Response of Ti6321 titanium alloy at different strain rates under tensile loading

. Production efficiency as well as the reduction of energy consumption and waste are the main drivers for the improvement of large-scale production in chemical industry. In addition, the demand for new processes – these days especially related to the chemical energy conversion as basis for the Energiewende – are additional triggers for innovation. Catalysis, well recognized by the public e.g. in form of the 3-way automobile catalyst, plays an important role for about 90% of all processes in chemical industry. The development of new and improved catalysts is a challenge for chemists – as is the search for new structural materials for mechanical engineers. Due to the often-necessary noble and thus expensive metals (e.g. palladium) in many catalysts, structural and chemical function have been developed separately in the two communities. Recent progress in catalytically active materials allows replacing expensive noble metals in selected catalytic processes by significant cheaper elements [1]. This offers the new perspective to combine structural and chemical functionality by innovative materials. Within this area, intermetallic compounds with their peculiar combination of crystal and electronic structure [2], represent an interesting class of materials to address this vision as will be shown in the contribution.

Magnesium alloys have been increasingly used in the automobile, aerospace and communication industries due to their low density, high strength to weight ratio, good impact resistance and castability. Magnesium alloys, previously not used in load bearing components and structural parts are strongly being considered for use in such applications. Impact events in vehicles and airplanes as well as developments in weaponry and high speed metal working are all characterized by high rates of loading. Understanding of the dynamic behaviour of materials is critical for proper design and use in different applications. In the current study, a cast magnesium alloy AZ91D has been investigated at quasi-static and higher strain rates in the range between 300 s-1 and 1500 s-1. The INSTRON machine was used to perform the quasi-static tests. High strain rate tests have been performed using the Split Hopkinson Tensile Bar (SHTB), a very useful and widely used tool to study the dynamic behaviour of variety of engineering materials. The results of a tensile testing indicate that the tensile properties including yield strength (YS), ultimate tensile strength (UTS) and the elongation at fracture (Ef) are affected by the strain rate variation. Higher stresses are associated with higher strain rates. The alloy AZ91D displays approximately 45% higher tensile stresses at an average strain rate of approximately 1215/s than at quasi-static strain rate. The dependence of the yield stress and tensile strength on the strain rate in the range of high strain rate above 1000 s-1 is larger than that at lower strain rates. The alloy AZ91D is observed to be more strain rate sensitive for strain rate higher than 1000 s-1. A decrease in the strain rate sensitivity is also observed with the increasing strain in the specimen. It is observed that the hardening behaviour of the alloy is affected with increasing the strain rate. At high strain rates, the fracture of magnesium alloy AZ91D tends to transit from ductile to brittle.

The effect of aging on mechanical properties of SAC 305 at low strain rate has been investigated. For high strain rate constitutive mechanical behavior, a number of researchers relied on Split Hopkinson Pressure bar and the strain rate range is from 500/s to 3000/s. However, for typical drop and shock, the strain rate range is from 1/s to 100/s. There is a general scarcity of data for solder materials in this strain rate range. Therefore knowing the mechanical properties of lead free solder at this high strain rate range is very important for design and optimization of package reliability. It is possible that failure may happen at initial shock incident or may result from cumulative damage from sequential shock and vibration events. In addition, isothermal aging and thermal cycling may cause significant changes of mechanical properties of solder alloys due to evolving of microstructure. These changes are large especially in harsh environment such as high temperature and long-term aging. Consequently, a complete understanding of high strain rate and high temperature behaviors of solder alloy after long period of aging is necessary to perform a better design and optimization in electronics. A viscoplastic model was proposed by Anand [1982, 1989] to describe materials that depend on both operating temperature and strain rate. Recently, it has been broadly used to characterize viscoplastic deformation of lead-free solder materials. However, the Anand constants of SAC305 for high strain rate and high temperature condition at long-term aging are not available. In order to compute the constants for this model, uniaxial tensile tests have been done at a wide range of high strain rate and high temperature conditions within different aging period. In this study, different weighted impact hammers were introduced which enable attaining different high strain rates around 1 to 100 /s. A load cell is on the top of the specimen-grip, which is used to calculate tensile load dynamically. Additionally, a small thermal chamber is used to control the operating temperatures. High-speed data acquisition system was built to capture the stress-strain curves of specimen. Tensile stress-strain curves have been plotted over a wide range of strain rates (8 =10, 35, 50, 75 /s) and temperatures (T = 25, 50, 75, 100, 125, 150, 175, 200°C) at different aging periods (Pristine, 60, 120, 180, 240, 300, 360 days). Totally, seven groups of Anand constants have been computed based non-linear least square curve fitting procedures. In addition, the correctness of the predicted model has been verified by comparing with experimental data.

