Hand-considered hypotheses, 1201–1300
Extrusion, moulding, fibre spinning, curing, lamination, composite layup, and the welding of thermoplastics.
Written one at a time, not composed. Each entry was drafted on its own terms and then labelled by the form of its argument, not by its subject: an attribution that may be wrong, a term nobody measured, a bound, a threshold, a reversal of the standard practice, a count of independent variables, an artefact that imitates a real effect. The labels repeat; the sentence structures were not allowed to. None has been tested. Where a figure is an order-of-magnitude estimate rather than a conversion or a definition, it is marked as such.
Extrusion
Misattribution
H1201. Swell measured on a filled extrudate is read as the matrix's elastic recovery, yet part of the growth with loading is the filler network failing to follow the radial contraction, which opens voids at the surface instead of expanding the bulk. The two mechanisms predict different densities at equal diameter. Extruding one compound through a long-land die at matched wall stress, then measuring extrudate density and diameter together, separates them.
Hidden term
H1202. A flush-mounted melt-pressure transducer reports polymer pressure plus a term from the diaphragm's thermal gradient, and that term grows with melt temperature, so a pressure-temperature curve taken at a single port carries the gauge's sensitivity inside it. Running two transducers of different diaphragm thickness in the same port, and cycling temperature with the port plugged, measures the term directly. Until it is removed, viscosity fitted from such data is partly a calibration curve.
Threshold
H1203. Sharkskin does not begin at a fixed wall shear stress; it begins when the die's residence time outlasts the surface layer's relaxation time, so a short capillary can run smooth where a long one is rough. The surface layer needs time at the wall to accumulate the stretch that later relaxes as a ripple. One diameter with lengths from 5 to 40 L/D, at matched apparent stress, puts the threshold on the right axis.
Count
H1204. Along a twin-screw extruder there are at most as many independent mixing events as there are kneading blocks, and the rest of the screw only convects, so a model crediting the whole barrel with distributed mixing has one parameter too many. A tracer response deconvoluted against block count tests the claim. A striation count on a frozen screw pull-out tests it again from the other side.
Scale argument
H1205. Residence-time width scales with the square root of the number of flights traversed, not with L/D, so geometric scale-up at constant L/D narrows the distribution while every drawing stays identical. Axial dispersion along a longer helical path is the mechanism. Two machines of 27 and 52 mm at one L/D and one specific output, with a single tracer injection each, should show the narrower curve on the larger machine.
Reversal
H1206. Raising screw speed normally raises melt temperature, but in a starve-fed machine past the point where the channel stops being full it can lower it, because wetted area falls faster than dissipation per unit mass rises. The turnover should sit at the maximum of specific mechanical energy. A speed ladder at two feed rates, with melt temperature and motor power logged together, finds it without a model.
Artefact mimics effect
H1207. Gels counted in extruded film are assumed to be crosslinked polymer, though a common class are unmelted resin skins that entered the feed throat late and never reached the melting zone. On that account their count should track feed-throat temperature and pellet size rather than the melt's history. Dropping cold slugs into a running machine and sectioning the resulting gels tests the attribution.
Conservation argument
H1208. Throughput equals drag flow minus pressure flow minus leakage, and leakage is the term nobody measures: it crosses the flight lands and grows with screw wear. A gravimetric feeder and a weighed die output disagree by exactly that term, which also appears as a back-pressure dependence of output. Two screws of different ages, swept over back pressure, yield the leak coefficient without opening the barrel.
Inversion of standard practice
H1209. Devolatilisation ports sit downstream of melting by convention, but a hygroscopic polymer may do better with the vacuum before the granules have melted, because water leaves a solid particle faster than it diffuses out of a melt. A first port in the feed-compression zone should then remove more water than one after melting. Karl Fischer water content at two port positions and one vacuum level decides it.
Unit trap
H1210. Specific mechanical energy is quoted both in kWh per tonne and in J per gram, which differ by 3.6; a scale-up that mixes them is wrong by that factor and the error usually gets absorbed into a scale-up constant. Recomputing one published dataset in consistent units should make the constant vanish. The check costs a spreadsheet and catches an error class that survives review.
