Predominant Failure Mode Research Articles

An experimental study of flank wear in the end milling of AISI 316 stainless steel with coated carbide inserts

Stainless steel 316 is a difficult-to-machine iron-based alloys that contain minimum of about 12% of chromium commonly used in marine and aerospace industry. This paper presents an experimental study of the tool wear propagation variations in the end milling of stainless steel 316 with coated carbide inserts. The milling tests were conducted at three different cutting speeds while feed rate and depth of cut were at (0.02, 0.06 and 01) mm/rev and (1, 2 and 3) mm, respectively. The cutting tool used was TiAlN-PVD-multi-layered coated carbides. The effects of cutting speed, cutting tool coating top layer and workpiece material were investigated on the tool life. The results showed that cutting speed significantly affected the machined flank wears values. With increasing cutting speed, the flank wear values decreased. The experimental results showed that significant flank wear was the major and predominant failure mode affecting the tool life.

DENTIN BOND EFFICACY OF COMPOSITE RESIN RESTORATIONS USING RESIN INFILTRANT

Aim: To evaluate the bond efficacy of direct resin composite restorations bonded by three different dentin adhesives an etch-and-rinse, self-etch and resin infiltrant (ICON) using microtensile bond strength testing and Analyze their failure mode. Methodology: Thirty molar teeth were selected and thoroughly cleaned. Each tooth was vertically embedded into self-curing acrylic resin up to the level of the cervical line. The occlusal enamel of teeth was removed perpendicular to the long axis of teeth to expose flat dentin surface at a standardized depth. The teeth were divided into three main groups of 10 teeth each; using Etch and rinse adhesive system control group A1 (All-bond Universal, Bisco), self-etch adhesive system group A2 (All-bond Universal, Bisco) and resin infiltrant group A3 (Icon). Direct resin composite nano-hybrid universal composite (FiltekTM Z250 XT, 3M ESPE) cores were build up on the flat dentin surfaces treated with different adhesive systems. The restored teeth were subjected to thermo-cycling at 5°C and 55°C for 2000cycle. Then each tooth was mounted on the cutting machine, sectioned into a series of 1 mm thick. The sticks were stressed to failure under tension using Universal Testing Machine to record the microtensile bond strength. The fractured sticks were evaluated for bond failure mode under a stereomicroscope at 40X magnification to detect the mode of failure. The collected data were submitted to ANOVA and Tukey’s test. Results: Etch-and-rinse (A1) control group showed the highest significant mean Microtensile bond strength (MPa) followed by Self-etch adhesive (A2) followed by Resin infiltrant (ICON) (A3) at p≤0.001. The result of the stereomicroscopic examination revealed adhesive and cohesive failure mode in composite. The predominant mode of failure using resin infiltrant group A3 (Icon) and self-etch adhesive system group A2 group was adhesive failure with a higher percentage in resin infiltrant A3 (Icon) group 100%. On the other hand cohesive in composite is the predominant mode of failure using the Etch and rinse adhesive system group A1 80%. Conclusion: The use of resin infiltrant (Icon) as an adhesive material impaired efficacy of the microtensile bond strength of direct resin composite to sound dentin .

Safety and efficacy of lobaplatin combined with 5-fluorouracil as first-line induction chemotherapy followed by lobaplatin-radiotherapy in locally advanced nasopharyngeal carcinoma: preliminary results of a prospective phase II trial

