Showing papers on "Charpy impact test published in 2018"

Impact damage resistance of 3D printed continuous fibre reinforced thermoplastic composites using fused deposition modelling

Abstract: Fused deposition modelling (FDM) is a promising additive manufacturing technology and an alternative of conventional processes for the fabrication of fibre reinforced composites due to its ability to build functional parts having complex geometries. Continuous fibre reinforced thermoplastic composites (CFRTPCs) are becoming more significant in industrial applications due to their inherit advantages such as excellent mechanical performance, recycling and potential lightweight structures [1,2]. However, a major concern affecting the efficient use of 3D printed composites is the effect of impact damage on the structural integrity, compared to conventional pre-preg composites. The aim of this study is to evaluate the effect of build orientation, layer thickness and fibre volume content on the impact performance of 3D printed continuous carbon, glass, and Kevlar® fibre reinforced nylon composites, manufactured by FDM technique. Charpy impact tests are carried out to determine impact strength. SEM images of fractured surfaces are examined to assess failure mechanics of the different configurations. It is observed that the effect of layer thickness of nylon samples on the impact performance was different for flat and on-edge samples. Impact strength increases as layer thickness increases in flat samples but, conversely, it decreases in on-edge samples, depicting a more brittle fracture. In addition, the results show that impact strength increases as fibre volume content increases in most cases. Glass fibre reinforced samples exhibits the highest impact strength and carbon fibre reinforced samples the lowest one and similar to nylon performance. Furthermore, on-edge reinforced samples exhibit higher values of impact strength than flat reinforced samples. Finally, the results obtained demonstrate that impact strength exhibited by 3D printed composites are significantly higher than the usual 3D printed thermoplastics and, in some cases, even better than common pre-preg materials.

Heat treatment effect on the mechanical properties and fracture mechanism in AlSi10Mg fabricated by additive manufacturing selective laser melting process

Abstract: Many researches have been conducted on the topic of the AlSi10Mg alloy, covering different aspects of the selective laser melting fabrication process. However, a database is still lacking much information and understanding regarding the properties of the material under different conditions, which will allow a tailoring of suitable properties to the required application. This work aims to provide a correlation between the mechanical properties of vertically built (Z samples) AlSi10Mg specimens subjected to different post-processing conditions and the change in properties in relation to these conditions and the fracture mechanism. Among these is the accepted T5 stress relief treatment, a modified T5 treatment, the as-built condition and a high temperature Hot Isostatic Pressing treatment. A more in-depth analysis of the fracture mode for the vertical build direction is provided with emphasis on the mechanism for each treatment as well as a quantitative analysis of the Full Width at Half Maximum via X-Ray diffraction measurements. The modified T5 treatment suggested was found to result in an increase in strength values beyond those of the as-built condition and a 64% increase in yield stress compared to the typical T5 treatment with a concurrent decrease in elongation values. It is suggested that at 200 °C nano-scale precipitation of Silicon particles occurs, responsible for the strength elevation. Charpy impact test results are provided for each condition and their fracture mode is compared to the tensile tests and discussed.

Effect of morphologies of martensite–austenite constituents on impact toughness in intercritically reheated coarse-grained heat-affected zone of HSLA steel

Abstract: By using the gleeble-3500 simulator, three different two-pass weld thermal cycles were applied to base metal of a high strength low alloy (HSLA) steel with the purpose of obtaining martensite-austenite (MA) constituents of different morphologies in intercritically reheated coarse-grained heat-affected zones (ICGHAZ). Morphology of each MA constituent was characterized by maximum length, maximum width and aspect ratio (maximum length/ maximum width). Toughness of thermal simulated specimens was examined by using an instrumented Charpy impact tester. Behaviour of cracks was present by Charpy impact curve and typical data. Correlation between behaviour of cracks and morphologies of MA constituents was further analysed by observing crack propagation and microstructure of MA constituent. Fracture modes of MA constituents with slender and massive shape were proposed. Results show that slender MA constituents are more harmful to toughness compared with massive ones.

