A micromechanical model of tension-softening and bridging toughening of short random fiber reinforced brittle matrix composites

A model has been formulated for the post-cracking behavior of a brittle matrix composite reinforced with randomly distributed short fibers. This model incorporates the mechanics of pull-out of fibers which are inclined at an angle to the matrix crack plane and which undergo slip-weakening or slip-hardening during the pull-out process. In addition, the random location and orientation of fibers are accounted for. Comparisons of model predictions of post-cracking tension-softening behavior with experimental data appear to support the validity of the model. The model is used to examine the effects of fiber length, snubbing friction coefficient and interfacial bond behavior on composite post-cracking tensile properties. The scaling of the bridging fracture toughening with material parameters is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29630/1/0000719.pd

Tensile failure mechanisms in synthetic fibre-reinforced mortar

The ultimate tensile behaviour of fibre-reinforced cementitious composites is closely related to its failure mechanisms which in turn are dependent on reinforcement parameters such as fibre characteristics and the fibre/matrix interface properties. Based on the direct tensile tests of mortar specimens reinforced with various synthetic fibres, this paper attempts to explain such relationships and to indicate directions towards more effective fibre reinforcement.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44705/1/10853_2004_Article_BF00553679.pd

Modelling of Fiber Pull-out from a Cement matrix

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/84694/1/ywang_CCLC88.pd

An Experimental Study of Synthetic Fiber Reinforced Cementitious Composites

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/84729/1/ywang_JMS87.pd

Analysis of Synthetic Fiber Pull-Out from a Cement Matrix

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/84740/1/ywang_MRS88.pd

Effect of Fiber-Matrix Bond Strength on the Crack Resistance of Synthetic Fiber Reinforced Cementitious Composites

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/84739/1/li_MRS88.pd

A Special Technique for Determination of the Critical Length of Fiber Pull-Out from a Cement Matrix

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/84731/1/ywang_JMSL88.pd

Breastfed 13 month-old infant of a mother with COVID-19 pneumonia: a case report

BACKGROUND: In China, mothers with confirmed or suspected COVID-19 pneumonia are recommended to stop breastfeeding. However, the evidence to support this guidance is lacking. There have been relatively few cases reported about direct breastfeeding an infant by a mother with SARS-CoV-2 pneumonia. Therefore, it is necessary to assess the safety of breastfeeding and the possible protective effects of breast milk on infants. CASE PRESENTATION: This report analyzes the case of a mother who continued breastfeeding her 13 month-old child when both were diagnosed with confirmed COVID-19 pneumonia. We describe the clinical presentation, diagnosis, treatment, and outcome. The presence of SARS-CoV-2 nucleic acid was determined in maternal serum, breast milk, nasopharyngeal (NP) swabs and feces, and in infant serum, NP swabs and feces. IgM and IgG antibodies against SARS-CoV-2 were assessed in maternal serum and breast milk and in infant serum. SARS-CoV-2 nucleic acid was not detected in the breast milk, and antibodies against SARS-CoV-2 were detected in the mother’s serum and milk. CONCLUSIONS: The present case further confirms that the possibility of mother-to-child transmission about SARS-CoV-2 via breast milk alone was very small, and breast milk is safe for direct feeding of infants

Time-dependent power output and elastic/plastic fracture analyses of porous thermoelectric ceramics for generators

If made in porous foam, thermoelectric ceramics for power generation can enhance the power output by directly extracting thermal energy from heat sources. This paper discusses the time-dependent power output and elastic/plastic fracture of the porous thermoelectric generator (TEG) with a small oblique-through crack. Analytical solutions of temperature and thermal stress of the TEG are derived based on an effective model of porous foam. The finite element numerical model is created to validate the analytical solutions and to explore more thermomechanical properties and constitutive behaviors of the porous materials. Comparing to the traditional bulk TEG, porous TEG can greatly improve the power output however the thermal stress is enhanced therefore the strength is substantially reduced. The power output gradually increases to a peak value and then decreases with the length of the TEG. Based on the criterion of fracture mechanics, a simplified and useful expression of the critical heat flux for crack propagation is identified. The critical heat flux for crack growth is inversely proportional to the porosity and the crack length. A more rigid contact between the TEG and the elastic boundary results in a larger thermal stress and a smaller critical heat flux. The velocity of crack propagation is mostly determined by the porosity and the ratio of the initial crack length to the arbitrary crack length. Also observed is that the length of plastic zone at the crack tips increases with the increasing porosity

Thermally induced delamination and buckling of a ceramic coating with temperature-dependent material properties from porous substrate at high temperatures

Ceramic coatings are ideal materials for thermal protection systems such as the thermal shield of the space shuttle. In a high-temperature environment, material properties of ceramics strongly depend on the temperature. The severe mismatch of material properties between the ceramic coating and the substrate can result in progressive mechanical failure of thermal protection system. This paper investigates delamination and buckling behaviors between a temperature-dependent ceramic coating and a porous substrate. The shear stress intensity factor at the tips of the delamination crack and buckling region are derived. Based on the stress intensity factor, the critical temperature of the coating buckling from the substrate is obtained. A fitting formula of the critical buckling temperature with respect to the length-to-thickness ratio of the coating, and the buckling region is obtained. It is found that the effect of the temperature dependence of material properties on delamination and buckling is more significant for higher temperatures than for lower temperatures. The critical temperatures of delamination and buckling are overestimated if the temperature dependence of material properties is neglected. The critical temperatures of delamination and buckling increase with the porosity of the substrate