Total Impact Energy Research Articles

Comparison of Impact Properties for Carbon and Low Alloy Steels

The impact properties of hot rolled carbon steel (used for the manufacture of reinforcement steel bars) and the quenched & tempered (Q&T) low alloy steel (used in the pressure vessel industry) were determined. The microstructure of the hot rolled carbon steel contained ferrite/pearlite phases, while that of the quenched and tempered low alloy steel contained bainite structure. Impact properties were determined for both steels by instrumented impact testing at temperatures between −150 and 200°C. The impact properties comprised total impact energy, ductile to brittle transition temperature, crack initiation and propagation energy, brittleness transition temperature and cleavage fracture stress. The Q&T low alloy steel displayed much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was a little higher than that of the hot rolled carbon steel. The results were discussed in relation to the difference in the chemical composition and microstructure for the two steels.

Evaluation of Bias for Two Charpy Impact Machines with the Same Instrumented Striker

Abstract Two Charpy machines were used to test NIST verification specimens at three energy levels: low energy (∼15 J at −40°C), high energy (∼100 J at −40°C), and super-high energy (∼240 J at room temperature). The study evaluates the differences observed for the bias between two impact machines and the variation in test data for instrumented versus non-instrumented impact tests. The machines used for testing were of very similar design, and all tests were performed with the same instrumented striker (switched between machines). After testing, the raw force/time data were used for the analyses, without correcting instrumented data by matching absorbed energies measured by the machine encoder (KV) and calculated under the force/deflection test record (Wt). The characteristic forces at general yield (Fgy) and the maximum forces (Fm) were determined in accordance with ASTM E2298-09 from the instrumented impact record that was used to calculate the total impact energy (Wt). The findings show the following: (1) one machine consistently produced higher absorbed energy values than the other machine; (2) the variation in Wt is significantly lower than the variation in absorbed energy measured in the non-instrumented test (KV) for a given machine and energy level; (3) the relative differences between KV and Wt increased with increasing absorbed energy levels; (4) variations in maximum force are lower than variations in absorbed energy values; (5) instrumented data indicate that the variation in the curves is very small up to maximum force, and that differences in absorbed energy mainly occur during fracture propagation (post-maximum force data); (6) data from these two independent measures of absorbed energy indicate that scatter is due primarily to material variability; and (7) the bias between the two machines is significantly reduced when the same striker is used for testing.

On the response of two commercially-important CFRP structures to multiple ice impacts

Carbon-fibre reinforced composites (CFRPs) are likely to feature heavily as structural elements of future aerospace vehicles due to their high stiffness and low densities. However, such components are likely to be subjected to a variety of impact-related events during their in-service lives. One area which has only received limited attention in the literature is that of ice impact on CFRP structures; e.g. hail stone impacts on aerospace components. In this study the response of two aerospace-grade CFRP structures (one woven and one uni-directional lay-up) to multiple ice impacts with cumulative impact energies in the range 72–1215 J was investigated. Six empirical damage categories were identified, ranging from no apparent surface damage (Type 1) to penetration accompanied by complete lay-up disruption (Type 6). Surface damage was found to correlate with changes in recovered panel properties; determined by ultrasonic C-Scan and compression-after-impact strength tests. With both CFRP structures sub-surface disruption and residual compressive strength varied linearly with total impact energy; suggesting that damage in such structures is cumulative in nature. Further, in line with previous studies, the woven structure consistently exhibited lower levels of damage at a given impact energy, even when damage extent was normalised by areal density.