Effect of low-temperature on mechanical behavior for an AISI 304 austenitic stainless steel

Abstract: An AISI 304 austenitic stainless steel (ASS) with average grain size of approximately 48 µm was selected to explore the effect of the low-temperature on mechanical behavior for commercial metastable ASS, which basing on tensile tests and Charpy V-notch impact tests under temperatures of 20–298 K, Feritscope testing and physical metallurgy. The results showed that both yield strength and tensile strength were enhanced by lowering temperatures; however, the uniform strain decreased with reducing temperatures. The yield strength at 20 K and 77 K were much higher than that at other temperatures, accompanying with an abrupt increase of thermally-induced martensite before tensile testing. The Charpy V-notch impact energy decreased faster in the range of 77–298 K and kept almost unchanged in the range of 20–77 K, and the ASS at 20 K still exhibited a dimple shaped fracture. Generally, the work-hardening rate ( Θ ) of the ASS at testing temperatures of 20–298 K dropped rapidly at the initial plastic strain range (Stage I) and then grew with the increase of tensile strain (Stage II), then following by a continuous decline to necking (Stage III), i.e., the generation of a peak of work-hardening rate. Specifically, the Stage I, II and III were terminated in advance and the peak value at the Stage II were increased obviously by reducing temperature from 298 K down to the range of 20–253 K. Furthermore, the work-hardening behavior of the ASS was discussed in view of the evolution of microstructure basing on Olson-Cohen model.

Comparative study of autogenous tungsten inert gas welding and tungsten arc welding with filler wire for dissimilar P91 and P92 steel weld joint

Abstract: Creep strength enhanced ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel is also designated as ASTM A335 used for out-of-core and in-core (piping, cladding, ducts, wrappers, and pressure vessel) of Gen IV reactors. In present investigation, the dissimilar weld joint of P91 and P92 steel were made using the autogenous tungsten inert gas (TIG) welding with single pass, double side pass and multi-pass gas tungsten arc (GTA) welding with filler wire. Microstructure evolution in sub-zones and mechanical properties of dissimilar welded joints were studied in as-welded and post weld heat treatment (PWHT) condition. Formation of δ-ferrite patches in weld fusion zone and heat affected zones (HAZs) and their influence on the mechanical behaviour of the welded joints were also studied. Presence of higher content of ferrite stabilizer in P92 steel have resulted the formation of δ-ferrite patches in weld fusion zone as well as HAZs. The δ-ferrite was observed in autogenous TIG welds joints. The δ-ferrite patches were formed in as-welded condition and remained in the microstructure after the PWHT. The δ-ferrite patches leads to reduction in Charpy toughness of autogenous TIG welds joint and also lower down the average hardness of weld fusion zone. Peak hardness and poor impact toughness were observed for autogenous TIG welds joint as compared to GTA welds. For microstructure characterization, field-emission scanning electron microscope (FESEM) with energy dispersive spectroscopy (EDS) and optical microscope were utilized.

On the toughness scatter in low alloy C-Mn steel samples fabricated using wire arc additive manufacturing

Abstract: Low alloy carbon manganese (C-Mn) steel builds were fabricated using a wire based additive manufacturing system developed at Oak Ridge National Laboratory. Specimens were fabricated in the X,Y and Z direction and detailed mechanical testing was performed. The mechanical testing results showed a significant scatter in tensile ductility and significant variation in Charpy toughness. Further detailed microstructure characterization showed significant microstructural heterogeneity in builds fabricated in each direction. The scatter in mechanical properties was then rationalized based on the microstructural observations and the underlying changes in the local heat transfer conditions. The results indicate that when fabricating parts using C-Mn low alloy steel welds the process parameters and tool path should be chosen such that the cooling rate from 800 °C to 500 °C is greater than 30 s to avoid formation of martensite austenite (MA) phases, which leads to toughness reductions.

