Numerical Study on Explosion Cutting Process of PMMA Plate and Key Factors Influence on Cutting Performance

Polymethylmethacrylate (PMMA) has been widely utilized to manufacture the covers of aircraft cockpits, naval vessels, car windows and so on, due to their high transmittance, low density, easy processing formability, high corrosion resistance and excellent mechanical properties. Under special conditions such as ejection lifesaving, the PMMA plate needs to be split precisely by explosion cutting technology. Hence, an accurate numerical simulation of PMMA structures is significantly important in engineering application. This paper aims to study the cutting behavior of PMMA plate numerically and investigate the influencing factors on cutting performance of PMMA plates. First of all, the simulation of explosion cutting process of PMMA plate is carried out by a non-linear explicit solver in LS-DYNA software using the fluid-solid coupling method. Jones-Wilkins-Lee (JWL) equation of state is used to simulate the relationship between the transient pressure and specific volume of explosives during explosion. The material model considering failure behaviors is used in the simulation. Additionally, the influence of explosive dosage as well as explosive type on the cutting performance of PMMA plate is investigated. Furthermore, the effect of PMMA geometry size on cutting performance is discussed. This study contributes to the knowledge for the design of PMMA structures which needs explosion cutting and the selection of explosive dosage and explosive type.

The Automatic Basketball Rebound System

In the sport of basketball, it is important to practice shooting the ball to develop the skill of making the shot in the basket at a high efficiency. Making shots at a high efficiency allows the player to succeed at a high level in the sport. The main focus of the paper describes the design and development of an automatic basketball rebound (ABR) system. The developed ABR provides a system that will launch the ball back to the player at any position on the court within a 50-foot radius. This is accomplished by a variable spring loaded launching mechanism that will compress a spring, depending on the players location, to generate the appropriate force required to launch the ball back to the player. The novel launching mechanism developed is mounted to a rotary table that ensures the launching mechanism is in the correct orientation with the player once the ball is launched. The player is outfitted with an inertial measurement unit to track their position using a method known as dead reckoning. This information is relayed back to a microcontroller that determines the system response. The ABR system is made from lightweight materials and is compact such that it is easy to move around compared to its predecessors.

Computational Design and Analysis of Nitinol-Based Arch Wedge Support

A nitinol-based arch wedge support (AWS) was designed using computational approach. Finite element analysis (FEA) was performed to on this design to assess the influence of loading, boundary conditions, and thickness on the mechanical response of the computer-aid design (CAD) model. Five loading conditions caused by different human movements, two boundary conditions, and three thicknesses are involved in this computational study. FEA results showed that the presented AWS design can resist forces caused by different human motions without generating any permanent deformation. The study features the first time to design and evaluate a thin-walled nitinol AWS model. The results of this study form the background of prototyping and experimental testing of the design in the next phase.

Sawing Status Prediction of Diamond Sawblade Sawing Concrete Based on the Characteristics of Material Composition

Diamond sawblade is an efficient tool to building renovation or demolition. Concrete used in construction is a typical composite material with random distribution, which is difficult to accurately identify and predict even under the same processing conditions, and tool life of diamond sawblade is difficult to control. In this paper, by cutting out single component of the hard and soft aggregate separately from concrete, the single component and concrete experiments were carried out to understand the sawing characteristics of different components. The wavelet decomposition was used to analyze the characteristic of each frequency band of the different components sawing force and vibration signals, and the sensitive frequency bands after correlation coefficient and energy ratio variation of each wavelet layer were extracted to judge the bluntness status of sawblade. By taking the Root-Mean-Square (RMS) value, the energy ratio of d2 and d5 wavelet layers and the standard deviation of sawing force and vibration signal as the characteristic values of the sawblade, a neural network optimized by bat algorithm was established to analyze the concrete processing signals and predict the working state of the sawblade. Evidence theory was adopted to combine the prediction results of sawing force and vibration samples to increase the overall prediction accuracy and reliability. The test sample showed that this method can correct inconsistent individual sensor predictions while being as close to the actual status value as possible. It provides an effective tool life prediction way of the diamond sawblade and a theoretical method for the monitoring of non-metallic materials with inhomogeneous components.

