Top Ply Research Articles

Demonstration of Bond Quality Improvement for Closed Loop Control of Thermoplastic Tape-Laying

In thermoplastic tape-laying, the temperature at the interface between the top ply and substrate is critical to achieving interlaminar bonding. Based on a three lump process model, a Kalman filter and a state feedback controller were built to successfully estimate and control the interlaminar bonding temperature during the process. A practical advantage of this controller is that the only measurement required is the heater temperature. In this work, two methods are used to examine the bond quality when applying this feedback control method. One method is a microscopy study and the other is a lap shear strength test. Specimens were manufactured using the developed controller to regulate the bonding temperature. The microscopy pictures show that the interlaminar bond width is reduced as the bonding temperature is increased. The lap shear strength tests show that the bond strength is significantly improved as the bonding temperature is raised. Both test results have consistently demonstrated the causal relationship between interlaminar bonding temperature and bond quality. The control method produces high quality laminates by using temperature feedback from the heater to estimate the interlaminar bonding temperature.

Demonstration of Bond Quality Improvement for Closed Loop Control of Thermoplastic Tape-Laying

In thermoplastic tape-laying, the temperature at the interface between the top ply and substrate is critical to achieving interlaminar bonding. Based on a three lump process model, a Kalman filter and a state feedback controller were built to successfully estimate and control the interlaminar bonding temperature during the process. A practical advantage of this controller is that the only measurement required is the heater temperature. In this work, two methods are used to examine the bond quality when applying this feedback control method. One method is a microscopy study and the other is a lap shear strength test. Specimens were manufactured using the developed controller to regulate the bonding temperature. The microscopy pictures show that the interlaminar bond width is reduced as the bonding temperature is increased. The lap shear strength tests show that the bond strength is significantly improved as the bonding temperature is raised. Both test results have consistently demonstrated the causal relationship between interlaminar bonding temperature and bond quality. The control method produces high quality laminates by using temperature feedback from the heater to estimate the interlaminar bonding temperature.

Ultrasonic study of multi-ply composites

Multi-ply composites are studied ultrasonically using transmission and reflection spectroscopy and time-resolved line focus acoustic microscopy. For quasi-isotropic multi-ply composites, the ultrasonic response does not exhibit isotropic behavior as, for example, is observed in mechanical tests. The amplitudes of the ultrasonic obliquely transmitted/reflected signals depend on the sample orientation relative to the incident plane as well as top ply orientation and ply sequence. In addition to the plane-wave study, the applicability of the time-resolved line focus acoustic microscopy for determination of elastic constants of composites is discussed and the results are compared to data obtained by the self-reference double-through-transmission ultrasonic bulk wave method. A theoretical model to predict ultrasonic wave propagation in the multi-ply anisotropic structure is described. The efficiency and performance of the transfer and global matrix methods are compared. The theoretical results are compared with experiment and used to interpret the complicated wave behavior in this material.

Processing, physical and thermal properties of BlackglasTM matrix composites reinforced with NextelTM fabric

The cure and pyrolysis behavior of a BlackglasTM resin and NextelTM 440 impregnated with BlackglasTM resin were studied. Cure of the BlackglasTM resin is an exothermic process and DSC studies indicate that with an increase of catalyst content from 0.1 to 1.0%, the onset and peak temperature of cure are decreased coupled with an increase in the enthalpy of cure indicating a greater extent of cross linking. However, pyrolysis char yield of the pyrolyzate is relatively insensitive to cure conditions. Cure pressure and pyrolysis environment are variables in the processing of BlackglasTM matrix composite reinforced with NextelTM 440 Plain weave fabric. Variations in cure pressure from 30 to 80 psi had no discernible effect on the chemistry of the pryrolyzate. However, the higher cure pressure resulted in top and bottom ply damage. Pyrolysis in an Ar environment resulted in incorporationj of up to 12 wt % C of which 8 wt % as graphitic in nature in the ceramic matrix. Pyrolysis in NH3 resulted in 3.9 wt % nitrogen and 1.5 wt % carbon in the matrix, with all the nitrogen and carbon bonded to Si. The cured panels have to be pyrolyzed/densified between 6–7 times to achieve required density and porosity content. Oxidation behavior of the composites at 1000°C indicate that the argon pyrolyzed CMC's lose more weight due to decomposition of the pyrolytic carbon, whereas, NH3 pyrolyzed CMC's are stable as both the N and C are bonded to Si in the matrix. Dielectric constants K′ and K′′ measured at 1 GHz in the as-processed condition are high in the argon pyrolyzed CMC, (K′ = 11−28) due to the presence of pyrolytic carbon. On the other hand NH3 pyrolyzed CMC exhibit low dielectric constant (K′ = 4). On oxidation, the dielectric constant in both the Ar and NH3 pyrolyzed panels is approximately 4.0.

