Rheological Characterization of Systems with Plastic Flow Behavior

Model suspensions with plastic flow behavior were investigated rheologically.Shear stress and first normal stress difference were measured simultaneously with shear flow start-up experiments.After the shear deformation is stopped,the stress relaxation begins,residual shear stress can appear.The relative residual shear stressτRR is the ratio of the residual shear stress to the steady state shear stress.The relative residual shear stress is considered as a measure of the structure of the system.In the case ofτRR=0.98,we assume that an elastic to plastic deformation is occurred,which is the yield point.The system with 7.5%Aerosil 380 has achieved withτRR=0.95 in the first approximation the transition to plastic flow,this is the yield point for the system,with a yield stress of 23 Pa.This is the only one known system with yield point.The systems withτRR>0.30 andτRR<0.95 at the first point,have no transition from elastic to plastic flow,but the structure is strongly destroyed.Analogous to the above,the shear stress at this point will be called yield stress.One requirement is that the start-up experiment is determined with a very low shear rate¾0.00071/s or 0.000961/s.The associated normal stress to the yield stress is called normal yield stress.The dependence of the normal stress of the systems with Aerosil 380 on the shear stress reached,after a short increase/decrease in the values,the straight line of the normal stress/shear stress of the liquid phase M20000.A linear relationship between normal stress and shear stress was found in the systems with Bentone 27 in Araldite GY260.With a certain measured normal stress/shear stress point,you can draw a straight line with 45°in the double logarithmic plot¾a way to receive the normal stress/shear stress points.

Low cycle fatigue estimation of low yield point steel

With the development of technology for earthquake resistant,the research of the low yield point(LYP) steel which used for the fabrication of energy dissipation damper were paid more and more attention.The common studies of the low yield point steel is mainly about the performance with constant amplitude and constant frequency.The low cycle fatigue properties of low yield piont steel were studied by series of test with continuous varying amplitude and varying frequency with the materials testing system by us.The test results showed that low yield point steel of Baosteel have excellent low cycle fatigue properties,which meet the requirement for steel used for the fabrication of energy dissipation damper completely.The low cycle fatigue performance of low yield point steel of Baosteel mainly depended on the amplitude in test.And the effect of varying frequency for the low yield point steel was more less than varying amplitude.

Crop Yield Forecasted Model Based on Time Series Techniques

Traditional studies on potential yield mainly referred to attainable yield： the maximum yield which could be reached by a crop in a given environment. The new concept of crop yield under average climate conditions was defined in this paper, which was affected by advancement of science and technology. Based on the new concept of crop yield, the time series techniques relying on past yield data was employed to set up a forecasting model. The model was tested by using average grain yields of Liaoning Province in China from 1949 to 2005. The testing combined dynamic n-choosing and micro tendency rectification, and an average forecasting error was 1.24%. In the trend line of yield change, and then a yield turning point might occur, in which case the inflexion model was used to solve the problem of yield turn point.

Grain-size effect on dislocation source-limited hardening and ductilization in bulk pure Ni

Dislocation source-limited hardening and ductilization is an effective strategy to obtain superior strength-ductility synergy in some engineering structural metals. Recent works demonstrated that the synergy could be enhanced by grain-size reduction. However, the mechanism of grain-size dependence is still a mystery. In this work, bulk pure Ni produced by electrodeposition and subsequent annealing, with grain sizes ranging from ∼20 nm to ∼20 µm, were methodically investigated to unravel the mechanism of the grain-size effect on dislocation source-limited hardening and ductilization. The high-density nano-twinning in the as-electrodeposited nanograined specimens exhibited better thermodynamic stability than the peers with random high-angle grain boundaries, leading to fine recrystallized grains with low-density dislocations. The low dislocation density enabled extra hardening beyond grain boundary strengthening via yield-point behavior with grain sizes ranging from ∼110 nm to ∼10 µm and extra ductilization over ∼500 nm. This work demonstrated that the prerequisite for dislocation source-limited hardening was that the dislocation density of the specimen should be lower than the size-dependent critical value of ((1.1 × 107 /d ) m^(–2), d is the grain size in unit of the meter) where a transition from forest-dominated hardening to dislocation source-limited hardening could occur. On the other hand, dislocation source-limited ductilization only worked when the grain size was comparable to/larger than the theoretical dislocation mean slip distance. Dislocation source-limited ductilization resulted from more room in grains for accumulation of dislocations and deformation nano-stacking faults enabling the higher work hardening rate. This work offered an altogether new avenue to obtain stronger and more ductile metallic materials through utilizing grain-size dependent dislocation source-limited hardening and ductilization.

Ultra-Fine Heterogeneous Microstructure Enables High Strength-Ductility in a Cold-Rolled Medium Mn Steel

The objective of the present study is to develop heterogeneous microstructure in cold-rolled medium Mn steels(MMSs)annealing strategy.The cold-rolled Fe-4.7Mn-0.15C(wt%)steel is annealed twice at different temperatures to produce an ultra-fine heterogeneous microstructure with lath-shaped and granular-shaped retained austenite.Excellent mechanical behavior of significant strength enhancement with negligible ductility loss can be achieved.The high strength-ductility properties are attributed to the active transformation induced plasticity effect over a broad strain range owing to dispersive mechanical stabilities of the heterogeneous austenite.Furthermore,the typical yield point elongation phenomenon which is commonly observed in cold-rolled MMSs can be effectively reduced by this microstructural strategy.

Properties and Metallurgical Aspects of Heavy Wall Q&T Line Pipe Steels

The production of Q&T line pipe steels for heavy wall pipe requires several properties to be fully matched.Among them is the yield strength for strain based criteria pipelines for subsea application.Yield strength must match the required minimum under elevated temperature conditions [60 & 160 ℃] and at the same time do not exceed the surface hardness that will make the welding inadequate.Maximum of 220 vickers hardness has been set for some of the subsea projects.Production in a busy Q&T line requires simple tools to predict the time and temperatures to achieve the desired properties.The classical strength and logarithm of time,after Bhadeshia [1],has been used with excellent results in these line pipe steels of different wall thickness.

Microstructure and Tensile Properties of a Nb–Mo Microalloyed 6.5Mn Alloy Processed by Intercritical Annealing and Quenching and Partitioning

The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P）,respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q ＆ P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity（TRIP） effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation（YPE） of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.