LY12CZ Aluminum Alloy Research Articles

Corrosion damage evolution and residual strength of corroded aluminum alloys

The LY12CZ aluminum alloy specimens were corroded under the conditions of different test temperatures and exposure durations. After corrosion exposure, fatigue tests were performed. Scanning electron microscopy and optical microscope analyses on corrosion damage were carried out. The definition of surface corrosion damage ratio was provided to describe the extent of surface corrosion damage. On the basis of the measured data sets of the corrosion damage ratio, the probabilistic model of corrosion damage evolution was built. The corrosion damage decreased the fatigue life by a factor of about 1.25 to 2.38 and the prediction method of residual strength of the corroded structure was presented.

Residual Strength of Stiffened LY12CZ Aluminum Alloy Panels with Widespread Fatigue Damage

Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage (WFD) are conducted. Nine stiffened LY12CZ aluminum alloy panels with three different types of damage are tested for residual strength. Each specimen is pre-cracked at rivet holes by saw cuts and subjected to a monotonically increasing tensile load until failure is occurred and the failure load is recorded. The stress intensity factors at the tips of the lead crack and the adjacent WFD cracks of the stiffened aluminum alloy panels are calculated by compounding approach and finite element method (FEM) respectively. The residual strength of the stiffened panels with WFD is evaluated by the engineering method with plastic zone linkup criterion and the FEM with apparent fracture toughness criterion respectively. The predicted residual strength agrees well with the experiment results. It indicates that in engineering practice these methods can be used for residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD can significantly reduce the residual strength and the critical crack length of the stiffened panels with WFD. The effect of WFD crack length on residual strength is also studied.

Reliability-based minimal sample factor formulation for a corrosion damage assessment in aluminium alloy plates

Accelerated corrosion tests and atmospheric exposure tests are conducted to investigate the corrosion performance of LY12CZ aluminium alloy. Based on the experimental data, the corrosion depth at different corrosion times is determined using a fuzzy discrimination method which follows a log-Gauss distribution. From the experimental observations, the minimal sample factor formulation and a power law function model with three parameters are presented to assess safe corrosion damage at different corrosion times and to describe the corrosion depth law with corrosion time. From the application examples of this model, it is shown that the data for corrosion depth are better defined by a three-parameter power law function shown in the figure. Statistical analysis shows a strong correlation between pit depth and observed corrosion time. Finally, the equivalent relationship between accelerated corrosion and atmospheric exposure corrosion is established.

A multiaxial fatigue criterion for various metallic materials under proportional and nonproportional loading

Proportional and nonproportional tension–torsion fatigue tests were conducted on LY12CZ aluminum alloy. Two types of tubular specimens were used, one is smooth and the other is notched. The experimental data are analyzed. A new critical plane criterion including the strain and stress parameters is proposed. The capability of fatigue life prediction for the proposed fatigue damage model is checked against the experimental data of LY12CZ aluminum alloy and two other metals under proportional and nonproportional loading, and the predicted results are compared with results from common multiaxial fatigue model. It is demonstrated that the proposed criterion gives better satisfactory results for all the three checked materials.

Analysis of modal acoustic emission signals of LY12CZ aluminum alloy at anodic and cathodic polarization

Modal acoustic emission technique was used to analyze corrosion signals produced by polarization corrosion of LY12CZ aluminum alloy. The results showed that there were two-type waveforms for both anodic and cathodic polarization. Only extensional signals appeared within 1800 s, but extensional and flexural signals both appeared beyond 1800 s. The frequency spectrums were presented and analyzed, and potential source identification was discussed.

A complete three-dimensional finite element analysis of the bar-bar tensile impact apparatus

A complete three-dimensional FEM model of the Bar-Bar Tensile Impact Apparatus (BTIA) is constructed, in which the slots in the bars and the glue layers between the bars and the flat-shaped specimen are included. For elastic-plastic specimen material, Ly12cz aluminum alloy, the process of tensile impact experiments is simulated and the matching relation between the specimen geometry and the bars is investigated. Based on the FEM analysis, an iterative method is proposed to design a reasonable specimen geometry for obtaining the true dynamic stress-strain relation for a certain specimen material.

