Rosette Strain Gauges Research Articles

Numerical and Experimental Studies of Fabrication-Induced Thermal Residual Stresses in Microelectronic Packages

Microelectronic packages are typically composed of different layers of materials with un-similar thermo-mechanical properties. Fabrication-induced residual stresses, resulting from the mismatch of layers' thermo-mechanical properties, may lead to adverse effects such as warpage and delamination at the interface of layers. In this study, the fabrication process of the ball grid array (BGA) package was simulated to predict the thermal residual stresses through the thickness of the package. A finite-element model incorporating realistic material behavior of the BGA package layers was developed. To this end, the epoxy molding compound (EMC) was modeled as a viscoelastic material, while the silicon chip, the die-attach, and the composite substrate were simulated using an elastic model during cooling. Since Young's modulus of EMC is time and temperature-dependent, three different process temperatures were simulated to investigate the impact of viscoelastic properties of EMC, defined using Prony coefficients, on numerical residual stresses. To verify the simulation results, the incremental hole-drilling method was used to experimentally measure the residual stress components. It includes drilling a small hole at the center of a rosette strain gauge bonded on the BGA package surface and measuring the released strains on the surface. The relaxed strains were then converted to the residual stresses using a calibration matrix whose coefficients are determined from a finite-element model. The reasonable agreement of numerical and experimental components of the residual stress throughout the thickness of the BGA package confirms the reliability of the proposed simulation approach in estimating residual stresses in microelectronics packages.

Laboratory earthquake prediction of granite

Earthquake prediction refers to predicting the magnitude, location, and time of earthquakes and is challenging. Four attempts to predict the magnitude, location, and time of the laboratory earthquake of granite were made. First, the stick-slip failure process of granite samples was studied by a homemade test setup, and the whole process was monitored in real-time by strip strain gauges, rosette strain gauges, and acoustic emission (AE) transducers. Second, six parameters related to the stress drop were selected: dry density, Young's modulus, loading rate, static friction coefficient of the interface, normal stress, and shear stress. The prediction model of stress drop was established based on a backpropagation neural network (BPNN) considering the above six parameters. The stress drop in this paper is positively correlated with the released energy (magnitude) when the simulated fault slips suddenly. Third, the simulated fault interface was scanned by a high-precision 3D topography scanner before the stick-slip tests, and then the 3D topography scanning image was quantitatively measured based on digital image processing (DIP). According to the measurement results, the relationship between the nucleation position and the microstructure of the simulated fault interface was discussed. Fourth, the characteristics of AE parameters (absolute energy, ringing count rate, amplitude, b1 value) in the stick-slip process were studied. This paper aims to determine the precursory factors of sudden slip. This study helps explain the mechanism of shallow-focus earthquakes.

Coupled Eulerian–Lagrangian prediction of thermal and residual stress environments in dissimilar friction stir welding of aluminum alloys

The evaluation of residual stresses (RS) induced by the friction stir welding (FSW) process is crucial in anticipating the performance of the welded structure. The existence of such residual stresses within a friction stir welded structure may lead to excessive distortion and weakness to afford the applied external loads. To assess quantitatively the effect of these residual stresses generated by FSW process, the current paper implements a Coupled Eulerian–Lagrangian (CEL) finite element simulation to analyze both thermal and subsequent resulted remaining stress environments in dissimilar friction stir welding of AA6061-T6 and AA2024-T3 alloys. The thermal analysis step was conducted first and followed by a mechanical analysis step in which the residual stresses distribution throughout the whole dissimilar FSWed alloys were captured. To validate the simulation results, K-type thermocouples, in addition to A-type rosette strain gauges, were planted to measure both temperature history and residual stress field generated as a consequence of the thermal environment. The effect of changing FSW working variables like rotation and traverse speeds on both the thermal and residual stress environments was investigated. The obtained results demonstrated that the temperature, as well as the residual stress, was higher in the sample retreating side rather than the proposed advancing side, and a fair correlation between the experimental and simulation results was attained. Quantitatively, the longitudinal residual stress was higher in contrast to the transverse value, and it varied from being tensile in the zone beneath the tool shoulder to compressive away from the welding tool. Furthermore, the plastic strain produced owing to the surface contact between the welding tool and the dissimilar aluminum sample was higher on the retreating side.