Injection molding. Influence of process parameters on mechanical properties of polypropylene polymer. A first study.

Abstract: This paper shows the first study results of the mechanical characterization of a commercial polypropylene (PP) polymer. Before testing, a mold for injection molding process has been designed and realized. Three different specimens can be produced, for three different tests: tensile, Charpy and Hopkinson bar. In-cavity pressure and temperature sensors are installed next to the molded item to have direct information about process phases. After the description of the instrumentation, the correlation between injection molding input parameters and mechanical behavior of the material has been assessed. In particular, tensile tests have been carried out to investigate the influence of: melt temperature, mold temperature, packing pressure and cooling time. A Design of Experiment plan has been set up to establish the tests to be performed. Results show the influence of mold temperature and holding pressure on mechanical strength of the polymer.

Study on the effect of ageing on laves phase evolution and their effect on mechanical properties of P92 steel

Abstract: P92 steel is candidate material for application in reactor pressure vessels in nuclear power plants. In present investigation, Laves phase evolution (at 650 °C) with varying ageing time (upto 3000 h) in P92 steel and their effect on mechanical properties have been investigated. During thermal ageing, the microstructure analysis showed the evolution of Laves phase that degrades the strength of P92 steel. The formation of Laves phase was observed after the thermal ageing of 720 h and it showed higher coarsening rate in ageing time range of 720 h −1440 h. The Laves phase formation was also confirmed by the XRD analysis, and line mapping. The strength and ductility decreased as a result of deprivation of solid solution strengthening and formation of Laves phase. The hardness of P92 steel was also affected by ageing time but less pronounced as compared to strength. Charpy toughness was also reduced continuously with increase in ageing time as a result of thermal straining of particles and Laves phase formation.

Fracture behaviour of cast in-situ TiAl matrix composite reinforced with carbide particles

Abstract: Three-point bending tests, Charpy impact tests and numerical simulations were carried out to study fracture behaviour of in-situ TiAl matrix composite reinforced with Ti2AlC particles prepared by centrifugal casting of Ti-44.5Al-8Nb-0.8Mo-0.1B-5.2C (at%) alloy. The brittle fracture behaviour of the in-situ composite includes crack deviation, microcrack formation, carbide fragmentation, delamination on the matrix-carbide interfaces and pull-out of the carbide particles from the TiAl matrix. The crack initiation and propagation is related to applied load, deflection and acoustic emission events measured during three-point bending tests. A critical stress leading to a crack initiation in the notch region is numerically calculated for quasi-static loading conditions using finite element analysis (FEA). The measured fracture toughness values are comparable to those of some in-situ TiAl matrix composites prepared by casting and reactive processing.

Mechanical properties of Inconel 718 welds performed by gas tungsten arc welding

Abstract: Gas tungsten arc welding (GTAW) was used to join plates of Inconel 718. The mechanical properties were determined by tensile, microhardness, and instrumented Charpy impact tests. An ERNiFeCr-2 filler metal fed by a semi-automatic mechanism was used. Partial dissolution of the strengthening phases, γ′ and γ″, induced a soft region (~ 225 HV1.0) in the heat-affected zone (HAZ) during welding. The yield strength (371.3 MPa) of the as-welded joint is approximately 45% of the base material in aged condition (822.7 MPa). The welds were subjected to a hardening recovery post weld heat treatment (HRPWHT). Impact testing of the hardened welds revealed a reduction of 17% in energy absorbed with respect the aged base material. Hardness measurements showed an increase to ~ 410 HV0.1 in the fusion zone; however, due to segregation of Nb and formation of carbides, the precipitation of γ″ is not fully completed, and the yield strength (719 MPa) of the heat-treated welded joint is lower than the base material in aged condition.