BackgroundDue to improvements in imaging and radiological techniques as well as the use of chemotherapy, distant metastasis has become the predominant mode of treatment failure in patients with locally advanced nasopharyngeal carcinoma (LA-NPC). Platinum-based systemic chemotherapy has shown survival benefits and is now the standard strategy for systemic therapy in patients with LA-NPC. Notably, the third-generation platinum reagent lobaplatin has shown anti-tumor effects in several solid tumors with lower incidences of gastrointestinal, hepatic and renal toxicity relative to other platinum drugs. However, the safety and efficacy of lobaplatin as a first-line regimen in patients with LA-NPC are undetermined.MethodsPatients with stage III–IVa-b NPC received lobaplatin at a dose of 30 mg/m2 on days 1 and 22 combined with a continuous 120-h intravenous injection of 5-fluorouracil at a dose of 4 g/m2 followed by lobaplatin at a dose of 50 mg/m2 on days 43 and 64 concomitant with intensity-modulated radiation therapy. Objective response rates and acute toxicity were assessed based on RECIST (1.1) and CTCAE v.3.0, respectively. Kaplan-Meier analysis was used to calculate survival rates.ResultsFifty-nine patients were enrolled, and 44 patients (74.6%) received allocated cycles of chemotherapy. The objective response rates were 88.1% (95% confidence interval [CI], 0.77 to 0.95) and 100% after induction chemotherapy (ICT) and concurrent chemoradiotherapy (CRT), respectively. With a median follow-up period of 44 months, the 3-year estimated progression-free survival and overall survival were 86.4% (95% CI, 69.8 to 98.8) and 94.9% (95% CI, 89.5 to 100), respectively. The most common grade 3–4 toxicities were neutropenia (8.5%) and thrombocytopenia (40.7%) after ICT and CRT, respectively.ConclusionLobaplatin combined with 5-fluorouracil followed by lobaplatin-RT treatment showed encouraging anti-tumor effects with tolerable toxicities in patients with LA-NPC. Randomized controlled trials of lobaplatin in patients with LA-NPC are warranted.Trial registrationThis trial was registered with the Chinese Clinical Trials Registry and approved on March 31st, 2012, number ChiCTR-ONC-12002060.

Effects of Cementing on Ligament Balance During Total Knee Arthroplasty.

Complications related to joint imbalance may contribute to some of the most predominant modes of failure in total knee arthroplasty (TKA). These complications include instability, aseptic loosening, asymmetric component wear, and idiopathic pain. Fixation may represent a step that introduces unchecked variability into the procedure and may contribute to the incidence of joint imbalance-related complications. The ability to quantify in vivo loading in the medial and lateral compartments would allow for the ability to confirm balance after fixation and prior to wound closure. This retrospective study sought to capture any variability and imbalance associated with cementing technique. A total of 93 patients underwent sensor-assisted TKA. All patients were confirmed to have quantifiably balanced joints prior to cementation. After cementing and final component placement, the sensor was reinserted into the joint to capture any cementation-induced changes in loading. Imbalance was observed in 44% of patients after cementation. There was no difference in the proportion of imbalance due to surgeon experience (P=.456), cement type (P=.429), or knee system (P=.792). A majority of knees exhibited loading increase in the medial compartment. It was concluded that cementation technique contributes to a significant amount of balance-related variability at the fixation stage of the procedure. The use of the sensor in this study allowed for the correction of all instances of imbalance prior to closure. More objective methods of balance verification may be important for ensuring optimal surgical outcomes. [Orthopedics. 2017; 40(3):e455-e459.].

Hybrid crowns – bonding protocols and shear bond strength

Abstract Aims The objective of the present study was to evaluate the effect of three different surface treatment protocols on the shear bond strength (SBS) of metal brackets to Vita Enamic® and Lava™ Ultimate CAD/CAM hybrid ceramics. Methods A total of 60 crowns were milled and divided into one of three etching groups which used 9.6% hydrofluoric acid, 35% phosphoric acid and 50 μ aluminum oxide microetching. The surface morphology of the ceramic was observed after each etching treatment using a scanning electron microscope to characterise the etched surface. Lower left first molar tubes (Ormco™) were bonded with light-cure composite, stored in artificial saliva for one week and subsequently thermocycled. The SBS test was performed using an Instron 5566 machine. Adhesive Remnant Index (ARI) scores were also assigned to determine the mode of bond failure. Data were analysed using an Independent Sample t-test. Results The SBS of all groups, except the HFA Enamic® group, were significantly lower than the mean SBS of the enamel control group (8.8 MPa). The mean shear bond strength values of Enamic® were significantly higher than those of Lava™ Ultimate (p-values < 0.05). Conclusions Statistically, only Enamic® treated with HFA exhibited sufficient SBS when compared with the enamel control. Adhesive failures between the bracket base and adhesive were the predominant mode of failure in all groups except in the PA Lava™ Ultimate group.

