Different Modes Of Fracture Research Articles

A continuum model for brittle nanowires derived from an atomistic description by Gamma -convergence

Starting from a particle system with short-range interactions, we derive a continuum model for the bending, torsion, and brittle fracture of inextensible rods moving in three-dimensional space. As the number of particles tends to infinity, it is assumed that the rod’s thickness is of the same order as the interatomic distance. For this reason, discrete terms and energy contributions from the ultrathin rod’s lateral surface appear in the limiting functional. Fracture energy in the Gamma -limit is expressed by an implicit cell formula, which covers different modes of fracture, including (complete) cracks, folds, and torsional cracks. In special cases, the cell formula can be significantly simplified—we illustrate this by the example of a full crack and also show that the energy of a mere fold is strictly lower for a class of models. Our approach applies e.g. to atomistic systems with Lennard–Jones-type potentials and is motivated by the research of ceramic nanowires.

Characterization of the Fracture Forming Limits by Radial Extrusion

This paper introduces a new formability test based on double-action radial extrusion to characterize material formability in the three-dimensional to plane-stress material flow transitions that are found in bulk metal-formed parts. The presentation draws from a multidirectional tool, which was designed to convert the vertical press stroke into horizontal movement of the compression punches towards each other, aspects of experimental strain determination, fractography, and finite element analysis. Results show that three-dimensional to plane-stress material flow transitions at the radially extruded flanges lead to different modes of fracture (by tension and by shear) that may or may not be preceded by necking, such as in sheet metal forming. The new formability test also reveals adequate characteristics to characterize the failure limits of very ductile wrought and additively manufactured metallic materials, which cannot be easily determined by conventional upset compression tests, and to facilitate the identification of the instant of cracking and of the corresponding fracture strains by combination of the force vs. time evolutions with the in-plane strains obtained from digital image correlation.

Self-healing of low-temperature cracks in asphalt mixture under different fracture modes

This research aims to investigate the self-healing of low-temperature cracks in asphalt mixture using semicircular bending tests at different modes of fracture. In this research, samples are fabricated with a 12.5 mm nominal size aggregate and PG58-22 binder. All aged and unaged asphalt samples are subjected to 10 cooling cycles. Also, the resting time between cooling cycles is applied to self-healed samples. The results show that cooling cycles significantly reduce the fracture energy and applying the resting time increases the healing, cracking resistance, and balanced cracking indices. In addition, the most effective of self-healing is observed at fracture mode II.

Optimized mechanical and impact performance of high strength tempo oxidized cellulose nanofibril (TOCNF)—epoxy laminates

In this work, TEMPO cellulose nanofibril (TOCNF) laminates were fabricated using a layup method. Two different TOCNF layers were tested, a neat TOCNF and a TOCNF with polyvinyl alcohol (PVA) strengthening aid with four different epoxy formulations as interlayers for the laminates. Flexural testing showed a correlation between the presence of stronger layers (TOCNFs + PVA) in the laminate with a higher flexural strength, bending modulus, and work of failure. Different modes of fracture within the laminates occurred based on epoxy type. A stiffer epoxy generated a reduced mechanical response and substantial intralayer damage. On the other hand, a more ductile epoxy increased the WOF of the laminates, inducing a higher delamination at the interface. The addition of a silane coupling agent (APTES) resulted in a higher compatibility between the TOCNFs and epoxy, generating an increased ultimate tensile strength (UTS) and a decreased energy to rupture associated with the reduction of crack digression mechanisms in the system. In general, laminates with stronger TOCNF layers (TOCNF + PVA) and increased adhesion (APTES), showed a flexural strength increase of 61%, a bending modulus increase of 80% and the same work of failure when compared with the original laminates. Finally, impact testing of TOCNF materials was performed for the first time in literature, the specific energy to rupture of laminates was comparable to those achieved by acrylic and borosilicate glass, while maintaining a higher or similar specific strength to glass. Laminates showed good transparency and low haziness.Graphic abstract

An IGA based nonlocal gradient-enhanced damage model for failure analysis of cortical bone

The fracture behavior of a cortical bone is significantly affected by its hierarchal structure and a high degree of material anisotropy. Recently, continuum damage models have proven to be an effective tool to characterize such kind of material behavior. However, these models suffer from drawbacks such as mesh dependency, spurious damage growth, and incorrect prediction of damage initiation during the initial stage of loading process. To this end, the objective of this work is to develop a nonlocal gradient-enhanced damage model in an isogeometric setting to predict the fracture behavior of a cortical bone. The numerical framework is formulated considering an additional diffusion equation in conjunction with the standard equilibrium equation. The material is assumed to be transversely isotropic to incorporate the anisotropy in damage evolution. The versatility of the proposed framework is tested by solving problems for different modes of fracture. For numerical simulations, samples are taken from different quadrants of bovine cortical bone, and the effect of anisotropy on the damage characteristics of the bone are investigated.

