Maximum Failure Load Research Articles

High mechanical performance of similar Al joints produced by a novel spot friction welding technique

In this study, the protrusion friction stir spot welding (PFSSW) was introduced in this study while a specially designed back plate (anvil) with a protrusion on its surface and a pinless tool were used. The effects of the tool dwell time (6, 12, 18 s) were investigated on the microstructure and mechanical properties of samples. Surface appearance of the welding zone showed that the keyhole was not formed and the appearance of weld was relatively smooth. Microstructure and mechanical results indicated that the welding zone with uniform and refine structure due to dynamic recrystallization presents higher hardness and strength than base metal while can be affected by dwell time. The tool penetration depth, the stir zone (SZ) depth and the bonding area at the interface of two sheets increased with increasing dwell time. Fracture surfaces of the failed specimens present the shear fracture at dwell times of 6 and 12 s and the interfacial fracture at 18 s. The proper dwell time of tools in this process was obtained 12 s. Considerable hardness (220 HV) and maximum failure load (6000 N) were obtained in present work compared to other welding methods.

The Primary Stability of a Bioabsorbable Poly-L-Lactic Acid Suture Anchor for Rotator Cuff Repair Is Not Improved with Polymethylmethacrylate or Bioabsorbable Bone Cement Augmentation.

The incidence of osteoporosis and rotator cuff tears increases with age. Cement augmentation of bones is an established method in orthopedic and trauma surgery. This study analyses if polymethylmethacrylate or bioabsorbable cement can improve the primary stability of a bioabsorbable suture anchor in vitro in comparison to a non-augmented suture anchor in osteoporotic human humeri. The trabecular bone mineral density was measured to ensure osteopenic human specimens. Then the poly-l-lactic acid Bio-Corkscrew® FT was implanted in the greater tuberosity footprint with polymethylmethacrylate Refobacin® cement augmentation (n=8), with Cerament™ Bone Void Filler augmentation (n=8) and without augmentation (n=8). Using a cyclic testing protocol, the failure loads, system displacement, and failure modes were recorded. The Cerament™ augmented Bio-Corkscrew® FT yielded the highest failure loads (206.7N), followed by polymethylmethacrylate Refobacin® augmentation (206.1N) and without augmentation (160.0N). The system displacement was lowest for Cerament™ augmentation (0.72mm), followed by polymethylmethacrylate (0.82mm) and without augmentation (1.50mm). Statistical analysis showed no significant differences regarding the maximum failure loads (p=0.1644) or system displacement (p=0.4199). The main mode of failure for all three groups was suture slippage. The primary stability of the Bio-Corkscrew® FT is not influenced by bone cement augmentation with polymethylmethacrylate Refobacin® or with bioabsorbable Cerament™ in comparison to the non-cemented anchors. The cement augmentation of rotator cuff suture anchors in osteoporotic bones remains questionable since biomechanical tests show no significant advantage.

Effect of Sleeve Plunge Depth on Microstructure and Mechanical Properties of Refill Friction Stir Spot Welding of 2198 Aluminum Alloy

Refill friction stir spot welding (RFSSW) is a new spot welding technology, by which spot joint without keyhole can be obtained. In this work, RFSSW was used to join 2-mm-thick 2198-T8 aluminum alloy sheets and effects of the sleeve plunge depth on microstructure and lap shear properties of the joints were mainly discussed. Results showed that when using small plunge depths of 2.4 and 2.6 mm, joints showed good formation and no defects were observed. Incomplete refilling defect was observed with increasing plunge depth due to material loss during welding. Size of the grains at sleeve-affected zone (SAZ) is smaller than that at the pin-affected zone, and the size becomes bigger with increasing the plunge depth. More secondary phase particles can be observed at SAZ with increasing the sleeve plunge depth. The lap shear failure load firstly increased and then decreased with increasing the sleeve plunge depth. The maximum failure load of 9819 N was attained with plug fracture mode when using 2.6 mm. Fracture morphologies show ductile fracture mode.

