parameters associated with their dynamic-fracture mechanics were evaluated under flexure with the help of a drop-weight impact tester equipped with a high speed imaging system. Bažant’s size effect model and the multifractal scaling model were employed to describe the size effect. It was seen that when subjected to comp...

Flexural and Impact Properties of Bamboo-Aluminum Sandwich Composites

Investigations have been conducted on the mechanical properties of bamboo-aluminum sandwich composites prototype fabricated in laboratory. Mechanical properties studied were flexural properties and impact properties. The failure mode related to each mechanical property was also observed and reported in this study.

Effect of Different Layers of Glass Cloth on Carbon Fiber Reinforced Hybrid Composite Core

The effect of different layers of glass cloth on carbon fiber reinforced hybrid composite core is studied in this work. Carbon fiber reinforced hybrid composite of different glass cloth content is made by pultrusion processing. Three point bending test and charpy impact test are taken to evaluate the toughness of different composite, and scanning electronic micro-scopy (SEM) and photograph are carried out to characterize the structure of different composite after destroyed. It is shown that, though at the cost of drop of tensile strength, the increase of glass cloth content in carbon fiber reinforced hybrid composite core improves the flexural strength and impact resistant, and does not affect the microscope destroy pattern and the microscopic structure of failure samples.

Impact of Millimeter-Size Silicon Microchips on the Mechanical Properties of Polymer Samples Tested under Flexural Bending, Long-Term Creep, and Impact Conditions

One way to continuously monitor the whole water distribution system is to equip pipes with many small sensors. If these sensors are to be integrated within the pipe walls, it is important to assess their impact on the structural integrity of the pipes, but embedding pipes with these microchips for testing would allow limited control of the position and orientation of the microchips. Therefore, microchips of a few millimeters in size and different shapes were embedded within small-scale polyethylene samples. Pipes are subject to a range of different stresses during their lifetime including hoop, bending, and potentially local impact stresses, and long-term creep effects. This paper focuses on the bending, flexural creep, and impact stresses, with some examples from the tensile tests also presented. The key findings are that there is little effect of the microchips on the 50-year flexural moduli and the short-term flexural properties of the polymer, although there was a significant improvement in the toughness and a reduction in the tensile strength.

Preparation and Mechanical Properties of Cotton Stalk Bast Fibers Reinforced Polypropylene Composites

The cotton stalk bast fibers are a new kind of natural cellulose fibers, which have the similar properties as the flax fibers. Polypropylene (PP) is a type of matrix material and commonly used in composites. The cotton stalk bast fibers as reinforced materials and PP as matrix were used to make a new kind of composite in the experiment. The composites were prepared by mixing, molding and cold forming. Orthogonal experiment table including mass fraction of fibers, molding temperature, molding pressure and molding time was devised. Then the flexural strength, tensile strength and impact strength were tested and the analysis of range was done. The optimal processing condition was obtained as follows: mass fraction of fibers was 30%, molding temperature was 190°C, molding pressure was 12MPa and molding time was 480s. The result showed that the cotton stalk bast fibers reinforced PP composites had good mechanical properties.

Nanocomposites of novolac type phenolic resins and organoclays: The effects of the resin molecular weight and the amine salt structure on the morphology and the mechanical properties of the composites

Nanocomposites of novolac-type phenolic resins having various molecular weights with a series of organoclays containing organic amine salts were prepared by melt processing. The effects of the molecular weight of novolac resin and the amine structure of organoclay on composite morphology and physical properties were examined. Composites containing organoclay exhibited the intercalated state with shifts in gallery spacing regardless of the molecular weight of novolac resin. The extent of silicate platelet intercalation increased as molecular weight of novolac resin increased and the number of long alkyl tails decreased from two to one. Novolac resin/organoclay composites cured with hexamethylenetetramine (HMTA) always exhibited better flexural and Izod impact strengths than the novolac resin cured with HMTA when the molecular weight of novolac resin was fixed. Among the nanocomposites prepared here using organoclays, those with higher platelet intercalation generally showed better flexural and Izod impact strengths. However, resin-coated sands prepared from organoclay containing one long alkyl tail exhibited only better flexural strength than that prepared from novolac resin.

