Charpy Impact Energy Research Articles

Experimental investigation of mechanical and fracture properties of offshore wind monopile weldments: SLIC interlaboratory test results

AbstractS355 structural steel is commonly used in fabrication of offshore structures including offshore wind turbine monopiles. Knowledge of mechanical and fracture properties in S355 weldments and the level of scatter in these properties is extremely important for ensuring the integrity of such structures through engineering critical assessment. An interlaboratory test programme was created to characterise the mechanical and fracture properties of S355 weldments, including the base metal, heat‐affected zone, and the weld metal, extensively. Charpy impact tests, chemical composition analysis, hardness tests, tensile tests, and fracture toughness tests have been performed on specimens extracted from each of the 3 material microstructures. The experimental test results from this project are presented in this paper, and their importance in structural integrity assessment of offshore wind turbine monopiles has been discussed. The results have shown a decreasing trend in the Charpy impact energy and Jmax values with an increase in yield stress from base metal to heat‐affected zone to weld metal. Moreover, the JIC fracture toughness value in the heat‐affected zone and weld metal is on average around 60% above and 40% below the base metal value, respectively. In addition, the average Charpy impact energy value in the heat‐affected zone and weld metal is around 5% and 30% below the base metal value, respectively. The effects of mechanical and fracture properties on the critical crack size estimates have been investigated, and the results are discussed concerning the impact of material properties on structural design and integrity assessment of monopiles.

Steel 51CrV4 under high temperatures, short-time creep and high cycle fatigue

The use of a material for a particular purpose is based on its properties. In this sense, the article deals with the analysis of the results of experimental researches performed on steel 51CrV4. Experimental studies included responses of material at room and high temperatures as well as creep and fatigue behaviors of considered material. Responses of the material at room and high temperatures are displayed in the form of engineering stress-strain diagrams. Based on these responses were determined mechanical properties such as ultimate tensile strength (770 MPa/20 °C; 98 MPa/700 °C), 0.2 offset yield strength (642 MPa/20 °C; 60 MPa/700 °C) and modulus of elasticity (198 GPa/20 °C; 37 GPa/700 °C). Short time creep curves show the behavior of material at certain high temperatures and stress strevels. Each creep process is performed at constant temperature and the corresponding constant stress. Charpy impact energy (average values: 20 J/20 °C; 65 J/200 °C) was tested at different temperatures, and consequently, fracture toughness was calculated based on these results. Finally, uniaxial fatigue limit in amount of 251 MPa was calculated based on uniaxial high cycle fatigue tests at stress ratio of R = − 1.

Influence of Heat Treatments on the Fracture Toughness of 2017A Aluminium Alloy

The present study was carried out on 2017A aluminium alloy, in order to determine the influence of heat treatments on the fracture toughness determined by three point bending tests and empirical formula correlations used Charpy impact energy. The three point bending test has shown that the minimum values of fracture toughness and maximum load were found in the annealed state. Moreover, the hardening heat treatment increases them considerably, especially in the artificially aged condition of the alloy where it provided the maximum values. Schindler’s empirical formula gave the best estimation of fracture toughness in all metallurgical states of 2017A aluminium alloy.

Mechanical properties and eddy current testing of thermally aged Z3CN20.09M cast duplex stainless steel

To study the thermal aging embrittlement of Z3CN20.09M duplex stainless steel produced in China, accelerated thermal aging experiments were carried out at 380 °C up to 9000 h. Microhardness measurements, Charpy impact and eddy current tests were performed on aged samples to characterize their thermal aging embrittlement. The results showed that the signal amplitude of eddy current decreased with the increase in aging time. Two quantitative correlations of the eddy current signal amplitude with both the Charpy impact energy, and the Vickers microhardness of the ferrite phase are obtained. The study showed that eddy current testing could be used to non-destructively evaluate the thermal aging embrittlement of cast duplex stainless steels.

