Servohydraulic Testing System Research Articles

Couple effects of temperature and fatigue, creep-fatigue interaction and thermo-mechanical loading conditions on crack growth rate of nickel-based alloy

The ambient and high-temperature fatigue crack growth behaviors in C(T) and SENT specimens of Ni-based superalloy for turbine disk application were studied in a wide interval of temperatures 25–750°C using a combination a electro- and servohydraulic test systems and fractographic investigations. The fatigue, creep-fatigue interaction and thermo-mechanical in-phase fatigue (TMF IP) crack growth tests are performed under isothermal and dynamic waveforms loading conditions. The interpretation of the experimental results is given in terms of the traditional stress intensity factors and C-integral as well as new normalized cyclic fracture diagrams. It is found that there are definite temperature-sensitive regions separate for harmonic fatigue and creep-fatigue interaction loading conditions in which the crack growth rate of Ni-based alloy increases sharply. Scanning electron microscopy in longitudinal sections containing cracks revealed the mechanisms responsible for fatigue crack initiation and growth. The couple effect of temperature ranging and isothermal and dynamic waveforms loading conditions on fatigue life was discussed.

Deformation behaviour and microscopic investigations of cyclically loaded railway wheels and tyres

Abstract Railway wheel and tyre steels were investigated by specimens from defined volume sections representing the local microstructure of original components. As a consequence of the industrial heat treatment and the size of the components, microstructural gradients exist in the wheel rim and tyre crosssection. The ferrite fraction of the ferritic – pearlitic microstructure and the cementite lamellae spacing vary depending on the distance to the running surface (tread). Stress-controlled load increase and single-step push– pull tests were carried out at ambient temperature with servohydraulic testing systems to study fatigue phenomena with special consideration of microstructural details. Mechanical stress– strain hysteresis, thermometrical, and electrical measurements were used for a comprehensive characterization and evaluation of the cyclic deformation behaviour. The measured physical quantities show a strong interrelation with the underlying fatigue process. Light, scanning, and transmission electron microscopy (TEM), together with digital image processing, allow to interpret the measured data on the basis of microstructural details. In defined fatigue states, TEM investigations were performed to correlate the loading conditions with the appearing dislocation structures.

Addition of the Sartorius Tendon Improves Biomechanics of a Four-Strand Hamstring Anterior Cruciate Ligament Autograft

The purpose of this study was to quantify and compare the biomechanical properties and change in graft size when adding the sartorius tendon as a fifth strand to a four-strand ST-G hamstring autograft. Additionally, the sartorius tendon was tested individually to quantify its independent biomechanical properties. Four-strand and five-strand hamstring tendon grafts were harvested from matched cadaveric knees (mean age: 81.6 ± 9.8). These matched grafts were biomechanically tested using a MTS servohydraulic test system at a rate of testing representative of physiologic tears. The mean diameter, cross-sectional area, and ultimate load to failure were quantified and compared with a one-sided, paired Student's t-test. A P < .05 was considered statistically significant. The mean diameter of thefive-strand graft was significantly larger than the four-strand graft (9.30 ± .84 mm vs 8.10 ± .42 mm; P= .002). Theaverage ultimate load to failure of the five-strand graft was 65.3% higher than the four-strand graft (2984.05 ± 1085.11 Nvs. 1805.03 ± 557.69 N; P= .009) and added 14.8% to the diameter of the four strand ST-G autograft. The addition of the sartorius tendon to a four-strand hamstring autograft significantly increased ultimate load to failure by 65%, graft cross-sectional area by 32%, and graft diameter by 15% compared to a traditional four-strand ST-G autograft. This information can be helpful to surgeons who wish to improve the strength of a four-strand ST-G autograft and for undersized grafts as an alternative to allograft supplementation. The addition of the sartorius to the four-strand ST-G hamstring autograft significantly increases the ultimate load to failure and overall graft diameter, which can be particularly helpful in undersized autografts as an alternative to allograft supplementation.

