scholarly journals Stiffness Reduction of Composite Laminates under Combined Cyclic Stresses

2001 ◽  
Vol 10 (3) ◽  
pp. 096369350101000 ◽  
Author(s):  
T. P. Philippidis ◽  
A. P. Vassilopoulos
Keyword(s):  
Normal Stress ◽  
Composite Laminates ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Cyclic Stress ◽  
Fibre Direction ◽  
Cyclic Stresses ◽  
Stiffness Reduction ◽  
Stress States ◽  
Modulus Reduction

Stiffness reduction due to fatigue of a [0/(±45)2/0]T Glass/Polyester (GRP) laminate under combined cyclic stress is investigated in this experimental study. Stress states combining all three components of in-plane stress tensor are induced by uniaxially testing specimens cut off-axis at various angles from the principal material coordinate system. Modulus reduction is related to the various failure modes exhibited under different states of combined stress. It is verified that shear and transverse normal stress induce more severe stiffness degradation compared to stress states where normal stress in the main fibre direction is dominant. For every loading condition and stress state, it is observed in general that stiffness decrease is more pronounced under lower stress levels than these inducing low cycle fatigue.

A Damage Model Containing Delamination in Composite Laminates

2006 ◽  
Vol 324-325 ◽  
pp. 43-46
Author(s):  
Yu Pu Ma ◽  
Xin Zhi Lin ◽  
Qing Fen Li ◽  
Zhen Li
Keyword(s):  
Composite Laminates ◽  
Damage Model ◽  
Laminated Composite ◽  
Shear Lag ◽  
Analysis Model ◽  
Transverse Cracks ◽  
Transverse Cracking ◽  
Stiffness Reduction ◽  
Laminated Composite Materials ◽  
Modulus Reduction

When stress is high, delaminate damage can be induced by transverse cracks. A complete parabolic shear-lag damage model containing delamination induced by transverse cracks is therefore proposed and applied to predict the stiffness reduction by transverse cracking in cross-ply laminated composite materials. The predictions of the complete parabolic shear-lag analysis model, the incomplete parabolic shear-lag analysis model, and the complete parabolic shear-lag damage model containing delamination proposed in this paper have been compared. Results show that the young’s modulus reduction values obtained by our analysis model are better agreement with the experimental ones than other models.

scholarly journals An extended invariant approach to laminate failure of fibre-reinforced polymer structures

2022 ◽  
pp. 1-24
Author(s):  
G. Corrado ◽  
A. Arteiro ◽  
A.T. Marques ◽  
J. Reinoso ◽  
F. Daoud ◽  
...  
Keyword(s):  
Composite Laminates ◽  
Composite Structures ◽  
Failure Modes ◽  
Three Dimensional ◽  
Failure Criteria ◽  
Design Tool ◽  
Advanced Composite Materials ◽  
Failure Envelopes ◽  
Out Of Plane ◽  
Stress States

Abstract This paper presents the extension and validation of omni-failure envelopes for first-ply failure (FPF) and last-ply failure (LPF) analysis of advanced composite materials under general three-dimensional (3D) stress states. Phenomenological failure criteria based on invariant structural tensors are implemented to address failure events in multidirectional laminates using the “omni strain failure envelope” concept. This concept enables the generation of safe predictions of FPF and LPF of composite laminates, providing reliable and fast laminate failure indications that can be particularly useful as a design tool for conceptual and preliminary design of composite structures. The proposed extended omni strain failure envelopes allow not only identification of the controlling plies for FPF and LPF, but also of the controlling failure modes. FPF/LPF surfaces for general 3D stress states can be obtained using only the material properties extracted from the unidirectional (UD) material, and can predict membrane FPF or LPF of any laminate independently of lay-up, while considering the effect of out-of-plane stresses. The predictions of the LPF envelopes and surfaces are compared with experimental data on multidirectional laminates from the first and second World-Wide Failure Exercise (WWFE), showing a satisfactory agreement and validating the conservative character of omni-failure envelopes also in the presence of high levels of triaxiality.

