Biaxial Strain Control Fatigue Testing Strategies for Composite Materials

Moncy, A.; Waldbjørn, Jacob Paamand; Berggreen, Christian

doi:10.1007/s11340-021-00725-6

Cited by 6 publications

(6 citation statements)

References 29 publications

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“…This requirement is met by a fast CoaXPress 2.0 camera acquiring more than 3 GB/s of image data sufficient to resolve 8.0 Â 7.7 mm 2 images with 5 μm/ pixel and a frame rate of 850 Hz in the biaxial case and 12.8 Â 4.4 mm 2 ones with the same resolution and 1500 Hz in uniaxial trials. So the integral strain measurement rate is about an order of magnitude faster than other real-time DIC systems [13][14][15][16][17] because it is optimised for the exchange of many small data packets between CPU and GPU with low latency under closed-loop conditions. As demonstrated in Figure 4, the temporal resolution of 850 Hz with a latency of about 3 ms enables strain-controlled crack growth in a worst-case situation on this test site.…”

Section: Comparison Between Crack Lengths Measured By Dic and Acpdmentioning

confidence: 99%

“…This path‐independence makes strain‐control robust against single mismeasurements potentially interrupting tracking because it does not depend on previous images or evaluation results. [ 16 ] Furthermore, the sample surface is not speckle‐painted, as it is necessary for most commercial systems. [ 28 ] Instead, it works marker‐free by correlating the microstructure of the specimen surface with a repeatability for load‐free in‐plain translations in the range of 0.1 μm for a broad variety of metal surfaces like cast iron, eroded surfaces or polished steel—corresponding to 10 microstrains at a base length of 10 mm.…”

Section: Closed‐loop Operation For Crack Growthmentioning

confidence: 99%

“…Without GPU, even integral strain measurement rates correlating only two or four subsets hardly exceed 100 Hz. [13][14][15][16][17] In this paper, we report the expansion of an implementation originally designed as a real-time extensometer measuring integral strain for comprehensive crack growth evaluation. [13,18] According to the scheme of Thiagu, it uses in-subset parallelism for the FFT-CC algorithm on the GPU with zero-order shape functions.…”

Section: Introductionmentioning

confidence: 99%

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Application of high‐performance DIC for a comprehensive evaluation of biaxial fatigue crack growth experiments

Blug

Conrad

Bertz

et al. 2023

Strain

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Precise determination of the remaining service life of technical components requires sufficient knowledge of fatigue crack growth behaviour and the growth rate of defects. Cracks in real components often experience multiaxial far field stresses due to their complex geometry and composite loadings acting on it. Digital image correlation (DIC) is well established for crack length and displacement measurements, but it usually requires sample preparation with speckle paint and interferes with mechanical extensometers. To overcome these limitations, we use a novel 2D DIC system combining a graphics processing unit (GPU) with a CoaXPress 2.0 camera, acquiring up to 3 GB/s of image data. It enables real‐time evaluation of both integral strain like an extensometer and full‐field DIC on images selected automatically in real‐time. This combination enables the use of one single sensor for strain‐controlled testing and fatigue crack growth characterisation. The full‐field displacement is compared to a finite‐element model (FEM) simulating the actual crack contour measured by the DIC system. The results show that high‐performance DIC has the potential to simultaneously simplify crack‐growth experiments and provide comprehensive fracture mechanical information.

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Section: Comparison Between Crack Lengths Measured By Dic and Acpdmentioning

confidence: 99%

Section: Closed‐loop Operation For Crack Growthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Application of high‐performance DIC for a comprehensive evaluation of biaxial fatigue crack growth experiments

Blug

Conrad

Bertz

et al. 2023

Strain

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“…Finally, it should be noted that this technology is not only used for test monitoring, but can also intervene in testing control. Moncy et al [46,94,95] highlighted the need to carry out strain control, which produces more adequate results than methodologies based on force or displacement control when studying crack growth. However, strain control requires taking into account material stiffness degradation.…”

Section: Strain Monitoring and Controlling Techniquesmentioning

confidence: 99%

Advances in Cruciform Biaxial Testing of Fibre-Reinforced Polymers

Muñoz

Moreno

2022

Polymers

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The heterogeneity and anisotropy of fibre-reinforced polymer matrix composites results in a highly complex mechanical response and failure under multiaxial loading states. Among the different biaxial testing techniques, tests with cruciform specimens have been a preferred option, although nowadays, they continue to raise a lack of consensus. It is therefore necessary to review the state of the art of this testing methodology applied to fibre-reinforced polymers. In this context, aspects such as the specific constituents, the geometric design of the specimen or the application of different tensile/compressive load ratios must be analysed in detail before being able to establish a suitable testing procedure. In addition, the most significant results obtained in terms of the analytical, numerical and experimental analyses of the biaxial tests with cruciform specimens are collected. Finally, significant modifications proposed in literature are detailed, which can lead to variants or adaptations of the tests with cruciform specimens, increasing their scope.

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“…For the force-controlled test, the forces were applied such that a similar volume averaged stress existed for the 25 mm wide and the 50 mm wide specimens. The strain-controlled tests were carried out using a cascade control algorithm with the strain constituting the outer control loop and the force forming the inner control loop as described by Moncy et al 37 Here, the strain signal was acquired through a real-time image point tracking technique using a digital image correlation (DIC) setup by Gesellschaft für Optische Messtechnik, (GOM). The DIC system comprised two Dalsa Falcon2 FA-80-12M1H Charged Coupled Device (CCD) cameras with a resolution of 12 megapixels and equipped with a F2.8/50 mm Titanar lens each.…”

Section: Specimens Materials System and Test Proceduresmentioning

confidence: 99%

Propagation of tunnelling cracks in composite materials under strain and force-controlled cyclic loading

Moncy

Sørensen

Castro

et al. 2022

Journal of Composite Materials

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In this paper, the propagation of tunnelling cracks in composite laminates subjected to uniaxial force-controlled and strain-controlled cyclic loading is analysed considering both interacting and non-interacting cracking scenarios. Glass fibre reinforced polymer laminates with [Formula: see text] layup are used in the analysis. For non-interacting cracks, a strain-controlled test under a single strain value is found to be sufficient to produce the slope of the Paris-Erdogan law type curve relating the crack front growth rate (CGR) with the energy release rate (ERR), but within a limited range of ERR. Whereas, a force-controlled test is found more suitable when characterising the variation of the CGR at a certain ERR value. For closely spaced cracks, commonly seen crack interaction scenarios are identified and the CGR of the crack front is investigated for both loading control modes. It is found that the CGR decreases when volume averaged stresses are reduced ahead of the crack front due to shielding effect at high crack densities. A relationship between these two parameters is presented. It is further found that the CGR of two collinear crack fronts growing towards each other for coalescence do not influence each other. But when the two crack fronts are not collinear the CGR of the crack fronts is significantly affected after they have grown past each other.

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Biaxial Strain Control Fatigue Testing Strategies for Composite Materials

Cited by 6 publications

References 29 publications

Application of high‐performance DIC for a comprehensive evaluation of biaxial fatigue crack growth experiments

Application of high‐performance DIC for a comprehensive evaluation of biaxial fatigue crack growth experiments

Advances in Cruciform Biaxial Testing of Fibre-Reinforced Polymers

Propagation of tunnelling cracks in composite materials under strain and force-controlled cyclic loading

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