Instrumented Charpy Impact Test Research Articles

FINITE ELEMENT MODELLING OF CRACKABLE CONNECTING RODS AT FRACTURE SPLITTING PROCESS

In this study crack propagation analysis of impul-sively loaded connecting rods with different microstuctures namely perlitic, bainitic, tempered martensitic were studied numerically for evaluation of fracture parameters. Fracture splitting parameters in experiments for uniform impact force distribution was concerned in numerical analysis. Brittle crack propagation at starting notchs was obtained by impulsive load. Dynamic crack propagation was studied by using two dimensional finite element model and crack tip positions were determined by remeshing algoritm. Dynamic stress intensity factors were calculated by J integral technique and celevage failure was detected according to dynamic fracture toughness parameters by instrumented Charpy impact test. Crack propagation, crack arrest times, cleavege times were found and compared numerically for three different microstructures. Predicted shear effective stress intensity calculations, crack tip velocity, crack extesion results are found supplementary data for experimental fracture parameter optimisation. DOI: http://dx.doi.org/10.5755/j01.mech.21.2.7748

The contribution of intragranular acicular ferrite microstructural constituent on impact toughness and impeding crack initiation and propagation in the heat-affected zone (HAZ) of low-carbon steels

We elucidate here the contribution of intragranular acicular ferrite (IAF) on impending crack initiation and propagation in the heat-affected-zone (HAZ) of low carbon steels based on Instrumented Charpy impact test. It was observed that both crack initiation energy and crack propagation energy of the steel in the presence of IAF were higher than steel that did not contain IAF, where the former situation was observed to have a large ductile fracture zone as compared to the latter. An analysis of the statistical distribution of voids in the cross-section of impact fracture indicated that IAFs increase the length of plastic zone at the tip of the main crack and impede crack initiation and enhance crack initial energy because of refined prior austenite grain and superior deformability. Furthermore, EBSD analysis of secondary cracks indicated that IAF impedes crack propagation and increases crack propagation energy by forming high angle grain boundaries with surrounding bainite and its own superior deformability.

Determination of slow crack growth behaviour of polyethylene pressure pipes with cracked round bar test

In this work, a short time test method to determine the slow crack growth behaviour of samples made out of pipes was evaluated. The cracked round bar (CRB) method used provides results below 48 h with brittle fracture surfaces, which indicates the type of slow crack growth failure. To evaluate the usability of the method, the results were compared with well-known tests such as notch pipe test, 2 notch creep test and instrumented Charpy impact tests. The results indicate that the CRB test can be used to predict long term slow crack growth behaviour of PE pipes.

Fabrication of Tungsten-Vanadium Hybrid Material with Sufficient Toughness for High-Temperature Applications by Diffusion Bonding

The design of fusion plasma-facing components is challenging, as their materials have to meet rigorous requirements in terms of low activation and high-temperature strength. At the same time, sufficient ductility is required even in the low-temperature range. Unfortunately, these properties are not found in conventional materials. To solve this problem, a hybrid material that combines the high strength of one material with the high ductility of the other material was developed. This paper presents the hybrid material, which consists of thin tungsten and vanadium layers. This hybrid material was produced by means of diffusion bonding at relatively low temperature in a vacuum chamber. Microstructural investigations and nanoindentation tests indicated no cracks, no delamination, and no brittle intermetallic phases along the bond interfaces. Investigations of the mechanical properties of the hybrid material by instrumented Charpy impact tests revealed a relatively low ductile-to-brittle transition temperature (DBTT) at 124°C (compared to the DBTT of polycrystalline tungsten of >441°C) with an absorbed Charpy impact energy of 4.53 J [kleinst (KLST)-specimen]. Additionally, the tested Charpy impact specimens were found to be not fractured thoroughly even at room temperature.

Influence of biodiesel sorption on temperature-dependent impact properties of polyethylene

In a previous paper we investigated the influence of sorbed biodiesel or diesel on mechanical properties of a typical polyethylene grade for tank applications. Besides the basic sorption and desorption behavior of these two fuels, the study addressed the concentration-dependent mechanical properties as revealed by a non-instrumented Charpy impact test and dynamic mechanical analysis (DMA). In the present paper we extend this investigation focusing on the temperature-dependent impact fracture behavior. Therefore, an instrumented Charpy impact test was employed, allowing a more detailed analysis of the fracture behavior. Furthermore, from the load-time-diagrams obtained from the instrumented impact test, corresponding fracture times can be calculated, allowing a clear correlation of the fuel sorption induced changes in fracture toughness with the enhanced β-relaxation observed by DMA. As in the previous study, the fracture surfaces of the impact tested specimens were analyzed in order to confirm the brittle or ductile character of the fracture indicated by impact strength and the corresponding load-deflection diagrams.