Effects of the Size of Wood Flour on Mechanical Properties of Wood-Plastic Composites

In this article, wood-plastic composites(WPCs) were manufactured with wood flour(80～120mesh、40～80mesh、20～40mesh、10～20mesh) combing with high density polyethylene(HDPE). Effects of the size of wood flour on mechanical properies and density of composites were investigated. Results showed that particle size of wood flour had an important effect on properitiesof WPCs. Change of mesh number had a outstanding effect on flexural modulus, tensile modulus and impact strength, howere, little effect on flexural strength and tensile strength. When mesh number of wood flour changed from 80～120mesh to 10～20mesh,flexural modulus and tensile modulus were respectively enhanced by 42.4% and 28.4%, respectively, and impact strength was decreased by 35.5%.Size of wood flour basically had no effect on density of composite within 10～120mesh. The use of wood flour or fiber as fillers and reinforcements in thermoplastics has been gaining acceptance in commodity plastics applications in the past few years. WPCs are currently experiencing a dramatic increase in use. Most of them are used to produce window/door profiles,decking,railing,ang siding. Wood thermoplastic composites are manufactured by dispering wood fiber or wood flour(WF) into molten plastics to form composite materials by processing techniques such as extrusion,themoforming, and compression or injection molding[1]. WPCs have such advantages[2]：(1)With wood as filler can improve heat resistance and strength of plastic, and wood has a low cost, comparing with inorganic filler, wood has a low density. Wood as strengthen material has a great potential in improving tensile strength and flexural modulus[3]；(2) For composite of same volume, composites with wood as filler have a little abrasion for equipment and can be regenerated；(3)They have a low water absorption and low hygroscopic property, They are not in need of protective waterproof paint, at the same time, composite can be dyed and painted for them own needs；(4)They are superior to wood in resistantnce to crack、leaf mold and termite aspects, composites are the same biodegradation as wood；(5)They can be processed or connected like wood；（6）They can be processed into a lots of complicated shape product by means of extrusion or molding and so on, meanwhile, they have high-efficiency raw material conversion and itself recycle utilization[4]. While there are many sucesses to report in WPCs, there are still some issues that need to be addressed before this technology will reach its full potential. This technology involves two different types of materials: one hygroscopic(biomass) and one hydrophobic(plastic), so there are issues of phase separation and compatibilization[5]. In this paper, Effects of the size of wood powder on mechanical properties of WPCs were studied.

Effect of the Chemical Treated Kevlar Fiber on the Behaviors of Cement Mortars

This work aims to evaluate the effect of Kevlar fibers with chemical treatment on the flexural strength, compressive strength and impact resistance of cement mortar. The experimental results exhibit that Kevlar fiber with a larger percentage can increase the flexural strength and improve the impact resistance of cement mortar, and the reinforcement effect of Kevlar fiber with chemical treatment is more obvious. The surface morphology of Kevlar fiber and the fracture surface of cement mortar reinforced with Kevlar fiber were observed by SEM, and the reinforcement mechanism of the Kevlar fiber on cement mortar was discussed.

Manufacturing Technique and Property Evaluation of Impact-Resistant Polypropylene/Glass Fiber Composites

Using the injection molding method, impact-resistant polypropylene (PP) and glass fibers (GF) with weight ratios of 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt% and 30 wt% were blended twice, completing high-impact PP/ GF composites. Next, the tensile strength test, flexural stress test and IZOD impact strength test measured the composites. According to the results, with an increase in glass fibers, the composites exhibited a greater tensile strength, which further reached to climax when the GF weight ratio was 25 wt%. However, tensile strength appeared inversely proportionate to the blending frequency. In addition, regardless of blending frequencies, the optimum flexural stress occurred when the GF weight ratio was 25 wt%; nevertheless, it started declining when the ratio was 30 wt%. Finally, indicated by IZOD impact test, the greater the GF weight ratio, the lower the impact strength the composites exited.