Probing chemical homogeneity within single cluster impact sites

AbstractWe have recently reported a nanoprobe technique based on time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) capable of obtaining molecular information from individual nanoobjects. The technique is based on event‐by‐event bombardment/detection, where information from individual objects is obtained via coincidental secondary ion emission from single projectile impacts. Here, we demonstrate that the event‐by‐event mode is sensitive to the chemical and/or physical separation of molecular species. As a test case, two nanoobject samples with the same chemical composition were prepared with different morphologies. Both consisted of polystyrene spheres deposited onto nanoalumina whiskers, but their structures differed. One sample contained 30 nm spheres intact, and the other produced nanoflake structures. Bombardment with Au4004+ at 136 keV total impact energy demonstrates that conventional mass spectra do not reflect differences between the morphologies, whereas the coincidental mass spectra show significant differences in coemission of aluminum‐based and carbon‐based secondary ions. Copyright © 2010 John Wiley & Sons, Ltd.

High Velocity Compaction of 316L Stainless Powder

High velocity compaction technology was used to press 316L stainless powders. Effects of impact times on stress wave, green density and ejection force were analyzed. It was found that under the same total impact energy, the first loading time and the actuation duration of the second impact in double impact process were longer when compared with single impact process, while the first delay time was shorter. Furthermore, the green density of compacts prepared by double impact was greater than that prepared by single impact, but no obvious variation in maximum ejection force can be observed between single impact and double impact process.

Electron Emission from Hypervelocity C60 Impacts

Secondary ion mass spectrometry (SIMS) performed in the event-by-event bombardment detection mode when coupled to an electron emission microscope allows one to investigate individual nano-objects. Two groups of Au and Al oxide nano-objects were compared with their bulk counterparts based on their secondary ion and electron emission from individual C60 impacts at 15 and 30 keV total impact energy. Our results show that electron yields depend on the size and surroundings of the nano-object, and at higher impact energies, these differences in electron emission are more pronounced. A second key observation for systems of similar chemical makeup but different surface topography and size is that the emission of secondary ions and electrons is independent of each other.

Effects of disc rotation speed and media loading on particle flow and grinding performance in a horizontal stirred mill

IsaMill™ is a high-speed stirred mill used in the mineral industry for a range of milling duties from ultra-fine to coarse grinding. In this work, numerical simulations based on the discrete element method (DEM) were performed to investigate the particle flow in a dry stirred mill with a similar configuration to that of an IsaMill™. The effects of operational variables such as mill loading and rotation speed on flow properties such as flow velocity, power draw, collision frequency, collision energy and total impact energy were analysed. The results showed that increasing mill loading or mill speed increases impact energy between particles. Moreover, physical experiments were conducted to quantify grinding performance under similar conditions. The experimental results showed that the grinding in the mill follows the first order kinetics, and the rate constant can be correlated to impact energy. The findings are useful to understand and optimise the particle flow and grinding behaviour of IsaMills™. The proposed methodology may also apply to other stirred mills.

Crystal orientation effects in δ18O for magnetite and hematite by SIMS

In situ high precision analysis of oxygen isotope ratios ( δ 18O) by secondary ion mass spectrometry (SIMS) reveals that instrumental bias in δ 18O for magnetite varies due to crystal orientation effects. Multiple analyses of δ 18O have an average precision of ± 0.4‰ (2SD) in single grains of magnetite, close to ± 0.3‰, that obtained for multiple grains of UWQ-1, a homogeneous quartz standard. In contrast, the average precision is five to ten times worse, ± 2–3‰ (2SD), from grain-to-grain of magnetite due to variation in instrumental bias with crystal orientation. Electron backscatter diffraction shows that individual grains of magnetite are single crystals and that crystal orientation varies randomly from grain-to-grain. The crystal orientation for each magnetite grain is plotted relative to the incident angle of the SIMS primary Cs + beam. High values of δ 18O are measured when the Cs + beam is parallel to < uv0>, from [110] to [100], preferred channeling and focusing directions for magnetite. Routine δ 18O analysis at WiscSIMS utilizes a Gaussian focused Cs + primary beam (deep-pit mode) at primary and secondary voltages of + 10 kV and−10 kV respectively (total impact energy 20 keV). Four analytical experiments were conducted in attempts to improve the grain-to-grain precision in measured δ 18O for magnetite: (1) applying an energy offset of 50 eV, (2) using a Köhler illuminated beam (shallow-pit mode), (3) reducing the total impact energy, and (4) varying the primary and secondary accelerating voltages. The best results were obtained in experiment (4) at primary/secondary accelerating voltages of + 3 kV/− 10 kV respectively with an incident Cs + beam angle of 14°. The grain-to-grain precision in measured δ 18O for magnetite improves from ± 2.9‰ to ± 0.8‰ (2SD) at + 10 kV/− 10 kV and + 3 kV/− 10 kV analysis respectively, while precision in single grains is ± 0.4‰ for both. Instrumental bias in δ 18O also varies with crystal orientation for hematite at similar levels as is seen for magnetite. The grain-to-grain precision in measured δ 18O for hematite improves from ± 2.1‰ to ± 1.0‰ (2SD) at + 10 kV/− 10 kV and + 3 kV/− 10 kV analysis respectively, while precision in single grains is ± 0.3‰ (2SD) for both. Importantly, crystal orientation effects have not been identified at levels of ± 0.3‰ for δ 18O in silicates or other minerals analyzed by WiscSIMS though many minerals remain to be examined.