Biomechanical study of Proximal humeral fracture fixation: Locking plate with medial support screw vs. locking plate with intramedullary fibular graft

BackgroundThe purpose of this study was to evaluate the biomechanical properties of two different fixation constructs in varus collapse proximal humerus fracture, locking plate with medial support screw and locking plate with intramedullary fibular graft. MethodsWe used 8 pairs of undamaged fresh-frozen humen cadaveric humeri and fibula from patients ranging in age from 62 to 81 years. We simulated a proximal humerus fracture with medial comminution using wedge shaped osteotomy. One group was fixed with locking plate with medial support screws, the other group with locking plate with intramedullary fibular graft. Biomechanical test was carried out using servohydraulic material testing system. We measured displacement of specimens under cyclic load test, maximum failure load, initial stiffness, and mode of failure under increasing load test. FindingsUnder cyclic loading, the displacement of the specimen was significantly less in the locking plate with fibular strut graft group than in the locking plate with medial support screws group. (p = 0.012) Under increasing load test, the Locking plate with fibular strut graft group showed higher values in both maximum failure load and initial stiffness than the Locking plate with medial support screws group, and this was statistically significant. (p = 0.012, p = 0.001). InterpretationIn biomechanical study, the locking plate with fibular strut graft showed significantly better results in all of the maximum failure load, initial stiffness, and gap depletion compared to the locking plate with medial support screws. Level of evidenceLevel IV.

Weak adhesion detection – Enhancing the analysis of vibroacoustic modulation by machine learning

Adhesive bonding is a well-established technique for composite materials. Despite advanced surface treatments and preparations, surface contamination and application errors still occur, resulting in localised areas with a reduced adhesion. The dramatic reduction of the bond strength limits the applicability of adhesive bonds and hampers further industrial adaptation. This study aims to detect weak-bonds due to manufacturing errors or contamination by analysing and interpreting the vibroacoustic modulation signals with the aid of machine learning. An ultrasonic signal is introduced into the specimen by a piezoceramic actuator and modulated through a low frequency vibration excited by a servo-hydraulic testing system. Tested samples are single-lap shear specimens, according to ASTM D5868-01, with artificial circular debonding areas introduced as PTFE-films or a release agent contamination. It is shown that an artificial neural network can identify various defects in the bonded joint robustly and is able to predict residual strengths and hence demonstrates great potential for non-destructive testing of adhesive joints.

The Ideal Cortical Button Location on the Lateral Femur for Anterior Cruciate Ligament Suspensory Fixation is 30 mm Proximal to the Lateral Epicondyle

PurposeTo determine the ideal location for anterior cruciate ligament (ACL) suspensory cortical button placement on the lateral femur with the highest failure load and to establish the relationship of tunnel diameter and cortical thickness on load to failure.MethodsComputed tomography (CT) data were obtained from 45 cadaveric distal femurs. A Cartesian coordinate system was established along the lateral femur with the lateral epicondyle (LE) as a reference point. Locations 0, 20 and 30 mm from the LE along lines 0°, 25°, 50°, and 75° posterioproximal from the axial plane were created. Tunnels connecting from each location to the center of the ACL footprint were simulated. Cortical thickness and long axis diameter of the oval cortical holes were determined for each location. Based on the CT data, custom drill guides were created and used to drill 4.5 mm tunnels at each lateral femur location to the ACL footprint on the cadaver femurs. Cortical buttons were placed at each location and pulled using a servohydraulic testing system. The correlation of tunnel diameter and cortical thickness to button failure load were analyzed using a regression analysis.ResultsSignificant differences were found for failure load (P<.0001) and cortical thickness between the locations tested (P<.0001). The location 30 mm proximal from the LE and 75⁰ from the axial plane had the highest failure load of 573 N. A regression analysis (R2 = .15) indicated that the cortical thickness was significantly correlated with load to failure (P <.0001), whereas the long-axis diameter was not (P = .33).ConclusionThe ideal cortical button location on the lateral femur for ACL suspensory fixation was located 30 mm proximal from the lateral epicondyle, based on this area’s high failure load. Oblique tunnel drilling of this proximal location may cause a larger long-axis diameter cortical hole, but the cortex is also thicker, which is more closely correlated with failure load.Clinical RelevanceDifferent ACL suspensory cortical button locations on the lateral femur have different failure loads based on the cortical thickness of the bone supporting the button. It is important for surgeons to understand which drilling techniques place the button in a proximal and posterior location, especially if the bone quality of the patient is of concern.