Dynamic Fracture Strength and Toughness of Continuous Alumina Fiber–Reinforced Glass Matrix Composites at Elevated Temperature

An instrumented drop-weight test rig was used in the investigation of the dynamic fracture strength and toughness tests of continuous alumina fiber reinforced glass matrix composites, which were carried out at room and elevated temperatures using charpy-type specimen configuration, and with fiber orientation perpendicular (0°) and parallel (90°) to impact load direction. Increasing test temperatures, the results show a dependency of dynamic flexural strength, toughness, and impact energy for unidirectional 0°and 90°fiber orientation Al2O3-borosilicate composite up to 950°C, whereas the Al2O3-96% silica composites showed little or no dependency on increasing test temperatures, before dropping off at temperatures higher than 750°C. This type of behavior for Al2O3-borosilicate composite could be due to the suppression of matrix microcracking as temperature increases due to increased plasticity of the matrix, resulting in increased dynamic flexural strength and toughness values. Scanning electron microscope (SEM) investigations of fractured surfaces show that there are two identifiable major damage modes: fibrous at room temperature, as in Al2O3-borosilicate composites, where weaker fiber-matrix interfacial bond exists, due to the difference in thermal mismatch at room temperature resulting in reduced fiber-matrix bond strength, matrix microcracking and apparent fiber debonding occurring during the dynamic flexure and toughness tests, resulting in longer fiber pullout; nonfibrous at high temperatures, as in Al2O3-96% silica composites, this occurs as temperature increases, the thermal mismatch between fiber-matrix decreases leading to an increase in fiber-matrix interfacial bonding and thus increasing tendency to embrittlement. This resulted in changing failure mechanisms from fibrous at room temperature to nonfibrous at higher temperatures. The important variables of this test were discussed and its usefulness in comparing dynamic flexural, toughness, and impact resistant ceramic matrix composite (CMC) materials are demonstrated.

Effect of low UD carbon fibre content on mechanical properties of in situ polymerised cyclic butylene terephtalate

Carbon fibre reinforced cyclic butylene terephtalate were produced by a low pressure method, the impregnating temperature and the cooling speed were investigated using plate–plate rheometry and differential scanning calorimetry. The effects of low fibre volume fraction of carbon fibre reinforcement (∼20 vol.‐%) on the mechanical properties were examined by tensile and flexural tests and Charpy dynamic impact test. The results showed a significant increase in Young’s modulus and ultimate strength and were supported by scanning electron microscopy pictures of the broken surfaces to study fibre wet‐out.

Three-dimensional braided fabrics-reinforced composites for load-bearing orthopedic applications Part I: mechanical performance

Abstract Composite materials are being used in orthopedics and traumatology in light of their reduced weight, radiolucency and their lower stiffness than that of metals. Studies on biostable fibrous composites have recently demonstrated that these materials have a range of properties which make them suitable for orthopedic applications. In this study, three different three-dimensional (3-D) braided composites, carbon fiber- epoxy (C3D/EP), Kevlar fiber-epoxy (K3D/EP) and carbon fiber-poly(methyl methacrylate) (C3D/PMMA), were assessed in terms of mechanical properties and in-vitro durability to evaluate the feasibility of these composites as potential biomaterials. In addition, comparisons with other reported composites in original strength and modulus and in-vitro degradation were also made. Our studies indicate that a material with an appropriate stiffness combined with sufficient flexural and shear strength and high impact strength can be gained by tuning the combination of fiber and matrix, which opens an effective way of replacing conventional metallic devices with fibrous composites.