Latent variable
H1211. Die pressure drifts over a long run while the set temperature is unchanged, and the drift is read as viscosity change, though some of it is polymer building up at the exit lip and lengthening the land. The two are separable because cleaning the lip mid-run produces a step and a viscosity change produces a slope. Continuous lip inspection with pressure logging over eight hours distinguishes them.
Crossover
H1212. Melt temperature against screw speed passes through a maximum: below it residence time dominates and heating rises, above it the shorter residence and lower fill fraction dominate and heating falls. The maximum should coincide with the peak in specific energy, which makes each measurement a check on the other. One speed ladder with both instruments recorded shows whether the peaks coincide.
Symmetry argument
H1213. A sheet die with a symmetric manifold delivers a symmetric thickness profile only when both halves sit at the same temperature, so a persistent skew indicts a heater or a thermocouple rather than the lip bolts. Swapping the two half-heaters should flip the skew if the thermal account is right. If the skew stays, the manifold itself is asymmetric and lip adjustment is the wrong remedy.
Irreversibility
H1214. Breaker-plate pressure drop is not a function of flow rate alone, since debris is forced into the screen on the way up and stays there, so ascending and descending sweeps trace different curves at the same rate. The gap is the screen's own history. A triangular ramp, a backflush, and a second ramp separate a clean screen's curve from a loaded one.
Memory
H1215. Melt elasticity carries the memory of the whole machine rather than of the die, so a die of L/D = 2 on one extruder can give the same swell as a die of L/D = 20 on another. The stress at the die entry was set upstream. One instrumented die run on two extruders with different screw geometries, at matched output and melt temperature, shows whether the die alone is being characterised.
Aliasing
H1216. In-line pressure sampled at one hertz and plotted against time folds the screw's pumping frequency into a slow beat that reads as surging, and the apparent period belongs to the sampling rate rather than the process. Sampling at a hundred hertz, or triggering once per revolution, should collapse the beat into the real waveform. A surge diagnosis built on a one-hertz logger is describing its own clock.
Moulding, packing and ejection
Misattribution
H1217. Sink marks are charged to volumetric shrinkage, but on a thick rib most of the visible depression is the rib's own bending after ejection, driven by differential shrinkage across the wall. Measuring the surface before ejection, after ejection, and after annealing separates the three contributions. A rib that sinks further after ejection is reporting its stiffness, not its shrinkage.
Threshold
H1218. A weld line is weak only when the interface temperature at meeting falls below the equivalent of the polymer's reptation time, so the controlling variable is a time and faster injection can heal a line that slower injection leaves weak. The interface must stay mobile long enough for chains to cross. Tensile bars gated at both ends, filled at four speeds, put the threshold on a time axis.
Count
H1219. A cavity-pressure trace has at most four independent landmarks: fill, gate freeze, packing end, and ejection. Controllers tuned on seven features are fitting the noise between them. Principal components of a large trace library should show four significant modes, and a fifth only when a sensor has drifted.
Identity claim
H1220. Jetting and the surface flow mark it leaves are one phenomenon seen from inside and outside: the jet folds on itself and fountain flow later covers the fold with a skin. Short shots that stop before coverage should show the jet's footprint exactly where the finished part shows the mark. If the footprint and the mark do not align, two mechanisms are at work.
Scale argument
H1221. Packing pressure decays from the gate exponentially, with a length that scales as the square root of thickness times gate-freeze time, so doubling wall thickness extends the packing distance about fourfold rather than doubling it. Transducers at three distances in two thicknesses test the exponent. A measured exponent near one would mean the decay is set by flow resistance rather than by solidification.
Reversal
H1222. Higher mould temperature normally reduces warpage, but in a part with one thick and one thin section it can increase it, because the thick section's slower cooling changes the differential shrinkage more than the overall relaxation does. A mould-temperature series at fixed packing, with warpage measured on one fixture, shows the sign change. The turnover temperature is where the two sections' cooling times cross.
Bound
H1223. Clamp force is bounded by cavity pressure times projected area only when the parting line is planar; with a stepped parting line the bound is set by the largest projected sub-area, so a small part with a tall step can demand more clamp than its footprint suggests. Pressure sensors in each sub-area would show which one carries the load. A stepped-plate mould run at rising clamp until flash appears locates the real bound.
