An improved collapse axis on the R6 FAD for combined tension and bending loading

1993 ◽  
Vol 28 (1) ◽  
pp. 23-29
Author(s):  
N ø Kristiansen ◽  
C E Turner
Keyword(s):  
Plastic Hinge ◽  
Constraint Factor ◽  
True Path ◽  
Loading System ◽  
Edge Notch ◽  
Path Lengths ◽  
The Moment ◽  
Moment Load ◽  
Bending Loading ◽  
Linear Loading

Experimental and computational studies were made of a number of single edge notch (SEN) specimens loaded through eccentric pins with notch depth ratios 0.21 and 0.52. It was found that as the applied load was increased the formation of a plastic hinge mechanism caused the ligament to shift sideways and in turn alter the ratio of bending to tension loading. The two different assumptions, constant and variable bending to tension ratio, gave very different paths in the moment-load ( M-Q) space, and failure lines when plotted on the R6 Fracture Analysis Diagram (FAD). An improved expression for normalized load, Sr, for SEN geometries under a linear loading system was obtained by including a plastic constraint factor in the uncreacked lower bound solution. For the pin-loaded SEN specimens under a non-linear loading system, it was shown that Sr based on ‘true path lengths’ in the yield diagram gave a failure curve which was in good agreement with the R6 Rev3 solution.

Fatigue and Crack Growth in 7050-T7451 Aluminum Alloy Under Constant- and Variable-Amplitude Loading

2012 ◽  
Author(s):  
James C. Newman ◽  
Justin W. Shaw ◽  
Balkrishna S. Annigeri ◽  
Brett M. Ziegler
Keyword(s):  
Crack Growth ◽  
Crack Closure ◽  
Constraint Factor ◽  
Wide Range ◽  
Single Spike ◽  
Edge Notch ◽  
High Crack ◽  
Stress Ratios ◽  
Low Constraint ◽  
Life Predictions

The 7050 aluminum alloy is used in many aerospace structural applications. Previous studies have identified that fatigue cracks develop very rough crack-surface profiles, which cause very high crack-closure levels due to a combination of plasticity, roughness and debris. Previously, tests were conducted on compact, C(T), specimens to generate crack-growth data from threshold to near fracture over a wide range in stress ratios (R). New threshold testing methods, based on compression precracking, were used to generate the data in the near-threshold regime. The plasticity-induced crack-closure model, FASTRAN, was used to correlate the data over a wide range in stress ratios and crack-growth rates from threshold to near fracture. To account for the very high crack-closure levels, a very low constraint factor, like plane-stress conditions, had to be used in the model. In addition, the crack-opening loads were measured during these tests using a local strain-gage method to generate another ΔKeff-rate curve. These two curves differed only in the near-threshold regime. Herein, fatigue-crack-growth tests were conducted on C(T) specimens under spike overloads and simulated aircraft spectrum loading. Also, fatigue tests were conducted on single-edge-notch bend, SEN(B), specimens over a wide range in loading conditions (constant amplitude and three aircraft spectra). All specimens were machined from a single forged block of 7050-T7451. However, no residual stresses were measured in both the SEN(B) and C(T) specimens. Two European standard spectra were used, but modified to have only tension-tension loading. The purpose of this paper was to evaluate the two different effective stress-intensity factor curves for making crack-growth and fatigue-life predictions. Small-crack theory was used to make fatigue-life predictions using inclusion-particle sizes from the literature. Fatigue predictions on the SEN(B) specimens agreed fairly well (± 30%) using a 12-micrometer semi-circular initial flaw located at the semicircular-edge notch under all loading conditions, except the model was unconservative (factor of 3) on one of the severe aircraft spectra (Mini-TWIST+, Level 1). For the C(T) specimens subjected to single-spike overloads, the life-prediction code produced much more retardation than observed in the tests. However, the predicted crack-length-against-cycles under the Mini-Falstaff+ spectrum were only about 15% longer than the tests. The discrepancy under the single-spike overloads and the severe aircraft spectra was suspected to be caused by the low constraint factor and/or crack paths meandering around overload plastic zones. Ideally, a roughness-induced crack-closure model, in addition to the plasticity model, would be needed to obtain more reasonable results.

Plastic Rotational Factor Calculation for Shallow-Notched SE(B) Specimens

2014 ◽  
Vol 783-786 ◽  
pp. 2322-2326 ◽  
Author(s):  
Yoichi Kayamori ◽  
Takehiro Inoue ◽  
Yukito Hagihara
Keyword(s):  
Plastic Hinge ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Edge Notch ◽  
New Equation ◽  
Hinge Model ◽  
Testing Standards ◽  
Crack Tip Opening ◽  
Rotational Factor

The plastic part of crack tip opening displacement (CTOD) is derived from the plastic hinge model for deep-notched single edge-notch bend (SE(B)) specimens in BS, WES and ISO CTOD testing standards, and a typical plastic rotational factor is given by a constant value of 0.4. This value is appropriate for deep-notched SE(B) specimens, but is not suitable for shallow-notched SE(B) specimens. In this study, a new equation of calculating the plastic rotational factor was obtained by using the Electric Power Research Institute (EPRI) scheme. The equation shows the effect of crack length and strain hardening on the plastic rotational factor, and is useful for evaluating CTOD in shallow-notched SE(B) specimens.

