Predicting Curing Distortion in Composite Manufacturing-A Fast and Cost-Efficient Numerical Simulation Method.

The method used in Austria for calculating building heating and cooling demand is a monthly quasi-steady-state calculation. This method is presented in the European draft ISO/FDIS 13790. The simplified monthly calculation method is based on utilization factors. For these factors there is no specific mathematical derivation. The factor is based on an empirical formula. For increasing the practicability of the simplified calculation methods, the precision of the method is important, as well as the prediction accuracy by modifying the building parameters. Both requirements for a simplified calculation method are verified in this investigation. A simplified investigation of the calculation method precision for the cooling demand for offices leads to a 40 percent margin of error when using the simplified method for Vienna climate. The prediction accuracy of the monthly balanced method for changing the building parameters was verified for a six zone office model. At the end, the precision of the simplified method was quantified for an office model for the heating and cooling demand. Safety factors for the simplified method resulted from the investigation of the office model. The imprecision of the simplified method is greater than the validation of the monthly calculation method, as is exposed in the draft ISO/FDIS 13790. For the cooling demand for Vienna, the safety factor is 1.25 for the one zone method and 1.15 for the multi-zone method. For the heating demand no safety factor is necessary if the simplified method is not used for low air change rates and uncoupled models.

PurposeTo validate a simplified RNA isolation method from biofabricating hydroxyapatite (HAp) scaffolds seeded with mesenchymal stem cells (MSCs) and to identify the appropriate reference gene.MethodsTen MSCs-HAp composites were used for RNA isolation by methods based on simplified homogenization steps and column-based purification procedures, while the remaining RNA (n = 13) was extracted by traditional single-step isolation methods. The differences between the two procedures regarding the operation time, RNA quantity and quality were evaluated. Quantitative real-time PCR (qRT-PCR) analysis was performed to identify the appropriate reference gene.ResultsThe simplified method showed significant superiority in operation time (P < 0.001), RNA concentration (P < 0.001), A260/280 ratio (P = 0.005) and A260/230 ratio (P < 0.001). The average integrity number and 28 s/18 s ratio of RNA yielded by the simplified method were 9.1 ± 0.2 and 1.3 ± 0.1, respectively. The qRT-PCR analysis results indicated that the cycle threshold (Ct) values of GAPDH were significantly higher than those of the remaining 2 reference genes (ACTB and RPL13A) in the RNA samples obtained by the simplified and traditional methods (P < 0.05). The standard deviations of the ΔCt value (the difference between the Ct value and the minimum) of ACTB were higher than those of GAPDH or RPL13A, regardless of the RNA isolation method.ConclusionThe simplified method could extract intact RNA from biofabricating MSCs-HAp scaffolds and was superior to the traditional single-step procedure in operation time, RNA quantity and quality. GAPDH was identified as the most appropriate reference gene in MSCs-HAp scaffold composites due to its high quantity and good stability.

While there have been significant advances in the design and construction of composite steel‐concrete building structures, their use in regions of high seismicity has been hindered by the lack of design criteria in building codes and specifications. This has prompted initiatives in the Building Seismic Safety Council and the American Institute of Steel Construction to develop seismic design provisions for composite structures. The 1997 edition of the AISC Seismic Provisions includes a new section with requirements for composite steel‐concrete structures that are cross‐referenced by the general seismic loading and design criteria in the 1997 NEHRP Provisions and the 2000 International Building Code (final draft). Intended to complement existing provisions for steel, reinforced concrete and composite structures in the AISC‐LRFD Specification and the ACI 318 Building Code , these new provisions provide an important resource for seismic design of composite structural systems, members, and connections.

3D printing of lightweight continuous carbon fiber reinforced plastics (CCFRP) in three dimensions changes the traditional composite manufacturing processes. The continuous carbon fibers reinforced plastic filament can be printed along the load transmission path and significantly improve the strength of composite structures. Compared to the three-axis computer numerical controlled (CNC) machine based printing process, industrial robots provide the possibility to manufacture complex, spatial and large-scale composite structures. Here, the concept to use multi-robot to print complex spatial CCFRP components simultaneously has been presented. More than one 6 degrees of freedom industrial robots can cooperate with each other and solve the contradiction between structural complexity and printing reachability. During the printing process, the deformation of composite structures may happen, especially for the self-supporting components. Thus, in this paper, a Light Detection and Ranging (LiDAR) method is introduced to detect the deformation of printed composite structure and the movements of two UR robots. To obtain the point clouds of the printed structure, a LiDAR camera D435i has been installed on one robot. A new approach by combining coordinate transformation and iterative-closest-point (ICP) algorithm has been developed to merge the point clouds collected from different shooting angles of the camera.