Test Results: Vehicle Responses to Simulated Drag Caused by Front Tire Tread Detachment — The Effect of Scrub Radius and Speed

The effects of reduced kingpin offset distance at the ground (scrub radius) and speed were evaluated under controlled test conditions simulating front tire tread detachment drag. While driving in a straight line at target speeds of 50, 60, or 70 mph with the steering wheel locked, the drag of a tire tread detachment was simulated by applying the left front brake with a pneumatic actuator. The test vehicle was a 2001 dual rear wheel four-wheel-drive Ford F350 pickup truck with an 11,500 lb. GVWR. The scrub radius was tested at the OEM distance of 125 mm (Δ = 0) and at reduced distances of 49 mm (Δ = −76) and 11 mm (Δ = −114). The average steady state responses at 70 mph with the OEM scrub radius were: steering torque = −24.5 in-lb; slip angle = −3.8 deg; lateral acceleration = −0.47 g; yaw rate = −8.9 deg/sec; lateral displacement after 0.75 seconds = 3.1 ft and lateral displacement after 1.5 seconds = 13.1 ft. At the OEM scrub radius, responses that increased linearly with speed included: slip angle (R2 = 0.84); lateral acceleration (R2 = 0.93); yaw rate (R2 = 0.73) and lateral displacement (R2 = 0.59 and R2 = 0.87, respectively). At the OEM scrub radius, steer torque decreased linearly with speed (R2 = 0.76) and longitudinal acceleration had no linear relationship with speed (R2 = 0.09). At 60 mph and 70 mph for both scrub radius reductions, statistically significant decreases (CI ≥ 95%) occurred in average responses of steer torque, slip angle, lateral acceleration, yaw rate, and lateral displacement. At 50 mph, reducing the OEM scrub radius to 11 mm resulted in statistically significant decreases (CI ≥ 95%) in average responses of steer torque, lateral acceleration, yaw rate and lateral displacement. At 50 mph the average slip angle response decreased (CI = 87%) when the OEM scrub radius was reduced to 11 mm.

An Empirically Determined Design Guideline for Rectangular Cross Section Nitinol Flexure Hinges With the Focus on Flexibility-Strength Trade-Off

In our group, we are developing flexure hinge based manipulators made of nitinol for minimally invasive surgery. On the one hand, sufficient flexibility is required from flexure hinges to be able to cover the surgical workspace. On the other hand, the bending amount of the flexure hinges has to be limited below the yielding point to ensure a safe operation. As a result of these considerations, it has to be questioned how much bending angle a nitinol flexure hinge with given geometric dimensions can provide without being subject to plastic deformation. Due to the nonlinearities resulting from large deflections and the material itself, the applicability of the suggested approaches in the literature regarding compliance modeling of flexure hinges is doubtful. Therefore, a series of experiments was conducted in order to characterize the rectangular cross section nitinol flexure hinges regarding the flexibility-strength trade-off. The nitinol flexure hinge samples were fabricated by wire electrical discharge machining in varying thicknesses while keeping the length constant and in varying lengths while keeping the thickness constant. The samples were loaded and unloaded incrementally until deflections beyond visible plastic deformation occured. Each pose in loaded and unloaded states was recorded by means of a digital microscope. The deflection angles yielding to permanent set values corresponding to 0.1% strain were measured and considered as elastic limit. A quasilinear correlation between maximum elastic deflection angle and length-to-thickness ratio was identified. Based on this correlation, a minimal model was determined to be a limit for a secure design. The proposed guideline was verified by additional measurements with additional samples of random dimensions and finite element analysis.