Thermoelastic Investigation of Carbon-Fiber-Reinforced Composites Using a Drop-Weight Impact Test

Composite materials are becoming more popular in technological applications due to the significant weight savings and strength offered by these materials compared to metallic materials. In many of these practical situations, the structures suffer from drop-impact loads. Materials and structures significantly change their behavior when submitted to impact loading conditions compared to quasi-static loading. The present work is devoted to investigating the thermal process in carbon-fiber-reinforced polymers (CFRP) subjected to a drop test. A novel drop-weight impact test experiment is performed to evaluate parameters specific to 3D composite materials. A strain gauge rosette and infrared thermography are employed to record the kinematic and thermal fields on the composites’ surfaces. This technique is nondestructive and offers an extensive full-field investigation of a material’s response. The combination of strain and infrared thermography data allows a comprehensive analysis of thermoelastic effects in CFRP when subjected to impacts. The experimental results are validated using numerical analysis by developing a MATLAB® code to analyze whether the coupled heat and wave equation phenomenon exists in a two-dimensional polar coordinate system by discretizing through a forward-time central-space (FTCS) finite-difference method (FDM). The results show the coupling has no significant impact as the waves generated due to impact disappears in 0.015 s. In contrast, heat diffusion happens for over a one-second period. This study demonstrates that the heat equation alone governs the CFRP heat flow process, and the thermoelastic effect is negligible for the specific drop-weight impact load.

Improvement and validation of residual stress measurement in composite laminates using the incremental hole-drilling method

In this paper, the incremental hole-drilling (IHD) method has been improved by attaching strain gauge rosettes on both top and bottom surfaces, and changing the calculation algorithm for solving the ill-conditioned problem. In order to assess the feasibility and accuracy of the improved IHD method, an experiment of measuring the in-plane stress distribution in a composite laminate under bending was proposed. The composite laminate, which is bended by an external pure bending moment and fixed in a stable state, contains an in-plane stress distribution with obvious gradients in thickness direction, which is essentially similar to residual stresses. A plain woven T800H/803 specimen was tested in the proposed experiment with the improved IHD method. The results calculated using both top-surface and bottom-surface measured strains, and by iteration algorithm, showed good agreement with the finite element method (FEM) simulation and high calculation efficiency.

Modular Test Stand for Fatigue Testing of Aeronautical Structures – Verification of Assumptions

Abstract The Modular Test Stand was developed and manufactured to decrease the cost of fatigue testing and reduce the time of its completion as well as to enable testing specimens under more complex load conditions. The stand consists of three connected sections, similar to a wing box, all being loaded in the same way. Thanks to that, several specimens can be tested simultaneously. This configuration requires that stress and strain distribution should be reasonably uniform, as assumed in the design stage. The structure can be loaded with bending or torsion. A whole section, selected structural node or a specimen mounted in the structure as well as a repair or a sensor can be a test object. Two stands, one for bending and one for torsion were prepared. This paper presents the verification of the assumed strain and stress distributions on the skin panels. The measurements were performed with the use of Digital Image Correlation (DIC) as well as strain gauges. DIC measurements were performed on one skin panel of the central section. Five strain gauge rosettes were installed on both panels of the one section. In addition, one rosette was applied to one skin panel in each of two other sections. Measurements were performed on the stand for torsion as well as on the stand for bending. The results of DIC analysis and strain gauge measurement during torsion show uniform shearing strain distributions on the panels. During bending, on the tensioned side, the strains obtained indicate quite uniform strain distributions. On the compressed side, local buckling of the skin panels results in high strain gradients. Strain levels obtained with the use of a DIC analysis and strain gauge measurements were similar. Moreover, horizontal displacements of markers in the spar axis during bending was determined based on a series of photographic. The deflection line obtained in this way has a shape similar to arc, which is characteristic of the constant bending moment. The stand was tested with torsional and bending loads in order to verify the design assumptions. The results of strain distributions on the skin panels with the use of DIC and strain gauges as well as the deflection line of the spar axis indicate that the Modular Test Stand performs as assumed and can be used for tests.

