LY12CZ Aluminum Alloy Research Articles

Life prediction model based on toughness exhaustion under combined high and low cycle fatigue loading

It is very important to establish a life prediction model that evaluates the combined high and low cycle fatigue (CCF) damage of materials. Based on the toughness exhaustion, this paper develops a CCF life prediction model considering loading interaction effect. The loading interaction factor is proposed to reflect the interaction effect between high cycle fatigue and low cycle fatigue. The proposed model does not require any additional material parameters and is convenient for application. The experimental data of four materials including GH4033 Ni-basis alloy, TC11 titanium alloy, LY12-CZ aluminum alloy, and 45 steel are applied to verify the proposed model. Comparing the prediction results of the proposed model with the Miner’s rule and the T-K model, the results show that the predicted results of the proposed model are more satisfactory.

Combined high and low cycle fatigue life prediction model based on damage curve method considering loading interaction effect

Through analyzing the characteristics of the Miner’s rule and the Manson-Halford (M-H) model, a nonlinear fatigue damage accumulation model is established based on the damage curve method under combined high and low cycle fatigue loading. In this model, an interaction factor related to the maximum stress and high cycle stress range is proposed to consider the loading interaction effect. Furthermore, the proposed model does not require any additional material parameters except for the S-N curve parameters. The experimental data of five materials, including TC11 alloy, 2024-T3 aluminum alloy, 45 steel, LY12-CZ aluminum alloy, and GH4033 Ni-based alloy, are introduced to verify the proposed model. Compared with the Miner’s rule and the M-H model, most of the prediction results by the proposed model are within the life factor range of 2, implying the established model has higher prediction accuracy.

Corrosion inhibition of LY12CZ aluminum alloy by 3‐pyridyl‐4‐amino‐1,2,4‐triazole‐5‐thiol and its cerium nitrate compound

The inhibition effect of 3‐pyridyl‐4‐amino‐1,2,4‐triazole‐5‐thiol (C7H7N5S) and its cerium nitrate (Ce(NO3)3) compound on the corrosion of LY12CZ aluminum in 3.5% NaCl was investigated by means of potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). Results showed that the inhibition efficiency reached 77.61% at 0.8 g L−1 concentration and was found to increase with increasing concentration of C7H7N5S. C7H7N5S is a mixed type inhibitor. The desorption onset potential was obtained from differential polarization curve. EDS data indicated that C7H7N5S can adsorb on the S phase and inhibit the cathode action of the S phase. Both kinetic and thermodynamic parameters were calculated and discussed. The adsorption of C7H7N5S on aluminum surface was found to obey the Langmuir adsorption isotherm, and being both physisorption and chemisorption. C7H7N5S and Ce(NO3)3 have an additive inhibition effect. The additive action improved the surface coverage of the aluminum and the stability of the adsorbed layer.

Study on Continuum Damage Mechanics Model for High Cycle Fatigue

A continuum damage mechanics model was proposed to predict the high cycle fatigue life. In order to consider mean stress effects, the Walker correction was introduced in proposed model. The model was verified by experimental data on LC4 and LY12CZ aluminum alloy under high cycle fatigue loading. The results showed that the predicted life of proposed model well correlated with experimental data.

Research on Fatigue Notch Factor of Aluminum Corrosion Pits

In the midst of highly corrosive marine environment the corrosion damage is very critical in the aircraft structure. Corrosion will reduce the fatigue strength and fatigue life of aircraft structure. The fatigue notch factor is a very important factor, and which directly affects the accuracy of the fatigue life estimation result. The LY12CZ aluminum alloy of aircraft structure was accelerated tested according to equivalent accelerated corrosion testing spectrum based on key environment data, then made a fatigue test. According to the fatigue test data fatigue notch factor was calculated and then the variation law of fatigue notch factor with the corrosion life was studied.

Monitoring Corrosion Fatigue Damage Process of LY12CZ Aluminum Alloy with and without Coating by Acoustic Emission

Corrosion fatigue (CF) of aluminum alloy is an important form of aircraft structural damage. Considering the real service conditions, it is necessary to study the effects of the coating on the CF process. The CF lifetime tests were conducted in 3.5% NaCl solution. The coating could well protect specimens before it damaged and markedly improved the resistibility of CF. According to results of S-N fatigue curves, at σmax=250MPa, real-time detection of the CF process for LY12CZ aluminum alloy with and without coating was performed using digital acoustic emission (AE) technique. Three damage modes, namely, coating damage, corrosion and crack propagation, were determined using AE parameters analysis, that is the distribution of amplitude and peak frequency.

