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Fracture, Fatigue and Structural Integrity of Metallic Materials

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Nguyễn Gia Hào

Academic year: 2023

Chia sẻ "Fracture, Fatigue and Structural Integrity of Metallic Materials"

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Fabrication and fatigue behavior of aluminum foam sandwich panel by liquid diffusion welding method. ces. Metals2019,9, 570.

Fabrication and Fatigue Behavior of Aluminum Foam Sandwich Panel via Liquid Diffusion

  • Introduction
  • Materials and Experimental Methods
  • Results and Discussion 1. Microstructure
  • Conclusions

Peel strength test was performed by WDW-10 universal testing machine (Loading speed 25 mm/min) to test the bond strength of the two kinds of AFS specimens according to the GB T. The molten Zn-10Al alloy has good wettability and diffusion on the surface of the Aluminum substrate during hot dip bonding process and metallurgical bonding process.

Figure 1. Two kinds of AFS (Aluminum Foam Sandwich) panels from different manufacturing process (a) metallurgical joining (b) adhesive joining.
Figure 1. Two kinds of AFS (Aluminum Foam Sandwich) panels from different manufacturing process (a) metallurgical joining (b) adhesive joining.

Research on Fatigue Strength for Weld Structure Details of Deck with U-rib and Diaphragm in

  • Fatigue Test for Weld Structure of U-Rib and Deck Plate
  • Stress Spectrum Calculation
  • Fatigue Life Assessment of the Concerned Point
  • Conclusions

The fatigue life of the steel bridge deck is related to the stress amplitude and the number of cycles under the action of vehicle load. The stress-time history curve and the worst loading position of the point in question are shown in Figures 10 and 11 respectively.

Table 1. The chemical compositions of Q345qD and the welding wire.
Table 1. The chemical compositions of Q345qD and the welding wire.

Effect of Repetitive Collar Replacement on the Residual Strength and Fatigue Life of Retained

Materials and Methods

The fasteners were assembled in accordance with [3] in single fastener lap joints made of 7075-T6 aluminum plate. After completion of the baseline tests, shear fatigue tests were performed on specimens subjected to multiple collar replacements.

Table 1. Mechanical properties of HL51-8-6 fastener pin [11].
Table 1. Mechanical properties of HL51-8-6 fastener pin [11].

Results

Therefore, the experimental samples of the shear fatigue test were subjected to five collar changes at 45,000 cycle intervals, based on the lower 98% confidence interval of the baseline fatigue life. All test samples failed in aluminum substrate fatigue, as previously shown in Fig. 4b.

Figure 6. (a) Average static tensile strength of fasteners: Baseline open symbol, collar replacement filled symbol (error bars represent ±1 standard deviation); and (b) collar failure of fastener assembly.
Figure 6. (a) Average static tensile strength of fasteners: Baseline open symbol, collar replacement filled symbol (error bars represent ±1 standard deviation); and (b) collar failure of fastener assembly.

Discussion

In aluminum substrate, the average clamping force of the fastener is found to be 1095 lbf (4.9 kN) between static shear and shear fatigue tests. From these tests, static shear results showed no decrease in the ultimate shear strength of the fastener as a function of collar replacement.

Table A1. Experimental data for static shear strength of fastener pins—Figure 5.
Table A1. Experimental data for static shear strength of fastener pins—Figure 5.

Fatigue Life Prediction of Steam Generator Tubes by Tube Specimens with Circular Holes

Experimental Procedure and Results 1. Experimental Procedure

The crack initiation is in the plane of maximum shear stress and is at a certain angle to the radial direction of the hole. As the crack propagates, the impact of the notch is weaker and the stress state changes.

Figure 2. Picture of the test device: (a) Test rig, and (b) diagrammatic sketch of clamping technique.
Figure 2. Picture of the test device: (a) Test rig, and (b) diagrammatic sketch of clamping technique.

Evaluation of Stress and Strain near the Hole 1. Finite Element Model

The elastic stress concentration factor is one of the important parameters in the local stress-strain method to estimate the fatigue life of notched specimens. At this stage, the fatigue damage in the middle part of the wall thickness is greatest. Figure 8 shows the stress distribution along the radial path of the bore (path P3 in Figure 3).

This is consistent with the formation mechanism of the three-region fracture from the stress state of the hole. In the notch fatigue analysis, the precise local stress field is the key to predicting the fatigue life of the notch.

Figure 5. Path diagrammatic sketch.
Figure 5. Path diagrammatic sketch.

Fatigue Life Analysis

In the analysis, the Neuber formula is also used to calculate the local notch stress and strain and predict the fatigue life of the notched component. In this work, the Neuber method is also used to analyze the local stress and strain of the notch to estimate the fatigue life. In addition, the equivalent fatigue life based on the notched specimen is mostly higher than the fatigue life of the material.

At higher load levels, these are more consistent, meaning that the low-cycle life range based on the Neuber method can more accurately predict the life of a heat transfer tube. The lifetime of the heat transfer tube was predicted and analyzed based on the local stress-strain field around the hole.