Experimental evaluation of topologically optimized manipulator-link using PLC and HMI based control system

The topology optimization method is one of the prominent techniques that help to reduce the needless densities from the structural components. For any change in the boundary condition, a new optimum topology is defined, hence the proper evaluation of the topologically optimized link is imperative. The optimized topology is generated using solid isotropic material with penalization (SIMP) approach. In this work, the development of a universal test setup is described for one degree of freedom manipulator-link. The experimental setup is developed to test any size of the manipulator-link with different payload capacity. Parameters such as motor current, torque, speed, strain, and stress developed in the link can be measured online for an optimized link. An industrial level automation architecture is designed to validate the simulation results experimentally. A 3-phase AC servo motor is controlled through a motor driver using a programmable logic controller (PLC) logic to enable variable speed and rotational span. Human-machine interface (HMI) screens are designed and assigned tags to the PLC for easy operation of the servo motor from the user end. A rectangular strain gauge rosettes are mounted on a manipulator-link at the desired location to measure the Von-Mises stress values experimentally. Acquisition of strain data and stress values are captured using data acquisition (DAQ) with LABVIEW software. The results obtained from theoretical simulations and experiments are in good agreement. The volume reduction of 50% helps in reducing the actuator-current by up to 42.6%.

Experimental and computational analyses on residual stress of composite plate using DIC and Hole-drilling methods based on Mohr's circle and considering the time effect

Due to residual stress effects in final parts, researchers have always been interested to measure residual stress in different structures as well as comparing and analysing different methods in order to increase the accuracy and select the best method to measure it in different conditions and materials. The hole-drilling by applying the rosette strain gauge is one of the most commonly used methods for measuring residual stress and besides, the use of digital image correlation (DIC) method is expanding because of its advantages in measuring residual stress. So, these two methods have been studied by researchers. In this study, the results of residual stress measurements on composite plate by the hole-drilling and DIC methods are compared, but employing the Mohr's circle in this comparison as an innovation is discussed to understand better this issue. Also, considering that the other researchers have usually paid attention to measure the residual stress immediately just after drilling in the hole-drilling method using the strain gauge. Thus, the effect of elapsed time on the residual stress measurement is investigated in the results application. In both of these methods, the residual stress is calculated based on the principles of calibration coefficient measurement and the finite element method (FEM).

Determination and Validation of Residual Stresses in CFRP/Metal Hybrid Components Using the Incremental Hole Drilling Method

Lightweight materials contribute to an efficient decrease in fuel consumption in the automotive and aircraft industries. Hybrid components made of metal and carbon fiber-reinforced plastics (CFRP) have a high potential in lightweight applications due to their high strength-to-weight ratio. For cost-effective processing of hybrid materials, advanced manufacturing processes such as the prepreg-press-technology have been developed, in which the bonding between a metallic component and a fiber compound is exclusively realized in the forming process. However, upon processing of these hybrid components at elevated temperature, the difference in thermal expansion coefficients of the two materials leads to the formation of tensile residual stresses upon cooling. It is well known that these tensile residual stresses can be detrimentally effective with respect to the durability of a hybrid component. The objective of this work is to accurately measure and analyze residual stresses in hybrid components made of unidirectional CFRP and steel through the incremental hole drilling method. Within this study, the evaluation formalism for orthotropic materials is employed for measuring non-uniform residual stresses in hybrid materials. In order to improve the measurement accuracy, a customized strain gauge with eight grids is employed and a drilling increment size of only 20 µm is utilized. The influence of the angle between the strain gauge rosette and the fiber direction on the evaluation of the residual stresses is investigated. In order to evaluate the reliability of the results determined, a bending test applying a well-defined load is carried out. By direct comparison of the experimentally determined stresses and stress values calculated by the finite element method, the applicability of the hole drilling method for robust determination of residual stresses in CFRP/metal hybrid components is finally validated.

Midline denture base strains of glass fiber-reinforced single implant-supported overdentures