Evaluation of material failure under a linear loading system

1981 ◽  
Vol 13 (7) ◽  
pp. 821-827
Author(s):  
P. V. Tikhomirov ◽  
S. P. Yushanov
Keyword(s):  
Material Failure ◽  
Loading System ◽  
Linear Loading

scholarly journals Stiffness characteristics and thermal deformations of the frame of high power marine engine

2007 ◽  
Vol 14 (1) ◽  
pp. 16-22 ◽  
Author(s):  
Lech Murawski ◽  
Marek Szmyt
Keyword(s):  
High Power ◽  
Thermal Deformation ◽  
Parallel Displacement ◽  
Marine Engine ◽  
Shaft Line ◽  
Thermal Deformations ◽  
Stiffness Characteristics ◽  
The Moment ◽  
Moment Load ◽  
Deformation Models

Stiffness characteristics and thermal deformations of the frame of high power marine engine In the subject-matter literature detail data on stiffness of the crankshaft foundation connected with the frame of marine main engine are still lacking. Thermal deformation models of the engine's casing, proposed by engine producers, are excessively simplified. However the parameters are crucial for the shaft-line alignment analysis as well as for the analysis of interactions between the shaft-line and engine crankshaft, especially in the case of high power engines. This paper presents a determination method of the marine engine body characteristics as well as results of example computations performed for a Sulzer 7 RTA 84 C engine installed on a ~3000 TEU container ship. It has been demonstrated that the producer's assumption about parallel displacement of the crankshaft axis in thermal working conditions is too rough. The thermal deformation of the engine is of hogging character, which results in significant change of the moment load exerted on the crankshaft and shaft line. The stiffness parameters recommended by the producers for the shaft-line alignment are estimated correctly, however they represent only engine's body flexibility, without taking into account ship's hull flexibility.

scholarly journals ADVANCED ANALYSIS OF STEEL FRAMES WITH EFFECTS OF JOINT DEFORMABILITY AND PARTIAL STRENGTH ACCOUNTED FOR

2004 ◽  
Vol 10 (3) ◽  
pp. 199-208
Author(s):  
Marian A. Gizejowski ◽  
Czeslaw J. Branicki ◽  
Anna M. Barszcz ◽  
Pawel Krol
Keyword(s):  
Plastic Hinge ◽  
Joint Stiffness ◽  
Initial Stiffness ◽  
Frame Design ◽  
Case Study Analysis ◽  
In Series ◽  
Advanced Analysis ◽  
Section Type ◽  
The Moment ◽  
Welding Processes

The paper summarises the current progress in methods of advanced analysis for design of frames with semirigid joints. The methods presented in the paper belong to general second‐order refined plastic‐hinge methods that allow for the combined effects of joint stiffness degradation and distributed plasticity along the member length as well as across the member sections. The advanced analysis for steel frame design, proposed by the authors, is based on the spring‐in‐series model. The effect of joint semi‐rigidity and partial strength is taken care of by specifying certain values of the initial stiffness, ultimate moment and the shape factor of the moment‐rotation characteristic for the spring representing the joint. The effect of imperfections affecting the performance of imperfect structural members in compression is modelled by the application of a simplified tangent modulus concept combined with the reduction of the initial value of the elasticity modulus. The effect of residual stresses is taken care of by specifying certain values of the shape parameter for the moment‐rotation characteristic of the spring representing the gradual yielding of the member. It is dependent upon the cross‐section type and fabrication method (ie upon the residual stress pattern resulting from rolling or welding processes). A case study analysis is presented. Concluding remarks referring to the application of advanced analysis in design, pertaining to the study case considered, are drawn.

Fatigue and Crack Growth in 7050-T7451 Aluminum Alloy Under Constant- and Variable-Amplitude Loading

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
James C. Newman, ◽  
Justin W. Shaw ◽  
Balkrishna S. Annigeri ◽  
Brett M. Ziegler
Keyword(s):  
Crack Growth ◽  
Crack Closure ◽  
Constraint Factor ◽  
Wide Range ◽  
Single Spike ◽  
Edge Notch ◽  
High Crack ◽  
Stress Ratios ◽  
Low Constraint ◽  
Life Predictions

