Increase In Fracture Load Research Articles

Characterization of thin-walled self-healing microcapsules reinforced with multi-walled carbon nanotubes

This study presents a novel approach to fabricating thinner shells and significantly enhancing the fracture strength of melamine-urea-formaldehyde (M-U-F) microcapsules reinforced with multi-walled carbon nanotubes (MWCNTs). Unlike previous studies that primarily focused on single-walled carbon nanotubes (SWCNTs) or MWCNTs in polyurea-formaldehyde (PUF) shells, this research advances microcapsule technology by exploring MWCNT reinforcement in M-U-F shells. We employed a dual experimental-numerical approach, combining the precision of micro-compression tests with the predictive capabilities of finite element analysis (FEA) to determine the elastic modulus of MWCNT-reinforced M-U-F microcapsules. This method offers new insights into the mechanical behavior of these microcapsules. Our findings indicate an 8.8% increase in fracture load and a 14.6% reduction in fracture displacement for MWCNT-reinforced microcapsules compared to conventional M-U-F microcapsules. Additionally, FEA confirmed the results of the micro-compression tests, showing that MWCNT-reinforced microcapsules had the best correlation with an elastic modulus of 4.00 GPa. Conventional M-U-F microcapsules corresponded to an elastic modulus of 2.25 GPa. These results provide a comprehensive understanding of how nano-reinforcement influences the structural properties of thin-walled microcapsules, with potential applications in composite damage repair and beyond.

Study on fracture performance and failure mechanism of hydraulic basalt fiber asphalt concrete by considering temperature effect

An asphalt concrete anti-seepage core wall may be faced with the risk of cracking due to problems like uneven settlement of the foundation during the service period. Considering that hydraulic asphalt concrete (HAC) has a high asphalt content while basalt fibers have excellent tensile properties and good compatibility with asphalt, adding basalt fibers into HAC may potentially form a useful material for hydraulic engineering. Therefore, it is of great significance to comprehensively examine the fracture properties of this new composite material from both macroscopic and mesoscopic perspectives. To explore the effect of basalt fibers on the fracture performance of HAC, an experimental study was carried out on hydraulic basalt fiber asphalt concrete (HBFAC) under different temperatures by considering 3 fiber lengths and 4 fiber contents. The results showed that, when the temperature remained constant, the fracture load, fracture toughness and fracture energy of HAC all exhibited an upward trend with the increase of fiber content, and reached the maximum values at the fiber content of 4‰. Of different fiber lengths, the maximum fracture load, fracture toughness and fracture energy were observed at the fiber length of 6 mm. With the growth of temperature, the fracture load and fracture toughness exhibited a decreasing trend, while the fracture energy showed an increasing trend. At the same time, the increase in fracture load and fracture toughness due to the fiber reinforcing effect was gradually enlarged, but the increase in fracture energy was gradually reduced. Overall, the optimum fiber length and fiber content were determined to be 6 mm and 4‰, respectively. Subsequently, the fiber properties were further investigated with the discrete element method, and the results of internal mesoscopic mechanical behavior, crack development and particle displacement indicate that basalt fibers play a positive role in dispersing stress and inhibiting crack development so as to improve the toughness and cracking resistance of HAC. Finally, the failure mechanism of HBFAC at different temperatures was revealed from a mesoscopic level. The outcome of this paper provides a theoretical basis for the research and application of basalt fibers in HAC.

Brittle fracture of three-dimensional lattice structure

This work aims to develop a greater understanding of fracture behaviour of a three-dimensional lattice structure. Octet-truss lattice was used in this study due to its high strength to density ratio and great potential in the advanced lightweight structure applications. The fracture toughness, KIC, was found to be almost isotropic while the modulus and strength were highly dependent on the model size and lattice orientation. The converged solution for the modulus and strength were obtained when model width is large compared to cell. The modulus can be varied by 20% and the strength can be doubled when lattice orientation was changed. The validity of linear elastic fracture mechanics (LEFM) was examined on different model geometries including single edge notch tension (SENT), compact tension (CT), single edge notch bending (SENB) and thumbnail crack model. It shows that the LEFM can be adequately used in the structures with linear crack fronts. In the thumbnail crack model, the curved crack front generates more complexity in the structure ahead of the crack tip which results in a significant discrepancy in measured toughness compared to the models with linear crack fronts. Moreover, great fracture performance was exhibited in the lattices, where an increase in fracture load was observed during the crack growth.

Previous Damage Accumulation Can Influence Femoral Fracture Strength: A Finite Element Study.