Statement of problemThe fracture incidence of implant-supported overdentures is more frequent in the area of attachment because of stress concentration and denture deformation in this area. How E-glass fiber reinforcement can address this problem is unclear. PurposeThe purpose of this in vitro study was to evaluate the influence of unidirectional E-glass fiber reinforcement on the mid-line denture base strains of single implant-supported overdentures. Material and methodsAn experimental acrylic resin cast was constructed with a single implant placed in the mid-line area and a ball attachment screwed to the implant. Twenty-four experimental overdentures were constructed and divided into 4 groups: group AP fabricated from autopolymerizing acrylic resin without fiber reinforcement, group APF fabricated from autopolymerizing acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix, group HP fabricated from heat-polymerized acrylic resin without fiber reinforcement, and group HPF fabricated from heat-polymerized acrylic resin with unidirectional E-glass fiber reinforcement running over the residual ridge and the ball matrix. A biaxial rosette strain gauge was attached to the incisor areas of each overdenture above the attachment level (Ch1, Ch2) and to a multichannel digital strain meter. A static vertical load of 100 N was applied to the first molar area bilaterally by using a universal testing device during strain measurement procedures. The differences in the mean strain and deflection values among the investigated groups were evaluated for statistical significance using 1-way analysis of variance (ANOVA) with the Tukey post hoc multiple comparison (α=.05). ResultsThe type of acrylic resin did not have a statistically significant effect on the mean strain values among groups (P=.350), while the reinforcement did significantly affect them (P<.001). The interaction between reinforcement and acrylic resin was not statistically significant (P=.552). Both strain gauge channels in group APF and group HPF recorded significantly lower strain values by almost 50% than those of group AP and group HP (P<.05). ConclusionsUnidirectional E-glass fiber reinforcement placed over the residual ridge and implant attachment significantly reduced denture base strains and deformation of single implant-supported overdentures.

Applications of the numerical methods in mechanical engineering experimental studies

Tremendous advances in computer science led to important progresses in science and technology. The significant feature of a computer, to rapidly and accurately perform calculi, was used for several purposes; the most important influence regarded the applied mathematics concepts where it was lifted the constraint concerning the necessary volume of calculi to be minimal when solving a complex problem. Conceptual advances also influenced the experimental mechanics domain, where numerical methods or numerical solving principles were applied to solve specific problems. The paper presents three original applications of the numerical methods in experimental mechanics. Reusability of the experimental projects’ results saves time and effort. For relevancy purposes many experimental studies’ results are expressed as diagrams. In the first example the approximation theory is used to solve interpolation problems. The output of the data processor consists of the spline function coefficients stored as CSV files or expressed as automatically generated computer codes, ready to be included in upper level applications. The second example is a particular study included in a hybrid model of an internal combustion engine, which outputs the states of strains and stresses in its cylinder block in running conditions. The particular study presents a method to compute the linear thermal expansion coefficient in the points where the temperatures are measured and to compute the temperatures in the inaccessible points, using the values of the previously computed coefficient. The experiment used strain gage rosettes bonded in 10 measurement points. The last original example presents a method to compute the analytical functions of the isostatics using as input data the pattern of isoclinic fringes of a photoelastic model or coating. Deep integration of the analytical, numerical and experimental studies is an important target in hybrid modelling.

P12. Lumbosacral residual rod strains in long PSR constructs often exceed in vitro rod bending strains

