Fracture analysis of various cracked configurations in sheet and plate materials

A two-parameter fracture criterion was derived which relates the linear-elastic stress-intensity factor at failure, the elastic nominal failure stress, and two material parameters. The fracture criterion was used previously to analyze fracture data for surface- and through-cracked sheet and plate specimens under tensile loading. The fracture criterion was applied to center-crack tension, compact, and notch-band fracture specimens made of steel, titanium, or aluminum alloy materials tested at room temperature. The fracture data included a wide range of crack lengths, specimen widths, and thicknesses. The materials analyzed had a wide range of tensile properties. Failure stresses calculated using the criterion agreed well (plus or minus 10 percent) with experimental failure stresses. The criterion was also found to correlate fracture data from different specimen types (such as center-crack tension and compact specimens), within plus or minus 10 percent for the same material, thickness, and test temperature

High temperature fatigue characteristics of P/M and hot-forged W-Re and TZM for X-ray target of CT scanner

The fatigue strengths at 1000 °C of layered W-Re/TZM, bulk W-Re and bulk TZM for x-ray target materials were successfully evaluated under load-controlled four-point bending by introducing a fatigue failure criterion as twotimes increase of initial compliance. The obtained fatigue strengths at 1000 °C for layered W-Re/TZM and bulk WRe were similar and 280 MPa and 290 MPa at 106 cycles, respectively, while that of bulk TZM was 200 MPa. During fatigue loading at 1000 °C, dominant fatigue damage would be multiple intergranular crack nucleation and propagation, which would induce the increase of compliance. The reasonability of the fatigue failure criterion was confirmed by the fatigue process observations and the results of room temperature fatigue tests of the specimens tested at 1000 °C up to the cycles corresponding to the fatigue failure criterion

Fracture analysis of surface and through cracks in cylindrical pressure vessels

A previously developed fracture criterion was applied to fracture data for surface- and through-cracked cylindrical pressure vessels to see how well the criterion can correlate fracture data. Fracture data from the literature on surface cracks in aluminum alloy, steel, and epoxy vessels, and on through cracks in aluminum alloy, titanium alloy steel, and brass vessels were analyzed by using the fracture criterion. The criterion correlated the failure stresses to within + or - 10 percent for either surface or through cracks over a wide range of crack size and vessel diameter. The fracture criterion was also found to correlate failure stresses to within + or - 10 percent for flat plates (center-crack or double-edge-crack tension specimens) and cylindrical pressure vessels containing through cracks

Systemic risk in dynamical networks with stochastic failure criterion

Complex non-linear interactions between banks and assets we model by two time-dependent Erd\H{o}s Renyi network models where each node, representing bank, can invest either to a single asset (model I) or multiple assets (model II). We use dynamical network approach to evaluate the collective financial failure---systemic risk---quantified by the fraction of active nodes. The systemic risk can be calculated over any future time period, divided on sub-periods, where within each sub-period banks may contiguously fail due to links to either (i) assets or (ii) other banks, controlled by two parameters, probability of internal failure $p$ and threshold $T_h$ ("solvency" parameter). The systemic risk non-linearly increases with $p$ and decreases with average network degree faster when all assets are equally distributed across banks than if assets are randomly distributed. The more inactive banks each bank can sustain (smaller $T_h$), the smaller the systemic risk---for some $T_h$ values in I we report a discontinuity in systemic risk. When contiguous spreading becomes stochastic (ii) controlled by probability $p_2$---a condition for the bank to be solvent (active) is stochastic---the systemic risk decreases with decreasing $p_2$. We analyse asset allocation for the U.S. banks.Comment: 7 pages, 7 figure

Evaluation of failure criterion for graphite/epoxy fabric laminates

The development and application of the tensor polynomial failure criterion for composite laminate analysis is described. Emphasis is given to the fabrication and testing of Narmco Rigidite 5208-WT300, a plain weave fabric of Thornel 300 Graphite fibers impregnated with Narmco 5208 Resin. The quadratic-failure criterion with F sub 12=0 provides accurate estimates of failure stresses for the graphite/epoxy investigated. The cubic failure criterion was recast into an operationally easier form, providing design curves that can be applied to laminates fabricated from orthotropic woven fabric prepregs. In the form presented, no interaction strength tests are required, although recourse to the quadratic model and the principal strength parameters is necessary. However, insufficient test data exist at present to generalize this approach for all prepreg constructions, and its use must be restricted to the generic materials and configurations investigated to date

Failure criterion of glass fabric reinforced plastic laminates

Failure criteria are derived for several modes of failure (in unaxial tensile or compressive loading, or biaxial combined tensile-compressive loading) in the case of closely woven plain fabric, coarsely-woven plain fabric, or roving glass cloth reinforcements. The shear strength in the interaction formula is replaced by an equation dealing with tensile or compressive strength in the direction making a 45 degree angle with one of the anisotropic axes, for the uniaxial failure criteria. The interaction formula is useful as the failure criterion in combined tension-compression biaxial failure for the case of closely woven plain fabric laminates, but poor agreement is obtained in the case of coarsely woven fabric laminates

Finite Element Analysis of FRP Debonding Failure at the Tip of Flexural/Shear Crack in Concrete Beam

One of the most common failure modes of strengthened RC beams with externally bonded FRP is intermediate crack (IC) debonding of FRP initiated at the tip of flexural/shear cracks. This study presents a method, using extended finite element method (XFEM), to model IC debonding in an FRP-strengthened concrete beam. In XFEM, as soon as a damage initiation criterion is reached in an element, additional degrees of element freedom are added to model crack initiation. Crack propagation is then modeled using fracture energy criterion. This method can be used to simulate debonding failure along an arbitrary, solution-dependent path without the requirement of remeshing. The numerical results are validated against experimental data and good agreement is found. A sensitivity analysis is conducted to study the effects of damage band properties and geometry on FRP debonding failure. This verifies that shear strength and critical mode II fracture energy are the parameters most affecting the FRP debonding model when the crack tip is subjected to mode II loading