In recent years composites have progressively been used for large-scale structures such as aircraft, ships, ground vehicles, and wind turbine blades. Traditional Nondestructive Evaluation (NDE) techniques have various limitations in assessing the performance of the large-scale composite structures. For instance, many techniques have the ability to measure either global or local properties but cannot measure both simultaneously. Nondestructive vibration detection techniques present a potential solution for evaluating both local and global large-scale composite structures, which are largely based on the fact that damage in a structure influences its dynamic characteristics such as modal parameters and Frequency Response Functions (FRF). This study investigates locating delamination in composite laminate plates under dynamic loading utilizing accelerometers during dynamic response as an alternative structural health monitoring method in composite structures. The test specimens were manufactured using unidirectional carbon fiber/epoxy creating 11 cross-ply composite laminate plates with [0,90,0,90]s orientation. Delaminated regions were placed at one inch increments, horizontally along the specimen. During testing, one side of each composite laminate plates were clamped using a custom fabricated fixture, cantilevered leaving the remaining edges free. An Unholtz-Dickie shake system excited the specimens. Dynamic response measurements using teardrop style piezoelectric accelerometers were taken along the surface face of each specimen, individually located along a 3 X 10 grid. Each response was compared collectively to examine any acceleration differences and damping between specimens. Finite element Modeling (FEM) ensured correlation of the flexural bending mode shapes between theoretical, analytical, and experimental. It was found that, the comparison between the results of the theoretical, Finite Element Analysis, and experimental data were in good agreement and delamination can be detected.

The demand for more efficient commercial aircraft with lower maintenance and operation cost has promoted more extensive use of composite materials for a significant reduction in weight and fuel consumption. Making a structure as light as possible suggests solving an optimization problem with the goal of mass minimization. To avoid failure modes related to composite structures, such as delamination and transverse matrix crack propagation, some design guidelines are commonly suggested by aircraft industries. These guidelines are: symmetry, covering ply, disorientation, percentage rule, balance, and contiguity of the layup. The manufacturability of the final design with available technologies must be guaranteed. Different regions may be subject to different loads in a large-scale structure. Laminate thickness may vary throughout the structure depending on the distributed loads in an optimized design. Additionally, for large-scale composite structures, such as an aircraft wing or fuselage, stiffeners are added to enhance structural performance in carrying compressive and tensile loads. The stiffeners divide the structure into smaller panels. To ensure manufacturability of a composite structure, it is crucial for the plies to be continuous among adjacent panels while the laminate thickness varies. Continuity of plies in adjacent panels, which is commonly referred to as blending, is a particularly difficult constraint to deal with. A feasible composite structure has to have sufficient stiffness and strength while complying with the aforementioned design and manufacturability guidelines. The feasibility of a composite structure is evaluated through the constraints added to the optimization problem. The variables in the design of a composite structure include, but are not limited to, ply stacking sequences and thickness distribution. Depending on the application, it may also be desirable to design the shape of a structure. Holes may be required in the design of parts such as ribs of aircraft wings to reduce the weight. Therefore, the shape and the topology may be additional variables in the design of a composite structure. Optimization of a composite structure subject to the design, manufacturing, and strength related guidelines is a very challenging problem. Fulfilling the manufacturability guideline in particular has been a major goal in recent studies. This confirms the interest of the experts in the field in the applicability of their proposed methods to real-life engineering problems. However, an investigation among the existing research, revealed that these methods require a significantly large number of computations and their inherent complexity makes them inadmissible for application to real structures. This motivated performing the present research with the goal of developing a design tool that can optimize complex fiber-reinforced composite structures in practice. The present research consists of a design tool for the optimization of variable stiffness composite structures (where fibers are not steered), and a method which is developed mainly for the optimization of an aircraft wing. To optimize a variable stiffness composite structure, the proposed method separates the optimization of stacking sequences from the optimization of the thickness distribution. A set of laminates with optimized stacking sequences with respect to the problem at hand is generated and stored in a reference table known as the Stacking Sequence Table (SST). The laminates in an SST must satisfy the desired laminate design guidelines. As long as the ply stacks in a design are selected from the SST, manufacturability of the final design is guaranteed. Next, a novel level-set gradient based method is introduced for the global optimization of ply drop locations. The proposed method aims at turning the discrete optimization problem associated with the integer number of plies into a continuous problem. This is done through the way the problem is parametrized; the design variables are never rounded in this approach. The level-set function gives the optimum thickness distribution over the structure for a specific SST. The developed method is verified by its application to the well-known horseshoe panel optimization problem. To investigate the performance of the method in dealing with a real problem, the proposed method is then applied to the layup optimization of a composite skin and rib structure of a wing. Local buckling and allowable strain are considered as the constraint of the problem and a standard finite element package is used to calculate buckling factors. The structural optimization of an aircraft wing is a highly complex problem. This is due to the large number of variables as well as structural and aerodynamics constraints influencing the design of skins and stiffeners. To make it computationally more efficient, a large problem can be decomposed into several smaller subproblems (subsystems) while preserving the couplings among these subproblems. A special method is subsequently introduced for the optimization of interacting skins and ribs of an aircraft wing box.

