Impact Bending Research Articles

Structural Aspects of Zones of Plastic Strain. Part II. Effect of Mass Transfer

The structure of steel 09G2S is studied after high tempering in different zones of plastic strain (ZPS) after testing for impact bending and dynamic crack resistance, i.e., in the starting zone, in the core, and in the region of the force impact of the hammer of the impact machine. The proportions, the sizes, and the elemental compositions of carbide particles in the matrix metal, in the zones closest to the place of the impact, and in the regions of mass transfer are determined. The features of the structure in the starting region of the ZPS and in the region of the force impact of the hammer are determined after additional annealing at 600°C for 1 h.

Optimization of test specimen dimensions for thermal power station exposure device

Degradation of metallic materials can decrease mechanical properties of metal constructions and components in thermal power plants during their operation and consequently lead to loss of safety and reliability. It is difficult to remove material from the pressure system of the equipment being operated. Therefore, the effort is to design, produce and subsequently install exposure channels, which will allow to remove and evaluate samples of exposed material without intervention into the pressure system. The exposure device for pressures and steam temperature in supercritical blocks, which would contain sufficient test material to produce conventional test specimens, is unrealistic in size, energy and economics. The way is to optimize the dimensions of the exposure device according to the miniaturized test specimens, which, in addition to the tensile test and the structural evaluation, can also carry out other required tests, such as bending impact tests with transition temperature, fracture toughness and fatigue tests. This paper deals with optimization of test specimens for the internal dimensions of the exposure device and shows the applicability of small sample methodologies for selected materials.

An experimental study on performance of jute‐polyester composite tubes under axial and transverse impact loading

AbstractThe efficacy of woven jute‐polyester (JP) composite tubes as structural energy‐absorbing countermeasures has been explored in the current study. In this connection, the behaviors of 3‐ply and 4‐ply JP composite tubes of square and double‐hat shaped sections subjected to axial quasi‐static and impact loads are considered, and compared with 4‐ply glass‐polyester (GP) tubes of similar geometric configurations. Initially, basic mechanical characterization of JP laminates is carried out using a Universal Testing Machine, which is followed up with axial quasi‐static and drop‐weight impact testing of JP tubes, along with similar tests carried out on GP tubes. A thorough comparison is made between the performances including failure patterns of JP and GP components under axial loading using metrics such as peak load, mean crush load, absorbed energy, and specific energy absorption (SEA). As many structural applications involve dynamic bending loads, a comparative study is carried out between double‐hat JP and GP components subjected to transverse impact loading. Based on the competitive values of mean load and SEA yielded by jute‐composite tubes in the present study for axial impact loading, and high mean load and moderate energy absorption till failure recorded by similar components under three‐point impact bending, it can be concluded that JP tubes can be capable of supporting impact loads under both axial and bending modes.

The impact toughness and mechanism of low-carbon steel fracture at low temperatures

The goal of the work is to study the effect of severe plastic deformation (SPD) on the impact toughness and fracture mechanism of St3sp low-carbon structural steel within a test temperature range of 293 – 213 K. The issues of deformation processing of steel St3sp billets using SPD method in conditions of the equal-channel angular pressing scheme (ECAP) are considered. The results of low-temperature tests by impact bending of Charpy steel samples in various states are presented. The impact toughness decreased by ~1.3 times as a result of ECAP in 16 passes. It is shown that the temperature dependence of the impact toughness of steel subjected to ECAP differs from that for steel in the delivery condition. A fractographic study of the fracture mechanisms of the steel in the initial state and after processing by ECAP at a test temperature of 293 – 213 K is carried out. It is shown that for the steel in the initial the transition from fracture with the formation of viscous and brittle fracture zones at 293 K to brittle at 213 K occurs through successive expansion of the brittle fracture area with decreasing temperature, whereas for hardened steel, the mixed fracture area appears in the local region at 233 K and expands to the entire cross section of the sample at 213 K. The microstructure formed as a result of ECAP in 16 passes in the temperature range up to 213 K prevents pure brittle fracture and leads to a mixed fracture pattern.

