John T. Berry

Solution to inverse heat conduction problems employing singular value decomposition and model-reduction

Abstract A new and simple method for solving linear, inverse heat conduction problems using temperature data containing significant noise is presented in this paper. The method consists in a straightforward application of singular-value decomposition to the matrix form of Duhamels principle. A physical interpretation of the method is given by discussing the frequency-domain interpretation of the decomposition. Basically, rows and columns are removed from the decomposed matrices that are associated with small singular values that are shown to be associated with frequencies where the signal-to-noise ratio is small. The technique is demonstrated by considering a standard one-dimensional example. Advantages of the new method are reduction in matrix size, robust treatment of noisy temperature data, optimal in the least-squares sense, and lack of ad hoc parameters.

Comparisons and improvements concerning the accuracy and robustness of inverse heat conduction algorithms

This article describes a detailed investigation concerning the accuracy and robustness of several algorithms for solving the inverse heat conduction problem (IHCP). A variety of existing methods are classified into three categories: the direct inverse solutions, the observer-based solutions, and the optimization type solutions. The typical methods in each category are briefly analyzed and reviewed, i.e., whole domain regularization, optimal solution, and singular value decomposition (SVD) in the direct inverse category; sequential estimation in the observer-based category; and conjugate gradient functional optimization in the optimization category. An algorithm calibration procedure is used to ensure the best performance with each method. A detailed uncertainty analysis including systematic uncertainties and auto-correlations is described and used to calculate the uncertainty due to system parameters and temperature measurements. Accuracy and robustness indices are suggested to evaluate the performance of each method considered. Finally, a zero-phase, low-pass filter post-processing technique is proposed to improve the robustness in performance of the methods with weak accuracy or robustness. Several simulation results show comparisons of the concerned algorithm in terms of accuracy and robustness, and the effect of the proposed post-processing technique.

Pore Formation in Laser-Assisted Powder Deposition Process

Pore formation remains a concern in the area of rapid manufacturing by the laser engineered net shaping process. Results usually conflict on the origin of these pores; whether it should stem from an effect due to the physical/mechanical properties of the material or from an effect purely related to the processing parameters. We investigated this problem spanning a range of process parameters for deposition and using three different material powders, namely, an AISI 410 grade stainless steel, AISI 316L grade stainless steel, and AISI 4140 grade medium-carbon low alloy steel. The volume fraction, number density, and size distribution of pores were quantified using X-ray computed tomography and optical microscopy. Pores formed both at the interface between the adjacent layers and within the bulk of the layer. They were systematically sensitive to both the powder material composition and the process parameters.

Development of Nano-Fibrous Eutectic and Primary Silicon Phases in Al-Si Cast Alloys for High Strength Structural Applications

Among the high strength lightweight materials, hypereutectic Al-Si cast alloys with constituent phases that possess nano-scale dimensions are highly desirable for automotive and aerospace applications. Recently, we have achieved ultra-high strength Al-Si alloys via directional solidification technology. In these directionally solidified alloys, both the eutectic and primary silicon phases have nano-sized fibrous morphologies. This paper describes the microstructure evolution and manufacturing of these advanced alloys and introduces ways of implementing these findings of directionally solidified casting into near-net shaped castings.

Microstructure and Performance of Four Casting Processes for Magnesium Alloy AZ91

The performance of four different casting processes for magnesium alloy AZ91 were evaluated through microstructure characterization, mechanical testing, and SEM analysis of fracture surfaces. Passenger car control arms were cast by indirect squeeze cast, low pressure permanent mold (LPPM), T-Mag, and ablation processes. Samples were cut from twelve locations of the control arms for microstructure characterization. The microstructure, grain size, porosity distribution, and defect analyses were performed using optical microscopy and an image analyzer. Five different defects including microporosity, oxide film, sponge shrinkage, gas pore, and a crack-like defect were identified. The mechanical behavior was characterized using four-point bending (FPB) and tensile tests. The four casting processes were evaluated in terms of reliability using two-parameter Weibull statistics of the ultimate bending strength (UBS) determined from the FPB test samples. Metallographic analyses were performed on these samples, revealing noticeable microstructural differences between them, with some showing possible evidence of oxide films.