Figure 11 shows the equivalent strain amplitude for the test samples. Moreover, the strain fatigue life curve of nickel-base alloy materials is also plotted
Figure 11 shows the equivalent strain amplitude for the test samples. Moreover, the strain fatigue life curve of nickel-base alloy materials is also plotted

Retardation of Fatigue Crack Growth in Rotating Bending Specimens with Semi-Elliptical Cracks

First, constant amplitude loading (CAL) tests are performed to confirm the serviceability of the crack. The factor is defined as the ratio of the reduced crack growth rate after overloading to the crack growth rate at the base load before overloading. Based on SEB tests, the suggested value is RF= 0.10, which is equivalent to the maximum reduction in da/dN with a delay effect of up to 10% of the crack growth rate before overloading.

A comparison of the crack propagation model with the results of the Overload Test #1 and #2, both with ROL= 2.0, is shown in Figure8. Delay effects, due to the overloads, significantly affect the crack growth rate leading to an improvement of the lifetime.

Table 1. Nominal chemical composition of investigated steel material in weight per cent [33].
Table 1. Nominal chemical composition of investigated steel material in weight per cent [33].

Fatigue Limit Improvement and Rendering Defects Harmless by Needle Peening for High Tensile Steel

Materials and Methods 1. Test Material and Specimens

An automatic welding machine (Kobe Steel, Ltd., Kobe, Japan) was used to make the shape and dimensions of the weld seam as consistent as possible. Figure 3 shows the flowchart of the sample preparation procedure and the types of samples used for the fatigue test. NP was performed on both sides of the weld seam of welded specimens using a portable pneumatic needle peening (PPP) unit.

The machining position of the WNS slot was at the bottom of the indentation created by the NP, as shown in Fig. 4b. The depth profiles of the weld tip hardness on the W and WN surface layers were measured with a Vickers micro hardness tester manufactured by Shimadzu Corp., Kyoto, Japan.

Table 1. Chemical composition of HT780 (mass %).
Table 1. Chemical composition of HT780 (mass %).

Results and Discussion 1. Fatigue Test Results

However, the fatigue limit of the sample treated with NP and WN was 9% higher than that of W. The longitudinal residual stress measurement of the weld metal for W and WN was performed before the fatigue test. The longitudinal residual stress measurement of the weld metal for W and WN was obtained before the fatigue test.

In-depth hardness profiles of the weld toe at the surface layer of W and WN were measured before the fatigue test. Depth hardness profiles of the weld toe at the surface layer of W and WN before the fatigue test were measured.

Figure 5. S-N diagram of (a) W and WN, (b) WS1.0 and WNS1.0 and (c) WS1.5 and WNS 1.5
Figure 5. S-N diagram of (a) W and WN, (b) WS1.0 and WNS1.0 and (c) WS1.5 and WNS 1.5

A Proposal for the Application of Failure Assessment Diagrams to Subcritical Hydrogen Induced Cracking

  • Background
  • Materials and Methods 1. Materials
  • Results
  • Discussion
  • Conclusions and Future Work

Therefore, a more brittle state takes place, which will lead to higher Kr values ​​in the FAD representation of the subcritical crack path propagation [6]. It consists in introducing a modification in the definition of the Kr coordinate (Kr=KI/Kmat) in each of the points that define the crack path propagation in the FAD. In the case of the least aggressive environment, cathodic protection (CP), the propagation across the cleavage region (TG) increased towards the tear region.

The first one was the definition of the start of the crack propagation in the elastic-plastic range using the iso-slope in its straight initial part. For this reason, the proposed optimization is an advance in the accuracy of the FAD prediction model.

Figure 1. Example of the implementation of GE-EPRI methodology [3,4,15].
Figure 1. Example of the implementation of GE-EPRI methodology [3,4,15].

Baking Effect on Desorption of Diffusible Hydrogen and Hydrogen Embrittlement on Hot-Stamped Boron

To clarify the baking effect on the desorption of diffusible hydrogen and the improvement of hydrogen embrittlement. In the case of the BH100 conditions, the diffusible hydrogen concentration decreased slightly to 0.3 wppm with 80% residual hydrogen after 30 minutes of baking. It appears that the residual diffusible hydrogen plays a role in the embrittlement in this range of hydrogen concentration.

Therefore, in the case of the BH150 conditions, the removal of diffuse hydrogen and the back-hardening effect interact to improve the hydrogen embrittlement property. For the BH150 conditions, the diffuse hydrogen was proportionally reduced as the baking time increased.

Table 1. Chemical composition of hot-press-formed steel (wt.%).
Table 1. Chemical composition of hot-press-formed steel (wt.%).

Environmentally Assisted Cracking Behavior of S420 and X80 Steels Containing U-notches at Two Different

Theoretical Overview 1. The Theory of Critical Distaces

As mentioned above, the use of the TCD in EAC analyzes has been previously presented in [20]. Half of the tests (corresponding to cathodic polarization at 5 mA/cm2) have been previously described in [20], while the other half are completely new. There is a clear notch effect and a much more moderate (but still significant) effect of the cathodic polarization level.

