scholarly journals Experimental and numerical investigation of strain distribution of notched lead fatigue test specimen

2018 ◽  
Vol 165 ◽  
pp. 05003 ◽  
Author(s):  
Audun Johanson ◽  
Luigi Mario Viespoli ◽  
Bård Nyhus ◽  
Antonio Alvaro ◽  
Filippo Berto
Keyword(s):  
Fatigue Test ◽  
Strain Distribution ◽  
Fatigue Testing ◽  
Cyclic Fatigue ◽  
Image Correlation ◽  
Power Cable ◽  
Valuable Insight ◽  
3D Fem ◽  
Element Analysis ◽  
Stress Concentrators

The work here presented focuses on the test methodology related to effect of stress concentrators in strain controlled structures. Cable sheathing as used in subsea power cables are investigated by cyclic fatigue testing, Digital Image Correlation (DIC) and 3D Finite Element Analysis. Focus is put on the strain distribution in conventional specimen geometries and under the presence of artificial notches. It is evident that standardized fatigue testing provides limited input to the final fatigue life of strain controlled power cable sheathing both accounting for expected and unintended stress concentrators. The limitations can be explained by measured strain distribution inherent in most fatigue test specimens. The use of DIC and 3D FEM provides valuable insight into both the theoretical and practical stress and strain distribution. This can help in understanding and overcoming geometrical test constraints, when compared to the actual component loading mode.

scholarly journals Towards a Planar Cruciform Specimen for Biaxial Characterisation of Polymer Matrix Composites

2010 ◽  
Vol 24-25 ◽  
pp. 115-120 ◽  
Author(s):  
Michael R.L. Gower ◽  
Richard M. Shaw
Keyword(s):  
Strain Distribution ◽  
Stress Raiser ◽  
Test Method ◽  
Image Correlation ◽  
Strain Gauges ◽  
Test Machine ◽  
Element Analysis ◽  
Full Field ◽  
Cruciform Specimen ◽  
Gauge Section

This paper details work undertaken towards the development of a standard test method for the biaxial response of planar cruciform specimens manufactured from carbon fibre-reinforced plastic (CFRP) laminates and subject to tension-tension loading. Achieving true biaxial failure in a cruciform specimen without the need for the inclusion of a stress raiser, such as a hole, in the gauge-section, is a subject attracting much research globally and is by no means a trivial exercise. Coupon designs were modelled using finite element analysis (FEA) in order to predict the stress and strain distributions in the central region of the specimen. An Instron biaxial strong-floor test machine was used to test the specimens. Strain gauges were used to measure the strain in the specimen arms and to assess the degree of bending. Digital image correlation (DIC) was used to measure the full-field strain distribution in the central gauge-section of the specimen and this was compared to values measured using strain gauges. The strain readings obtained from strain gauges, DIC and FEA predictions were in good agreement and showed that the strain distribution was uniform in the central gauge-section, but that strain concentrations existed around the tapered thickness zone. These regions of strain concentration resulted in interlaminar failure and delamination of the laminate propagating into the specimen arms.

Method for Fatigue Testing of Subsea Wellhead Connector Segments

2020 ◽  
Author(s):  
Pedro Barros ◽  
Agnes Marie Horn ◽  
Anders Wormsen ◽  
Per Osen ◽  
Kenneth A. Macdonald
Keyword(s):  
Fatigue Testing ◽  
Primary Objective ◽  
Full Scale ◽  
Test Method ◽  
Image Correlation ◽  
Stress Fields ◽  
Element Analysis ◽  
Test Fixture ◽  
Drilling Rig ◽  
The Coefficient Of Friction

