Damage and fracture of PVDF at 20°C

International audienceFlexible oil pipelines are multilayered structures used for the transport of crude oil or natural gas from the seabed to the surface in offshore oil fields. Because of severe service conditions, composite structure made of metallic and polymeric layers must be used. PVDF is a good candidate as it accommodates tensile and flexural deformations and guarantees watertightness. The present paper focuses on the mechanical properties of PVDF at 20°C. Several specimens with different geometries were tested: notched specimen and cracked specimen under tension. Fracture surfaces were examined to determine fracture mechanisms. Based on mechanical testing and microscopic observations, a modified Gurson-Tvergaard-Needleman model for semi-crystalline polymers is proposed. The model allows to represent the non-linear behavior and the cracking of polymer structures

MiR-21 Deficiency Alters the Survival of Ly-6Clo Monocytes in ApoE -/- Mice and Reduces Early-Stage Atherosclerosis.

Objective- To determine the role of miR-21 on the homeostasis of monocyte subsets and on atherosclerosis development in ApoE -/- mice. Approach and Results- In ApoE -/- mice, miR-21 expression was increased in circulating Ly-6Clo nonclassical monocytes in comparison to Ly-6Chi monocytes. The absence of miR-21 significantly altered the survival and number of circulating Ly-6Clo nonclassical monocytes in ApoE -/- mice. In the early stages of atherosclerosis, the absence of miR-21 limited lesion development both in the aortic sinus (by almost 30%) and in the aorta (by almost 50%). This was associated with less monocyte availability in circulation and increased apoptosis of local macrophages in plaques. At later stages of atherosclerosis, lesion size in the aortic root was similar in ApoE -/- and ApoE -/- miR-21 -/- mice, but plaques showed a less stable phenotype (larger necrotic cores) in the latter. The loss of protection in advanced stages was most likely because of excessive inflammatory apoptosis related to an impairment of local efficient efferocytosis. Conclusions- Gene deletion of miR-21 in ApoE -/- mice alters Ly-6Clo nonclassical monocytes homeostasis and contribute to limit early-stage atherosclerosis.This work was supported by Institut National de la Santé et de la Recherche Médicale

Damage and fracture of polyvinylidene fluoride (PVDF) at 20°C: Experiments and modelling

International audienceFlexible oil pipelines are multilayered structures used for the transport of crude oil or natural gas from the seabed to the surface in offshore oil fields. Because of severe service conditions, composite structures made of metallic and polymeric layers must be used. PVDF is a good candidate as it accommodates tensile and flexural deformations and guarantees water tightness. The present paper focuses on the mechanical properties of PVDF at 20°C. Several specimens with different geometries were tested: smooth specimens, notched specimens and cracked specimens under tension and bending. Fracture surfaces were examined to determine fracture mechanisms. Based on mechanical testing and microscopic observations, a modified Gurson–Tvergaard–Needleman model for semi-crystalline polymers is proposed. The model allows both the non-linear behavior and the cracking of polymer structures to be represented