A nonlinear cumulative evolution model for corrosion fatigue damage

A nonlinear cumulative evolution model for corrosion fatigue damage was proposed. Corrosion fatigue damage was considered as a nonlinear cumulative result of stress corrosion damage and fatigue damage. The influences of stress corrosion damage and fatigue damage on corrosion fatigue damage and damage evolution life were studied from a phenomenological point of view. The relevant damage parameters were determined by the experimental results of the LY12CZ aluminum alloy, and the corrosion fatigue life evaluation model based on damage evolution law was established. The corrosion fatigue life predicted by evaluation model agrees well with the experimental result. The damage evolution model in this study can provide a new method for theoretical research and life prediction of corrosion fatigue.

Effect of laser shock processing on fatigue life of fastener hole

The fatigue properties of laser shock processing (LSP) on both side surfaces of fastener hole with diameter of 3 mm in the LY12CZ aluminum alloy specimens were investigated. The superficial residual stress was measured by X-ray diffraction method. Fatigue experiments of specimens with and without LSP were performed, and the microstructural features of fracture of specimens were characterized by scanning electron microscopy (SEM). The results indicate that the compressive residual stress can be induced into the surface of specimen, and the fatigue life of the specimen with LSP is 3.5 times as long as that of specimen without LSP. The location of fatigue crack initiation is transferred from the top surface to the sub-surface after LSP, and the fatigue striation spacing of the treated specimen during the expanding fatigue crack is narrower than that of the untreated specimen. Furthermore, the diameters of the dimples on the fatigue crack rupture zone of the specimen with LSP are relatively bigger, which is related to the serious plastic deformation in the material with LSP.

Fatigue damage rule of LY12CZ aluminium alloy under sequential biaxial loading

A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ aluminium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter α which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental data for two-level loading, multi-level loading of LY12CZ aluminium alloy, and multi-level loading of 45 steel. Fatigue lives predicted are within a factor of 2 scatter band.

SEM<i> In Situ</i> Study on Pre-Corrosion and Fatigue Cracking Behavior of LY12CZ Aluminum Alloy

Corrosion fatigue is a form of degradation subjected to combined damage of mechanical stress and corrosive medium, which is an issue in aircraft industry. Experimental investigations on prior corrosion fatigue cracking behavior of LY12CZ were conducted with scanning electron microscope (SEM). Results indicate corrosion damage is important for the fatigue small cracking behavior of LY12CZ aluminum alloy. The effect of corrosion pit on fatigue crack can be characterized by the depth of corrosion pit. Based on small crack, another way to evaluate crack growth rate for AALY12CZ is proposed.

Research on Aircraft LY12CZ Aluminum Alloy Corrosion Damage Prediction Based on ARIMA Model

The corrosion of LY12CZ aluminum alloy in aircraft under service environment is regarded as a stochastic process and the time series theory is used to analyze and to predict the corrosion depth of LY12CZ under airport environment by means of ARIMA(3,1,1)model.The application result show that the ARIMAmodel can predict the value and propagation trend of corrosion depth realistically and effectively,demonstrating the expedient and easy application of time series theory and method.

Study on the Initial Discontinuity State Distribution of LY12CZ Aluminum Alloy

The initial discontinuity state (IDS) concept was developed just several years ago in an attempt to describe the as-manufactured or as-produced state of material. As a geometric and material characteristic, IDS is the major parameter of holistic life assessment methodology which establishes the initial analysis condition. In this paper, a number of IDS values were determined for several types of smooth specimens. A crack growth analysis software was used to develop the IDS. The results obtained indicate that the calculated IDS values scatter widely. A statistical analysis shows that the distribution of the calculated IDS values fit well with Weibull distribution.

Simulation of Residual Stress Field of Diagonal Laser Shock Processing

Laser shock processing (LSP) is an innovative surface treatment technique. According to the theory of residual stress field formation by laser shock wave, laser overlapping shock processing of LY12CZ aluminium alloy was analyzed. The diagonal shock process is simulated by FEM using LS-DYNA codes, and the residual stress field in different angle of fall and pressure are predicted. The results indicate that the value of residual tension stress can be increased when diagonal shock, and the value of residual compressive stress will be decreased. The simulated results can provide the basis for experimental studying the diagonal laser shock processing and laser facular overlap.

Research on Corrosion Fractal Character of LY12CZ Aluminum Alloy Based on Image Processing Technique

The number of corrosion pits with different corrosion times were got through extracting the corrosion character of LY12CZ aluminum alloy based on binary image disposal technique, through statistical fractal theory we can see that the distribution of corrosion pits have fractal character; the fractal dimension and weight loss rate increased with the corrosion time and the change rule of fractal dimension with different corrosion time consistent with weight loss rate, both are accordant with power function, so the fractal dimension can be regarded as an important parameter to evaluate the corrosion degree.

