Low Strain Rate Tensile Tests Research Articles

Evaluation of Hydrogen Embrittlement of Electroless Ni-P Plated 6061-T6 Aluminum Alloy by Three-Point Bending and Rotating Bending Fatigue Tests

In this study, 6061-T6 aluminum alloys were plated with electroless Ni-P with different phosphorus content and three-point bending and rotary bending fatigue tests. The effects of hydrogen due to plating on mechanical properties were investigated. It was shown that the ductility decreased immediately after low-phosphorus type and high-phosphorus type Ni-P plating by three-point bending test because a hydrogen was introduced into the alloys. The fatigue strength of the low-phosphorus type Ni-P plated specimen was higher than that of the untreated specimen, while that of the high-phosphorus type plated specimen was much lower. It is clear that the fatigue strength differs greatly depending on the phosphorus content in the plating film. 6061-T6 aluminum alloy have been reported to exhibit no hydrogen embrittlement in low strain rate tensile tests under wet condition. However, it was found that hydrogen embrittlement occurred when 6061-T6 aluminum alloy was plated with the high-phosphorus type electroless Ni-P and fatigue-tested on rotary bending machine.

Ductility and fatigue properties of low nickel content type 316L austenitic stainless steel after gaseous thermal pre-charging with hydrogen

The susceptibility of low nickel content type 316L austenitic stainless steel to hydrogen was quantified using low strain rate tensile tests and strain-controlled low-cycle fatigue life measurements. Both tests were performed under air condition after charging with high-pressure 10-MPa hydrogen gas at 300 °C for eight days. No significant influence of hydrogen was recognized in 0.2% proof stress, but the strain at fracture and reduction area was decreased significantly in both hydrogen pre-charged and in gaseous hydrogen conditions compared to companion tests conducted in air. The decrease of fatigue life in the high strain amplitude region was related to a significant decrease in the plastic component while the effect of hydrogen on the elastic component was negligible. Highly localized deformation and a pronounced martensite transformation occurred near the site of the fracture surface in the high strain amplitude regime, resulting in the early formation of abundant micro-surface cracks in this regime of the hydrogen pre-charged samples.

Characteristic time of strain induced crystallization of crosslinked natural rubber

Real time Wide-Angle X-ray Scattering (WAXS) measurements during cyclic tensile tests at high strain rates (from 8 s−1–280 s−1) and at room temperature on crosslinked Natural Rubber (NR) are performed thanks to a specific homemade device. From the observed influence of the frequency on the crystallization index at the maximum sample elongation, a characteristic crystallization time is deduced. This is done taking into account the material self-heating during such unusually high strain rates. Two regimes for the dynamic process of strain induced crystallization are evidenced. For the NR tested, the obtained characteristic time is around 20 ms when the material average elongation during the cyclic test is above a critical elongation value λc. λc is the minimum elongation needed to induce crystallization during low strain rate tensile tests. Moreover, a rapid increase of this characteristic time is found when the average elongation decreases below this critical value.

Viscoelastic modelling of tennis ball properties

An explicit finite element (FE) tennis ball model which illustrates the effects of the viscoelastic materials of a tennis ball on ball deformation and bounce during normal impacts is presented. A tennis ball is composed of a rubber core and a fabric cover comprised of a wool-nylon mix which exhibit non-linear strain rate properties during high velocity impacts. The rubber core model was developed and validated using low strain rate tensile tests on rubber samples as well as high velocity normal impacts of pressurised cores at velocities ranging from 15 m/s to 50 m/s. The impacts were recorded using a high speed video (HSV) camera to determine deformation, impact time and coefficient of restitution (COR). The material properties of the core model were tuned to match the HSV results. A two component anisotropic fabric model was created which included artificial Rayleigh damping to account for hysteresis effects, and the core model 'tuning' process was used to refine the cloth layer. The ball model's parameters were in good agreement with experimental data at all velocities for both cores and complete balls, and a time sequenced comparison of HSV ball motion and FE model confirmed the validity of the model.

