Dip Test Research Articles

Effects of nitride distribution on internal stress during high temperature deformation of 12%Cr–15%Mn austenitic steels

Many investigations on internal stress of various materials have been performed as the internal stress is considered to be an important factor to control high temperature deformation. The present authors have researched the effect of very fine and dense vanadium nitride (VN) precipitates on internal stress and effective stress which were measured by a strain dip test during high temperature creep of 12%Cr-15%Mn austenitic steels. In the present study, the authors have investigated the difference of the response to a strain dip test among the 12%Cr-15%Mn materials which are alloyed with small amounts of V, Ti and Ta and have different distributions of nitrides formed by an aging treatment, and have discussed the effect of nitride distribution on the interaction of dislocations with the precipitates.

Technical Notes: Detecting Impact Damage of Sweet Onions Using Muriatic Acid and X-rays

Damage received by Granex-Grano type sweet onion bulbs may not be clearly evident with the naked eye because the effect of damage may be internal rather than on the surface of the onion. Damage may result from disease, insects, or mechanical means. Considering mechanical damage, layers of dry skin on the surface of an onion may shield the surface while transmitting an impact force to within the onion bulb. Methods of nondestructively examining sweet onions are being sought. Both a muriatic acid dip test and an X-ray CT have been found to provide some indication of damage under certain conditions. For freshly harvested sweet onions, muriatic acid has been found to cause the flesh of a sweet onion to appear yellow and become a sticky gel in the vicinity of damage, thus enhancing the visibility of damage. X-rays have been found to aid in viewing the internal structure of a sweet onion and thus damage that may have occurred. These techniques may lead to a further understanding of how sweet onions should be cared for in order to keep damage to a minimum.

The rate-dependent mechanical behavior of modified 9wt.%Cr-1wt.%Mo steel at 538 °C

Uniaxial, strain controlled tests at strain rates ranging from 5.0 × 10 −3 to 1.0 × 10 −7 s −1 combined with relaxation tests were performed to determine the mechanical behavior and the influence of recovery of state and other softening mechanisms. In addition, attempts were made to measure the equilibrium (back) stress of modified 9wt.%Cr-1wt.%Mo steel at 538 °C using McLean-type dip tests. Testing was performed with an MTS servohydraulic computer-controlled testing machine, a clamshell furnace and an MTS high temperature extensometer which measured the strain on the gauge length of the specimen.

Effective and recovery stresses in deformation studies of polyvinyl chloride and polypropylene using the modified strain transient dip test

Partitioning the applied stress into internal stress components (effective and recovery) using the modified strain transient dip test is a useful approach towards a better understanding of the viscoelastic nature of polymers. The internal stresses of polyvinyl chloride (PVC) and polypropylene (PP) were measured successfully using this test on a computer-controlled electro-servo hydraulic tensile testing machine which was designed for rapid step unloading in less than 1 s to avoid memory effects of the polymers. A power-law relationship can be used to describe the variation of the internal stress components with strain. Actual yield strains occurred at smaller values (less than 2%) than those obtained from a conventional stressstrain diagram (which for PVC and PP exceed 3.5% and 7%, respectively). This observation indicated that plastic yielding occurred much earlier and yield strains from conventional stress-strain diagrams may be overestimates. For very ductile material (PP) the activation volumes were comparable in magnitude to that obtained conventionally; whilst for less ductile material (PVC), the activation volume was four times higher. One of the main advantages of stress partitioning is for the detailed definition of the extrapolated yield point which otherwise will be missed out in a conventional plot of applied stress and strain.

Assessment of intrinsic creep resistance evolution based on the results of constant load creep tests

In the present study a method to assess the intrinsic creep resistance evolution by using data of constant load creep tests is proposed. The investigation has been performed on the austenitic steels X6 CrNi 18 11 and X8 CrNiMoNb 16 16. To develop the constitutive equation describing the intrinsic creep resistance evolution a simple structural mechanical model has been used. The applied model is based on a modification of the Levy‐Mises equation for plasticity to consider creep time effects. The proposed model has been verified experimentally. The experimental creep resistance evolution curves have been derived with the aid of strain transient dip test performed in transient, steady state and accelerated creep stage.