Probabilistic Predictions for Piping Fatigue Including the Effects of Ultrasonic Examinations

2003 ◽  
Author(s):  
F. A. Simonen
Keyword(s):  
Crack Initiation ◽  
Fatigue Cracks ◽  
Wall Stress ◽  
Cyclic Stress ◽  
Ferritic Steels ◽  
Cyclic Stresses ◽  
Stress Cycles ◽  
Low Levels ◽  
Stress States ◽  
Failure Probabilities

This paper presents a methodology for estimating failure probabilities of piping welds that experience cyclic stresses and that are subject to ultrasonic examinations designed to detect growing fatigue cracks. Fatigue cracks can start as either preexisting fabrication flaws or as cracks initiated after an accumulation of stress cycles. Low levels of cyclic stresses and/or small numbers of cycles produce low failure probabilities, with the failures caused mainly by fabrication flaws. More severe cyclic stress conditions produce higher failure probabilities, with the failures caused mainly by fatigue cracks that initiate during the life of the component. Numerical results are presented to address both crack initiation and crack growth. The calculations cover both stainless and ferritic steels, inservice inspections with different inspection intervals, and stress states with and without high levels of through-wall stress gradients. It is shown that effective inspection programs can significantly reduce failure probabilities, and that such programs require suitable NDE sensitivities and adequate inspection frequencies.

Low Cycle Fatigue Crack Initiation of Rotating Structures Under Biaxial Stress States

2009 ◽  
Author(s):  
Chao Zhang
Keyword(s):  
Stress State ◽  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Cyclic Stress ◽  
Biaxial Stress ◽  
Test Results ◽  
Primary Stress ◽  
Biaxial Stress State ◽  
Fatigue Characteristics ◽  
Stress States

Rotating structures can experience biaxial stress states with a wide range of biaxiality ratios on structure surfaces. Low cycle fatigue (LCF) crack initiation in such conditions demonstrates different fatigue characteristics in terms of crack orientation, fatigue life, etc. The biaxial stress states can be categorized into two types: in-phase and out-of-phase under which fatigue characteristics can be significantly different according to rig test results. This paper presents an investigation of LCF crack initiation under in-phase and out-of-phase biaxial stress states based on rig test results of a nickel alloy. The crack orientations are reviewed and discussed at different stress states. Relations of biaxial LCF life debit factor vs biaxiality ratio are derived (the debit factor is defined as a ratio of the LCF life at a biaxial stress state to the LCF life at corresponding uniaxial stress state which has same cyclic and mean stresses as the primary cyclic and mean stressees of the biaxial stress state). The rig test results showed that the crack orientation is usually normal to the primary stress vector under in-phase biaxial stress states but is inclined to the primary stress vector under out-of-phase stress states. As per the derived biaxial LCF life debit factors, the LCF life was found to be slightly reduced with increasing biaxiality ratios under in-phase biaxial stress states but significantly reduced under out-of-phase biaxial stress states compared with corresponding uniaxial primary stress states. The equivalent cyclic stress fatigue criterion is also employed to theoretically model the biaxial LCF life debit factor under in-phase biaxial stress states. The hydrostatic cyclic stress is included in the equivalent cyclic stress in order to take into account the hydrostatic cyclic pressure effects. The equivalent cyclic stress in the criterion can physically reflect the materials’ ductility reduction under in-phase multiaxial stress states.

Modeling and Simulation of the Failure and Stiffness Degradation of a Graphite Epoxy in a Three Point Bending Test

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
E. H. Irhirane ◽  
M. Abousaleh ◽  
J. Echaabi ◽  
M. Hattabi ◽  
A. Saouab ◽  
...  
Keyword(s):  
Composite Laminates ◽  
Experimental Approach ◽  
Failure Modes ◽  
Failure Criteria ◽  
Bending Test ◽  
Geometrical Parameters ◽  
Three Point Bending ◽  
Stiffness Reduction ◽  
Biaxial Tests ◽  
Macroscopic Failure

