Impact Bending Research Articles

Testing common hornbeam (Carpinus betulus L.) acetylated with the Accoya method under industrial conditions

Hornbeam wood is known for its high density, hardness, toughness, and wear resistance, but due to its low durability (Class 5 according to EN 350), limited wood quality, and rather small sawmill yield, it is mainly utilized as firewood today. The potential for hornbeam to be used as solid, high-quality wood material exists if its durability and dimensional stability can be increased. Hornbeam boards were acetylated under industrial conditions and tests were carried out to evaluate the treatability of this wood species by acetylation. In this study, the examination of physical, mechanical, and durability properties of acetylated hornbeam wood are described and compared to untreated hornbeam and to acetylated beech, which has a similar anatomical structure to hornbeam. Acetylated hornbeam was also compared to acetylated radiata pine, which is the main product of Accsys Technologies. These comparisons include the determination of the equilibrium moisture content, density, dimensional stability, accelerated checking, color change, water uptake, decay resistance, compression strength, modulus of rupture (MOR), modulus of elasticity (MOE), impact bending strength, Janka hardness, Brinell hardness, and impact bending strength. The aim of this project is the creation of a new product thereby widening the usage of this species.

Comparison of Wood Quality of Douglas Fir and Spruce from Afforested Agricultural Land and Permanent Forest Land in the Czech Republic

This study compares the quality of wood from two distinct sites in the Czech Republic—from former afforested agricultural land and forest land. We compared the properties of Norway spruce wood (Picea abies Karst.) and Scots pine wood (Pinus sylvestris L.), the most important domestic tree species, to Douglas fir (Pseudotsuga menziesii (Mirbel) Franco), a North American tree species and a potential substitute for the domestic spruce. Wood density, modulus of elasticity (MOE), modulus of rupture (MOR) and impact bending strength were the properties tested that were used for comparing tree species. Without taking into consideration the site, the highest density values from the tested tree species were obtained for Douglas fir (0.568 g·cm−3), followed by the pine (0.508 g·cm−3) and the spruce (0.463 g·cm−3). The Douglas fir also dominated in the remaining assessed properties, whilst the influence of site was not confirmed, with the exception of MOE and MOR, and only for the Douglas fir wood, wherein higher values were obtained for forest land. In terms assessed Douglas fir properties, it exceeds the domestic softwoods and represents a possible suitable replacement for them. The site only plays a role in terms of the Douglas fir, and only for certain properties.

Determination of the Temperature Dependences of the Fracture Energy Components of Specimens of Various Types in Impact Bending Tests

Determination of the Temperature Dependences of the Fracture Energy Components of Specimens of Various Types in Impact Bending Tests

Modelling the Impact Strength of Polymeric Materials

A theoretical analysis of the process of determining the impact strength under double-support impact bending (the Charpy notched impact strength), aN, is carried out, on the basis of which analytical dependences of aN on the elastic modulus, the parameters of the relaxation mobility of the polymer, the temperature, and the content of reinforcing fillers are proposed. The results of experiments confirm the correctness of the proposed methods for calculating aN.

Influence of energy dissipation at the interphase boundaries on impact fracture behaviour of a plain carbon steel

The paper deals with the impact deformation and fracture behaviour of commercial plain carbon pipe steel 17Mn1Si. The explicit account of the internal grain structure, temperature and geometry of the notch have been made in theoretical physical mesomechanics formulation aiming at in depth understanding of the role of strain energy factors in dynamic fracture. Theoretical method of excitable cellular automata and laboratory impact bending tests followed by fractographic analysis were paired with time–frequency analysis of acoustic emission accompanying local deformation and fracture processes. It was shown that formulation of the crack opening criterion under dynamic loading conditions should explicitly account for rotation energy accumulation and incorporate the microscopic temporal and spatial details of defect generation from internal (grain) boundaries. A fairly good agreement has been found between the strain energy characteristics obtained from mechanical loading data and independently measured acoustic emission signal being distinguished in terms of consumed and released energy. The impact toughness almost linearly decreased with temperature, which was consistent with fractographic observations. At the stage of crack initiation, when the energy dissipation processes at the internal structure elements significantly affect the initiation of dynamic fracture, the acoustic emission energy reduced in proportion to the expended mechanical energy, which considerably decreased with temperature. The vital role of the energy release at interface/grain boundaries and its decreased significance with decreasing temperature was demonstrated both in numeric simulations and in dynamic experiments.