Shear Bond Strength of Lining Materials to Calcium-silicate Cements at Different Time Intervals.

To compare the shear bond strength of three different light-curing, flowable composites (Ionoseal [IS], Vertise flow [VF], and Futurabond NR + Grandio Flow [GF]) on MTA-Angelus [MTA] or Biodentine [BD] at three different time intervals. Freshly mixed MTA or BD was applied into 180 identical plaster molds. Three minutes, 15 min, and 2 days after mixing, specimens of IS, VF, and GF with standardized size and diameter were applied on MTA and BD specimens (n = 10 per material and time interval). Subsequently, all specimens were stored at 36°C and 100% humidity for 28 days. The shear bond strength was determined using a universal testing machine. Statistical evaluation was performed using multifactorial ANOVA and post-hoc Tukey's Test (p < 0.05). Multifactorial ANOVA did not show any significant influence of the combinations "lining material × time" (p = 0.257) and "calcium-silicate cement × lining material × time" (p = 0.241). Significant influences were detected for the interactions "calcium-silicate cement × lining material" (p = 0.000) and "calcium-silicate cement × time" (p = 0.009) and for the parameters calcium-silicate cement (p = 0.000), lining material (p = 0.000), and time (p = 0.008). The predominant failure mode of the restorative materials to the cement surfaces was mixed. Already 3 min after mixing, IS, VF, and GF achieved shear bond strengths on MTA or BD that were similar to those after 15 min and 2 days.

Numerical and Experimental Investigation of the Hydrostatic Performance of Fibre Reinforced Tubes

The increasing demands in subsea industry such as oil and gas, led to a rapidly growing need for the use of advanced, high performance, lightweight materials such as composite materials. E-glass fibre laminated pre-preg, filament wound and braided tubes were tested to destruction under hydrostatic external pressure in order to study their buckling and crushing behaviour. Different fibre architectures and wind angles were tested at a range of wall thicknesses highlighting the advantage that hoop reinforcement offers. The experimental results were compared with theoretical predictions obtained from classic laminate theory and finite element analysis (ABAQUS) based on the principal that the predominant failure mode was buckling. SEM analysis was further performed to investigate the resulting failure mechanisms, indicating that the failure mechanisms can be more complex with a variety of observed modes taking place such as fibre fracture, delamination and fibre-matrix interface failure.

Characterization of Cavitation Eroded Surfaces at Different Temperatures Using Wavelet Method

In the present work, the image features of cavitation erosion surfaces at different temperatures are extracted using wavelet decomposition transform. The results obtained indicate that the extract parameters, wavelet energy, and entropy can characterize the cavitation intensity in a similar manner to that of the mass loss and average particle size at different temperatures. Based on the analysis of the eroded surface and particle morphologies for different temperatures, it was found that the predominant failure mode was fatigue.

Adhesive Cementation Promotes Higher Fatigue Resistance to Zirconia Crowns.

The aim of this study was to investigate the influence of the cementation strategy on the fatigue resistance of zirconia crowns. The null hypothesis was that the cementation strategy would not affect the fatigue resistance of the crowns. Seventy-five simplified molar tooth crown preparations were machined in glass fiber-filled epoxy resin. Zirconia crowns were designed (thickness=0.7 mm), milled by computer-aided design/computer-aided manufacturing, and sintered, as recommended. Crowns were cemented onto the resin preparations using five cementation strategies (n=15): ZP, luting with zinc phosphate cement; PN, luting with Panavia F resin cement; AL, air particle abrasion with alumina particles (125 μm) as the crown inner surface pretreatment + Panavia F; CJ, tribochemical silica coating as crown inner surface pretreatment + Panavia F; and GL, application of a thin layer of porcelain glaze followed by etching with hydrofluoric acid and silanization as crown inner surface pretreatment + Panavia F. Resin cement was activated for 30 seconds for each surface. Specimens were tested until fracture in a stepwise stress fatigue test (10,000 cycles in each step, 600 to 1400 N, frequency of 1.4 Hz). The mode of failure was analyzed by stereomicroscopy and scanning electron microscopy. Data were analyzed by Kaplan-Meier and Mantel-Cox (log rank) tests and a pairwise comparison (p<0.05) and by Weibull analysis. The CJ group had the highest load mean value for failure (1200 N), followed by the PN (1026 N), AL (1026 N), and GL (1013 N) groups, while the ZP group had the lowest mean value (706 N). Adhesively cemented groups (CJ, AL, PN, and GL) needed a higher number of cycles for failure than the group ZP did. The groups' Weibull moduli (CJ=5.9; AL=4.4; GL=3.9; PN=3.7; ZP=2.1) were different, considering the number of cycles for failure data. The predominant mode of failure was a fracture that initiated in the cement/zirconia layer. Finite element analysis showed the different stress distribution for the two models. Adhesive cementation of zirconia crowns improves fatigue resistance.

