Damage and Fracture Mechanisms during Mode I and III Loading of Wood

Holzforschung ◽  
2001 ◽  
Vol 55 (5) ◽  
pp. 525-533 ◽  
Author(s):  
E.K. Tschegg ◽  
K. Frühmann ◽  
S.E. Stanzl-Tschegg
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Fracture Energy ◽  
Fracture Mechanisms ◽  
Mode I ◽  
Mode Iii ◽  
Initiation Energy ◽  
Specific Fracture Energy ◽  
Damage And Fracture ◽  
Specific Fracture

Summary Tests under mode I and mode III loading were performed on side grooved Compact-Tension specimens of larch and beech under steady state crack propagation to study the damage and fracture behaviour and the influence of two fibre orientations. From the complete load-displacement diagram, all important damage and fracture mechanical values (stiffness/compliance, microstructural damage, crack initiation energy, specific fracture energy, etc.) have been determined. Crack initiation energy and specific fracture energy are approximately ten times higher for mode III loading than for mode I loading in both wood species. Crack initiation occurs in mode III under external mode III loading, crack propagation, however, takes place under mode I, owing to crack surface interference. The influence of fibre orientation on the (fracture) mechanical properties of beech and larch is different. This difference may be explained mainly by the high number of rays in beech.

Fracture Behaviour of Modified Spruce Wood: A Study Using Linear and Non Linear Fracture Mechanics

Holzforschung ◽  
2002 ◽  
Vol 56 (2) ◽  
pp. 191-198 ◽  
Author(s):  
Alexander Reiterer ◽  
Gerhard Sinn
Keyword(s):  
Fracture Energy ◽  
Heat Treatments ◽  
Critical Stress Intensity Factor ◽  
Mode I ◽  
Mode Iii ◽  
Fracture Properties ◽  
Specific Fracture Energy ◽  
Wedge Splitting Test ◽  
Splitting Test ◽  
Specific Fracture

Summary The fracture properties of unmodified and modified (heat treatments under various conditions and acetylation) sprucewood are investigated using the wedge splitting test. Fracture parameters measured include critical stress intensity factor and specific fracture energy under Mode I loading and specific fracture energy under Mode III loading. The Mode I fracture properties are reduced by all kinds of modification. However, acetylation leads to a reduction of only 20%whereas heat treatments reduce the properties to a much greater extent, approximately 50%to 80%. The Mode III fracture properties are influenced less. SEM pictures of the fracture surfaces support the described findings.

scholarly journals Dynamic crack propagation in weak snowpack layers: Insights from high-resolution, high-speed photography

2021 ◽  
Author(s):  
Bastian Bergfeld ◽  
Alec van Herwijnen ◽  
Benjamin Reuter ◽  
Grégoire Bobillier ◽  
Jürg Dual ◽  
...  
Keyword(s):  
High Resolution ◽  
Crack Propagation ◽  
Fracture Energy ◽  
High Speed ◽  
Image Correlation ◽  
Crack Speed ◽  
Specific Fracture Energy ◽  
Weak Layer ◽  
Specific Fracture ◽  
Insight Into

Abstract. To assess snow avalanche release probability, information on failure initiation and crack propagation in weak snowpack layers underlying cohesive slab layers are required. With the introduction of the Propagation Saw Test (PST) in the mid-2000s, various studies used particle tracking analysis of high-speed video recordings of PST experiments to gain insight into crack propagation processes, including slab bending, weak layer collapse, crack propagation speed and the frictional behavior after weak layer fracture. However, the resolution of the videos and the methodology used did not allow insight into dynamic processes such as the evolution of crack speed within a PST or the touchdown distance, which is the length from the crack tip to the trailing point where the slab sits on the crushed weak layer at rest again. Therefore, to study the dynamics of crack propagation we recorded PST experiments using a powerful portable high-speed camera with a horizontal resolution of 1280 pixels at rates up to 20,000 frames per second. By applying a high-density speckling pattern on the entire PST column, we then used digital image correlation (DIC) to derive high-resolution displacement and strain fields in the slab, weak layer, and substrate. The high frame rates allowed time derivatives to obtain velocity and acceleration fields. On the one hand, we demonstrate the versatile capabilities and accuracy of the DIC method by showing three PST experiments resulting in slab fracture, crack arrest and full propagation. On the other hand, we present a methodology to determine relevant characteristics of crack propagation: the crack speed and touchdown distance within a PST, and the specific fracture energy of the weak layer. To estimate the effective elastic modulus of the slab and weak layer as well as the weak layer specific fracture energy we used a recently proposed mechanical model. A comparison to already established methods showed good agreement. Furthermore, our methodology also provides insight into the three different propagation results found with the PST and reveals intricate dynamics that are otherwise not accessible.