Evaluation of Influence of Thermal Methods of Metal Separation Cutting on Welding Quality

We have investigated a possibility of obtaining high-quality welded joints after oxygen and plasma cutting of steel С355 without removing the heat-affected zone (HAZ), in which the changes in chemical, phase and structural compositions are observed. Numerical and experimental studies of the effect of heat input of MAG and Submerged Arc welding on the quality of welded joints are performed. In particular, it was found that when the heat input of welding is at least 6.5 kJ/cm, the metal of HAZ of the edges after cutting is heated during the welding to temperatures above Ас3, which leads to its full recrystallization. When the heat input of welding is at least 10 kJ/cm, the edges after cutting are completely melted and become a part of the welding seam metal. The presence of extensive areas of melting and recrystallization of the edges in the welding process contributes to obtaining high-quality welded joints without removing the HAZ of the edges after cutting. To verify the results of numerical studies, experimental tests of control welded joints were conducted, which showed that the values of bending angle and impact toughness of the welding seam metal and heat affected zone are significantly above the regulatory requirements to quality of welded joints, and not less than the same requirements for steel С355. The obtained results confirm the possibility of revising domestic regulatory requirements for the steel constructions production in terms of the preparation of edges for welding using technologies of thermal cutting without subsequent machining.

Impact bending strength as a function of selected factors: 2 – Layered materials from densified lamellas

This article examines the effect of selected factors (wood species, lamella combination, type of adhesive, number of loading cycles) on the impact bending strength (IBS) of laminated wood. The IBS was tested on specimens made from beech (Fagus sylvatica L.) and aspen lamellas (Populus tremula L.). The laminated wood was densified by 10% and 20% of the original thickness. For bonding the wood, polyvinyl acetate (PVA) adhesive was used, and the product was compared with laminated wood bonded with polyurethane adhesive (PUR). The wood species and lamella combination had significant effects on IBS. The highest values of IBS were found for beech wood lamellas.

Toughness and Impact Strength in Dynamic Bending of Wood as a Function of the Modulus of Elasticity and the Strength in Compression to the Grain

Toughness is the mechanical property that determines the wood strength when a force acts in a short time interval. Its value is determined in the bending impact test. Timber has to resist to impact forces in several applications, nevertheless this property is not widely studied to tropical wood species from Brazil. This study aimed to correlate the toughness and the impact strength of wood with the modulus of elasticity and the strength in the compression parallel to grain test. Therefore ten tropical species, from different strength classes, grown in Brazil were tested according to the Brazilian Standard Code ABNT NBR 7190:1997. The studied species were: Cedro (<i>Cedrella</i> sp.), Cambará Rosa (<i>Erisma</i> <i>uncinatum</i> Warm), Cedrorana (<i>Cedrelinga</i> <i>cateniformis</i>), Catanudo (<i>Calophyllum</i> sp.), Cupiúba (<i>Goupia</i> <i>glabra</i>), Angelim Saia (<i>Parkia</i> spp.), Tatajuba (<i>Bagassa</i> <i>guianensis</i> Aubl.), Guaiçara (<i>Luetzelburgia</i> sp.), Cumaru (<i>Dipteryx</i> <i>odorata</i>) and Angelim Vermelho (<i>Dinizia</i> <i>excelsa</i> Ducke). It was developed a relation between the studied properties through regression models, evaluated according to the variance analysis (ANOVA). The results of the statistical analysis revealed led to the conclusion that there is no correlation between the proposed properties for the analyzed species.