Influence of Processing Aids and Hydroxyapatite as Fillers on Flow Behaviour and Mechanical Properties of Ultra High Molecular Weight Polyethylene/High Density Polyethylene Composites

In this study, blends of ultra high molecular weight polyethylene/high density polyethylene/polyethylene glycol (UHMWPE/HDPE/PEG) and the composites containing Hydroxyapatite (HA) as reinforcement filler were prepared via single screw extruder nanomixer followed by compression moulding. PEG (2phr) was used as processing aid and HA loadings were varied from 10 to 50 phr. HDPE and PEG were introduced to improve the extrudability of UHMWPE. Rheological behavior was studied via capillary rheometer while flexural and izod impact tests were conducted in order to investigate the mechanical properties of the blends and composites. Melt viscosity of the blends was found to decrease with increasing shear rate indicating a pseudoplastic behaviour. Incorporation of PEG shows a synergism effect on the reduction of blends viscosity. Blend of 40% UHMWPE/ 60% HDPE/ 2 phr PEG was chosen as the optimum blend composition with a balance properties in terms of the mechanical properties and processability. The incorporation of HA fillers from 10 to 50 phr into the blend resulted in the increase of flexural modulus and flexural strength with a slight decline of impact strength values. It can be concluded that the composites having adequate strength and modulus within the range of cancellous bone properties were succesfully developed to be used as biomedical implant devices.

Effect of Flame Retardants on Wood Plastic Composites-HDPE Based

Recently, research on natural fiber reinforced polymer composites has gained importance due to the abundant sources of fibers that can be obtained at very low cost. In this study, wood plastic composite (WPC) materials is made by mixing (compounding) high density polyethylene (HDPE) and (ligno) cellulose fiber, i.e. rice husk reinforced with sawdust have been manufactured using a high volume process using counter rotating twin screw extruder. Different fire retardant agents have been employed in order to improve fire behavior in this study. The flammability and thermal stability of WPC-HDPE based in different compositions have been carried out by fire test method according to ASTM D635-06 and evaluated by thermo gravimetric analysis respectively. The properties of flexural strength and impact strength were also included.

Study on disinfection effectiveness and properties of acrylic resin via microwave irradiation sterilization

Objective The purpose of this study was to evaluate the disinfection effectiveness and properties of acrylic resin via microwave irradiation. Methods Forty acrylic resin base dentures fabricated in a standardized procedure were chosen and divided into Group A,B,C and D randomly. Group A,B and C were immersed in 200ml distilled water and submitted to microwave irradiation at 700W for 3,4,5 minutes individually. Group D was used as positive control. Bacteria specimens from each group were got for culture and numbers were calculated. Then the four groups were tested for the flexural strength and impact strength by universal test machine before and after microwave irradiation sterilization. Results The germicidal ratio of Group B was more than 90% ,while the ratio of group C was 100%. There was no significant difference in flexural strength and impact strength between group C and group D. Conclusions Microwave irradiation for 5 minutes at 700W produced sterilization of dentures contaminated with all bacteria whereas the denture strength is not affected. Microwave irradiation at 700W solution for 5 minutes was effective to sterilize acrylic resin base dentures. Key words: Microwave irradiation; Disinfection; Acrylic resin; Flexural strength; Impact strength

Grafting of Poly(n-butylacrylate)-b-poly(2-hydroxyethyl methacrylate) on Carbon Fiber and its Effect on Composite Properties

A treatment method based on the grafting of block copolymer on carbon fiber (CF) surface was proposed for obtaining a controlled interface between carbon fibers and epoxy resin. The block copolymer poly(n-butylacrylate)-b-poly(2-hydroxyethyl methacrylate) (PnBA-b-PHEMA) was grafted on the CF by controlled polymerization. Research shows that the grafting block copolymer can improve interfacial adhesion, and the chain structure, lengths and grafting density of block copolymer can affect the fiber/matrix interfacial adhesion. The study of mechanical properties indicated the introduction of PnBA-b-PHEMA in the interface could both improve the flexural strength, modulus and impact toughness of composites.