The use of composite materials with continuous fibers in the aeronautic and aerospace industries requires reliable and precise methods for the prediction of failure. Predicting failure stresses and failure modes in composite laminates is very difficult. The choice between failure criteria is complex, and there is a lack of experimental study to validate the result obtained partly because the biaxial tests are still difficult to perform. This work employs a mixed methodology based on a theoretical and an experimental approach to develop a procedure for the choice and the validation of the failure criterion. The comparison is concerned not only with the macroscopic failure but also with the succession of the failure, the failure mode, and the effect of the geometrical parameters of the test specimen. The most general failure criteria are tested by using two approaches of the stiffness reduction. A finite element code has been elaborated within our laboratory for postfailure treatment. The numerical simulation results are compared with the experimental ones and permit us to make a conclusion on the validity of the failure criteria used.

scholarly journals The Bending Responses of Sandwich Panels with Aluminium Honeycomb Core and CFRP Skins Used in Electric Vehicle Body

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Yong Xiao ◽  
Yefa Hu ◽  
Jinguang Zhang ◽  
Chunsheng Song ◽  
Xiangyang Huang ◽  
...  
Keyword(s):  
Electric Vehicle ◽  
Failure Modes ◽  
Sandwich Panels ◽  
Vehicle Body ◽  
Stacking Sequence ◽  
Honeycomb Core ◽  
Fibre Direction ◽  
Element Analysis ◽  
Honeycomb Sandwich ◽  
Carbon Fibre Reinforced Plastic

The aim of this paper was to investigate bending responses of sandwich panels with aluminium honeycomb core and carbon fibre-reinforced plastic (CFRP) skins used in electric vehicle body subjected to quasistatic bending. The typical load-displacement curves, failure modes, and energy absorption are studied. The effects of fibre direction, stacking sequence, layer thickness, and loading velocity on the crashworthiness characteristics are discussed. The finite element analysis (FEA) results are compared with experimental measurements. It is observed that there are good agreements between the FEA and experimental results. Numerical simulations and experiment predict that the honeycomb sandwich panels with ±30° and ±45° fibre direction, asymmetrical stacking sequence (45°/−45°/45°/−45°), thicker panels (0.2 mm∼0.4 mm), and smaller loading velocity (5 mm/min∼30 mm/min) have better crashworthiness performance. The FEA prediction is also helpful in understanding the initiation and propagation of cracks within the honeycomb sandwich panels.

The Revised Universal Slope Method to Predict the Low-Cycle Fatigue Lives of Elbow and Tee Pipes

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Hiun Nagamori ◽  
Koji Takahashi
Keyword(s):  
Experimental Data ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Experimental Studies ◽  
High Accuracy ◽  
Universal Method ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Slope Method ◽  
Stress States

The stress states of elbow and tee pipes are complex and different from those of straight pipes. The low-cycle fatigue lives of elbows and tees cannot be predicted by Manson's universal slope method; however, a revised universal method proposed by Takahashi et al. was able to predict with high accuracy the low-cycle fatigue lives of elbows under combined cyclic bending and internal pressure. The objective of this study was to confirm the validity of the revised universal slope method for the prediction of low-cycle fatigue behaviors of elbows and tees of various shapes and dimensions under conditions of in-plane bending and internal pressure. Finite element analysis (FEA) was carried out to simulate the low-cycle fatigue behaviors observed in previous experimental studies of elbows and tees. The low-cycle fatigue behaviors, such as the area of crack initiation, the direction of crack growth, and the fatigue lives, obtained by the analysis were compared with previously obtained experimental data. Based on this comparison, the revised universal slope method was found to accurately predict the low-cycle fatigue behaviors of elbows and tees under internal pressure conditions regardless of differences in shape and dimensions.

