Thixotropic Strength Research Articles

Deformation Behavior of Aluminum Alloy during Semi-Solid Compression

By semi-solid aluminum alloy compression test, deformation mechanism of semi-solid aluminum alloy was investigated, the thixotropic strength existing in semi-solid aluminum alloy was verified and the influences of temperature and strain rate on the deformation mechanism and thixotropic strength were discussed. The results show that there are 4 stages in the process of compression deformation for semi-solid aluminum alloy: stress swift growth stage, stress drop stage, steady stress stage and stress gradual growth stage. The semi-solid billet has a thixotropic strength, which is sensitive to temperature and strain rate. The higher the temperature or the higher the strain rate is, the smaller the thixotropic strength of the semi-solid alloy.

Thixotropic properties of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena. With the increase of mass ratio ( R) of HTlc to CS, the equilibrium viscosity ( η eq ) and the consistency coefficient ( m) values of the suspensions increase in the range of neutral and alkaline pH (higher than 6.5) while decrease in the range of acid pH (lower than 6.5). With the increase of pH value, the η eq and m values of the suspensions in the R range of 0–0.08 studied increase initially and then decrease, appearing a maximum value at about pH 7.41 ± 0.25 . The CS/HTlc suspensions display viscid character and the yield point of the suspensions was not observed except the suspension with R = 0.08 in the pH range of 7.66–9.70, which showed a yield point and viscoelasticity. The CS/HTlc suspensions may display different thixotropic types: negative, complex or positive thixotropy, depending on pH and R value. The thixotropic type of the CS/HTlc suspension may be transformed from negative (pure CS solution), through complex ( R = 0.02 ), into positive thixotropy ( R = 0.05 and 0.08) with the increase of R in the studied R range of 0–0.08, and the thixotropic strength of the suspensions increases initially and then decreases with pH value in the pH range studied. The mechanism of the thixotropic phenomenon is discussed.

Mechanical behavior and microstructure during compression of semi-solid ZK60-RE magnesium alloy at high solid content

Mechanical behavior during compression of semi-solid ZK60-RE magnesium alloy at high solid content is researched in this paper. The alloy was prepared from ZK60 alloy and rare earth elements by casting, equal channel angular extruding, and liquidus forging. Semi-solid isothermal pre-treatment was carried out to make the grains globular before the compression. Here, several groups of true strain–true stress curves with different variables during compression are given to make comparisons of their mechanical behaviors. Liquid paths were the most essential to deformation, and its variation during compression depends on the strain rate. Here, thixotropic strength is defined as the true stress at the first peak in the true stress–true strain curve.

Influence of Shear Rate on Thixotropic Suspensions

The thixotropic type of a suspension can be specified by first shearing the suspension at high shear rate to destroy the structure of the suspension, then monitoring the change of the viscosity or stress with time under low shear (D l), i.e., to study the process of structure recovery. The shear history and D l can influence the recovery process, so they have an influence on the thixotropic type of a suspension. In this paper, the influence of D l on the thixotropy of Fe–Al–Mg‐mixed metal hydroxide (MMH for short)/Na‐montmorillonite (MT for short) suspensions is reported. The system with a weight ratio (R) of MMH/MT of 0 and with R = 0.013 both show positive thixotropy in the D 1 range of 10–1022 s−1, i.e., D l does not change the thixotropic type of the suspensions. The suspension with R = 0.051 shows complex thixotropy under lower D l values (10 and 170 s−1), but shows positive thixotropy under higher D l values (511 and 1022 s−1). The system with R = 0.091 shows negative thixotropy at lower D l values (10 and 170 s−1), but shows complex thixotropy at higher D l values (511 and 1022 s−1). With increasing D l, the viscosity of these suspensions decreases gradually, and the degree of change in η ∼ t slows down, i.e., the thixotropic strength becomes weak. The mechanism for these changes is discussed.

Effect of Aging and Stress History on the Undrained Strength of Ultra-Weak Cohesive Soils

This work is concerned with the mechanical properties of freshly-deposited cohesive sediments. It was previously established by the authors that the undrained shear strength in the ultra-low stress range is effective stress dependent and increases with bed age. This paper consists of an experimental program to quantify the strength gain with time, and to study the effect of stress history on the strength of the sediment bed. The experimental program was conducted on fully consolidated Boston Blue Clay beds of various ages, 3.5 to 11 cm in thickness deposited from concentrated slurries. The bed age varied between 2 and 23 days, and the undrained shear strength measured with the Automated Fall Cone Device varied between 10 and 120 Pa for effective stress values below 400 Pa. For a given water content, the strength exhibited a two-fold increase over the 21 day period attributed to thixotropy. This thixotropic strength gain was mainly a function of the existing effective stress with some dependence on water content. Although no measurable swelling occurred upon unloading (unloaded effective stress up to 190 Pa), the shear strength decreased substantially depending mainly on the magnitude of the unloaded and the remaining effective stresses, but also on the existing water content.

