TRIP effect in austenitic–martensitic VNS9-Sh steel at various strain rates

The mechanical properties of austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) steel are studied at a static strain rate from 4.1 × 10^–5 to 17 × 10^–3 s^–1 (0.05–20 mm/min). It is found that, as the strain rate increases, the ultimate tensile strength decreases and the physical yield strength remains unchanged (≈1400 MPa). As the strain rate increases, the yield plateau remains almost unchanged and the relative elongation decreases continuously. Because of high microplastic deformation, the conventional yield strength is lower than the physical yield strength over the entire strain rate range under study. The influence of the TRIP effect on the changes in the mechanical properties of VNS9-Sh steel at various strain rates is discussed.     

Responses of single arterioles in vivo in cat skeletal muscle to change in arterial pressure applied at different rates

The concept of a rate-dependent, dynamic as well as a static component in the myogenic control has been suggested in some previous in vitro and whole organ investigations. The present study is an attempt to reveal a dynamic component in the myogenic response directly on single arterioles by a vital microscopic technique. The study was made on the autonomically blocked vascular bed of cat tenuissimus muscle and performed by analysing the arteriolar diameter changes to an arterial pressure increase and decrease when applied at two different rates. The results demonstrate a transient, dynamic constrictor response upon the phasic increase in pressure and a transient, dynamic dilator response upon the phasic decrease in pressure, the magnitudes of which being related to the rate of the pressure change. The static response developing during the steady-state phase of constant increased pressure was also shown. The dynamic responses were confined to arterioles smaller than about 20 micrometers while the steady-state response was present in larger arterioles as well. Even if the metabolic control system partly could be responsible for the obtained responses, arguments are given that the described reactions are mainly myogenic in nature.     

Plastic deformation of delta-ferritic iron at intermediate strain rates

The plastic deformation of delta-ferritic iron, represented by an electrolytic iron and Fe-0.028 C, Fe-0.044 C and Fe-3.0 Si alloys, has been measured for the temperature range 1200 to 1525‡C and the strain rate range 2.8 x 10^-5 to 2.3 x 10^-2 s^-1. For the bamboo-like tension specimens the plastic flow behavior is approximately nonlinear viscous. Delta-ferrite is more than four times weaker than austenite, and does not exhibit dynamic recrystallization. At the melting point of iron the extrapolated steady-state flow stress increases from 0.31 to 1.86 MN/m² (45 to 370 psi) over the range of strain rate examined.     

Tensile failure of austenitic iron at intermediate strain rates

The basic failure behavior of austenitic iron has been established for the temperature range 950 to 1350°C and the strain-rate range 2.8 x 10^-5 to 2.3 x 1(10^-2 s^-1. Failure in zone-refined iron is determined solely by plastic deformation, leading first to multiple necking, continuing by the exclusive growth of a single neck, and concluding by separation at a point within that neck. With the increasing impurity content of electrolytic iron, Fe-0.05 C and Fe-5.2 Mn, this failure process is interrupted at the lower temperatures by fracture at either second-phase particles or grain boundaries. The regimes of these two fracture modes have been determined as functions of strain rate, deformation temperature, and annealing temperature. Recrystallization is prevalent during the plastic deformation of austenitic iron and influences the necking process to some extent. Recrystallization is more influential as a means of stabilizing arrays of intergranular cracks, thereby allowing the cracks to undergo appreciable plastic deformation during the final stage of failure. The concept of failure diagrams is introduced as a simple means of representing the complex interposition of plastic instability, recrystallization, and fracture during the failure process.     

Plastic deformation of austenitic iron at intermediate strain rates

The plastic deformation of austenitic iron, represented by a zone-refined iron, an electrolytic iron, an Fe−0.05 C alloy, and an Fe−5.2 Mn alloy, has been documented for the temperature range 950 to 1350°C (1740 to 2460°F) and the strain-rate range 2.8 × 10⁻⁵ to 2.3 × 10⁻² s⁻¹. The intrusion of recrystallization during deformation restricts the documentation to initial periods of strain usually less than 0.10. The general problem of retaining grain structures representative of polycrystals in specimens annealed at temperatures above 0.95T _m is recognized, and a basis for its solution is presented. Chemical composion appears to influence the plastic-flow behavior of austenitic iron primarily through its effect on the grain structure. Thus, the large-grained zone-refined iron is relatively weak, and the difference in behavior between the Fe−0.05 C alloy and the Fe−5.2 Mn alloy is small. Formerly Associate Scientist, U.S. Steel Corporation.     