Identification of Failure Modes Under Design Extension Conditions

2015 ◽  
Author(s):  
Naoto Kasahara ◽  
Izumi Nakamura ◽  
Hideo Machida ◽  
Hitoshi Nakamura ◽  
Koji Okamoto
Keyword(s):  
High Temperature ◽  
Nuclear Power ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
External Pressure ◽  
Lessons Learned ◽  
Local Failure ◽  
Severe Accident ◽  
Mitigation Measures ◽  
Loading Mode

As the important lessons learned from the Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure became essential against severe accident and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premise under design extension conditions such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, best estimation for these failure modes are required for preparing countermeasures and management. Therefore, this study focused on identification of failure modes under design extension conditions. To observe ultimate failure behaviors of structures under extreme loadings, new experimental techniques were adopted with simulation materials such as lead and lead-antimony alloy, which has very small yield stress. Postulated failure modes of main components under design extension conditions were investigated according three categories of loading modes. The first loading mode is high temperature and internal pressure. Under this mode, ductile fracture and local failure were investigated. At the structural discontinuities, local failure may become dominant. The second is high temperature and external pressure loading mode. Buckling and fracture were investigated. Buckling occurs however hardly break without additional loads or constraints. The last loading is excessive earthquake. Ratchet deformation, collapse, and fatigue were investigated. Among them, low-cycle fatigue is dominant.

scholarly journals Hysteretic Behavior of Geopolymer Concrete with Active Confinement Subjected to Monotonic and Cyclic Axial Compression: An Experimental Study

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 3997 ◽  
Author(s):  
Huailiang Wang ◽  
Yuhui Wu ◽  
Min Wei ◽  
Lang Wang ◽  
Baoquan Cheng
Keyword(s):  
Failure Modes ◽  
Peak Stress ◽  
Hysteretic Behavior ◽  
Stress And Strain ◽  
Geopolymer Concrete ◽  
Cement Concrete ◽  
Cyclic Compression ◽  
Stress States ◽  
Loading Modes ◽  
Good Agreement

This paper investigated the performance of actively confined geopolymer concrete (GPC) through experiments. The mechanical properties of GPC under triaxial stress states were analyzed and discussed from the prospects of failure modes, axial peak stress and strain, monotonic and cyclic constitutive relationships. The experimental results demonstrated that the loading modes (monotonic loading and cyclic loading) had little effect on the failure mode and axial peak stress and strain. The improvement of the strength and ductility of GPC with the increase in confinement level was consistent with that of the conventional cement concrete while the strain enhancement of confined GPC was lower than that of confined conventional cement concrete at the same confinement level. The curves of the monotonic stress–strain and the envelop of cyclic compression were predicted through Mander’s model with good accuracy. The unloading/reloading models proposed by Lokuge were modified and the predicted cyclic hysteresis curves for actively confined GPC were in good agreement with the cyclic compression results. Findings from this study provide references for the application of geopolymer concrete.

scholarly journals Numerical Modeling of the Degradation of the Normal Stress Under Large Number of Shearcycles

2021 ◽  
Vol 31 (3) ◽  
pp. 118-133
Author(s):  
Assia Bellayoune ◽  
Salah Messast ◽  
Marc Boulon
Keyword(s):  
Numerical Modeling ◽  
Normal Stress ◽  
Horizontal Stress ◽  
Cyclic Stress ◽  
Simple Expression ◽  
Shear Tests ◽  
Cyclic Shear ◽  
Explicit Formulation ◽  
Number Of Cycles

Abstract The evaluation of friction is an important element in the verification of stability and the determination of the bearing capacity of piles. In the case of cyclic stress, the soil-pile interface has a relaxation which corresponds to a fall in the horizontal stress which represents the normal stress at the lateral surface of the pile. This paper presents an explicit formulation to express the degradation of the normal stress after a large number of shear cycles as a function of cyclic parameters. In this study we are interested in the exploitation of the cyclic shear tests carried out by Pra-ai [1] with imposed normal rigidity (CNS) in order to demonstrate the phenomenon of falling of the normal stress. The approach presented in this paper consists in proposing a simple expression for estimating the degradation of normal stress as a function of cyclic shear parameters after a large number of cycles. The validation of this approach is verified by the application of this formulation to a real case where the comparison of the simulations made by this approach with those recorded on site shows the good adaptation of this approach to this type of problems.

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