Studies on the weldability, mechanical properties and microstructural characterization of activated flux TIG welding of AISI 321 austenitic stainless steel

Abstract: The presence of titanium in AISI 321 austenitic stainless steel, mitigates the corrosion when deployed in specific applications such as boiler shells, aircraft exhaust manifolds and process equipment. Using Commercial flux purchased from Edison Welding Institute (EWI), studies were conducted to note the effect of Activated Tungsten Inert gas (A-TIG) welding on the surface morphology of type 321 austenitic stainless steel welds and compared with conventional TIG welding. A thin flux layer was applied to the surface of the 6 mm thick plate, followed by a conventional TIG welding process. The bead on trial results shows that compared with the TIG welding process, the flux causes the weld depth to increase, weld bead width to decrease and weld area to increase. This incredible depth of penetration (DOP) has been accomplished by the mechanisms of reversal of Marangoni flow and Arc constriction. From various experimental trials, arc length of 3 mm, welding current of 220 Amps and welding speed of 120 mm min−1 were found to be optimal and subsequently used as input parameters to produce a good quality A-TIG welded butt joint. The welded joint is subjected to transverse and longitudinal tensile and bend tests, charpy impact toughness tests, microhardness, optical microscope, x-ray diffraction analysis, ferrite number measurement and Scanned electron fractography. The welded joint exhibited improved tensile strength, bend and charpy impact toughness and hardness. The weld metal microstructure was observed to be austenite, delta-ferrite and TiC intermetallic compounds (Titanium carbides). The XRD pattern indicates that austenite and ferrite phases are present in both base and weld metal. The results of Fischer Feritscope FMP30 (ferrite measurement) show that the content of delta-ferrite in the weld metal (5.9 FN) is much higher than the parent metal (1.2 FN) and shows excellent mechanical properties in the A-TIG welded joint. Scanned electron fractography indicates that the failure of weld metal and base metal occurs in the ductile mode of fracture.

The effect of the austenite grain refinement on the tensile and impact properties of cast Hadfield steel

Abstract: This paper studied the effect of the austenite grain refinement on the tensile and impact properties of a cast Hadfield steel (12 % Mn, 1.2 %C and 0.65 % Si). The austenite grain refinement was obtained by hafnium inoculation. Microstructural characterization showed that the Hf-refined cast Hadfield steel featured a grain size of 600 µm, while the non-refined condition presented a grain size of 3000 µm. Mechanical test results indicated that the austenite grain refinement promoted an increase in the values of the yield stress (6%), the ultimate tensile strength (37%), the toughness (88%), the work-hardening coefficient (50%) and the Charpy absorbed energy (15%). Microscopic characterization of the fractured test-pieces indicated that the grain refinement increased the proportion of plastic deformation by the twinning mechanism and furthermore improved the values of the mechanical properties of the cast Hadfield steel considerably.

The effect of pouring temperature and surface angle of vortex casting on microstructural changes and mechanical properties of 7050Al-3 wt% SiC composite

Abstract: In this investigation, the effect of pouring temperature and the surface angle of vortex casting on microstructural evolution and mechanical properties of 7050Al-3 wt%SiC composite was studied. Two pouring temperatures of 700 °C and 800 °C were employed during the vortex casting. As well, two surface angles of 45° and 90° were used for the vortex casting. Cast microstructures were analyzed by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and optical microscope. Mechanical properties were measured by uniaxial tensile test, Vickers hardness and Charpy impact test. Microstructural studies showed a uniform distribution of SiC particles in the 7050 Al matrix is achievable by increasing the pouring temperature from 700 °C to 800 °C and also by decreasing the surface angle from 90° to 45°. This uniform distribution of particles was coincided with the breaking of the dendrite arms in the microstructure of 7050 Al-3 wt% SiC. Mechanical properties measurements showed that the yield strength, hardness and fracture energy of the composite were increased by increasing the pouring temperature and reducing the surface angle during the vortex casting.

