Stretching and forming limit curve of steel-glass fibre reinforced and non-reinforced polyamide-steel sandwich materials

This paper focuses on investigating the forming behaviour of sandwich materials composed of steel sheets and glass fibre-reinforced polyamide 6 (GF-PA6), i.e., thermoplastic-based fibre metal laminates (FML). Stretching and forming limit curve (FLC) determination of FML with different cover/core layer thickness ratios at various forming temperatures, i.e., at room temperature (RT), 200 and 235 ◦C, are the main approaches for characterizing their formability. In addition, the formability of mono-materials and non-reinforced sandwich materials is investigated as a reference. For a successful test and reliable results, several technical issues are considered, such as the suitable lubrication configuration and digital image correlation at elevated forming temperatures. The results revealed that the formability of non-reinforced sandwich materials with different core layer thicknesses exhibited compared formability to their monolithic steel sheet and no remarkable improvement in their formability with increasing the temperature up to 200 ◦C. Conversely, the formability of FML shows significant improvement (approx. 300%) with increasing temperature with a forming depth of about 33 mm at 235 ◦C compared to only 12 mm at RT

Deep drawing behaviour of steel-glass fibre-reinforced and non-reinforced polyamide-steel sandwich materials

Thermoplastic-based fibre metal laminates (FMLs) have gained increasing interest in the automotive industry due to their forming potential—especially at higher temperatures—into complex components compared to thermoset-based ones. However, several challenges arise while processing thermoplastic-based FMLs. One the one hand, forming at room temperature (RT) leads to early failure modes, e.g., fracture and delamination. On the other hand, warm forming can extend their forming limits, although further defects arise, such as severe thickness irregularities and wrinkling problems. Therefore, this study focuses on developing different approaches for deep drawing conditions to deliver a promising, feasible, and cost-effective method for deep-drawn FML parts. We also describe the defects experimentally and numerically via the finite element method (FEM). The FMLs based on steel/glass fibre-reinforced polyamide 6 (GF-PA6/steel) are studied under different deep drawing conditions (temperatures, punch, and die dimensions). In addition, mono-materials and sandwich materials without fibre reinforcement are investigated as benchmarks. The results showed that the best deep drawing condition was at a temperature of 200 ◦C and a die/punch radius ratio of 0.67, with a gap/thickness ratio of ≤2.0. The FEM simulation via Abaqus 6.14 was able to successfully replicate the anisotropic properties and wrinkling of the GF-PA6 core in an FML, resembling the experimental results

A mixed numerical-experimental method to characterize metal-polymer interfaces for crash applications

Metallic (M) and polymer (P) materials as layered hybrid metal-polymer-metal (MPM) sandwiches offer a wide range of applications by combining the advantages of both material classes. The interfaces between the materials have a considerable impact on the resulting mechanical properties of the composite and its structural performance. Besides the fact that the experimental methods to determine the properties of the single constituents are well established, the characterization of interface failure behavior between dissimilar materials is very challenging. In this study, a mixed numerical–experimental approach for the determination of the mode I energy release rate is investigated. Using the example of an interface between a steel (St) and a thermoplastic polyolefin (PP/PE), the process of specimen development, experimental parameter determination, and numerical calibration is presented. A modified design of the Double Cantilever Beam (DCB) is utilized to characterize the interlaminar properties and a tailored experimental setup is presented. For this, an inverse calibration method is used by employing numerical studies using cohesive elements and the explicit solver of LS-DYNA based on the force-displacement and crack propagation results

Influence of adhesion properties on the crash behavior of steel/polymer/steel sandwich crashboxes: an experimental study

The energy absorption behavior of crashboxes made of steel/polymer/steel (SPS) sandwich sheets can be influenced by numerous parameters, such as the materials used, their thicknesses and stacking, and the adhesion properties between their layers. Therefore, in the present study, the impact of steel/polymer adhesion quality on the occurring failure modes of the crashboxes and the resulting energy absorptions are experimentally analyzed. For this purpose, axial crushing and three-point bending tests on double-hat and top-hat crash boxes were performed, respectively. Three levels of adhesion quality are investigated: none, weak, and strong adhesion strengths. Additionally, the structural crash properties, such as energy absorption and maximal intrusion, are determined and analyzed at both of the quasi-static and highly dynamic loading rates. The results of these investigations show that the adhesion strengths chosen here significantly influence both the failure modes and the energy absorption values. In particular, the structural parameters, in the case of no adhesion, are at most half of those in the case of strong adhesion. However, it is also shown that, in the case of weak adhesion, the structural characteristics are slightly reduced. Based on these results, the possibility to adjust the adhesion strength—globally and/or locally—could be used in future activities to purposefully tailor the failure behavior of hybrid crashboxes

