Actual Test Values Research Articles

Evaluation of one-, two-, and three-dimensional finite element and experimental models of internal fixation plates

A combined experimental and finite element model study was carried out for an internal fixation plate configuration. The experimental model was an aluminum tube (bending stiffness equal to the human femur) plated using a titanium alloy (Ti-6Al-4V) plate. The model was subjected to a four-point flexural test and strains were measured with strain gauges mounted at the midplane of the tube and plate. One-, two-, and three-dimensional finite element models were generated of the experimental model and various loads were applied including the actual flexural test values. Experimental and finite element model strain results were compared allowing evaluation of the three types of finite element models commonly used for orthopedic stress analyses. Results of this study indicated that three-dimensional models should be utilized for analysis of screw stresses or contact stresses, but one-dimensional models are equivalent to two-dimensional models in less complex areas. Screw stress analysis indicated that the outermost screws are most likely to fail between the tube (bone) and plate. Shear stress levels at the screw-tube (bone) interface were also determined. Reduction of tube (bone) stress levels on the plated side of the tube suggest that plated bone in this area could become weakened during remodeling subsequent to initial fracture healing. Results of this study indicate the validity of a combined experimental and finite element approach for biomechanical analyses of internal fixation devices.

POPULATION DISTRIBUTION OF HEAT RISE CURVES AS A SIGNIFICANT VARIABLE IN HEAT STERILIZATION PROCESS CALCULATIONS

ABSTRACT— Sterilization levels found in inoculated test packs are commonly in disagreement with predicted values. This study was made to determine if predicted sterilization values would be closer to actual test values if the population distribution of the slope indices from a sample of heat rise curves were used instead of the traditional slowest or mean single value of slope index in the sterilization calculations. A computer was programmed to calculate from the basic equations of thermal death times and heat penetration, the amount of sterilization achieved at designated time intervals in a population of food packages. Means and standard deviations of slope indices from both real and postulated heat penetration tests were fed into the computer together with specified processing conditions. Predicted spoilage levels were very close to those obtained from actual inoculated test packs. From input of postulated heat penetration values, it was demonstrated that the larger the standard deviation, the greater the error will be if only a single value of the slope index is used. Manual procedures are given for an accurate determination of the minimum process time required for sterilization. Methods are also given for data expansion to show a curve illustrating the complete relationship between process time and food sterility.

Optimum vehicle suspension designs by computer simulations

Computer simulation techniques are being used by vehicle suspension designers in an effort to obtain the optimum combination of suspension components to provide the maximum cross-country mobility for a vehicle. The ultimate effectiveness of the suspension will be dependent upon the ability of the computer simulation to accurately compute the dynamic responses of the vehicle as it traverses a cross-country terrain profile. The high degree of accuracy can only be obtained by exercising great care in the mathematical modelling procedures. Actual dynamic characteristics of the vehicle and suspension are required, which include their non-linear and discontinuous characteristics which develop as the vehicle traverses a cross-country terrain profile. When extreme care is exercised during the development of the mathematical model, the computer analysis of vehicle response will correlate within a few per cent of actual full-scale test values. This suspension technique will provide the suspension designer with a reliable method of obtaining an optimum design in a short period of time at a low programme cost.

Automatic component assembly in the telephone industry

The paper describes an improved assembly and testing machine designed to have sufficient flexibility for the batch production of a variety of printed wiring boards. The machine is controlled by punched paper tape, the necessary encoded information being derived from specially arranged drawings and stocklists. The instructions are interpreted by digital type electronic circuits which initiate and monitor the movements of the various mechanical members. In addition to performing the assembly operation the machine can drill component fixing holes in the boards and test the components prior to assembly. For this latter operation programmed measuring circuits are used. Incorrect and out-of-tolerance components are automatically rejected and in addition the programme can cause actual test values to be recorded if desired. Standardization of component shapes and improved information handling facilities are needed for the wide application and continuous operation of such machines. Progress in these matters is discussed.

Damping effect of D-C marine propulsion motors on vibrations produced in drive shafts by large propellers

D-c machines often are employed in ship-propulsion drives where maneuverability and a wide speed range are required. The d-c machine also has the advantage of serving as a source of damping if propeller pulsation should coincide with the natural frequency at some speed. This damping force arises because of the fact that any change in speed of the motor will cause a corresponding change in load current and torque. This torque change acts to oppose the original speed change, thus providing an effective damping force. The necessary equations and circuits are developed for calculating this damping effect and an illustrative calculation is included with actual test values for comparison.

Damping Effect of D-C Marine Propulsion Motors on Vibrations Produced in Drive Shafts by Large Propellers

D-c machines often are employed in ship-propulsion drives where maneuverability and a wide speed range are required. The d-c machine also has the advantage of serving as a source of damping if propeller pulsation should coincide with the natural frequency at some speed. This damping force arises because of the fact that any change in speed of the motor will cause a corresponding change in load current and torque. This torque change acts to oppose the original speed change, thus providing an effective damping force. The necessary equations and circuits are developed for calculating this damping effect and an illustrative calculation is included with actual test values for comparison.