Three dimensional modelling of ancient colonnade structural systems subjected to harmonic and seismic loading

One of the major threats to the stability of classical columns and colonnades are earthquakes. The behavior of columns under high seismic excitation loads is non-linear and complex since rocking, wobbling and sliding failure modes can occur. Therefore, three dimensional simulation approaches are essential to investigate the in-plane and out-of-plane response of such structures during harmonic and seismic loading excitations. Using a software based on the Distinct Element Method (DEM) of analysis, a three dimensional numerical study has been performed to investigate the parameters affecting the seismic behaviour of colonnades' structural systems. A typical section of the two-storey colonnade of the Forum in Pompeii has been modelled and studied parametrically, in order to identify the main factors affecting the stability and to improve our understanding of the earthquake behaviour of such structures. The model is then used to compare the results between 2D and 3D simulations emphasizing the different response for the selected earthquake records. From the results analysis, it was found that the high-frequency motion requires large base acceleration amplitude to lead to the collapse of the colonnade in a shear-slip mode between the drums. However, low-frequency harmonic excitations are more prominent to cause structural collapse of the two-storey colonnade than the high-frequency ones with predominant rocking failure mode. Finally, the 2D analysis found to be unconservative since underestimates the displacement demands of the colonnade system when compared with the 3D analysis.

Causes of Flexor Tendon Repair Failures in Two Common Repair Techniques: A Cadaver Study.

Flexor tendon repair failures have primarily been attributed to either core suture rupture or core suture pull out. Recent studies have suggested that knot unravelling may also cause failure of a tendon repair. The aim of this study was to investigate the causes of core suture failure in two types of common flexor tendon repairs. Twenty four cadaver tendons were divided into three groups of eight. Each group tested a specific flexor tendon repair. The repairs tested included an Adelaide repair using 4/0 Ethibond (Ethicon), an Adelaide repair using 4/0 Fiberwire (Arthrex) and the Tsai repair with 4/0 Fiberloop (Arthrex). The repaired tendons were pull-tested to failure. The mechanism of failure, maximum tensile strength and 2 mm gap force were recorded. The predominant mode of failure was by the knot unravelling. This occurred in 50-88% of the tendon repairs. The sequence of failure was initiated with gapping at the repair site followed by failure of the epitendinous suture. Next the core suture knot unravels. Once the knot unravels, the suture thread slips out of the tendon resulting in the repair failure. Failures due to knot slippage occurred at a lower maximum tensile strength in Ethibond and Fiberloop sutures than failure due to core rupture or pull out. However, given the small number of tendons tested, this result was not significant. This study has clearly demonstrated one of the main causes of flexor tendon repair failure in two common repair techniques is knot unravelling.