Impact of Flax and Basalt Fibre Reinforcement on Selected Properties of Geopolymer Composites

The submitted paper deals with the physical and mechanical properties of geopolymer composite materials reinforced with natural fibres. For this study, we aimed to develop a geopolymer composite reinforced with long flax fibres, which were implemented in the geopolymer in the form of a nonwoven fabric that reinforced the structure of the geopolymer over the entire thickness of the board. In order to compare the properties of the developed composite with natural fibres, a geopolymer without fibres and a geopolymer reinforced with basalt fibres were also produced. The monitored mechanical properties were impact bending, bending strength and compressive strength. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and microscopic analysis were also carried out. The results clearly showed the positive effect of the addition of natural fibres on impact bending and bending strength. However, the addition of natural fibres in the form of a nonwoven fabric significantly increased the variability of the properties of the developed composites. In addition, a different pattern of joint failure was noted between geopolymer reinforced with flax fibres and geopolymer reinforced with basalt fibres.

Impact of heat treatment on the quality of tree-of-heaven wood

Ailanthus altissima (Miller) Swingle is a deciduous, fast-growing species that can tolerate extreme climatic conditions and is particularly invasive. In the framework of climate change, and the imperative need for carbon greenhouse gases sequestration, this species could acquire increasing importance through its utilization in the construction of wood based products and structures, due to its satisfying properties combined with its fast growth. This study determines for the first time the influence of thermal treatment, under different conditions (190 ºC, 210 ºC, 230 ºC for 2 hours), on some crucial physical, hygroscopic and mechanical properties of wood, in an attempt to improve its intense hygroscopic nature and not so desirable colour. Thermal treatment affected the dimensional stability and water absorbing capacity of wood in a positive way, decreasing EMC, swelling (tangential–radial) and adsorption percent, compared to untreated wood. The anisotropy of wood was decreased only to a small extent. The total surface colour differences (ΔΕ*), prior and after treatment, ranged between 0.48 and 54.57, and appeared to be well correlated with treatment temperature. Only the most intensive treatment influenced negatively the modulus of rupture and impact bending strength of wood, while the elasticity and compression strength of treated wood were proved to be similar to those of untreated wood. Tree-of-heaven could benefit from a mild or medium intensity heat treatment process, in order to be modified to an aesthetically pleasing wood with enhanced hygroscopic nature and properties, facilitating its use in cabinetry and in variable indoor and outdoor non-structural applications.

The Impact of Paraffin-Thermal Modification of Beech Wood on Its Biological, Physical and Mechanical Properties

The European beech (Fagus sylvatica L.) wood was thermally modified in the presence of paraffin at the temperatures of 190 or 210 °C for 1, 2, 3 or 4 h. A significant increase in its resistance to the brown-rot fungus Poria placenta (by 71.4%–98.4%) and the white-rot fungus Trametes versicolor (by 50.1%–99.5%) was observed as a result of all modification modes. However, an increase in the resistance of beech wood surfaces to the mold Aspergillus niger was achieved only under more severe modification regimes taking 4 h at 190 or 210 °C. Water resistance of paraffin-thermally modified beech wood improved—soaking reduced by 30.2%–35.8% and volume swelling by 26.8%–62.9% after 336 h of exposure in water. On the contrary, its mechanical properties worsened—impact bending strength decreased by 17.8%–48.3% and Brinell hardness by 2.4%–63.9%.

The Method of Reducing of Springback Effect during Impact Bending of Sheet Steel Blanks

Results of experimental research of bending of steel sheet blanks on hammer with standard ram and ram with fillets are presented. The increasing of impact time (up to 1.5 times) and reducing of angle of springback (up to 7 times) by using of ram with fillets is obtained. Obtained data will be used for developing of optimal parameters of ram with fillets for increasing dimensional quality of produced parts.

