Additive Manufacturing of Structural Cores and Washout Tooling for Autoclave Curing of Hybrid Composite Structures

This paper presents a study combining additive manufactured (AM) elements with carbon fiber-reinforced polymers (CFRP) for the autoclave curing of complex-shaped, lightweight structures. Two approaches were developed: First, structural cores were produced with AM, over-laminated with CFRP, and co-cured in the autoclave. Second, a functional hull is produced with AM, filled with a temperature- and pressure-resistant material, and over-laminated with CFRP. After curing, the filler-material is removed to obtain a hollow lightweight structure. The approaches were applied to hat stiffeners, which were modeled, fabricated, and tested in three-point bending. Results show weight savings by up to 5% compared to a foam core reference. Moreover, the AM element contributes to the mechanical performance of the hat stiffener, which is highlighted by an increase in the specific bending stiffness and the first failure load by up to 18% and 310%. Results indicate that the approaches are appropriate for composite structures with complex geometries

Composites Part Production with Additive Manufacturing Technologies

Additive Manufacturing (AM) is of particular interest in the context of composite part production as AM promises the production of integrated, complex structures with low lead times. Currently, AM is used for tooling and sandwich cores with added functionalities. This paper presents four design principles that improve the production of composites parts during layup, handling, curing and post processing in the layup process. Design principles are applied to a hat-stiffener, a highly integrated aircraft instrument panel and a novel insert eliminating drilling operations. Results show that AM can reduce the part count, assembly steps and deformations during curing

Obeticholic acid for the treatment of non-alcoholic steatohepatitis: interim analysis from a multicentre, randomised, placebo-controlled phase 3 trial

Background Non-alcoholic steatohepatitis (NASH) is a common type of chronic liver disease that can lead to cirrhosis. Obeticholic acid, a farnesoid X receptor agonist, has been shown to improve the histological features of NASH. Here we report results from a planned interim analysis of an ongoing, phase 3 study of obeticholic acid for NASH. Methods In this multicentre, randomised, double-blind, placebo-controlled study, adult patients with definite NASH,non-alcoholic fatty liver disease (NAFLD) activity score of at least 4, and fibrosis stages F2–F3, or F1 with at least oneaccompanying comorbidity, were randomly assigned using an interactive web response system in a 1:1:1 ratio to receive oral placebo, obeticholic acid 10 mg, or obeticholic acid 25 mg daily. Patients were excluded if cirrhosis, other chronic liver disease, elevated alcohol consumption, or confounding conditions were present. The primary endpointsfor the month-18 interim analysis were fibrosis improvement (≥1 stage) with no worsening of NASH, or NASH resolution with no worsening of fibrosis, with the study considered successful if either primary endpoint was met. Primary analyses were done by intention to treat, in patients with fibrosis stage F2–F3 who received at least one dose of treatment and reached, or would have reached, the month 18 visit by the prespecified interim analysis cutoff date. The study also evaluated other histological and biochemical markers of NASH and fibrosis, and safety. This study is ongoing, and registered with ClinicalTrials.gov, NCT02548351, and EudraCT, 20150-025601-6. Findings Between Dec 9, 2015, and Oct 26, 2018, 1968 patients with stage F1–F3 fibrosis were enrolled and received at least one dose of study treatment; 931 patients with stage F2–F3 fibrosis were included in the primary analysis (311 in the placebo group, 312 in the obeticholic acid 10 mg group, and 308 in the obeticholic acid 25 mg group). The fibrosis improvement endpoint was achieved by 37 (12%) patients in the placebo group, 55 (18%) in the obeticholic acid 10 mg group (p=0·045), and 71 (23%) in the obeticholic acid 25 mg group (p=0·0002). The NASH resolution endpoint was not met (25 [8%] patients in the placebo group, 35 [11%] in the obeticholic acid 10 mg group [p=0·18], and 36 [12%] in the obeticholic acid 25 mg group [p=0·13]). In the safety population (1968 patients with fibrosis stages F1–F3), the most common adverse event was pruritus (123 [19%] in the placebo group, 183 [28%] in the obeticholic acid 10 mg group, and 336 [51%] in the obeticholic acid 25 mg group); incidence was generally mild to moderate in severity. The overall safety profile was similar to that in previous studies, and incidence of serious adverse events was similar across treatment groups (75 [11%] patients in the placebo group, 72 [11%] in the obeticholic acid 10 mg group, and 93 [14%] in the obeticholic acid 25 mg group). Interpretation Obeticholic acid 25 mg significantly improved fibrosis and key components of NASH disease activity among patients with NASH. The results from this planned interim analysis show clinically significant histological improvement that is reasonably likely to predict clinical benefit. This study is ongoing to assess clinical outcomes

An optimality criteria-based algorithm for efficient design optimization of laminated composites using concurrent resizing and scaling

