Impact Bending Research Articles

衝撃曲げ荷重を受ける管状部材のエネルギー吸収性能を向上させる断面形状の検討

衝撃曲げ荷重を受ける管状部材のエネルギー吸収性能を向上させる断面形状の検討

Evaluation of physical and mechanical properties of wild cherry wood heat-treated using the thermowood process

The aim of this study is to determine the change of some physical properties (oven-dry density, weight loss, swelling and anti-swelling efficiency) and mechanical properties (compression strength parallel to grain, bending strength, modulus of elasticity in bending, janka-hardness (cross-section, radial, tangential), impact bending strength and tension strength perpendicular to grain) of wild cherry woods after heat treatment under different durations. Specimens are exposed to temperature levels of 212 °C for time spans of 1,5 and 2,5 h. Based on the findings in this study, the results showed that oven-dry density, swelling, compression strength parallel to grain, bending strength, modulus of elasticity in bending, janka-hardness (Cross-section, Radial, Tangential), impact bending strength and tension strength perpendicular to grain values decreased with increasing treatment time.

Mechanical response of a fibre reinforced earthen material under static and impact loadings

This study examines the improvements provided by the insertion of hemp fibres with different weight fractions and lengths in an earthen material. The structural response of the materials was investigated by means of static and impact bending tests carried out on notched samples. The main focus of the analyses was in the characterization of the structural properties of the materials in terms of fracture resistance, post-cracking performance and energy absorption capability. The results of the study show that hemp fibres improve significantly the mechanical and fracture properties of the earthen material under both static and dynamic bending. It was also found that the structural properties of unreinforced and reinforced earthen materials are highly sensitive to the stress-rate, with higher strength and fracture resistance under impact loading than under static loading.

Analysis of the Dynamic Stress Intensity Factor of an Impacted Freely Supported Bend Specimen Based on Modified Timoshenko's Beam Theory

A freely supported bending specimen momentarily disengages from the anvils during the impact bending tests, which will be called one-point bending. The time history of the dynamic stress intensity factor is analyzed for a dynamic one-point bending test in which an edge-cracked specimen is impacted at the midspan which is freely supported. The mode shape functions and the natural frequency equations of the cracked beam in freely supported boundary conditions are derived from modified Timoshenko beam equations, in which the rotary inertia caused by the shear deformation of the beam is considered, by treating the crack as a discontinuity in the moment of inertia. The transverse beam deflection is derived by the mode superposition method employing the orthogonality conditions of the vibration normal mode function when a point-load excitation is applied at the midspan. Assuming the dynamic stress intensity factor is proportional to the difference between the displacement of the specimen at the midspan and that at the end, a simple formula is employed for calculating the time history of the dynamic stress intensity factor for a dynamic one-point bending test. It is shown that the natural frequency and the dynamic stress intensity factor are reduced due to the shear deformation of the beam based on the Timoshenko beam theory comparing to the results based on the Euler- Bernoulli beam theory, and the effect of the rotary inertia caused by the shear deformation is evident when the frequency is high based on the modified Timoshenko beam theory.

Effect of spacing on some mechanical properties of narrow leaved ash (Fraxinus angustifolia) wood

In this study, conducted to test the effect of spacing on wood quality; the effect of four different spacing types, applied in Adapazari Suleymaniye plantation (Region 1; 3x2 m; Region 2; 3x2,5 m; Region 3; 3,75x3,75 m; Region 4; 4x4 m), on some mechanical properties of narrow leaved ash (Fraxinus angustifolia) have been studied. In the present study, some mechanical properties such as the compression strength parallel to grain, tensile stress perpendicular to grain, bending strength, impact bending strength and modulus of elasticity were determined. As a result, the ash wood, grown in region 4 with a wide range of planting, has high mechanical properties. However, when analyzed in terms of wood quality characteristics, it has been found that spacing in region 1 (2x3 m) is more suitable for applications of ash plantations.