Thixotropic strength measurement of oil sand fine tailings

Les steriles fins des sables bitumineux sont un sous-produit de la production d'huile brute synthetique provenant des operations minieres localisees dans le nord de l'Alberta. Les steriles fins forment une boue a teneur en eau elevee contenant de l'eau, du silt, de l'argile et du bitume, qui consolide lentement. Un des facteurs qui peuvent affecter la consolidation sous leur propre poids des steriles fins est le gain de resistance du materiau. Pour en arriver a un modele comprehensible de consolidation a long terme de steriles fins, les proprietes de resistance du materiau en fonction du temps doivent etre comprises. Des essais d'expansion de cavite ont ete developpes pour mesurer le gain thixotropique de resistance dans les steriles fins de sable bitumineux. Des steriles fins a cinq differentes teneurs en eau ont ete testes pour des intervalles de temps s'etendant de 0 a 450 jours. La resistance thixotropique a augmente avec l'âge des steriles fins selon une fontion du second degre et augmentait toujours a la fin de la periode d'essai de 450 jours. Des augmentations thixotropiques substantielles de la resistance ont ete observees pour des steriles fins ayant des teneurs en eau inferieures a 150%. Lorsque la teneur en eau diminuait de 400 a 150%, le gain thixotropique de resistance etait plus faible par rapport a celui correspondant a une diminution de 150 a 100%. Le rapport de resistance thixotropique atteignait un minimum a une teneur en eau de 150%. La teneur en eau des steriles fins influencait de facon significative le developpement de de la resistance thixotropique. Plus la teneur en eau est faible, plus la resistance thixotropique est elevee. Les resultats obtenus des essais d'expansion de cavite ont ete compares a ceux donnes par les essais au scissometre et au viscosimetre. Le changement de resistance obtenu par les trois procedures d'essai ont suivi des tendance similaires, mais les essais d'expansion de cavite ont donne des resistances substantiellement plus elevees.

Thixotropic strength measurement of oil sand fine tailings

Thixotropic strength measurement of oil sand fine tailings

AGE HARDENING OF AGRICULTURAL TOP SOILS

SummaryChanges in the strength of remoulded agricultural top soil with ageing are studied for two sandy loam soils from South Australia and a clay soil from Queensland. There is evidence of significant thixotropic behaviour in these soils around the water contents at which tillage is usually performed.For the Urrbrae soil, in which the dominant clay minerals are illite and kaolinite. the maximum thixotropic strength ratio was obtained at a water content just below the plastic limit. For the Strathalbyn soil, which contains illite and actinolite. and for the Waco soil which contains montmorillonite. the maximum thixotropic strength ratios occurred at water contents between the plastic and liquid limits.The age hardening for these soils was investigated using probe penetration, tensile strength and compression resistance measurements. The effect was still apparent after sterilization and after removal of organic matter.

Permeability of three compacted tropical soils

Summary This paper presents studies of permeabilities of three soil samples of widely differing properties at various degrees of saturation, various compactive efforts and various thixotropic strength ratios. The soils studied consist of a soft clay shale–attapulgite, a black cotton soil, and a lateritic kaolinitic soil. The results indicate the attapulgite to be the most structure sensitive and the lateritic soil the least structure sensitive. The permeabilities reflect these structural behaviours of the soils. Based on the test results, a practical back pressure is recommended for complete saturation of these compacted soils. The influence of moulding moisture contents on permeabilities are presented and values of thixotropic strength ratios for the three soils are also recommended.

Fundamental Aspects of Thixotropy in Soils

Thixotropic phenomena and previous investigations on behavior of thixotropic systems are summarized; hypothesis for thixotropic behavior based on initial nonequilibrium of interparticle forces after remolding or compaction, and effects of nonequilibrium on subsequent structure changes within soil, is offered as possible explanation of phenomenon; thixotropic strength increases warrant consideration in design. (31 refs.)

Fundamental Aspects of Thixotropy in Soils

Thixotropic phenomena and previous investigations on behavior of thixotropic systems are summarized; hypothesis for thixotropic behavior based on initial nonequilibrium of interparticle forces after remolding or compaction, and effects of nonequilibrium on subsequent structure changes within soil, is offered as possible explanation of phenomenon; thixotropic strength increases warrant consideration in design. (31 refs.)

Thixotropic Characteristics of Compacted Clays

Previous investigations summarized; existence of thixotropic effects in compacted clays and their variation with soil composition; test data illustrating magnitude of thixotropic strength increases with time for compacted clays in normal compression tests and under repeated loading conditions; effects of thixotropy on results of tests conducted.

Thixotropic Characteristics of Compacted Clays

Previous investigations summarized; existence of thixotropic effects in compacted clays and their variation with soil composition; test data illustrating magnitude of thixotropic strength increases with time for compacted clays in normal compression tests and under repeated loading conditions; effects of thixotropy on results of tests conducted.