Cracking Properties of Warm Mix Asphalts Containing Reclaimed Asphalt Pavement and Recycling Agents under Different Loading Modes

This paper aims to evaluate the influence of two recycling agents (RAs) on the cracking behavior of warm mix asphalt (WMA) containing up to 50% reclaimed asphalt pavement (RAP). Two chemically different types of recycling agents, namely aromatic extracts and triglycerides/fatty acids, together with a WMA additive (Sasobit®) were introduced to the mixture. A hot mix asphalt (HMA) mixture (as control mixture) and seven WMA mixtures containing three different dosages of RAP (0, 25, and 50%) and modified by two RAs were prepared. The fracture toughness and energy of the above-mentioned asphalt mixtures were evaluated under pure modes of I and II and mixed mode I/II using the semi-circular bending (SCB) test at mid and subzero temperatures. The results indicated that the cracking resistance of the WMA mixtures without RAP is better than the HMA mixtures under different modes of fracture regardless of the temperature (−15 °C and 25 °C). In addition, at −15 °C, the presence of RAP in the WMA mixtures reduced the fracture toughness and energy while at 25 °C, it results in an increase in fracture toughness and energy. Moreover, the addition of RAs to the WMA mixtures containing RAP increased the fracture toughness and energy at −15 °C. Although RAs decreased the fracture toughness and energy of the RAP blended WMA mixtures at mid-temperature, the performance of these mixtures was better than the HMA mixture.

Fracture Characteristics and Energy Dissipation of Textile Bamboo Fiber Reinforced Polymer.

The fracture theory of fiber-reinforced polymer (FRP) composites is complicated compared to that of homogeneous materials. Textile FRPs need to consider crimp, fiber off-axis and various weaving parameters in a two-dimensional scale, which makes research of failure and fracture difficult. The objective and main contribution of the present research lie in taking textile bamboo FRP as an example and using tools such as toughness, load and deflection curves analysis, energy analysis, and first-order derivative signals to establish the preliminary information needed for fracture theory. This is followed by observing the fracture characteristics of the material under bending. The identification of fracture modes, corresponding energy, and energy dissipation are all prerequisites for developing fracture models in the future. Differences in the direction of force, weaving method, and number of laminates will cause the amount and direction of fibers to vary, which makes the type and progression of fracture different. Combining signal analysis, fracture images and energy dissipation curves, there are different modes of fracture between various groups due to different energy storage forms and crack types, which ultimately lead to different energy dissipation behaviors.

Investigation of damage accumulation and delamination propagation in polymer composite materials based on two-level fracture models

The work is devoted to the study of deformation and fracture processes occurring in layered composites under combined loading modes. The aim of the work is numerical analysis of different modes of fracture, which are simultaneously realized in the samples of laminated composite material. Models of laminated composite material with imitation of technological defects in the form of material debonding are constructed. The delamination process is implemented using the virtual crack closure technique. The processes of damage accumulation and fracture of laminated composites are set on the basis of the models for reduction of stiffness properties using the Hashin criterion and Matzemiller model. The models are based on the laws corresponding to brittle and plastic fracture. Several models of fracture and degradation of elastic properties have been compared. A multiscale approach was used to solve the difficulties related to the precise description of the composite's internal structure. The essence of the approach is that the analysis of a laminated composite can be performed on three different scales: macro level, meso level and micro level. At the macro level, an equivalent material is used for which the effective properties are determined by homogenization methods, in particular by the mean field method. The multiscale finite element modeling is implemented, in the course of which macroscopic parameters of material sample at each step depend on characteristics and properties of components at the micro-level. The behavior of two samples of laminated polymer composite material was studied with different configuration of embedded defects under the load of two types: uniaxial compression and torsion, and only uniaxial compression. The influence of internal defects on the processes of damage accumulation and material delamination has been established.