The 7050 aluminum alloy is used in many aerospace structural applications. Previous studies have identified that fatigue cracks develop very rough crack-surface profiles, which cause very high crack-closure levels due to a combination of plasticity, roughness and debris. Previously, tests were conducted on compact, C(T), specimens to generate crack-growth-rate data from threshold to near fracture over a wide range in stress ratios (R). New threshold testing methods, based on compression precracking, were used to generate the data in the near-threshold regime. The plasticity-induced crack-closure model, FASTRAN, was used to correlate the data over a wide range in stress ratios and crack-growth rates from threshold to near fracture. To account for the very high crack-closure levels, a very low constraint factor, like plane-stress conditions, had to be used in the model. In addition, the crack-opening loads were measured during these tests using a local strain-gauge method to generate another ΔKeff-rate curve. These two curves differed only in the near-threshold regime. Herein, fatigue-crack-growth tests were conducted on C(T) specimens under spike overloads and simulated aircraft spectrum loading. Fatigue tests were also conducted on single-edge-notch bend (SEN(B)), specimens over a wide range in loading conditions (constant amplitude and three aircraft spectra). All specimens were machined from a single forged block of 7050-T7451. However, no residual stresses were measured in both the SEN(B) and C(T) specimens. Two European standard spectra were used, but modified to have only tension-tension loading. The purpose of this paper was to evaluate the two different effective stress-intensity factor curves for making crack-growth and fatigue-life predictions. Small-crack theory was used to make fatigue-life predictions using inclusion-particle sizes from the literature. Fatigue predictions on the SEN(B) specimens agreed fairly well (±30%) using a 12-micrometer semicircular initial flaw located at the semicircular-edge notch under all loading conditions, except the model was unconservative (factor of three) on one of the severe aircraft spectra (Mini-TWIST+, Level 1). For the C(T) specimens subjected to single-spike overloads, the life-prediction code also produced much more retardation than observed in the tests. However, the predicted crack-length-against-cycles under the Mini-Falstaff+ spectrum were only about 15% longer than the tests. The discrepancy under the single-spike overloads and the severe aircraft spectra was suspected to be caused by the low constraint factor and/or crack paths meandering around overload plastic zones. Ideally, a roughness-induced crack-closure model; in addition to the plasticity model, would be needed to obtain more reasonable results.

scholarly journals Cyclic Loading Performance of Radius-Cut Double Coke-Shaped Strip Dampers

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 3920
Author(s):  
Jaehoon Bae ◽  
Chang-Hwan Lee ◽  
Minjae Park ◽  
Robel Wondimu Alemayehu ◽  
Jaeho Ryu ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Plastic Hinge ◽  
Seismic Retrofitting ◽  
Width Ratio ◽  
Reduced Beam Section ◽  
Moment Distribution ◽  
Sufficient Energy ◽  
Loading Tests ◽  
The Moment ◽  
Cyclic Loading Tests

Conventional slit dampers are widely used for the purpose of seismic retrofitting, however, the structure of these dampers is susceptible to fractures, due to stress concentration at the ends of the strips in the event of large earthquakes. To address this issue, a novel radius-cut coke-shaped strip damper featuring improved ductility is proposed herein. This damper was developed based on the moment distribution over the strip when both its ends were constrained. The height-to-width ratio of the strip was increased to induce bending rather than shear deformation, and the reduced beam section method was employed. A radius-cut section was used to intentionally focus the stress to induce the plastic hinge. This reduced the fracture fragility of the specimen, resulting in an increased inelastic deformation capacity. Cyclic loading tests were conducted to verify damping performance against earthquakes. Experiments and finite element analyses proved that the coke-shaped damper exhibits improved ductility. The final fracture occurred in the radius-cut section after sufficient energy dissipation during cyclic loading. The results also indicated further improvements in strength due to the membrane effect under cyclic loading, caused by the tensile resistance of the strip due to its constrained ends.

scholarly journals Research on Control Algorithm of Electric Linear Loading System

2018 ◽  
Vol 220 ◽  
pp. 08007
Author(s):  
Jianjie Lei ◽  
Yuanxun Fan ◽  
Weidong Pan ◽  
Dejia Tang ◽  
Jian Tao ◽  
...  
Keyword(s):  
Control Algorithm ◽  
Fuzzy Controller ◽  
Dynamic Performance ◽  
Reference Value ◽  
Response Speed ◽  
Ball Screw ◽  
Current Loop ◽  
System Combination ◽  
Loading System ◽  
Linear Loading

This paper mainly focused on the problems of low loading accuracy in electric linear loading system, Firstly, the mathematical model is done on loading motor, loading motor driver and ball screw in the system. Then, the current loop proportional control is introduced, which improves the response speed of the load motor; In order to improve the loading accuracy and restrain excess force, a parallel algorithm based on fuzzy PID and repetitive control is designed in the force loop. The fuzzy controller improves the dynamic performance and anti-interference ability of the system. The repetitive controller periodically adjusts the deviation, which reduces the steady-state error of the system. Combination of the two controller results in good dynamic and static characteristics. The simulation results show that the proposed control algorithm is feasible, which has a certain engineering reference value.

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