Assessing serpentinite compressive strength using regression analysis

Introduction. Today, the express method for assessing rock compressive strength using the Schmidt hammer is becoming more and more relevant and demanded. Compared to laboratory methods, measurements by this non-destructive express method result in the height of striker rebounding. The device has to be calibrated for further transition from the rebound height Hr to compressive strength in the UCS sample of the rock type under study. Research methodology included selection of hand specimen on the slopes of the Kiembai chrysotile asbestos open pit for laboratory tests. The height of striker rebounding was measured of Proceq RockShmidt Type N Schmidt hammer according to the ASTM method in local areas of exposed massif. Compressive strength of rock samples was tested in the laboratory using Wille Geotechnik servo hydraulic testing system. Research results. Based on the obtained data, an empirical formula has been established describing the dependence between compression strength of serpentinite in the UCS sample and striker height of rebounding of a Schmidt Type N hammer. The author’s results were compared to the ones obtained by the predecessors using a Schmidt Type L hammer when studying physical and mechanical properties of serpentinite in another field. The difference in the empirical formulas is due to the difference in physical and mechanical properties of serpentinite building up the deposits under consideration, as well as the difference in impact energy of the working Schmidt hammers

Low Cycle Fatigue of an Ultrafine Grained AA5083 Aluminum Alloy Composite Produced by Cryomilling

Low cycle fatigue (LCF) properties were investigated for a novel cryomilled AA5083 aluminum composite with duplex coarse and ultrafine grain sizes and reinforced with boron carbide particulates, referred to as trimodal material. Fully reversed cyclic tests were conducted under plastic strain control at plastic strain amplitudes from 0.15 to 0.6 pct using a constant plastic strain rate in a servo-hydraulic testing system. A nonlinear elastic modulus was used to calculate the elastic contribution to the measured total strain. The LCF performance of this trimodal material is compared to previous results for unreinforced AA5083 aluminum alloy with bimodal grain size (85/15 pct CM/UM) and its coarse-grained wrought counterpart, AA5083-H131. Stress response curves for the trimodal material revealed slow hardening until failure associated with the presence of particulate reinforcements. The very small asymmetry between tension and compression stresses reflects a lack of strain localization beyond the initial cycles. The trimodal and 85/15 pct CM/UM alloys have similar and superior low cycle fatigue strength compared to AA5083-H131. From the Coffin-Manson plot, the trimodal material has a shorter fatigue life than 85/15 pct CM/UM alloy and AA5083-H131 for high plastic strain amplitudes, but nearly identical life at low amplitudes. Microcracks were observed near the dominant crack on trimodal specimen surfaces at failure. Back-scattered images revealed that particulates altered the crack propagation direction; cracks nearly always propagated around particulates.

Mechanical Behavior, Energy Release, and Crack Distribution Characteristics of Water‐Saturated Phyllite under Triaxial Cyclic Loading

Many geological engineering hazards are closely related to the dynamic mechanical behaviors of rock materials. However, the dynamic mechanical behaviors of phyllite are less studied. In this study, we have carried out a series of triaxial cyclic tests on dry and water‐saturated phyllite by employing the MTS 815 servohydraulic testing system and AE testing equipment to reveal the mechanical behavior, energy release, and crack distribution characteristics of phyllite. Results show that phyllite is a water‐sensitive rock. Water and cyclic loading substantially affect the compressive strength, crack damage stress, deformation parameters, dilatancy, energy release, and crack distribution characteristics of phyllite. Furthermore, based on the dissipated energy, a new damage variable for phyllite is established. The critical damage variable for phyllite is approximately 0.80; this variable can be used as an index to predict the failure of phyllite. The water saturation effect of phyllite is very obvious; that is, it results in the weakness of mechanical properties of phyllite and changes the AE energy release and crack distribution characteristics of phyllite. This research can provide guidance for engineering construction and disaster prevention and control.