Piezoelectric transducer (PZT) based structural health monitoring (SHM) technology has been proved to be effective in increasing safety and reliability of composite aircraft structures. However, the attachment of PZT network to the host structure is considered as a weak link when facing the long term durability requirement of aerospace SHM, which should be overcome for aerospace SHM. In this paper, a surface-mounted co-curing method is creatively proposed to realize in-situ integration of large-scale PZT network and composite structure. By jointly controlling curing temperature and pressure, the proposed method can realize integration of large-scale PZT network and structural surface with high reliability and performance consistency. Compared with the conventional integration methods, the proposed method does not affect the manufacturing process or reduce the mechanical property of structure, and can be easily implemented whenever the host structure is available. To evaluate the effectiveness of the proposed integration method, a large-scale PZT network with an overall dimension of 1100 mm × 600 mm is integrated with a carbon fiber composite panel of wing box. The integration caused influence on functional integrity is first assessed by performing electro-mechanical impedance based theoretical analysis and experimental investigation. Then guided wave signals of the integrated large-scale PZT network are also acquired and analyzed, which proves the good signal repeatability and consistency of the network. At last, the SHM performance of the network is verified by conducting impact damages on the composite panel and performing damage monitoring, experimental results show that accurate monitoring is realized.

Review of digital image correlation application to large-scale composite structure testing

A novel simplified simulation method for the precooler based on the virtual source term: modeling, validation and application

Aircraft Smart Composite Skin (ASCS) which has the capability of Structural Health Monitoring (SHM) for large-scale aircraft composite structures to monitor impact needs to be developed because the poor impact resistance of composite structures may lead to barely visible impact damage and result in stiffness degradation and a significant loss of structural integrity. However, the impact is an instantaneous event so that it needs to be monitored on-line continuously during the whole service lifetime of the ASCS. Thus considering the strict restrictions of aerospace application, an impact monitoring system and sensor network is required to be low weight, low power consumption and high reliability. In this paper, an impact monitoring system with advantages of compactness, ultra-thin, light weight, ultra-low power consumption and high efficiency is developed to meet the strict requests of on-line application. Differently from conventional impact monitoring systems, the complex circuits are greatly simplified and the whole impact monitoring process is achieved in a digital way by turning the output of the piezoelectric sensors directly into digital sequences through a two-level digitalized mechanism which is realized by combing diode array with a Micro-Process Unit (MPU). A simple but efficient impact-region localization method is implemented in the MPU. In addition, the impact monitoring system is realized in a flexible way so that it can be embedded onto the composite structure to be a mechatronic system to realize impact monitoring on-line continuously. To illustrate the capability of the impact monitoring system, it is integrated with a flexible piezoelectric sensor array to construct a large-scale impact monitoring sensor network system. The network system is integrated on the surface of a large-scale stiffened carbon fiber reinforced plate to become an ASCS and the impact monitoring ability of the ASCS is validated.