Creep and tensile behaviour of austenitic Fe–Cr–Ni stainless steels

The control of creep behaviour during service of reformer tubes made of HP-40 austenitic stainless steels is still limited by the knowledge of creep mechanisms in these alloys. Two different HP-40 alloys modified with a low-level addition of Nb were studied. Creep tests were carried out at 980 and 1050 °C with different stress levels, in the range of 20–50 MPa, and their results were plotted in a Norton-type diagram. Also, low strain rate tensile tests were performed at temperature of 950, 980 or 1000 °C. As low strain rate tensile tests showed a plateau at nearly constant stress for a given strain rate, they could be somehow linked with creep tests. Accordingly, tensile and creep results were plotted together on a Larson–Miller (LMP) diagram. The fracture modes of tensile and creep samples were investigated and the effect of different parameters such as sample dimensions, temperature and atmosphere, was also studied.

Comportement mécanique de l'acier inoxydable martensitique 17-4 PH en corrosion sous contrainte et à la fragilisation par l'hydrogéne environnemental

Age hardened martensitic stainless steels have high resistances to mechanical stress, to friction corrosion and to stress-corrosion cracking (after certain ageing heat treatments). These steels have also high mechanical toughness levels. The mechanical strength of these steels increases when performing specific heat treatments in order to promote the precipitation of hardening phases such as copper-rich ε and/or chromiumrich α′. However, it is well known that the susceptibility to stress-corrosion cracking and to hydrogen embrittlement increases when the mechanical strength of the martensitic steels is high. This paper is devoted to a study the mechanical behaviour of the 17-4 PH martensitic stainless steel with respect to stress-corrosion cracking and to embrittlement by environnemental hydrogen in different ageing conditions, i.e. ageing temperatures (200 to 650 °C) and ageing times (1 and 4 hours). The two behaviours were studied by carrying out low strain rate tensile tests (ε′ = 2.7×10 −6 s −1) in H 2SO 4 1N. By using differential scanning microcalorimetry, we have identified the precipitation mechanisms of ε and α′ phases, and calculated their activation energies by applying KISSINGER'S relationship. The results obtained show that the susceptibility to stress-corrosion cracking and to hydrogen embrittlement is maximum at the optimum ageing temperature for which the strength level is maximum. The optimum ageing temperature increases when the ε phase, initially coherent, becomes non-coherent. The fracture mechanism changes from cleavage to intergranular mode, respectively. Finally, the fracture mechanism by stress-corrosion cracking is the same as that provoked by hydrogen embrittlement.

The epoxy-polycarbonate blends cured with aliphatic amine?II. Thermal and mechanical properties mechanisms

The transamidation reaction converts the carbonate and amine into N-aliphatic aromatic carbamate and urea, causing the equivalent of oxirane and amine nonstoichiometric in the primary cure stage. After postcure, the substitution reaction takes place and results in a more tightly crosslinked structure. Such a higher crosslinking density is responsible for higher Tg, tensile strength, and tensile modulus in the postcure stage than that in the primary and secondary cure stages. This trend is more pronounced in those PC–epoxy blends containing higher molecular weight aliphatic amine or a higher content of PC. This phenomenon is due to the difference in the fraction of amino group of aliphatic amine consumed in the transamidation. PC–epoxy/aliphatic amine blends show minor improvement in the high strain rate Izod impact tests, while toughness improvement for some blends is substantial at low strain rate tensile tests. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2183–2191, 1997

Hydrogen embrittlement in the duplex stainless steel Z2CND2205 hydrogen-charged at 200°C

Physical and mechanical properties of austeno-ferritic stainless steels depend on the microstructure and phase transformations: many intermetallic phases, carbides and nitrides precipitate at different tempering temperatures. Hydrogen behaviour in steels is affected by the morphology and by the presence of precipitates, both for its diffusional behaviour and for the importance of trapping phenomena. In this paper, the hydrogenation of a 22Cr-5Ni duplex stainless steel has been achieved at 200°C in molten salts bath in potentiostatic conditions, and hydrogen embrittlement has been characterised using low strain rate tensile tests. The influence on hydrogen embrittlement of different intermetallic phases, carbides and nitrides has been considered via tempering heat treatment with tempering temperatures between 200 and 1050°C. The possibility of the recovery of the mechanical properties of charged steel outgassing at room temperature has been considered, investigating also the influence of different intermetallic phases, carbides and nitrides. Moreover, a new thermal technique based on high-temperature outgassing tests has been performed in order to calculate the hydrogen coefficient of diffusion.