Distributed optical fibre sensor based monitoring of thermoplastic carbon composite cylinders under biaxial loading: Experimental and numerical investigations

Composite tubes are used in numerous applications including aerospace, mechanical, civil and transport sectors, where they may be susceptible to combined loading especially axial compression and torsion and suffer failure due to their intrinsic weakness under such loads. An experimental cum numerical investigation is performed to understand the behaviour of hollow composite tubes with cut-outs under combined axial compression and torsional loadings. Carbon fibre reinforced thermoplastic CF/PEEK tubes with different diameters and varied lay-up sequences, were robotically manufactured using an Automated Fibre Placement (AFP) machine. These specimens were mechanically tested using a novel biaxial test jig, designed specifically to be compatible with an INSTRON 8852 axial/torsion servo hydraulic test system. A standard acrylate coated optical fibre was affixed on the surface of the cylinder for distributed strain sensing using an optical backscatter reflectometer (OBR) interrogator to obtain spatial strain data. Surface strains measured using distributed optical fibre sensing (DOFS) and strain rosettes were compared against finite element analysis predictions to successfully validate the numerical model created using Ansys ACP Pre-Post simulation package. Directional deformations around the cut-outs of these tubes were also numerically characterised and compared with digital image correlation (DIC) results from the experimental tests.

The Biaxial Compressive Mechanical Properties and Strength Criterion of Recycled Aggregate Concrete Under Different Dynamic Strain Rates

In this paper, the tests under biaxial compression were conducted on five kinds of recycled aggregate concrete (RAC) by stress ratios (0:−1, −0.1:−1, −0.25:−1, −0.5:−1, −0.75:−1, and −1:−1) at the strain rates of 10–5/s, 10–4/s, 10–3/s, and 10–2/s. This study was accomplished in the servo-hydraulic multi-axial testing system, which was carried at Dalian University of Technology. The experimental phenomena of RAC under biaxial compression are described, and the experimental results of biaxial compressive strength of RAC are analyzed. The effects of strain rate, stress ratio, and substitution percentages of recycled coarse aggregate (RCA) on the biaxial compressive strength of RAC were studied. During the experiments, the failure modes of concrete have not been changed because of the increased impact of the RCA on RAC. The strength of RAC is improved with the increase in strain rates. With the increase in stress ratios, the biaxial compressive strength increases at first. However, the strength then decreases. Based on the strength theory of common concrete and analysis of experimental data, this paper built a new dynamic strength criterion. The biaxial compressive strength criterion describes the characteristics of structural RAC at different stress ratios and strain rates. This strength criterion can provide theoretical foundation for future concrete multi-axis dynamic tests and the design specification with the considerations of multi-axis dynamic strength and nonlinear analysis. The feature of the model is that it can take into account the influence of strain rates.

All-suture anchor and unicortical button show comparable biomechanical properties for onlay subpectoral biceps tenodesis