Shear performance of single steel-plate concrete composite beams with various transverse reinforcement configurations

Detailed simulation of buildings’ thermal performance can provide useful information for building designers and engineers. However, deployment of detailed simulation involves a number of challenges, including time and effort expenditures not accounted for in many typical building delivery processes. In this context, careful application of simplified methods may provide – at least for a specific class of applications – a reasonable alternative. The present contribution explores this possibility via a specific case study involving a large sample of residential buildings in Gaza, Palestine. This sample includes some fifty multi-unit apartment buildings representing the bulk of residential building stock in Gaza. These buildings were subjected to computational cooling energy demand assessment, whereby both numeric simulation and derivative simplified methods were applied. Numeric simulations were performed using EnergyPlus. For simplified calculations, a regression-based procedure was derived. Toward this end, a number of candidate independent variables (e.g., compactness, effective window-to-wall ration, LEK value, mean effective U-value) were considered and the level of their association with the computed values of the designated building performance indicators was observed. The comparison of the results of the simplified and simulation-based methods revealed a reasonable level of agreement. In other words, the application of the simplified method provides in the majority of the cases performance indicator values that are close enough to the corresponding results of the simulation-based method. This implies that simplified methods and associated prescriptive procedures may provide an attractive alternative to highly detailed simulation studies in cases were the paucity of information and/or computational resources may represent a challenge (e.g., early design stages, insufficient preparedness of the professional community, contextual constraints).

The paper provides a brief overview of domestic and foreign guidelines (manuals) for the design of composite steel and concrete structures: steel-concrete slabs on profiled flooring, combined beams, and columns with rigid reinforcement. The necessity of creation of the actual manual corresponding to the modernlevel of development of construction science, normative documents and design practiceslinked to the new formulary SP 266.1325800.2016 is proved. It will facilitate the design, reduce labor expenditures and improve the reliability of composite steel and concrete structures. The new guidance provides general recommendations for the design of composite steel and concrete structures and the basic regulations for the calculations. The new guidance describes recommendations for modeling of composite steel and concrete structures and elements in the calculated complexes, the recommendations for calculation of combined beams fully concreting rectangular and T-section, partially concreting along with support slab on the lower flange of the beam, columns with rigid reinforcement, shear a connection of composite beams. Recommendations on the registration of creep, shrinkage and crack formation in the appointment of the modulus of elasticity are given. Recommendations on the use of diagrams of the state of concrete, reinforcement, and steel in the calculation of steel-concrete elements on a nonlinear deformation model are given. Recommendations on the use of the range of sheet flooring for steel-reinforced concrete slabs, as well as metal profiles as steel beams and rigid reinforcement in the cross sections of columns and combined beams, are presented. Recommendations on a design of units and details of composite steel and concrete structures are given, refined recommendations on buffer are presented. The examples of connection of steel beams with columns with rigid reinforcement are given. The examples of calculation of composite steel and concrete structures taking subject to the recommendations given in the Manual are presented.

Grillage topologies are commonly used in many composite structural applications to produce low mass designs that have a high stiffness. While composite failure criteria are being compared in many different simple structures, for example plates and tubes, literature must also compare more complicated applications, including grillages, as there are distinct differences in behaviour. This paper therefore performs analysis of grillage structures with more up to date failure criteria, taken from the world wide failure exercise, than previously investigated. The grillage theory selected is that of Navier theory with elastic equivalent properties due to its low computational expense for use with a genetic algorithm to optimise a composite structure. The results take an example from leisure boatbuilding showing the grillages produced from the different limit states, comparing the cost and mass. The final results show that the method allows a rapid analysis of grillages and that the selection of the limit state has an important effect on the optimised grillage topology.

Simplified methods for bridge designs have been allowed to use for many years by various North American bridge design codes. However such methods have not yet been permited to use in Hong Kong. The use of simplified methods will not only shorten the time spent on analysis, but will also permit the designer to retain a “feel” of behaviour of the bridge which is usually lost in traditional analyses. This paper constitutes the first report on the development of simplified methods of bridge analysis for use in Hong Kong. It presents the simplified method for the analysis of girder bridges with two lanes with the objective of generating discussion from practising designers which may lead to the enhancement of the proposed method and other methods currently under development. The results from the proposed method do not deviate significantly from those obtained by other analysis methods. The basis of simplified methods and various simplified methods adopted in recent North American bridge design codes are presen...