Mechanical properties of chemically modified portuguese pinewood

To turn wood into a construction material with enhanced properties, many methods of chemical modification have been developed in the last few decades. In this work, mechanical properties of pine wood were chemically modified, compared and evaluated. Maritime pine wood (Pinus pinaster) was modified with four chemical processes: 1,3-dimethylol-4,5-dihydroxyethyleneurea, N-methylol melamine formaldehyde, tetra- alkoxysilane and wax. The following mechanical properties were assessed experimentally: Modulus of elasticity measured statically, stiffness stabilization efficiency in different climates (30 and 87% of relative humidity), modulus of rupture, work maximum load, impact bending strength, compression, tensile and shear strength at indoor conditions (65% of relative humidity). In both types of active principle of modification, cell wall or lumen fill, no significant changes on the bending stiffness (modulus of elasticity) were found. In the remaining properties analysed significant changes in the modified wood-material took place compared to unmodified wood control: - Cell wall modification was the most effective method to achieve high stiffness stabilization efficiency (up to 60%) and also increased compression strength (up to 230%). However, modulus of rupture, tensile, shear and the impact bending strength were reduced by both resins, but in a varying extent, where the N-methylol melamine formaldehyde endured less reduction than 1,3-dimethylol-4,5-dihydroxyethyleneurea resin. In the latter, reduction up to 60% can take place. - In the lumen fill modification: tetra-alkoxysilane has no effect in the mechanical properties. Although, a slight increase in shear strength parallel to the grain was found. Wax specimens have shown a slight increase in bending strength, compression, tensile and shear strength as well as in the absorption energy capacity.

Modelling of composite failure during vehicle crash using cohesive elements

Composite utilisation for vehicle crash applications currently relies on extensive testing since numerical simulation tends to be complex and time consuming. Simulation of inter- and intralaminar failure commonly employs highly refined meshes, while full vehicle crash models commonly use coarse shell meshes. Here, axial impact and three-point bending impact tests were conducted and simulated using a layered shell approach. Coarse meshes and cohesive elements were used with several plies grouped into individual shells to reduce the number of degrees of freedom and thus enhance the numerical efficiency. Cohesive element properties were then simultaneously calibrated against the test data using adaptive response surface methodology. After calibration simultaneous simulation of both failure modes in axial crushing and three-point-bending proved to be difficult. In particular, the peak load for axial crushing and the deformation depth for three-point-bending could not be replicated. The results demonstrate the current limitations of composite failure modelling using coarse cohesive and shell elements with respect to full vehicle simulations and future routes forward are discussed.

An Experimental Method for Dynamic Delamination Analysis of Composite Materials by Impact Bending

An improved experimental method for characterizing dynamic delamination growth in composite structures has been developed and verified using high speed photography and explicit finite element simulation. The method is based on a three-point bending device. End notch flexure carbon fiber composite beam specimens were subjected to both quasi-static and impact rates of Mode II loading. The experimental results showed no significant strain rate dependency of the delamination fracture toughness. This important result complements the scarce and conflicting data available in the literature, and serves as a reference for calibration of numerical modeling strategies.

Structure and ductility of the heat-affected zone of welded joints of a high-strength steel

Methods of optical microscopy and scanning and transmission electron microscopy have been used to study the structure of welded joints of a high-strength structural steel with different types of the weld metal. The impact toughness of the heat-affected zone (HAZ) has been determined at temperatures of +20 and −40°C. Based on the fractograph investigations of the character of the fracture of the welded joints after tests for impact bending, the regions that are the most dangerous for crack initiation have been determined. Structural factors that affect the brittleness of the near-weld zone of welded joints with the austenite metal of the weld are indicated, including the existence of an austenite-bainite structure and coarse carbides, as well as the specific distribution of hydrogen.

Influence of Stress Mode on Failure Micromechanisms of Nodular Cast Iron

The paper deals with comparison of the failure micromechanisms of nodular cast iron at static, impact and fatigue stress. Several specimens of ferrite-pearlitic nodular cast irons with different content of ferrite in a matrix were used for metallographic analysis, mechanical tests and microfractographic analysis. Mechanical properties were found out by static tensile test, impact bending test and fatigue tests. The microfractographic analysis was made with use of scanning electron microscope on fracture surfaces of the specimens fractured by these mechanical tests. Fracture surfaces of analysed specimens are characteristic of mixed mode of fracture. Failure micromechanism of nodular cast irons is dependent on mode of stress.

Mechanical properties and chemical composition of beech wood exposed for 30 and 120 days to white-rot fungi

Abstract The effects of exposing specimens of Oriental beech [Fagus sylvatica subsp. orientalis (Lipsky) Greuter and Burdet] to the white-rot fungi Pleurotus ostreatus (Jacq.: Fr.) Kummer and Trametes versicolor (L.: Fr.) Pilát strain 325 have been studied concerning the mechanical properties and chemical composition in terms of carbohydrates, cellulose, and lignin. Biological decay tests were carried out in accordance with the EN 113 standard specifications for 30 and 120 days. P. ostreatus had nearly the same deteriorating effects on the mechanical properties and chemical composition as that caused by T. versicolor. High and significant correlations were found between some mechanical properties with chemical components; for instance, the correlation coefficient (R2) between impact bending and carbohydrate content was about 0.96. The changes of components influence the various mechanical properties to a different degree. Incipient fungal decay caused severe changes for impact bending and carbohydrate loss. Several other properties declined at 120-day exposure time, such as the hardness, compression strength parallel to grain, and cellulose and lignin losses.