Tensile and impact properties of cost‐effective hybrid fiber metal laminate sandwich structures

Abstract: Hybrid composite materials, which combine two or more types of fiber in a single matrix, have currently drawn the interest of researchers. This research investigates the tensile and impact properties of hybrid kenaf/glass reinforced metal laminates (FMLs) with different fiber orientations and stacking configurations. FMLs were formed by sandwiching the annealed aluminum 5052 sheets to the composite laminates using hot press molding compression technique. The tensile test was performed at a quasi-static rate of 2 mm/min with reference to ASTM E8 whereas Charpy impact test was conducted using impact pendulum tester according to ASTM E23. Results showed that improvement in tensile and impact strength was observed in hybrid FMLs compared to kenaf fiber reinforced FMLs. Fiber orientation of ±45° reduced the tensile strength but increased the impact strength of FMLs in comparison with fiber orientation of 0°/90°. Overall, hybrid FMLs incorporated with a fiber stacking sequence of glass/kenaf/glass showed superior characteristic in tensile and impact performance.

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

Abstract: S355 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.

Evaluating the Properties of Dissimilar Metal Welding Between Inconel 625 and 316L Stainless Steel by Applying Different Welding Methods and Consumables

Abstract: The current work was carried out to characterize welding of Inconel 625 superalloy and 316L stainless steel In the present study, shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) with two types of filler metals (ERNiCrMo-3 and ERSS316L) and an electrode (ENiCrMo-3) were utilized This paper describes the selection of the proper welding method and welding consumables in dissimilar metal joining During solidification of ERNiCrMo-3 filler metal, Nb and Mo leave dendritic cores and are rejected to inter-dendritic regions However, ERSS316L filler metal has small amounts of elements with a high tendency for segregation So, occurrence of constitutional super-cooling for changing the solidification mode from cellular to dendritic or equiaxed is less probable Using GTAW with lower heat input results in higher cooling rate and finer microstructure and less Nb segregation The interface between weld metal and base metal and also unmixed zones was evaluated by scanning electron microscopy and energy dispersive X-ray (EDX) analysis Microhardness measurements, tensile test, and Charpy impact test were performed to see the effect of these parameters on mechanical properties of the joints

Interrelationships between yield strength, low-temperature impact toughness, and microstructure in low-carbon, copper-precipitation-strengthened, high-strength low-alloy plate steels

Abstract: Interrelationships between room-temperature yield strength and low-temperature impact toughness are examined for low-carbon, copper-precipitation-strengthened, high-strength low-alloy (HSLA) plate steels. Three steels, designated as HSLA-80, HSLA-80/100, and HSLA-100, are compared based on plots of yield strength versus 50% shear fracture-appearance transition temperature, followed by comparison of yield strength versus energy absorbed during Charpy V-notch testing at −84 °C. Analysis of both approaches produced similar outcomes, indicating that either is acceptable for predicting the influence of microstructure on the combination of strength and toughness. Data from over 15 studies including over 160 data points are amassed into a single master plot. Strengthening for the highest-strength steels is associated with a strength-toughness vector with slope equal to −0.67 J/MPa. A grain-refinement vector is associated with a slope of approximately +0.18 J/MPa. Since austenite grain size variation was virtually nonexistent in this study, variation of effective grain size was related to the differences in crystal size and/or packet size for low-carbon martensite (finest), low-carbon bainite, and polygonal ferrite (coarsest). A detrimental effect of untempered, brittle, medium-carbon martensite islands was hypothesized. Tempering of this microconstituent during aging heat treatment reduces, but does not eliminate, the negative effect of these islands. Base microstructures of low-carbon martensite show a superior combination of strength and impact toughness, followed by low-carbon martensite with islands of stable austenite, low-carbon bainite, and polygonal ferrite. A vector approach to strength-toughness in HSLA-100 steels is used to clarify property differences from previous studies. Future developments for this class of steels should address grain refinement and changes in processing or alloying that avoid islands of medium-carbon martensite.