Hidden term
H1224. Reported cycle time includes the robot's extraction and the mould's thermal recovery, so a cooling-time reduction achieved by shortening hold can simply move the delay to the interval after ejection. A full-cycle timing breakdown, instrumented at the clamp, the ejector, and the robot, separates polymer cooling from machine motion. Without it, cycle-time improvements are bookkeeping.
Artefact mimics effect
H1225. Gloss differences between two cavities are credited to steel polish, but a release agent's transfer film builds faster in the hotter cavity and can produce the same difference. Running the same mould without release, and then swapping the two cavities' heater setpoints, should move the gloss with the film rather than with the steel. Polishing is expensive; the film is free.
Selection effect
H1226. Warpage statistics gathered on parts that came out of the mould easily under-report the distribution, because the parts that stuck are the most warped and are removed with force or scrapped. Logging every stuck part, and measuring it after the clamps are relaxed, recovers the parts the statistic normally omits. A shop reporting warpage only from free parts is reporting its ejection success.
Unit trap
H1227. Shrinkage is written as a percentage and as mm/mm, and the two differ by a hundred; a mould cut to 0.6 in one convention and checked in the other is off by two orders of magnitude. One dimensional audit of a drawing against a first-article report catches it. The error is rare, and when it happens it is neither subtle nor believed.
Latent variable
H1228. Cavity-to-cavity differences in a multi-cavity mould often follow the manifold's fill sequence rather than the cavities' dimensions, and the sequence is set by the runner's thermal history. Rotating the heater zones should carry the pattern with them. If the pattern follows the heaters, the cavities are innocent and the manifold's balance is the variable.
Crossover
H1229. The holding-pressure optimum moves with melt temperature faster than with hold pressure, so a pressure window quoted at one temperature is misleading at another. Lower melt temperature stiffens the gate earlier, shortening the effective packing. A three-by-three grid of melt temperature and hold pressure, with sink and residual stress measured, maps the window's migration.
Conservation argument
H1230. Shot mass equals part plus runner plus the change in cushion, and when the cushion is not metered, short shots and flash can both come from one feed inconsistency. Weighing the cushion every cycle closes the balance. Two machines with the same nominal shot but different check-ring wear should show different cushion scatter for the same part.
Hysteresis
H1231. The mould's thermal state depends on the previous cycle's heat input, so the first parts after a stoppage differ from later ones even at the indicated mould temperature. The recovery is a curve, not a step. Controlled stoppages of one, five, and twenty minutes, with the first ten parts measured after each, give the curve and its time constant.
Derived quantity
H1232. Cooling time from the classic plate formula is a derived number: it assumes a fixed ejection temperature and a constant diffusivity, while the real constraint is the part's stiffness at ejection. The formula therefore gives a lower bound. Ejecting at increasing times and measuring deflection, rather than temperature, shows where the bound actually sits.
Masking
H1233. High packing pressure masks the effect of gate-freeze time, so a design of experiments that varies both reports gate freeze as unimportant. Holding packing at a low level should expose it. A two-level design run at two packing levels, with the same gate inserts, shows whether the factor was masked or genuinely absent.
Threshold
H1234. Below a minimum injection speed the fountain flow does not develop and the surface stays dull whatever the melt temperature, and the threshold scales with the gate's hydraulic diameter. Gloss then measures a flow regime rather than a thermal one. Gates of three diameters, each run over a speed ladder, place the threshold on a capillary number.
Fibre spinning and drawing
Misattribution
H1235. Fibre strength is credited to draw ratio, yet at fixed draw ratio the quench rate sets the skin-core split and with it the strength. Two fibres drawn identically but quenched in air at different temperatures should differ. A quench-rate series at one draw ratio, with skin thickness measured by microscopy, separates the two causes.
Hidden term
H1236. Tension measured at the godet includes air drag over the whole path and the finish applicator's drag, both rising with speed and with finish viscosity, so spinning stress is not the fibre's stress. Measuring tension with the applicator disengaged, and again in a partial vacuum, gives the two terms. Without that subtraction, high-speed data contain the wind, not the polymer.
