Relating matrix stress to local stress on a hard microstructural inclusion for understanding cleavage fracture in high strength steel

Macroscale cleavage fracture toughness of high strength steels is strongly related to the fracture of hard microstructural inclusions. Therefore, an accurate determination of the local stress on these inclusions based on the matrix stress is necessary for the statistical modelling of macroscale cleavage fracture. This paper presents analytical equations to quantitatively estimate the stress of the microstructural inclusions from the far-field stress of the matrix. The analytical equations account for the inclusion shape, the inclusion orientation, the far-field stress state and matrix material properties. Finite element modelling of a representative volume element containing a hard inclusion shows that the equations provide an accurate representation of the local stress state. The equations are implemented into a multi-barrier model and compared with CTOD experiments with two different levels of constraint.

Localized Proteotoxic Stress in Mitochondrial Intermembrane Space and Matrix Elicits Sub-compartment Specific Response Pathways Governed by Unique Modulators

The complex double-membrane architecture of mitochondria is essential for its ATP synthesis function and divides the organelle into two sub-mitochondrial compartments, inter-membrane space (IMS) and matrix. The folding environments of IMS and matrix are significantly different owing to its dissimilar oxido-reductive environments and distinctly divergent protein quality control (PQC) machineries. Here, by inducing proteotoxic stress restricted to IMS or matrix by targeting three different stressor proteins, we show that the cellular response to IMS or matrix-localized misfolding stress is distinct and unique. IMS and matrix stress response pathways are quite effective in combatting stress despite significant stress-induced alteration in mitochondrial phenotypes. IMS misfolding stress leads to specific upregulation of IMS chaperones and components of TOM complex while matrix chaperones and cytosolic PQC components are upregulated during matrix stress. Notably, the amplitude of upregulation of mitochondrial chaperones is not overwhelming. We report that cells respond to mitochondrial stress through an adaptive mechanism by adjourning mitochondrial respiration while upregulating glycolysis as a compensatory pathway. We show that subunits of TOM complex act as specific modulators of IMS-stress response while Vms1 precisely modulates the matrix stress response.

Comparison of Residual Stress Measured by Diffraction Method and Matrix Etching Method in SiC Fiber Reinforced Titanium Matrix Composites

Measurement and modeling of residual stresses in SiC fiber reinforced titanium matrix composites (SiCf/Ti) are still a challenge. Diffraction method and matrix etching method can characterize the strains of matrix and fiber, respectively. A In this work, SiCf/Ti samples with perpendicular and parallel cross-sections to the fibers have been fabricated, and the residual stresses were measured by X-ray diffraction and matrix etching. The results showed that the axial matrix stress in sample with perpendicular cross-sections to the fibers was larger than that in sample with parallel cross-sections to the fibers, while the axial matrix stress calculated from etching was consistent with that from X-ray diffractions based on triaxle stress model, confirming the reliability of triaxle stress model.

Generalized Shear-Lag Analysis Including Imperfect Interfaces

Two recent papers showed that shear-lag analysis can be an effective tool for stress analysis of composites when done properly and when applied to problems for which it is appropriate. This paper extends the prior analysis of concentric cylinders to a generalized shear-lag analysis in which the transverse variations of shear stress are described by arbitrary shape functions. The shear-lag analysis and solution can be derived in terms of averages of the new shape functions. The shape functions can be specified after analysis and tailored to suit specific problems. This paper also extends shear-lag analysis of both concentric cylinders and multilayered structures to model imperfect interfaces between the layers. The generalized methods were applied to several issues in fibre/matrix stress transfer modelled as two concentric cylinders. By modifying prior shape functions, it was possible to extend shear-lag analysis to work for any fibre volume fraction. Prior shear-lag models were all unacceptable at low fibre volume fraction. The full shear-lag analysis can model stress transfer for both isotropic and anisotropic fibres. The new imperfect interface capability was used to interpret experimental results for fibre/matrix stress transfer in terms of interface quality.