Estimation of the SIF in FGM spherical pressure vessel

ABSTRACT One of the key factors in the design of the spherical pressure vessels is the lack of study of the SIF in different modes of fracture. In the present research, the SIF evaluation in three modes of fracture was investigated in FGM spherical pressure vessel. The walls of the spherical vessel consisting of semi-elliptical and semi-circular cracks were considered. The simulation and numerical solutions of the problem were done in ABAQUS software. The modelling of FGM spherical vessel was done using the power function and the effect of crack angles on the SIF was evaluated under p, pd and ph . The obtained results illustrated that in homogeneous and FGM vessels, the variation of the SIF directly related to p, so that, with increasing p, the SIF also increases. Also, it was observed that the most variation in the SIF was associated with the ceramic phase of the wall of the vessel where the elastic modulus reduced. In addition, the minimum variation takes place in the steel phase of the wall where the elastic modulus increases. In addition, the results were indicated the minimum variation for this parameter relates to crack at = 90°. Abbreviations: BEM: boundary element method; EFE: enriched finite element; EFGM: element-free Galerkin method; FEA: finite element analysis; FEM: finite element method; FEs: finite elements; FGMs: functionally graded materials; FG: functionally graded; GFEs: graded finite elements; ITM: interaction integral method; LEFM: linear elastic fracture mechanics; LFM: linear fracture mechanics; SIFs: stress intensity factors; WFs: weight functions; 3D: three dimensional; CWF: coefficients of weight function; SC: semi-circular; SE: semi-elliptical.

Process parameter optimisation in pinless friction stir spot welding of dissimilar aluminium alloys using Multi-start algorithm

Friction stir spot welding, a solid-state metal joining process has been utilised to join dissimilar aluminium alloys using pinless tools. The optimal welding conditions were predicted using the Multi-start algorithm with 25 starting points and were validated by confirmation tests. The Multi-start algorithm predicted the maximum tensile shear force of 6.28 kN at the tool rotational speed of 841.83 r/min, plunge depth of 0.618 mm, shoulder diameter of 24.99 mm, plunging speed of 0.04 mm/s and dwell time of 8 s. The scanning electron microscopy analysis revealed the formation of flatter hooks in the weld zone. The electron backscatter diffraction scans revealed a decrease in grain size at the lower sheet (Al 5754) due to the action of 30 kN axial force during pinless friction stir spot welding. Two different modes of fracture were observed: (i) nugget pull-out with necking; (ii) shearing. The fracture modes were observed to be dependent on the process parameters like shoulder diameter and plunge depth.

Comparison of fracture behaviour of a composite laminate with Cross-ply & Angle ply lay-up subjected to Thermal rise loading

Abstract There is an increased usage of advanced composite structures due to several inherent benefits that they offer in comparison with the monolithic materials. But the application of these materials is being limited by the fact that the knowledge about the crack propagation and strength behaviour under application of loads and environmental conditions is not extensive. So, undertaking research in this direction is still very much important. In this paper, a circular crack which is present in the middle of a composite laminate made up with a cross-ply (0/90) and Angle-ply (-45/+45) was modelled and then subjected to thermal loading conditions where the temperature was considered to be rising to study the fracture behaviour. The fracture behaviour of the composite laminate was studied using the strain energy release rate (SERR) value calculated using Virtual crack closure technique (VCCT). Comparison of fracture behaviour between the cross-ply and angle-ply layups the thermal loading conditions on the SERR value in the 3 different modes of fracture with a circular crack located in the middle of the composite laminate was studied and the influence of these parameter was discussed in this paper

Study of fracture behaviour of a composite laminate with central circular hole subjected to thermo-mechanical loading with Temperature fall

Abstract There is an increased usage of advanced composite structures due to several inherent benefits that they offer in comparison with the monolithic materials. But the application of these materials is being limited by the fact that the knowledge about the crack propagation and strength behaviour under application of loads and environmental conditions is not extensive. So, undertaking research in this direction is still very much important. In this paper, a circular crack which is present in the middle of a composite laminate was modelled and then subjected to combined (temperature + pressure) loading conditions where the temperature was considered to be falling and pressure remaining constant to study the fracture behaviour. The fracture behaviour of the composite laminate was studied using the strain energy release rate (SERR) value calculated using Virtual crack closure technique (VCCT). The effect of temperature fall, fiber angle and the combined thermo-mechanical loading conditions on the SERR value in the 3 different modes of fracture with a circular crack located in the middle of the composite laminate was studied and the influence of these parameter was discussed in this paper

Using the generalized maximum tangential stress criterion to predict mode II fracture of hot mix asphalt in terms of mode I results – A statistical analysis