BACKGROUND CONTEXT Surface strain on instrumentation spanning the lumbosacral junction is often recorded during in vitro studies evaluating the biomechanical effects of different pedicle screw and rod (PSR) configurations. Rod strains recorded while releasing the rods from the screws after testing, much like strains recorded while securing the rods to screws prior to testing, are telling of the residual (additive) pre-strains that the rods are subjected to during multi-directional loading. PURPOSE The objectives of this study were to analyze lumbosacral rod strains from multiple rod locations (L5-S and S1-S2, posterior and lateral sides) during PSR L2-S1 vs L2-S2AI rod release, and to compare these to strains observed during multi-directional bending of the same constructs immediately before release. STUDY DESIGN/SETTING In vitro biomechanical study using human cadaveric specimens. PATIENT SAMPLE A total of 13 (L1-Pelvis) cadaveric spines (11F/2M, 58.7 ±6.1 yrs, DEXA 0.734 (±0.110) g/cm2) were studied. OUTCOME MEASURES Primary rod strains at L5-S and S1-2 on posterior and lateral sides. METHODS Thirteen cadaveric specimens were instrumented with ALIF at L5-S1 and PSR instrumentation spanning first L2-S1 and then L2-S2AI. Titanium rods were manually contoured with a French bender by a trained neurosurgeon to fit inside all poly-axial screw heads without significant reduction required, and then instrumented with 4 stacked rosette strain gauges (C2A-06-G1350-350/SP70) facing posteriorly (post) and laterally (lat) at both L5-S and S1-S2 (right side rod). Multi-location rod strains were recorded for both conditions (L2-S1 and then L2-S2AI, with full bilateral rod release and reattachment between conditions) while tested in a 6DOF robot under continuous dynamic loading to 7.5 Nm in flexion, extension, lateral bending (right and left), and axial rotation (right and left), followed by 400 N compression. In both cases after testing (L2-S1 and then L2-S2AI), rod strains were recorded during rod-from-screw release, performed sequentially level by level, caudal to cranial. Differences between rod release strains (from beginning to end) for the different conditions (including all gage locations: L5-S, S1-S2, lateral and posterior) were compared using 1-way ANOVA (p RESULTS The test max rod strains during in vitro multi-directional bending and compression were: 785 uE (L5-Spost - compression), 851 uE (S1-2post - compression), 429 uE (L5-Slat - right axial rotation), and 250 uE (S1-2lat - left axial rotation). The mean (±1 SD) rod release strains immediately following testing were: 426±374 uE [L5-Spost (S1)], 690±375 uE [L5-Spost (S2AI)], 256±147 uE [L5-Slat (S1)], 744±709 uE [L5-Slat (S2AI)], 921±822 uE [S1-2post (S2AI)], and 666±655 uE [S1-2lat (S2AI)] (Fig. 1, p=0.08). The number of cases when release strains after testing were greater than test max strains were: 17% [L5-Spost(S1)]; 31% [L5-Spost(S2AI)]; 46% [S1-2post(S2AI)]; 18% [L5-Slat(S1)]; 69% [L5-Slat(S2AI); and 77% [S1-2lat(S2AI)]. CONCLUSIONS Securing contoured rods to pedicle screws while instrumenting cadaveric spines with L2-S1 and L2-S2AI PSR instrumentation result in considerable lumbosacral rod strains on both the posterior and lateral sides of the rods, with magnitudes often (up to 77% of cases on the lateral side with S2AI) exceeding those recorded during multi-directional loading of the same constructs. Strains experienced during activities of daily living are additive to pre-strains observed during attachment, with high overall strains increasing the risk of 1) rod fracture through fatigue mechanisms and 2) pedicle screw loosening. Thus, these results have clinical implications with regard to rod fit and contouring. FDA DEVICE/DRUG STATUS PSR (Approved for this indication)

Circumferential Rosette Design for Extended Depth Hole-Drilling Residual Stress Measurements

The radial design for strain gauge rosettes used for hole-drilling residual stress measurements was established over 50 years ago and has remained almost unchanged since then. The design was developed to promote strain sensitivity, but was made without regard for ability to identify interior stresses. Consequently, only near-surface residual stresses can be identified. The aim of this study is to investigate rosette geometric features that may be refined to enable a significant increase in ability to identify interior stresses without significant loss of strain sensitivity. A finite element analysis was undertaken to model the influence of various geometrical factors on the depth response of a strain gauge rosette. It was found that that circumferentially oriented strain gauges allow residual stress measurements to be made to twice the depth of traditional radial strain gauges, with only minor loss in strain sensitivity. A new circumferential strain gauge rosette design based on the presented analysis is proposed for use where extended depth measurements are desired.

Differences in the principal strain angles during activities performed on natural hilly terrain versus engineered surfaces

BackgroundTibial stress fractures in military recruits occur beginning with the fourth week of training. In and ex vivo tibial strain experiments indicate that the repetitive mechanical loading during this time may not alone be sufficient to cause stress fracture. This has led to the hypothesis that the development of tibial stress fracture is mediated by the bone remodeling response to high repetitive strains. This study assesses the differences in the strain and angle of the principal strain during military field activities versus common civilian activities. MethodsIn vivo strain measurements were made from a rosette strain gauge bonded to the midshaft of the medial tibia. Measurements of principal strains and their angles were made while performing level and inclined walking and running on an asphalt surface, while fast walking up and down stairs, while performing a standing vertical jump and while zig-zag running up and down a 30° inclined dirt hill. FindingsThe angle of the principal strain varied little (5.40° to +2.74°) during activities performed on engineered surfaces. During zig-zag running on a dirt hill the strain levels were higher (maximum shear = 4290 με). At the pivot points of zig-zag running the angle of the principal strain varied between −115° to −123° downhill and between −32.8° to −51° uphill. InterpretationActivities that mimic those performed by infantry recruits on irregular hilly surfaces result in higher tibial strains and have more variation in principal strain angles than activities of ordinary civilian life performed on engineered surfaces.

Experiment and Numerical Simulation for the Compressive Buckling Behavior of Double-Sided Laser-Welded Al-Li Alloy Aircraft Fuselage Panel.