An investigation of creep behaviour of a low carbon 18Cr12Ni (304L type) stainless steel at 873–1173 K

Creep behaviour of a low carbon 18Cr-12Ni (304L type) stainless steel was investigated in a broad region of temperatures and applied stresses. The apparent activation energy of creep Q c and the applied stress sensitivity parameter of minimum creep rate m were determined. By neglecting a slight dependence of Q c on applied stress and accepting its weighted average value Q c av, the slight temperature dependence of m was avoided. The parameter m was found to increase approximately linearly with applied stress from about 4 at σ20 MPa to about 8 at σ300 MPa. The value of Q c av is significantly higher than that of the activation enthalpy Δ H L of lattice diffusion, to which self-diffusion of Fe, Cr and Ni contributes. Nevertheless, the creep is probably lattice diffusion controlled; the difference between Q c av = 366 kJmol −1 and Δ H L 290 kJ mol −1 is accounted for by the temperature dependence of shear modulus G. It was shown that the creep in the low carbon 18Cr-12Ni stainless steel cannot be interpreted in terms of the natural third-power-law creep equation by replacing in it the applied stress σ by the difference σ− σ 1, where σ 1 is the internal stress measured by the strain transient dip test techniques. The implications of this finding are briefly discussed.

Results of selective screening for inborn errors of metabolism in the former East Germany.

Since the early 1970s selective screening for inherited metabolic disorders has been performed in larger children's hospitals or metabolic centres of the former East-Germany. As a rule the following methods were employed: initially paper chromatography, drop, dip and spot tests, later on thin-layer chromatography and more recently enzyme analysis, gas chromatography, mass spectrometry and HPLC. Normally urine, blood or leucocytes were investigated. The diagnoses were confirmed in metabolic centres in Greifswald, Berlin or Leipzig or in collaboration with specialized laboratories abroad. About 130,000 subjects from former East Germany as well as from different East European countries were investigated, of which 365 patients were diagnosed and classified into roughly 40 various metabolic diseases. The proportion of positive diagnoses was 1 in 400.

12%Cr-15%Mn鋼の高温クリープ変形中の内部応力に及ぼす微細析出物(VN)の影響

The objective of the present study is to investigate the effects of fine precipitates of vanadium nitride on the creep deformation behaviors of 12%Cr-15%Mn austenitic steels through the measurement of internal stress and effective stress. These stresses were obtained by strain dip tests. The internal stress of VN free materials was determined as a unique function of applied stress. On the other hand, that of VN containing materials was not obtained uniquely as a function of applied stress. This indicates that fine precipitates of VN with high number density are strong barriers for the dislocation motion in spite of wide range variation of stress applied on the dislocations. At lower applied stress, the change of deformation rate during the strain dip test of the VN containing materials was very small and could not be detected with the increase of deloaded stress. Consequently this means that the forward or backward motion of almost all dislocations were inhibited by the precipitates. At higher applied stress, the VN containing materials showed the decrease of deformation rate with the slight deloading during strain dip test. This means that there exist movable dislocations which can glide without being blocked by the precipitates. The difference of stress dependence of minimum creep rate between at lower applied stress and at higher one was considered to be caused by such interaction of the fine precipitates with dislocation motion.

Apple, Insecticide DIP Test (Tabm vs. Insecticides), 1993

Abstract A large commercial apple grower reported failure in attempts to control TABM with airblast applications of Penncap M (2 pt/acre) combined with methomyl (3 pt/acre). At the time of the grower applications larval hatch had begun and most larvae were in the first or second instar. By the time larvae were entering the third instar (10 days after spray application) it was apparent that commercially acceptable control had not been achieved. In 1992 this grower also had poor control when Penncap M was applied to suppress redbanded leafroller and experiments showed that tolerance of Penncap M was present in the resident RBLR population (Horsburgh et al. 1992). This laboratory bioassay was begun on 3 Sep to determine tolerance of the TABM population to Penncap M and other insecticides. Seven treatments (including a water control) were selected and rates calculated on the basis of 300 gal of spray being applied per acre. The appropriate dosage of pesticide for each treatment was mixed with 1 gallon of 77°F water in clean 1 gallon battery jars. Twenty plastic petri dishes containing moistened filter paper were prepared and served as individual cages for twenty 3rd instars per treatment. The larvae, on single leaves, were immersed in the appropriate solutions for five seconds and the leaf placed on the moist filter paper. The petri dish cover was put in place and the cages held at room temperature (80°F) for the duration of the test. All larvae were examined at 24 hour intervals and mortality was recorded. Death of larvae was assumed when no movement was observed when the larvae were gently prodded with a blunt steel probe.