Achilles Tendon Allograft Incorporated with Autologous Mesenchymal Stem Cells

Category: Basic Sciences/Biologics Introduction/Purpose: Achilles tendinopathy and rupture are common and generally can heal without aggressive intervention. When a large defect of Achilles tendon is left by trauma or severe tendinopathy, however, it is a challenge to restore the function of Achilles tendon, because of the size of the tendon and the limitation in Achilles autograft. In contrast, allograft of Achilles tendon does not have restrain of supply. The biology, biomechanics and function of the transplanted Achilles allograft, however, are unknown. Particularly, the revitalization of Achilles allograft is a concern. Mesenchymal stem cells (MSCs) are known for their capability of multi-lineage differentiation and regenerative potentials. Methods: Achilles allografts were harvested from donor rats (approved by Institutional Animal Care and Usage Committee) and kept at -80ºC before transplantation. Subcutaneous adipose tissue was harvested from the would-be allograft recipient rats for isolation of MSCs. MSCs were culture expanded and characterized. On the day of allograft transplantation, adipose tissue derived MSCs were collected and applied onto allografts (1x105 per allograft). Achilles tendon was resected from the left hind limb of the adipose tissue donor rats. Achilles allograft, with or without autologous MSCs, was implanted and sutured with calf muscles proximately and calcaneus distally. Animal gait was recorded in the week prior to Achilles allograft transplantation (week 0) and every week postoperatively, using a CatWalk system. The transplanted Achilles allografts, with or without MSC incorporation, as well as the normal Achilles tendon in the opposite limbs were harvested at 4 weeks for biomechanical testing and histology. Results: The operated limbs altered gait significantly. By week 4, the recoveries of stand index (speed at which the paw loses contact with ground) and duty cycle (percentage of the stance phase in a step cycle) of the reconstructed limbs were not statistically different between the Achilles allograft group and Achilles allograft+MSCs group. Maximum load of failure among Achilles allograft group (27.2±11.5 N), Achilles allograft+MSCs group (27.6±6.4 N) and normal Achilles tendon group (19.9±9.9 N) was not significantly different. On histology, cellularity was generally higher in Achilles allograft+MSCs group than Achilles allograft group (average cellularity grade 2.7±0.5 vs 1.7±0.5). Type III collagen staining was more intense in the Achilles allograft+MSCs group than in the Achilles allograft group. Conclusion: In this pilot study, the allograft incorporated with autologous MSCs demonstrated no significant differences from Achilles allograft alone in maximum failure load and gait analysis. Supplementation of MSCs increased the cellularity and led to more active matrix remodeling in the allograft but these biological improvements did not translate into rat gait and the strength of the implanted allograft. It may be necessary to follow up the animals for an extended period because the remodeling of Achilles allograft takes longer than 4 weeks. In addition, the small size of the rat Achilles allograft might falsely show an accelerated revitalization.

Friction spot welding of dissimilar 6063/5083 aluminium alloys

ABSTRACTIn this work, friction spot welding (FSpW) was used to weld dissimilar 6063/5083 aluminium alloys, and the effects of the sleeve plunging speed on joint microstructures and the lap shear properties were discussed. Results showed that the keyhole can be eliminated using FSpW. Bending hooks changed to a flat morphology when the plunging speed was increased. Excellent bonding was formed at the lap interface in the sleeve-affected zone. As the sleeve plunging speed was increased from 40 to 110 mm min−1, the lap shear failure loads for the joints first increased and then decreased. A maximum failure load of 8017 N was attained when using a sleeve plunging speed of 80 mm min−1. All joints fractured at the lap interface.

Structural and Anatomic Restoration of the Anterior Cruciate Ligament Is Associated With Less Cartilage Damage 1 Year After Surgery: Healing Ligament Properties Affect Cartilage Damage.