Numerical optimization is an indispensable part of the design process of laminated composite structures. Several optimality criteria-based algorithms exist which rely on a sequential resizing and scaling approach. This paper presents a novel design algorithm applicable for stiffness and eigenfrequency optimization of composite structures with concurrent consideration of resizing and scaling operations. A method is introduced that allows for an efficient consideration of nonlinear constraints. This is done by determining stable concurrent scaling parameters from first-order constraint change ratio estimations. Optimization is carried out using optimality criteria in three independent steps, namely with respect to fiber angles, ply thickness ratios, and total laminate thickness. Sensitivity analyses are performed analytically at low computational costs. Numerical examples demonstrate the efficiency and fast convergence of the method. Compared to established algorithms, the number of required function evaluations is reduced significantly.ISSN:1615-147XISSN:1615-148

Efficiency of Particle Damping on Lightweight CFRP Structures

ISSN:0148-7191ISSN:2688-362

Design of a Test Stand for Lifetime Assessment of Flat Belts in Power Transmission

Flat belts are machine elements used for the power transmission between rotating elements. Compared to chain or gear drives, belt drives express advantages such as low-noise, and shock- and vibration-damping characteristics. Additionally, the simple, low maintenance and cost effective setup as well as high energy efficiency up to 98 % make them an attractive choice. Since they transfer power based on friction, they are subject to wear and consequently are expendable parts. Hence, there is a demand to increase the service lifetime of power transmission flat belts to decrease cost and downtime due to belt failure. This requires a deeper understanding on the fundamental transmission mechanics of flat belts as well as the failure mechanism limiting their lifetime. Experimental investigation is key in achieving both goals. Existing test stands are not able to replicate high performance applications and accelerating the lifetime assessment of flat belts due to limited capabilities in belt force and speed. Therefore, in this work an innovative test stand was designed and build, with a maximum belt tension of 1500 N and a maximum belt speed of 50 m/s, enabling the transfer of 75 kW. The design of the test stand was governed by modularity regarding multiple aspects. First, a variety and range of reproducible adjustable parameters were required. Second, the test stand had to be flexible regarding the emulation of possible drive configurations. Lastly, auxiliary instrumentation had to be accommodated by the test stand and its data acquisition system. The solution concepts for specific components were evaluated using morphological analysis.ISSN:2212-827

Analytical flat belt drive model considering bilinear elastic behaviour with residual strains

In this work an analytical model of a steady-state flat belt drive with multiple driving and driven pulleys is presented. The belt is characterised by a novel bilinear elastic constitutive description with a superposition of residual strain due to viscoelastic effects, such as relaxation, and considering inertia effects. Both prevalent tensioning methods for the drive are examined: the pretensioning of the belt to a target pre-strain, and the utilization of a tension pulley to ensure adequate tension in the drive. The model is discussed based on a case study. The enhanced accuracy in modelling the mechanical response of the belt results in more accurate estimation of the maximal transmissible power as well as the state of tensile strain of the belt. Traditionally, the maximal transmissible power and tensile strain of the belt are overestimated. Consequently, the potential for failures arising from drives operating proximate to their operational thresholds can be effectively mitigated. The more accurate description of the belt state can lead to better utilization of the belt capabilities and a larger design space when dimensioning the belt drive. Furthermore, the advantages of employing a tension pulley for belt drive tensioning are demonstrated under the assumed conditions.ISSN:0094-114

Book of Abstracts. Symposium Lightweight Design in Product Development: Zurich, 14.06. – 15.06.2018

The symposium Lightweight Design in Product Development (LWD-PD18) was held June 14th – 15th 2018 at ETH Zurich, Switzerland. Today more than ever, economic growth, prosperity and mobility need to be balanced with the limited availability of natural resources and energy reserves. In this context, lightweight systems play a central role by the realization of sustainable products and components, minimizing material and energy consumption over the entire design life. The design space available to engineers is continuously expanded by novel material systems and fabrication technologies entering the market. At the same time, novel multidisciplinary design tools, methods and approaches, new data and information technologies are revolutionizing products and the way they are designed and fabricated. The symposium thus selectively addressed and discussed actual topics along the entire value chain from material to design and fabrication, sharing research achievements at the leading edge of research and application and discussing and exchanging ideas on future trends

Precisely Adjustable Inserts for Stiffness-Driven CFRP Sandwich Structures

Carbon fiber reinforced plastic application, as a substitute for more traditionally applied materials like steel and aluminum, allows for combining lower mass with higher stiffness, and thus an increase in performance of highly-dynamic multiaxial testing machines. A novel through-the-thickness insert was developed to allow load transfer in stiffness-driven CFRP sandwich structures. The insert consists of two parts, is machined with an economical turning process, and features a fine thread which allows it to be accurately tuned, compensating for any potential CFRP sandwich thickness variations. The insert's external surfaces can be milled, meeting the tolerances needed for mating with other components.ISSN:2212-827