Explore the vast range of titles available.

Electrochemical migration (ECM) on the surface of printed circuit boards (PCBs) continues to pose a significant reliability risk in electronics. Nevertheless, the existing literature lacks studies that address the solder mask and solder pad design aspects in the context of ECM. Therefore, the objective of this study was to assess the impact of solder mask type with varying roughness and solder pad design on the susceptibility to ECM using a water drop test and thermal humidity bias test. Hot air solder leveling-coated PCBs were tested. Furthermore, the ECM tests were conducted on PCBs with applied no-clean solder paste to evaluate the influence of flux residues on the resulting ECM behavior. The results indicated that the higher roughness of the solder mask significantly contributes to ECM inhibition through the creation of a mechanical barrier for the dendrites. Furthermore, lower ECM susceptibility was also observed for copper-defined pads, where a similar effect is presumed. However, the influence of the no-clean flux residues can prevail over the effects of the solder mask. Therefore, the use of a rough solder mask and a copper-defined pad design is recommended if the PCB is to be washed from flux residues after the soldering process.

This paper focuses on the crash response characteristics related to the collapse mechanism and occupant injury during a vertical drop test, which is crucial for evaluating the crashworthiness of fuselage section. A simplified three-frame typical large aircraft fuselage section is designed using the equivalent design methods for weight and moment of inertia, which including two sets of triple seats and four 50th-percentile FAA Hybrid III Anthropomorphic Test Devices (ATDs). A vertical drop test is conducted at a velocity of 6.02 m/s, and the collapse mechanism and occupant injury are analyzed. To evaluate the aircraft’s crashworthiness, a comprehensive evaluation is performed considering the survivable volume, retention strength, occupant injury and emergency evacuation, and the Integrated Crashworthiness Index (ICI) is also obtained by a scoring method. It has been proven that the failure position and failure sequence of fuselage structures affect the unrolling failure mode (three plastic hinges failure mode) and the flattening failure mode (multiple plastic hinges failure mode) of fuselage section, providing valuable insights into the crashworthiness design of aircraft fuselage section.

In the present work, sheet-forming processes, i.e. super plastic forming and single-point incremental forming, have been adopted for the manufacturing of custom prostheses, instead of subtractive and additive techniques that are time- and cost-consuming for a single-piece production. Regarding concerns of the material, three different titanium alloys were used: pure titanium and two grades of the alloy Ti-6Al-4V (the standard one and the extra low interstitial one). Since no standard protocol exists to assess the mechanical performance of cranial implants, an experimental procedure has been designed and used in this work for producing polymethylmethacrylate supports, on which the cranial prostheses were firmly connected and subjected to impact puncture tests (drop tests). An experimental campaign could thus be conducted to investigate the effect on the mechanical response of (a) the titanium alloy, (b) the initial blank thickness and (c) the manufacturing process. Drop tests, carried out according to the proposed procedure, have shown no failure of the prostheses, neither in the area of the impact nor in the anchoring region and have revealed that, irrespective of the adopted manufacturing process, which does not alter the material, the amount of energy absorbed by the implants is always larger than 70%.

Reinforced concrete (RC) slabs may be exposed to the low-velocity impact load during their service periods. In low-velocity impact scenarios, the effect of strain rates has been remarkably higher than quasi-static loading because the loading duration is very short. Thus, structural responses and failure modes will be different. The present study aims to investigate dynamic response and failure modes of simply supported two-way RC slabs exposed to low-velocity impact load. In the experimental part of this study, nine RC slabs with the dimension of 1,000 × 1,000 × 80 mm were tested. The reinforcement ratio of RC slabs and the input impact energy applied to RC slabs were experimental variables investigated. A drop-weight test setup was utilized to apply impact load to RC slabs. By varying drop-height as 1,000, 1,250 and 1,500 mm, three different impact energies have been applied to RC slabs via a hammer of which weight is 84 kg. The time histories of the accelerations, displacements and impact loads were recorded. The dynamic responses obtained by tests and the failure modes observed has been interpreted in detail. Besides, a finite element model where explicit dynamic analysis is performed has been established for verification of the experimental results. There was observed good accordance between numerical and experimental results. Consequently, it is considered that the present finite element treatment can be used for the evaluation of the dynamic responses and failure modes of RC slabs exposed to low-velocity impact load.

•Plastilina used as a ballistic witness material (BWM) behind the armour to evaluate the backface signature (BFS).•Experimental and modelling approaches to determine the response of the specific ballistic plastilina.•High-speed camera used for measuring the penetration depth of a steel ball into the plastilina from drop test.•Numerical simulation of the drop test performed by taking into account the mechanical properties of the plastilina. Plastilina is often used as a ballistic witness material (BWM) behind the armour to evaluate the backface signature (BFS). Indeed, it is cheap, reusable and it keeps its deformation after being impacted. Moreover, while it aims at evaluating the performance of ballistic protections when no perforation occurs, it can be subjected to a very wide range of strain/shear rates during a ballistic impact. Therefore, there is a need to improve the knowledge about the mechanical/rheological response of such a material. This paper proposes both experimental and modelling approaches to determine the response of the specific ballistic plastilina red Weible® over a wide range of shear/strain rate. A capillary rheometry analysis with control of temperature was performed up to 8.104 s−1. The corrections of Rabinowitsch and Bagley were applied and an attempt of the analysis of Mooney was considered. From the rheology of plasticine, a two-parameters based power-law constitutive equation was deduced. An experimental drop test was carried out using a specific standard setup. A high-speed camera was used for measuring the penetration depth of a steel ball into the plastilina. A numerical simulation of the drop test was performed by taking into account the mechanical properties of the plastilina. A good correlation was observed between the experimental and numerical results in terms of indentation depth evolution.