Background:Abnormal joint motion has been linked to joint arthrosis after anterior cruciate ligament (ACL) reconstruction. However, the relationships between the graft properties (ie, structural and anatomic) and extent of posttraumatic osteoarthritis are not well defined.Hypotheses:(1) The structural (tensile) and anatomic (area and alignment) properties of the reconstructed graft or repaired ACL correlate with the total cartilage lesion area 1 year after ACL surgery, and (2) side-to-side differences in anterior-posterior (AP) knee laxity correlate with the total cartilage lesion area 1 year postoperatively.Study Design:Controlled laboratory study.Methods:Sixteen minipigs underwent unilateral ACL transection and were randomly treated with ACL reconstruction or bridge-enhanced ACL repair. The tensile properties, cross-sectional area, and multiplanar alignment of the healing ACL or graft, AP knee laxity, and cartilage lesion areas were assessed 1 year after surgery.Results:In the reconstructed group, the normalized graft yield and maximum failure loads, cross-sectional area, sagittal and coronal elevation angles, and side-to-side differences in AP knee laxity at 60° of flexion were associated with the total cartilage lesion area 1 year after surgery (R 2 > 0.5, P < .04). In the repaired group, normalized ACL yield load, linear stiffness, cross-sectional area, and the sagittal and coronal elevation angles were associated with the total cartilage lesion area (R 2 > 0.5, P < .05). Smaller cartilage lesion areas were observed in the surgically treated knees when the structural and anatomic properties of the ligament or graft and AP laxity values were closer to those of the contralateral ACL-intact knee. Reconstructed grafts had a significantly larger normalized cross-sectional area and sagittal elevation angle (more vertical) when compared with repaired ACLs (P < .02).Conclusion:The tensile properties, cross-sectional area, and multiplanar alignment of the healing ACLs or grafts and AP knee laxity in reconstructed knees were associated with the extent of tibiofemoral cartilage damage after ACL surgery.Clinical Relevance:These data highlight the need for novel ACL injury treatments that can restore the structural and anatomic properties of the torn ACL to those of the native ACL in an effort to minimize the risk of early-onset posttraumatic osteoarthritis.

Production and characterization of the mechanical and thermal properties of expanded polystyrene with recycled material

&lt;p&gt;Three materials were made with mixtures of virgin expanded polystyrene (EPS) grade S3 and recycled material from multipurpose EPS packaging. The latter was subjected to washing and grinding in a blade mill, with percentages by weight of recycled material 10, 15, and 20%. The mechanical properties of these materials were evaluated by testing compressive strength and flexural, impact, and thermal properties using the techniques of differential scanning calorimetry and thermogravimetry. Hot plate and steady state temperature profiles in a non-steady state were simulated with Octave 3.6.4. The results obtained for the three mixtures showed little variation in the properties of compression, impact, glass transition, and thermal diffusivity with respect to the reference material. The regularity of the decline in mass loss as a function of temperature evidences homogeneity in the samples. The flexural strength decreased the maximum failure load compared to the virgin material, and the thermal conductivity exceeded 0.06W/mK, reducing their insulating capacity. These materials can be industrially manufactured in order to produce packaging, caissons, and spheres, among other things.&lt;/p&gt;

Refill Friction Stir Spot Welding of 2198-T8 Aluminum Alloy

Refill friction stir spot welding (RFSSW) technology was used to weld 2 mm-thick 2198-T8 aluminum alloy in this work. As one of the most significant factors affecting the joint mechanical properties, effect of the tool rotating speeds on microstructure and mechanical properties of the RFSSW joint was mainly discussed. Results showed that keyhole could be successfully refilled after the RFSSW process. Due to the complicated movement of the tool components, different material flow behaviors could be obtained at the pin affected zone and sleeve affected zone, leading to different microstructures at the two regions. By undergoing through different heat cycle during welding, the secondary phase particles (Al2Cu) showed different morphologies and sizes at different regions. The lap shear failure load of the joint firstly increased and then decreased with increasing in the rotating speed. The maximum failure load of 9298 N was obtained when using 1600 rpm. All the joints showed lap-shear fracture mode.

Effect of rotation speed on microstructure and mechanical properties of refill friction stir spot welded 6061-T6 aluminum alloy

Refill friction stir spot welding (RFSSW) has been used to weld 6061-T6 aluminum alloy, and keyhole free joints were successfully obtained. Effect of tool rotation speed on microstructure and mechanical properties of joint was investigated. The joint was divided into four zones, i.e., the base material (BM), heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and stir zone (SZ) according to microstructural evolution. Defect was not found on the surface of welded joint, but inner defects of partial bonding, bonding ligament, hook, and voids were observed within the welded joint. The microhardness of HAZ and TMAZ was lower than that of the BM, while the maximum microhardness was obtained in the SZ of welded joints. With increasing tool rotation speed from 1100 to 1700 rpm, microhardness decreased with increasing grain size in the weld. The maximum tensile shear failure load of 7522 N was obtained for the joint under tool rotation speed of 1500 rpm. Two different failure modes of plug fracture and tensile-shear mixed fracture were observed during the tensile shear tests.

