Stress concentrations and fatigue behavior of bird-beak SHS overlap K-joints subjected to brace in-plane force

The surface condition of carbon fibre reinforced plastic (CFRP) substrates is decisive to obtain high bond strength and lifetime of adhesively bonded parts. Those surfaces were adjusted in terms of their microscopic topography by means of peel plies and release foils. The subsequent surface treatment via atmospheric pressure plasma jet or vacuum blasting allowed the modification of the microscopic roughness as well as the surface chemistry. Those configuration were assessed using surface analytic methods as well as quasi-static and cyclic fracture tests on single lap shear specimens. The microscopic surface roughness, if at all, only showed a small influence on the bond strength. Despite release agent residues, fracture was found within the fiber-matrix interface, which caused difficulties in evaluating the effect of surface pretreatments on the adhesion strength. Fatigue tests revealed a lifetime reduction of uneven microscopic rough surfaces, which was assigned to stress concentrations at the tip of asperities. The crack propagation was accelerated in case of release agent residues. If surfaces were free of contaminations, no differences between microscopically smooth and slightly structured surfaces were found. Overall, fatigue testing on single lap shear specimens showed an increased sensitivity with regard to the assessment of surface morphology.

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Development of Predictive Models for Fatigue Crack Growth in Rails

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.488-489.13 ◽

2011 ◽

Vol 488-489 ◽

pp. 13-16

Author(s):

Antonio De Iorio ◽

Marzio Grasso ◽

George Kotsikos ◽

F. Penta ◽

G. P. Pucillo

Keyword(s):

Crack Growth ◽

Fatigue Behavior ◽

Service Condition ◽

Fatigue Tests ◽

Analytical Models ◽

The Finite Element Method ◽

Stress Concentrations ◽

Initiation Point ◽

Fatigue Failures ◽

The Web

Fatigue failures of rails often occur at the rail foot, since the geometry of this zone gives rise to stress concentrations under service loads or defects during rail manufacture and installation. In this paper, the fatigue behavior of cracks at the web/foot region of a rail is analyzed numerically. Analytical models in the literature for a semi-elliptical surface crack in a finite plate assume that the geometry of the front remains semi-elliptical during the whole propagation phase and the ellipse axes do not undergo translations or rotations. Fatigue tests show that this is not the case for such cracks in rails. A predictive model for crack growth has been developed by assuming an initial small crack at one probable initiation point between the web and foot of the rail in reference to a service condition loading. SIF values have been estimated by means of the finite element method and the plastic radius correction. The results attained were compared with crack growth experimental data.

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Stress concentration factors and fatigue behavior of square bird-beak SHS T-joints under out-of-plane bending

Engineering Structures ◽

10.1016/j.engstruct.2015.05.033 ◽

2015 ◽

Vol 99 ◽

pp. 677-684 ◽

Cited By ~ 12

Author(s):

Bin Cheng ◽

Qin Qian ◽

Xiao-Ling Zhao

Keyword(s):

Stress Concentration ◽

Fatigue Behavior ◽

T Joints ◽

Bird Beak ◽

Out Of Plane ◽

Concentration Factors ◽

Plane Bending ◽

Stress Concentration Factors

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CFRP strengthening system to increase fatigue resistance of bridges

IABSE Congress, New York, New York 2019: The Evolving Metropolis ◽

10.2749/newyork.2019.1464 ◽

2019 ◽

Author(s):

Roman Sedlmair ◽

Lothar Stempniewski

Keyword(s):

Strain Distribution ◽

Fatigue Behavior ◽

Dynamic Loads ◽

Fiber Reinforced Polymers ◽

Stress Concentrations ◽

Carbon Fiber Reinforced Polymers ◽

Cfrp Laminates ◽

External Reinforcement ◽

Externally Bonded ◽

Strengthening Technique

<p>Carbon fiber reinforced polymers (CFRP) laminates externally bonded with epoxy resins are an often used strengthening technique of aged and overloaded structures, e.g. bridges. A well-known, though not commonly discussed, problem is the stiff bond behavior of the used adhesives. Their use leads to stress concentrations in the CFRP and concrete at the location of cracks and an uneven strain distribution of internal and external reinforcement. On that basis, the usage of such a strengthening technique for components subjected to dynamic loads is limited or almost impossible due to premature debonding of the CFRP.</p><p>The present paper focuses on numerical analysis of reinforced concrete bending beams strengthened with CFRP using the finite element method. In our analysis we focus on contact modelling techniques. The effect of differing adhesives on the overall behavior of the strengthened beams and strain distribution of internal and external reinforcement is shown. Numerical investigations demonstrate the relevance of the used adhesive on the static and fatigue behavior of the strengthened component. Modified and optimized material properties of the adhesive lead to a strengthening system which is even capable of carrying dynamic loads.</p>