Effect of Fine Vanadium Nitride Precipitates on Internal Stress during High-Temperature Creep of 12%Cr-15%Mn Steels

The objective of the present study is to investigate the effects of fine precipitates of vanadium nitride (VN) on the creep deformation behavior of 12%Cr-15%Mn austenitic steels through the measurement of internal stress and effective stress. These stresses are obtained by strain dip test. The internal stress of VN free materials was unequivocally determined as a function of applied stress. On the other hand, the change of deformation rate during the strain dip test of the VN containing materials was very small and could not be detected in a range of reduced applied stress. Consequently, the internal stress and effective stress of VN containing material showed a band range of values as a function of applied stress. This range indicates that fine and dense precipitates of VN become strong barriers to the dislocation motion in a wide variation of stresses worked on the dislocations. The temperature dependence of internal and effective stresses of the VN containing material was also clarified. The difference between the stress dependence of minimum creep rate at the lower applied stress and that at the higher one was also discussed to be caused by the behavior of internal and effective stresses

An estimate of internal stress evolution in the primary creep based on the composite model of dislocation structure

Abstract The paper gives an estimate of the average internal stress which can be measured by the strain transient dip test technique in the heterogeneous dislocation structure consisting of cells or subgrains bounded by low-angle subboundaries. The structure is described by the two-component model of hard and soft regions and the process of creep is considered an iso-strain rate deformation process. An evolution of the internal stress is derived from the evolution of dislocation structure characteristics in the normal primary creep and is evaluated for alpha iron from experimental data which were published earlier by the present author ( Philos. Mag., 25 (1972) 865; 28 (1973) 891, 1099). As an illustration of local conditions, local stresses and local strain rates are evaluated. The results document a growth of the mean internal stress in creep and changes of local stresses in the hard and the soft region. The internal stress values are relatively low and do not approach the value found experimentally in the steady-state creep which reaches the value of long-range internal stress in the soft region. A suggested interpretation of this discrepancy is based on an assumption that the actual steady-state creep has not yet been reached in the region of constant creep rate.

Constant structure creep in metals after stress reduction in steady state stage

Constant structure creep in several metals and alloys was investigated in structures corresponding to the steady state creep conditions. Results were interpreted by means of the back stress concept. In accord with postulates of the strain transient dip test technique, the residual effective stress is considered the controlling stress for dislocation glide. The suggested interpretation of constant structure creep data allows to obtain some information about parameters of the dislocation kinetics in the steady state creep. From the interpretation, a pronounced applied stress dependence of the mobile dislocation density as well as a specific relation between the activation area and the effective stress in steady state creep under various creep conditions result.

Apple, Pesticide Dip Test #1, 1992

Abstract Four pesticides, carbaryl (Sevin XLR 3.75 ml per liter [3 pt/100 gal]); methyl parathion (Penncap M 7.5 ml/liter [1 pt/100 gal]); chlorpyrifos (Lorsban 50W 4.78 g/liter [3.99 lb/100 gal]); azinphosmethyl [Guthion 35W 4.78 g/liter] + methomyl (Lannate 7.5 ml/ liter [3.89 lb + 3 pt/100 gal respectively]), and a water control were evaluated (6X concentration) where X = 50 gal/acre in this experiment. RBLR larvae of various sizes and ages were collected in their leaf spin-ups from a commercial orchard where populations were sampled in our 1991 studies. Foliage used in the experiment was collected from unsprayed apple trees at the experiment station in Winchester. Solutions of each treatment pesticide were prepared in 1 gal jars. Twigs bearing more than 40 leaves (for each treatment) were dipped in the appropriate solution for 15 s and air dried in a fume hood. Twenty cages (1 larva per cage) per replicate were prepared as follows: two 9 dram plastic bottles made up the basic cage unit, one filled with water served as the basal unit. Two plastic vial covers with a small (.64 cm) hole centered in each were stapled together and put in place on top of the base vial. Two apple leaves (previously dipped and dried) were placed so as one leaf lay in close proximity to the other with the petioles extending through the container caps into water in the basal container. The point where the petioles passed through the cap was tightly closed with absorbent cotton to prevent larval escape. One field collected larva was gently removed from its spin-up with a camel’s hair brush and placed between the two leaves in each cage. Finally, the second ventilated plastic vial (which had a 3/4-in hole cut in the bottom that was covered with glued-in-place 100 mesh nylon screening) was inverted over the basal vial and snapped into place in the uppermost of the two previously prepared plastic covers. All cages were held in a room under normal light at 80°F (144°C). Larvae were examined after 24, 48, 72, 96, 120, 144 h for mortality. Death was determined if the larva exhibited no movement after being probed gently.