The Effect of Applied Pressure During Feeding of Critical Cast Aluminum Alloy Components With Particular Reference to Fatigue Resistance

the medium to long freezing range alloys of aluminum such as A356, A357, A206, 319 for example are known to exhibit dispersed porosity, which is recognized as a factor affecting ductility, fracture toughness, and fatigue resistance of light alloy castings. The local thermal environment, for example, temperature gradient and freezing from velocity, affect the mode of solidification which, along with alloy composition, heat treatment, oxide film occlusion, hydrogen content, and the extent to which the alloy contracts on solidification, combine to exert strong effects on the porosity formation in such alloys. In addition to such factors, the availability of liquid metal and its ability to flow through the partially solidified casting, which will be affect by the pressure in the liquid metal, must also be considered. The supply of molten metal will thus be controlled by the volume of the riser available for feeding the particular casting location, its solidification time, and its location together with any external pressure that might be applied at the riser.

Pressurised feeding systems

Pressurised feeding is by no means new. Whitworth patented a method for pressurising steel in refractory lined ingot moulds in the mid 1800s, while accounts of pressurising aluminium castings during solidification appeared in the 1930s, and the pressurisation of risers in steel and iron castings surfaced in the 1950s. It is appropriate to distinguish between cases where the whole casting and rigging has been pressurised and those where the feeder heads alone were pressurised. Generally speaking, pressurising the whole casting has not proved especially effective. Early experiments with aluminium involved top pouring of moulds contained in an autoclave. The considerable height through which the metal fell undoubtedly mitigated results. Furthermore, since the alloys were of a non-skin forming variety (i.e. long freezing range) the puncture of the partially solidified surface led to further property degradation. Work of Watmough and Berry in the US in 1961, repeated by Irani and Kondic at Birmingham published eight years later, employed aluminium sand cast bars with pressurised feeder heads surrounded by stout insulating sleeves. The results of both sets of experiments with long-freezing range alloys, showed excellent promise in terms of reducing dispersed porosity. During the nineties Fischer-Disa picked up this concept and successfully implemented it on a production basis for both aluminium and ductile iron. Most recently MSU in collaboration with US metal casters has applied the technique to tilt-poured permanent moulding (gravity-die casting). The results of this recent work will be described in detail.

A study of component surface refurbishment

The act of surface refurbishment of worn components is of itself both environmentally friendly and something which can be accomplished in a timely and convenient manner. It is environmentally friendly since it conserves both material and energy which would be otherwise expended in producing new components. It thus follows that it is also a convenient time-saver. There are many approaches to surface refurbishment, which include Laser Engineered Net Shaping (LENS), and weld repair, to name just two. All are likely to involve machining in the generation of the new surface. It is true to say that, indeed, most metallic surfaces will have experienced some degree of machining. This leads to the possibility that the properties of surfaces generated by machining are likely to be affected by their superficial state of stress and characteristics of the refurbished layer. Therefore our proposed research is in the characterization of the machinability of the remanufactured surface and the subsequent component performance. Such characteristics include fatigue, corrosion and oxidation.

Quality Aspects of A356 Castings with Multiple Gates

This work examines the quality aspects of multiple gated castings in aluminum A356 alloys. During the casting of parts in which multiple ingates are used to distribute the liquid melt throughout the mold, oxidation of the surface may prevent the adherence of the opposing fronts upon rejoining, thus producing sites prone to defect formation referred to as confluence welds. This phenomenon is investigated by the production of thin vertically sand-cast plates via the Electromagnetic Pump Green Sand (EPGS) process developed by the Foundation for the Research and Development in Transport and Energy (CIDAUT), Valladolid, Spain. For this research, three multiple-gated designs and one single-gated design were used to research an optimal configuration for melt delivery throughout the mold cavity. A series of numerical simulations were developed for each of the gating designs in order to compare modeling results with plates cast in the overseas counterpart’s foundry. Four-point bend testing was used to obtain information about the mechanical properties of the castings, and from this data, a Weibull statistical analysis was performed in order to quantify specimen failure rate for each of the configurations. Metallographic analysis was carried out using optical microscopy and fractography using a field emission gun scanning electron microscope (FEG-SEM). The numerical and experimental studies provided interesting insights on the formation of defects associated with the confluence of flow fronts.

Connection between filling, feeding and applied pressure in cast aluminium alloys

Abstract Oxide bifilms often appear to be linked with the dispersed type of porosity observed in longer freezing range aluminium alloys. Although measures exist to help prevent the inadvertent incorporation and subsequent unfurling of these bifilms into potential pores, little information would seem to be available specific to feeder design for this class of alloys. This is in contrast to the information available concerning the design of feeding systems for short freezing range alloys, in particular low carbon steels, where macroscale shrinkage is liable to occur. The various measures required regarding solidification order, required feeder volume, range of feeding action are plentiful for this second class of alloys and are more than adequately covered by Campbells feeding rules. The present study attempts to draw together facts that might help to better quantify the necessary guidelines for long feeding freezing range aluminium alloys.