EFFECTS OF NANO-SILANE ON THE PHYSICAL AND MECHANICAL PROPERTIES OF ORIENTED STRAND LUMBER (OSL)

Cette étude s’est penchée sur les effets de la teneur en résine et en composés de nano-silane (NS) sur les panneaux struc- turaux orientés (OSB), un important pro- duit en bois reconstitué. Des panneaux OSB ont été fabriqués avec de la résine d’urée-formaldéhyde (UF) à 8 % et à 10 % (sur poids sec des panneaux), avec appli- cation de NS à deux teneurs en fonction de la teneur en résine UF. Nos résultats montrent que les traitements aux deux teneurs différentes en résine donnent des valeurs très proches pour les modules de rupture et d’élasticité, la flexion au choc et la résistance à la traction. Cela indique que la compacité élevée des lamelles de la matrice OSB est le facteur déterminant des propriétés mécaniques globales des panneaux composites. L’interaction entre NS et résine UF affaiblit significativement ces propriétés dans la plupart des cas de traitement à 10 % NS, alors que le dosage de NS à 20 % est suffisant pour contri- buer activement au processus de collage des lamelles et compense les pertes en partie. L’analyse par cluster indique que les propriétés mécaniques sont générale- ment davantage fonction de la compacité de la matrice composite que de la teneur en résine. Dès lors, l’étude conclut que le NS n’est pas à recommander à l’industrie en raison de ses effets négatifs sur la plu- part des propriétés physiques et méca- niques des panneaux OSB.

The Spread of Corrosion in Cast Iron and its Effect on the Life Cycle of Transportation Vehicles

This article deals with the spread of corrosion in material at different exposure times, and its effect on the measured brittle fracture and notch impact strength under different temperature conditions. To assess the degradational effect of corrosion on the material characteristics represented by the measured impact strength, we conducted a fractographic analysis of fracture surfaces, the aim of which was to evaluate the spread of corrosion in the material. In the first part of the experiment, two corrosion tests are simulated with a duration time of 432 and 648 hours, to compare the degradation effect of corrosion on the notch impact strength, depending on the duration of the corrosion tests. The following part shows the results of the impact bending test, where the experiment was conducted in an area of reduced and increased temperatures. The final part summarizes the results of the fractographic analysis of sample fracture surfaces from the impact bending tests. Based on the measured the length of the corrosion cracks, we analyzed the sample at the notch and from the material surface after the impact bending test.

The Impact of Bending Stress on the Performance of Giant Magneto-Impedance (GMI) Magnetic Sensors.

The flexibility of amorphous Giant Magneto-Impedance (GMI) micro wires makes them easy to use in several magnetic field sensing applications, such as electrical current sensing, where they need to be deformed in order to be aligned with the measured field. The present paper deals with the bending impact, as a parameter of influence of the sensor, on the GMI effect in 100 µm Co-rich amorphous wires. Changes in the values of key parameters associated with the GMI effect have been investigated under bending stress. These parameters included the GMI ratio, the intrinsic sensitivity, and the offset at a given bias field. The experimental results have shown that bending the wire resulted in a reduction of GMI ratio and sensitivity. The bending also induced a net change in the offset for the considered bending curvature and the set of used excitation parameters (1 MHz, 1 mA). Furthermore, the field of the maximum impedance, which is generally related to the anisotropy field of the wire, was increased. The reversibility and the repeatability of the bending effect were also evaluated by applying repetitive bending stresses. The observations have actually shown that the behavior of the wire under the bending stress was roughly reversible and repetitive.

Experimental and theoretical investigation of hollow polyester fibers effect on impact behavior of composites

In this paper, the effect of utilizing hollow polyester fibers as reinforcement in composite material in comparison with solids is investigated. The three-point bending impact test is carried out to study the impact behavior and mode of failure of composites. After that, the finite element method is used for theoretical investigation and modeling the behavior of two different reinforced composites during impact tests. It was found that the fiber–matrix interface failure is the most dominant mode of failure and the crack was initiated at the middle of the bottom surface of composites. It was also found that the impact resistance of the hollow fiber composite is more than the others. Theoretical results showed good correlation with experimental results as well. The stress distribution and the maximum value of strain energy density was found as two factors which lead to improvement in the impact behavior of hollow fiber composites.