Impact Toughness of 0.3 Mass% Carbon Tempered Martensitic Steels Evaluated by Instrumented Charpy Test

The effect of tempering temperature on the impact toughness of 0.3 mass% carbon martensitic steels with prior austenite grain (PAG) size of about 6 μm and 30 μm were investigated. Instrumented Charpy impact test (ICIT) method was used to evaluate the impact toughness. The tempering temperature of 723K gives the largest difference in the Charpy impact energy at room temperature (RT) between the specimens with two different PAG sizes. Investigation of the test temperature dependence of Charpy impact energy in the 723K tempered steels shows a steep transition at around 200 K for the 6 μm PAG specimen, while it shows a continuous slow transition in a wide range of temperature for the 60 μm PAG specimen. ICIT waveform analysis shows that the fracture propagation energy in stead of the fracture initiation energy mainly controls the temperature dependence of the impact energy. The carbide size distribution in these two specimens was investigated by SEM and TEM. The 60 μm PAG specimen shows the distribution of coarser carbides than does the 6 μm PAG specimen, which seems to be the main reason for the observed difference between them in the Charpy impact energy and the other properties of impact fracture.

0.23C-1.9Mn-1.6Si钢中的残余奥氏体对韧塑性的影响

采用优化的IQ&P工艺处理成分为0.23C-1.9Mn-1.6Si厚度为6.5 mm的低碳硅锰钢,制备出由亚温铁素体、马氏体以及残余奥氏体构成、抗拉强度为1000 MPa的多相组织高强钢。用SEM、XRD、拉伸以及示波冲击等手段对其显微组织和力学性能进行表征,并与同等抗拉强度的IQ&T钢和Q&T钢对比,研究了钢中残余奥氏体对韧塑性的影响。结果表明,在室温下IQ&P多相钢具有更高的冲击韧性、更好的延伸性能和强塑积,综合韧塑性要远优于其它钢种。该钢的性能,与其多相组织结构有密切的关系。大量弥散分布于铁素体和马氏体框架内的残余奥氏体在形变过程中发生TRIP效应,显著改善了钢的韧塑性,从而使其综合力学性能提高。

Experimental Investigation on the Aging Response, Hardness and Total Impact Energy Absorption of Sr-Modified Heat-Treatable Cast Automotive Aluminum Alloys

In this study, a computer-aided instrumented Charpy impact test was used to produce the load–time information in addition to data concerning the energy absorbed of unmodified and Sr-modified cast automotive Al alloys. The total energy was used to discuss the impact properties of the alloy with respect to the different alloying elements and melt processing parameters. Effects of alloying elements, Sr-modification, and cooling rate were specifically evaluated. Aging response of the Al alloys at 185 °C indicated a rise in hardness and decline in impact toughness during the first 4 h of aging. The cooling rate is found to have a direct effect on the size and distribution of microstructural phases in a casting, and in turn, on the impact toughness as well.

Evaluation of fracture toughness and impact toughness of laser rapid manufactured Inconel-625 structures and their co-relation

The present study involves evaluation of fracture toughness and Charpy impact toughness of Inconel 625 structures fabricated by laser based additive manufacturing. The results of crack tip opening displacement (CTOD) fracture toughness are close to those reported for the Inconel 625 weld metal. The nature of the load–time traces of instrumented Charpy impact tests revealed that the alloy Inconel 625 in laser fabricated condition was associated with fully ductile behavior with Charpy V-Notch impact energy in the range of 48–54J. Stress relieving heat treatment at 950°C for 1h has resulted in marginal improvement in the impact toughness by about 10%, whereas no clear evidence of such improvement is seen in the CTOD fracture toughness. Fractographic examination of the Charpy specimens and the results of the instrumented impact tests imply that the mechanism of crack growth was propagation controlled under dynamic loading conditions. Dynamic fracture parameters were estimated from the instrumented impact test data and compared with the experimentally evaluated fracture toughness results.

Fracture Mechanics Properties of Polymorphic Polypropylene

Polypropylene (PP) is a widely used thermoplastic and polymorphic polymer. Three different types of PP were prepared, namely non-nucleated, α- and β-nucleated PP. These materials were pressed using different cooling rates to influence the degree of crystallinity χ within the materials, which was determined by differential scanning calorimetry (DSC). The materials resistance against stable crack propagation was described by R-curves. The Jd–Δa curves were determined using the instrumented Charpy impact test (ICIT) to apply single edge notch bending specimens (SENB) with a high loading velocity. The results show not only the influence of the cooling rate on the degree of crystallinity but also a correlation between the degree of crystallinity and the materials resistance against stable crack propagation. The lower the cooling rate of the material is the higher is the degree of crystallinity and the higher seems to be the materials resistance against stable crack propagation.