HypothesisThe purpose of this study was to biomechanically evaluate onlay subpectoral long head of the biceps (LHB) tenodesis with all-suture anchors and unicortical buttons in cadaveric specimens.MethodsAfter evaluation of bone mineral density, 18 fresh-frozen, unpaired human cadaveric shoulders were randomly assigned to 2 groups: One group received an onlay subpectoral LHB tenodesis with 1 all-suture anchor, whereas the other group received a tenodesis with 1 unicortical button. The specimens were mounted in a servo-hydraulic material testing system. Tendons were initially loaded from 5 N to 100 N for 5000 cycles at 1 Hz. Displacement of the repair constructs was observed with optical tracking. After cyclic loading, each specimen was loaded to failure at a rate of 1 mm/s.ResultsThe mean displacement after cyclic loading was 6.77 ± 3.15 mm in the all-suture anchor group and 8.41 ± 3.17 mm in the unicortical button group (P = not significant). The mean load to failure was 278.05 ± 38.77 N for all-suture anchor repairs and 291.36 ± 49.69 N for unicortical button repairs (P = not significant). The most common mode of failure in both groups was LHB tendon tearing. There were no significant differences between the 2 groups regarding specimen age (58.33 ± 4.37 years vs. 58.78 ± 5.33 years) and bone mineral density (0.50 ± 0.17 g/cm2 vs. 0.44 ± 0.19 g/cm2).ConclusionAll-suture anchors and unicortical buttons are biomechanically equivalent in displacement and load-to-failure testing for LHB tenodesis. All-suture anchors can be considered a validated alternative for onlay subpectoral LHB tenodesis.

Pullout strength and failure mode of industrially manufactured and self-made all-suture anchors: a biomechanical analysis

This study presents a new technique for assembling an all-suture anchor from existing medical products. The biomechanical characteristics of this self-made anchor (SMA) are compared with those of an industrially manufactured all-suture anchor. The SMAs were made from established medical products (FiberWire #2and 2-mm FiberTape; Arthrex, Naples, FL, USA). Pretesting was performed in biphasic polyurethane foam blocks. In the next step, 10 SMAs and 10 industrially made anchors (IMAs; 1.8-mm double-loaded Y-KnotFlex all-suture anchor; ConMed Linvatec, Largo, FL, USA) were applied with an insertion tool and tested in fresh porcine femora using a servohydraulic testing system, with a preload of 10 N and a displacement rate of 12.5 mm/s. Pullout strength and failure mode were recorded. The mean load at failure in the foam blocks was 459 ± 124 N in the SMA group and 538 ± 83 N in the IMA group. In porcine bone, failure occurred at 461 ± 102 N in the SMA group and 431 ± 135 N in the IMA group. The differences in pullout strength between the 2 types of anchor were not statistically significant, either in the foam blocks (P = .17) or in porcine bone (P = .62). A handmade all-suture anchor using 2 high-strength sutures woven into a 2-mm strip of high-strength tape did not show statistically different failure loads in polyurethane foam or in porcine metaphyseal bone in comparison with a commercially produced double-loaded all-suture anchor. The principal mode of failure in porcine bone in both groups was anchor pullout.

Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of 2 different LCP systems.

This study compares the mechanical stability and surgical usability of 2 locking plate systems (Kyon ALPS-20 and Synthes PIP-LCP system) for arthrodesis of the equine proximal interphalangeal joint (PIJ). The experimental ex vivo study included 6 pairs of cadaver distal limbs (n = 12). All specimens were derived from Warmblood horses of various ages that were euthanized for non-orthopedic reasons. Of the 12 limbs collected, 3 left and 3 right distal limb specimens were randomly assigned to each system for implantation. Two abaxial 4.5-mm cortical screws were inserted transarticularly in all cases. Both systems were implanted according to the manufacturer's instructions with the plates placed centrally between the 2 transarticular screws. The ALPS-20 systems were implanted using Kyon B-6.4-mm monocortical locking screws in all positions. The LCP systems were implanted axially using 2 Synthes 5-mm locking screws in the proximal and distal positions, with a standard 4.5-mm cortical screw inserted in the middle position. All constructs underwent CT-scans after implantation and biomechanical testing to detect implant deformation. Uniaxial mechanical loading was applied via a servo-hydraulic test system at a test speed of 50 mm/s, up to a maximum displacement of 80 mm. The resulting load-displacement curves were used to calculate yield point, stiffness, and maximum force for each construct. The measured values were evaluated for statistical significance (p < 0.05) between the 2 plate systems via one-factor ANOVA (Tukey test). The statistical power was verified for yield force, stiffness, and maximum load. No statistically significant differences between the 2 preparation groups were calculated across all of the measured parameters (p > 0.05). The ALPS system implants showed no signs of deformation, either in the plates or the screws. In contrast, the LCP demonstrated visible deformation, which had already occurred at the time of implantation from the tightening of the middle screw, as well as during the subsequent testing of the implants. After biomechanical testing, deformations ranging between 3.1° and 7.0° were measured in 4 LCPs. A total implant failure was observed for 2 LCPs. Both systems demonstrated comparable mechanical properties in the present study's ex vivo test model for equine PIJ arthrodesis. As such, the Kyon ALPS-20 may be a good alternative to the Synthes LCP for equine PIJ arthrodesis.