Bending impact behaviour of sandwich beams with expanded polystyrene foam core: Analysis

This study addresses the bending impact behaviour of sandwich beams made of a low density core bonded to two metal face sheets under low-velocity impact. The geometrical and material non-linearities were considered in the explicit dynamic analysis. The face sheets and core were made of aluminum and expanded polystyrene foam. The effects of design parameters, such as foam density, foam thickness, plate thickness, on the impact energy absorption of the joint were investigated. The foam material was modelled as a crushable foam material, and the cohesive response of the adhesive interface was analysed using the cohesive zone model. Experimental low-speed impact tests were carried out to validate the finite element analysis, and the temporal variations of the contact force and the permanent central deflections at the top and bottom faces of the sandwich beams were in good agreement.

Effects of external patch configuration on repaired composite laminates subjected to multi-impacts

This work intends to study the impact performance of repaired composites by the overlap patch technique and, for this purpose, experimental tests were carried out on single and double-patch specimens. In order to evaluate the impact fatigue strength, both configurations were submitted to multi-impacts, until the full perforation occurs. It was possible to conclude that the double-patch geometry supports higher maximum loads, lower displacements and promotes higher elastic energies. Relatively to the impact energy of 6J, for example, the maximum load and the elastic energy is 97.1% and 51.2% higher, respectively, but the maximum displacement is about 50% lower than the values obtained with the single-patch geometry. Higher impact fatigue life was also observed, as consequence of its higher stiffness. The impact bending stiffness confirms the difference of stiffness between them, and shows to be a parameter able to monitor the damage progression.

The effects of brown-rot decay on select wood properties of poplar (Populus cathayana Rehd.) and its mechanism of action

Abstract The effects of brown-rot decay on the mechanical and chemical properties of poplar (Populus cathayana Rehd.) wood were investigated, while the correlation of several properties to the decay degree and to each other were quantified. During the decay process, the losses in impact bending strength (IBS) and modulus of rupture (MOR) increased logarithmically with the degree of decay, whereas the losses in modulus of elasticity (MOE) and compressive strength parallel to grain (CS∥) increased slowly with linear trends. The ranking of the four mechanical parameters for the response speed to decay and the degree of the influence of decay were IBS&gt;MOR&gt;MOE&gt;CS∥. Hemicelluloses were preferably decomposed by the brown-rot fungus. The prominent degradation of cellulose began from a weight loss (W L) of 18.7%, where the relative crystallinity decreased. In summary, the degradation of hemicelluloses caused a fast and significant decrease in IBS while the subsequent removal of paracrystalline cellulose resulted in MOR loss. The variation of MOE was in correlation with the cellulose content. A decrease in CS∥ was due to the slow deterioration of crystalline cellulose.

Temperature Effect on Deformation and Fracture Mechanisms under Impact Loading of 17Mn1Si Steel with Explicit Accounting Structural Heterogeneity

The effect of the microstructure parameters as well as the testing temperature on the impact toughness of 17Mn1Si steel has been studied. The interrelation between the testing temperature during impact bending and deformation and fracture energy consumption has been studied. The relation between fracture energy characteristics at high-rate impact bending and the microstructure of the steel has been established. It is shown that the decrease of the testing temperature leads to almost linear reduction of the impact toughness.

