Bin Jun Fei

Experiment Research of Environment Effects on Fatigue Life of Carbon/Bismaleimide Composite Laminates with Central Hole

The effects of humidity and ultraviolet radiation aging on fatigue properties of carbon/ bismaleimide composites and coating protection action were presented. Specimens with central hole are made of carbon/bismaleimide laminates. Compression-compression (C-C) fatigue tests under normal lab environment were operated respectively for four groups of specimen, (1) specimen under normal lab environment, (2) specimen under UV radiation aging with dryness, (3) specimen under UV radiation aging with moisture, and (4) specimen with coating under UV radiation aging with moisture. Variance analysis of experimental outcomes gave significances of the environment effects on C-C fatigue life of specimens. The results reveal that UV radiation have remarkable effects on the C-C fatigue life of the composite laminates under the same humidity, whereas combined action of UV radiation (300MJ/ m2) and humidity have no significant effects on the C-C fatigue life. Coating can provide effective protect the specimen from UV radiation aging.

Tensile Strength Prediction of Woven Composite Bonded Joint

A progressive damage method is adopted to predict the structural strength of a woven out-of plane composite bonded π joint. A 3D progressive damage model is established and analyzed via a user defined subroutine embedded into the general FEA package. The numerical prediction gives the information of damage onset, damage propagation and final failure pattern, initial and final failure strength. Three samples of woven composite π joint under tensile load are tested to verify the numerical results. The numerical prediction agrees well with the experimental outcomes. All the numerical and experimental results provide insight into the basic understanding of static strength of woven composite bonded π joint.

Crack Growth Life Estimating for MSD Panel

The problem of multiple site damage (MSD) has got more attention in ageing structures. Cumulative effects of interacting cracks may significantly degrade the damage tolerance capacity of structures. Cracks caused by MSD are extremely difficult to detect and greatly reduce the residual strength, fatigue life and overall structural integrity of aircraft panels. This paper presents a simple numerical method, which use the principles of fracture mechanics and the computation results, to predict the fatigue crack growth life of MSD structure. Comparing with calculating crack growth life cycle by cycle, this method will save much time. To verify the validity of the proposed method, experiment was conducted and reported with simulation specimen of representative MSD structure with 5 details. The comparison between the calculated a-N curves and the crack growth lives and the test results shows that the prediction result with this fast method is acceptable. A discussion was carried out by numerical analysis; in with typical MSD structures with different initial crack length were adopted. Crack interaction effect was found obviously, but it occurred mainly in the last part of the crack growth lives. The relative size of MSD cracks depends significantly on the distribution of the initial cracks.

Oxidation Study of APS Thermal Barrier Coatings in Elevated Temperatures

TBCs is a type of multilayer systems, mainly used in the thermal parts of aero engine, acting as the part of heat insulation. The using temperature of parts can be improved because of the being of TBCs. TBCs is one of the most advanced high temperature coatings, and it has many perfectly properties, including the chemical property at high temperature, anti-erode and thermal insulation [1,2]. If TBCs spall from the base, the base will expose in the high temperature, then, rapidly destroy. TBCs generally include three layers, superalloy, bonding layer, insulation layer, and the thermally grown oxide (TGO) between the bonding layer and insulation layer. Justly because of the being of TGO, the TBCs easily failed [3,4]. Although many researchers studied the oxidation of TBCs, the investigation of the relations between oxidation and oxide temperature has not been done by far. So, the work put the emphases on the discussion of APS TBCs’ oxidation property in different temperatures by experiment.

Stochastic Characteristics of Fatigue Crack Propagation for TA15 Titanium Alloy

Crack propagation tests are conducted on TA15 titanium alloy in three stress levels to investigate the stochastic characteristics of FCG. A random variable probability FCG model, base on the Paris’ law, is used to characterize the stochastic performance. Distribution significance test has been done, which shows that the random variable X can be considered reasonably to follow log-normal distribution in all the three stress levels. The probability distribution of crack size at any specified loading cycle and the probability distribution of the random fatigue life at which a given crack size is reached are discussed. Variance analysis indicates that the standard deviations of the log fatigue crack growth rate (FCGR) under the three stress levels do not differ from each other significantly. The scatter of crack initiation life under the lowest stress level is the largest, however, the scatter for crack propagation life shows no significant difference in the three stress levels.

Determination of Creep Crack Growth Threshold by Experiments under Elevated Temperature with Pre-Stressed Specimens

A novel test method is presented in this paper for determination of the creep crack growth threshold. In this method, a wedge is placed in the notch of a standard compact tension (CT) specimen with a pre-crack, which provides an evaluable stress fields characterized with stress intensity factor (K) at the crack tip. Then the specimen is kept in the test temperature for a certain time. The creep crack growth threshold of the material at a given temperature can be obtained by extrapolating the curves of the crack growth rate vs. K in the double logarithmic coordinates. Since it does not need mechanical testing machine and several specimens can be tested simultaneously, the proposed method is economical in both costs and time. Tests on a nickel-based powder metallurgy superalloy FGH97 are conducted using this method at 600°C, 650°C and 750°C, which indicate its feasibility.

Evaluating the Critical Temperature of Creep-Fatigue Interaction a Nickel-Based Powder Metallurgy Superalloy

For the components working in high temperature and enduring fatigue loading, the fatigue fracture properties will be reduced remarkably when the working temperature is higher than the critical temperature of creep-fatigue interaction Tc of the material. In consequence, the damage mechanism from creep-fatigue interaction becomes more complex. A method is presented in this paper to determine the Tc of a nickel-based powder metallurgy superalloy. Pure fatigue crack growth and creep-fatigue crack growth tests were conducted in several different elevated temperatures. The fracture mechanism was investigated via observing the fractographic characteristics using scanning electron microscope (SEM). The test results show that the Tc of this superalloy is a little bit lower than a half of the melting temperature Tm.

Experimental Research on Compression/Compression Fatigue Performance of Impacted Composite Laminates

Low velocity impact tests were carried out on T300/QY8911 and CCF300/QY8911 composite laminates, which led to similar impacted damage characterized by dent depths on laminates. Compression/compression fatigue strength tests of the impacted laminates were further conducted. The comparison of the compression/compression fatigue performance between the two types of composite laminates with similar impacted damage shows the compression/compression fatigue behaviors of T300/QY8911 and CCF300/QY8911 are similar. It follows that the CCF300/QY8911 is an effectively alternative to the T300/QY8911 in damage tolerance behavior.

Damage Resistance Behaviors of CCF300/5428 under Various Impact Energies

Damage resistance behaviors of CCF300/5428 laminates under five levels of impact energies have been researched by using progressive damage method. The progressive damage models (PDM) are composed of 3D finite element models, Hashin-type failure criteria and Camanhos degradation rules. The impact procedure has been simulated by the progressive damage analysis with user defined subroutines which have been developed and embedded into the general finite element analysis package. The history curves of the contact force and the impact point displacement are plotted. The global damage at typical events for various impact energies is investigated.

Failure Analysis of CCF300/5428 Laminates under Low Velocity Impact Based on Properties of Advanced Composite Material

A progressive damage model (PDM) composed by 3D FEM, Hashin and Ye failure criteria and Changs degradation rules was established to deeply understand the failure of a new material system CCF300/5428 under low velocity impact. User defined subroutines were developed and embedded into the general FEA software package to carry out the failure analysis. Numerical simulations provide more information about the failure of composite laminates under low velocity impact, including initial damage status, damage propagation and final failure status. The history of the impact point displacement and various damage patterns were detailed studied.