Low-temperature cracking of asphalt pavements is among the most important deteriorations in flexible pavements. Different modes of fracture may occur in a pavement depending on the vehicle wheel load position relative to the existing crack. Therefore, it is needed to test the fracture performance of asphaltic materials at different modes, which is time and cost consuming. Therefore, finding a statistical approach to correlate different modes of fracture of asphalt mixtures can be very beneficial. In this research, several semi-circular bending (SCB) specimens were tested under mode I and mode II fracture conditions. Then, the predictability of experimental mode II test results in terms of mode I fracture toughness data was investigated using the generalized maximum tangential stress (GMTS) theory. The Weibull distribution curves were also used for statistical analyses of the test data. It was found that the GMTS criterion successfully predicts the Weibull parameters of mode II results in terms of mode I fracture data.

A 3D study of the relationship between leaf vein structure and mechanical function

We investigate the structures and mechanical properties of leaf midribs of Ficus microcarpa and Prunus dulcis, which deposit calcium oxalate crystals, and of Olea europaea midribs which contain no mineral deposits, but do contain lignified fibers. The midrib mechanical performance contributes to the leaf’s ability to maintain a flat conformation for light harvesting and to efficiently reconfigure to reduce wind drag. We use a novel approach involving 3D visualization of the vein structure during mechanical load. This involves the use of customized mechanical loading devices that fit inside a microCT chamber. We show that the elastic, compression and torsional moduli of the midribs of leaves from the 3 species examined vary significantly. We also observed different modes of fracture and buckling of the leaves during compression. We assess the contributions of the calcium oxalate crystals to the mechanical and fracture properties. In F. microcarpa midrib linear arrays of calcium oxalate crystals contribute to resisting the bending, in contrast to P. dulcis leaves, where the calcium oxalate crystals do not resist bending. In both F. microcarpa and P. dulcis isolated calcium oxalate crystals enable high torsional compliance. The integrated microCT – mechanical testing approach could be used to investigate the structure-mechanics relationships in other complex biological samples. Statement of significanceLeaves need to maintain a flat conformation for light harvesting, but they also need to efficiently reconfigure to reduce wind drag. The leaf central vein (midrib) is a key structural component for leaf mechanicss. 3D visualization of the vein structure under mechanical loads showed that veins can be stiffened by reinforcement units composed of calcium oxalates crystals and lignin. The stiffening units can influence the bending and fracture properties of the midribs, and can contribute to determine if buckling will occur during folding. Mineral stiffening elements could be a widespread strategy to reinforce leaf veins and other biological structures. This structural-mechanical approach could be used to study other complex biological samples.

Experimental and numerical investigations of mixed-mode ductile fracture in high-density polyethylene

High-density polyethylene (HDPE) is widely used in the production of fuel tanks and natural gas distribution systems, and therefore better understanding its fractural behavior under different loading conditions is essential. The present study is an extension of our previous work, in which J–Q theory was applied to study elastic–plastic fracture in HDPE. In this study, we explore the mixed-mode ductile fracture in HDPE using Brazilian disk samples. Brazilian disk test is commonly used to create different modes of fracture; however, its application has been limited to the linear elastic fracture mechanics. This work has merit to characterize mixed-mode ductile fracture from the experimental data. The combined experimental finite element (CEFE) method introduced in our previous studies was employed to calculate ductile fracture parameters. To validate experimental results, the CEFE results were compared to finite element results, and the difference was less than 7%. The effects of the factors like crack angle and sample’s thickness on Q values were also investigated.

Fracture characterization of multi-layer wire mesh rubberized ferrocement composite slabs by means of acoustic emission

This study investigated the fracture behaviour of multi-layer ferrocement composite slabs with partial replacement of tire rubber powder as filler utilizing acoustic emission (AE) technique for characterization. Ferrocement slab specimens prepared using normal-compact cement mortar, self-compact cement mortar, fly ash, and rubberized self-compact cement mortar –with varying steel mesh reinforcement layers– were statically loaded to failure. The inclusion of 10% rubber powder (by weight) was found capable of altering the failure mode of composite slabs from brittle to ductile with a slight reduction in the ultimate flexural strength. Fracture development of the specimens was closely monitored using AE for enhanced characterization. It is seemingly evident that the measured AE parameters could be effectively processed to distinguish different modes of fracture. The collected AE data was utilized to quantify stiffness reduction in the specimens due to progressive damage.