Impact Toughness of an NM400 Wear-Resistant Steel

An NM400 wear-resistant steel was hot rolled and then the plates were heat-treated by direct quenching and tempering (DQT) and reheat quenching and tempering (RQT) techniques, respectively. The Charpy impact test was carried out with an instrumented Charpy impact tester. The microstructure and fracture surface were investigated by a combination of optical microscopy, transmission electron microscopy and scanning electron microscopy methods. It was found that the impact toughness of DQT specimen was much higher than that of RQT specimen. The microstructure of both DQT and RQT specimens was characterized by a mixture of tempered lath martensite and lower bainite. The lower bainite in DQT specimen extended into prior austenite grains and the content was higher than that in RQT specimen. The lower bainite in DQT specimen improved the impact toughness by increasing the proportion of large-angle boundaries and relieving the stress concentration at the crack tip. A number of fine and dispersed carbides in DQT specimen also contributed to the improvement of the impact toughness.

Charpy impact properties of 9CrODS ferritic steels

The toughness of 9CrODS steels was evaluated by using an instrumented Charpy impact test machine, focusing on various processes such as hot-forging and hot-rolling. The upper-shelf energy (USE) of the hot-forged specimens is superior; their full-size USE converted from the miniaturized specimen lies within the published data for ODS steels, whereas hot-rolling leads to poor toughness. The total absorbed energy was separated into the energies for crack initiation and propagation. The hot-forged 9CrODS steels provide similar crack initiation energy to ferritic/martensitic steels (FMSs); their low absorbed energy is attributed to a limited amount of crack propagation energy induced by plastic deformation.

Developing higher strength microalloyed medium carbon steel capable of being fracture split after laser transformation notching

High proof strength (>600 MPa) microalloyed medium carbon steels are being developed to replace high carbon steels in the production of internal combustion engine components which are manufactured by processes involving fracture splitting. The target steels are required to achieve a balance between the ability to fracture when initiated by a novel laser transformation notch (LTN) and the properties required by the application. In this study, the effect of phosphorus (P) and sulphur (S) and the depths of LTN on the fracture process of these forged steels were investigated by using an instrumented Charpy impact tester. The impact specimens were notched by a fibre laser with no removal of material. The depth of the notch showed a significant influence on the force–displacement curves, the Charpy impact energy and the associated fracture surfaces. The steel with combined high S and P contents showed the lowest Charpy impact energy of 2·9 J when the depth of LTN was >0·4 mm compared to 5·5 J with the steel containing only a higher S content and 11·2 J for the reference base steel with normal S and P contents. It was observed that MnS inclusions in the originally forged materials were redistributed to the resolidified grain boundaries in the melted region of the LTN. The distribution of P could not be identified in the LTN but presumably it also segregated to the interdendritic regions and the columnar grain boundaries during freezing. The steel containing enhanced contents of S and P was shown to be potentially suitable for fracture splitting and higher load applications.

Assessment of Fracture Behaviour under Impact Loading with Simultaneous Recording of Acoustic Emission

Abstract The objective of this paper is the assessment of the toughness of glass fiber-reinforced polypropylene and polybutene-1 by means of fracture mechanics concepts to describe the resistance against unstable crack initiation for these materials. In addition, the acoustic emissions during the instrumented Charpy impact test were recorded, which allows the characterization of the damage kinetics. For this purpose, the recorded transient signals of the acoustic sensor were analyzed with the wavelet transform. Thus, it was possible to describe the onset of the damage in the time domain, as well as the load Fs and the corresponding deflection fs. In dependence on the bonding conditions of the materials, the damage onset was detected for polypropylene before and for polybutene-1 at the transition from elastic to elastic-plastic behaviour.

Impact tests of the tungsten coated stainless steels prepared by using magnetron sputtering with ion beam mixing or electron beam alloying treatment

Tungsten films were deposited on stainless steel (SS) with ion beam mixing (IBM) or electron beam alloying (EBA) treatment. The ductile–brittle transition behaviors of the specimens were investigated by means of instrumented Charpy impact test at a series of temperature, and SEM was used to observe the morphology of the cross section. Impact tests show that different treatment methods with W films do not have much influence on crack initiation, while EBA treatment with W films can more effectively prevent crack propagation, namely improve the impact toughness of SS than using IBM treatment. The reason that caused this difference was discussed.