Effect of Processing Aids on the Performance of High Filled Polypropylene

In this paper, we mainly introduces the influence of the processing aids TR131 which namely the lubricating and dispersion agents on the properties of high filled polypropylene. The experiment compared the melt flow rate, tensile strength, bending strength and impact strength of the high filled polypropylene with processing aids TR131 and without it. The results show that high filled polypropylene with Calcium Carbonate could improve the bending strength and impact strength of the pure polypropylene, but the melt flow rate and tensile strength decreased. Incorporation of processing aids TR131 could improve the melt flow rate and the tensile strength of the high filled polypropylene.

Some physical and mechanical properties of reinforced laminated veneer lumber

In this study, poplar laminated veneer lumber (LVL) was produced using phenol formaldehyde adhesive, and reinforced LVL (RLVL) was produced by inserting woven glass fibers between the veneer sheets. Some tests were conducted to analyze the effects of the reinforcement on the properties of the LVL. Some physical properties, such as density, moisture content, and swelling were determined, as were the mechanical properties of impact bending, specific impact bending, and shear strength. The test results indicated that density, impact bending, and shear strength increased. Conversely, tangential swelling, volumetric swelling, moisture content, and specific impact bending decreased. Increased dimensional stability of wood-based materials is a preferred property for many applications due to the increased service life. In addition, the increases in impact bending and shear strength, especially in the connection points and load-bearing points in structural applications, were the most important results of the study.

Tensile and bending properties of biaxial weft-knitted and cross-ply thermoplastic composites

In this study, within the scope of experiments, two kinds of biaxial weft-knitted (BWK) fabrics with aramid (AR) and polyamide 66 (PA66) stitch fibers were used as reinforcement systems to fabricate thermoplastic composites with PA66 resin yarn. Then final composite became BWK with AR stitch yarn and cross-ply. The mechanical properties of composites were investigated by conducting tensile and three-point bending tests on specimens. In all specimens, PA66 was commingled with AR yarn. AR was used as reinforcement. In preliminary studies, AR unidirectional composites with AR/PA66 commingled fibers and with various twisting angles were produced and appropriate twisting angle was found by conducting tensile and three-point bending impact tests on specimens. Because of the higher volume fraction of the cross-ply composites, tensile and three-point bending properties of the cross-ply composite structures had higher than the BWK composites with the AR stitch yarn.

Reinforcing of Cement Composites by Estabragh Fibres

The influence of Estabragh fibres has been studied to improve the performance characteristics of the reinforced cement composites. The concrete shrinkage was evaluated by counting the number of cracks and measuring the width of cracks on the surface of concrete specimens. Although, the Estabragh fibres lose their strength in an alkali environment of cement composites, but, the ability of Estabragh fibres to bridge on the micro cracks in the concrete matrix causes to decrease the width of the cracks on the surface of the concrete samples in comparison with the plain concrete. However, considering the mechanical properties of specimens such as bending strength and impact resistance, the specimens with 0.25 % of Estabragh fibre performed better in all respects compared to the physical and mechanical properties of reinforced cement composite of concrete. Consequently, by adding 0.25 % of Estabragh fibres to the cement composite of concrete, a remarkable improvement in physical and mechanical properties of fibre-containing cement composite is achieved.

Investigations of Microstructure and Mechanical Properties of 60-mm-Thick Type 316L Stainless Steel Welded Plates by Multipass Tungsten Inert Gas Welding and Electron Beam Welding for Fusion Reactor Applications

Austenitic Type 316L stainless steel plates of very large thicknesses are considered for use in vacuum vessel fabrication in advanced fusion reactors. The possible options for welding of higher-thickness plates are multipass tungsten inert gas (TIG) welding, narrow gap–TIG welding, and electron beam welding (EBW). The manufacture of double-wall vacuum vessel inner components like keys, shells, and ribs are planned to be fabricated using EBW, and some components like field joints are to be fabricated using TIG welding processes. The present paper reports the fabrication of 60-mm-thick Type 316L stainless steel welded samples with multipass TIG welding and EBW processes and sample property characterization studies. The fabricated weld samples have been tested for weld defects with nondestructive tests using X-ray radiography and ultrasonic scan tests. The welded samples have been characterized for mechanical properties such as tensile, bend, Vickers hardness, and Charpy V-notch impact tests. Microstructure analysis has been carried out for both welded samples for the base metal, heat-affected zone, and weld zone. Impact-tested sample fracture analysis has been done by scanning electron microscopy.