Investigation on dynamic mechanical properties of fly ash/slag-based geopolymeric recycled aggregate concrete

By harnessing the benefits from both construction and demolition waste recycling and geopolymer binders, geopolymeric recycled aggregate concrete (GRAC) can contribute to the green and eco-friendly construction material products. In this study, the compressive behavior of GRAC based on fly ash and slag was experimentally investigated under both quasi-static and dynamic loadings. Quasi-static compressive tests were performed by using a high-force servo-hydraulic test system, while dynamic compressive tests were carried out by using a Ø80-mm split Hopkinson pressure bar (SHPB) apparatus. The compressive properties of GRAC under dynamic loading, including stress-strain curves, energy absorption capability, and failure modes were obtained and compared with those under quasi-static loading. The results show that the compressive properties of GRAC exhibit a strong strain rate dependency. Although the recycled aggregate replacement decreases the quasi-static compressive strength, it exhibits a slight effect on the compressive strength at high strain rates. The dynamic increase factor (DIF) for compressive strength exhibits an significant increasing trend with the recycled aggregate replacement. On the other hand, the incorporation of slag increases the quasi-static compressive strength, dynamic compressive strength, and DIF. As for the energy absorption capacity, a minor enhancement is achieved with the recycled aggregate replacement, while a significant improvement is identified after the inclusion of slag. Empirical DIF formulae for compressive strength of GRAC are proposed, in which the DIF increases approximately linearly with the strain rate in a logarithmic manner.

Effect of induced external damage on fatigue life of carbon fiber reinforced (CFC) composite

The various advantages of CFC composite materials have lead to its application in lots of area especially in aerospace industry for structural applications. This paper highlights the effect of external damage and its location on the fatigue life of CFC composites. The introduction of the crack of 1 mm width at an angle of 45° was created on the specimens. All the tests were performed using a computer controlled 250 KN servo-hydraulic test system in load mode at room temperature, on one crack and two crack composite specimens. The fatigue strength degradation was monitored through stiffness measurement, which was done using load displacement data obtained during the fatigue loading. The CFC specimens with one inclined crack at the center and two inclined cracks at ends were subjected to constant amplitude loading for stress ratio R = 0.5. The CFC specimens with one crack showed a significant reduction in fatigue life. The fatigue properties for both cracked specimens were evaluated. Fatigue life for one crack specimen was much lower than the two crack specimen. A considerable reduction in stiffness was also observed for both one crack and two cracks specimen.

Effect of Auto-Tuning on Serrated Flow Behavior

The mechanical response of a servo-hydraulic testing system is affected by the stiffness of test specimens. An adaptive controller helps in auto-tuning the system by setting the optimal proportional-integral-derivative values for the subsequent test as the stiffness changes. This paper presents the effect of auto-tuning of various channels on the flow response of several commercial Al and Mg alloys and a mild steel. Strain-controlled monotonic tensile tests were performed at a given strain rate of 1 × 10−4 s−1 after auto-tuning of position, load, and strain channels in different combinations. Serrated flow or Portevin–Le Chatelier effect was observed in the Al alloys after auto-tuning of either position channel only or position and load channels. However, the serrations of Al alloys were shielded after further auto-tuning of strain channel. The stress-strain curves of Mg alloys and mild steel were observed to be basically free of serrations under any combinations of auto-tuning, which confirms that the serrated flow is a property of specific materials rather than a machine system noise.

