A survey of post-peterson stress concentration factor data

The effects of porosity architecture and volume fraction on the homogenized elastic moduli and elastic-plastic response of perforated thin metal sheets are investigated under three fundamental loading modes using an efficient homogenization theory. Steel and aluminum sheets weakened by circular, hexagonal, square, and slotted holes arranged in square and hexagonal arrays subjected to inplane normal and shear loading are considered with porosity volume fractions in the range 0.1―0.6. Substantial variations are observed in the homogenized elastic moduli with porosity shape and array type. The differences are rooted in the stress transfer mechanism around traction-free porosities whose shape and distribution play major roles in altering the local stress fields and thus the homogenized response in the elastic-plastic domain. This response is characterized by four parameters that define different stages of micro- and macrolevel yielding. The variations in these parameters due to porosity architecture and loading direction provide useful data for design purposes under monotonic and cyclic loading.

Elastic and Plastic Response of Perforated Metal Sheets With Different Porosity Architectures

An analytical procedure for predicting thrust chamber life is developed. The hot-gas wall ligaments separating the coolant and combustion gas are subjected to pressure loading and severe thermal cycling. The resulting stresses interact during plastic straining causing incremental bulging of the ligaments during each firing cycle. This mechanism of plastic ratcheting is analyzed and a method using a yield surface for combined bending and membrane loading is developed for determining the incremental permanent deflection and progressive thinning near the center of the ligaments. Fatigue and tensile instability are analyzed as possible failure modes. Results of the simplified analyses compare favorably with available experimental data and finite element analysis results for OFHC (Oxygen Free High Conductivity) copper. They are also in reasonably good agreement with experimental data for NARloy Z, a copper-zirconium silver alloy.

Simplified design and life prediction of rocket thrust chambers

Effects of temperature and strain rate on the tensile properties of Cu-Cr-Zr-Ti alloy in annealed condition were investigated by varying the initial strain rates from 10−4 s−1 to 10−1 s−1 at RT, 300 °C, 450 °C, 600 °C and 700 °C The yield strength (YS) and ultimate tensile strength (UTS) of the alloy increased with an increase in strain rate at RT and 300 °C, whereas at 450 °C, the material exhibited the highest YS and UTS at the lowest strain rate of 10−4 s−1 At 600 °C, the YS and UTS of the alloy increased with an increase in strain rate and showed the highest YS compared to all the temperatures tested The alloy showed serrated yielding at 300 °C and at an initial strain rate of 10−4 s−1 whereas at 450 °C, serrated yielding was observed at 10−3 s−1 and 10−4 s−1 strain rates Microstructural observations showed the presence of creep cavities at 450 °C and strain rate of 10−4 s−1 The creep cavities were present at higher strain rates as the test temperature is increased Fractography indicates that the fracture is predominantly dimple fracture at RT and 300 °C and intergranular cracks were observed at 600 °C and 700 °C

Effects of temperature and strain rate on tensile properties of Cu-Cr-Zr-Ti Alloy

Simplified Creep Analysis of Perforated Plates Under Steady Creep Condition

Steady creep solutions are obtained for perforated materials under various loading conditions. Norton’s creep power law is used and the plane stress problem is analyzed for both the triangular and square penetration patterns of circular holes. Maximum local stresses at the hole boundaries are obtained for calculating creep rupture damage. Local creep strain concentration factors are also obtained. The interrelations between the elastic, plastic and creep solutions are investigated.

Stress and Strain Concentrations in Perforated Structures Under Steady Creep Conditions

An analytical design procedure for predicting thrust chamber life considering cyclically induced thinning and bulging of the hot gas wall is developed. The hot gas wall, composed of ligaments connecting adjacent cooling channel ribs and separating the coolant flow from the combustion gas, is subjected to pressure loading and severe thermal cycling. Thermal transients during start up and shut down cause plastic straining through the ligaments. The primary bending stress superimposed on the alternate in-plane cyclic straining causes incremental bulging of the ligaments during each firing cycle. This basic mechanism of plastic ratcheting is analyzed and a method developed for determining ligament deformation and strain. The method uses a yield surface for combined bending and membrane loading to determine the incremental permanent deflection and pregressive thinning near the center of the ligaments which cause the geometry of the ligaments to change as the incremental strains accumulate. Fatigue and tensile instability are affected by these local geometry changes. Both are analyzed and a failure criterion developed.

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Development of a simplified procedure for thrust chamber life prediction

Plastic Strain Concentrations in Perforated Structures Subjected to Alternating Loads

Bounds on inelastic strain ranges and maximum residual stresses introduced by transient operating conditions are obtained. These strain ranges and maximum residual stresses can be used to determine fatigue damage and creep rupture damage. Methods for integrating creep rupture damage during relaxation of surface stresses are also included. The solutions are based on uniaxial models.

J. S. Porowski

Papers

Stress and Strain Concentrations in Perforated Structures Under Steady Creep Conditions

Development of a simplified procedure for thrust chamber life prediction

Plastic Strain Concentrations in Perforated Structures Subjected to Alternating Loads

Simplified Inelastic Analysis Methods for Bounding Fatigue and Creep Rupture Damage