Football helmet certification tests are performed without a facemask attached to the helmet; however, the facemask is expected to contribute substantially to the structure and dynamics of the helmet through the effects of added mass and added stiffness. Facemasks may increase the peak acceleration and severity index; therefore, as-used helmets may not mitigate head impacts as effectively as certification tests indicate. Furthermore, the effect is expected to depend on the helmet design as well as the orientation and speed of the impact. This study examined the influence of the facemask on impact behavior in a NOCSAE-style linear drop test and the interactions with location, velocity, and helmet model. Increases in peak acceleration and severity index of up to 36% were observed when helmets were tested with the facemask.

The investigation of wave propagation in the geological environment is warranted, and will ultimately help to provide a better understanding of the response of subsoil to excitation. Frequently utilized physical modeling represents a simplification of the global natural system for the needs of the investigation of static and dynamic phenomena with regard to the time domain. The determination of appropriate model materials is probably the most important task for physical model creation. Considering that subsoil represents a crucial medium for wave propagation, an evaluation of suitable model materials was carried out. A plate load test with a circular plate is a non-destructive method for determining the static bearing capacities of soils and aggregates, which are usually expressed by the deformation modulus Edef,2 (MPa) and the static modulus of elasticity E (MPa). A lightweight deflectometer test was used to characterize the impact modulus of deformation Evd (MPa), which is determined based on the pressure under the load plate due to the impact load. A representative propagation of the load–settlement curve for the PLT and the acceleration–time curve for the hammer drop test were investigated. The calculated E values were found to be in the interval between 2.6 and 5.7 kPa, and depending on the load cycle, the values of E ranged from 2.6 to 3.1 kPa. The modulus E from the hammer drop test was significantly larger than the interval between 10.6 and 40.4 kPa. The values of the dynamic multiplier, as a ratio of the hammer drop value to the PLT value, of the modulus E ranged from 4.1 to 13.0. The output of the plate load testing was utilized for the calibration of the finite element method (FEM) numerical model. Both the physical and numerical models showed practically ideal linear behavior of the mass. However, the testing of gelatin-like materials is a complex process because of their viscoelastic nonlinear behavior.

In this work, impact puncture tests (drop tests) have been used to both tune numerical models and correlate the performance of customised titanium cranial prostheses to the manufacturing process. In fact, experimental drop tests were carried out either on flat disk-shaped samples or on prototypes of titanium cranial prostheses (Ti-Gr5 and Ti-Gr23 were used) fabricated via two innovative sheet metal forming processes (the super plastic forming (SPF) and the single point incremental forming (SPIF)). Results from drop tests on flat disk-shaped samples were used to define the material behaviour of the two investigated alloys in the finite element (FE) model, whereas drop tests on cranial prostheses for validation purposes. Two different approaches were applied and compared for the FE simulation of the drop test: (i) assuming a constant thickness (equal to the one of the undeformed blank) or (ii) importing the thickness distribution determined by the sheet forming processes. The FE model of the drop test was used to numerically evaluate the effect of the manufacturing process parameters on the impact performance of the prostheses: SPF simulations were run changing the strain rate and the tool configuration, whereas SPIF simulations were run changing the initial thickness of the sheet and the forming strategy. The comparison between numerical and experimental data revealed that the performance in terms of impact response of the prostheses strongly depends on its thickness distribution, being strain hardening phenomena absent due to the working conditions adopted for the SPF process or to the annealing treatment conducted after the SPIF process. The manufacturing parameters/routes, able to affect the thickness distribution, can be thus effectively related to the mechanical performance of the prosthesis determined through impact puncture tests. Graphical abstract

Wood–Textile Composites (WTCs) are a new type of composite material based on willow wood strips and polypropylene that combines the properties of classic natural-fiber-reinforced polymers with an innovative textile wood design. While the basic quasi-static properties have already been investigated and described, there is a lack of knowledge about the behavior of the material under dynamic-cyclic and dynamic-impact loading as well as in relation to basic wood construction parameters. The present study is intended to contribute to the later use of the developed material, e.g., in architecture. For this purpose, fatigue tests, dart drop tests (impact and penetration), impact bending tests, and embedment tests were carried out. It was shown that embedding wood fabrics in a thermoplastic matrix leads to a significant increase in resistance to impact loads compared to the neat basic materials. It was also shown that the ratio of the failure stress in the fatigue test to the tensile strength of the WTC corresponds to that of other fiber-reinforced thermoplastics at around 70%. The embedment tests showed that WTC has good values compared to neat wood.

The landing gear of an aircraft serves to mitigate the vibration and impact forces transmitted from the ground to the fuselage. This paper addresses magneto-rheological (MR) damper landing gear, which provides high shock absorption efficiency and excellent stability in various landing conditions by adjusting the damping force using external magnetic field intensity. The performance and stability of an MR damper was verified through numerical simulations and drop tests that satisfied aviation regulations for aircraft landing gear. In this study, a prototype MR damper landing gear, a drop test jig, and a two-degree-of-freedom model were developed to verify the performance of the MR damper, with real-time control, for light aircraft landing gear. Two semi-active control algorithms, skyhook control and hybrid control, were applied to the MR damper landing gear. The drop tests were carried out under multiple conditions, and the results were compared with numerical simulations based on the mathematical model. It was experimentally verified that as the shock absorption efficiency increased, the landing gear’s cushioning performance significantly improved by 17.9% over the efficiency achieved with existing passive damping.