Buccal Corridors: A Fact or a Myth in the Eyes of Laymen?

AIM: This study aimed to investigate laymen knowledge of the existence of the buccal corridor and whether it was an important factor for them in judging smile attractiveness and the effect of introducing the knowledge to them on their further judgment.MATERIALS AND METHODS: Nine subjects were randomly selected with variable buccal corridor percentages. They were coached to smile in a posed fashion and full face smile photographs were taken from a standardised distance. The photographs were randomly arranged in a power point presentation and displayed to a panel of thirty-nine randomly selected laymen judges. The judges made their beauty judgment on a visual analogue scale (VAS) and filled a questionnaire. After their education about the buccal corridor, they were asked to make a second judgment on a second sheet with VAS and with a different random sequence of the photographs.RESULTS: Intra-class correlation agreement for all the judges between the first and second scores was 0.713. The Spearman's rho Correlation coefficient indicated a positive correlation for all the photos. For the male judges, the agreement between the ratings was 0.839, and the correlation was positive for all the photos. For the female judges, the agreement between the ratings was 0.510, and the correlation was positive for all the photographs. Hundred percent of the judges were not familiar with the buccal corridor. Eighty percent of the female judges and 44.4% of the male judges mentioned that it would affect their further judgment.CONCLUSION: Laymen build their esthetic judgments on what we teach them, and modifying treatment plans to include corrections of buccal corridors for esthetic reasons only is a myth

The Role of Cardiac Catheterization after Cardiac Arrest

Coronary angiography after cardiac arrest is important to ascertain potential treatable causes of cardiac arrest, salvage myocardium, and potentially increase long-term survival. The cause of adult out-of-hospital cardiac arrest is typically myocardial ischemia. More than 50% of such resuscitated individuals will have an acutely occluded epicardial coronary on emergency coronary angiography. This includes three in four with ST-segment elevation and one in three without ST-segment elevation. In the latter the only reliable method of detection is coronary angiography. Numerous cohort studies, now including more than 8000 patients, have shown an association between survival and early coronary angiography and/or percutaneous coronary intervention. Public reporting of percutaneous coronary intervention 30-day mortality rates has been an impediment for extending this therapy to all resuscitated individuals who experienced out-of-hospital cardiac arrest, since current databases to do fully risk-adjust rates for this subgroup. Sincere efforts are under way to correct this situation

Effect of Er,Cr:YSGG on Remineralization Using CPP - ACPF (MI - Paste Plus) after Enamel Erosion Caused by Carbonated Soft Drink in Primary Teeth: In-Vitro Study

BACKGROUND: Erosion is a widespread phenomenon with higher predilection in primary dentition. AIM: The aim of the present study is to assess the remineralising effect of Er,Cr:YSGG laser application combined with CPP-ACPF after erosive demineralisation by Coca-Cola in primary teeth. METHODS: Fifty teeth (n = 10) were divided into; Group I: Artificial saliva, (Saliva natural, Medac, UK), Group II: CPP-ACPF (MI Paste Plus, GC Corp, USA), Group III: Er,Cr:YSGG (Waterlase iPlus, USA), Group IV: CPP-ACPF + Er,Cr:YSGG, Group V: Er,Cr:YSGG + CPP-ACPF. Teeth were immersed in Coca-Cola for 10 min, 5 times/day for 5 days. DIAGNOdent (DD) measurements were taken before and after the experiment. RESULTS: There was a significant increase in DD readings after erosive-treatment cycles in all test groups. The highest reading was in samples immersed in artificial saliva, and the lowest was in those subjected to combined CPP-ACPF and Er,Cr:YSGG laser application, regardless of the sequence used. There was no significant difference between samples immersed in artificial saliva, and after CPP-ACPF application. Similarly, there was no significant difference between samples treated by combined treatment of CPP-ACPF and Er,Cr:YSGG application. However, there was a significant difference between samples immersed in artificial saliva or treated with CPP-ACPF application and those subjected to combined treatment CPP-ACPF along with Er,Cr:YSGG. CONCLUSION: Combining Er,Cr:YSGG laser and CPP-ACPF paste significantly increased enamel remineralisation, regardless of the sequence implemented. Saliva naturally and CPP-ACPF application had a comparable effect on remineralisation