The viscoplastic behavior of hastelloy-X single crystal

A viscoplastic constitutive model for simulating the behavior of Hastelloy-X single crystal material was derived based on crystallographic slip theory. To determine the appropriate constitutive model constants and to test the predictions of the model, tests on Hastelloy-X crystals were carried out, including the rate sensitivity, cyclic hardening, nonproportional hardening, relaxation, and strain rate dip tests. It was found necessary to include cube slip in the model in order to correlate the uniaxial behavior of the single crystal, to incorporate the interaction effects in both the hardening and the dynamic recovery evolution equations for the drag stress, and to successfully capture correct strain rate sensitivity under biaxial tension-torsion loading conditions.

Internal stress and unloading experiments in creep

Internal stresses are developed during deformation and have an important role in determining the mechanical properties and, in particular, the creep properties of crystalline materials. The strain transient dip test is the generally accepted method for the determination of internal stresses developed during creep. The strain transient dip test has been analysed using a number of very general creep models and it is concluded that, for glide-controlled creep, the dip test can only be interpreted if the relation between dislocation velocity and the force on the dislocation is linear. When this is the case it measures not an average internal stress but an average back stress for all the dislocations, mobile and immobile, where the back stress is the resolved component of the internal stress plus the glide component of the line tension force divided by the Burgers vector. The dip test does not allow separation of the back stress into internal stress and line tension components. For recovery models the results of the dip test cannot be simply interpreted because expressions for the creep rate do not define a unique average internal stress or back stress. However, for the recovery model in which strain occurs by athermal or jerky glide there will be a reverse yield stress, i.e. there will be a stress reduction below which there will be “instantaneous” reverse strain followed by reverse creep. By averaging the instability condition for all the dislocations participating in jerky glide it is shown, subject to assumptions, that the sum of the average internal stress experienced by dislocations involved in both forward and reverse creep can be obtained from the reverse yield stress. Separate values for these internal stresses cannot be obtained, however. Determination of the reverse yield stress for recovery creep is the experiment equivalent to the strain transient dip test for glide-controlled creep.

Internal and effective stresses in high-temperature creep evaluated from transient dip tests and dislocation bowing

Because creep of metals and alloys is modelled on the basis of microstructural observations, it has been shown that there is a difference between the mathematical treatment of high-temperature deformation and the real material behaviour. One idea to consider is to split the applied stress into a part depending on the substructure (the internal stress which has to be reached to start dislocation motion) and a part describing the resistance to the glide motion of dislocations (the effective stress). For ferritic chromium steel these quantities have been measured by means of the stress transient dip test technique. This leads to mean values of internal and effective stresses for the whole specimen. Additionally, local stresses acting on individual dislocations are evaluated from dislocation bowing for a wide range of applied stresses. The results show that the ratio of internal to applied stress decreases with increasing applied stresses, which, on the other hand, causes a large increase of effective stresses. Dislocation bowing stresses show a similar dependence. Compared to the results of dip tests, the determination of local stresses leads to less accurate results and to a large deviation of results within small regions of one specimen. Therefore, it is only valuable for comparison purposes.

Effect of precipitate type and morphology on high-temperature creep and internal stress in Al-Li based alloys