Effect of Welding Speed on Joint Features and Lap Shear Properties of Stationary Shoulder FSLWed Alclad 2024 Al Alloy

Using alclad 2024-T4 aluminum alloy as the research object, stationary shoulder technology was used in friction stir lap welding process to investigate its performance in this study. Joint features and mechanical properties of the lap joints were mainly investigated. Results show that lap joint with smooth surface, without shoulder marks and inner defects can be obtained using the stationary shoulder technology. With increasing the welding speed from 40 to 130 mm/min, effective sheet thickness (EST) at the advancing side (AS) shows rather stable values (from 1.17 to 1.31 mm), EST at the retreating side (RS) increases from 0.57 to 1.13 mm, and stir zone width decreases from 4.95 to 4.44 mm. Lap shear failure load of the SSFSLW joints firstly increases and then decreases with increasing the welding speed. Using 100 mm/min, the maximum failure loads of 15.85 and 9.01 kN were obtained when the RS and AS of the joint bear the main load during the lap shear test. Shear fracture mode and tensile fracture mode can be obtained during the lap shear test. All joints present ductile fracture mode.

Fibrin Glue Increases the Tensile Strength of Conduit-Assisted Primary Digital Nerve Repair.

An ideal peripheral nerve repair construct does not currently exist. Our primary goal was to determine whether fibrin glue adds to the tensile strength of conduit-assisted primary digital nerve repairs. Our secondary goal was to evaluate the impact of varying suture number and location on the tensile strength. Ninety cadaveric digital nerves were harvested and divided equally into the following repair groups: A (4/4), B (2/2), C (0/2), D (0/1), and E (0/0) with the first number referring to the number of sutures at the coaptation and the second number referring to the number of sutures at each proximal and distal end of the nerve-conduit junction. When fibrin glue was added, the group was labeled prime. The nerve specimens were transected and then repaired with 8-0 nylon suture and conduit. The tensile strength of the repairs was tested, and maximum failure load was determined. The results were analyzed with a 2-way analysis of variance. The Tukey post hoc test compared repair groups if the 2-way analysis of variance showed significance. Both suture group and glue presence significantly affected the maximum failure load. Increasing the number of sutures increased the maximum failure load, and the presence of fibrin glue also increased the failure load. Fibrin glue was found to increase the strength of conduit-assisted primary digital nerve repairs. Furthermore, the number of sutures correlated to the strength of the repair. Fibrin glue may be added to a conduit-assisted primary digital nerve repair to maintain strength and allow fewer sutures at the primary coaptation site.

Dextromethorphan upregulates osteoblast and osteoclast activity but does not attenuate ovariectomy-induced osteoporosis

AimsStudy on the in vivo regulatory role of glutamate in osteoblast (OB) and osteoclast (OC) differentiation is less advanced. The present study investigated the effect of dextromethorphan (DXM), an N-methyl-d-aspartate receptors (NMDARs) antagonist, on osteoporosis development. Main methodsIn order to examine the role of glutamate in bone metabolism, ovariectomized (Ovx) female Wistar rats were injected three times per week for 8weeks with either saline, or 15μg/kg of β-estrodiol, or DXM (40mg/kg) intraperitoneally. Serum samples were collected every two weeks for measuring osteocalcin and C-terminal telopeptide of type I collagen (CTX-1) level. Rats were then sacrificed at week 8 and the femurs harvested for micro-CT scanning and mechanical strength. Key findingsIn saline-treated group, osteocalcin level significantly lower than that of sham-operated rats at 8weeks after operation, while CTX-1 levels were not affected. Estrogen treatment, as a positive control, partially inhibited the Ovx-induced reduction of osteocalcin serum level. DXM injection prevented the Ovx-induced reduction of osteocalcin expression and significantly upregulated CTX-1 expression. The micro-CT scan showed that the bone volume density decreased significantly in DXM treated rats compared to the sham-operated rats. In the mechanical strength assay, the maximum failure load for DXM treatment was significantly lower than the other groups. SignificanceTreatment with DXM upregulated OB and OC markers in Ovx rats, however with a greater effect on the OC marker, and had no significant benefit on bone volume density or bone strength.