Temperature dependence of fracture behavior of PA6/OMMT nanocomposites

AbstractThe aim of this work was to characterize the fracture behavior of polyamide 6 (PA6) and PA6 reinforced with clay (organically modified montmorillonite) [PA6/OMMT] at different temperatures and under higher loading rate. Pure PA6 and PA6 with different amounts and two types of OMMT were investigated. The structure and morphology of the nanocomposites were analyzed by X‐ray diffraction technique and transmission electron microscopy. The fracture behavior was evaluated using the instrumented Charpy impact test at different temperatures starting from −30 °C up to 50 °C. To determine the fracture toughness KId at higher temperatures, the equivalent‐energy concept was used. Based on the J‐value versus temperature diagrams, the brittle‐to‐tough transition temperature TBTT of the materials was determined. It was found that the crack toughness as a function of temperature and the TBTT are influenced by the content of OMMT and the morphology. There are indications that at low OMMT contents, the deformation behavior is dominated by the matrix properties. With increasing filler content, the influence of the nanostructure on TBTT increases. The crack toughness of the nanocomposites with an intercalated morphology is higher than that of exfoliated ones, due to additional energy‐dissipating mechanisms. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci, 2013

Microstructural characteristics and toughness of the simulated coarse grained heat affected zone of high strength low carbon bainitic steel

Abstract The correlation of microstructural characteristics and toughness of the simulated coarse grained heat affected zone (CGHAZ) of low carbon bainitic steel was investigated in this study. The toughness of simulated specimens was examined by using an instrumented Charpy impact tester after the simulation welding test was conducted with different cooling times. Microstructure observation and crystallographic feature analysis were conducted by means of optical microscope and scanning electron microscope equipped with electron back scattered diffraction (EBSD) system, respectively. The main microstructure of simulated specimen changes from lath martensite to coarse bainite with the increase in cooling time. The deterioration of its toughness occurs when the cooling time ranges from 10 to 50 s compared with base metal toughness, and the toughness becomes even worse when the cooling time increases to 90 s or more. The MA (martensite–austenite) constituent is primary responsible for the low toughness of simulated CGHAZ with high values of cooling time because the large MA constituent reduces the crack initiation energy significantly. For crack propagation energy, the small effective grain size of lath martensite plays an important role in improving the crack propagation energy. By contrast, high misorientation packet boundary in coarse bainite seems to have few contributions to the improvement of the toughness because cleavage fracture micromechanism of coarse bainite is mainly controlled by crack initiation.

RETRACTED: Simulation Charpy impact energy of functionally graded steels by modified stress–strain curve through mechanism-based strain gradient plasticity theory

Abstract In the present work, Charpy impact energy of functionally graded steels produced by electroslag remelting composed of graded ferritic or austenitic layers in both crack divider and crack arrester configurations has been modeled by finite element method. The yield stress of each layer was related to the density of the statistically stored dislocations of that layer and assuming by Holloman relation for the corresponding stress–strain curves, tensile strengths of the constituent layers were determined via numerical method. By using load–displacement curves acquired from instrumented Charpy impact tests on primary specimens, the obtained stress–strain curves from uniaxial tensile tests were modified. The data used for each layer in finite element modeling were predicted modified stress–strain curves obtained from strain gradient plasticity theory. A relatively good agreement between experimental results and those obtained from simulation was observed.

RETRACTED: Application of strain gradient plasticity theory to model Charpy impact energy of functionally graded steels using modified stress–strain curve data

Abstract Functionally graded ferritic and austenitic steels were produced through electroslag refining by setting the austenitic and carbon steels with appropriate thickness as electrode. Charpy impact energy of the specimen has been studied and modeled regarding the mechanism-based strain gradient plasticity theory. The hardness of each layer was related to the density of the dislocations of that layer and then by using a linear relation, the predicted hardness was related to its corresponding yield stress. Afterwards; by assuming Holloman relation for the corresponding stress–strain curves, tensile strengths and tensile strains of the constituent layer were determined via numerical method. By using load–displacement curves acquired from instrumented Charpy impact tests on primary specimens, the obtained stress–strain curves from uniaxial tensile tests were modified. Charpy impact energy each layer was related to the corresponding area under modified stress–strain curve of that layer and finally by applying the rule of mixtures, Charpy impact energy of functionally graded steels was determined. The obtained results of the proposed model are in good agreement with the experimental ones.

RETRACTED: Modeling Charpy impact energy of functionally graded steel based on the strain gradient plasticity theory and modified stress–strain curve data

Abstract Functionally graded ferritic and austenitic steels were produced through electroslag refining by setting the austenitic and carbon steels with appropriate thickness as electrode. Charpy impact energy of the specimen has been studied and modeled regarding the mechanism-based strain gradient plasticity theory. The yield stress of each layer was related to the density of the statistically stored dislocations of that layer and assuming Holloman relation for the corresponding stress–strain curves, tensile strengths of the constituent layer were determined via numerical method. By using load–displacement curves acquired from instrumented Charpy impact tests on primary specimens, the obtained stress–strain curves from uniaxial tensile tests were modified. Charpy impact energy of each layer was related to the corresponding area under its modified stress–strain curve and finally by applying the rule of mixtures, Charpy impact energy of functionally graded steels was determined. The obtained results of the proposed model are in good agreement with the experimental ones.