Threshold
H1237. Fibrillation begins above a critical draw ratio set by the ratio of amorphous orientation to crystalline bridging, and the threshold moves with quench air. A colder quench should raise it by making the skin more oriented before drawing. A draw series at two quench rates, with fibrillation counted on abraded filaments, tests the shift.
Identity claim
H1238. Swell in the spinline and the onset of spinning instability may be one capillary instability observed at two amplitudes, in which case the instability speed should coincide with the maximum in swell ratio. Measuring both on one spinline over the same speed range is enough to see whether the two events are one. A gap between them would mean surface tension is not the controller.
Scale argument
H1239. The quench boundary layer grows as the square root of distance over speed, so cooling rate scales with the square root of speed and inversely with diameter; doubling speed raises cooling by only 1.41, not 2. A diameter series at two speeds, with an inline infrared temperature, tests both exponents at once.
Reversal
H1240. Higher take-up speed usually raises orientation and modulus, but past a point the surface cools so fast that a brittle skin forms and the effective draw falls, so modulus should plateau and then decline. The turnover should scale with the polymer's glass transition and the quench rate. A speed ladder with modulus and skin thickness measured together locates it.
Artefact mimics effect
H1241. The apparent skin-core difference in fibre birefringence can be an artefact of radial averaging through a cylindrical lens, which weights the centre more than the edge. Confocal measurement or a microtomed section should reduce it. One fibre measured both ways, at the same draw ratio, shows how much of the profile belongs to the optics.
Conservation argument
H1242. Fibre mass balance sets extruded volumetric rate equal to take-up speed times linear density over density, so any mismatch at high speed is either die swell changing the effective diameter or linear density measured at the wrong tension. Weighing a known length at two tensions separates the two. A discrepancy that grows with speed is the balance reporting a real change in diameter.
Inversion of standard practice
H1243. Drawing warm is the standard route to drawability, but a fibre quenched into a skin-core structure may gain more from a cold first stage and a warm second, because the skin is oriented before the core is mobilised. The order should matter at the same total draw. Two-stage draws at reversed temperatures, with strength and skin orientation measured, test the inversion.
Latent variable
H1244. The godet's surface temperature, not the bath's, sets the effective draw temperature at high speed, because contact time is short and the film of finish mediates the transfer. A bath-temperature series at fixed godet temperature should therefore show little effect. Thermocouples on the godet shell and in the bath, run together, reveal which one the fibre follows.
Unit trap
H1245. Denier and decitex differ by about eleven percent, while tenacity in cN/tex against g/den differs by nearly nine, so a specification written in one system and tested in the other can pass a fibre that is far out of tolerance. One conversion audit of a supplier's certificate, checked against a measured linear density, catches it.
Crossover
H1246. Orientation rises with draw ratio and then saturates when the amorphous phase is fully extended, and the saturation should coincide with the point where the amorphous halo in wide-angle scattering stops narrowing. A draw series measured by both modulus and halo width places the crossover. A crossover in modulus without one in the halo would mean the scattering is not seeing the load-bearing phase.
Hysteresis
H1247. Fibre shrinkage on heating depends on the prior cooling rate, so two fibres with the same orientation but different quench shrink differently, and a shrinkage test is measuring thermal history as much as structure. A matched-orientation pair, quenched hot and cold, with free shrinkage measured in one bath, shows the size of the history term.
Path dependence
H1248. The spinline remembers the die's capillary length for hundreds of diameters downstream, so two dies of different L/D give different orientation at the same draw ratio and throughput. The memory is in the melt's extensional stress at exit. One polymer through two dies, with orientation measured at three take-up speeds, shows how far the memory reaches.
Saturation
H1249. Take-up tension saturates once once the extensional viscosity reaches its strain-hardening plateau, and the saturation speed is a material property rather than a machine limit. Beyond it, more speed adds orientation without adding stress. A speed ladder on two polymers of different hardening index should saturate at different speeds if the mechanism is right.
Null result
H1250. Were the spinline's stress purely viscous, changing the ambient humidity would not alter tension for a non-hygroscopic polymer, and a null result across a humidity series would rule out a surface-energy contribution. Running one polymer at twenty and eighty percent relative humidity, with tension and diameter logged, is a cheap way to find nothing or something.