STRAIN RATE DEPENDENCE ON MECHANICAL PROPERTIES IN SOME COMMERCIAL ALUMINUM ALLOYS

The flow stress and ductility of some commercial aluminum alloys (1050, 3003, 3004, 5182 and 7N01) have been investigated as a function of strain rates over the range from 1x10 s to 4xl0s at room temperature. The maximum flow stress of both 1050 and 3003 alloys increases with increasing strain rate , but the maximum flow stress of 3004, 5182 and 7N01 alloy decreases with increasing strain rate in the low and intermediate ranges from lx l 0 3 to lxl0 s 1 .The above three alloys which showed the particular behavior of flow stress in this strain rate range contain magnesium atoms in solute. So, this behavior of flow stress in these alloys seemed to be concerned with the interaction between magnesium atoms in solute and dislocations. The elongation in failure increases with strain rate for most of the present alloys except for the 7N01 alloy. 1-INTRODUCTION Recently many kinds of commercial aluminum alloys have been used in press forming, and the forming rates in use are in the strain rate range from 1 to 100 s 1 . Therefore, the investigation of the mechanical properties of commercial aluminum alloys in these forming rates is important to use these alloys appropriately. It is well known that the change of flow stress of aluminum[l] and aluminum alloys[2) with strain rate at room temperature is negligible in a low strain rate range below 10 s; but the flow stress increases rapidly with strain rate in high strain rate ranges over 10s. A few reports about mechanical properties for aluminum alloys, however, were made for the strain rate ranges from 10' s 1 to 10sM31. Therefore, the flow stress and ductility of some commercial aluminum alloys(1050, 3003, 3004, 5182 and 7N01) have been investigated as a function of strain rates over the range from lx lO 3 to 4xl0 s' at room temperature. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1991349 C3-342 JOURNAL DE PHYSIQUE IV 2-EXPERIMENTAL PROCEDURE The chemical composition of the commercial aluminum alloys used in this study is given in Table 1. Tensile specimens, machined from hot rolled plates, had their tensile axes normal to the rolling direction. The gauge length of the specimen is 4.5 mm and the diameter is 3 rnm. All specimens were heated to 643 K with a heating rate of 47 K / hour and then annealed for 2 hours in air. The optical microstructures of these alloys after annealing are shown in Fig. 1 (a)-(e) respectively. The grains were elongated to the direction of rolling and fiber-structures are observed for all alloys. (a) 1050 alloy (b) 3003 alloy (c) 3004 alloy (dl 5182 alloy (e) 7N01 alloy Fig.1 The optical microstructures for all alloys after annealing Low strain rate tensile tests (lx103 l ~ l O ' s ~ ) were performed with an instron machine. and intermediate strain rate tensile tests (1x10-1-3x102s1) were performed with the hydraulic tensile testing machine, and the dynamic tensile tests (4x102 -4x103s-l) were performed using a split Hopkinson pressure bar system which incorporates a specific attachment. The incremental strain rate tests were performed by the hydraulic tensile testing machine. This machine has a valve corresponding proportionally to given voltage. Therefore, using a computer with a controlling voltage pattern, the constant strain rate tests or the incremental strain rate tests can be performed. Table 1 The chemical composition of the commercial aluminum alloys ELEMENT ( w t % ) ALLOY Z n Mg Cu Mn ~r Z r T i F e S i

Creep life assessment by low strain rate tensile testing

A testing method, originally proposed by Rajakovics, 5 has been investigated for its ability to extrapolate creep rates from the results of short-term tests. Low constant strain rate tensile tests have been performed on a number of high temperature materials in the virgin, service-aged and welded conditions in the temperature range from 525°C to 1050°C. A technique has been developed that permits one to determine the steady-state creep rate under a known stress or the creep stress for a given creep rate. A step towards a quantitative residual life assessment of service-aged materials has been made. The results of the proposed extrapolation technique are compared with results from creep tests.