Gap formation following primary repair of the anterior cruciate ligament: A biomechanical evaluation

BackgroundHistorically, inconsistent and unpredictable results of open primary anterior cruciate ligament (ACL) repair were reported. Recently, however, good results of arthroscopic primary ACL repair of proximal tears have been reported. Purpose of this study was to assess the direct postoperative gap formation and maximum failure load following simulated knee motion after primary ACL repair. MethodsSix matched-paired human cadaveric knees (mean age: 52years, range: 48 to 56years) were used. After primary proximal ACL repair with either suture button fixation or suture anchor fixation, knees were cycled five, 50 and 100 times with a simulated active quadriceps force. Gap formation between the femoral wall and ligament was measured using a digital caliper and maximum failure load was tested. ResultsGap formation after five, 50 and 100cycles of the knee were 0.30mm (±0.23), 0.75mm (±0.55) and 0.97mm (±0.70), respectively, with no significant differences between both fixation techniques. The overall maximum failure load was 243N (±143) with no difference between both techniques. Most common failure mode was slipping of suture from the fixation. ConclusionFollowing proximal ACL repair, gap formation of approximately one millimeter was measured after repetitious knee cycling with mean maximum failure load of 243N. These findings are likely to be sufficient for careful early active range of motion (ROM) when extrapolating from other available studies. Future studies with second-look arthroscopy are necessary to assess the gap formation and healing in patients treated with primary repair.

Characterizing the Compression Behavior of Al2O3/Si3N4 Nano Sized Particulate Reinforced Ceramic Matrix Composites

Objectives: Nano sized objects are exhibiting extra ordinary potential in all the aspects of properties. Objective of this work is to develop the composite of alumina reinforced with nano sized silicon nitride particles to analyze the compression behaviour of the developed composite materials against compacting pressure and % of reinforcement. Methods: Powder metallurgical techniques were used to manufacture the sample specimens of composites. The specimens were prepared with various proportions Si3 N4 reinforcement ranges from 1 wt% to 20 wt%. Alumina was functionalized with 5 wt% of Poly Vinyl Alcohol (PVA) at 80°C using water as plasticizer to enhance the dispersion and flow behaviour essential for forming the material. The composites were cold formed in two cycles where compacting pressure was maintained as 510 MPa and 725 MPa. The sintering temperature was maintained as 1400°C for soaking period of 30 minutes. Findings: The results revealed that the reinforced composites showed 35% more compressive strength than unreinforced monolithic material. It was found that the reinforcement content of silicon nitride increased the compressive strength of the composite as expected. The barrelling behaviour was not observed during compression. The compressive strength of monolithic alumina at 725 MPa was 0.7 times greater than of 510 MPa. It was observed that 12.5% of reinforcement experienced maximum peak load of failure. The 1400°C for sintering was observed as not sufficient to make plastic flow in powder metallurgical preforms. Application/Improvements: The betterment in result can be achieved by increasing the sintering temperature to 1800°C for soaking time 30 minutes. This study reveals that this particular combination of ceramic matrix composites exhibit better results in compressive behaviour. This can be further analyzed for wear and can be used as outstanding material in hybrid ceramic bearings. Keywords: Ceramic Matrix Composites, Compression Behaviour, Hybrid Bearings, Powder Metallurgy, PVA

Effect of tool rotating speed on microstructure and mechanical properties of friction stir lap welded Ti–6Al–4V alloy

In the present study, friction stir lap welding (FSLW) of 1 + 1.8 mm Ti–6Al–4V alloy was carried out using different rotating speeds. Effect of tool rotating speed on defect, phase transformation, and mechanical properties of the joints was mainly discussed. Results show that void defect at the joint bottom can be eliminated by decreasing the rotating speed. Microstructure shows difference along thickness due to big temperature gradient. Hardness values of the joints are higher than the base material and bigger hardness values can be obtained using low rotating speed. Lap shear properties of the joints when the retreating sides (RS) of the upper sheets bear the main loads (configuration B) are higher than those of the joints when the advancing sides (AS) of the upper sheets bear the main loads (configuration A). The maximum failure load of 19.08 KN is attained using 150 rpm and configuration B. Shear fracture mode and tensile fracture mode can be obtained during the lap shear test.