To manage osteoporotic hip fracture risk, it is necessary to understand failure mechanisms of bone at both the material and organ level. The structural response of bone is dependent on load history. Repeated loading causes progressive microstructural cracking, resulting in reduced apparent-level stiffness and, if damage is significant, reductions to peak load bearing capability. However, the effect of previous damage accumulation has not been well explored at the organ level. It was hypothesized that femoral fracture load and fracture pattern may be sensitive to damage accumulation from previous loading events. Six cadaveric specimens were used to develop patient specific finite element (FE) models from quantitative tomographic (qCT) scans. Material properties were assigned from qCT intensity at each element location, and damage evolution was predicted using a previously validated quasi-brittle FE model. Three scenarios were investigated: stumble followed by another stumble (S-S), fall followed by another fall (F-F), and stumble followed by a fall (S-F). Fracture load and pattern were compared to FE predictions for a single stumble (S) or single fall (F) loading event. Most specimens were resilient to accumulated damage, showing little (<5%) change in fracture load from the multiple-load scenarios (S-S, F-F, and S-F) compared to an equivalent single load scenario (S or F). Only one specimen demonstrated moderate (5-15%) reductions in strength from all three multiple-load scenarios. However, two specimens experienced moderate (20-30%) increase in fracture load in some load cases. In these cases, initial damage caused the load to be more evenly distributed upon subsequent loading events. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2197-2203, 2019.

Alumina reinforced zirconia implants: Effects of cyclic loading and abutment modification on fracture resistance

ObjectiveThe aim of the study was to evaluate the thermomechanical behavior of alumina-toughened zirconia (ATZ) oral implants in the artificial mouth and the fracture resistance (fracture load and bending moment) in a subsequent static fracture load test. The effects of abutment modification and different cyclic loadings were evaluated. MethodsA total of 48 implants were used. 24 implants were left as machined (Group A), and 24 implants were shape modified at the abutment (Group B). Groups were divided into three subgroups composed of 8 samples each (A1/B1: no cyclic loading; A2/B2: 1.2 million cycles; A3/B3: 5 million cycles). Subsequently, all implants were statically loaded to the point of fracture. ResultsThe implants showed the following survival rates after the artificial mouth: A2 and B2 100%; A3 and B3 87.5%. The following average fracture resistance values were found (fracture load [N]/bending moment [Nmm]): A1 (583/2907), B1 (516/2825), A2 (618/2737), B2 (550/3150), A3 (802/3784) and B3 (722/3809). After 5 million loading cycles a significant increase in fracture load and bending moment was found. Modification of the abutment significantly decreased the fracture load of implants without foregoing dynamic loading. However, the shape modification altered the lever arm. For that reason, a smaller load resulted in the same bending moment. Therefore, abutment modification had no significant influence on the fracture resistance of ATZ. SignificanceNeither thermomechanical cycling in an aqueous environment nor modification of the abutment had a negative effect on the fracture resistance of ATZ.

Fracture load of milled polymeric fixed dental prostheses as a function of connector cross-sectional areas

Polymeric computer-aided design/computer-aided manufacturing (CAD/CAM) blocks exhibit various advantages in contrast to conventionally processed resin restorations. However, the influence of connector dimensions on resin fixed dental prostheses (FDPs) has not yet been investigated. This study evaluated the impact of connector cross-sectional area (CSA) on the fracture load of 3-unit CAD/CAM FDPs and compared this with conventionally fabricated ones. Anatomically shaped 3-unit FDPs with the CSAs of 6, 9, 12, and 16 mm(2) (N=240, n=15 per material and per CSA) were fabricated from the following CAD/CAM materials: artBloc Temp (AT), TelioCAD (TC), CAD-Temp (CT), and one conventional resin material, CronMix K (CMK) as the control group. The fracture load was tested and the data were analyzed with 2-way ANOVA, 1-way ANOVA, the Scheffé post hoc test, and Weibull statistics (α=05). CMK showed the significant lowest values for all CSAs followed by CT, except for the 12 mm(2) connector (P<.001). The CAD/CAM FDPs exhibited a significant increase in fracture load with the increase of CSA (P<.001). Conventionally fabricated FDPs presented an increase of values up to the CSA of 12 mm(2). For TC, the shape increased with a larger CSA. The other materials exhibited no tendencies in this regard. Among the 12 mm(2) groups, AT exhibited the highest shape value (19.1), and among the 16 mm(2) groups, TC showed the highest shape value (17.0). The CMK FDPs with a CSA of 16 mm(2) showed almost half as high a shape parameter (6.4) than the other three CSAs. CAD/CAM resin FDPs revealed significantly higher fracture load values than conventionally fabricated FDPs and showed a significant increase in fracture load with the increase of the CSA.