Improving the Interfacial Adhesion of Highly Filled PP—Bagasse Composites Designed by Taguchi Method

In the present article, three different types of coupling agents at various concentrations were used to prepare high-content polypropylene/bagasse composites (65—75 wt%). Maleated polypropylene (PP-g-MA), glycidyl methacrylate-grafted polypropylene (PP-g-GMA), and thermoplastic starch (TPS) were chosen as the coupling agent to generate these wood—plastic composites in a lab-scale counter rotating twin-screw extruder. The changes in the morphological, thermal, and mechanical properties were investigated. Morphological studies showed that the fiber dispersion, wetting, and interfacial tension were improved in the presence of PP-g-MA and PP-g-GMA. Flexural properties, impact resistance, and heat deflection temperature of samples increased with incorporation of PP-g-MA and PP-g-GMA. The Cox’s model used to predict the flexural modulus exhibited a good fitting with the experimental data. With increasing coupling agent content; the thermo-mechanical properties of the composites were improved. The compatibilizing effect of PP-g-MA and PP-g-GMA is more obvious than TPS.

Investigation of various factors effects on mechanical properties of Poly(propylene)/organo-modified Montmorillonite/Magnesium hydroxide composites

The combined effects of organo-modified montmorillonite (O-MMT) gallery polarity, surface modification of magnesium hydroxide (MDH), maleic anhydride grafted polypropylene (MA-g-PP) and antioxidant (Irganox 1010) addition, together with mixing time and rotor speed of the mixer on the measured flexural modulus, maximum (max) flexural (flex) strength and impact strength of the composites were studied. A two-level factorial experimental design of these variables was used to examine their simultaneous effects. The 16 composite samples were prepared by melt mixing in an internal mixer at 200 °C and their properties were measured. The flexural modulus and max flex strength of the samples containing high level of both MDH and O-MMT reached the highest and lowest amount respectively. Effect of the factors and their interactions on impact strength and max flex strength was almost in the same order and by decreasing the amount of O-MMT/or MDH, these properties were increased. The regression equations showed the most effective factors and their interactions which were in good agreement with the obtained results. Addition of 1%w/w O-MMT to 50%w/w MDH/PP composites led to the best mechanical properties.

Study on the Properties of Epoxy Thermosets Cured by ImHBPs under Lower Temperature

The 2-methylimidazole (Im) -terminated hyperbranched polyesters (ImHBPs) with different generations were prepared and used in diglycidyl ether of bisphenol A (DGEBA) as curing agents and tougheners in this work. It was found that the ImHBPs had better latent property than Im which indicated that the ImHBPs were proper to be used as low temperature curing agent in epoxy curing system. It was also found that the tensile strength, the flexural strength and impact strength of epoxy thermosets cured by ImHBPs under 90 were much higher than those of CYD-128/2-methylimidazole thermoset, which indicated that the ImHBPs obviously improved the mechanical properties of epoxy thermosets, and the thermoset cured by ImHBP with two generation had the best performance among the thermosets.

The Mechanical and Physical Properties of Thermoplastic Natural Rubber Hybrid Composites Reinforced with Hibiscus cannabinus, L and Short Glass Fiber

Thermoplastic natural rubber hybrid composites reinforced with kenaf and short glass fibers were compounded by melt blending method using an internal mixer, Thermo Haake 600P. Thermoplastic natural rubbers (TPNR) were prepared from polypropylene (PP), natural rubber (NR) and liquid natural rubber (TPNR) with ratio 70:20:10, which were blended using internal mixer for 12 minutes at 180°C and rotor speed 40 r.p.m. Glass fiber was treated with silane coupling agent while TPNR reinforced kenaf fiber composite is using MAPP as a compatibilizer. TPNR hybrid composite with kenaf/glass fibers was prepared with fiber content (5, 10, 15, 20 volume % of fiber). Mechanical properties of the composites were investigated using tensile test[ 1 ], flexural, impact, and hardness test and scanning electron microscope (SEM)[ 1 ]. The incorporation of the treated or untreated fiber into TPNR has result in an increment of almost 100% of flexural modulus and impact strength as compared to TPNR matrix. However, the maximum strain decreased with increasing fiber content. The optimum composition for hybrid composite is at the fiber ratio of 30% kenaf fiber and 70% glass fiber. The SEM micrograph had shown, that the composite with coupling agent or compatibilizer promote better fiber-matrix interaction.