Analyse biomécanique d’une plaque de fixation des butées de type Latarjet

Introduction The use of a mini-plate for coracoid fixation during the Latarjet procedure has recently been described, with encouraging radiographic outcomes. The purpose of this study was to determine the biomechanical properties of mini-plate fixation for the Latarjet procedure, and to compare these findings to various screw fixation configurations. Materials and methods Eight fixation groups ( n = 5 specimens per group) were tested at a screw insertion angle of 0° including I) 3.75 mm single-screw, II) 3.75 mm double-screw, III) 3.75 mm double-screw with washers, IV) 3.75 mm double-screw with mini-plate, V) 4.00 mm single-screw, VI) 4.00 mm double-screw, VII) 4.00 mm double-screw with washers, and VIII) 4.00 mm double-screw with mini-plate. In addition, for groups I-III and V–VII, 30 additional specimens ( n = 5 per group) were tested at a screw insertion angle of 15° (groups IX–XIV). To maintain specimen uniformity, rigid polyurethane foam blocks were used. For all specimens, testing parameters included a preload of 214 N for 10 seconds, cyclical loading from 184–736 N at 1 Hz for 100 cycles, and failure loading at a rate of 15 mm/min until 10 mm of displacement or specimen failure occurred (ElectroPuls E10000, Instron, United Kingdom). In addition, a full-field stereo-optical measurement system (ARAMIS, GOM mbH, Germany) was utilized to evaluate graft strain, graft displacement and screw displacement and rotation. Results All specimens in groups I and V (single screw constructs) and 77% of specimens within groups IX–XIV (screw insertion angle of 15°) failed prior to the completion of cyclical loading; all but one of the other specimens survived and underwent maximum load to failure testing (1 specimen in group VII failed). Across all groups, group VIII (4.00 mm; plate) demonstrated the highest maximum failure load ( P > 0.001), averaging loads 770 N higher than the next highest group ( P > 0.001). There was no significant difference in displacement during cycling between specimens with plate fixation (groups V and VIII, P > 0.05). All specimens in groups IX–XIV (insertion angle of 15°) had significant lower maximum loads to failure compared to their specimens in groups II, II, IV, VI, VII, and VIII, respectively ( P > 0.001 for all). Conclusions This is the first study to report on the biomechanical properties of the mini-plate for coracoid fixation in the Latarjet procedure. The results indicate significantly superior failure loads with the mini-plate compared to other constructs, which may have clinical implications, particularly in the high-demand contact athlete. Clinical studies with analysing patient outcomes and failure rates are necessary to determine the clinical implications of these biomechanical findings.

Gas metal arc brazing of galvannealed steel sheets

An advanced gas metal arc welding technique with controlled short-circuiting mode of metal transfer and arcing at low power was employed for brazing of galvannealed steels using CuSi3 filler wire. The brazed joints showed the presence of an interface layer with Fe–Si intermetallic compounds (IMC). Increase in heat input resulted in an increase of the interface layer thickness. The maximum failure load of 2.5 kN was achieved for a heat input of 105 J mm−1 with the corresponding interface layer thickness of 2.7 µm. Heat inputs beyond 105 J mm−1 led to excessive spatter of zinc and increase in interface layer thickness with hard Si-rich IMC. In contrast, heat input values lower than 80 J mm−1 produced inadequate wetting of the steel surface by the molten filler wire deposit and resulted in low joint strength.