Evolution of the Structure and Mechanism of the Formation of Welded Joints of Medium-Carbon Steels upon Rotary Friction Welding

The structure of the contact lines and of the thermomechanically affected zone of welded joints of medium-carbon steels obtained by rotary friction welding have been studied using metallography and scanning electron microscopy supplemented with X-ray electron microprobe analysis. The results of the microhardness distribution over the cross section of the welded joint are presented. The phase transformations realized at each stage of the technological process of welding in the regions subjected to the thermodeformation influence have been analyzed. The results of the uniaxial tensile and impact bending tests supplemented by the fractography of the fracture surface are presented.

Choice of metal materials for responsible parts and vehicle assemblies operating under the conditions of low temperatures

The purpose of the present study is to evaluate the cold resistance and develop an algorithm for selecting metals that are widely used for manufacturing critical parts and components of vehicles operating in a wide range of low temperatures.To achieve this goal, the tests were made on impact bending of the studied metals in the temperature range of climatic cold, followed by the study of fractures of metal samples.The studies were carried out using methods of optical and electron microscopy and fracto-graphic studies. During the study, data were obtained on the change in toughness, the mechanisms of metal destruction for a wide range of low temperatures, as well as the temperature of the viscous-brittle transition of the studied metals.It has been found that materials with an FCC and HCP lattice exhibit greater resistance to fracture at low temperatures. It is shown that a change in the fracture mechanism is closely related to their crystal structure features and thermal conductivity.As a result of the research, an algorithm for the selection of cold-resistant materials was developed, and on its basis- a program.

Fracture mechanism characteristics of ultra-thin chopped carbon fiber tape-reinforced thermoplastics hat-shaped hollow beam under transverse static and impact loadings

This paper aims to experimentally and numerically explore fracture mechanism characteristics of ultra-thin chopped carbon fiber tape-reinforced thermoplastics (UT-CTT) hat-shaped hollow beam under transverse static and impact loadings. Three distinct failure modes were observed in the impact bending tests, whereas only one similar progressive collapse mode was observed in the transverse bending tests. The numerical model was to incorporate some hypothetical inter-layers in UT-CTT and assign them with the failure model as cohesive zone model, which can perform non-linear characteristics with failure criterion for representing delamination failure. The dynamic material parameters for the impact model were theoretically predicted with consideration of strain-rate dependency. It shows that the proposed modeling approach for interacting damage modes can serve as a benchmark for modeling damage coupling in composite materials.

Properties of Longitudinal Welded Steel Pipes for Piled Foundations Built under Cryolithic Zone Conditions

The mechanical properties of the base metal and the welded joints are estimated during tension, impact bending, drop weight tearing, static bending, flattening tests, and the Vickers hardness and the residual tangential stresses in them are determined for the longitudinal welded pipes 219–1020 mm in diameter and 8–12 mm in wall thickness manufactured by the AO Vyksunskii Metallurgical Plant. The hardness distribution over the pipe perimeter and the cross section is uniform and the cracking resistance of the pipes at negative temperatures up to –60°C is high. Local heat treatment of the welded seam and high-temperature tempering of the entire pipe ensure a high strength and high cold resistance of the pipes. The longitudinal pipes subjected to local and bulk heat treatment can be used like seamless pipes and as piles for the bases of buildings and structures erected in the cryolithic zone.

