Cold-worked Holes Research Articles

Elastic-plastic analysis of a finite sheet with a cold-worked hole

An exact elastic-plastic solution is obtained for the residual stress and strain field in a finite circular sheet having a cold-worked or interference fitted hole on the basis of J 2 deformation theory together with a modified Ramberg-Osgood law. Many factors influencing the residual stresses are then analysed. Further, comparison with finite element results and experimental data for rectangular sheets containing cold-worked holes is made. It is shown that the solution of a finite circular sheet can be used to predict the residual stresses on the minimum cross-section in a rectangular sheet with a cold-worked hole quickly and effectively, so long as the diameter of the circular sheet is equal to the width of the sheet.

Elastic-plastic analysis of a finite sheet with a cold-worked hole

An exact elastic-plastic solution has been obtained for the residual stress and strain field in a finite circular sheet having a cold-worked or interference fitted hole on the basis of J 2 deformation theory together with a modified Ramberg-Osgood law. Many factors influencing the residual stresses are analysed. Comparison with finite element results and experimental data for rectangular sheets containing cold-worked holes is made. It is shown that the solution of a finite circular sheet can be used to predict the residual stresses on the minimum cross section in a rectangular sheet with a cold-worked hole fast and effectively, so long as the diameter of the circular sheet is equal to the width of the sheet.

A Method for Estimation of the Radius of Elastic-Plastic Boundary Around Cold-Worked Holes

AbstractThe radius of an elastic-plastic boundary was measured by the strain gage method around the cold-worked region in L72-aluminum alloy. The relative radial expansion was varied from 2.5 to 6.5% during the cold-working process using mandrel and split sleeve. The existing theoretical studies in this area are reviewed. The experimental results are compared with existing experimental data of various investigators and with various theoretical formulations. A model is developed to predict the radius of elastic-plastic boundary, and the model is assessed by comparing with the present experiments.

MODELLING RESIDUAL STRESSES AND FATIGUE CRACK GROWTH AT COLD‐EXPANDED FASTENER HOLES

AbstractThis paper describes a model developed for predicting residual stresses and crack growth in residual stress fields, and the application of the model to crack growth from cold‐worked fastener holes in thick section aircraft components. Comparison with experimental results demonstrates that the model can provide useful predictions of critical crack length, and a capability for correctly predicting the maxima and minima in the crack growth rate for cracks from cold‐expanded holes. It also permits the observed asymmetry in cracking from cold‐worked fastener holes to be better understood.

On improving the fatigue performance of a double-shear lap joint

Different methods of improving the fatigue performance of a double-shear lap joint which is representative for airframe structures are discussed. Considering all aspects concerning fatigue performance, fabrication problems and cost, one method is recommended for practical application in aviation. This method involves the installation of cylindrical fasteners with a low degree of interference-fit into cold-worked holes.

Simple optical processing of moiré-grating photographs

The three fundamental optical phenomena of diffraction, two-beam interference, and transformation by a lens form the basis of modern moire strain-measurement techniques. The improved understanding of diffraction by superimposed gratings and optical spatial filtering leads to a general gain of freedom in designing moire experiments. Benefits characteristic of refined but very simple optical-data-processing techniques include simpler apparatus, less-demanding procedure, possible large gains in sensitivity, and the ability to choose certain moire parameters, such as sensitivity,after an experiment is concluded and the raw data stored. Sample results from a study of strains near cold-worked holes demonstrate that acceptable results can be had with elementary apparatus and systematic exploitation of optical-data processing.

Prediction of Fatigue Crack Growth at Cold-Worked Fastener Holes

A methodology for the quantitative prediction of crack-growth behavior of cracks emanating at cold-worked fastener holes under fatigue cyclic loading has been developed. The proposed prediction technique is based on an 4'effective stress field'1 concept that accounts for the amount of the compressive residual stress existing at the edge of the cold-worked hole. Stress-intensity factor ranges (A/0 and crack-growth rates (da/d/i) are all formulated in terms of the effective stress field. An existing fatigue-crack-growth analysis computer program has been modified to account for these changes. This program was subsequently used to study the fracturemechanics design development test data. Good correlations have been obtained.

Stress Measurements on Cold-Worked Fastener Holes

Magnitude and distribution of residual stresses around cold-worked holes in 1045 steel were measured with the Fastress automatic stress X-ray analyzer. Permanent interferences between 0.8% and 6.2% at a hole with 0.5 in. diameter produced compressive hoop and radial stresses up to -60 ksi and -40 ksi respectively. The size of the zone with compressive stress is significantly wider than existing analysis predicts.

Cracks emanating from precracked coldworked holes

An experimental investigation was carried out to evaluate the retardation phenomenon of precracked cold-worked holes with and without fasteners (zero load transfer). The material used was extruded 7075-T6511 aluminum 0.25 in. thick. The fastener system was HiLok HL 18 alloy steel. In all cases the holes were precracked (0.05 in. corner crack) before applying the cold work and installing the fastener system. The baseline data was obtained from open holes without cold working. All tests were conducted in constant amplitude loading at stress ration ( R) of ±0.8 at maximum stress of 35–40 ksi. A limited number of tests were conducted to investigate the over-loading effects. Tensile and compressive overloads of 45.0 and 22.5 ksi, respectively, were applied at about half the endurance of the baseline specimens. The results indicate that cold working does retard crack propagation from fastener holes but overloads can influence the overall results.

Stress intensity factors for some through-cracked fastener holes

A stress intensity factor solution is developed for a large plate containing radial hole cracks loaded with arbitrary crack face pressure. When the pressure is defined as the unflawed hoop stress surrounding a mechanical fastener, stress intensity factor calibrations are readily computed by the linear superposition principle. Results obtained in this manner agree well with previous solutions determined for open holes loaded in remote tension. The potential usefulness of the present analysis is further demonstrated with application to specific fastener configurations, including interference fit fasteners, pin-loaded plates, and cold-worked holes.