Plastic deformation of austenitic iron at intermediate strain rates

The plastic deformation of austenitic iron, represented by a zone-refined iron, an electrolytic iron, an Fe-0.05C alloy, and an Fe-5.2 Mn alloy, has been documented for the temperature range 950 to 1350°C (1740 to 2460°F) and the strain-rate range 2.8 x 10^-5 to 2.3 x 10^-2 s^-1. The intrusion of recrystallization during deformation restricts the documentation to initial periods of strain usually less than 0.10. The general problem of retaining grain structures representative of polycrystals in specimens annealed at temperatures above 0.95T _mis recognized, and a basis for its solution is presented. Chemical composion appears to influence the plastic-flow behavior of austenitic iron primarily through its effect on the grain structure. Thus, the large-grained zone-refined iron is relatively weak, and the difference in behavior between the Fe-0.05 C alloy and the Fe-5.2 Mn alloy is small. M. F. HOLMES, formerly Associate Scientist, U.S. Steel Corporation.     

Plastic deformation of delta-ferritic iron at intermediate strain rates

The plastic deformation of delta-ferritic iron, represented by an electrolytic iron and Fe-0.028 C, Fe-0.044 C and Fe-3.0 Si alloys, has been measured for the temperature range 1200 to 1525‡C and the strain rate range 2.8 x 10^-5 to 2.3 x 10^-2 s^-1. For the bamboo-like tension specimens the plastic flow behavior is approximately nonlinear viscous. Delta-ferrite is more than four times weaker than austenite, and does not exhibit dynamic recrystallization. At the melting point of iron the extrapolated steady-state flow stress increases from 0.31 to 1.86 MN/m² (45 to 370 psi) over the range of strain rate examined.      

Tensile failure of austenitic iron at intermediate strain rates

The basic failure behavior of austenitic iron has been established for the temperature range 950 to 1350°C and the strain-rate range 2.8 x 10^-5 to 2.3 x 1(10^-2 s^-1. Failure in zone-refined iron is determined solely by plastic deformation, leading first to multiple necking, continuing by the exclusive growth of a single neck, and concluding by separation at a point within that neck. With the increasing impurity content of electrolytic iron, Fe-0.05 C and Fe-5.2 Mn, this failure process is interrupted at the lower temperatures by fracture at either second-phase particles or grain boundaries. The regimes of these two fracture modes have been determined as functions of strain rate, deformation temperature, and annealing temperature. Recrystallization is prevalent during the plastic deformation of austenitic iron and influences the necking process to some extent. Recrystallization is more influential as a means of stabilizing arrays of intergranular cracks, thereby allowing the cracks to undergo appreciable plastic deformation during the final stage of failure. The concept of failure diagrams is introduced as a simple means of representing the complex interposition of plastic instability, recrystallization, and fracture during the failure process.     

Microstructures of aluminum compressed at various rates and temperatures

Specimens of 1100 aluminum were compressed uniformly to a logarithmic strain of 0.7 (50 pct reduction) at constant true strain rates in a Cam Plastometer. Tests were conducted at strain rates between 220 and 0.1 sec^?1 and between 500°C and 20°C. Exmination of the microstructures by electron microscopy indicated that the deformed structure consisted of dislocation cells or subgrains. As the temperature of testing was raised or the strain rate lowered, the resulting subgrains were larger, and the dislocations in the subboundaries were arranged in more orderly arrays. The cell sizes are related quantitatively to the flow parameters. The dependence of dynamic recovery on temperature and strain rate is compared to the dependence observed in extrusion of a similar alloy. At high strain rates at 400° and 500°C, partial recrystallization occurred while the specimens were cooling to room temperature.     