Comparing fast inductive tempering and conventional tempering: Effects on microstructure and mechanical properties

Induction heating processes are of rising interest within the heat treating industry. Using inductive tempering, a lot of production time can be saved compared to a conventional tempering treatment. However, it is not completely understood how fast inductive processes influence the quenched and tempered microstructure and the corresponding mechanical properties. The aim of this work is to highlight differences between inductive and conventional tempering processes and to suggest a possible processing route which results in optimized microstructures, as well as desirable mechanical properties. Therefore, the present work evaluates the influencing factors of high heating rates to tempering temperatures on the microstructure as well as hardness and Charpy impact energy. To this end, after quenching a 50CrMo4 steel three different induction tempering processes are carried out and the resulting properties are subsequently compared to a conventional tempering process. The results indicate that notch impact energy raises with increasing heating rates to tempering when realizing the same hardness of the samples. The positive effect of high heating rate on toughness is traced back to smaller carbide sizes, as well as smaller carbide spacing and more uniform carbide distribution over the sample.

Effect of Fly Ash Addition on the Physical and Mechanical Properties of AA6063 Alloy Reinforcement

Aluminum-fly ash particulate-reinforced composites (AA6063-FA) have been used in various engineering fields, such as automotive and aerospace industries, due to their low density and good mechanical properties. There are many fabrication techniques available to manufacture these composites according to matrix and reinforcement materials. The compocasting technique for the fabrication of the AA6063 matrix composite reinforced with fly ash particles is the focus of this research. Fly ash content was in the range of 0–12 wt % in increasing increments of 2%. Fly ash particles were added to the molten AA6063 alloy until they were completely blended and cooled down just below the liquidus to keep the slurry in the semi-solid state. After this, the molten AA6063-FA composites were cast into prepared cast iron molds. Bulk density and apparent porosity measurements, Charpy impact testing, Vickers microhardness measurements, Field Emission Scanning Electron Microscope (FESEM), Variable Pressure Scanning Electron Microscope and Energy Dispersive X-ray spectroscope (EDS) elemental mapping were used to evaluate these materials. The results showed that an increase in the fly ash content in the melted leads results in an increase in the microhardness and porosity in the composites. In contrast, the bulk density and Charpy impact energy of the composites decreased with an increase in the fly ash content.

Mehanical Properties of Electron Beam Welded Joints in Thick Gage CA6NM Stainless Steel

Design of hydroelectric turbine components requires high integrity welds (without detectable volumetric defects) in heavy gage sections of stainless steel materials, such as ASTM A743 grade CA6NM—a low carbon 13% Cr-4% Ni martensitic stainless steel that is manufactured in cast form. In this work, 90-mm-thick plates of CA6NM were joined using a single-pass autogenous electron beam (EB) welding process and the mechanical properties were evaluated in the as-welded condition to characterize the performance of the joints. The static tensile properties that were evaluated in two directions—transverse and longitudinal to the EB weld seam—demonstrated conformance of the joints with the requirements of the ASME Section IX standard. The Charpy impact energies of the EB welds—measured at −18 °C on samples with V-notch roots located in the fusion and heat-affected zones—met the minimum requirements of 27 J specified in ASME Section VIII standard. In addition, bend tests that were conducted on the entire weld cross section displayed no discontinuities on the tension side of the bent joints. Hence, the developed EB welding process was demonstrated to render high-performance joints and promises key advantages for industrialization, such as cost savings through reductions in consumable material, production time and labor intensity.

Fracture Toughness and Charpy CVN Data for A36 Steel with Wet Welding

This study presents KIC data obtained from KIC-CVN correlations from Charpy CVN values. For this study, T-welded connections were manufactured from ASTM A36 and E6013 electrodes in dry conditions. Then, a rectangular grinding at the weld toe was carried out and filled with wet welding. Charpy specimens were extracted to obtain CVN values. An exhaustive search through the literature of several authors was performed to collect experimental CVN data about wet welding being applied to A36 steel for comparison with CVN data obtained in this study. By using Charpy impact energy (CVN), KIC values could be predicted by KIC-CVN correlations. In addition, correlations were presented to obtain KIC values in the lower shelf, transition temperature zones and different zones for the energy-temperature curve of A36 steel. Of these correlations, Barsom’s equation was adopted, because he applied the stress yield (σYS) of the material and it can be applied in all zones for the energy-temperature curve. The results revealed that CVN values are proportionate to KIC, this data decreases as water depth increases. This took place because several discontinuities, such as, porosity, slag inclusion, non-metallic inclusion, cracking and microstructures are present in the wet welding.