Application of a stress triaxiality dependent fracture criterion in the finite element analysis of unnotched Charpy specimens

Nonlinear dynamic finite element analysis (FEA) is conducted to simulate the fracture of unnotched Charpy specimens of steel under pendulum impact loading by a dedicated, oversized and nonstandard Bulk Fracture Charpy Machine (BFCM). The impact energy needed to fracture an unnotched Charpy specimen in a BFCM test can be two orders of magnitude higher than the typical impact energy of a Charpy V-notch specimen. To predict material failure, a phenomenological, stress triaxiality dependent fracture initiation criterion and a fracture evolution law in the form of strain softening are incorporated in the constitutive relations. The BFCM impact energy results obtained from the FEA simulations compare favorably with the corresponding experimental data. In particular, the FEA predicts accurately the correlations of the BFCM impact energy with such factors as specimen geometry, impactor tup width and material type. The analyses show that a specimen’s progressive deterioration through the thickness dimension displays a range of shear to ductile fracture modes, demonstrating the necessity of applying a stress state dependent fracture initiation criterion. Modeling the strain softening behavior helps to capture the residual load carrying capability of a ductile metal or alloy beyond the onset of damage. The total impact energy can be significantly under predicted if a softening branch is not included in the stress–strain curve. This research supports a study of the puncture failure of railroad tank cars under dynamic impact loading. Applications of the presented fracture model in failure analyses of other structures are further discussed.

Investigation of the Hydrogen Embrittlement on the 65Mn Steel from the Nuclear Power Plant with Small Punch Method

Damage of metals due to the influence of hydrogen is quite frequent and leads to dangerous failures. The characteristics of the hydrogen embrittlemnt of the 65Mn steel were evaluated with small punch test. With the increment of the amount of the hydrogen absorbed into the alloy at room temperature, the strength and the toughness of the material reduce. From the small punch experimental results, it is found the total impact energy, the fracture strain and the fracture stress decrease with the increment of the cathodic hydrogen charging time. The fracture surfaces change from the typical ductile fracture with big voids to the typical intergranular brittle fracture mode after hydrogen absorbed in the specimens with higher charging current density.