The Dynamic Mechanics Behavior on Triaxial Compression of the Recycled Aggregate Concrete

The tests under triaxial compression states were conducted on recycled aggregate concrete (RAC) by different stress ratios (-0.1: -0.1: -1; -0.1: -0.25: -1; -0.1: -0.5: -1; -0.1: -0.75: -1; -0.1: -1: -1) at the strain rates of 10-5/s, 10-4/s, 10-3/s, and 10-2/s. This study was accomplished in the servo-hydraulic multi-axial testing system. The experimental phenomena and failure modes of recycled aggregate concrete under triaxial compression are described, the results of triaxial compressive strength of recycled aggregate concrete are presented, the effects of the strain rate and stress ratio on the triaxial compressive strength of recycled aggregate concrete are studied. This paper built a new dynamic strength criterion. The strength criterion describes the characteristics of structural RAC at different stress ratios and strain rates. The feature of the model is that it can consider the influence of strain rates.

A Superolaterally Placed Anchor for Subscapularis “Leading-Edge” Refixation: A Biomechanical Study

To compare a conventional single-row (SR) repair technique and 2 double-row (DR) repair techniques to restore and protect the superolateral aspect of the subscapularis (SSC) tendon and ensure SSC leading-edge reconstruction in a cadaveric model. The native footprint was measured in 15 pairs of human cadaveric shoulders (N= 30) with a mean age of 67.2years. According to the Fox-Romeo classification, a 25% defect or 50% defect in a superior-inferior direction was created. Specimens were mounted onto a servohydraulic test system to analyze contact variables at 0° and 20° of abduction with a force-controlled ramped program up to 50N. In addition, each specimen was cyclically loaded (10-100N, 300 cycles). The tears were repaired with 1 of 3 constructs: a 2-anchor medially based conventional SR construct, a 2-anchor-based hybrid DR construct, or a 3-anchor-based DR construct. The outcome variables were ultimate tensile load, displacement, and pressurized footprint coverage. All reconstructions resulted in stable constructs with peak loads exceeding 450N(P= .68). The overall displacement during cyclic loading was between 1.2 and 3.0mm(P= .70). A significant difference was seen when the 2 arm positions of 0° and 20° of abduction were compared, showing a constant reduction of pressurized footprint coverage with the arm abducted (P= .01). Analyzing footprint coverage with respect to the region of interest-the leading edge of the SSC-we observed a significant difference between the SR construct and a construct using a superolaterally placed anchor (25% defect, P= .01; 50% defect, P= .01), whereas no statistical differences were detectable between the hybrid DR construct and the DR construct. The leading edge of the SSC tendon can best be restored by using a superolateral anchor, whereas no statistical difference in load to failure in comparison with an SR construct or with the addition of a third anchor was detectable. The SSC is critical for proper shoulder function. Without an increase in the number of implants, a significantly better footprint reconstruction can be achieved by placing an anchor superior and lateral to the native footprint area close to the entrance of the bicipital groove.

Failure analysis of an aircraft GTE compressor disk on the base of imitation modeling principles

This study is concerned with failure analysis of an aircraft gas turbine engine (GTE) compressor disk made from titanium alloy on the base of imitation modeling principles. The failures have occurred by part-through surface cracks in a disk and blade “dovetail type” attachment. On the base of this attachment dimensions the two geometries of imitation models of GTE compressor disk are developed. The loading conditions of the imitation models are found and numerically verified to reproduce the loading conditions in the compressor disk at operation. The comparisons of stress-strain state at critical zones of compressor disk and imitation models are presented. Experimental fixtures are designed to reproduce operation loading conditions in compressor disk during the tests on a servo-hydraulic test system. It is demonstrated that proposed imitation modeling principles allow estimating residual life of compressor disk with taking into account crack initiation and growth at critical zones. The possibility of using experimental imitation modeling for calibration of the theoretical crack growth rate model including the fracture process zone sizes and nonlinear fracture resistance parameters is considered.