Comparison of the Strength of Binary Dislocation Junctions in fcc Crystals

Discrete dislocation dynamics were used to determine the relative strengths of binary dislocation junctions in fcc crystals. Equilibrium junctions of different types Lomer, glissile, coplanar, and collinear were formed by allowing parallel dislocations of unequal length to react. The strengths were determined from the computed minimum strain rate versus the applied shear stress plots. The collinear configuration was found to be the strongest and coplanar the weakest. It was seen that the glissile junction could exist as two variants depending on which parent slip system the shear stress is applied. One variant of the glissile junction was found to be as strong as the collinear configuration.

Time–space relationships among structural and metamorphic aureoles related to granite emplacement: a case study from the Serre Massif (southern Italy)

Tectonic and thermal perturbations, related to emplacement of granodiorite in the upper continental crust, have been investigated in the late-Hercynian basement exposed in southern Calabria (Italy). Here, the structural aureole is marked by the presence of a major rim fold adjacent to the intrusive contact for a length of at least 20 km. Geometrical analysis of the structural aureole and related foliations, lineations and crenulations reveals that the perturbed zone is at least 3000 m wide and characterized by an open synform trending nearly parallel to the intrusive contact. This pattern is compatible with a laccolith-like mode of magma emplacement, related to the accretion of the pluton that shouldered weak phyllitic and slaty wall rocks. The metamorphic aureole, about 1800 m wide, is characterized by biotite, cordierite and andalusite that appear sequentially in spotted schists and hornfelses approaching the intrusive contact. The peak assemblage equilibrated between 535 and 590°C at pressures between 175 and 200 MPa, confirmed by Al-in-hornblende barometry on granodiorite. Microstructural analysis allowed the inference of a time lag between the thermal and tectonic perturbations. With the aid of thermal modelling it was possible to quantify the time required to reach the peak temperature at a distance from the intrusive contact where cordierite spots and andalusite porphyroblasts clearly overprint crenulations. This estimate represents the time limit to accomplish deformation in the inner portion of the aureole and thus indicates a minimum strain rate of 4 × 10−14 s−1 within the country rocks during granodiorite intrusion.

Experimental Study on Creep Life of Granite under Direct Uniaxial Tension

Experiments of direct tension creep on granite under uniaxial tensile stress condition were conducted to study the behaviors of long-term deformation and characteristics of acoustic emission. Test results indicate that there exists linear relationship between minimum strain rate and creep life on log-log coordinate, and that relationship between minimum strain rate and remaining creep life is also linear on log-log plot. According to the relationships, equations were developed to predict tension creep life of rocks. In the tertiary creep stage, there exists inversely-proportional relationship between axial strain and residual life, and the relationship was used to estimate residual life of a rock material.

On the Creep Rupture Prediction of Composite Pressure Vessels

This article illustrates a concept of predicting the time dependent deformation and creep rupture strength of carbon fibre reinforced plastics (CFRP). In the presented concept the viscoelastic behaviour of the resin is determined by creep rupture tests at different temperature and load levels. Out of the experiments the relaxation spectrum of the resin is modelled including the spread. With the help of the classical rule of mixture and a modified classical laminate theory the minimum strain rate for the composite will be determined. The results will be compared to experimental data. Furthermore the Monkman-Grant approach is used to determine the time-to-failure strain-rate relation. Therefore an elastic solution of the classical laminate theory is used including Puck’s failure criteria to compute the Monkman-Grant relation. A Monte Carlo Simulation will be done to include the spread of the Monkman-Grant relation. The results will be compared to experimental results of unidirectional specimens. Finally it will be explained how the lifetime of a pressure vessel can be computed using the explained concept.

Tensile Creep Behavior in Lutetia-doped Silicon Nitride Ceramics

We studied tensile creep behavior in two silicon nitride ceramics, i.e., 4.8 mol% Lu2O3 (SN48) and 1.2 mol% Lu2O3 (SN12), at 1400–1500 °C under applied stress of 137–300 MPa. Time to failure of SN48 increased with decreasing applied stress and minimum strain rate. The stress–rupture parameter was 10.7 at 1400 °C and 11.4 at 1500 °C. Pore formation was confirmed in a creep-tested specimen of SN48 by transmission electron microscopy. These results suggest that SN48 was fractured by creep rupture. The minimum strain rate of SN12 was almost below the measurement system limitation at temperatures below 1500 °C. Time to failure tended to increase with decreasing applied stress. The stress–rupture parameter was 41 at 1400 °C and 73 at 1500 °C. These results suggest that SN12 was fractured by subcritical crack growth.

The localization of strain and c-axis evolution in anisotropic ice

Using a series of combined compression–simple-shear experiments, it has been possible to investigate strain distributions and crystal-orientation fabrics related to varying layer orientation in ice. A variety of flattening strains accompanied by layer buckling, simple shear and the development of a lenticular layering are produced in anisotropic ice masses. In samples where the creep curve has only just reached a minimum strain rate, the c-axis preferred orientation is similar to that in the starting material, with specific c-axis concentrations affected by the extent of preserved host grains. At shear strains where γ ≤ 1, it was found that the c-axis preferred orientations were highly variable depending on the magnitude of strain, strain distribution and upon the modification and degree of rotation of initial c-axis preferred orientation. However, once recrystallization dominates in high-strain zones (γ ≥ 1), there is a rapid development of an asymmetric two-maxima fabric with little evidence of any contributions from inherited fabric elements. The final c-axis pattern is asymmetric with respect to the direction of shortening, with a strong maximum at ∼80° to the shear zone, with a sense of asymmetry in the direction of the shear, and a secondary maximum lying at ∼50° to the plane of shearing.

Some Implications of a Nonlinear Viscoelastic Constitutive Theory Regarding Interrelationships Between Creep and Strength Behavior of Ice at Failure

This study explores several possibilities for a correspondence in the behavior of ice at failure during uniaxial creep (constant stress) and strength (constant strain rate) experiments. The usual notion of failure in ice is employed (i.e., the occurrence of a minimum strain rate during a creep test and a peak or maximum stress during a strength test), and the behavior at failure is discussed in terms of a recently proposed nonlinear viscoelastic constitutive model for ice. It is demonstrated that no correspondence between creep and strength data can be expected in general; however, several approximate interrelationships do occur for the experimentally motivated special case of a constant (independent of stress and strain rate) failure strain.

Closure Rate of a 700 m Deep Bore Hole at Mizuho Station, East Antarctica

Measurements of the bore-hole diameter were made with three-contact-point calipers from the shallow layer to a depth of 700 m at Mizuho Station, East Antarctica, in 1984–86. The minimum strain-rate (i.e. secondary creep rate) of the bore-hole closure was estimated from the observed creep curve at each depth. A relation between stress and strain-rate was deduced for a temperature of −35°C and a stress range from 0.8 to 1.65 MN m−2, as where is the effective strain-rate (s−1) and τ is the effective shear stress (MN m−2). This result shows that, for comparable overburden stresses and temperature, the bore-hole closure rates at Mizuho Station are higher than those measured in bore holes at Byrd Station and in the Northern Hemisphere ice caps (Paterson 1977).