The International Organization for Standardization Technical Committee for Metallic Materials—Tensile Testing stated in 2011 that temperature and strain rate variations would induce a change in the results of tensile tests, termed as the measurement uncertainty of tensile mechanical properties in metals. The uncertainty means that the tensile testing results of a specimen at a temperature and strain rate are not the original mechanical properties possessed prior to the testing. Hence, since the time of Galileo the results of tensile testing have been incorrectly interpreted as the original mechanical properties of specimens, thereby forming a paradox. At the turn of the 21st century, the micro-theory of metallic elastic deformation was proposed, identifying that a change in microstructure at atomic level could occur during elastic deformation, leading to a change in the concentration of solute (impurity) at grain boundaries/around dislocations. The micro-theory has been used to explain the mechanism of the measurement uncertainty. Different tensile temperatures and strain rates correspond to different durations of elastic deformation during tensile testing, different concentrations of solute at grain boundaries/dislocations, and thus different mechanical properties. On this basis, a new technology system of tensile testing is suggested, i.e., a “mechanical property–tensile strain rate” curve at a given test temperature can be used to evaluate the original mechanical property. The higher the strain rate is, the closer the property on the curve is to the original property. Therefore, to determine the original mechanical property of the tested metal, a sufficiently high strain rate is required. The curve can also characterize the property variation of the tested metal in service with the service time. In addition, the property characterized by a point on the curve can represent the property of the tested metal when processing-deformed with the corresponding strain rate. As an example of the application of the new technology system, the property of high-entropy alloys is represented with a curve. The results show that the new technology system could change the conceptual framework and testing technology system of metallic mechanics.

A characterization of mechanical and micromechanical properties of SAC305 solder wire under varied strain rates and temperatures was performed using tensile and nanoindentation tests. The evolution of SAC305 lead-free solder wire grains was compared in samples that were subjected to various strain rates and temperatures using tensile tests based on ASTM E12 standards. Different behaviours of mechanical properties, micromechanical properties, and microstructure evolution of SAC305 solder wire were observed when either temperature or strain rate was held constant and the other varied. Both tensile and nanoindentation tests produced qualitative results, such as dynamic recovery and occurrence of pop-in events, that reflected changes of microstructure. It was observed that some of the mechanical properties of SAC305 solder wire, namely yield strength (YS), ultimate tensile strength (UTS) and Young’s modulus, showed the same trends, but with lower values, compared to micromechanical properties obtained from nanoindentation tests based upon hardness and reduced modulus. Microstructure examination further confirms that the YS, UTS and hardness values increase with more solder wire grain refinement. SAC305 solder wire also maintained an equiaxed structure under various strain rates and temperatures.

The present study concerns the deformation and fracture behavior of two ferrite–martensite dual phase steels (FMDP660 and FMDP780) with different phase fractions subjected to different strain rate (0.001 s−1 to 1000 s−1) tensile testing. For both steels, the yield strength (YS) monotonically increased with strain rates, whereas the values of ultimate tensile strength (UTS), uniform elongation (UE) and post-uniform elongation (PUE) were maintained stable at the low strain rate range (0.001–0.1 s−1), followed by a significant increase with strain rate at high strain rate levels (0.1–1000 s−1). The FMDP780 steel with a higher fraction of martensite possessed a stronger strain rate sensitivity of tensile strength and elongation (UE and PUE) values at the high strain rate stage, compared with the FMDP660 sample. The change of UTS and UE with different strain rates and phase fractions was highly related to the strain hardening behavior, which was controlled by the dislocation multiplication in ferrite, as validated by transmission electron microscopy (TEM). The fracture surface of the two steels was characterized by dimpled-type fracture associated with microvoid formation at the ferrite–martensite interfaces, regardless of the strain rates. The change of the dimple size and PUE value of the two steels with strain rates was attributed to the effect of adiabatic heating during tensile testing.