Fracture Toughness of Z3CN20.09M Cast Stainless Steel with Long-Term Thermal Aging

Accelerated thermal aging tests were performed at 400 °C for nearly 18,000 h on Z3CN20.09M cast stainless steel which was used for primary coolant pipes of nuclear power plants. A series of Charpy impact tests were conducted on Z3CN20.09M after different long-term thermal aging time. The test results indicated that the Charpy impact energy of Z3CN20.09M cast stainless steel decreased rapidly at an early stage and then almost saturated after thermal aging of 10,000 h. Furthermore, J-resistance curves were measured for CT specimens of longitudinal and circumferential pipe orientations. It showed that there was no obvious difference in the fracture characteristics of Z3CN20.09M in different sampling directions. In addition, the observed stretch zone width (SZW) revealed that the value of initiation fracture toughness J SZW was significantly lower than that of fracture toughness J IC, indicating a low actual crack initiation energy due to long-term thermal aging.

Effect of powder oxidation on the impact toughness of electron beam melting Ti-6Al-4V

Powder quality in additive manufacturing (AM) electron beam melting (EBM) of Ti-6Al-4V components is crucial in determining the critical material properties of the end item. In this study, we report on the effect of powder oxidation on the Charpy impact energy of Ti-6Al-4V parts manufactured using EBM. In addition to oxidation, the effects on impact energy due to hot isostatic pressing (HIP), specimen orientation, and EBM process defects were also investigated. This research has shown that excessive powder oxidation (oxygen mass fraction above 0.25% and up to 0.46%) dramatically decreases the impact energy. It was determined that the room temperature impact energy of the parts after excessive oxidation was reduced by about seven times. We also report that HIP post-processing significantly increases the impact toughness, especially for specimens with lower or normal oxygen content. The specimen orientation effect was found to be more significant for low oxidation levels.

Data Mining and Modelling of Charpy Impact Energy for Alloy Steels Using Fuzzy Rough Sets

When considering data-driven modelling, uncertainties, errors and inconsistencies in the data can more often than not lead to sub-optimal predictions. A new framework based on rough sets theory is proposed and applied to an industrial data set obtained from a Charpy impact energy test for alloy steels. The inconsistent/consistent data sets are then used to train a series of artificial neural networks (ANN) for Charpy impact energy prediction for alloy steels. A k-nearest neighbor is used to classify the data points; if an object is classified as consistent, the ANN trained with the consistent data set provides a single prediction while if the object is classified as inconsistent, several ANN trained with different sets of inconsistent data are used to provide an interval prediction. Experimental results show an improvement in the consistent data set compared with a benchmark model. Also, the interval prediction provided by the various ANNs in the inconsistent data set represents a better alternative to the single point prediction results.

Strength and toughness of clean nanostructured bainite

ABSTRACTA nanostructured steel has been produced using a clean steel-making technique. The mechanical properties have been comprehensively characterised. The maximum strength of the material recorded was 2.2 GPa at yield, with an ultimate tensile strength of 2.5 GPa, accompanied by a Charpy impact energy of 5 J, achieved by heat treatment to refine the prior austenite grain size from 145 to 20 µm. This increased the strength by 40% and the Charpy V-notch energy more than doubled. In terms of resistance of the hardness to tempering, the behaviour observed was similar to previous alloys. Despite reducing the hardness and strength, tempering was observed to reduce the plane-strain fracture toughness.