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Fatigue behavior of diamond bird-beak T-joints and design recommendations

Tubular Structures XVI ◽

10.1201/9781351210843-57 ◽

2017 ◽

pp. 449-456

Author(s):

L.W. Tong ◽

G.W. Xu ◽

Y.Q. Liu ◽

D.Q. Yan ◽

X.L. Zhao

Keyword(s):

Fatigue Behavior ◽

T Joints ◽

Design Recommendations ◽

Bird Beak

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Fatigue Behavior of Riblet Structured High Strength Aluminum Alloy Thin Sheets at Very High Cycle Numbers

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.664.199 ◽

2015 ◽

Vol 664 ◽

pp. 199-208 ◽

Cited By ~ 1

Author(s):

Sebastian Stille ◽

Tilmann Beck ◽

Lorenz Singheiser

Keyword(s):

Aerodynamic Drag ◽

Fatigue Behavior ◽

Fatigue Cracks ◽

Axial Loading ◽

High Strength ◽

Threshold Value ◽

Special Focus ◽

Stress Concentrations ◽

Aerospace Applications ◽

Aa 2024

The VHCF behavior of age hardened 2024 and 7075 aluminum sheets was studied. The experiments were performed at frequencies of ≈ 20 kHz with fully reversed axial loading (R = -1). Special focus was put on the influence of AA 1050 claddings and riblet-like surface structures, which are used in aerospace applications to reduce aerodynamic drag. The fatigue life and fatigue limit of the AA 2024 bare material are – compared to the non-structured case – significantly reduced by the stress concentrations induced by the riblet structure. However, the fatigue behavior of the clad AA 2024 material is less sensitive to the surface structure. In this case, we obtained a sharp transition from HCF failure up to 5x106 cycles to run-outs at ≥ 2x109 cycles. This threshold value for failure differs with cladding thickness as well as with riblet geometry. We attribute this to the modified stress distribution near the interface (cladding/substrate) as well as to a locally reduced thickness of the cladding in the riblet valleys. Fatigue cracks are – even in the case of run-outs – always initiated at the surface of the clad layer and grow easily to the substrate. Samples only fail, if the threshold for further crack growth into the substrate is exceeded. Both Alclad 2024 and 7075 show the same failure mechanism.

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Monotonic and fatigue behavior of five clinically relevant conventional and highly crosslinked UHMWPEs in the presence of stress concentrations

Journal of the Mechanical Behavior of Biomedical Materials ◽

10.1016/j.jmbbm.2013.07.024 ◽

2013 ◽

Vol 28 ◽

pp. 244-253 ◽

Cited By ~ 7

Author(s):

Michael C. Sobieraj ◽

James E. Murphy ◽

Jennifer G. Brinkman ◽

Steve M. Kurtz ◽

Clare M. Rimnac

Keyword(s):

Fatigue Behavior ◽

Stress Concentrations

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Influence of chord wall interaction on stress concentrations of square bird-beak SHS X-joints

Tubular Structures XVI ◽

10.1201/9781351210843-24 ◽

2017 ◽

pp. 201-206

Author(s):

C. Li ◽

B. Cheng ◽

Q. Qian ◽

Y. Lou ◽

X.L. Zhao

Keyword(s):

Stress Concentrations ◽

Bird Beak ◽

Wall Interaction

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Characterization and Modelling of Multiple Intralaminar Cracking Initiation under Tensile Quasi-Static and Fatigue Loading

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.774.467 ◽

2018 ◽

Vol 774 ◽

pp. 467-472

Author(s):

H. Ben-Kahla ◽

Janis Varna

Keyword(s):

Cyclic Loading ◽

Fatigue Behavior ◽

Crack Density ◽

Fatigue Loading ◽

Shear Stresses ◽

Stress Concentrations ◽

Density Region ◽

Static Tests ◽

Distribution Parameters ◽

Intralaminar Cracking

The first failure mode in tensile quasi-static and in tension-tension fatigue (cyclic) loading of composite laminates is intralaminar cracking in layers with off-axis fiber orientation. These tunnel-building cracks are result of combined action of in-plane transverse and shear stresses. We assume that due to non-uniform fiber distribution (clustering) which leads to local stress concentrations, different positions in the layer have different resistance to crack initiation (initiation strength). If so, the weakest position in quasi-static loading is also the weakest in fatigue and some of the distribution parameters for fatigue behavior can be obtained in quasi-static tests, thus significantly reducing the number of required fatigue tests. Methodology is suggested and validated for cases when the cracking is initiation governed-initiated crack almost instantly propagates along fibers. Distribution parameters are identified using data in low crack density region where stress perturbations from cracks do not interact. Monte-Carlo simulations are performed for cracking in layers under quasi-static and cyclic loading using novel approach for computationally efficient stress state calculation between existing cracks.

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