Mechanics guided design of hybrid laser/waterjet system for machining of hard and brittle materials

The two main objectives of this work is 1) to develop a mathematical model to efficiently capture the fracture behavior of materials undergoing thermal shock and 2) to design and develop a mechanics based hybrid laser/waterjet manufacturing process that will be able to machine hard and brittle materials at higher speeds and with better cut quality. The mathematical model relates the temperature generated during the machining process to the fracture behavior observed during machining. The hybrid manufacturing processes produces a synergetic effect of both laser and waterjet processes and overcomes the disadvantages of both of them. The temperature distribution is obtained from the Green\u27s solution of the Fourier Heat Conduction equation. Uncoupled thermoelastic stresses are obtained from the temperature distribution which in-turn is related to the stress intensity factor/Griffith Energy for Mode I crack growth by Bueckner\u27s weight function approach. This model can also be used to predict fracture behavior for given laser processing conditions. This model can also be used to manipulate transformational stresses that occur during machining of high conductive materials. This model can be easily extended to many multi-physics problems involving thermo-elastic behavior

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Mechanics guided design of hybrid laser/waterjet system for machining of hard and brittle materials

The two main objectives of this work is 1) to develop a mathematical model to efficiently capture the fracture behavior of materials undergoing thermal shock and 2) to design and develop a mechanics based hybrid laser/waterjet manufacturing process that will be able to machine hard and brittle materials at higher speeds and with better cut quality. The mathematical model relates the temperature generated during the machining process to the fracture behavior observed during machining. The hybrid manufacturing processes produces a synergetic effect of both laser and waterjet processes and overcomes the disadvantages of both of them. The temperature distribution is obtained from the Green's solution of the Fourier Heat Conduction equation. Uncoupled thermoelastic stresses are obtained from the temperature distribution which in-turn is related to the stress intensity factor/Griffith Energy for Mode I crack growth by Bueckner's weight function approach. This model can also be used to predict fracture behavior for given laser processing conditions. This model can also be used to manipulate transformational stresses that occur during machining of high conductive materials. This model can be easily extended to many multi-physics problems involving thermo-elastic behavior.</p

NUMERICAL AND EXPERIMENTAL STUDIES ON THE DEVELOPMENT OF VARIABLE DENSITY NANOCOMPOSITES FOR STRUCTURAL APPLICATIONS

Numerical and experimental studies performed to develop nanocomposites with varying carbon nanotube (CNT) alignment density within an epoxy matrix are presented. A 3-D numerical model has been developed that looks at the behavior of CNTs in epoxy resin subjected to non-uniform electric fields by explicitly accounting for electric field coupled with fluid flow and particle motion considering the transient resin viscosity. The transient nature of resin viscosity has been incorporated into the simulation study with data related to resin viscosity variation with time and temperature generated experimentally. The response of CNTs due to the induced dielectrophoretic force was studied using the numerical model. The model facilitated the design of an optimal electrode configuration for the processing of variable density composites. A computer controlled Arduino UNO based circuitry was developed to control supply of voltage to the electrodes during sample fabrication. The circuit was then integrated with AC voltage supply units and the electrode set-up for fabricating the variable density composite samples. Low weight fractions of CNTs (0.05 wt.% and 0.1 wt.%) in epoxy resin were used for the experimental work and preliminary experimental studies were conducted. Electrical characterization results of the variable density nanocomposites indicate over 100% and 30% increase in electrical resistance measured across sample widths in 0.05 wt.% and 0,1 wt.% CNT samples, respectively. The measured sample resistance values confirmed that variation in CNT alignment density was achieved across the samples

Obtaining a Relationship Between Process Parameters and Fracture Characteristics for Hybrid CO2 Laser∕Waterjet Machining of Ceramics