Effect of Heat Treatment on Microstructure Evolution and Mechanical Behavior of SKLB3 Alloy

In this paper, the effect of heat treatment on the microstructure and mechanical properties of hot forging Cu-Ni alloy was studied. Specimens of hot forged Cu-Ni alloy were subjected to first solution treated at 900oC for 2hrs and then aged at different temperatures for 2hrs. The mechanical properties including tensile performance and impact energy, and the microstructure were measured for specimens before and after heat treatment. The results show that both solution and aging treatment have an influence on the grain growth. After heat treatment, the tensile strength decreases very slightly but the yield strength decreases seriously from 235.96MPa to 136.12MPa, while the elongation increases sharply from 36% to 48%. It was also observed that hardness values of the heat-treated alloys are all lower than that of the hot forged alloy. The measurement of Charpy impact energy with V-type notch was performed at 298K and 77K for different specimens. At both temperatures, the impact energies of the specimens are higher than 200J. The microstructure results show that at both temperatures, the alloys are fractured in a ductile mode.

Abnormal temperature dependence of impact toughness in AlxCoCrFeNi system high entropy alloys

In this work, the effect of Al contents and the associated phase transformations on the impact toughness of AlxCoCrFeNi high-entropy alloys (HEAs) (x denotes Al molar ratio; x = 0, 0.1, 0.75, and 1.5) in the as-cast state were investigated at T = 77 K, 200 K, and 298 K. For the alloys with x = 0 and 0.1, the alloys have the FCC structure, and an inverse temperature dependence of impact toughness between 298 K and 77 K was observed. The enhanced impact toughness (397.87 J) at 77 K is attributed to the capability of extensive nano-twinnings as well as ductile dimple fracture. Increasing Al contents to x = 0.75 and 1.5 induces the formation of brittle BCC phase and ordered B2 compound and accordingly embrittlement, leading to tremendously reduced Charpy-impact energies. The present study demonstrates that FCC AlxCoCrFeNi system HEAs with low Al contents (x < 0.5) may be well suitable for cryogenic applications.

Constitutive modeling and fracture behavior of a biomedical Ti–13Nb-13Zr alloy

The dynamic compression tests were performed at various strain rates (0.01, 1700, 2700 and 3500/s) and temperatures (25, 200, 400 and 600°C) for a biomedical Ti–13Nb-13Zr alloy. Based on experimental data, constitutive models were established using the Modified Johnson-Cook (J-C) model, Modified Khan–Huang–Liang (KHL) model and Artificial neural network (ANN) model, respectively. The new modified J-C model considers the coupled effects of strain hardening, strain rate hardening and thermal softening. In this work, a radial basis function artificial neural network (RBF-ANN) model was also developed to predict the high strain rate flow curves of Ti–13Nb-13Zr alloy. The results demonstrate that the flow behavior of Ti–13Nb-13Zr alloy is considerably influenced by the strain rate and temperature. The modified KHL model and ANN significantly enhance the predictability. The deformation behavior represented by dynamic recrystalization (DRX) and the instability flow has been discussed with reference to microstructural evolution during high strain rate compression. The validation of the developed constitutive model is embedded in the finite element analysis (FEA) to perform numerical simulations with ABAQUS/Standard to obtain the charpy impact energy.

Flame Retardancy of Carbon Fibre Reinforced Sorbitol Based Bioepoxy Composites with Phosphorus-Containing Additives.

Carbon fibre reinforced flame-retarded bioepoxy composites were prepared from commercially available sorbitol polyglycidyl ether (SPE) cured with cycloaliphatic amine hardener. Samples containing 1, 2, and 3% phosphorus (P) were prepared using additive type flame retardants (FRs) resorcinol bis(diphenyl phosphate) (RDP), ammonium polyphosphate (APP), and their combinations. The fire performance of the composites was investigated by limiting oxygen index (LOI), UL-94 tests, and mass loss calorimetry. The effect of FRs on the glass transition temperature, and storage modulus was evaluated by dynamic mechanical analysis (DMA), while the mechanical performance was investigated by tensile, bending, and interlaminar shear measurements, as well as by Charpy impact test. In formulations containing both FRs, the presence of RDP, acting mainly in gas phase, ensured balanced gas and solid-phase mechanism leading to best overall fire performance. APP advantageously compensated the plasticizing (storage modulus and glass transition temperature decreasing) effect of RDP in combined formulations; furthermore, it led to increased tensile strength and Charpy impact energy.