System Wear Life Estimation Under Uncertainty

In this paper, a new model is proposed for system degradation evaluation under sliding wear failure mechanism. This model estimates the material loss by progression of sliding distance. This model is generated by considering physical and geometrical aspects of system under wear mechanism. Several sets of experimental data are used for validation of the presented model. These experimental data are related to pin-on-disc test of Tungsten Carbide pins. These sets of data include initially conformal and non-conformal contacts. One set of data of pin-on-disc test by ASTM-G99 standard is used for additional validation of the model and for investigation of normal load effects on the parameters of presented model. Finally, uncertainty analysis is done by Monte-Carlo simulation to determine the variations of the predicted wear caused material loss.

A Method for Constructing Standard Involute Gear Tooth Profile

A simple but accurate combined computationaland graphical method for creating drawings and solid models of standard involute gears is presented. The method is predicated on the fact that the gear tooth angle at the base circle is fixed for a gear of specified module or size. As the contact point moves along the involute curve from the base circle point through the pitch point to the addendum circle point; the involute and gear tooth contact angles change continuously but their sum is fixed at the value it was at the base circle. This allows the coordinates of points on the involute curve to be generated analytically without employing the roll angle as current available methods. The generated data can be implemented in any computer design drafting (CDD) package platform to create an accurate gear tooth profile. The computations are done with Microsoft Excel which generates the graphical data for the gear tooth profile that are used in the CDD package. The required inputs to the Excel spreadsheet are the gear module size, the pressure angle, the number of teeth and the radial number of steps. A gearset example is considered and created with this method. The solid model of the example gearset in mesh and 2D drawing of the pinion are presented.

Side Structure Integrity Research for Passenger Rail Equipment

The U.S. Department of Transportation (DOT) Federal Railroad Administration (FRA) began promulgating regulations for the structural crashworthiness of passenger rail equipment at 49 Code of Federal Regulations (CFR) Part 238 on May 12, 1999. These Passenger Equipment Safety Standards (PESS) [1] include requirements affecting the designs of sidewall structures on passenger rail equipment. The FRA’s Office of Research, Development and Technology and the DOT’s Volpe National Transportation Systems Center are conducting research to evaluate the side impact strength of Tier I passenger rail equipment designs that have been constructed according to the current side structure regulations in §238.215 and §238.217. Following a fatal 2011 accident in which a highway semitrailer truck impacted the side of a passenger train that was transiting a grade crossing in Miriam, NV, the National Transportation Safety Board (NTSB) recommended that the FRA “develop side impact crashworthiness standards (including performance validation) for passenger railcars that provide a measurable improvement compared to the current regulation for minimizing encroachment to and loss of railcar occupant survival space” [2]. This paper describes the status of the current FRA research related to side structure integrity and describes the planned next stage of the research program which will include analyzing the performance of generalized passenger railcar structures in side impact collision scenarios. A discussion of the technical challenges associated with analyzing side impacts on passenger rail equipment is also presented.

Statistical Time Domain Feature Based Approach to Assess the Performance Degradation of Rotary Seals

In oil and gas industry, machineries and mechanical components are designed with high reliability to meet the demand of the oil field. Rotating machinery is a widely used equipment and any failure of critical components within the machinery could lead to delays and large expenses. Failure of rotary seal is one of the foremost causes of breakdown in rotary machinery and such a failure can affect the other process operations in oil and gas plants. Assessing seal degradation and severity estimation are very important for maintenance decision-making. Extracting meaningful and sensitive features that can show seal degradation from raw signals is a challenging task of degradation assessment. However, no extensive works are dedicated in this area of seals. In this paper, we perform accelerated aging and testing to capture the behavior of seals through their cycle of operation and demonstrated a statistical time domain feature based approach for extracting the sensitive features that can show seal degradation. Out of eleven statistical features extracted, seven extracted features such as mean, RMS, maximum, squared mean rooted absolute amplitude, impulse factor, crest factor, margin factor are found to be significant factors which have a potential to differentiate severity levels in seals. The findings from our work show that our approach has a potential to assess the severity in seals. As a possible extension, extracted features can be used to build a classification model to classify severity in seals which could be of great interest to the users and manufacturers of rotary seals.