Curing and thermosets
Misattribution
H1251. The exotherm peak in a thick thermoset block is read as kinetics, yet much of its height comes from the mould's insulating boundary slowing heat loss, so thin and thick samples of one formulation show different peak shapes at the same conversion. A thickness series at one formulation, with peak area normalised by sample mass, separates kinetic heat from the boundary's. A peak area that grows with thickness is describing the tooling.
Hidden term
H1252. Dielectric cure monitoring's signal contains the sensor's own electrode polarisation, which grows as the resin vitrifies, so the ion viscosity reported late in cure is partly an electrode property. Two sensors of different electrode area in one resin should diverge at the same conversion. Until that divergence is measured, dielectric cure indices near vitrification are instrument readings.
Order dependence
H1253. Gelation and vitrification are different events, and a schedule that passes through vitrification before gelation leaves a different network from one that gels first, even at the same final conversion, because diffusion limitation arrives earlier in the first case. Two schedules run to identical final conversion, compared by swelling and modulus, show whether order or extent controls the network.
Identity claim
H1254. Cure shrinkage from dilatometry and residual stress from curvature are one quantity seen at two constraints: a low-shrinkage resin with high modulus can generate more stress than a high-shrinkage resin with low modulus, so the two rankings need not agree. Measuring both on the same four resins should show whether the rankings cross.
Bound
H1255. Post-cure cannot raise Tg beyond the value set by the network's crosslink density, so a reported Tg above that bound is measuring the sample's thermal lag or the pan's. The same crosslink density is what the rubbery plateau modulus measures, so the two can be checked against each other. A series of post-cure times on one resin should flatten at the Tg that the modulus predicts.
Reversal
H1256. A reactive diluent lowers viscosity and improves impregnation, but past a point it lowers the final Tg enough that dimensional stability at service temperature worsens while the processing looks easier. The two effects have different optima. A diluent ladder with viscosity, Tg, and a dimensional-stability test at temperature shows the crossing and where it sits.
Count
H1257. A single-heating-rate DSC cure curve supports at most three independent kinetic parameters before the baseline choice absorbs the rest, so a model with five fitted constants is trading physics for baseline freedom. Fitting the same data at three heating rates should leave the parameters unchanged if they are real. Parameters that move with heating rate are describing the baseline.
Scale argument
H1258. The thermal-runaway threshold for a curing part scales with thickness squared over diffusivity times reaction rate, so a 10 mm section that cures safely says nothing simple about 20 mm: the margin falls roughly fourfold. A thickness series in an instrumented mould, with the exotherm's peak recorded, tests the exponent. If the peak rises linearly with thickness, the mechanism is adiabatic and the squared scaling does not apply.
Artefact mimics effect
H1259. A rise in Tg after storage at room temperature is read as continued cure, yet physical ageing produces the same DSC signature in a fully cured glass. Reheating the sample and comparing the enthalpy overshoot with a spectroscopic conversion measurement separates them. A resin whose conversion is unchanged while Tg rises is ageing, not curing.
Inversion of standard practice
H1260. Vacuum degassing before cure is standard, but in a filled system the vacuum can strip the sizing from the filler and the voids may reappear on re-pressurisation, so a short vacuum at low pressure can leave more voids than a long one at moderate pressure. Void content against vacuum level and hold time, in one filled resin, maps the reversal.
Latent variable
H1261. The autoclave's indicated temperature is the air's, not the part's, and the part's lag depends on the tooling's thermal mass, so two parts on one cycle can receive different cure integrals. Thermocouples in the tool and on the part, run through one cycle, give the lag. Cure schedules written against air temperature are schedules for the autoclave.
Conservation argument
H1262. Heat released by cure equals resin mass times enthalpy, so a measured exotherm smaller than the DSC enthalpy means either unreacted resin or heat lost to the tooling, and the sign of the difference tells which. Running the same part in an instrumented mould with a heat-flow sensor closes the balance. A deficit that scales with tooling mass is loss, not conversion.