Fracture Energy Test for Highway Concrete: Determining the Effect of Coarse Aggregate on Crack Propagation Resistance

2000 ◽  
Vol 1730 (1) ◽  
pp. 10-17 ◽  
Author(s):  
Elin A. Jensen ◽  
Will Hansen
Keyword(s):  
Fracture Toughness ◽  
Blast Furnace ◽  
Crack Propagation ◽  
Fracture Energy ◽  
Blast Furnace Slag ◽  
Coarse Aggregate ◽  
Fracture Properties ◽  
Specific Fracture Energy ◽  
Specific Fracture ◽  
Furnace Slag

Portland cement concrete fracture properties—specific fracture energy, fracture toughness, and brittleness—were investigated for typical Michigan highway concretes containing different coarse aggregates and varying in age: 7,28, and 91 days. These fracture properties can be determined from the complete load-deflection curve of a notched beam. The effective beam is 965 mm long, 100 mm wide, and 200 mm high, with a 100-mm center notch. Results show that the specific fracture energy, which determines the resistance to crack propagation, for a concrete pavement mix is controlled primarily by the coarse aggregate type. Differences of 100 percent were obtained between aggregate types. A glacial gravel yielded the highest resistance (160 N/m), and the dolomitic limestones and blast furnace slag yielded the lowest resistance (80–100 N/m), although the concretes all had similar strength properties. The fracture toughness, resistance to crack initiation, was found to be linear related with concrete strength. Typically this results in improved early age fracture toughness for concretes containing dolomitic limestone and blast furnace slag as coarse aggregate, compared to glacial gravel, because natural aggregate concrete typically has slower strength gain initially. Concrete brittleness, based on the entire load-deflection response, showed that concretes containing stronger coarse aggregate, such as glacial gravel, are significantly less brittle at early ages than are concretes containing weaker aggregate. However, these stronger aggregate concretes become more brittle, and thus crack sensitive, over time.

scholarly journals Probabilistic Fracture Energy Assessment of Natural Fibre Reinforced Concrete by Two Parameter Weibull Distribution

2018 ◽  
Vol 7 (3.12) ◽  
pp. 407
Author(s):  
Neha P Asrani ◽  
Murali G ◽  
Arthika J ◽  
Karthikeyan. K ◽  
Haridharan. M.K
Keyword(s):  
Weibull Distribution ◽  
Fracture Energy ◽  
Plain Concrete ◽  
Natural Fibre ◽  
Test Results ◽  
Specific Fracture Energy ◽  
Energy Assessment ◽  
Experimental Process ◽  
Specific Fracture ◽  
Two Parameter

Fracture energy is the post-crack energy absorption ability of the material that represents the energy absorbed by the structure at the time of failure. Its analysis has gained importance and hence requires a powerfulmethod for its development. A two parameter Weibull distribution proves to be an efficient tool in analysing the scattered experimental test results. In this paper, the specific fracture energy of plain concrete and concrete reinforced with natural fibres of hemp, wheat straw and elephant grass are statistically analysed by two parameter Weibull distribution by using graphical method. For determining Weibull parameters, 21 equations have been used and the best equation is taken for the reliability analysis. A Weibull reliability curve is plotted, which shows the specific fracture energy at each reliability level. This curve enables an engineer to choose the fracture energy of a particular mix based on its reliability requirement and safety limit. Therefore, reliability curves are a pioneer in statistical analysis as they eliminate the time-consuming and costly experimental process. This method can be applied in areas with similar uncertainties.  

The Contribution of Different Fracture Modes on Drilling Delamination Crack Propagation

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Mohammad Reza Vaziri Sereshk ◽  
Hamed Mohammadi Bidhendi
Keyword(s):  
Crack Propagation ◽  
Crack Nucleation ◽  
Dominant Mode ◽  
Mode I ◽  
Minor Effect ◽  
Pure Mode ◽  
Mode Iii ◽  
Major Mode ◽  
Drill Point ◽  
Drilling Conditions

Delamination as the main defect created during drilling of composite laminate is principally a crack nucleation and propagation phenomenon. The fracture-based investigation is performed to identify the significance of different modes involving in this process. The sensitivity analysis is implemented to evaluate magnitude and importance of each mode. As a result, mode I is a dominant mode while drill point removes the material; however, the crack continues to propagate under pure mode III for a while after drilling due to contact of flutes with spalls. This paper investigates the crack formation process for wide variety of drilling conditions and tool geometries. It is demonstrated that although mode III contributes, its minor effect might be neglected if comparing with fracture mode I. Therefore, it may be vanished as a tool design strategy. It is indicated that chisel edge plays a great role in crack propagation under major mode I; therefore, any further design approach which limits or eliminates opening action of chisel edge decreases delamination significantly. Material removal starting from hole perimeter as well as implementing small predrilled holes (such as action of primary cutting lips in step drill) are examined as solutions based on this approach.