Deformation of poly (dienes) below T g

Cross-linked poly(dienes) (polychloroprene, polyisoprene and polybutadiene) are shown to exhibit crazing when subjected to low strain-rate tensile tests at low temperatures. Conditions for crazing to occur in the polybutadienes are examined. It is found that observable crazing occurs providing the rubbers are (a) slightly oriented, (b) stretched below their glass transition temperature (Tg) and (c) deformed in an environment which is close to its liquefaction or sublimation point. Gases evolved after low temperature testing are shown to be dissolved gases from the test environment. The interrelationship between the mechanical properties of the rubbers, quantity of gas absorbed and the radicals formed by scission of the network molecules is explored.

Ｆｅ‐Ｎｉ合金の水素誘起現象と水素ぜい化について

To study the effect of nickel content in iron-nickel alloys on the hydrogen-induced phenomena and susceptibility to hydrogen embrittlement, X-ray diffraction analysis and low strain rate tensile tests were performed for hydrogen charged iron-nickel alloys containing nickel 29∼50%.The results obtained are summarized as follows.(1) Hydrogen generated by elecrolytic charging reacts with iron-nickel alloys to form a solid solution and f. c. c. hydride.(2) The tendency for hydride formation increases with increasing nickel content.(3) Electrolytic charging of hydrogen into lower nickel alloys causes the same martensitic transformation as in the cases of cold working and subzero treatment.(4) Hydrogen existing in the form of solid solution suppresses the martensitic transformation in subzero treatment.(5) In 33% nickel alloy, no or little hydrogen embrittlement occurs. Alloys containing nickel either below or above 33% embrittled. This embrittlement in lower nickel alloys is due to martensite formation during hydrogen charging, tensile tests and subzero treatment, while in higher nickel alloys it is due to hydride formation.

A new interpretation of the mechanical properties of the Gibeon Meteorite

A set of results on the temperature and strain rate dependence of the tensile properties of the Gibeon meteorite reported by Gordon in 1970 is reinterpreted. It is shown that these results indicate that the meteorite material undergoes a ductile-brittle transition in low strain rate tensile tests at about 50°K. It is estimated that under asteroidal impact conditions the transition temperature would be about 200°K. Thus provided that the internal hydrostatic pressure did not depress the transition temperature significantly, the material would fragment in a brittle manner yielding meteoritic fragments free of plastic deformation. An approximate calculation of the effect of pressure on the transition temperature shows that brittle behavior would not occur in asteroids having radii greater than about 140 km. Thus since meteoritic fragments rarely show signs of gross plastic deformation, it is concluded that this is an approximate upper limit to the size of the parent asteroids. Work on the nickel composition profile in octahedrites by J. A. Wood (1964) led to an estimate of the radii of the parent asteroids of about the same magnitude. Our value of 140 km is probably subject to an error of about 50% in either direction. The larger asteriods now present in the solar system are of about this size.

Strain ageing effects and stress relaxation in iron during shock loading

The influence of prestraining and ageing upon the stress relaxation, which follows the elastic precursor wave during shock loading of iron, has been determined experimentally. Prestraining through the Lüders strain is observed to eliminate this stress relaxation under shock loading. Suitable time-temperature ageing treatments after prestraining cause a reappearance of the shock stress relaxation. Thus the influence of prestraining and ageing upon the stress relaxation in iron is qualitatively the same as the influence of these treatments upon the upper to lower yield point drop in conventional low strain rate tensile tests. Quantitative differences between the influence of strain ageing upon the shock stress relaxation and the conventional yield drop are observed. The return of the shock stress relaxation by ageing of prestrained iron (containing both nitrogen and carbon) appears to be governed by the diffusion of carbon while the return of the conventional yield drop appears to be governed by the diffusion of nitrogen. Further, for a given ageing temperature, the critical ageing time for the return of shock stress relaxation is from one to two orders of magnitude longer than the critical ageing time for return of the conventional yield drop. The relationship of these results to the current theories of dislocation behavior in iron containing small amounts of carbon and nitrogen is discussed.