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

2013 ◽  
Vol 28 ◽  
pp. 244-253 ◽  
Author(s):  
Michael C. Sobieraj ◽  
James E. Murphy ◽  
Jennifer G. Brinkman ◽  
Steve M. Kurtz ◽  
Clare M. Rimnac
Keyword(s):  
Fatigue Behavior ◽  
Stress Concentrations

Surface Topography Influences on the Fatigue Behavior of Composite Joints

2019 ◽  
Vol 809 ◽  
pp. 341-346 ◽  
Author(s):  
Torsten Thäsler ◽  
Jens Holtmannspötter ◽  
Hans Joachim Gudladt
Keyword(s):  
Bond Strength ◽  
Fatigue Testing ◽  
Fatigue Behavior ◽  
Surface Condition ◽  
Atmospheric Pressure Plasma ◽  
Fatigue Tests ◽  
Stress Concentrations ◽  
Release Agent ◽  
Structured Surfaces ◽  
Lap Shear

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.

Development of Predictive Models for Fatigue Crack Growth in Rails

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.

CFRP strengthening system to increase fatigue resistance of bridges

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>

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

2015 ◽  
Vol 664 ◽  
pp. 199-208 ◽  
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.

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

2021 ◽  
Vol 161 ◽  
pp. 107446
Author(s):  
Fenghua Huang ◽  
Bin Cheng ◽  
Yinghao Duan ◽  
Man-Tai Chen ◽  
Jiajie Tian
Keyword(s):  
Fatigue Behavior ◽  
Stress Concentrations ◽  
Bird Beak

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

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.

Fatigue Evaluation of 8630 Cast Steel Subjected to Post-Weld Heat Treatment and Stress Relieving

2014 ◽  
Author(s):  
Alireza Shirazi ◽  
Ihab Ragai
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Fatigue Behavior ◽  
Cast Steel ◽  
Fatigue Tests ◽  
Filler Materials ◽  
Stress Concentrations ◽  
Element Analysis ◽  
Stress Relieving ◽  
Weld Heat

The effect of post weld heat treating and stress relieving on the fatigue strength of AISI 8630 cast steel, weld repaired with different filler materials, is the primary objective of the study. To determine the material properties, experiments included monotonic tensile tests, load-controlled fatigue tests as well as hardness tests. Moreover, specimens were micro-etched to examine the morphology of the fracture surface. The results of the fatigue tests are presented in the form of S-N charts. The test findings are then employed in a generalized numerical solution to predict the fatigue behavior of similar components. Finite element models are used to calculate stresses in tested samples, stress concentrations, and in fatigue life comparisons. Stress-life predictions were performed using the modified Goodman criterion to account for the mean stress effects caused by the stress ratio R = 0.1 loading. Predictions based off of finite element analysis and analytical solution for fatigue life provided reasonable estimates which are confirmed by the experimental results.

Notched Fatigue Behavior under Multiaxial Stress States

2014 ◽  
Vol 891-892 ◽  
pp. 185-190
Author(s):  
Nicholas R. Gates ◽  
Ali Fatemi ◽  
Darrell F. Socie ◽  
Nam Phan
Keyword(s):  
Crack Growth ◽  
Fatigue Behavior ◽  
Damage Analysis ◽  
Stress Concentrations ◽  
Axial Torsion ◽  
State Of Stress ◽  
Notch Geometry ◽  
Fatigue Damage Analysis ◽  
Evolution Stage ◽  
Stress States

Most engineering components and structures contain stress concentrations, such as notches. The state of stress at such concentrations is typically multiaxial due to the notch geometry, and/or multiaxiality of the loading. Significant portions of the fatigue life of notched members are usually spent in crack initiation (crack formation and microscopic growth) and macroscopic crack growth. Synergistic complexity of combined stress and stress concentration has been evaluated in a limited number of studies. Available experimental evidence suggests the current life estimation and fatigue damage analysis techniques commonly used may not be capable of accurate predictions for such complex and yet highly practical conditions. This paper investigates notched fatigue behavior under multiaxial loads using aluminum alloys. Many effects involved in such loading conditions are included. These include the effects of stress state (axial, torsion, combined axial-torsion), geometry condition (smooth versus notched), and damage evolution stage (nucleation and micro-crack growth versus long crack growth).

Sem Examinations of Glass Knives

1970 ◽  
Vol 28 ◽  
pp. 282-283
Author(s):  
J. Temple Black
Keyword(s):  
Plastic Deformation ◽  
Tensile Loading ◽  
Resultant Force ◽  
Stress Concentrations ◽  
Edge Chipping ◽  
Surface Flaws ◽  
Edge Defects ◽  
Microscopic Surface

There are two types of edge defects common to glass knives as typically prepared for microtomy purposes: 1) striations and 2) edge chipping. The former is a function of the free breaking process while edge chipping results from usage or bumping of the edge. Because glass has no well defined planes in its structure, it should be highly resistant to plastic deformation of any sort, including tensile loading. In practice, prevention of microscopic surface flaws is impossible. The surface flaws produce stress concentrations so that tensile strengths in glass are typically 10-20 kpsi and vary only slightly with composition. If glass can be kept in compression, wherein failure is literally unknown (1), it will remain intact for long periods of time. Forces acting on the tool in microtomy produce a resultant force that acts to keep the edge in compression.

Glass Knife Geometry as Seen by the SEM

1971 ◽  
Vol 29 ◽  
pp. 454-455
Author(s):  
J. Temple Black
Keyword(s):  
Low Cost ◽  
Amorphous Material ◽  
Stress Concentrations ◽  
Basic Tool ◽  
Tool Materials ◽  
Optical Inspection ◽  
Surface Flaws ◽  
Slip Planes ◽  
Glass Knife ◽  
Diamond Knife

In ultramicrotomy, the two basic tool materials are glass and diamond. Glass because of its low cost and ease of manufacture of the knife itself is still widely used despite the superiority of diamond knives in many applications. Both kinds of knives produce plastic deformation in the microtomed section due to the nature of the cutting process and microscopic chips in the edge of the knife. Because glass has no well defined slip planes in its structure (it's an amorphous material), it is very strong and essentially never fails in compression. However, surface flaws produce stress concentrations which reduce the strength of glass to 10,000 to 20,000 psi from its theoretical or flaw free values of 1 to 2 million psi. While the microchips in the edge of the glass or diamond knife are generally too small to be observed in the SEM, the second common type of defect can be identified. This is the striations (also termed the check marks or feathers) which are always present over the entire edge of a glass knife regardless of whether or not they are visable under optical inspection. These steps in the cutting edge can be observed in the SEM by proper preparation of carefully broken knives and orientation of the knife, with respect to the scanning beam.

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