The primary factor for suture configuration at rotator cuff repair: Width of mattress or distance from tear edge

ObjectivesThe aims of this study was first to investigate whether the bite size or the bite distance from the tear edge is of primary importance in mattress suture configuration for rotator cuff repair. Secondly, whether the use of a 450 left side bent Arthro-Pierce™ (Smith & Nephew, Andover, USA) during suture passage can be more effective on the strength of the configuration compared to a straight Arthro-Pierce™. Materials and methodsTwenty-eight bovine infraspinatus muscle tendons were randomized into four groups. Group 1; 5 mm wide ‘bite size’ × 15 mm length ‘distance from the tear edge's mattress’; Group 2: 7.5 mm × 10 mm; Group 3: 15 mm × 5 mm ‘using straight Arthro-Pierce™’ and Group 4: 5 mm × 15 mm using left sided 450 bent Arthro-Pierce™. The repair specimens underwent cyclic loading prior to loading the failure testing. Cyclic elongation (mm), peak-to-peak displacement (mm), ultimate load (N), stiffness (N/mm) and failure mode were recorded for each specimen. ResultsThe mean ultimate load in Group 1 was higher compared to group 3. The peak to peak displacement was higher in Group 4 compared to Group 1 (p < 0.05). The predominant failure mode in Groups 1, 2 and 4 was suture rupture. The Group 3 most specimens failed due to suture cut through the tendon. ConclusionBite size from the edge of the tendon seems to be more important than the width of the mattress. The curve of the suture passing device may also have an effect on the strength of the suture tendon interface.

Feasibility of electromagnetic pulse-assisted incremental drawing with a radial magnetic force for AA-5052 aluminum alloy sheet

In the conventional drawing process, the predominant failure modes of a sheet metal are wrinkling and fracture. Wrinkling during the forming process can often be treated as a recoverable defect as it can be eliminated though the appropriate control of the blank holding force. Fracture, however, is a fatal flaw. When the fracture occurs, the drawing process cannot continue. We propose a new forming method that can handle large height/diameter ratios. The new method uses electromagnetic pulse-assisted incremental drawing (EMPAID) together with radial magnetic force and a suitable auxiliary coil structure and size. Both the calculated and experimental results indicate that the magnetic force generated by the auxiliary coils can increase the flange material flow and significantly improve the ability of the sheet metal to resist fracture. When only the auxiliary coil is used in the experiment, the drawing depth increases by 21.8 % (with respect to conventional drawing) if the auxiliary coils discharge once. The drawing depth can be increased by as much as 36.7 % when multiple discharges are applied. When the auxiliary coil is used in combination with other electromagnetic forming coils in the experiment, the maximum drawing height of the cylinder cup increases by 141.6 %, after multiple discharges.

Determining the temporal development of dentin-composite bond strength during curing

ObjectivesAs composite restorations cure a competition develops between bond formation and shrinkage stress at the composite-dentin interface. Thus, understanding the temporal development of tooth-composite bond strength should enable better assessment of tooth-composite debonding. MethodsIn this study, bond strengths of composite-dentin specimens obtained from tensile test at different curing times were used to determine the bond formation rate. By varying the composite thickness and output from the curing light, their effects on the rate of bond formation for two different materials (a conventional and a bulk-fill composite) were also investigated. The proportions of cohesive and adhesive failure were determined by analysis of electron micrographs of the fractured surfaces. ResultsThe development of dentin-composite bond strength (S) with time (t) can be described by the equation: S=Smax(1−exp(−αt)), where Smax is the final bond strength (∼12MPa for both composites) and α the rate of bond formation. Using bulk-fill and thinner specimens gave faster bond formation. In fact, the higher the irradiance at the interface, the higher the rate of bond formation. However, α had a maximum value of ∼0.6s−1 and the rule of reciprocity did not hold. A minimum dose of ∼2J/cm2 was required to achieve adequate bond strength. The predominant failure mode changed from cohesive in the composite and adhesive to interfacial at the adhesive-dentin interface, indicating the latter to be the weakest link in the cured dentin-composite assemblies considered. SignificanceWhen combined with the temporal development of shrinkage stress, the current results will help determine the likelihood of tooth-composite debonding.

