In the current research, the use of tailor-welded blanks (TWBs) comprising Usibor® 1500-AS laser welded to more ductile Ductibor® 500-AS is considered. The TWBs were hot stamped to form top-hat cross-section channels with axially tailored properties. Axial crush rails were assembled by spot welding together two of these hot stamped channels along their flanges. The tailored rails were crush tested under dynamic (crash) and quasi-static conditions using an 855 kg crash sled facility at 10.6 m/s impact speed, and a 670 kN servo-hydraulic press at 0.5 mm/s, respectively. Non-tailored channels composed entirely of Ductibor® 500-AS were also tested for base material characterization and as a comparison to the tailored conditions. Numerical models of the crash experiments were developed. The material models include measured fracture loci using the generalized incremental stress state dependent damage model (GISSMO), with rate sensitive constitutive behavior. Spot weld failure was also considered based on tests of spot welded coupons. The accuracy of the predicted force-displacement and energy absorption response, extent of parent metal cracking, and extent of weld failure are evaluated in comparison to the experiments. The difference in response between quasi-static and dynamic testing is also evaluated.

This paper studies the effect of loading rate on mode I interlaminar fracture of unidirectional carbon/epoxy laminates. Double cantilever beam (DCB) test geometry was used to test quasi-static and dynamic fracture toughness. The DCB specimens were loaded symmetrically by a novel electromagnetic Hopkinson bar system at the maximum loading rate 30 m/s. The crack initiation is monitored by a pair of strain gage mounted on the surface of DCB arms. The hybrid experiment-numerical methods was used to calculate the fracture toughness by employing J-integral technique for quasi-static and dynamic tests. The finite element model takes use of incident stress wave as the boundary conditions for dynamic tests. It shows that the fracture toughness is rate positive at high loading rates, and rate insensitive at low loading rates.

The use of nickel electroless plating to enhance the mechanical properties of stainless steel micro lattice structures manufactured using selective laser melting is described. A coating thickness of 17μm is achieved, and this increases micro lattice specific stiffness by 50% and specific strength by 75%. There is scope for improving the coating process, and hence improving micro lattice mechanical performance. The methodology described here provides a new potential for optimizing micro lattice mechanical performance and can be extended to other cellular materials with different coating technology.

One of the major challenges for the realization of ultra-light weight and intelligent materials with advanced sensing/actuation capabilities, is related to, among other things, the integration in the material of non-invasive but indeed highly performing sensors and actuators. The reduction in scale, weight, and flexibility of the sensing devices represents a critical aspect to reach this goal. These unique properties are here reached by using flexible piezoelectric polymer (Polyvinylidene fluoride, PVDF) nanofibers as sensing elements. The nanofibers, that in this case study are randomly distributed , form an ultra-thin nanostructured porous mat that was deposited through a far field electrospinning approach. The process was optimized to obtain a dominant β phase in the polymer to enhance the piezoelectric response. The electrospun fibers were characterized at different scales: at the molecular level to understand the β phase content (FTIR spectroscopy), as well as at the macroscopic level to investigate the resulting ferroelectric and electromechanical response The results presented in this paper show the great capability of the nanostructured porous mat to work as ultra-light weight dynamic sensing system. Its scalable size and intrinsic properties make it an ideal solution for the development of advanced intelligent materials that can work at different length-scales.

The objectives of the work are to increase the direct use of geothermal resources for circular food production systems. The focus is on circular agricultural production processes: combining recirculating aquaculture systems and hydroponics into one system, including water treatment and waste recovery processes. The main outputs are vegetables, fish, fertilizers and potentially, algae and biogas. These outputs can generate revenue streams that can cover the costs of heat extraction while supporting viable businesses. The results and conclusions from a pilot case that was conducted in Iceland in recent years are presented, and the next steps are discussed. The pilot setup is now in the process of expansion to a semi-commercial production unit. However, there are still scientific, technical and commercial challenges to be solved. The scientific challenges are interdisciplinary and relate mainly to the optimization of the overall production system. Optimization involves creating good environmental conditions for each production unit while maintaining optimal oxygen, carbon dioxide, relevant pH and temperature levels and supplying all necessary nutrients. Additionally, accumulation of salts or other unwanted substances must be prevented. The primary technical challenges are to develop the circular food production system for optimized production while controlling the expenditure of energy, water, nutrients and manpower resources. Optimization also involves careful choices of species and the integration of new ideas into the value chain, both of which increase the synergy between the different components of the system. Furthermore, energy efficiency needs to be improved through using excess heat for other parts of the system and developing enhanced heating and cooling cycles. The aim is to transform the semi-commercial unit into a showcase model for solving commercial challenges while presenting a feasible business model for installing and operating a geothermal well for circular food production, making the most use of all available resources, securing optimum production conditions and minimizing waste.

A combination of a Michelson interferometer, a micro-optic element and a hyperspectral imager is used with broadband illumination to measure depth-resolved out-of-plane displacements without any scanning. Reference and deformed states of a transparent sample are recorded in single shots and used to evaluate the displacement field at different interfaces.

A new method to measure small displacement of crack width

A new experimental technique has been developed to investigate the confined shear behavior of concrete under dynamic conditions. The technique is based on the ‘Punch through shear test’ and consists in pre-stressing a concrete sample prior to testing it under shear. The pre-confinement is applied by means of a metallic cell instrumented with gages to register the stresses during the test; it consists in deforming the cell with a compressive load and then inserting the specimen into the cell. When the load is released, the cell applies a confinement to the sample. Two notches are performed from each side of the specimen and a displacement is applied to the central part in order to produce shear inside the vertical ligament. Dynamics tests are done with the Split Hopkinson Bar setup where a striker, an incident and two output bars are used. Two sets of specimens have been tested, saturated and dry concrete.

In this paper, dynamic fracture process and strain rate effect of a porous SiC ceramic were investigated. The failure process under dynamic loading conditions was monitored by a high-speed camera. Digital image correlation (DIC) method was further utilized to calculate the surface strain field. The high-speed images show that crack initiates in the center of the specimen and then propagates to the entire specimen under dynamic loading. In addition, DIC result showed that cracks occur on the surface of the specimen formed a band. And the band finally caused the collapse of the specimen. The test results showed that compressive strength of the porous SiC ceramic is rate sensitive. Under quasi-static conditions, the compressive strength is about 120 MPa, while in dynamic conditions strength increased to 247 MPa. Energy absorption during the deformation process is much larger under dynamic loading.

Ultrasonic transducers are used in many fields of application, including medical imaging/treatment, non-destructive testing and material characterization. To assure the quality of the ultrasonic investigation transducers require regular checks for possible deterioration and accurate calibration. Current methods rely on point-by-point scanning of the ultrasound field with a needle hydrophone, which is expensive and time consuming. Recently, we have developed a new concept, in which a fast full-field visualization of the radiation field is achieved through Acoustically induced PiezoLuminescence (APL). Here, we report on an improved ultrasonic beam visualization and provide further insights into the mechanism underlying APL and mechanoluminescence.