Elasto-plastic failure of locally supported silos with U-shaped longitudinal Stiffeners

Ranging from agriculture to food processing, from mining to industrial processing, all these sectors have a need for the temporary storage of (dry) powdered, granular, and bulk materials between different stages of all kinds of manufacturing processes and between manufacturing process and transportation, or vice versa. Silos are therefore the perfect solution to meet this need, because they can easily store large volumes on a relatively limited floor space. Frequently, silos have a circular platform and are placed in elevated position. The latter can be achieved by a limited number of discrete equidistant supports around the barrel circumference. However, in such cases, large loads have to be transferred to the limited number of supports, causing locally high axial compressive stress concentrations, and consequently premature failure due to plastic yielding and/or elastic buckling (depending on the thickness of the silo wall). A possible answer to avoid these problems is to provide a partial-height U-shaped longitudinal stiffener above each support. Such stiffeners allow for a more gradual load transfer to the supports, increasing the maximum failure load. This paper aims to map the influence of the dimensions of such longitudinal stiffeners (i.e. the parameters of the cross-section and the height) on the failure behaviour of thick-walled silos. All results and findings are based on geometrically and materially non-linear analyses or GMNA performed with finite element software. The simulations indicate that correctly, for thick-walled silos, failure will always occur by (elasto-)plastic yielding. Depending on the longitudinal stiffener cross-section, the location of failure will occur in the stiffened zone of the silo just above the supports for silos with stiffeners with a small cross-section, whereas for stiffeners with larger cross-sections, failure occurs in the unstiffened zone just above the terminations of the stiffeners. In addition, the stiffener width in circumferential and radial direction have respectively an advantageous and a disadvantageous influence on the failure load. Finally, the stiffener height only has a positive impact on the failure load when failure occurs in the unstiffened silo wall. This can be addressed to the distribution of the supporting force over the entire circumference with higher stiffeners.

Adhesive bond strength and compressive strength of a novel bulk fill composite with zirconia nano-hybrid filler

The aim of the study was to investigate the adhesive bond and compressive strength of novel bulk fill resin composite with zirconia (Zr) nano-hybrid filler. Sixty molars were mounted in acrylic resin with flat occlusal surface. Half of the specimen (n = 30) were bonded using total etch (TE) and the other half with self-etch (SE) technique. Specimens treated with SE (n = 30) and TE (n = 30) bonding protocol were divided into three groups, based on the type of bulk fill build-up materials (ZC–ZirconCore, MC–MulticCore Flow and LC–Luxacore Dual), resulting in six study groups [MC-TE, MC-SE, LC-TE, LC-SE, ZC-TE, ZC-SE]. Cylindrical (3 × 3 mm) build-ups were performed followed by shear bond strength testing (crosshead speed-1 mm/min). Ten specimens for each bulk fill build-up material (MC, LC and ZC) were prepared for compressive strength testing. All specimens were tested for maximum failure loads (crosshead speed−0.5 cm/min). Analysis of variance and paired t-test were performed to statistically analyze the data. TE technique showed significantly higher bond strength values as compared to SE technique (p < 0.001) for all three materials (MC, LC and ZC). Shear bond strength for MC [TE,17.88(2.00)-SE,9.43(0.98)] and LC [TE,18.91(2.57)-SE,6.35(1.12)] groups were significantly higher than ZC group [TE,13.99(1.09)-SE,4.61(0.84)]. Specimens in ZC group (266.73 ± 9.76) showed significantly higher compressive strength in comparison to MC (247.66 ± 9.72) (p = 0.004) and LC (249.87 ± 13.17) (p < 0.001) groups. Zirconia nano-hybrid filler resin bulk fill material has comparatively high compressive strength and low bond strength making them suitable for clinical applications in the posterior region with favorable conditions for adhesive bonding.

Evolving properties of friction stir spot welds between AA1060 and commercially pure copper C11000

Friction stir spot welding technique was employed to join pure copper (C11000) and pure aluminium (AA1060) sheets. The evolving properties of the welds produced were characterized. The spot welds were produced by varying the rotational speed, shoulder plunge depth using different tool geometries. The presence of a copper ring of different lengths was observed on both sides of the welds indicating that Cu extruded upward into the Al sheet which contributed to obtaining strong welds. The microstructure showed the presence of copper particles in the aluminium matrix which led to the presence of various intermetallics observed by the energy dispersive spectroscopy and X-ray diffraction. The maximum tensile failure load increases with an increase in the shoulder plunge depth, except for the weld produced at 800 r/min using a conical pin and a concave shoulder. A nugget pull-out failure mode occurred in all the friction stir spot welds under the lap-shear loading conditions. High peaks of Vickers microhardness values were obtained in the vicinity of the keyhole of most of the samples which correlated to the presence of intermetallics in the stir zone of the welds.