A multi-objective approach to optimize the weight and stress of the locking plates using finite element modeling

© IMechE 2021. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1177/09544119211048286This paper aims to identify an optimum bone fracture stabilizer. For this purpose, three design variables including the ratio of the screw diameter to the plate width at three levels, the ratio of the plate thickness to the plate width at three levels, and the diameter of the bone at two levels were selected for analysis. Eighteen 3D verified finite element models were developed to examine the effects of these parameters on the weight, maximum displacement and maximum von Mises stress of the fixation structure. Considering the relations between the inputs and outputs using multivariate regression, a genetic algorithm was used to find the optimal choices. Results showed that the diameter of the bone and the amount of load applied on it did not have a significant effect on the normalized stresses on the structures. Furthermore, in all ratio of the plate thickness to the plate width, as the ratio of the screw diameter to the plate width increased, the amount of stress on the structure decreased. But, by further increasing the ratio of the screw diameter to the plate width, the amount of stress on the structure increased. On the other hand, by increasing the value of the ratio of the plate thickness to the plate width, the maximum amount of stress on the structure decreased. Finally, optimal solutions in terms of the weight and the maximum amount of stress on the structure were presented.Peer reviewedFinal Accepted Versio

Comparison of mechanical properties in interference screw fixation technique and organic anterior cruciate ligament reconstruction method: a biomechanical study

© 2021 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Background Bone and Site Hold Tendon Inside (BASHTI) technique is an organic implant-less technique for anterior cruciate ligament (ACL) reconstruction with some clinical advantages, such as speeding up the healing process, over implantable techniques. The study aims to compare the mechanical properties of BASHTI technique with the conventional interference screw technique. Methods To investigate the mechanical properties, 20 in-vitro experimental tests were conducted. Synthetic dummy bone, along with fresh digital bovine tendons, as a graft, were used for experiments. Three loading steps were applied to all specimens, including a preconditioning, a main cyclic, and a pull-out loading. Results The mechanical characters of an interference screw technique using an 8 mm tendon diameter, including fixation strength, average cyclic stiffness (ACS), and average pull-out stiffness (APS) were found to be 439 ± 132 N, 10.3 ± 5.3 kN/mm, and 109 ± 40 N/mm, respectively. In the case of an interference screw using a 9 mm tendon, the fixation strength, ACS, and APS were obtained 549 ± 87 N, 10.3 ± 4.7 kN/mm, and 91 ± 13 N/mm, respectively. In parallel, the fixation strength, APS, and ACS of BASHTI technique using an 8 mm tendon were 360 ± 123 N, 3.3 ± 0.6 kN/mm, and 79 ± 27 N/mm, respectively, while, for 9 mm tendon 278 ± 103 N, 2.4 ± 1.2 kN/mm, and 111 ± 40 N/mm, were reported for fixation strength, APS, and ACS respectively when BASHTI technique was used. Conclusion About 50% of interference screw samples showed superior mechanical properties compared to BASHTI technique, but in another half of the samples, the differences were not significant (N.S.). However, due to organic advantages of BASHTI technique and lower cost, it could be used as a substitute for interference screw technique, especially where fast recovery is expected.Peer reviewe

Effect of geometry on the fixation strength of anterior cruciate ligament reconstruction using BASHTI technique

© 2020 Thieme Publishing Group. This is an accepted manuscript of an article accepted for publication in Journal of Knee Surgery; https://dx.doi.org/10.1055/s-0040-1716371.The goal of this study is to investigate the effects of tendon and cannulated drill bit diameter on the strength of the bone and site hold tendon inside (BASHTI) fixation technique for an anterior cruciate ligament (ACL) reconstruction. Bovine digital tendons and Sawbones blocks were used to mimic the ACL reconstruction. Mechanical strength of the specimens was measured using a cyclic loading continued by a single cycle pull-out load until failure to simulate the real post-surgical loading conditions. Finally, failure modes of specimens and ultimate failure load were recorded. The maximum possible tendon surface strain (i.e. tendon compression) for tendon diameters of 6, 7, 8, and 9 mm were 0.73, 0.8, 0.7, and 0.65, respectively. 80% of the specimens with tendon diameter of 6 mm and 20% of specimens with tendon diameter of 7 mm failed on the torn tendon. All samples with larger tendon diameters (i.e. 8 and 9 mm) failed on the fixation slippage. The maximum fixation strength according to the most suitable core bones for 6, 7, 8 and 9 mm tendons were 148±47 N (core 9.5 mm), 258±66 N (core 9.5 mm), 386±128 N (core 8.5 mm) and 348±146 N (core 8.5 mm), respectively. The mode of tendon failure was significantly influenced by the tendon diameter. Also, an increase in tendon compression (TC) raised the fixation strength for all tendon diameters; however, tendon over compression decreased the fixation strength for the 8 mm tendon group. Finally, an empirical equation was proposed to predict BASHTI fixation strength.Peer reviewedFinal Accepted Versio