Effects of panel zone yielding on seismic behavior of welded-flange-plate connections

In this study, effects of panel zone yielding on the seismic performance of welded-flange-plate (WFP) connections are investigated. In this work, four full-scale beam-to-column connections were used to run the experiments under cyclic loading. The obtained results can potentially lead to a better understanding of the influence of the panel zone inelastic shear deformation on the cyclic behavior of WFP connections for external joints in steel moment resisting frames (SMRFs). The main parameter in the testing program was the panel zone strength having a wide variation to gain the different levels of panel zone yielding. Results showed that all specimens had a high connection rotation capacity to satisfy the requirements of special moment frame connections. However, specimens with different panel zone strengths could provide the different amount of energy dissipation. Severe beam buckling was followed by tearing along the k-line region of the beam in the plastic hinge location, as well as tearing of the beam at the nose of the bottom flange plates which were both observed as a predominant failure mode in the specimens with a stronger panel zone. However, specimens with weak panel zone could develop a significant plastic rotation without causing any major problem to the beam-to-column connection groove welds. Based on mentioned observations and considering the effect of panel zone yielding because of different panel zone strengths on the hysteresis behavior of specimens, failure modes, plastic rotation capacity, and energy dissipation, some modifications were proposed for design requirements of the panel zone strength.

The Retentive Strength of Cemented Zirconium Oxide Crowns after Dentin Pretreatment with Desensitizing Paste Containing 8% Arginine and Calcium Carbonate.

The effect of dentin pretreatment with Desensitizing Paste containing 8% arginine and calcium carbonate on the retention of zirconium oxide (Y-TZP) crowns was tested. Forty molar teeth were mounted and prepared using a standardized protocol. Y-TZP crowns were produced using computer-aided design and computer-aided manufacturing (CAD-CAM) technology. The 40 prepared teeth were either pretreated with Desensitizing Paste or not pretreated. After two weeks, each group was subdivided into two groups, cemented with either Resin Modified Glass Ionomer Cement (RMGIC) or Self Adhesive Resin Cement (SARC)). Prior to cementation, the surface areas of the prepared teeth were measured. After aging, the cemented crown-tooth assemblies were tested for retentive strength using a universal testing machine. The debonded surfaces of the teeth and crowns were examined microscopically at 10× magnification. Pretreating the dentin surfaces with Desensitizing Paste prior to cementation did not affect the retention of the Y-TZP crowns. The retentive values for RMGIC (3.04 ± 0.77 MPa) were significantly higher than those for SARC (2.28 ± 0.58 MPa). The predominant failure modes for the RMGIC and SARC were adhesive cement-dentin and adhesive cement-crown, respectively. An 8.0% arginine and calcium carbonate in-office desensitizing paste can be safely used to reduce post-cementation sensitivity without reducing the retentive strength of Y-TZP crowns.

Influence of Irrigating Solutions on Push-Out Bond Strenght of Intraradicular Posts to Dentine

The aim of this study was to evaluate the influence of irrigating solutions commonly used during endodontic treatment on the push-out bond strength of intrarradicular fiber posts to dentin. Thirty single rooted teeth were divided into 3 groups according to the solution used during instrumentation: G1, NaOCL 5.25%; G2, 2% chlorhexidine; G3, distilled water. The root canals were prepared and obturated, and the glass fiber posts were cemented with RelyX ARC®. The specimens were submitted to push-out bond test and the results were analyzed by using the One-way ANOVA. The failure mode data were analyzed using the Chi-square test (P &lt; 0.05). There were no statistically significant differences regarding the irrigant solution factor (P &gt; 0.50). The most predominant failure mode was between posts and resin cement. It was concluded that the different irrigant solutions commonly used in endodontic treatment did not affect the push-out bond strength of fiber posts cemented with resin cement.