Experimental Analyses for The Mechanical Behavior of Pressed All-Ceramic Molar Crowns with Anatomical Design

Ceramic restorations show considerable variation in strength and structural reliability regarding to the type of material, and design characteristics. The fracture of ceramics occurs with little or no plastic deformation, with cracks propagated in an unstable manner under applied tensile stresses. The aim of the study was to assess experimental analyses of pressed monolithic ceramic crowns with anatomical design used in the posterior areas in order to understand their mechanical behavior before following their clinical use. Experiments were conducted on a complete molar crown preparation. Experiments show different modes of fracture for the tested samples. Digital images from the fractured pieces of the crowns were used to verify the fragments in all cases final fracture occurred by splitting into two and often more parts. The graphically representation of the displacement depending on the load highlights a series of peaks that can be correlated with cracks occurred in crowns. The development of well-designed mechanical experiments could be useful to help to predict clinical survival of these new all-ceramic restorative techniques and materials. Because failure is often accompanied by complete cracking of the crowns, preliminary research should represents a compulsory goal.

Effect of core ceramic grinding on fracture behaviour of bilayered zirconia veneering ceramic systems under two loading schemes

ObjectiveThe aim of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered zirconia under two loading schemes. MethodsInterfacial surfaces of sandblasted zirconia disks (A) were ground with 80 (B), 120 (C) and 220 (D) grit diamond discs, respectively. Surface roughness and topographic analysis were performed using a confocal scanning laser microscope (CSLM) and a scanning electron microscopy (SEM). Relative monoclinic content was evaluated using X-ray diffraction analysis (XRD) then reevaluated after simulated veneer firing. Biaxial fracture strength (σ) and Weibull modulus (m) were calculated either with core in compression (subgroup Ac-Dc) or in tension (subgroup At-Dt). Facture surfaces were examined by SEM and energy dispersive X-ray spectroscopy (EDS). Maximum tensile stress at fracture was estimated by finite element analysis. Statistical data analysis was performed using Kruskal–Wallis and one-way ANOVA at a significance level of 0.05. ResultsAs grit size of the diamond disc increased, zirconia surface roughness decreased (p<0.001). Thermal veneering treatment reversed the transformation of monoclinic phase observed after initial grinding. No difference in initial (p=0.519 for subgroups Ac-Dc) and final fracture strength (p=0.699 for subgroups Ac-Dc; p=0.328 for subgroups At-Dt) was found among the four groups for both loading schemes. While coarse grinding slightly increased final fracture strength reliability (m) for subgroups Ac-Dc. Two different modes of fracture were observed according to which material was on the bottom surface. Components of the liner porcelain remained on the zirconia surface after fracture for all groups. SignificanceTechnician grinding changed surface topography of zirconia ceramic material, but was not detrimental to the bilayered system strength after veneer application. Coarse grinding slightly improved the fracture strength reliability of the bilayered system tested with core in compression. It is recommended that veneering porcelain be applied directly after routine lab grinding of zirconia ceramic, and its application on rough zirconia cores may be preferred to enhance bond strength.

Fracture of human femur tissue monitored by acoustic emission sensors.

The study describes the acoustic emission (AE) activity during human femur tissue fracture. The specimens were fractured in a bending-torsion loading pattern with concurrent monitoring by two AE sensors. The number of recorded signals correlates well with the applied load providing the onset of micro-fracture at approximately one sixth of the maximum load. Furthermore, waveform frequency content and rise time are related to the different modes of fracture (bending of femur neck or torsion of diaphysis). The importance of the study lies mainly in two disciplines. One is that, although femurs are typically subjects of surgical repair in humans, detailed monitoring of the fracture with AE will enrich the understanding of the process in ways that cannot be achieved using only the mechanical data. Additionally, from the point of view of monitoring techniques, applying sensors used for engineering materials and interpreting the obtained data pose additional difficulties due to the uniqueness of the bone structure.

Analysis of Shear Strength of Wood

This paper presents the analysis of different types of shear strength of wood which can differ very much due to its structure and different orientations of applied load. These combinations of wood structure and load orientations lead to different modes of fracture. The main aim of the paper is to find a relation among all types of shear strength of the wood and to reduce the number of shear tests. Furthermore, different shear strengths will be analyzed both experimentally and numerically, i.e. experimentally by testing appropriate specimens and numerically with the help of the finite element structural analysis solver Robot AutoDesk. The testing specimens will be loaded parallel and perpendicular to the wood fibres and the radial and tangential planes will be analyzed. The paper will also investigate the relation to other strengths of wood (i.e. tensile strength parallel and perpendicular to the fibres) in order to simplify the testing procedure for shear strength determination.