Electronics products may often be exposed to high temperature during storage, operation and handling in addition to high strain rate transient dynamic loads during drop-impact. Electronics subjected to drop-impact, shock and vibration may experience strain rates of 1–100 per sec. There are no material properties available in published literature at high strain rate at elevated temperature. High temperature and vibrations can contribute to the failures of electronic system. The reliability of electronic products can be improved through a thorough understanding of the weakest link in the electronic systems which is the solder interconnects. The solder interconnects accrue damage much faster when subjected to Shock and vibration at elevated temperatures. There is lack of fundamental understanding of reliability of electronic systems subjected to thermal loads. Previous studies have showed the effect of high strain rates and thermal aging on the mechanical properties of leadfree alloys including elastic modulus and the ultimate tensile strength. Extended period of thermal aging has been shown to affect the mechanical properties of lead free alloys including elastic modulus and the ultimate tensile strength at low strain rates representative of thermal fatigue [Lee 2012, Motalab 2012]. Previously, the microstructure, mechanical response and failure behavior of leadfree solder alloys when subjected to elevated isothermal aging and/or thermal cycling [Darveaux 2005, Ding 2007, Pang 2004] have been measured. Pang [1998] has showed that young’s modulus and yield stress of Sn-Pb are highly depending on strain rate and temperature. The ANAND viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components. Previously, Mechanical properties of lead-free alloys, at different high strain rates (10, 35, 50, 75 /sec) and elevated temperature (25 C-125 C) for pristine samples have been studied [Lall 2012 and Lall 2014]. Previous researchers [Suh 2007 and Jenq 2009] have determined the mechanical properties of SAC105 at very high strain rate (Above 1000 per sec) using compression testing. But there is no data available in published literature at high strain rate and at elevated temperature for aged conditions. In this study, mechanical properties of lead free SAC105 has been determined for high strain rate at elevated temperature for aged samples. Effect of aging on mechanical properties of SAC105 alloy a high strain rates has been studied. Stress-Strain curves have been plotted over a wide range of strain rates and temperatures for aged specimen. Experimental data for the aged specimen has been fit to the ANAND’s viscoplastic model. SAC105 leadfree alloys have been tested at strain rates of 10, 35, 50 and 75 per sec at various operating temperatures of 50°C, 75°C, 100°C and 125°C. The test samples were exposed to isothermal aging conditions at 50°C for different aging time (30, 60, and 120 Days) before testing. Full-field strain in the specimen have been measured using high speed imaging at frame rates up to 75,000 fps in combination with digital image correlation. The cross-head velocity has been measured prior-to, during, and after deformation to ensure the constancy of cross-head velocity.

Strain rate dependent deformation and failure behavior of laser welded DP780 steel joint under dynamic tensile loading

The flow stress of metals is generally observed to increase with strain rate• The literature on the dependence of properties on strain rate is extensive, but for new alloys, and high-strength materials in particular, data are far more difficult to obtain. Commercial AI -L i alloys show combinations of strength and toughness that are comparable with, and in some cases superior to, traditional highstrength A1 alloys [1]. Investigations of properties at high strain rate have shown an increase in strength with increasing strain rate in the range of strain rates 10-5-103 s -1, with the effect being far more pronounced in tension than in compression [2]. Chiem et al. [2] showed that fracture strain increases with strain rate at high strain rates. However , their values reported at the high strain rates are well below the quasi-static ductilities• Kobayashi et al. [3], on the other hand, showed that the elongation at high strain rates is superior to that measured at quasi-static strain rates for A1-Li alloys• This letter contributes to the database on AI -L i alloys by characterizing the properties of an alloy in compression over the strain rate range 10 .3 to 6 x 103 S 1 . The AI L i alloy used in this study was Alcan 8090-T82551 in the form of rectangular extruded bar of dimensions 100 m m x 25 mm. The alloy has nominal values of 0.2% proof stress, ultimate tensile stress and elongation of 475 MPa, 525 MPa and 5.0%, respectively, which concur with values given in [1]. At the lowest strain rate (10 .3 s -1) compression tests were performed with the cylinder axis in the extrusion, short transverse (thickness) and long transverse (width) directions, and using two different lubrication conditions, viz. a Teflon tape and a Teflon grease (Dupont Kryotox 240 AC). At the higher strain rates all tests were with the specimen axis in the short transverse direction and using only the Teflon tape. The range of strain rates was achieved using a screw-type hydraulic drop weight with a piezoelectric load cell, and direct impact Hopkinsons bar techniques, which were described in detail in [4-6]• Fig. 1 illustrates four typical stress-strain curves for specimens with the cylinder axis in the short transverse direction• The two curves at the strain rate of 1.3 x 10 .3 s -I are typical results for the two types of lubrication. Up to the maximum load the curves were identical within observed specimen-tospecimen scatter• Beyond a maximum load the Teflon tape-lubricated specimens most commonly failed in shear at a strain of the order of 0.2, whereas 600