In situ sulfur isotope analysis of sulfide minerals by SIMS: Precision and accuracy, with application to thermometry of ∼ 3.5 Ga Pilbara cherts

Secondary ion mass spectrometry (SIMS) measurement of sulfur isotope ratios is a potentially powerful technique for in situ studies in many areas of Earth and planetary science. Tests were performed to evaluate the accuracy and precision of sulfur isotope analysis by SIMS in a set of seven well-characterized, isotopically homogeneous natural sulfide standards. The spot-to-spot and grain-to-grain precision for δ34S is ±0.3‰ for chalcopyrite and pyrrhotite, and ±0.2‰ for pyrite (2SD) using a 1.6nA primary beam that was focused to 10µm diameter with a Gaussian-beam density distribution. Likewise, multiple δ34S measurements within single grains of sphalerite are within ±0.3‰. However, between individual sphalerite grains, δ34S varies by up to 3.4‰ and the grain-to-grain precision is poor (±1.7‰, n=20). Measured values of δ34S correspond with analysis pit microstructures, ranging from smooth surfaces for grains with high δ34S values, to pronounced ripples and terraces in analysis pits from grains featuring low δ34S values. Electron backscatter diffraction (EBSD) shows that individual sphalerite grains are single crystals, whereas crystal orientation varies from grain-to-grain. The 3.4‰ variation in measured δ34S between individual grains of sphalerite is attributed to changes in instrumental bias caused by different crystal orientations with respect to the incident primary Cs+ beam. High δ34S values in sphalerite correlate to when the Cs+ beam is parallel to the set of directions <uuw>, from [111] to [110], which are preferred directions for channeling and focusing in diamond-centered cubic crystals. Crystal orientation effects on instrumental bias were further detected in galena. However, as a result of the perfect cleavage along {100} crushed chips of galena are typically cube-shaped and likely to be preferentially oriented, thus crystal orientation effects on instrumental bias may be obscured. Test were made to improve the analytical precision of δ34S in sphalerite, and the best results were achieved by either reducing the depth of the analysis pits using a Köhler illuminated primary beam, or by lowering the total impact energy from 20keV to 13keV. The resulting grain-to-grain precision in δ34S improves from ±1.7‰ to better than 0.6‰ (2SD) in both procedures. With careful use of appropriate analytical conditions, the accuracy of SIMS analysis for δ34S approaches ±0.3‰ (2SD) for chalcopyrite, pyrite and pyrrhotite and ±0.6‰ for sphalerite. Measurements of δ34S in sub-20µm grains of pyrite and sphalerite in ∼3.5Ga cherts from the Pilbara craton, Western Australia show that this analytical technique is suitable for in situ sulfur isotope thermometry with ±50°C accuracy in appropriate samples, however, sulfides are not isotopically equilibrated in analyzed samples.

Behaviour of an Impact Attenuator for Formula SAE Car under Dynamic Loading

A Formula SAE car must have structural devices that able to absorb most of the kinetic energy by means of progressive crushing therefore minimizing the forces and decelerations transferred to the occupant during frontal collisions. This paper presents the prediction of dynamic behaviour of an impact attenuator for a Formula SAE car under frontal impact conditions by using numerical and experimental approaches. The impact attenuator construction is a combination of sandwich panels and aluminium inner sheets. Firstly, the analysis of sandwich structures is carried out to better understand their behaviour and model them properly in the numerical simulation using LS-DYNA. In order to obtain the best configuration for the impact attenuator in terms of maximum absorbed energy, minimum deceleration and weight saving, its length and the number of inner sheets are optimised. Finally, a crash-test is performed on the impact attenuator to compare the experimental results with the numerical ones. The results obtained show that the impact attenuator is able to absorb the total impact energy with progressive and plastic deformation to contain the average deceleration as below 20 g.

Microstructural Study of a High Bainite Dual Phase (HBDP) Steel Austempered at Different Temperatures