The aim of this work was to study the buckling behavior and failure mode of the double-sided laser-welded Al–Li alloy panel structure under the effect of axial compression via experimental and numerical simulation methods. In the test, multi-frequency fringe projection profilometry was used to monitor the out-of-plane displacement of the laser-welded panel structure during the axial compression load. In addition, the in-plane deformation was precisely monitored via strain gauge and strain rosette. The basic principles of fringe projection profilometry were introduced, and how to use fringe projection profilometry to obtain out-of-plane displacement was also presented. Numerical simulations were performed using the finite element method (FEM) to predict the failure load and buckling modes of the laser-welded panel structure under axial compression, and the obtained results were compared with those of the experiment. It was found that the fringe projection profilometry method for monitoring the buckling deformation of the laser-welded structure was verified to be effective in terms of a measurement accuracy of sub-millimeter level. The structural failure was caused by local buckling of the skin. The observed failure modes such as local buckling of the skin, bending deformation of the stringers, continuous fracture of several welds, and failure of local strength and stiffness were attributed to the deformed laser-welded panel structure under the axial compression. The predicted failure load in the numerical simulation was slightly smaller than that of the experimental test, and the error of the simulation result relative to the test result was −2.7%. The difference between them might be due to the fact that the boundary and loading conditions used in the FEM model could not be completely consistent with those used in the actual experiment.

Efficiency of Plasticity Correction in the Hole-Drilling Residual Stress Measurement.

This paper focuses on the analysis of the plasticity effect in the measurement of the residual stress by the hole-drilling method. Relaxed strains were evaluated by the computational simulation of the hole-drilling experiment using the finite element method. Errors induced by the yielding were estimated for uniaxial tension, plane shear stress state and equi-biaxial stress state at various magnitudes of residual stress uniformly distributed along the depth. The correction of the plasticity effect in the evaluation of residual stress was realized according to the method proposed by authors from the University in Pisa, which was coded in MATLAB. Results obtained from the MATLAB script were compared to the original input data of the hole-drilling simulation and discussed. The analyses suggested that the plasticity effect is negligible at the ratio of applied equivalent stress to yield stress, being 0.6, and that the correction of the plasticity effect is very successful at the previous ratio, being 0.9. Failing to comply with the condition of the strain gauge rosette orientation according to the principal stresses directions causes an increase in the relative error of corrected stresses only for the case of uniaxial tension. It affects the relative error negligibly for the plane shear and equi-biaxial stress states.

Effect of printing direction on stress distortion of three-dimensional printed dentures using stereolithography technology

Fabrication of complete dentures using a 3D printer is quicker and more economic than conventional methods. However, the photopolymer resins used in 3D printers has a lower flexural strength than heat-cured resin. Furthermore, photopolymer resins exhibit anisotropic properties depending on the printing direction, but no studies have evaluated their mechanical properties. The impact of stress distribution caused by changing the printing direction of the 3D printed denture has not been clarified. This study aimed to investigate the effect of different printing directions (0°, 45°, and 90°) of stereolithography (SLA) 3D printed dentures on stress distribution. Artificial mucosa was fabricated to fit a maxillary edentulous model, which was scanned to generate a standard tessellation language (STL) file. Subsequently, the upper denture was designed using computer-aided design (CAD) software, output as an STL file (master data), and set in three different printing directions (0°, 45°, and 90°). It was printed by the SLA 3D printer using photopolymer resin (n=6, in each printing direction). The stress distributions of the dentures were monitored using four rosette strain gauges, which were cemented to the midline of each denture as follows: above the labial frenum (A), at the incisive papilla (B), at the endpoint of the denture (D), and at the mid-point of B and D (C). A load was applied to the posterior region at a loading rate of 20 N/s from 0 N to 200 N using a universal testing machine. Changes in the applied load and strain at each point were recorded. The maximum principal strain (MPS) and the direction of the MPS (θ) were calculated. Each mean MPS was compared using Kruskal–Wallis and Steel–Dwass multiple comparison tests (p < 0.05). The stress distribution showed that the MPS for 45° printing was the lowest at each measurement point except for A under 200 N loading. The MPS at C for 0° was significantly different from that at C for 45° and 90°. The MPS at D in all the printing directions showed significant differences. The MPS at B for 45° was significantly different from that at B for 90°. The MPS at A in all printing directions showed no significant difference. Within the limitations of this study, differences in printing direction affected the stress distribution of SLA 3D printed dentures. The results showed that the stress distribution of the denture printed at 45° by the 3D printer system was the smallest compared with dentures printed at 0° and 90°. These results suggest that a printing direction of 45° is preferable when fabricating dentures using a 3D printer in clinical setting.

