Weight Specific Strength Research Articles

Inferring material properties from FRP processes via sim-to-real learning

Fiber reinforced polymers (FRP) provide favorable properties such as weight-specific strength and stiffness that are central for certain industries, such as aerospace or automotive manufacturing. Liquid composite molding (LCM) is a family of often employed, inexpensive, out-of-autoclave manufacturing techniques. Among them, resin transfer molding (RTM), offers a high degree of automation. Herein, textile preforms are saturated by a fluid polymer matrix in a closed mold.Both impregnation quality and level of fiber volume content are of crucial importance for the final part quality. We propose to simultaneously learn three major textile properties (fiber volume content and permeability in X and Y direction) presented as a three-dimensional map based on a sequence of camera images acquired in flow experiments and compare CNNs, ConvLSTMs, and Transformers. Moreover, we show how simulation-to-real transfer learning can improve a digital twin in FRP manufacturing, compared to simulation-only models and models based on sparse real data. The overall best metrics are: IOU 0.5031 and Accuracy 95.929 %, obtained by pretrained transformer models.

Digital light 3D printing of a polymer composite featuring robustness, self-healing, recyclability and tailorable mechanical properties

Producing lightweight structures with high weight-specific strength and stiffness, self-healing abilities, and recyclability, is highly attractive for engineering applications such as aerospace, biomedical devices, and smart robots. Most self-healing polymer systems used to date for mechanical components lack 3D printability and satisfactory load-bearing capacity. Here, we report a new self-healable polymer composite for Digital Light Processing 3D Printing, by combining two monomers with distinct mechanical characteristics. It shows a desirable and superior combination of properties among 3D printable self-healing polymers, with tensile strength and elastic modulus up to 49 MPa and 810 MPa, respectively. Benefiting from dual dynamic bonds between the linear chains, a healing efficiency of above 80% is achieved after heating at a mild temperature of 60 °C without additional solvents. Printed objects are also endowed with multi-materials assembly and recycling capabilities, allowing robotic components to be easily reassembled or recycled after failure. Mechanical properties and deformation behaviour of printed composites and lattices can be tuned significantly to suit various practical applications by altering formulation. Lattice structures with three different architectures were printed and tested in compression: honeycomb, re-entrant, and chiral. They can regain their structural integrity and stiffness after damage, which is of great value for robotic applications. This study extends the performance space of composites, providing a pathway to design printable architected materials with simultaneous mechanical robustness/healability, efficient recoverability, and recyclability.

Formability of roll-formed carbon fibre reinforced metal hybrid components and its experimental validation

Carbon Fibre Reinforced Metal Hybrid (CFRMH) materials that combine a sheet metal substrate with a reinforcing carbon fibre patch represent a promising solution to reduce weight while increasing the structural and crash performance of future automotive vehicles. CFRMHs cannot be formed with conventional stamping processes and at high volumes. This currently reduces their widespread application. Roll forming is increasingly used in the automobile industry for the forming of lightweight and high-strength metal structural components. The major deformation mode in roll forming is simple bending and this reduces interlaminar shear and compressive stresses that lead to fibre failure and delamination issues when stamping CFRMH sheet materials. This work analyses the potential of applying the conventional roll forming process for the manufacture of a simple top hat section shape from CFRMH sheet. For this, first, the material is produced in a hot press and then formed to shape in a laboratory roll forming facility at room temperature. Different layup sequences are tested, and component quality is analysed after roll forming by visual inspection. The results suggest that roll forming presents a promising manufacturing method for the production of automotive components from CFRMH sheets. The roll formed open shells are joined to produce crash box structure and tested in 3-point bending. The results show that depending on the fibre orientation a significant increase in weight specific strength is achieved.

Shell offset enhances mechanical and energy absorption properties of SLM-made lattices with controllable separated voids

Additive manufacturing has enabled surface-based sheet lattice to emerge as a new mechanical metamaterial with exceptional weight specific strength properties and multifunction. A novel design method of shell offset has been developed here for enhancement of mechanical properties and domain controllability of separated spaces by sheet lattice. Using selective laser melting, Ti6Al4V lattice samples were fabricated for compression experiments, followed by Micro-CT reconstruction. Manufacturing deviations with mean values of statistical analysis were taken into numerical simulations for prediction of mechanical properties. Investigation results show that increasing the shell offset is an effective strategy to improve mechanical properties and energy absorption of sheet lattices by more than 200% competing with net lattices, which is attributed to the higher second moment of area and successive layer-by-layer deformation mechanism of optimized unit type. In addition, a feasible adjustment region of 30–55% has been found, in which spatial volume fraction of the two independent void phases can be controlled for flow regulation of heat exchange without changing their mechanical properties. Those design concepts of sheet lattices will be valuable in future thermal management applications with lightweight protection.