Nondestructive Evaluation of Interlaminar Bonding for in Situ Consolidation of Polymer Composites

A sensor for detecting poor interlaminar bonding between a topmost ply and composite substrate was developed and validated. The sensor was designed for the specific application of real time process control for in situ consolidation processes, such as thermoplastic tow placement. The sensor design consists of two piezoelectric transducers oriented in a pitch catch arrangement. The transmitting transducer is angled so as to produce surface waves in the composite panel. These waves interact with defects at the top ply/substrate interface. The received signal was analyzed for wave speed, attenuation and energy dissipation (power spectral density). Experimental validation of the sensor is presented. Several composite panels were made under various manufacturing conditions so as to create poor interlaminar bonding at the topmost ply. Interlaminar bonding was then evaluated by destructive and nondestructive measures. There was good agreement between the destructive and nondestructive measures of top ply bond strength.

Modeling and Control of the In-Situ Thermoplastic Composite Tape-Laying Process

In thermoplastic tape-laying with in-situ consolidation, a laminated composite is constructed by the local application of heat and pressure. A moving head, applying heat and pressure, lays down and bonds a new layer to the previously bonded layers (substrate). The temperature at the interface between the top ply and the substrate is critical to achieving interlaminar bonding. Recent research on the in-situ thermoplastic composite tape-laying process has focused on modeling, numerical analysis and experimental analysis, but little research has considered the control of this process. In this work, a method is proposed for modeling and control of in-situ thermoplastic composite tape-laying. The key to the control algorithm is predicting the temperature at the interface between the top ply and the substrate. Based on a process model, a state feedback controller and a state estimator for temperature are designed for closed-loop control using the linear quadratic method. Two different approaches are used to develop the process model for real-time closed-loop control through temperature feedback. In the first approach, a low-order lumped parameter model is constructed from a finite difference scheme. The second approach constructs an empirical model through system identification. The structures of the two models are identical, but the parameters differ. The experimental results have shown that the developed estimator and controller can accurately estimate and control the bonding temperature using temperature feedback indicating that the proposed modeling and control methodology can produce a high quality thermoplastic composite laminate.

Coal type and rank variation in Tatu Mine, New Zealand

Tatu State Mine in Taranaki, North Island, New Zealand, worked a Miocene subbituminous coal seam about 2 m thick over an area of nearly 3 km 2. Detailed face sampling of the seam from 1940 to 1961 provided 46 proximate and 15 proximate and ultimate analyses. They show great variation, particularly in moisture, volatile matter, calorific value and sulphur content. The relations between the various analytical parameters exemplify and amplify those found generally within coals from New Zealand and many other countries, providing basic elements for geological study of coal properties. The detailed inferences are: 1. (1) The relation between bed moisture and moisture in coal air dried under standard conditions of 20°C and 70% relative humidity (R.H.) is M B = ∼ 1.1 × M ADS(af). 2. (2) Sulphur content decreases from roof to floor of the seam, with a minor increase close to the floor. Although the sulphur contents of the top ply samples range from >6% to <2% (daf), the decrease from top to bottom plies is in all cases 1.5–2.0%. 3. (3) On the basis of the full seam thicknesses, sulphur content shows a clear areal pattern of variation, ranging from >6% to <1.5% (daf). 4. (4) At one sampling site, sampled in 9 plies, the following relations show the effects of coal type variations: Volatile matter and calorific value (dmmsf): +1% VM = +0.2 MJ/kg Volatile matter (dmmsf) and bed moisture (af): + 1% VM =c.−0.4% M 5. (5) Almost all coals lie within the New Zealand Coal Band. A few are lower in volatile content; rather more are higher. 6. (6) On the basis of the full seam thickness, volatile matter, ranging from >51% to <45%, shows a clear areal pattern of variation. 7. (7) The patterns of variation of volatile matter and sulphur are similar, the relation between them being: + 1% S (daf) = +1.5% VM (dmmsf). Although sulphur, introduced from sea water when overlying marine beds were deposited, appears to have affected coal type, as judged by volatile matter, petrographic data are needed to study this further. 8. (8) Rank of dry coal, in terms of Rank (S) (Suggate, 1959), increases westwards from rank ∼7.5 to >8.5. 9. (9) Moisture content shows no significant rank-related variation. 10. (10) Taken individually, almost all samples would be ASTM rank subbituminous A, but particularly high-volatile samples would be High-volatile C and B bituminous. Production from the mine has always been subbituminous coal.

Repair of a Side Chair with Perforated Plywood Seat

The repair of a mahogany side chair with a perforated, bent plywood seat is detailed.Broken fragments of the seat were rejoined by pushing the parts up into a tentlike formation and pressing them down so that the fractures would mesh. Based on six specific requirements of the adhesive needed for this repair, a survey of over 300 different glues was conducted, and a list of some 40 possibilities was established. After tests were made to determine the rate of shrinkage, an aliphatic liquid glue was injected into the fractures flexed into place. The voids in the seat were filled with thin pieces of plywood of which the top ply was replaced with mahogany veneer, which was fitted and glued in. The replacements were stained, finished with shellac and rubbed down with paraffin oil. Many small lacunae were filled with a colored synthetic wax. A perforated plywood support, a former repair, was removed from beneath the seat, but the underside of the chair was left as found.