Abstract For subsea well drilling, the drilling rig is connected to the subsea well by a marine riser and subsea BOP equipped with a remotely controlled wellhead connector latched onto the subsea wellhead profile. The level of cyclic loading on subsea wellheads is steadily increasing due to use of increasingly larger drilling rigs with larger BOPs, the drilling of wells in harsher environments characterized by strong high waves. The remotely controlled wellhead connector forces a series of locking dogs into an externally machined profile on the wellhead. This external profile is generally referred to as a wellhead profile. The fatigue resistance of this safety-critical connection is typically estimated by FE analysis. Due to the large size of the equipment, and high cost of testing, very limited fatigue testing, if any, has been carried out. A test method has therefore been developed, where a special test fixture is used to apply realistic boundary conditions and variable tensile loads to a small sector or segment of a wellhead connector. A primary objective is to generate fatigue-critical stress fields in the segments under tensile test load that closely replicates the stress fields in a full-scale connector subject to bending loads. A secondary objective is to support the introduction of the practice of testing several segments cut from a single wellhead connector. The testing of narrow sector segments allows the use of readily available test apparatus. It is thereby envisaged that the total cost of testing (specimens and test laboratory costs) can be substantially reduced in comparison with full-scale connector fatigue testing. This paper describes the text fixture, the connector locking dog, and wellhead segments designed to replicate the stress fields in a full-scale wellhead connector. The test fixture and test specimens are designed to match conditions and fatigue stress of the full-scale connector. The test specimens are instrumented with strain gauges at fatigue hotspots. Digital image correlation (DIC) is used to measure the relative motion between the wellhead segment and the locking dog. The measured strains are compared with corresponding values from finite element analysis of the test. The DIC results are also used for estimating the coefficient of friction between wellhead profile and locking dog. Very good agreement is found between measured hotspot strains and strains from the FE analyses for consistent load conditions. The test fixture is therefore considered suitable for segment fatigue testing, where the test results can be used to estimate the bending fatigue capacity of a full-scale wellhead connector. Results from fatigue testing by this test method are presented in a separate OMAE2020 paper.

Characterization and Validation of Fatigue Strains for Superelastic Nitinol using Digital Image Correlation

2021 ◽  
Author(s):  
Koray Senol ◽  
Hengchu Cao ◽  
Sakya Tripathy
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Digital Image Correlation ◽  
Strain Amplitude ◽  
Digital Image ◽  
Fatigue Testing ◽  
Image Correlation ◽  
Element Analysis ◽  
Local Material ◽  
Mean Strain

Abstract Fatigue is a major challenge encountered in cardiovascular implant design. While the properly heat-treated Nitinol can exhibit up to 6-7% recoverable strains allowing for minimally invasive transcatheter delivery of cardiovascular implants, the cyclic in-vivo loading can cause premature fracture of the implant if the fatigue strain is too high. Strain-based criteria have been adopted for the development of Nitinol fatigue resistance. Lacking experimental tools to characterize the local material fatigue strain, fatigue testing of Nitinol specimens has largely relied on the finite element analysis to compute the cyclic strain amplitude and mean strain based on experimentally derived constitutive parameters using phenomenological strain energy theory. Without a consistent computational standard, previous works have resulted in controversy and inconsistency in the impact of mean strain on the fatigue resistance of Nitinol in terms of strain amplitude limit at high cycle fatigue regime. In this paper, digital image correlation (DIC) technique is used to experimentally determine local material strains of Nitinol fatigue specimens using monotonic and cyclic loading conditions. These local strains are compared with strains computed from finite element analysis. It was found that strains from DIC and FEA are comparable in the single-phase states (pure austenitic or martensitic), whereas the measured strains can show significant difference from simulation computed strain during the transformation stage where both austenite and martensite phase co-exist. These observations have significant implications to nitinol fatigue testing and implant reliability assessment.

scholarly journals Fatigue Test of Low-Cost Flexible-Shank Monolimb Trans-Tibial Prosthesis

2006 ◽  
Vol 30 (3) ◽  
pp. 305-315 ◽  
Author(s):  
Winson C. C. Lee ◽  
Ming Zhang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Fatigue Test ◽  
Structural Integrity ◽  
Static Load ◽  
Fatigue Testing ◽  
Structural Strength ◽  
Low Cost ◽  
Element Analysis ◽  
Thermoplastic Material