The tensile creep of a series of aluminium-lithium-based alloys, two binary alloys containing δ′ precipitate, and the 2090 alloy containing δ′ and T1 precipitate, has been studied over a range of stresses at 150°C. In some cases the internal stress developed during creep has been determined using the strain transient dip test. The results have been compared with similar data previously obtained for the 8090 alloy containing δ′ and S precipitates. The solid solution alloy and the binary alloy containing shearable δ′ particles exhibited normal Class II behaviour, with the development of sub-grains and a stress dependence of the creep rate given by a single stress exponent,n, between 4 and 5 at all applied stresses. The alloys containing particles not easily sheared by dislocations, coarse δ′, S and T1, exhibited similar stress dependencies of the creep rate at low stresses but exhibited large values ofn, between 18 and 35 at high stresses. The internal stress, σi, in these alloys was found to be approximately constant at high stresses possibly due to partial shearing of the coarse δ′, T1, and the S on sub-boundaries. The stress dependence of the minimum creep rate, $$\dot \varepsilon $$ , could be represented at all applied stresses, σa, by $$\dot \varepsilon \propto (\sigma _a - \sigma _\iota )^n $$ , where (σa−σi) is the effective stress driving dislocations during creep, andn is a single stress exponent of between 5 and 6 for all applied stresses. The internal stress, which increases with applied stress, at least at a low applied stress, arises from inhomogeneity of plastic deformation, due to hard sub-boundaries or hard particles which are Orowan looped. These two types of contribution to the internal stress are of similar magnitude in the alloys containing coarse δ′ and T1 but the majority of the internal stress in the 8090 alloy may arise as a result of the hardening of sub-boundaries by the S precipitate.

High-temperature creep of the particlehardened commercial Al-Li-Cu-Mg alloy 8090

Creep of the particle-hardened commercial Al-Li 8090 alloy has been studied at temperatures of 425 and 445 K. The measured stress sensitivity of the minimum creep rates changes abruptly at a given applied stress with stress exponents being around 4–6 at low stresses and 30–40 at high stresses. Creep activation enthalpies were determined by both temperature cycling and by comparing creep rates at two temperatures at a given applied stress, the results from both gave the same unrealistically high values. The internal stresses, σi, developed during creep were determined using the strain-transient dip test. These increased linearly with the applied stress, σa, at low stresses and were effectively constant at high stresses. The minimum creep rate was found to be a simple function of the effective stress, σa-σi, with a stress exponent of between 5 and 6, at all applied stresses. The dislocation and precipitate structure of the alloy was examined before and after creep using thin-film electron microscopy. The initial structure consisted of pancake grains with a well-developed {1 1 0}〈1 1 2〉 type texture. The grains contained well-developed sub-cells and δ′ and S precipitates. The structure developed during creep consisted of dislocation pairs, single dislocations and dislocations loops. There was evidence to suggest that slip took place on both {1 0 0} and {1 1 1} planes. The dislocation loops were most likely to have been Orowan in character and around the rodlike S precipitate, with the coherent δ′ precipitate being sheared by pairs of dislocations. The measured internal stresses result from inhomogeneity of plastic deformation. These stresses increase continuously with applied stress up to the observed macroscopic yield stress, and then become constant. The internal stresses are likely to have arisen from the Orowan loops around S and the behaviour of sub-grain boundaries. The increases in internal stress may have resulted from an increased loop density with increasing applied stress. This rate of increase is likely to slow down if S particles are sheared or fractured at high applied stresses.

On the relation between dislocation structure and internal stress measured in pure metals and single phase alloys in high temperature creep

A survey of experimental studies of a relation between dislocation structure and internal stress σ i measured by means of the strain transient dip test technique in high temperature (mostly steady-state) creep of various metals and single phase alloys is given. Application of various approaches, i.e. direct evaluation of σ i from quantitative structure data, correlation of σ i and parameter of dislocation strengthening Gb √ ϱ ( G is the shear modulus, b Burgers vector length and ϱ dislocation density), stochastic model of σ i in a three-dimensional dislocation network, reveals the problem of strengthening by a homogeneously distributed dislocation density from several points of view. Attention is paid to the strengthening effect of polygonized substructure. Discussion of the presented results leads to conclusions about various sources of internal stress in the dislocation structure and substructure formed in creep and about the influence of temperature on dislocation structure in relation to the temperature dependent measured internal stress.

Pore formation in PM iron-based ferritic oxide dispersion strengthened (ODS) superalloys during high temperature heat treatment: D. Sporer et al, (Metallwerk Plansee, Reutte, Austria), Powder Metall. Int., Vol 23, No 2, 1991, 162–165

The creep properties of oxide dispersion strengthened (ODS) steels, DT and DY alloys, were investigated in the temperature range 500–700°C. The evaluation of the creep threshold stress was performed by creep dip tests. The Norton's creep law, corrected with this experimental threshold stress, gives a good description of the creep behaviour of DT and DY alloys. Transmission electron microscopy (TEM) observations showed the dislocations to be pinned to the small oxide particles based on thermally activated dislocation detachment from oxide particles. The results are discussed in the light of Arzt's model.