5 research outputs found
The Intimate Relationship between Cavitation and Fracture
Nearly three decades ago, the field of mechanics was cautioned of the obscure
nature of cavitation processes in soft materials [Gent, A.N., 1990. Cavitation
in rubber: a cautionary tale. Rubber Chemistry and Technology, 63(3)]. Since
then, the debate on the mechanisms that drive this failure process is ongoing.
Using a high precision volume controlled cavity expansion procedure, this paper
reveals the intimate relationship between cavitation and fracture. Combining a
Griffith inspired formulation for crack propagation, and a Gent inspired
formulation for cavity expansion, we show that despite the apparent complexity
of the fracture patterns, the pressure-volume response follows a predictable
path. In contrast to available studies, both the model and our experiments are
able to track the entire process including the unstable branch, by controlling
the volume of the cavity. Moreover, this minimal theoretical framework is able
to explain the ambiguity in previous experiments by revealing the presence of
metastable states that can lead to first order transitions at onset of
fracture. The agreement between the simple theory and all of the experimental
results conducted in PDMS samples with shear moduli in the range of 25-246
[kPa], confirms that cavitation and fracture work together in driving the
expansion process. Through this study we also determine the fracture energy of
PDMS and show its significant dependence on strain stiffening
The intimate relationship between cavitation and fracture
Nearly three decades ago, the field of mechanics was cautioned of the obscure nature of cavitation processes in soft materials [A. Gent, Cavitation in rubber: a cautionary tale, Rubber Chem. Technol., 1990, 63, 49–53]. Since then, the debate on the mechanisms that drive this failure process is ongoing. Using a high precision volume controlled cavity expansion procedure, this paper reveals the intimate relationship between cavitation and fracture. Combining a Griffith inspired formulation for crack propagation, and a Gent inspired formulation for cavity expansion, we show that despite the apparent complexity of the fracture patterns, the pressure–volume response follows a predictable path. In contrast to available studies, both the model and our experiments are able to track the entire process including the unstable branch, by controlling the volume of the cavity. Moreover, this minimal theoretical framework is able to explain the ambiguity in previous experiments by revealing the presence of metastable states that can lead to first order transitions at onset of fracture. The agreement between the simple theory and all of the experimental results conducted in PDMS samples with shear moduli in the range of 25–246 [kPa] confirms that cavitation and fracture work together in driving the expansion process. Through this study we also determine the fracture energy of PDMS and show its significant dependence on strain stiffening
Volume-controlled cavity expansion for probing of local elastic properties in soft materials
Cavity expansion can be used to measure the local nonlinear elastic properties in soft materials, regardless of the specific damage or instability mechanism that it may ultimately induce. To that end, we introduce a volume-controlled cavity expansion procedure and an accompanying method that builds on the Cavitation Rheology technique [J. A. Zimberlin et al., Soft Matter, 2007, 3, 763-767], but without relying on the maximum recorded pressure. This is achieved by determining an effective radius of the cavity that is based on the volume measurements, and is further supported by numerical simulations. Applying this method to PDMS samples, we show that it consistently collapses the experimental curves to the theoretical prediction of cavity expansion prior to the occurrence of fracture or cavitation, thus resulting in high precision measurement with less than 5% of scatter and good agreement with results obtained via conventional techniques. Moreover, since it does not require visual tracking of the cavity, this technique can be applied to measure the nonlinear elastic response in opaque samples
Simian Foamy Virus Infections in a Baboon Breeding Colony
AbstractThe prevalence, transmission, and variation of simian foamy viruses (SFVs) in baboons was investigated. Over 95% of adult baboons in the breeding colony as well as recently imported adult animals had high titers of anti-SFV serum IgG. Maternal antibody was detectable in infants' serum up to 6 months of age. Approximately 30% of infants in breeding harems experienced SFV infections by 1 year of age. Shedding of SFV in oral secretions was common, with 13% of samples from normal adult animals and 35% from immunosuppressed animals containing infectious SFV. SFV was isolated from three baboon subspecies (olive, yellow, and chacma baboons) and sequences from both the pol and the LTR regions of the provirus were amplified by PCR and sequenced. Phylogenetic analysis indicated that all baboon isolates formed a single lineage distinct from SFVs of other African monkey species. Within the baboon SFV lineage, two distinct clades were apparent, which consisted of isolates from yellow and olive baboons and isolates from chacma baboons. Competition ELISAs indicated that, while SFV isolates of these two groups were very closely related, antigenic differences do exist between them. SFV isolates from a drill and a mandrill were distinct from baboon SFV isolates, both genetically and antigenically