Monolimb refers to a kind of trans-tibial prostheses with the socket and shank moulded into one piece of thermoplastic material. If properly designed, the shank of a monolimb can deflect which may compensate for the lost ankle plantarflexion and dorsiflexion to some extent. However, provision of shank flexibility is usually accompanied by reduced structural strength of the entire prosthesis. In the recent work using finite element analysis and the Taguchi method, the dimensions of the shank for the monolimb were derived which aimed at giving high shank flexibility and reasonable strength to resist static load. Yet, fatigue testing has not been performed. Fatigue failure may happen when a relatively low level of load is applied repeatedly. This study aimed to document the fatigue life of two flexible-shank monolimbs, by applying cyclic force of 800 N at the forefoot region for 500,000 cycles. Results showed that the design of the foot bolt adaptor played an important role in the structural integrity of the monolimb. One monolimb completed the fatigue test of 500,000 cycles without visual material yield, but with 3.8° change in dorsiflexion angle when the load was removed.

Analysis of Static Stress in an Alloy Wheel of the Passengercar

2015 ◽  
Vol 16 ◽  
pp. 17-25 ◽  
Author(s):  
S. Nallusamy ◽  
N. Manikanda Prabu ◽  
K. Balakannan ◽  
Gautam Majumdar
Keyword(s):  
Fatigue Life ◽  
Aluminium Alloy ◽  
Fatigue Test ◽  
Fatigue Testing ◽  
Testing Machine ◽  
Manufacturing Companies ◽  
Passenger Cars ◽  
Element Analysis ◽  
Static And Dynamic Analysis ◽  
Alloy Wheel

The vehicle may be towed without the engine but it is not possible without the wheels. Road wheel is a significant structural member of the vehicular suspension system that supports the static and dynamic loads encountered during vehicle operation. As in the case of an automobile wheel maximum load is applied on the alloy wheel. Proper analysis of the alloy wheel plays a significant role for the safety of the passenger cars. Alloy wheels which are intended for normal use on passenger cars, undergo three tests and have to pass before going into the production: Dynamic Cornering Fatigue Test, Dynamic Radial Fatigue Test and Impact Test. Most of aluminium alloy wheels manufacturing companies have done several testing of their product however information of their method on simulation test is often kept limited. During a part of research a static and fatigue analysis of aluminum alloy wheel A356.0 was carried out using FEA package. The 3-D model was imported from CATIA into ANSYS using the appropriate format. Finite element analysis (FEA) is carried out by simulating the test conditions to analyze stress distribution and fatigue life of the aluminium alloy wheel rim of passenger car. Experimental analyses are carried out by radial fatigue testing machine for evaluation of fatigue life under influence of camber angle. The test indicates that integrating FEA and nominal stress method is a good and efficient method to predict alloy wheels fatigue life. In this paper by observing the results of both static and dynamic analysis the aluminium alloy is suggested as better material.

scholarly journals Optimization Design of a Small-Sized Cruciform Specimen for Biaxial Fatigue Testing

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1148
Author(s):  
Zheng Lu ◽  
Jia-Yu Zhao ◽  
Chang-Yu Zhou ◽  
Xiao-Hua He
Keyword(s):  
Fatigue Test ◽  
Optimization Design ◽  
Fatigue Testing ◽  
Orthogonal Experiment ◽  
Testing Machine ◽  
Complex Stress State ◽  
Image Correlation ◽  
Minimum Thickness ◽  
Cruciform Specimen ◽  
Biaxial Fatigue

The in-plane biaxial specimen can well reflect the complex stress state of sheet metal. However, there is no standard for small-sized specimens used in the low-power biaxial fatigue testing machine. The main goal of this paper is to apply the finite element method and orthogonal experiment method to design the cruciform specimen, considering the influence of three main parameters including the diameter of the central semispherical thinning area, the minimum thickness of the center and the arm thickness of the specimen. According to the central strain dispersion coefficient and the strain concentration coefficient proposed in this paper, we ensured that the distribution of strain in the gauge area is uniform and the strain it at its maximum value at the same time. The optimized specimen is verified by a biaxial fatigue test with the digital image correlation (DIC) technique. It is found that the fatigue crack appears in the center region, which proves that the optimized specimen can be effectively used for biaxial fatigue test.