Sheet metal with variable mechanical properties over its thickness

The influence of one-sided accelerated cooling of A32 plate shipbuilding steel with thickness of 10·10–3 m on structure and mechanical properties was investigated. As a result of such cooling, continuous spectrum of microstructures from ferrite-bainite on the rapidly cooled surface to ferrite-perlite on the opposite surface is formed along the billet thickness. Therefore, over the billet thickness strength properties are reduced from rapidly cooled surface to the opposite one. Thus, the gradient of strength characteristics (hardness, yield strength and rupture strength) along the billet thickness is directed to rapidly cooled surface. For comparative analysis, other batches of billets were subjected to normalization and hardening with high tempering. The analysis of mechanical properties has shown that strength and plastic properties of the samples at unilateral accelerated cooling are at level of heat-strengthened state. Testing on impact strength of the samples with variable distribution of mechanical properties over their thickness has shown that the impact depends on correlation of gradient directions of strength properties and load application. In impact bending test at the temperature of –40 °C, if the direction of load application is opposite to gradient of strength properties, the impact work was more than 300 J (the sample did not collapse). At coincidence of directions of the gradient deformation resistance and load, energy of the blow was 262 J. Thus, if the direction of deformation resistance gradient coincides with the direction of external applied load, then it leads to an increase in plasticity of steel. It is shown that, knowing distribution of strength characteristics over the sample thickness, it is possible to calculate integral values of yield strength and rupture strength of the sample. Value of relative through-thickness elongation increases from the rapidly cooled surface to the opposite one. Integral elongation of the billet is less than the smallest relative through-thickness elongation. With changing thickness strength of the billet during bending, displacement of the neutral deformation line relative to the geometrically average line in the direction of the strength properties gradient is inevitable. The position of neutral line of deformation during bending is proposed to be determined by the value of experimental integral yield strength (rupture strength).

Influence of the Direction of Propagation of the Main Crack on the Fracture Mechanism upon Impact Bending of Samples of High-Viscous Steel with a Filamentary Structure. Compression Region

Influence of the Direction of Propagation of the Main Crack on the Fracture Mechanism upon Impact Bending of Samples of High-Viscous Steel with a Filamentary Structure. Compression Region

Influence of the Direction of Propagation of the Main Crack on the Fracture Mechanism upon Impact Bending of Samples of High-Viscous Steel with a Filamentary Structure. Tensile Region

Abstract—The fracture profiles and distribution of the microhardness in regions adjacent to the fracture surface in the region of tension of Charpy samples of the high-viscous 08G2B steel (0.08 C; ~2 Mn; 0.2 Mo; ≈0.15 Σ(Ti–V–Nb); 0.004 N; 0.04 Al; 0.004 S; 0.007 P wt %) with a filamentary structure formed by non-recrystallization controlled rolling with an accelerated cooling have been studied. The factors that provide the extremely high impact toughness of steel in the case of the fracture of the Charpy samples perpendicular to the surface of filaments have been revealed.

Impact and bending analysis of composite scarf adhesive joints modified with MWCNTs at room and hot temperatures

Scarf adhesive joints (SAJs) have attracted an increasing attention in joining/repairing of carbon-fiber reinforced epoxy (CFRE) composite structures due to their zero eccentricity, which provides better aerodynamic surfaces. This study evaluated for the first time, the performance of SAJs in CFRE composites under thermo-mechanical impact loads. The adhesive was modified with optimum percentage of multi-walled carbon nanotubes (CNTs). The impact tests were performed at room temperature of +25°C, +50°C and +75°C. The residual flexural properties of the unfailed impacted joints were measured using three-point bending test. Results from impact tests at temperature of 25°C, 50°C and 75°C showed improvement in the impact bending stiffness of the modified SAJs with CNTs by 8.3%, 7.4% and 11.8% and maximum contact force by 15.6%, 21.3% and 18.9%, respectively. The energy at failure of the CNT-SAJs was increased by 15.2% and 16.4% respectively at temperatures of 25°C and 50°C. At test temperature of 75°C the SAJs have hysteresis load-displacement behavior and energy-time curve with rebound energy of 35% and absorbed (damage) energy of 65%. The residual flexural strength of the modified and unmodified SAJs is 98.2% and 86.1% respectively, while their residual moduli have remarkable decrease to 71.7% and 81.3%.

