Papers by Keyword: Internal Defect

Abstract: The deformation and internal defect in the flat-wedge cross-wedge rolling (CWR) of GH4169 superalloy were investigated numerically using a coupled thermo-mechanical finite element analysis (FEA) model. The simulation analysis showed that the temperature distribution in the work piece was non-uniform during the flat-wedge CWR. When the initial temperature of the work piece was relatively low, the work piece temperature increased, a heating effect of the plastic deformation, while relatively high initial work piece temperatures resulted in cooling the work piece, caused by the work piece contact with the tools. It is noted that the increase of tools moving speeds is helpful to reduce the generation of internal defects in the flat-wedge CWR of GH4169 alloy. An important tendency is that both increasing the tools temperature and decreasing friction coefficient all can contribute to avoiding the center defects in the flat-wedge CWR of GH4169 alloy

Abstract: The present paper presents an optimization model for quality control of industrial products by using two non-destructive techniques (NDT): infrared termography and ultrasonic methods. The main purpose it is to determinate the best analyzing method using multi-criteria analysis by taking into account the results that outcome from the two non-destructive evaluations. There have been studied defects like: internal defects and surface defects. Therewith were taking into consideration: safety, efficiency of the method and the cost of the equipment used in controlling the product. For this study it was created a concrete slab with embedded defects which had different depths. The sample was tested using active thermography and impact echo methods and the results were studied and integrated in an multi-criteria analysis to reveal the best method for this case.

Abstract: The present paper presents a non-destructive technique (NDT) using active pulse infrared thermography with a thermal excitation consisting in two photographic flash laps controlled by a signal generator. For this work we used two bioceramics samples, having the same size, 15, 30 mm diameter and 3, 75 mm thickness. A non-defect sample was used as the basis to demonstrate the temperature differences in the defected zone between the healthy and the defective one. In the second sample was created an internal defect. The main advantage of this method represents its possibility to detect the internal defects in bioceramic materials, the method being more reliable then the microscopic method. Other two advantages of this method are represented bythe rapidity of testing and the maintenance of material properties after the thermal excitation.

Abstract: Forming process of 4Cr9Si2 martensite refractory steel by cross wedge rolling was simulated by means of rigid-plastic finite elementDEFROM-3D software. From wedge tip angle to analyze the central defeats: The increase of maximum stress and its duration time is resulted from the rise of wedge tip fillet (R); the maximum shear stress and maximum shear strain did not change significantly, but its duration time will enlarge with increasing of wedge tip fillet; these factor will lead to the higher possibility of internal defeats. Rolling experiments are carried out to verify the correctness of the FEM and feasibility of simulation results by the experiment: internal defeats have appeared in the conditions of R=12mm.

Abstract: Metal materials have been used in aero industry widely because of its excellent characteristics. So its internal defects are very important. Ultrasound detection technology for detecting metal materials internal defects is related to piezoelectric ultrasonic sensor. This has a few of disadvantages. So the double wavelength optical fiber F-P ultrasound sensing system is designed in this paper. The ultrasound detecting experiment devices for internal defects of metal materials is established based on the optical fiber F-P sensing system. Experimental research of detecting the internal defects is developed. The experimental results show this sensor can detect the ultrasound signals effectively. And it’s proved that this method can be effective used in the internal defect of metal materials.

Abstract: Cross wedge rolling valve roughcast is charactered by minor diameter, long stretching and heavy section shrinkage; however, it is hard to select a set of suitable machining process parameter and prone to rolling internal defect. In order to research this problem, a whole forming process of valve roughcast by single cross wedge rolling is simulated with finite element simulation software DEFORM-3D 6.0, which focuses on the stress and strain of the center point of rolled piece under different forming angles. The rolling experiment under different forming angles was done on H500 rolling mill to calculate and analysis of the areas of the centre holes for each rolled piece. The influence of forming angle on internal defect is discovered by a method combining finite element simulation and experiments. At last, it is concluded that forming angle of 28°can improve the internal defect of valve roughcast formed by single cross wedge rolling.

Abstract: This paper focus on the problem of asymmetrical evaluation level caused by the difficult of discrimination of internal and external defects of MFL inspection signals of oil well pipes to analyze the difference of change trend between the peak-to-peak value of normal detection signals of internal and external defects and the liftoff distance z. The liftoff characteristic is verified through experiments that the liftoff effect of internal defects has a gently change rate but the external has a sharp change rate. A double liftoff inspection method was further proposed, that was, there were double layers magneto sensors arraying in line in the normal direction to accomplish grads measure of two special spaced points in the liftoff direction. Then made cross correlation contrast of detection signals. Result in a new evaluation using the damping decrement of the peak-to-peak of inspection signals in the direction of liftoff. Finally, the unitary damping decrement as an evaluation value used for direct judgment was presented and confirmed by experiments, indicating that the proposed approach was of feasibility.

Abstract: For meeting the requirements of high-precision and high-speed in on-line detection for strip and plate’s internal defects, in the paper, based on elaborating methods and principle of conventional ultrasonic testing, the research status of traditional ultrasonic testing technology and non-contact ultrasonic testing techniques, there analysis and discuss the problems and causes in the process of detection. In the end, the trend of development is given.

Abstract: Watermelons are usually sorted by theirs weight and internal quality. Some automated watermelon weight sorters have been developed and operated in watermelon production areas. However, inspection of internal quality of watermelon is still performed by manually. Principal method of identifying internal defect of watermelon is analyzing the percussion sound of watermelon by human experts. Development of non-destructive evaluation technique for internal quality of watermelon is required to reduce human decision errors. The objective of this study was to develop a non-destructive sorting system which can detect internal defect of watermelons. The internal defect evaluation system has a constant-force hitting hammer to generate the acoustic sound, a multi-point sound signal acquiring system, a noise removal circuit, and a signal processing and quality evaluation program. An internal quality prediction model by PLSR (Partial Least Square Regression) was developed by analyzing the percussion sound of watermelons. Using the developed model, the prediction result shows that the overall prediction accuracy was 90.1%, and severely defected watermelons were identified perfectly.

Abstract: This study is aimed to analyze the thermal imaging patterns presented by infrared(IR) thermography at which the metal with internal defects are thermally heated. Through the knowledge of non-destructive testing which infrared thermography can be applied to detect the defects inside the materials, there are two materials experimented; one is stainless steel and the other is cast-iron. Thermally, each material of specimens is heated at the base of the material and kept with constant temperature, The artificial defects in the specimen are formulated. Under the shape and location of the defects, temperature profiles are also measured and validated using the computer simulation. It is concluded that the characteristics of thermal patterns obtained from IR thermography are consistent with those of measurement and computations.