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Metal matrix composites are one of the essential materials that are employed in various engineering fields including automotive, civil, aerospace, etc. Developing low-cost and light composites having superior mechanical and dynamic properties for those fields is one of the critical goals for researchers. Based on this motivation, the experimental free vibration analysis of the manufactured aluminum potassium-feldspar metal matrix composite plate is conducted in the free-free boundary condition. For this purpose, an aluminum (A356) K-feldspar composite square plate with dimensions of 250x250x8 mm is manufactured by stir casting technique considering 0.5% wt. of reinforcement material. For comparison, the A356 square plate having the same dimension is developed as a reference material. Both materials are compared regarding the modulus of elasticity values and vibration characteristics. The experimental free vibration analysis is conducted by initiating the impulse response via PCB 086C01 model impact hammer. The vibration signals are obtained by using three PCB 352A24 model accelerometers whose sensitivity is 100 mV/g and each one has a mass of 0.8gr. The accelerometers are capable to operate within the frequency range of 0.4 – 12000 Hz. The vibration signals are sampled at 8 kHz and gathered via NI PXI 4496 data acquisition system using LabVIEW software. According to the experimental results, the manufactured aluminum K-feldspar composite material has a 10% higher modulus of elasticity value than that of A356. Such a difference in the modulus of elasticity is also experimentally observed in the fundamental vibration frequencies of the aluminum K-feldspar metal matrix composite plate. Keywords: Free Vibration, K-feldspar, Aluminum, Metal Matrix Composites. Acknowledgment: This study was supported by the Research Project Grant (Project number: 2018.KB.FEN.045) from Dokuz Eylül University Scientific Research Projects (BAP). We also would like to thank CMS Wheels for their support.

The earthquakes of September 19, 1985 (M=8.1) and 2017 (M=7.1) together have been the most devastating earthquakes and with the highest number of observed losses, this requires a review of the seismic risk. Thus, this study presents a seismic vulnerability and risk assessment of the urban building stock in Mexico City, an expousure model is proposed using data from the city's Housing Cadastre. In the 1985 event, the greatest damage was concentrated in medium-rise concrete buildings (6-12 stories) both those with rigid frames such as those with waffle slabs, most of them located in Lake Zone (Cuauhtémoc Municipality). During the 2017 event, medium-rise buildings with flat waffle slabs, built before 1985 were again damaged. After the 19, September 2017 we elaborated a database with a total of 1093 damaged buildings, 28% of these structures were classified with damage degree from medium to severe (Grade 3, Grade 4 and Grade 5, of EME98 scale), in Cuauhtémoc Municipality was reported the highest number of damaged buildings with 147 structures. The database was subdivided in ten different typologies of building, including number of levels, age, structural system, floor system. To quantify and characterize the typologies of residential buildings, a statistical study of the buildings from the 16 different Municipalities was carried out, subdividing the database according to the different construction periods, location and number of levels of the buildings. A catalog of vulnerabilities is established through the development of fragility functions for the different typical building classes and combining them with analytics models for risk assessment in Mexico City. Thus, the exposure model is based in the public construction statistics obtained from the cadastre, and census information to characterize the building groups. The seismic hazard is the most studied component required to evaluate the seismic risk in Mexico City. However, there are no specific investigations related to spectral attenuation functions that include local effects. Thus, an probabilistic seismic hazard model was implemented which includes the site effects, where six seismic zones were characterized. The differentiation is made between origin of the earthquakes as interplate and intraplate source mechanism. For each zone, regression models were developed in order to establish the attenuation functions, in this way the site effects are directly included. The seismic hazard assessment was carried out using the classical probabilistic method that allowed to estimate hazard curves and Uniform Hazard Spectra (UHS) for different return periods. Earthquake risk assessment is achieved by means of a probabilistic analysis generating exceedance probability curves, and the probability of damage of each typology was estimated for seismic events with return periods of 40, 100, 250, 475, 975 and 2475 years. The study identified the Municipalities that have the most vulnerable buildings according to their height and year of construction, and thus determine rehabilitation plans and emergency programs.

In this paper, the dynamic stiffness at high frequencies of various elastic elements has been assessed through a set of laboratory tests, where a simple mass-element-mass-isolator test rig based on the proposals presented in ISO 10846 has been used for performing the measurements. In this context, three existing experimental approaches for the dynamic characterization of elastic elements have been compared: the indirect method proposed by ISO 10846, a frequency-independent characterization method based on the transmissibility peak, and an existing methodology for in-situ applications that in this work has been proposed to be used for laboratory assessments. In order to compare these methodologies, the axial dynamic stiffness of different elastic components has been obtained thought the three methods proposed. Moreover, the existing in-situ approach has been used to also determine the rotational dynamic stiffness of the characterized specimens. The application of the approach also showed that the rotational components of the response must be considered in the characterization elastic elements, especially when their rotational stiffness is low and, consequently, the rotational degrees of freedom are significant for the motion of the upper mass of the setup under the testing excitations. Results show that the in-situ method applied to laboratory-based setups allows for obtaining accurate results for a wide range of frequencies with a simple experimental setup.

Explosions generated from the detonation of unconfined explosive-charges produce high-intensity impulsive pressures. These pressures can induce excessive stresses over masonry buildings and therefore threaten their structural safety. Masonry as a construction material is commonly found in historical structures and widely used in modern constructions around the world. Masonry is a composite, anisotropic and brittle material, and these characteristics bring a special layer of complexity to the numerical simulations of their response, especially under extreme impulsive loads such as blast loads. To ensure realistic simulation results, all pertinent characteristics of masonry, including their response to high-strain rates of loading, should be accounted for. Moreover, the attributes of the impulsive loading need to be accurately considered. To this end, this study employs a mesoscale modelling approach that can include the geometry of masonry structures and the texture of brick units both in-plane and out-of-plane leading to a better understanding of their response. As brick-mortar interfaces are, mostly, the weak planes along which cracks can initiate and propagate through masonry, these planes of weakness mainly control the response of unreinforced masonry (URM) structural elements. The results of a series of parametric analyses to varying blast loads intensity, with time and standoff distances, are carried out and the effect of brick-mortar interface parameters and loading parameters upon the response of URM Walls is investigated. Important conclusions are offered on the practical implementation of complex numerical simulations and the range of demand parameters that can be considered more damaging to masonry structural subassemblies.