The quasi-static behavior of hybrid corrugated composite/balsa core sandwich structures in four-point bending: Experimental study and numerical simulation

This study aims to investigate the effect of the insertion of a corrugated composite into the typical balsa core sandwich structure under four-point bending (FPB). The proposed sandwich structure is composed of aluminum face sheets, balsa wood with an average density of 125 kg/m3 and E-glass woven fabric. For obtaining full-field strains and deflection distribution, a digital image correlation (DIC) technique was employed. Based on continuum damage mechanics (CDM), a three-dimensional finite element model (FEM) was developed to predict the ultimate load-bearing capacity and failure mechanisms of the sandwiches. To this end, the material damage models for balsa wood and corrugated composite were implemented in ABAQUS software via VUMAT subroutine. After validating the numerical model, the effect of geometric parameters of the corrugated composite on the response of the sandwich structure was explored numerically. The findings demonstrated that the proposed hybrid core not only prevents catastrophic failure but also increases weight-specific strength by 38.4%. However, it appears that the hybrid core has no significant influence on the weight-specific stiffness under FPB. The parametric study showed that with increasing the corrugation angle and thickness, the specific strength/stiffness exhibits an ascending trend. Moreover, rectangular-shaped corrugation contributed to the best mechanical performance.

Determining the Co-Efficient of End Constraint of Stretch Formed Microtruss Materials

Microtruss cellular metals are a class of multifunctional materials, composed of a regular arrangement of supporting struts. They can be fabricated by stretching perforated metal sheets out of plane by applying force at strut intersections. Once fabricated, external loads are resolved axially along the struts resulting in stretch dominated deformation, yielding enhanced weight specific strength and stiffness at lower densities compared to conventional metallic foams. Given the slenderness of the struts making up the microtruss architecture, failure often occurs by inelastic buckling and is therefore dependent on the rigidity of the strut end constraints. During column buckling the limiting conditions are pin jointed (k=1) and rigid jointed (k=2), with microtruss struts typically having end constraints intermediate to these boundaries. Experimental and finite element methods were used to determine the value of k in IN600 microtrusses. Because of the non-linear stress-strain behavior of the parent metal, the relative significance of end constraint uncertainty is a function of the strut slenderness ratios and the material in question.

Corrugated all-composite sandwich structures. Part 2: Failure mechanisms and experimental programme

A novel corrugated composite core, referred to as a hierarchical corrugation, has been developed and tested experimentally. Hierarchical corrugations exhibit a range of different failure modes depending on the geometrical properties and the material properties of the structures. In order to understand the different failure modes the analytical strength model, developed in part 1 of this paper, was used to make collapse mechanism maps for the different corrugation configurations. If designed correctly, the hierarchical structures can have more than 7 times higher weight specific strength compared to its monolithic counter part. The difference in strength arises mainly from the increase in buckling resistance of the sandwich core members compared to the monolithic version. The highest difference in strength is seen for core configurations with low overall density. As the density of the core increases, the monolithic core members get stockier and more resistant to buckling and thus the benefits of the hierarchical structure reduces.

Non-destructive evaluation to control new casting processes

Light metal alloys with optimal weight specific strength are increasingly being applied for casting of critical components in larger constructions, for example automotive components or components in aircraft. The application sectors set continuously higher demands to the quality control, which is inherently due to the available new and faster production methods. An important parameter is that defective castings are worthless and that defects usually do not occur isolated, but are due to process errors. Hence there is a need for 100% inspection, as well as an aspiration that the information extracted from the non-destructive analysis is used for iterative process improvements. Specifically, the joining of quality issues and process parameters pertaining to new casting technologies, forms the basis for a broad EU-research project - QUME (On-line process & quality optimisation for the manufacturing of cast metallic parts), a project on NDT integrated with process management. Even though the specific project entails casting process optimisation and process management, there are many general applications for the developed principles and methods.

About composite materials and their use in bone surgery

Composite materials consist of two or even more different material components or phases, which are combined with the aim to improve physical, mechanical and/or biological properties. Such structurs are designed to fulfil very specific requirements with respect to a selected device application making full use of their higher weight-specific strength and/or stiffness. Furthermore, these materials offer an opportunity for constructing radiolucent devices. In medical technology, composite materials mainly consist of a polymer matrix and fibres as a reinforcement phase. Composites similar to those known from technical applications reveal a number of specific biological problems. This is due to the materials and manufacturing processes available for the construction of such composites preventing their unrestricted use in direct bone contact. Nevertheless, an application potential for these materials in bone surgery exists and justifies further research and development efforts.