Effect of Framework Design on Fracture Resistance in Zirconia 4-unit All-ceramic Fixed Partial Dentures

The purpose of this study was to conduct static load-bearing tests on 4-unit Y-TZP all-ceramic fixed partial denture (FPD) frameworks with different cross-sectional areas and forms to evaluate the influence of connector design on fracture load. Each of the central, mesial and distal connectors was prepared with one of 2 different cross-sectional areas and one of 3 different forms (one circular and two oval forms) to give a total of 18 designs. Five frameworks were then prepared for each design, making a total of 90. Each framework was cemented to the test model with glass ionomer cement. Fracture load was measured with a universal testing machine at a cross-head speed of 1.0 mm/min. A three-way ANOVA revealed significant differences in fracture load depending on cross-sectional area, central connector cross-sectional form, or mesial/distal connector cross-sectional form (p<0.01). No interaction was observed, however, between any two connector design elements. The results of a Tukey analysis revealed a significant difference between the two connector cross-sectional areas investigated, with an increase in connector cross-sectional area resulting in an increase in fracture load. Fracture load decreased as the height of the mesial or distal connector decreased. Fracture load was significantly higher in frameworks in which the height of the central connector was greater than that of the distal or mesial connector. In conclusion, these results suggest that sufficient height needs to be maintained in the mesial/distal connector to secure a high fracture load in zirconia 4-unit all-ceramic FPDs. Moreover, even when this is not possible, a high fracture load may still be obtained by making the height of the central connector as great as possible. Furthermore, extending the connector cross-sectional area is effective in increasing fracture load.

The effect of E-glass fibers and acrylic resin thickness on fracture load in a simulated implant-supported overdenture prosthesis

Implant overdenture prostheses are prone to acrylic resin fracture because of space limitations around the implant overdenture components. The purpose of this study was to evaluate the influence of E-glass fibers and acrylic resin thickness in resisting acrylic resin fracture around a simulated overdenture abutment. A model was developed to simulate the clinical situation of an implant overdenture abutment with varying acrylic resin thickness (1.5 or 3.0 mm) with or without E-glass fiber reinforcement. Forty-eight specimens with an underlying simulated abutment were divided into 4 groups (n=12): 1.5 mm acrylic resin without E-glass fibers identified as thin with no E-glass fiber mesh (TN-N); 1.5 mm acrylic resin with E-glass fibers identified as thin with E-glass fiber mesh (TN-F); 3.0 mm acrylic resin without E-glass fibers identified as thick without E-glass fiber mesh (TK-N); and 3.0 mm acrylic resin with E-glass fibers identified as thick with E-glass fiber mesh (TK-F). All specimens were submitted to a 3-point bending test and fracture loads (N) were analyzed with a 2-way ANOVA and Tukey's post hoc test (α=.05). The results revealed significant differences in fracture load among the 4 groups, with significant effects from both thickness (P<.001) and inclusion of the mesh (P<.001). Results demonstrated no interaction between mesh and thickness (P=.690). The TN-N: 39 ±5 N; TN-F: 50 ±6.9 N; TK-N: 162 ±13 N; and TK-F: 193 ±21 N groups were all statistically different (P<.001). The fracture load of a processed, acrylic resin implant-supported overdenture can be significantly increased by the addition of E-glass fibers even when using thin acrylic resin sections. On a relative basis, the increase in fracture load was similar when adding E-glass fibers or increasing acrylic resin thickness.

Analysis of friction and surface roughness effects on edge crack evolution of thin strip during cold rolling

Experimental investigation and mechanical analysis have been carried out to study the edge crack formation during cold strip rolling using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The effects of friction and surface roughness on edge crack initiation and growth rate have been discussed. Friction leads to an increase in fracture loads and decreasing the friction coefficient is effective in preventing the microcracks. Surface roughness variation along the strip width contributes to stress distribution and inhibits crack nucleation. The findings reveal that the behaviour of crack evolution is influenced by fracture surface roughness as well as rolling friction.

Femoroplasty – augmentation of the proximal femur with a composite bone cement – feasibility, biomechanical properties and osteosynthesis potential

Background Analogous to vertebroplasty, cement-augmentation of the proximal femur (“femoroplasty”) could reinforce osteoporotic bones. This study was to evaluate (i) the feasibility of femoroplasty with a composite cement (Cortoss™), (ii) its influence on femoral strength by mechanical testing and (iii) the feasibility of stable osteosynthesis of the augmented fractured bones. Methods Nine human cadaveric femora were augmented with a composite bone cement, the surface heat generation monitored, and then tested biomechanically against their native contralateral control to determine fracture strength. Subsequently, thirteen reinforced and fractured femora were osteosynthetized by different implants and tested against their osteosynthetisized, non-augmented contralateral control. Findings Cement could be injected easily, with a moderate temperature rise. A positive correlation between BMD and fracture load and a significant increase in fracture load (+43%) of the augmented femora compared to their native controls (6324 N and 4430 N, respectively) as well as a significant increase in energy-to-failure (+187%, 86 N m and 30 N m, respectively) was found. Osteosynthesis was possible in cement-augmented femora. Osteosynthetisized femora showed equivalent strength to the intact controls. Interpretation Augmentation of the proximal femur with composite bone cement could be of use in prophylaxis of fractures in osteoporotic femurs. Osteosynthesis of the fractured augmented bones is a challenging procedure but has a good chance to restore strength.