Low velocity bending impact behavior of foam core sandwich beams: Experimental

Abstract This experimental study addresses the low velocity impact bending response of sandwich beams with expanded polystyrene (EPS) foam core reinforced by aluminum face-sheets using adhesive bonding technique. The deformation behaviour and the effects of the geometric and mechanical design parameters were investigated to improve the impact energy absorbing capability. The bending impact tests were performed for different foam density, foam and plate thicknesses for three impact energy levels: 4.45 13.05, 26.78 J. The photographs of the permanent deformation geometries of the sandwich beams were presented and the contact force and kinetic energy histories were discussed. The specimens with higher foam core density and thicker foam core resulted in the lowest permanent central deflections and contact force variations. As the foam core density and thickness were increased, the energy absorbing capability was improved. The specimens having thinner face-sheets exhibited higher contact force variations and the lower permanent deflection than those of the specimens with thicker face-sheet even for the lowest impact energy. However, as the impact energy was increased, the specimen with thinner face-sheet exhibited lower contact force levels and higher permanent deflections than those of the specimens having thicker face-sheets. In addition, the plastic dissipation energy was increased in the face-sheets. The face-sheet thickness was more effective on the permanent deflections, whereas the foam core density was more effective on the energy absorbing capability.

Low-speed bending impact behavior of adhesively bonded single-lap joints

This study addresses the low-speed impact behavior of adhesively bonded single-lap joints. An explicit dynamic finite element analysis was conducted in order to determine the damage initiation and propagation in the adhesive layers of adhesive single-lap joints under a bending impact load. A cohesive zone model was implemented to predict probable failure initiation and propagation along adhesive–adherend interfaces whereas an elasto-plastic material model was used for the adhesive zone between upper and lower adhesive interfaces as well as the adherends. The effect of the plastic deformation ability of adherend material on the damage mechanism of the adhesive layer was also studied for two aluminum materials Al 2024-T3 and Al 5754-0 having different strength and plastic deformation ability. The effects of impact energy (3 and 11 J) and the overlap length (25 and 40 mm) were also investigated. The predicted contact force-time, contact force-central displacement variations, the damage initiation and propagation mechanism were verified with experimental ones. The SEM and macroscope photographs of the adhesive fracture surfaces were similar to those of the explicit dynamic finite element analysis.

Impact Bending Strength as a Function of Selected Factors

This article examines the influence of selected factors (wood species, densification, thickness, glue type, and number of cycles) on the impact bending strength (IBS) of solid and laminated wood. The evaluated properties were measured on samples of European beech (Fagus sylvatica L.) and common aspen (Populus tremula L.). Two types of glues were used for laminated wood: polyvinyl acetate (PVAc) and polyurethane (PUR). The highest IBS values were recorded in laminated beech specimens glued with polyvinyl acetate glue that were not subjected to cyclical loading.

Interface improvement of carbon fiber/methylphenylsilicone resin composites by fiber surface coating of polyhedral oligomeric silsesquioxanes

To enhance interfacial properties of carbon fibers (CFs)-reinforced methylphenylsilicone resin (MPSR) composites, we introduced an appropriate interface reinforced by trisilanolphenyl-polyhedral oligomeric silsesquioxanes (trisilanolphenyl-POSS) between CFs and MPSR with a liquid phase deposition strategy. Chemical bonds among silanol groups of trisilanolphenyl-POSS, hydroxyl-functionalized CF (CF–OH), and silanol end groups of MPSR in the coating were expected to be formed through condensation reaction during the prepared process. CFs with and without sizing treatment-reinforced MPSR composites were prepared by a compression molding method. X-ray photoelectron spectroscopy revealed that trisilanolphenyl-POSS particles enhanced the contents of fiber surface oxygen-containing groups and silicon-containing functional groups. Scanning electron microscopy and atomic force microscopy images showed that trisilanolphenyl-POSS nanoparticles have been introduced onto the fiber surface obviously and the surface roughness increased sharply. Dynamic contact angle analysis indicated that trisilanolphenyl-POSS-modified sizing agent could improve the fiber wettability and surface energy significantly. Short-beam bending test and impact toughness test results showed that the interlaminar shear strength and impact resistance of the sized CFs composites were enhanced greatly with increasing amplitudes of more than 35 and 27% in comparison with those of untreated CF composites, respectively. Cryo-fractured surface topographies of composites confirmed that interfacial adhesion between CFs and MPSR has been improved after sizing treatment. Meanwhile, the sizing treatment does not decrease single fiber tensile strength.