A combined experimental and analytical approach is undertaken to identify the relationship between process parameters and fracture behavior in the cutting of a 1mm thick alumina samples by a hybrid CO2 laser∕waterjet (LWJ) manufacturing process. In LWJ machining, a 200W power laser was used for local heating followed by waterjet quenching of the sample surface leading to thermal shock fracture in the heated zone. Experimental results indicate three characteristic fracture responses: scribing, controlled separation, and uncontrolled fracture. A Green’s function based approach is used to develop an analytical solution for temperatures and stress fields generated in the workpiece during laser heating and subsequent waterjet quenching along the machining path. Temperature distribution was experimentally measured using thermocouples and compared with analytical predictions in order to validate the model assumptions. Computed thermal stress fields are utilized to determine the stress intensity factor and energy release rate for different configurations of cracks that caused scribing or separation of the workpiece. Calculated crack driving forces are compared with fracture toughness and critical energy release rates to predict the equilibrium crack length for scribed samples and the process parameters associated with transition from scribing to separation. Both of these predictions are in good agreement with experimental observations. An empirical parameter is developed to identify the transition from controlled separation to uncontrolled cracking because the equilibrium crack length based analysis is unable to predict this transition. Finally, the analytical model and empirical parameter are utilized to create a map that relates the process parameters to the fracture behavior of alumina samples.This article is from Journal of Engineering Materials and Technology 31 (2008): 011005, doi:10.1115/1.3026547. Posted with permission.</p

Development and characterization of electric field directed preferentially aligned CNT nanocomposites

The present work demonstrates a novel method to preferentially orient carbon nanotubes (CNTs) in an epoxy matrix using a non-uniform electric field. The alignment method is based on the principle of dielectrophoresis. Aligned CNT/epoxy composites containing 0.01, 0.05 and 0.1 wt. % CNTs, respectively were fabricated using the method. The elastic modulus and hardness of the samples evaluated using nanoindentation technique were observed to increase with increasing CNT loading. The tensile strength of nanocomposite samples containing 0.1 wt. % CNTs increased by approximately 27% due to CNT alignment in epoxy matrix

A review of biomarkers in peri-miniscrew implant crevicular fluid (PMICF)

Abstract Background The temporary anchorage devices (TADs) which include miniscrew implants (MSIs) have evolved as useful armamentarium in the management of severe malocclusions and assist in complex tooth movements. Although a multitude of factors is responsible for the primary and secondary stability of miniscrew implants, contemporary research highlights the importance of biological interface of MSI with bone and soft tissue in augmenting the success of implants. The inflammation and remodeling associated with MSI insertion or loading are reflected through biomarkers in peri-miniscrew implant crevicular fluid (PMICF) which is analogous to the gingival crevicular fluid. Analysis of biomarkers in PMICF provides indicators of inflammation at the implant site, osteoclast differentiation and activation, bone resorption activity and bone turnover. The PMICF for assessment of these biomarkers can be collected non-invasively via paper strips, periopaper or micro capillary pipettes and analysed by enzyme-linked immunosorbent assay (ELISA) or immunoassays. The markers and mediators of inflammation have been previously studied in relation to orthodontic tooth movement include interleukins (IL-1β, IL-2, IL-6 and IL-8), growth factors and other proteins like tumour necrosis factor (TNF-α), receptor activator of nuclear factor kappa-B ligand (RANKL), chondroitin sulphate (CS) and osteoprotegerin (OPG). Studies have indicated that successful and failed MSIs have different concentrations of biomarkers in PMICF. However, there is a lack of comprehensive information on this aspect of MSIs. Therefore, a detailed review was conducted on the subject. Results A literature search revealed six relevant studies: two on IL-1β; one on IL-2, IL-6 and IL-8; one on TNF-α; one on CS; and one on RANKL/OPG ratio. One study showed an increase in IL-1β levels upon MSI loading, peak in 24 hours (h), followed by a decrease in 21 days to reach baseline in 300 days. A 6.87% decrease in IL-2 levels was seen before loading and a 5.97% increase post-loading. IL-8 showed a 6.31% increase after loading and IL-6 increased by 3.08% before MSI loading and 15.06% after loading. RANKL/OPG ratio increased in loaded compared to unloaded MSIs. Conclusions Cytokines (mainly ILs and TNF-α) and RANKL/OPG ratio showed alteration in PMICF levels upon loading of MSIs as direct or indirect anchorage