A new development of measurement technique for residual stresses generated by the cold tube drawing process with a fixed mandrel

The residual stresses during the cold tube drawing process affect the quality of the final tube products significantly. In this study, a new development of measurement technique that is built on the removing layer method (RLM) is developed to measure the axial and the hoop residual stresses (ARS, HRS) inside the tube wall for AISI 1010 steel. The tube is produced by the cold tube drawing process with a fixed straight mandrel (fixed plug). The RLM by milling process is performed on the inner and the outer surfaces of the tubes while the tee rosette strain gages (TRSGs) are fixed at the inner and the outer tube surfaces respectively for strain measurements. An axisymmetric finite element model (AFEM) based on explicit dynamic analysis is also performed to predict the ARS and the HRS within tube thickness. The experimental and finite element results are compared with variable X-ray diffraction (XRD) results. It is found that the results are in good agreement and the RLM is proved to be one of the appropriate methods to measure residual stresses inside the tube wall. The results showed that residual stresses present inside the tube wall are completely different by different reduction of areas of R = 16 and 23%.

Mobile bearing leads to less proximal medial tibial strain following UKA in comparison with fixed bearing in a cadaver setup

Aims and Objectives:Inexplicable pain to the medial proximal tibia is a frequent finding leading to revision after unicondylar knee arthroplasty (UKA). This study is an effort to find out, if there are any differences between mobile (MB) and fixed bearing (FB) UKA designs in terms of resulting strain in the medial proximal tibia as measured in an in vitro cadaver setup. It was hypothesized that MB UKA would result in lower bone strain.Materials and Methods:Five pairs of fresh-frozen full leg cadaver specimens were mounted in a kinematic rig that applied a dynamic squatting motion knee flexion after prior 3D CT. The rig allowed for 6 degrees-of-freedom at the knee while forces were applied to the quadriceps and hamstrings. During testing, an infrared camera system tracked the location of reflective markers attached to the tibia and femur with bicortical bone pins. Tibial cortical bone strain was measured with stacked strain gauge rosettes attached at predefined anterior and posterior positions on the medial cortex. Sensor outputs were recorded at 2000 Hz and synchronized with kinematic data prior and after pairwise implantation of MB and FB UKA directly comparing those between left and right knees from the same donor.Results:Bone strain values consistently increased with increasing flexion angle. FB UKA significantly increased strain in the anterior region of the medial tibial bone, while MB closely replicated strain values of the native knee.Conclusion:Proximal tibial bone strain seems to be lesser following MB UKA in comparison with FB UKA. Clinical studies will have to show, if this translates into a higher rate of pain problems with FB UKA.

PMHS and WorldSID Kinematic and Injury Response in Far-Side Events in a Vehicle-Based Test Environment.

Far-side kinematics and injury are influenced by the occupant environment. The goal of the present study was to evaluate in-vehicle human far-side kinematics, kinetics and injury and to assess the ability of the WorldSID to represent them. A series of tests with five Post-Mortem Human Subjects and the WorldSID were conducted in a vehicle-based sled test environment. The surrogates were subjected to a far-side pulse of 16.5 g in a 75-degree impact direction. The PMHS were instrumented with 6 degree-of-freedom sensors to the head, spine and pelvis, a chestband, strain gauge rosettes, a 3D tracking array mounted to the head and multiple single 3D tracking markers on the rest of the body. The WorldSID lateral head excursion was consistent with the PMHS. However, forward head excursion did not follow a PMHS-like trajectory after the point of maximum lateral excursion. All but one PMHS retained the shoulder belt on the shoulder during the entire test. However, the WorldSID consistently slipped out of the shoulder belt. The PMHS sustained an average of five rib fractures for which the seatbelt was observed to be the largest contributor. The WorldSID showed a maximum rib deflection of 25 mm. The first rib fracture occurred no later than 50 ms into the event. Anatomical differences between the WorldSID and the PMHS rib cage prevented the WorldSID from capturing the injury mechanisms related to interactions of the occupant with the seatbelt and the seat.