4340 steel bars were austenitized at 850oC for 1 hour followed by heating at 700oC (ferrite and austenite region) for 90 min and quenching into a salt bath with different temperatures of 300, 350, 400 and 450oC. The steel bars were held for 1 hour at these temperatures before air cooling to room temperature. Various ferrite-bainite microstructures with 34% volume fraction of ferrite and different bainite morphologies were obtained. The results of SEM studies showed that by increasing the austempering temperature, the morphology of bainite varies from lower to upper bainite. According to the T-T-T diagram of the studied steel, the bainite transformation will not complete for the holding time of 1 hour at 400 and 450oC austempering temperatures and there can be 9 and 23Vol% of martensite at these temperatures respectively. Microstructural studies of specimens austempered at these temperatures showed complex microstructures of ferrite, bainite and martensite. Mechanical testing results showed reduction in yield and ultimate tensile strengths, hardness, uniform and total elongations and impact energy with increase of the austempering temperature from 300 to 400oC. But for dual phase steel austempered at 450oC, the yield and tensile strengths and hardness increased and a severe reduction in total elongation and impact energy was obtained. This brittle behaviour was related to martensite formation during cooling from this austempering temperature.

Phase separation and mechanical properties of polyketone/polyamide polymer alloys

AbstractWe have investigated polyketone (PK)/polyamide 6 (PA) polymer alloys having enhanced Charpy impact energy greater than that of polycarbonate (PC) as a result of moisture absorption. From the results of differential scanning calorimetry (DSC), Raman spectroscopy, and transmission electron microscope (TEM) observation of the polymer alloys, it was found that PK‐rich and PA‐rich phases exist at the nanometer level in the polymer alloys; however, a microscopic interaction phase formed between the two phases. 3D‐TEM observations, electron energy loss spectroscopy, and small‐angle X‐ray scattering measurements revealed that a co‐continuous nanolayer formed from the PA‐rich phase and lamella network of the PK‐rich phase. Moreover, the interaction and mobility of PK and PA molecular chains were investigated by using a 13C cross polarization/magic angle sample spinning NMR technique. It was found that moisture absorption markedly enhances the mobility of PA molecular chains in PK/PA alloys. This suggests that the wet (moisture‐absorbed) PA phase of PK/PA alloys allows quick deformation upon impact stimulation. On the other hand, the results of Charpy impact tests showed that the total impact energy (Etotal) of the wet polymer alloy was much higher than that of the dry one. An examination of the load‐displacement curves revealed that the wet samples showed a pronounced increase in displacement compared with the dry ones. From these results, it was concluded that the lamella network of the PK‐rich phase sustains the maximum stress and that the large displacement of the PA‐rich phase increases the impact energy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The effect of bainite morphology on the mechanical properties of a high bainite dual phase (HBDP) steel

4340 steel bars were austenitized at 850 °C for 1 h followed by heating at 700 °C for 90 min and quenching into a salt bath at the temperature range of 300–450 °C for 1 h to obtain dual structures with 34 vol.% fraction ferrite and various bainite morphologies. SEM studies showed that by increasing the austempering temperature, bainite morphology varies from lower to upper bainite. Tensile, impact and hardness tests revealed that increasing the austempering temperature from 300 to 400 °C leads to a reduction in yield and ultimate tensile strength, hardness, uniform and total elongation and impact energy. But in dual phase steel produced by austempering at 450 °C, yield and tensile strength and hardness increased and severe reduction in total elongation and impact energy obtained. Fractography of tensile specimens showed brittle behavior for this austempering temperature. Fatigue test results showed that fatigue limit decreases with increasing austempering temperature from 300 to 400 °C. Finally, fractography studies showed cleavage fracture at the surface of fatigue specimens austempered at 400 °C, which confirms the tendency to brittle behavior.

Cluster-induced crater formation

Using molecular-dynamics simulation, we study the crater volumes induced by energetic impacts (v=1–250km/s) of projectiles containing up to N=1000 atoms. We find that for Lennard–Jones bonded material the crater volume depends solely on the total impact energy E. Above a threshold Eth, the volume rises linearly with E. Similar results are obtained for metallic materials. By scaling the impact energy E to the target cohesive energy U, the crater volumes become independent of the target material. To a first approximation, the crater volume increases in proportion with the available scaled energy, V=aE/U. The proportionality factor a is termed the cratering efficiency and assumes values of around 0.5.

