scholarly journals Generic failure mechanisms in adhesive bonds

Holzforschung ◽  
2013 ◽  
Vol 67 (2) ◽  
pp. 207-215 ◽  
Author(s):  
Philipp Hass ◽  
Falk K. Wittel ◽  
Peter Niemz
Keyword(s):  
Crack Propagation ◽  
Urea Formaldehyde ◽  
Failure Mechanisms ◽  
Tensile Tests ◽  
Propagation Path ◽  
Adhesive Properties ◽  
Adhesive Bonds ◽  
Stable Crack Propagation ◽  
Order Of Magnitude

Abstract The failure of adhesive bondlines has been studied at the microscopic level via tensile tests. Stable crack propagation could be generated by means of samples with improved geometry, which made in situ observations possible. The interaction of cracks with adhesive bondlines under various angles to the crack propagation was the focus of this study, as well as the respective loading situations for the adhesives urea formaldehyde (UF), polyurethane (PUR), and polyvinyl acetate (PVAc), which have distinctly different mechanical behaviors. It has been shown how adhesive properties influence the occurrence of certain failure mechanisms and determine their appearance and order of magnitude. With the observed failure mechanisms, it becomes possible to predict the propagation path of a crack through the specimen.

scholarly journals Crack Propagation Behavior of a Ni-Based Single-Crystal Superalloy during In Situ SEM Tensile Test at 1000 °C

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1047
Author(s):  
Wenxiang Jiang ◽  
Xiaoyi Ren ◽  
Jinghao Zhao ◽  
Jianli Zhou ◽  
Jinyao Ma ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Tensile Test ◽  
Single Crystal ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Single Crystal Superalloy ◽  
Propagation Path ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

An in situ scanning electron microscope (SEM) tensile test for Ni-based single-crystal superalloy was carried out at 1000 °C. The stress displacement was obtained, and the yield strength and tensile strength of the superalloy were 699 MPa and 826 MPa, respectively. The crack propagation process, consisting of Model I crack and crystallographic shearing crack, was determined. More interestingly, the crack propagation path and rate affected by eutectics was directly observed and counted. Results show that the coalescence of the primary crack and second microcrack at the interface of a γ/γ′ matrix and eutectics would make the crack propagation rate increase from 0.3 μm/s to 0.4 μm/s. On the other hand, crack deflection decreased the rate to 0.05 μm/s. Moreover, movement of dislocations in front of the crack was also analyzed to explain the different crack propagation behavior in the superalloy.

scholarly journals Crack Propagation in Metallic Glass Ribbon as a Function of the Position of Stress Concentrators

2017 ◽  
Vol 891 ◽  
pp. 494-499
Author(s):  
Mária Huráková ◽  
Kornel Csach ◽  
Jozef Miškuf ◽  
Alena Juríková ◽  
Václav Ocelík ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Tensile Axis ◽  
Shear Bands ◽  
Glass Ribbon ◽  
Tensile Tests ◽  
In Situ Observation ◽  
Band Formation ◽  
Stress Concentrators ◽  
As Stress

An amorphous metallic ribbon of Fe40Ni40B20 was used for in-situ observation of the crack propagation and shear band formation during tensile tests. Prior to the tensile tests, two holes (with different positions with respect to the tensile axis) were made by laser ablation as stress concentrators. The nucleation and propagation of shear bands on the ribbon surface during tensile tests were analysed with scanning electron microscopy (SEM). At room temperature inhomogeneous plastic deformation of amorphous alloy occurs via the development of primary and secondary shear bands. The influence of the different loading geometry on the topology of shear bands and crack propagation was studied.

scholarly journals Hydrogen-Assisted Crack Growth in the Heat-Affected Zone of X80 Steels during in Situ Hydrogen Charging

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2575 ◽  
Author(s):  
Qu ◽  
Feng ◽  
An ◽  
Bi ◽  
Du ◽  
...  
Keyword(s):  
Hydrogen Embrittlement ◽  
Base Metal ◽  
Current Density ◽  
Heat Affected Zone ◽  
Tensile Tests ◽  
Electron Back Scatter Diffraction ◽  
Propagation Path ◽  
Hydrogen Charging ◽  
X80 Steels

Herein, the hydrogen embrittlement of a heat-affected zone (HAZ) was examined using slow strain rate tension in situ hydrogen charging. The influence of hydrogen on the crack path of the HAZ sample surfaces was determined using electron back scatter diffraction analysis. The hydrogen embrittlement susceptibility of the base metal and the HAZ samples increased with increasing current density. The HAZ samples have lower resistance to hydrogen embrittlement than the base metal samples in the same current density. Brittle circumferential cracks located at the HAZ sample surfaces were perpendicular to the loading direction, and the crack propagation path indicated that five or more cracks may join together to form a longer crack. The fracture morphologies were found to be a mixture of intergranular and transgranular fractures. Hydrogen blisters were observed on the HAZ sample surfaces after conducting tensile tests at a current density of 40 mA/cm2, leading to a fracture in the elastic deformation stage.