Corrosion Parameters Distribution Rule and Influence Factors of LY12CZ Aluminum Alloy

The corrosion depth, corrosion area, corrosion pit volume and area of LY12CZ aluminum alloy with different corrosion time were obtained from accelerated corrosion experiment. Four distribution models such as normal, Gumbel, Logistic and double parameter Weibull were used to test their distributions. It can found that the corrosion depth and corrosion area obey Gumbel distribution and the area and volume of corrosion pits obey double parameter Weibull distribution; Choose ten variables as the parameters of influence corrosion fatigue life, through grey relational analyze we can found that the deepest corrosion depth is the biggest influence gene of corrosion fatigue life, and the corrosion grade is an important influence gene almost equal to the deepest depth because it considered the influence of corrosion area and corrosion depth, so we can use it as an parameter to evaluate the calendar life of corrosion conditions.

Lifetime Assessment of Aircraft Structural Components in Coastal Environments

To explore the lifetime of aircraft structural components in coastal environments, the failure process of LY12CZ aluminum alloy stringer servicing in the coastal environment of the Fiji Islands was analyzed. The whole lifetime process of structural components was divided into four stages: coating failure, pit nucleation and growth, short-crack growth, and long-crack expansion. The failure time of coating was assessed by way of formulation and implementation of accelerated environmental spectrum, and a four-stage model was established by analysis of pitting corrosion and derivation of the crack expansion equation. The assessment was virtually consistent with the stringer. Findings showed that pit nucleation and growth and short-crack growth account for approximately 75 % of the entire lifetime. After aircraft structural components have been in service for approximately 14 years, the crack will expand rapidly to the extent that the components will rip apart.

Experimental Study of the Electrical Potential Technique for Crack Monitoring of LY12-CZ Plate Specimen

The electrical potential technique was applied to monitor the crack initiation and propagation in LY12-CZ plates. The feasibility of this method was validated by a simulation experiment firstly. Then fatigue crack monitoring experiment based on LY12-CZ aluminum alloy center-hole plate specimen was carried out. After a special coating sensor was prepared on the monitoring area of the specimen by surface technology, a set of fatigue crack monitoring experiments were carried out. The changes in the potential values of the coating sensor resulting from crack damage were documented. Since the property of the coating sensor and the introduced current were constant, the measured voltage values would only relate to the crack’s length and position. Based on the experimental results, the relation curves between voltage values and crack lengths were obtained, and a set of empirical formulae were deduced.

Research on Evaluation of Corrosion Grade Based on Image Processing Technique

The corrosion images of LY12CZ aluminum alloy with different corrosion time were obtained from accelerated corrosion experiment. The changing law of pits corrosion ratio at different corrosion time and corresponding corrosion grade were attained through image processing technique based on binary characteristic extraction. A new thought of corrosion damage evolvement law for aluminum alloy was proposed based on Corrosion grade which was regarded as the evaluation standard of corrosion damage for aluminum alloy.

Corrosion fatigue behavior of fastening hole structure and virtual crack propagation tests

The fatigue crack propagation behavior of the LY12CZ aluminum alloy fastener involving a central hole in air or in 3.5wt% NaCl solution was investigated. The experimental results indicated that the corrosion fatigue crack growth rate decreased with the increasing loading frequency, and in a corrosive environment, the crack growth rate was slightly larger than that in air. Based on the experimental results, the virtual corrosion fatigue crack propagation tests were investigated and the stochastic process method and the AFGROW simulation method were presented. The normal process and lognormal process were considered for the stochastic process method based on the numerically fitted Paris equation. The distribution of crack size and the corresponding probabilistic model of crack length distribution for a given number of cycles can be found by integrating the stochastic process over time. Using the AFGROW software, the virtual simulation was carried out to analyze the corrosion fatigue crack growth behavior and the predicted crack growth curve was in good agreement with the experimental results.

Acoustic emission study of fatigue crack closure of physical short and long cracks for aluminum alloy LY12CZ

Crack closure of physical short and long cracks of LY12CZ aluminum alloy during fatigue process was investigated using acoustic emission (AE) technique. Results showed that the effective fatigue crack growth curve (d a/d N vs. Δ K eff) of physical short and long cracks obtained by the AE technique was consistent with the effective fatigue crack growth curve at high stress ratio ( R = 0.8), which implied that the AE technique could measure the crack closure level, especially for physical short crack. The growth rate of physical short crack was much higher than that of long crack at the same Δ K, and the lower crack closure level of short crack was the main reason.