Core bone diameter in an organic implant-less technique affecting the biomechanical properties of the anterior cruciate ligament fixation; an in-vitro study

© 2021 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Background Bone and site hold tendon inside (BASHTI) is an implant-less technique that can solve some of the problems associated with other anterior cruciate ligament (ACL) reconstructive methods. This study aims to investigate the effect of core bone diameter variation on the biomechanical properties of a reconstructed ACL using BASHTI technique. Methods A number of 15 laboratory samples of reconstructed ACL were built using bovine digital tendons and Sawbones blocks. Samples were divided into three groups with different core bone diameters of 8 mm, 8.5 mm, and 9 mm. The double-stranded tendon size and bone tunnel diameter were 8 mm and 10 mm, respectively. A loading scenario consisting of two cyclic loadings followed by a single cycle pull-out loading was applied to the samples simulating the after-surgery loading conditions to observe the fixation strength. Results Results showed that the core bone diameter had a significant effect on the failure mode of the samples (P = 0.006) and their fixation strength (P < 0.001). Also, it was observed that the engaging length and the average cyclic stiffness (ACS) of them were influenced by the core bone diameter significantly (engaging length: P = 0.001, ACS: P = 0.007), but its effect on the average pull-out stiffness was not significant (P = 0.053). Conclusions It was concluded that core bone diameter variation has a significant impact on the mechanical properties of ACL reconstruction when BASHTI technique is used, and it should be noted for surgeons who use BASHTI technique.Peer reviewe

Proceedings of Abstracts, School of Physics, Engineering and Computer Science Research Conference 2022

© 2022 The Author(s). This is an open-access work distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For further details please see https://creativecommons.org/licenses/by/4.0/. Plenary by Prof. Timothy Foat, ‘Indoor dispersion at Dstl and its recent application to COVID-19 transmission’ is © Crown copyright (2022), Dstl. This material is licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: [email protected] present proceedings record the abstracts submitted and accepted for presentation at SPECS 2022, the second edition of the School of Physics, Engineering and Computer Science Research Conference that took place online, the 12th April 2022

Strain-rate Dependent Fracture Load Prediction of Lead-free Solder Joints

The critical strain energy release rate at crack initiation, Jci, has been shown to govern the fracture of short solder joints. The present work measured Jci for 2 mm long SAC305 solder joints as a function of the strain rate and phase angle using DCB specimens. A drop tester was designed and built to perform the experiments at higher strain rates. Jci increased about 70% from quasi-static to strain rates of 0.05-1 s-1 (intermediate strain rates), and then decreased by more than 67% from intermediate strain rates to 42 s-1. In the all strain rate regimes, Jci substantially increased with the phase angle. Next, the effects of five significant processing parameters on Jci were investigated. Jci was found to be only a weak function of the solder composition, time above liquidus, and aging. The effects of solder thickness and local end geometry were found to be significant only at the higher strain rates. To investigate the discrepancy in fracture behavior of solder joints between DCB and Arcan specimens, Jci was measured using both of these specimens. Jci values obtained from Arcan-type specimens were much smaller than those obtained from DCB specimens. The modeling showed that the differences in the degree of constraint and plastic dissipation in the solder layers of these two specimens were responsible for this large difference. Finally, BGA test vehicles were assembled and prepared in different geometries. The specimens were loaded at two strain-rate regimes. A strain-rate dependent mode I cohesive zone model (CZM) was shown to be sufficient to predict the fracture load of these joints. Two different modeling approaches were used: the first method utilized mode I Jci obtained from the 2 mm model DCB specimens as the fracture energy in the CZM and the peak traction was calibrated using the calibration specimen; in the second approach, the peak traction was assumed to be the solder yield stress at the corresponding strain rate regime and the mode I fracture energy was obtained using the calibration specimen. The predicted fracture loads obtained from both methods were in reasonable agreement with the measured forces.Ph.D

Built-In Self-Test for Signal Integrity

Unacceptable loss of signal integrity may harm the functionality of SoCs permanently or intermittently. We propose a systematic approach to model and test signal integrity in deep-submicron high-speed interconnects. Various signal integrity problems occurring on such interconnects (e.g. crosstalk, overshoot, noise, skew, etc.) are considered in a unified model. We also present a test methodology that uses a noise detection circuitry to detect low integrity signals and an inexpensive test architecture to measure and read the statistics for final observation and analysis

Signal Integrity Fault Analysis Using Reduced-Order Modeling

This paper aims at analysis of signal integrity for the purpose of testing high speed interconnects. This requires taking into account the effect of inputs as well as parasitic RLC elements of the interconnect. To improve the analysis/simulation time in integrity fault testing, we use reduced-order modeling that essentially performs the analysis in the frequency domain. To demonstrate the generality and usefulness of our method, we also discuss its application for test pattern generation targeting signal integrity loss