Tailoring the Microstructure of a Metal-Reinforced Ceramic Matrix Composite

2000 ◽  
Vol 122 (3) ◽  
pp. 363-367 ◽  
Author(s):  
O. Sbaizero ◽  
G. Pezzotti
Keyword(s):  
Crack Propagation ◽  
Ceramic Matrix Composite ◽  
Spectroscopic Technique ◽  
In Situ Raman Spectroscopy ◽  
Stable Crack Propagation ◽  
Grain Sizes ◽  
In Situ Raman ◽  
Bridging Stresses ◽  
Good Agreement

Alumina matrix was prepared with varying amounts of metal molybdenum particles of two different grain sizes. R-curves were determined during stable crack propagation and a piezo-spectroscopic technique was used to assess the bridging stresses developed along the crack wake (at the metal/matrix interface) at the critical condition for crack propagation. In both kinds of composites, the toughness monotonically increases with the amount of molybdenum added. In addition, bridging stress and therefore toughness were higher when coarser particles were present. The theoretical R-curves calculated from the discrete (microscopic) bridging stress distribution obtained by in situ Raman spectroscopy were in good agreement with the experimental data. [S0094-4289(00)02003-X]

Macro- and micromechanical characterization of wood-adhesive bonds exposed to alternating climate conditions

Holzforschung ◽  
2010 ◽  
Vol 64 (6) ◽  
Author(s):  
Jürgen Follrich ◽  
Frank Stöckel ◽  
Johannes Konnerth
Keyword(s):  
Bond Strength ◽  
Mechanical Performance ◽  
Urea Formaldehyde ◽  
Tensile Tests ◽  
Tangential Direction ◽  
Wood Adhesive ◽  
Bond Line ◽  
Adhesive Bonds ◽  
Climate Conditions ◽  
Micromechanical Characterization

Abstract Three-part specimens were produced from Norway spruce wood (Picea abies Karst.) and bonded with the following adhesives: melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and a two-component emulsion polymer isocyanate (EPI). The effect of alternating climate conditions on bond strength was studied by tensile tests. The specimens were exposed to a three-step ageing cycle lasting for 7 days [50°C/95% relative humidity (RH), -20°C/65– 70% RH and 75°C/15% RH] which was repeated 24 times. In general, a decrease in internal bond strength of all exposed specimens was observed but it was highest in the case of MUF-bonded joints. Furthermore, a significant decrease of the tensile strength of the wood adherend perpendicular to the grain in the tangential direction was determined after the cyclic climatic changes. The mechanical performance of the different adhesives in the bond line was tested by means of nanoindentation. Reduced values of elastic modulus, hardness, and total indentation were observed after climatic treatment, particularly for the rigid MUF adhesive, whereas the flexible adhesive EPI did not show such changes.

Study on Fracture Mechanisms of TiAl Alloys by In Situ Tensile Tests

2007 ◽  
Vol 353-358 ◽  
pp. 34-37
Author(s):  
Rui Cao ◽  
Jian Hong Chen ◽  
J. Zhang
Keyword(s):  
Crack Propagation ◽  
Main Crack ◽  
Applied Load ◽  
High Stress ◽  
Lamellar Microstructure ◽  
Tensile Tests ◽  
Fracture Mechanisms ◽  
Tial Alloys ◽  
Lamellar Interfaces

Combining in-situ tensile tests with detailed observations of fracture surfaces of a two-phase TiAl alloy, the fracture process and fracture mechanisms of TiAl alloys are investigated. The results reveal that Cracks prefer to initiate and propagate along lamellar interfaces, which are the weakest link in the near fully lamellar microstructure. The interlamellar strength calculated is less than the translamellar strength. The tensile stress is the driving force for crack initiation and propagation. In specimens with a slit notch, most cracks are initiated directly from the notch root and extended along lamellar interfaces. The main crack can be stopped or deflected into a delamination mode by a barrier grain with a lamellar interface orientation deviated from the direction of crack propagation. In this case, new cracks are nucleated along lamellar interfaces of grains with favorable orientation ahead the barrier grain. The main crack and a new crack are then linked by the translamellar cleavage fracture of the barrier grain with increasing applied load. In order to extend the main crack, further increases of the applied load are needed to move the high stress region into the ligament until final fracture. The process of a new crack nucleation with a bridging ligament formation decreases the crack propagation resistance rather than increases it.

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