Effect of Low Level Laser Therapy on Gingival Inflammation in Patients undergoing Fixed Orthodontic Treatment: A Randomized Clinical Trial

AIM: The aim of this study was to compare the effect of low level laser therapy (LLLT) with non-LLLT as an adjunct to mechanical debridement in patients who develop gingival inflammation during fixed orthodontic treatment. MATERIALS AND METHODS: Thirty subjects undergoing comprehensive fixed orthodontic treatment were randomly allocated. Split mouth design was applied for each patient, where the four quadrants were randomly allocated to receive full mouth debridement. The test group (quadrant) received three laser sessions (days 1, 3, and 5) besides debridement while the control group (quadrant) received debridement only. Both bleeding index (BI) and plaque index (PI) were measured after 1 and 3 months, while the total colony forming units (CFU) were measured after 2 and 6 weeks. RESULTS: Clinical assessments (BI and PI) showed a statistically significant decrease at the first follow-up (after 1 month) and a slight increase in the second (after 3 months) that did not reach the base line. While, the total CFU showed a significant decrease in both follow-ups. CONCLUSION: Laser showed superior results in the treatment of gingival inflammation induced by fixed orthodontic appliances other than debridement only

Perceived Recovery States and Physical Fitness in Reserve Officers’ Training Corps Cadets

Reserve Officers’ Training Corps (ROTC) cadets are challenged mentally, emotionally, and physically with the physical fitness requirements (e.g., Army Combat Fitness Test or ACFT) required within their military science curriculum. Common physical fitness tests such as those for strength, power, and balance can provide insight into the recovery and readiness status of tactical athletes. PURPOSE: The purpose of this study was to explore the relationship between scores on the Short Recovery and Stress Scale (SRSS) and performance on a physical fitness test battery assessing balance, mobility, body composition, muscular strength, and power in collegiate ROTC cadets. METHODS: Seventeen ROTC cadets (20.1 ± 1.2y, 171.1 ± 11.2cm, 76.7 ± 21.0kg) volunteered to participate in a test battery and complete the eight items on the SRSS during the same week they conducted the ACFT. The test battery included measures of body composition (skinfolds), muscular strength (hand-grip), power (vertical jump), balance (Y-Balance), and mobility (sit and reach test). The SRSS consisted of the short recovery scale (SRS) and the short stress scale (SSS). The SRS contains 4 items on physical (PPC) and mental performance capabilities (MPC), emotional balance and overall stress. The SSS contains 4 items on muscular stress (MS), lack of activation (LA), negative emotional state (NES), and overall stress (OS). Descriptive statistics and correlations were calculated using SPSS version 28 (IBM Corp, Armonk, NY). RESULTS: For the SRS, significant correlations were found between 1) vertical jump power and both PPC (r = 0.59, p = 0.02) and MPC (r = 0.74, p \u3c 0.01), 2) MPC and body composition (r = -0.64, p = 0.01), and 3) PPC and right hand-grip (r = 0.52, p = 0.03). For the SSS, significant correlations were found for 1) vertical jump power and MS (r = -0.59, p = 0.02), LA (r = -0.51, p = 0.04), and OS (r = -0.51, p = 0.04), 2) NES and Y-Balance composite score for the right side of the body (r = 0.57, p = 0.02), and 3) OS and body composition (r = 0.64, p = 0.01). CONCLUSION: Conducting regular physical tests such as hand grip strength or vertical jump to give ROTC cadets feedback on current performance status may help increase awareness of the impact of physical, mental and emotional stress on their readiness for the demanding requirements of the military science curriculum