Compressive Failure Stress Research Articles

HYGROTHERMAL AND MECHANICAL BEHAVIOUR OF ABRASIVE AGGLOMERATE. APPLICATION TO RECTIFICATION WHEELS DRYING.

ABSTRACT The distribution of the water content and temperature have been modelised and numerically investigated within the body of unbaked rectification wheels during convective drying. The obtained profiles have been applied to mechanical stress distribution simulations, fitting process parameters in order to avoid crack formation. The thermophysical, cinetical and mechanical properties of the abrasive agglomerate were determined experimentally. The transport phenomena within the medium have been described by a classical water vapour diffusion and thermal conduction model with convective boundary conditions. The water vapour diffusivity and thermal conductivity were obtained respectively by water content profile analysis during 1-D isothermal diffusional water vapor transfer and by the flash method. The heat and mass transfer coefficients at the boundaries were calculated on the basis of [itterature correlations. The set of coupled non-linear differential equations was discretized in the space domain by the finite-volume method and integrated in the time domain by Runge-Kutta-Fehlberg procedure widi ACSL package. A finite-element variational formulation with elasto-plastic behaviour laws has been used to assess the mechanical strain and stress distribution resulting from the pre-calculated water content and temperature profiles. The simulations were carried out with the industrial Abaqus package. The shrinkage coefficient was measured by means of a laser beam displacement detector on samples dried by micro-wave radiation. The elasticity modulus, tangential plastic modulus, compression and tension failure stress were determined by compression and bending tests on hygro thermally conditioned samples.

Hydration swelling effects on time‐dependent deformation of zeolitized tuff

Long‐duration creep deformation experiments were performed on zeolitized tuffs from Yucca Mountain, Nevada, at temperatures of 35°–75°C, confining pressure of 5 MPa, and water pore pressure of 0.1 MPa. The test samples were initially loaded to a relatively small fraction of the uniaxial compressive failure stress, and allowed to creep; then the stress was increased periodically until creep failure occurred. The strain versus time creep curves exhibit the classical phenomenological phases of primary, secondary, and tertiary creep analogous to those for ductile metals, although the tuffs deform by dilational microcracking and fail by brittle fracture. Mechanical “steady state” or secondary creep strain rates as low as 1 × 10−10 s−1 were observed in the tests. Tertiary creep axial failure strains averaged about 6 × 10−3. The early, water saturation phases of the tests are characterized by large hydration swelling strains associated with water absorption by the zeolite minerals in the tuffs. The hydration was often incomplete after one month of immersion, and slow, continued hydration affected the creep curves so that the samples appeared to lengthen against axial differential stresses as high as 55 MPa. This strong chemical‐mechanical coupling suggests that in situ hydration state changes could generate stresses of similar magnitude.

EFFECT OF HEAT TREATMENT ON THE QUALITY OF COOKED CARROTS

ABSTRACTWe investigated the effect of heat treatment on the quality of cooked carrots (texture, chemical, and sensory evaluation). Slices of three carrot varieties (Rubika, Kundulus, and Rothild) were cooked at 90–120°C for 2–70 min. Compressive failure stress and rupture work were a by a Zwick Universal Testing Machine. Textural softening could be expressed by an exponential equation of the type: S = A exp(‐kt), where 6 = rupture stress, t = cooking time, and A and k are constants. Plotting k versus l/T (T = cooking temperature, °K) revealed an Arrhenius‐type relationship with apparent activation energy of about 28, 27, and 22 Kcal/mole for Rubika, Rothild, and Kundulus varieties, respectively. Chemical analysis (dry matter and p‐carotene) showed that the cooking process caused insignificant changes. Statistical analysis of the sensory assessments showed an overall significant preference for 3 mm slice thickness and 110°C cooking temperature.