Phosphorylation of myosin regulatory light chain eliminates force-dependent changes in relaxation rates in skeletal muscle

The rate of relaxation from steady-state force in rabbit psoas fiber bundles was examined before and after phosphorylation of myosin regulatory light chain (RLC). Relaxation was initiated using diazo-2, a photolabile Ca2+ chelator that has low Ca2+ binding affinity (K(Ca) = 4.5 x 10(5) M(-1)) before photolysis and high affinity (K(Ca) = 1.3 x 10(7) M(-1)) after photolysis. Before phosphorylating RLC, the half-times for relaxation initiated from 0.27 +/- 0.02, 0.51 +/- 0.03, and 0.61 +/- 0.03 Po were 90 +/- 6, 140 +/- 6, and 182 +/- 9 ms, respectively. After phosphorylation of RLC, the half-times for relaxation from 0.36 +/- 0.03 Po, 0.59 +/- 0.03 Po, and 0.65 +/- 0.02 Po were 197 +/- 35 ms, 184 +/- 35 ms, and 179 +/- 22 ms. This slowing of relaxation rates from steady-state forces less than 0.50 Po was also observed when bundles of fibers were bathed with N-ethylmaleimide-modified myosin S-1, a strongly binding cross-bridge derivative of S1. These results suggest that phosphorylation of RLC slows relaxation, most likely by slowing the apparent rate of transition of cross-bridges from strongly bound (force-generating) to weakly bound (non-force-generating) states, and reduces or eliminates Ca2+ and cross-bridge activation-dependent changes in relaxation rates.     

The deformation of silicon at high temperatures and strain rates

Polycrystalline and 〈100〉 single crystalline semiconductor grade silicon samples have been subjected to uniaxial compression at strain rates from 10⁻⁵ to 12 s⁻¹ at temperatures ranging from 1100 to 1380 °C. Both intrinsic and p-type polycrystalline material and p-type single crystalline material were tested. Except at the highest temperature and lowest strain rate, no steady state deformation was observed for the polycrystalline material. In all other cases strain hardening was observed which increased with increasing strain rates. The polycrystalline material could be compressed by as much as 50 pct at 1380 °C and a strain rate of 7 s⁻¹ without cracking. An axial stress of approximately 170 MPa produces a strain rate of 5 s⁻¹ at 1380 °C. The stress necessary to produce a given strain rate increases rapidly with decreasing temperature while the ductility rapidly decreases. A preliminary forming limit diagram has also been determined for the polycrystalline material at 1380 °C. The deformation rate-controlling process in the polycrystalline material at high stresses could be the production of vacancies on jogged dislocations. Formerly with the Department of Materials Science and Engineering, University of Pennsylvania     

Compression of semi-solid dendritic Sn-Pb alloys at low strain rates

The behavior of semi-solid dendritic Sn-Pb alloys was studied at one degree above the eutectic. Small cylindrical samples were deformed at an initial strain rate of 1.3 x 10⁻² s⁻¹ in a parallel-plate apparatus. The friction between the sample and the plates was found to affect strongly both the strength of the material in compression and the resultant liquid-solid segregation. For low friction a maximum stress occurred at strains of about 0.3. Above this strain large cracks were observed. High friction resulted in a much higher degree of segregation than observed for low friction. No maximum stress and no cracking was observed, even for strains as large as 1.2 for high friction. Cylindrical samples were extruded through cylindrical dies at constant piston velocities ranging from 8.5 x 10≓5 ms~’ to 8.5 X 10≓4 ms≓1, and with reduction of area ranging from 2:1 to 8:1. The deformation occurred in two distinct modes. First, a “compaction≓ mode, during which liquid was expelled and the solid compacted but did not flow through the die, under increasing stress. Second, a “flow≓ mode, during which compacted solid flowed through the die, under a constant stress, σ_rextr, which was found to be proportional to the natural logarithm of the area reduction. Experiments involving compression over a filter and compression between parallel plates of alloys of different compositions were performed to examine the effects of the fraction liquid on the rheology of semi-solid dendritic alloys. The stress required for deformation was seen to exhibit the same pseudo-plastic strain-rate dependence for parallel plate, piston-filter and in forward extrusion experiments. This strain-rate dependence can be summarized by the power-law expression: σ ∝ ɛ^0.23. D. A. Pinsky, formerly with the Massachusetts Institute of Technology Department of Science and Engineering P. O. Charreyron, formerly Visiting Scientist at Massachusetts Institute of Technology     

gamma-AChR/epsilon-AChR switch at agrin-induced postsynaptic-like apparatus in skeletal muscle