CVN–KJC correlation model for API X65 gas pipeline

Abstract Reliable determination of fracture toughness of different materials is critically important. However, standard fracture toughness testing methods are difficult and costly. In order to simplify the determination of fracture toughness, several correlations between fracture toughness and Charpy impact energy (CVN) have been proposed by different researchers. In the present work, a new linear model was developed for estimation of fracture toughness (KJC), based on CVN, and yield strength data, in base, seam weld, and girth weld metals of an API X65 gas pipeline. The predicted values of KJC from the suggested relation, with maximum and mean error values of 6.7% and 4.4%, respectively, was found to be in good agreement with the valid fracture toughness test results obtained from compact tension specimens following ASTM E1820 standard.

Enhancement of low temperature toughness of nanoprecipitates strengthened ferritic steel by delamination structure

This study investigated the effects of aging and thermomechanical treatments on the microstructure evolution and mechanical properties of a nanoprecipitates strengthened ferritic steel. The toughness of steel at various temperatures was measured carefully and correlated with microstructural features. Tensile tests show that aging can improve the mechanical strength without scarifying the ductility. With high yield strength of ~1000MPa, excellent low temperature Charpy impact energy more than 300J at −80°C can be obtained. The ductile brittle transition temperature (DBTT) is lower than −80°C. The high strength can be contributed by the nanocluster precipitation as determined by small angle neutron scattering and transmission electron microscopy. The excellent low temperature toughness is attributed to the delamination structure of the steel, which blunts the cracks and restrains the crack propagation.

Ductile-fatigue transition fracture mode of welded T-joints under quasi-static cyclic large plastic strain loading

Welded structures experiencing a small number of large plastic strain reversals during a strong earthquake, can lead to ductile or fatigue fracture. Experimental study on a series of welded T-joints under cyclic large plastic strain loading is carried out to clarify their failure mechanisms in the ultra low cycle fatigue range commonly with a crack initiation life of several dozens of cycles. Effects of post-weld treatment, notch size, notch location and loading protocol on the failure process of the joints are studied. The experimental results indicate that the fracture is a transition mode of ductile and fatigue fracture. It is also found that the post-weld treatment can greatly improve the crack initiation lives of the joints, and the Charpy impact energy has a great effect on the cracking propagation rate. Formulae to evaluate the crack initiation lives of the tested specimens respectively in terms of ductility ratio and equivalent plastic strain are also proposed, and the effect of small strain amplitudes on the damage accumulation is explained based on the test results under various loading protocols.

Effect of Ti interlayer on the bonding quality of W and steel HIP joint

Tungsten (W) and steel bonding is one of the key technologies for blanket First Wall (FW) manufacture in thermal fusion reactor. The W/Steel joints are prone to fail without interlayer for the different thermo physical properties. To study the effect of titanium (Ti) interlayer on the bonding quality of W and steel joints, W/Steel Hot Isostatic Pressing (HIP) experiments with Ti interlayer were conducted under 930 °C, 100 MPa for 2 h. Intermetallics caused by atom interdiffusion would affect the bonding quality of W/Ti/Steel HIP joints, the bonding quality was evaluated by microstructure analysis and mechanical tests. All the HIP joints were well bonded and results showed no intermetallics occurred between W/Ti interfaces, meanwhile multiply phases were found between Ti/Steel interfaces. Shear tests indicated when Ti thickness was 100–500 μm, the maximum shear strength of W/Ti/Steel HIP joints would be up to around 151 MPa. Charpy impact tests showed the W/Ti/Steel HIP joints all broke in a brittle manner and the maximum Charpy impact energy was ∼0.192 J. Nano-indentation tests demonstrated W/Ti interfaces could be enhanced by solid solution hardening and formation of brittle phases has conducted high hardness across the Ti/Steel interfaces.