Hysteresis
H1263. Viscosity at a given temperature on the way up differs from viscosity at the same temperature on the way down, because conversion has advanced, so a viscosity-temperature map is a path and not a surface. A programmed ramp up and down on one sample, with conversion measured at three points, shows the loop's width. An impregnation window drawn from the ascending branch alone is optimistic on the descent.
Derived quantity
H1264. Degree of cure from residual enthalpy assumes the unreacted resin has the same enthalpy as the reacted resin, and for a diffusion-limited cure that assumption fails, so the number saturates below unity while the reaction continues slowly. Comparing residual-enthalpy conversion with a spectroscopic one on the same samples shows the divergence. Where they part, the thermal method has stopped seeing the reaction.
Lamination and coating
Misattribution
H1265. Adhesion in a laminated film is credited to adhesive chemistry, but at nip pressures below a threshold much of the variation is the thickness of entrapped air, which is a machine property. Laminating in vacuum and at atmosphere with the same adhesive separates them. A bond that improves in vacuum was never about the adhesive.
Hidden term
H1266. Peel strength includes the substrate's plastic bending work, which scales with thickness cubed, so a stronger bond on a thicker film can be the same interface with more bending. Peeling one laminate at two substrate thicknesses, and correcting for the measured bending work, tests it. Without the correction, adhesion specifications compare thicknesses.
Threshold
H1267. There is a minimum nip residence time for wetting, set by the adhesive's viscosity and the substrate's roughness, below which the bond is a contact-area bond rather than an adhesion bond. The transition should appear as a change in the failure locus, not only in strength. A nip-speed series with the failure surface examined separates the regimes.
Reversal
H1268. Raising lamination temperature usually improves bond strength, but with a biaxially oriented substrate it can shrink the film and pull the interface apart during cooling, so strength falls while the process looks hotter and better. A temperature series on two substrates, one oriented and one not, shows the divergence. The oriented film's optimum should sit below its shrinkage onset.
Count
H1269. A peel curve yields at most two independent fracture parameters, a work of fracture and a characteristic length, so a model with three fitted constants is absorbing the test's compliance. Fitting one laminate at two peel angles should leave two parameters constant and move the third if it is an artefact. Two constants that hold across angles are the material's.
Artefact mimics effect
H1270. Corona treatment's apparent adhesion promotion can be surface roughening that increases mechanical interlock rather than a chemical change, and a smooth surface of the same surface energy would separate the two. Treating a smooth and a rough version of one polymer, with surface energy matched by titration, tests it. If the rough one bonds better at equal energy, the treatment is a texturing step.
Scale argument
H1271. Air entrapped at a nip scales with the nip's radius times the speed ratio, so doubling line speed doubles the entrained layer's thickness and roughly halves apparent bond strength. A speed series at fixed nip pressure, with bond strength and void area measured, tests the scaling. A strength that falls faster than the layer grows means the air is also cooling the interface.
Inversion of standard practice
H1272. Corona treatment is applied to the difficult side by convention, but treating the easy side can give the stronger laminate, because failure then runs in the adhesive rather than along the weak interface, and the total energy to failure can rise even when the treated interface is weaker. Laminates treated on one side or the other, peeled at one angle, decide the direction.
Selection effect
H1273. Laminates peeled from the edge under-report bond quality in the middle, because edge-initiated failure selects the weakest path available at the boundary. A narrow strip cut from the centre and peeled should give a different, usually higher, value. The difference measures how much of the specification is edge preparation.
Unit trap
H1274. A bond strength quoted in N per 15 mm and in N per 25 mm differs by 1.67, so a specification written in one width and tested in the other can pass a failing laminate or reject a good one. Recomputing a certificate at the correct width is a one-line check. Mixed widths survive because both numbers look plausible.
Composite layup and preforming
Misattribution
H1275. Voids in a vacuum-bagged laminate are attributed to volatiles, yet at moderate vacuum the larger source is air left in the inter-ply gaps, which is a layup property rather than a resin one. A debulk series at fixed resin and fixed vacuum separates the two, because debulking removes inter-ply air and leaves volatiles. Void content that falls with debulk time was never volatile-driven.