Reliability and failure behavior of CAD-on fixed partial dentures

ObjectivesTo estimate the reliability and failure behavior of fixed partial dentures (FPDs) fabricated using the CAD-on technique. MethodsFPDs (n=25) were fabricated using a CAD/CAM system: IPS e.max ZirCAD – Crystall./Connect and IPS e.max CAD (Ivoclar). The restoration type (“three-unit bridge”) and design method (“multilayer”) based on Biogenerics were used. Framework and porcelain structures were united using a fusion ceramic (Crystall./Connect, Ivoclar). Mechanical fatigue was tested in a servohydraulic load frame machine at a cyclic loading (frequency: 2Hz; load ratio: 0.1). Based on previous data from specimens tested in fast fracture, three different stress profiles were used. The lifetime data were analyzed using an inverse power law-Weibull cumulative damage model (ALTA PRO, Reliasoft). All failed specimens were examined under a field emission scanning electron microscope. ResultsPorcelain chipping was the predominant (60%) mode of failure for FPDs tested in fast fracture and connector failure was predominant (67%) under fatigue. For fast fracture data, the Weibull modulus (β) of FPDs was 7.8 combining the two failure modes. When chipping and connector fracture data were analyzed separately, β values were 7.9 and 2.9. For the step stress fatigue test, β values were lower than estimated using fast fracture, being 1.6 for connector fracture and 1.3 for porcelain chipping. SignificanceThe test method (fast fracture or fatigue) significantly influenced the reliability of FPDs fabricated using the CAD-on technique, but it did not influence their failure behavior.

Serial MRI evaluation following arthroscopic rotator cuff repair in double-row technique.

So far, recurrent rotator cuff defects are described to occur in the early postoperative period after arthroscopic repair. The aim of this study was to evaluate the musculotendinous structure of the supraspinatus, as well as bone marrow edema or osteolysis after arthroscopic double-row repair. Therefore, magnetic resonance (MR) images were performed at defined intervals up to 2years postoperatively. Case series; Level of evidence, 3. MR imaging was performed within 7days, 3, 6, 12, 26, 52 and 108weeks after surgery. All patients were operated using an arthroscopic modified suture bridge technique. Tendon integrity, tendon retraction ["foot-print-coverage" (FPC)], muscular atrophy and fatty infiltration (signal intensity analysis) were measured at all time points. Furthermore, postoperative bone marrow edema and signs of osteolysis were assessed. MR images of 13 non-consecutive patients (6f/7m, ∅ age 61.05±7.7years) could be evaluated at all time points until ∅ 108weeks postoperatively. 5/6 patients with recurrent defect at final follow-up displayed a time of failure between 12 and 24months after surgery. Predominant mode of failure was medial cuff failures in 4/6 cases. The initial FPC increased significantly up to 2years follow-up (p=0.004). Evaluations of muscular atrophy or fatty infiltration were not significant different comparing the results of all time points (p>0.05). Postoperative bone marrow edema disappeared completely at 6months after surgery, whereas signs of osteolysis appeared at 3months follow-up and increased to final follow-up. Recurrent defects after arthroscopic reconstruction of supraspinatus tears in modified suture bridge technique seem to occur between 12 and 24months after surgery. Serial MRI evaluation shows good muscle structure at all time points. Postoperative bone marrow edema disappears completely several months after surgery. Signs of osteolysis seem to appear caused by bio-absorbable anchor implantations.

A hybrid approach for modeling of breakable granular materials using combined finite-discrete element method

It is well known that particle breakage plays a critical role in the mechanical behavior of granular materials and has been a topic subject to intensive studies. This paper presents a three dimensional fracture model in the context of combined finite-discrete element method (FDEM) to simulate the breakage of irregular shaped granular materials, e.g., sands, gravels, and rockfills. In this method, each particle is discretized into a finite element mesh. The potential fracture paths are represented by pre-inserted non-thickness cohesive interface elements with a progressive damage model. The Mohr–Coulomb model with tension cut-off is employed as the damage initiation criterion to rupture the predominant failure mode at the particle scale. The particle breakage modeling using combined FDEM is validated by the qualitative agreement between the results of simulated single particle crushing tests and those obtained from laboratory tests and prior DEM simulations. A comprehensive numerical triaxial tests are carried out on both the unbreakable and breakable particle assemblies with varied confining pressure and particle crushability. The simulated stress–strain–dilation responses of breakable granular assembly are qualitatively in good agreement with the experimental observations. The effects of particle breakage on the compressibility, shear strength, volumetric response of the fairly dense breakable granular assembly are thoroughly investigated through a variety of mechanism demonstrations and micromechanical analysis. This paper also reports the energy input and dissipation behavior and its relation to the mechanical response.