Diametal Compression Characteristics of Cohesive Ash Powder Pellets at High Temperature.

The increase in the cohesive properties of fly ash under elevated temperature conditions up to 1123 K, was investigated by a diametral compression test of ash powder pellets. Under conditions of relatively low temperatures (below 1000 K), the strength of ash powder pellets increases gradually in proportion to temperature. A remarkable increase in strength of the powder pellets is observed in the high temperature range above 1123 K. At these high temperatures, plastic deformation (during a diametal compression test) and enhancement in the time dependent on increase in fracture load of ash powder pellets is observed.

Differential effects of systemic prostaglandin E2 on bone mass in rat long bones and calvariae.

Prostaglandin E2 (PGE2) has been shown to possess anabolic properties when administered systemically. All the experiments performed so far examined long bones from animals of varying age and bone status. In this study we compared the changes in bone mass of long bones (femur, tibia and humerus) to those in calvariae after a 3-week daily administration of 6 mg/kg PGE2 into 3-week-old rats. This regimen inhibited body weight gain (by 14.1%) as well as longitudinal growth of long bones (by 2.2-3.5%) but increased their mass. Ash weight (measuring both cancellous and compact bone) increased by 10.1-14.1% but tibial cancellous bone area was elevated by 54%. Radial growth was slightly reduced due to transient inhibition of mineral apposition rate at the periosteal envelope but the expansion of the marrow cavity was inhibited to a greater extent, resulting in an 8.1% increase in the relative compact bone area. The increased bone mass was associated with greater mechanical strength of the femoral neck (24.2% increase in fracture load and 19% in stiffness). In contrast, PGE2 administration did not affect calvarial thickness or mineral apposition rate but increased its density, i.e. reduced the area of marrow spaces due to stimulation of endocortical bone formation at this site. The pattern of bone mass changes documented in this study closely correlates with that of the induced expression of early-response genes following a single dose of PGE2 as we recently reported. These data, therefore, support the hypothesis that in vivo administration of an anabolic dose of PGE2 increases bone formation and augments bone mass largely by stimulating the recruitment of new osteoblasts via induction of the proliferation and/or differentiation of bone marrow osteogenic precursors.

Fracture strengths of provisional restorations reinforced with plasma-treated woven polyethylene fiber

Statement of problem. Fracture strength of interim fixed partial prosthesis is of great concern, especially in long-span restorations or areas of heavy occlusal stress.Purpose. Effects of a plasma-treated woven polyethylene fiber (Ribbond) on the fracture strength of polymethyl methacrylate (Coldpac) and a resin-based two-phase curing provisional restorative material (Provipont DC) were evaluated.Material and methods. A polyvinyl siloxane template was used to fabricate three-unit posterior provisional prostheses on a stainless steel die with two abutments 22 mm apart. The reinforced groups were fabricated by affixing 3 mm wide pieces of fiber treated with methyl methacrylate monomer or polyisocyanate (activator part of Provipont DC) on the occlusal surfaces of abutments. The interim materials were mixed, according to the manufacturers' specifications, and placed in the template. The template was pressed on the die and held secure until complete setting of the material occurred by light curing (Provipont DC) or autopolymerization (PMMA). The specimens were divided into 4 groups of 10 each (A, reinforced Provipont DC; B, unreinforced Provipont DC; C, reinforced PMMA; and D, unreinforced PMMA). A central compressive load force was exerted on the specimen to determine the fracture load of the restorations.Results. The data revealed mean fracture loads of A, 65.59 ± 11.27 kg; B, 46.59 ± 14.84 kg; C, 53.46 ± 7.76 kg; and D, 49.86 ± 14.44 kg.Conclusion. Plasma-treated polyethylene reinforced PMMA restorations showed no significant increase in fracture loads when compared with unreinforced restorations ( p > 0.10), whereas reinforced resin-based restorations revealed significantly higher fracture loads ( p < 0.01) than the unreinforced resin-based and PMMA provisional restorations. (J Prosthet Dent 1997;78:447-50.)

The effects of crack surface friction and roughness on crack tip stress fields

A model is presented which can be used to incorporate the effects of friction and tortuosity along crack surfaces through a constitutive law applied to the interface between opposing crack surfaces. The problem of a crack with a saw-tooth surface in an infinite medium subjected to a far-field shear stress is solved and the ratios of mode I stress intensity to mode II stress intensity are calculated for various coefficients of friction and material properties. The results show that tortuosity and friction lead to an increase in fracture loads and alter the direction of crack propagation.