Fatigue Assessment of “Corroded” Mooring Chain

2019 ◽  
Author(s):  
David A. Baker ◽  
Zhen Li ◽  
Sue Wang ◽  
Xiying Zhang ◽  
Yunliang Shao ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Fatigue Test ◽  
Best Practice ◽  
Fatigue Testing ◽  
Fatigue Tests ◽  
Element Analysis ◽  
Cycle Count ◽  
Remaining Fatigue Life ◽  
Mooring Chain

Abstract Assessment of corroded mooring chain for continued service is a challenging task faced by industry. Current best practice relies heavily on qualitative inspection information collected during inspection campaign. There has been little investigation into this practice and whether it is an appropriate technique or can be improved. To address this issue, the Fatigue of Corroded Mooring Chains (FoCCs) Joint Industry Project (JIP), initiated in 2016 with fifteen (15) participating organizations, including oil majors, chain manufactures, consulting firms, and classification societies, to examine assessment methods for evaluating remaining fatigue life. JIP teams were formed to progress fatigue testing and finite element objectives. One such team, comprised of ExxonMobil, ABS and Asian Star Anchor Chain, has performed an additional series of fatigue tests beyond the core JIP work effort. A fatigue test was conducted to 1) demonstrate the utility of finite element analysis in the assessment of fatigue life and 2) demonstrate performance of simulated damage. This unique fatigue test program was conducted on mooring chain with manufactured “corrosion pits” of different dimensions. All chain surface features were digitally recorded and converted into finite element models. These models were subsequently analyzed to compare with test results — both cycle count and failure location. This paper presents the findings from these fatigue tests and finite element analyses and how they can be utilized for assessment of remaining fatigue life.

A Method for Investigating Multi-Axial Fatigue in a PWR Environment

2021 ◽  
Author(s):  
Peter Gill ◽  
Paul Onwuarolu ◽  
Russell Smith ◽  
Ben Coult ◽  
Mark Kirkham ◽  
...  
Keyword(s):  
Fatigue Testing ◽  
Strain Range ◽  
Test Method ◽  
Image Correlation ◽  
Von Mises Stress ◽  
304L Stainless Steel ◽  
Element Analysis ◽  
Uniaxial Test ◽  
Number Of Cycles ◽  
Cycles To Failure

Abstract A significant amount of fatigue testing has taken place over the years to generate relationships between applied stress or strain range and cycles to failure. This has mainly been conducted on uniaxial test specimens in an air environment. More recently, fatigue testing has been conducted in a PWR environment as it is now well known that this has a deleterious impact on life. The test method presented in this paper considers bi-axial loading on a specimen that is compatible with PWR fatigue testing rigs. In order to achieve this, a specimen was designed to convert a uniaxial load into a biaxial load with no internal mechanism. Finite Element Analysis (FEA) was conducted to develop and refine the design, which accounted for frictional contact and bolt up stresses. Initial testing was conducted on a 304L stainless steel specimen in a room temperature air environment. Digital Image Correlation (DIC) was used to validate the FEA and there was excellent agreement between predicted and observed strains. Once the strains were validated, a fatigue test was conducted to confirm that cracking was in the expected location, and that the number of cycles to failure was reasonable. Direct Current Potential Drop (DCPD) was used to indicate when a fatigue crack initiated, which was confirmed by visual inspection. The results showed that cracking occurred in the location of highest accumulated plastic strain and Von Mises Stress, and the number of cycles to failure was slightly lower than predicted but still within scatter.

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