Effect of various loop lengths on mechanical properties of biaxial weft-knitted thermoplastic composites

Within the scope of experiments, five kinds of biaxial weft-knitted (BWK) fabrics with various loop lengths (8.0, 9.2, 10.5, 11.9, and 13.5 mm) were used as reinforcement systems to fabricate thermoplastic composites with polypropylene (PP) resin yarn. Then, the final composite became BWK composite with various loop lengths. The mechanical properties of the composites were investigated by conducting tensile, three-point bending, and three-point bending impact tests on specimens. In all specimens, PP was commingled with glass yarn. Glass was used as the reinforcement material. Fiber volume fraction of weft fibers with the 8.0 mm loop length was the highest compared with the other four types of specimens. Because of the higher volume fraction of the BWK composites with the 8.0 mm loop lengths, tensile, three-point bending, and three-point bending impact properties of the 8.0 mm loop were higher than the other four types (9.2, 10.5, 11.9, and 13.5 mm) of composite structures.

Mechanical properties of biaxial weft-knitted and cross-ply thermoplastic composites

Within the scope of experiments, two kinds of biaxial weft-knitted (BWK) fabrics with aramid (AR) and polyamide (PA) 66 stitch fibers were used as reinforcement systems to fabricate thermoplastic composites with PA66 resin yarn. Then, the final composite became BWK with AR stitch yarn and cross-ply. The mechanical properties of composites were investigated by conducting tensile and three-point bending impact tests on specimens. In all specimens, PA66 was commingled with AR yarn. AR was used as reinforcement. In preliminary studies, AR unidirectional composites with AR/PA66 commingled fibers and with various twisting angles were produced and appropriate twisting angle was found out by conducting tensile test on specimens. Due to the random multiple cracks that changed the fracture behavior of BWK composites with AR stitch, the tensile properties of the BWK composites with AR stitch became lower compared with the cross-ply. However, the three-point bending impact properties of the BWK composites with AR stitch fiber were higher compared with the cross-ply.

Effect of various knitting techniques on mechanical properties of biaxial weft-knitted thermoplastic composites

Within the scope of experiments, five kinds of biaxial weft-knitted (BWK) fabrics with various knitting techniques (plain, interlock, tuck, tuck-miss, and interlock2) were used as reinforcement systems to fabricate thermoplastic composites with polypropylene (PP) resin yarn. Then, the final composite became BWK composites with various knitting types. The mechanical properties of composites were investigated by conducting tensile, three-point bending, and three-point bending impact tests on specimens. In all specimens, PP was commingled with glass yarn. Glass was used as reinforcement. Fiber volume fraction ( Vf) of weft fibers of the interlock2 was the highest, and the length of straight part of loop shape was the longest in the interlock2 compared with the other four types of specimens. Because of the higher Vf of the BWK composites with the interlock2, tensile, three-point bending, and three-point bending impact properties of the interlock2 was higher than the other four types (plain, interlock, tuck, and tuck-miss) of composite structures.

Inclusion of Strain-Rate Effects in Low Velocity Impact Simulation of Laminated Composites

Composite materials are widely used in aircraft, automotive, marine and railway applications and are exposed to impact loads, in particular low velocity impact. As material properties of composites are affected by strain-rate [, finite element analysis (FEA) by using static properties would not predict their impact behaviour accurately. Thus, the objective of this study was to include strain-rate effects in the simulation of composite laminates under low velocity impact. This was achieved using ABAQUS anisotropic damage model (ADM) by taking account of material properties changes as a function of log strain-rate using user-defined ABAQUS/VUSDFLD subroutine Strain-Rate Dependent ADM (SRD ADM). Results obtained from SRD ADM were validated using simple tensile test done by Okoli [. Subsequently a three-point bending impact event of a simple composite laminate beam by a cylindrical steel impactor was simulated using both the original ABAQUS Static ADM and the user-defined SRD ADM, and compared with experimental impact test results done by [. The results show that reductions in errors of predicted maximum impact reaction force (compared to experimental data) were achieved from 29% using Static ADM to 14% using SRD ADM and from 35% using Static ADM to 15% using SRD ADM respectively for impactor speeds of 2 ms-1 and 5 ms-1.