Overload effects on corrosion fatigue crack initiation life and life prediction of aluminum notched elements under variable amplitude loading

In this study, corrosion fatigue tests under both constant and variable amplitude loading are carried out to investigate the overload effect on the corrosion fatigue crack initiation (CFCI) life and life prediction model of the notched specimens of LY12CZ aluminum alloy sheets, which has the continuous strain hardening characteristics. Analysis of test results of CFCI life in 3.5% NaCl solution environment shows that overload increases the CFCI threshold but has no appreciable effect on the CFCI resistance coefficient, and thus increases the CFCI life. Further analysis gives the overload effect factor for CFCI life, z, which can be used to characterize the load interaction effect in load spectrum. Furthermore, three load spectra are designed and used for testing and predicting the CFCI lives under variable amplitude loading (VAL). Test results of CFCI life under above mentioned load spectra show that the load pattern has great effect on CFCI life of LY12CZ alloy notched elements even the difference among the load spectra is small. It means that the overload effect should be taken into account in CFCI life prediction under VAL. Finally, the equivalent stress amplitude approach is put forward to predict the CFCI life under VAL by using Miner’s rule and the CFCI life expression considering the overload effect. The predicted CFCI lives of LY12CZ alloy notched elements under VAL agree well with test results. Based on the above test results and analysis, it may be thought that Miner’s rule can be used to predict the CFCI life of notched elements of metals with continuous strain hardening characteristics if the overload effect on CFCI life is taken into account in life prediction under VAL.

ANALYSIS OF THE MECHANICS OF NORMAL PERFORATION OF METALLIC PLATES BY HIGH-SPEED PROJECTILES

An analytical model that considers the projectile deformation has been developed to describe the plugging process due to the impact of high speed projectiles into metallic plates of finite thicknesses. Both projectile and target materials are considered as strain rate independent and are rigid/plastic linear work hardening with respect to nominal stress-engineering strain relationships. The model identifies two projectile modes: heading and rigid. For each projectile mode, the target perforation process is described consisting of the following stages: (i) erosion, (ii) indentation. (iii) plug formation, and (iv) plug ejection. The plastic wave theory is used with the equations of motion to predict the sequence of the perforation stages of the different projectile modes that represent the complete perforation process of metallic plates.The model is capable of predicting the time histories of target resisting force, velocity of different moving masses, and projectile penetration depth through the target. It can also estimate the projectile residual velocity, the plug thickness and the final length of projectile after perforation. For each impact velocity, the initial interface area of the projectile front is the only empirical factor in the analysis which is needed to run the model. The model predictions are compared with the experimental results of other investigators; good agreement is obtained. In addition, two thicknesses of LY12-CZ aluminium alloy plates are used as targets to specify the perforation process due to their impact by steel projectiles with velocity range up to 650 m/s. Predicted samples of the model results are presented. The model is also used to discuss the influence of projectile deformation on the different predicted time histories and post perforation results.

Large sample size experimental investigation on the statistical nature of fatigue crack initiation and growth

Abstract A statistical investigation of the fatigue crack initiation and growth process is conducted in this paper. A total of 102 replicate constant-amplitude crack initiation and growth tests were designed and carried out on Ly12-CZ aluminium alloy. According to the post-mortem fractographic examination by scanning electron microscopy (SEM), some qualitative observations of the spatial correlation between fatigue striations are developed to reveal the statistical nature of the intrinsic material inhomogeneity during the crack growth process. From the experimental data, the distributions of crack initiation life N i and growth life N g are found to be accepted as log-normal distributions, and the statistical characteristics of crack growth rate d a d N are also investigated. All of these results would be able to provide solid test foundation for the study of probabilistic fatigue, probabilistic fracture mechanics, fatigue reliability and its engineering applications.

A novel method for measuring plane stress dynamic fracture toughness

By using the self-designed Rotating Circular Disk direct tensile impact apparatus, a novel test method has been developed for studying the fracture properties of materials under impact loading. A double edge notch specimen under a plane stress state is used in fracture test conditions; the material exhibits elastic-plastic behavior at the crack tip. The SHPB technique is used to measure the dynamic loads and the displacements of the specimen; crack opening displacement is measured by applying the self-designed photoelectric transformation setup. For the evaluation of dynamic fracture toughness, the extended J-integral with the inertial effect is calculated by Rice's formula using the average load-displacement curve. The time to crack initiation is determined by the compliance changing rate method. The fracture toughness of LY12cz aluminum alloy at a loading rate K ID greater than 10 6 MPa √m/sec is obtained.

The fatigue damage criterion and evolution equation containing material microparameters

Fatigue tests were performed on LY12CZ aluminum alloy by combining macro- and micro-analysis. Then, samples were taken of fatigue samples for different cycle numbers. The change in its microstructure in the fatigue process was observed under a transmission electron microscope. The relationship between damage and microparameters, the value to be taken for the size of the damaged region, the damage criterion and evolution equation are studied from the point of view of damage mechanics.

The fatigue life estimation of notched specimens under random loading

The LY12-cz aluminium alloy sheet specimens with a central hole were tested under constant amplitude loading, Rayleigh narrow band random loading and a typical fighter broad band random loading. The fatigue life was estimated by means of the nominal stress and the Miner's rule. The stress cycles were distinguished by the rainflow count, range count and peak value count, respectively. The comparison between the estimated results and the test results was made. The effects of random loading sequence and small load cycles on fatigue life were also studied.