Effect of Preliminary Hydroabrasive Cutting on the Imperfection of Welded Joints and Their Mechanical Properties

The structure of the welded joints of high-strength steel sheets, which were made using hydroabrasive cutting, is studied by optical microscopy, scanning electron microscopy, and electron-probe microanalysis. Uniaxial tensile and impact bending tests are performed on an instrumented pendulum impact testing machine and loading diagrams are recorded. Faulty fusion defects and slag inclusions are revealed during a fractographic investigation of the fracture surfaces of tensile and impact specimens. These defects are shown not to be related to the use of hydroabrasive cutting for cutting rolled sheets.

Experimental analysis of composite scarf adhesive joints modified with multiwalled carbon nanotubes under bending and thermomechanical impact loads

Scarf adhesive joints have attracted an increasing attention in joining/repairing of carbon fiber reinforced epoxy composite structures due to their zero eccentricity, which provides lower stress distribution across the adhesive layer and better aerodynamic surfaces compared to other bonded joints. The main objective of this study is to evaluate the performance of the scarf adhesive joints in carbon fiber reinforced epoxy composites under thermomechanical impact loads, which is very important for the aerospace and automotive industries. The adhesive was modified with optimum percentage of multiwalled carbon nanotubes. The impact tests were performed at 25 ℃, 50 ℃, and 75 ℃. The residual flexural properties of the unfailed impacted joints were measured using three-point bending test. Results from impact tests at 25 ℃, 50 ℃, and 75 ℃ showed improvement in the impact bending stiffness of the modified scarf adhesive joints by 8.3%, 7.4%, and 11.8% and maximum contact force by 15.6%, 21.3%, and 18.9%, respectively. The energy at failure of the modified scarf adhesive joints with multiwalled carbon nanotubes was improved by 15.2% and 16.4% respectively at 25 ℃ and 50 ℃. At test temperature of 75 ℃, the scarf adhesive joints have hysteresis load–displacement behavior and energy–time curve with rebound energy of 35% and absorbed (damage) energy of 65%. The residual flexural strength of the modified and unmodified scarf adhesive joints is 98.2% and 86.1% respectively, while their residual moduli have remarkable decrease to 71.7% and 81.3%.

Effects of board density and mixing ratio on the physio-mechanical properties of cement – Bonded particle board produced from Ceiba pentandra Sawdust

The study evaluated the physical and mechanical properties of cement–bonded particleboards produced from the sawdust of Ceiba pentandra . The production variables investigated were two board densities (1300kg/m 3 and 1200kg/m 3 ) and three different mixing ratios (1:2, 1:2.5 and 1:3). Mean values of Water absorption (WA) and Thickness swelling (TS) after immersion in cold water for 24 hours ranged from 7.64 % to 9.53 % and 2.36 % to 2.99 % respectively. Board density at 1300kg/m 3 and mixing ratio 1:3 had the highest average Modulus of Rupture (MOR), Modulus of Elasticity (MOE) and Impact Bending (IMB) of 4.32 Nmm -2 , 1262.03 Nmm -2 and 12.70J/M 2 respectively. The board density had a significant influence (P < 0.05) on the physical and mechanical properties of the boards. Based on the result, 1300kg/m 3 board density and 1:3 mixing ratio produced the best board for mechanical properties and dimensional stability and can be used for several structural applications. Keywords: Ceiba pentandra , Sawdust, Board density, mixing ratio, physio-mechancial properties

Dynamic response of spiral groove liquid film seal to impact conditions

Abstract The dynamic response of the spiral groove liquid film seal to three types of impact are studied by developing a three-DOF dynamic model which takes average flow model, cavitation effect, squeeze effect and face contact into account. A Gaussian pulse function is first applied to simulate the impact to the seal. Results indicate that the seal can maintain hydrodynamic lubrication regime to avoid significant face contact regardless of the impact type. The pressure variation impact does not necessarily induce leakage due to the dramatically narrowed sealing gap. The shaft drifting and bending impact conditions can bring about leakage risk, but the symptomatic flow rate induced by the former is much heavier than that by the latter at the representive moment.