We transfected the extrajunctional region of denervated soleus muscles in adult rats with neural agrin cDNA to induce myofibers to form postsynaptic-like apparatus containing acetylcholine receptor (AChR) aggregates. By 1 week approximately 30% of the AChR aggregates contained a mixture of epsilon-AChRs and gamma-AChRs while approximately 70% had only gamma-AChRs. If the transfected muscles were reinnervated in the original junctional region, the postsynaptic-like apparatus, despite the absence of apposed axon terminals, gradually came to have only epsilon-AChRs. We conclude that at the postsynaptic apparatus of ectopic neuromuscular junctions formed by a foreign nerve implanted into the extra-junctional region of denervated muscles, agrin secreted by the axon terminal plays a direct role in the gamma-AChR/epsilon-AChR switch that occurs as the apparatus reaches maturity. Our findings, together with results from other studies, indicate further that agrin and acetylcholine are the only nerve-derived factors required for this switch.     

Increased effects of machining damage in beryllium observed at high strain rates

Metallurgical and Materials Transactions A -     

Prediction of steel flow stresses at high temperatures and strain rates

The flow behavior of steels during deformation in the roll gap was simulated by means of single hit compression tests performed in the temperature range 800 °C to 1200 °C. Strain rates of 0.2 to 50 s⁻¹ were employed on selected low-carbon steels containing various combinations of niobium, boron, and copper. The stress/strain curves determined at the higher strain rates were corrected for deformation heating so that constitutive equations pertaining to idealized isothermal conditions could be formulated. When dynamic recovery is the only softening mechanism, these involve a rate equation, consisting of a hyperbolic sine law, and an evolution equation with one internal variable, the latter being the dislocation density. When dynamic recrystallization takes place, the incorporation of the fractional softening by dynamic recrystallization in the evolution equation makes it possible to predict the flow stress after the peak. These expressions can be employed in computer models for on-line gage control during hot-rolling.     

Cardiac output during cardiopulmonary resuscitation at various compression rates and durations

Cardiac output during cardiopulmonary resuscitation (CPR) was measured by a modified indicator-dilution technique in 20 anesthetized dogs (6-12 kg), during repeated 1- to 2-min episodes of electrically induced ventricular fibrillation, by a mechanical chest compressor and ventilator. With compression rates from 20 to 140/min and compression durations (duty cycles) from 10 to 90% of cycle time, cardiac output (CO) was predicted by the equation: CO = CR . SVmax . [DC/(k1 . CR + DC)] . [(1 -- DC)/k2 . CR + 1 - DC)], where CR is compression rate, DC is duty cycle, SVmax (19 ml) is the effective capacity of the pumping chamber, and k1 (0.00207 min) and k2 (0.00707 min) are ejection and filling constants. This expression predicts maximal CO for DC = 0.40 and cR = 126/min and 90-100% of maximal CO for 0.3 less than DC less than 0.5 and 70 less than CR less than 150/min. Such mathematical analysis may prove useful in the optimization of CPR.     

Neuregulins and erbB receptors at neuromuscular junctions and at agrin-induced postsynaptic-like apparatus in skeletal muscle

This study has characterized the repertoire of the anion exchanger (AE) family members expressed within the guinea pig organ of Corti, the auditory neuroepithelia. Both AE2 and AE3 cDNAs were present, but AE1 cDNA was not detected. The more abundant AE2 was sequenced and its expression characterized in the cochlea. The 3888 base pairs (bp) AE2 sequence, compiled from multiple clones, includes 150 bp of upstream non-coding sequence and 3717 bp of open reading frame encoding a protein of 1238 amino acids. Immunoblot of cochlear homogenate revealed a single AE2-immunoreactive band of Mr 180 kDa. In situ hybridization and immunohistochemical analysis localized AE2 expression to several tissues and cell types within the guinea pig inner ear, including superior half of the spiral ligament and within the interdental cells lining the spiral limbus. However, AE2 was not clearly detected in the outer hair cells (OHC) of the organ of Corti by either immunohistochemistry or in situ hybridization. The results of these studies imply a physiologic role of AE2 in the cochlear homeostasis, but do not support its role as a potential 'motor protein' in mediating the in vitro-observed voltage-gated, ATP-independent OHC motility.