Thermal aging effect on Z3CN20.09M Cast Duplex Stainless Steel

Instrumented impact tests were performed on Z3CN20.09M Cast Duplex Stainless Steel (CDSS) aged at 400 °C for up to 3000 h. The material was cut from the primary pipe of a PWR to investigate the accelerated thermal aging embrittlement effect on the dynamic fracture properties. The load–deflection curves from the instrumented impact tests described both the loading and the fracture stages, from which the dynamic ultimate loading level and the dynamic ultimate strengths were calculated as a function of increased aging time. The increase in the dynamic ultimate strengths with aging time is much higher than those for the static ultimate strengths. With the increment of the aging time, both the crack initiation energy and the crack propagation energy decrease, which are separated form the total impact energy taking the maximum loading level as the crack initiation point. It is shown that the reduction tendency of the fracture propagation energy is the predominant reason for the reduction of the impact energy. With the increment of the aging time, the unloading slopes reflecting the crack propagation speed increase and the fracture surface patterns change from ductile fracture with shallow dimples to cleavage brittle fracture caused by dislocations piling up in the ferrite matrix. Mechanical properties of inner wall with fine equi-axed grains are much better than those of the outer wall with coarse columnar structures.

Cluster-induced sputtering of molecular targets

Using molecular-dynamics simulation, we study the cluster-induced sputtering of a diatomic (O2) and a triatomic (H2O) molecular target and compare it to the sputtering of an atomic target (Ar). In all three systems, sputtering occurs by the flow of gasified material out of the spike volume into the vacuum above it. Above a threshold, the sputter yield and also the number of dissociations and reactions increase linearly with the total impact energy. The number of reactions occurring is significantly higher than the number of surviving dissociations. The degrees of freedom of the sputtered molecules are not in thermal equilibrium with each other. While for the diatomic target, the internal energy amounts to only 10–20% of the translational energy, it is 40% for H2O. The translational energy distributions of sputtered monomers are strongly reduced at high energies due to molecule dissociations.

Effect of multiple impacts on high velocity pressed iron powder

High velocity compaction (HVC) process is a promising method for preparing high density powder metallurgy (PM) components with cost-effective. In the paper water atomized pure iron powder with 0.5 wt.% zinc stearate added was compacted by HYP35-7 High Velocity Compaction Machine. A computer controlled universal testing machine was used to measure the bending strength of samples. The effect of multiple impacts on the green density, the bending strength and the stress wave was discussed. The results show that at the identical total impact energy the green density and the bending strength of compacts pressed by double impact are the highest, whilst that of compacts prepared by triple impact is the lowest. In addition, the response time of stress wave is shortened gradually with increasing compacting numbers. Furthermore, the duration of stress wave of the second impact of double impact is the longest, but no obvious difference between that of single impact and the third impact of triple impact can be brought out. The comprehensive effect of the pressure and the duration results in the green density and the green strength increasing.

Effect of slurry properties on particle motion in IsaMills

IsaMill™ is a high-speed stirred mill for a range of milling duties from ultra-fine to relatively coarse grinding in the mineral processing industry. This work investigated particle and slurry flow in a mill using a combined Discrete Element Method and Computational Fluid Dynamics (DEM-CFD) approach. Slurry properties, such as flow density and viscosity, were varied to study their effects on the flow properties in terms of flow velocity, power draw, collision frequency, collision energy and total impact energy. Significant differences were observed when slurry was introduced and other conditions unchanged. With increasing density, fluid and particle flows showed stronger circulation in the axial direction due to the larger drag forces. Increased relative velocity and interaction between particles with disc led to higher collision frequency and collision energy. Increase in flow viscosity limited particles from moving towards the outer wall and the particles were more dispersed due to the larger circulating velocity in the axial direction. The total impact energy of the media and power draw also increase with slurry density and viscosity. The developed model provides a useful framework for further analysis of particle–slurry interactions in IsaMills™.