The values ​​of the critical distance that provides the best fit (least squares) to the experimental results (LEAC-BF) when using both PM (Eq. (11)) and LM (Eq. (12)) are also collected in Table 5. Some predictions provide essentially the same values ​​as those produced by the best fit.

Figure 1. Definition of the point method (PM) methodology. Stress (σ 1 )-distance from the notch tip (r) curves due to two different notches in fracture analysis.
Figure 1. Definition of the point method (PM) methodology. Stress (σ 1 )-distance from the notch tip (r) curves due to two different notches in fracture analysis.

Conclusions

In each case, both PM and LM were found to provide accurate predictions of KNIEAC, regardless of the material, environment, and notch radius being analyzed. Acknowledgment: The authors of this work would like to express their gratitude to the Spanish Ministry of Science and Innovation for the financial support of projects MAT2014-58738-C3-3-R and MAT2014-58443-P developed by the University of Cantabria. Cracks and Notches: Analogies and Differences of Corresponding Stress Distributions and Practical Implications in Fatigue Limit Prediction.

The stress field near a large V level of the ground tip and the application of the critical level stress intensity factor (NSIF) concept to the fracture toughness of highly brittle materials. An elasto-plastic reformulation of critical distance theory to estimate the life of toothed components failing in the low/medium cycle fatigue regime.J.

Finite Fracture Mechanics Assessment in Moderate and Large Scale Yielding Regimes

FFM Criteria

The first condition of the FFM states that the average energy available to increase the crack length l (evaluated by integrating the crack driving force Goverl) is higher than the fracture energy Gc. Assuming that the notch tip radius ρ is sufficiently small in relation to the notch depth, the stress field along the notch bisector could be expressed as [29]. Note that KV,ρIc represents the apparent generalized fracture toughness (ie, the generalized fracture toughness measured as if the V-notch were sharp): it depends on the root radius, unlike GSIF,KVI [25–27].

This value must then be inserted into the latter equation to obtain the apparent generalized fracture toughnessKV,ρIc. Note that the presence of the parameterm in Equation (7) prevents obtaining a closed-form solution for the integrand function as in [28]: In the present analysis, the integral is calculated numerically by applying an adaptive Simpson quadrature formula in a recursive manner.

Comparison with Experimental Results

Finally, Figure 7 shows the averaged FFM plots of apparent generalized fracture toughness and critical crack extension versus root radius. In this work, in the spirit of previous articles [12,16], the FFM approaches proposed by Leguillon [5] and Carpinteri et al. On the ability of the equivalent material concept in predicting the ductile failure of U-notches under conditions of moderate and severe yielding. Phys.

Application of the equivalent material concept to the prediction of ductile failure of blunt V-notches encountering moderate scale yielding.Int. Elastic-plastic fracture analysis of notched Al 7075-T6 plates using the local energy combined with the corresponding material concept. Phys.

Critical Distance Default Values for Structural Steels and a Simple Formulation to Estimate the Apparent

  • The Theory of Critical Distances
  • Materials and Methods
  • Derivation of Default Values of L and Apparent Fracture Toughness Estimations
  • Summary

For this purpose, it is proposed to use a 95% confidence level value of fracture toughness (Kmat, 0.95). Results are also shown when using the previously proposed lower bound values, which provide more conservative estimates of the material's apparent fracture toughness. Experimental values ​​of apparent fracture toughness (KmatN ) and values ​​of shear radii are normalized by the corresponding fracture toughness (Kmator Kmat, 0.95) obtained under cracked conditions and by default values ​​derived for the critical distance (Ld), respectively, representing 394 tests /Klmats in (1)mat

Application and Validation of the Notch Master Curve in Medium and High Strength Structural Steel.J. Experimental determination of fracture toughness via microscratch tests: application to polymers, ceramics and metals.J.

Feasibility Study on Application of Synchrotron Radiation μCT Imaging to Alloy Steel for

Non-Destructive Inspection of Inclusions

Material and Methods 1. Material

In this form, the maximum axial stress amplitude was obtained in the center of the neck. The voltage amplitude at the top and bottom edges of the image volume was 95% of the maximum applied voltage amplitude of the measured area. Figure 7 shows the locations of the inclusions identified from the reconstructed images before fatigue loading.

The diameter of the fatigue origin shot was about 20 μm and the Vickers hardness was 435 HV. Substituting the values ​​into the following equation for internal recording gives an estimate of the fatigue strength for the sample.

Hình ảnh

Figure 3. Optical microscope images of AFS joining parts (a,b) Metallurgical joining (c,d) Adhesive joining.
Figure 6. Appearances of Peel Fractures of two types of samples (a) Adhesive joining samples (b) Metallurgical joining samples.
Figure 9. Fatigue fracture morphology of two types of AFS (a) adhesive joining samples (b) metallurgical joining samples.
Figure 1a shows the microstructures of the steel specimen, the steel specimen had a ferrite and pearlite banded structure
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