Fracture Energy of Elastomers in Mode I (Cleavage) and Mode III (Lateral Shear)

1975 ◽  
Vol 48 (5) ◽  
pp. 896-901 ◽  
Author(s):  
A. Ahagon ◽  
A. N. Gent ◽  
H. J. Kim ◽  
Y. Kumagai
Keyword(s):  
Fracture Energy ◽  
Strain Energy ◽  
Sheet Thickness ◽  
Shear Mode ◽  
Mode I ◽  
Input Energy ◽  
Mode Iii ◽  
Lateral Shear ◽  
Test Sheet ◽  
Filled Elastomers

Abstract Attention has been drawn here to three different reasons why measurements of fracture energy by different methods may not agree: (1) When the test involves propagation of a tear by stored strain energy, as in the method shown in Figure 1, the energy available to cause rupture will be less than that supplied, because of dissipation within the elastomer. Calculation of the fracture energy on the basis of input energy would then lead to an overestimate, by about 100 per cent or more for typical filled elastomers. (2) As shown in Figures 4a and 5, the tear path is sometimes wider than the thickness of the test sheet. In consequence, fracture energy calculated from the sheet thickness would be too large, by about 40 per cent in the cases considered here. (3) Even when allowance is made for the true width of the tear path, measurements of fracture energy in shear (Mode III) are about 50 per cent larger than in cleavage (Mode I). This is attributed to frictional work expended in sliding the rough torn surfaces past each other.

Optimizing Ceramic Matrix Composite Interlaminar Fracture Toughness (Mode I) Wedge Test

2016 ◽  
Author(s):  
Frank Abdi ◽  
Saber DorMohammadi ◽  
Jalees Ahmad ◽  
Cody Godines ◽  
Gregory N. Morscher ◽  
...  
Keyword(s):  
Finite Element ◽  
Fracture Energy ◽  
Crack Growth ◽  
Failure Mode ◽  
Mixed Mode ◽  
Crack Growth Resistance ◽  
Mode I ◽  
Multi Scale ◽  
Fracture Evolution ◽  
Damage And Fracture

ASTM test standards for CMC’s Crack Growth Resistance (CGR) may exhibit a zig-zag (wavy) crack path pattern, and fiber bridging. The experimental parameters that may contribute to the difficulty can be summarized as: specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes I crack growth resistances, GI were analytically determined at ambient temperature using wedge test, a modified double cantilever beam (DCB). Several Finite Element (FE) based Multi-scale modeling potential techniques were investigated: a) Multi-scale progressive failure analysis (MS-PFA); b) Virtual Crack Closure Technique (VCCT). Advantages and disadvantages of each were identified. The final modeling algorithm recommended was an integrated damage and fracture evolution methodology using combined MS-PFA and VCCT. The material tested in this study was a slurry-cast melt-infiltrated SiC/SiC composite with Tyranno ZMI fibers (Ube Industries, Kyoto, Japan) and a BN interphase. The fiber architecture consisted of eight plies of balanced 2-D woven five-harness satin. The total fiber volume fraction was about 30% with half of the fibers in the 0° direction and half in the 90° direction. All specimens had a nominal thickness of 4 mm. An alumina wedge with 18° head angle (2α) was used. In this method, a splitting force is created by inserting a vertically-moving wedge in a notch causing the arms to separate and forcing an interlaminar crack at the sharpest end of the notch The MS-PFA numerical model predicted the damage and fracture evolution and utilized the GENOA UMAT (User Material Subroutine) for Damage and FEM (Finite Element Model) stress intensity and LEFM (Linear elastic Fracture Model), Cohesive Model for Fracture. The analysis results (Fracture energy vs. crack length, Fracture energy vs. load, Fracture energy vs. crack opening displacement) matched the Mode I coupon tests and revealed the following key findings. Mode I-Wedge specimen exhibits: 1) failure mode is due to interlaminar tension (ILT) only in the interface section and a zig-zag pattern observed; 2) VCCT crack growth resistance is well matched to the test data; and 3) failure mode is a mixed mode behavior of Interlaminar tension (ILT) to interlaminar shear (ILS). The final Wedge test specimen configuration optimization includes the sensitivity of design parameters to CGR: a) wedge contact coefficient of friction; b) lever arms thickness, and c) inclined head angle, distance between the initial crack and wedge tip.

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