A γ-base TiAl alloy with duplex microstructure of lamellar colonies and equiaxed γ grains was prepared with a reactive sintering method. Tensile tests and fracture toughness tests at loading velocities up to 12 m/s (strain rate for tensile tests up to 3.2×102/s) were carried out. The micro-structure of the alloy before and after tensile deformation was carefully examined with a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The fractography of the tensile specimens and fracture toughness specimens was studied. The experimental results demonstrated that the ultimate tensile strength (UTS) and yield strength (YS) increase with increasing strain rate up to 10/s and subsequently level off. The UTS and YS exhibited similar strain rate sensitivity. The strain rate sensitivity exponent at strain rates lower than 10/s is about 1.5×10−2 and at higher strain rates is almost zero. In this study, fracture toughness was found to be less sensitive to the loading velocity, having values of around 25 MPa √m, which is believed to be attributed to the high strain rate experienced at the crack tip. The predominant deformation mechanism for the strain rates used in this study was found to be twinning. However, in the low strain rate range, the dislocation motion mechanism was operative at the initial deformation stage and twinning dominated the later stage of the deformation process. In the high strain rate range, the entire deformation process was dominated by twinning. The interaction between deformation twinning and grain boundaries resulted in intergranular fracture in the γ grains and delamination of α 2/γ interfaces in the lamellar colonies.

Under dynamic loading the stabilising effect of increased strain rate sensitivity of the material restrains neck formation in tension tests and leads to an increase in ductility. On the other hand the adiabatic character of the deformation process reduces the flow stress and promotes instability, localisation and adiabatic shear band initiation. Furthermore, the notch sensitivity of the material increases with increasing strain rate. Dynamic and quasi-static tension and compression tests were carried out on the age hardenable aluminium wrought alloy AA7075. There, dispers distributed precipitations are often the starting point for ductile fracture caused by impact due to the nucleation, growth and coalescence of voids and micro-cracks in case of tension. Neck formation under tensile loading and instabilities like shear bands in case of compression are discussed on the basis of the theory of imperfections under consideration of the increased strain rate sensitivity of the material and the adiabatic character of the deformation process at high strain rates. In case of tensile loading, tests with various notched geometries allowed the study of the influence of degree of multiaxiality. Through combination of experiment and simulation, the influence of strain rate on the local fracture strain could be determined for tensile and compression loading.

Influence of strain rate on ultimate tensile stress of coarse-grained and ultrafine-grained copper

Investigations on the effect of strain rate on tensile properties of two materials, namely, aluminum alloy 7075 T651 and IS 2062 mild steel, are presented. Experimental studies were carried out on tensile split Hopkinson pressure bar (SHPB) apparatus in the strain rate range of 54–164/s. Uncertainty analysis for the experimental results is presented. Johnson–Cook material constitutive model was applied to predict the tensile yield strength of the tested materials at different strain rates. It is observed that the tensile yield strength is enhanced compared with that at quasi-static loading. During tensile SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. An explanation to this is provided based on the increase in dislocation density and necking in the tested specimens during high strain rate loading and the consequent stress wave attenuation as it propagates within the specimen. The fracture behavior and effect of high strain rate testing on microstructure changes are examined. The peak force obtained based on strain gauge mounted on the transmitter bar is lower than the peak force obtained based on strain gauge mounted on the incident bar. There is an increase in tensile yield strength at high strain rate loading compared with that at quasi-static loading for both materials. The enhancement is more for IS 2062 mild steel than that for aluminum alloy 7075 T651. In the range of parameters considered, the strength enhancement factor was up to 1.3 for aluminum alloy 7075 T651 and it was up to 1.8 for IS 2062 mild steel. Generally, there was a good match between the experimental values and the Johnson–Cook model predictions.

Dynamic increase factors of concrete-like materials at very high strain rates

The effect of strain rate on mechanical properties and microstructure of a metastable FeMnCoCr high entropy alloy