Hidden term
H1276. Fibre volume fraction by burn-off includes the sizing's mass, typically half a percent to one percent (estimate), so a nominal 55 percent may be 54.5 percent and the bias is one-directional. Thermogravimetry on sized and desized fibre gives the sizing fraction directly. Reported fibre fractions that never subtract it are systematically high.
Threshold
H1277. Wrinkles form only above a critical tow compressive strain set by the tool's corner radius and the ply's friction, and the threshold can be raised by interleaving rather than by laying more slowly. The tow must slide or buckle. A corner-radius series with and without interleaves, wrinkle amplitude measured by shadow moire, locates both the threshold and its shift.
Identity claim
H1278. Bridging and wrinkling are one geometric event seen before and after compaction: a ply that bridges a corner becomes a wrinkle when the bag presses it down. Stopping the cure after bagging, and sectioning the corner, should show the bridge that later becomes the wrinkle. If the bridge and the wrinkle sit in different places, the identity fails.
Bound
H1279. How much compaction pressure a prepreg stack can transmit is bounded by the fibre bed's permeability to resin flow, so raising autoclave pressure past a point adds stress to the tooling without removing voids. The bound moves with bleed rate. A pressure series with void content and resin content measured together shows where extra pressure stops buying anything.
Scale argument
H1280. Resin flow distance during cure scales with the square root of time times permeability over viscosity, so doubling part thickness quadruples the bleed time needed to reach the same resin content. A thickness series at one bleed schedule, with resin content measured at the centre and the surface, tests the exponent. A centre that stays rich at twice the thickness is the square-root law reporting itself.
Reversal
H1281. Adding plies usually adds strength, but at fixed thickness substituting a 90-degree ply for a zero-degree one can cut tensile strength by more than the ply's load share, because the transverse ply cracks first and seeds delamination. A laminate series with one ply rotated, tested in tension with acoustic emission, shows the loss and its onset strain.
Count
H1282. A symmetric balanced laminate's ABD matrix has at most the independent constants its distinct ply angles allow, so a characterisation reporting more elastic constants than angle groups is measuring the test fixture. Imposing the angle-group count on the same coupon data should not worsen the fit. If it does, the extra constants are real and the count is wrong.
Artefact mimics effect
H1283. Apparent fibre waviness on a polished section can be the section plane's angle to the tow rather than a real undulation, since a straight tow cut obliquely appears wavy with a spacing set by the tow width and the angle. Sectioning the same region at two angles should change the apparent wavelength, not the fibre's path. Waviness that moves with the cut is a saw mark.
Inversion of standard practice
H1284. Bleeder cloth removes excess resin by design, but on a thin laminate it can wick resin away from the surface and leave a resin-starved skin that is weaker than a slightly rich one, so the cleaner process gives the lower strength. Surface resin content and flexural strength on bleeder and no-bleeder panels, at matched total resin, test the inversion.
Latent variable
H1285. Bag leakage rate is the hidden variable behind void-content scatter between ostensibly identical panels, because a slow leak admits air throughout the cure while a fast one is caught by the vacuum gauge. Helium leak testing of bags before cure, with void content measured afterwards, should rank panels better than any process parameter does. Scatter that tracks leak rate is not material variability.
Conservation argument
H1286. Resin mass in equals resin in the part plus bleed plus flash, so when the balance does not close, a void content from acid digestion is measuring the wrong denominator. Weighing all three streams on one panel run closes it. A shortfall that matches the bleeder's gain is bookkeeping, not porosity.
Hysteresis
H1287. Loading a fibre bed and unloading it to the same pressure give different thicknesses, because tows rearrange irreversibly, so one compaction curve is a path and the pressure depends on how it was reached. Loading and unloading in steps, with thickness measured at each, shows the loop. Voids predicted from the loading branch alone will be underestimated.
Crossover
H1288. Void content falls with compaction pressure and then rises at very high pressure, because the fibre bed collapses and permeability drops faster than voids can escape. The minimum should move with the resin's viscosity. A pressure series at two viscosities, with void content by microscopy, locates the minimum and its migration.
Aliasing
H1289. Periodic wrinkles on a tape-laid surface can be an aliasing of the tow feed-rate oscillation against the layup speed, so the apparent wavelength belongs to the machine's control loop rather than to the placement path. Changing layup speed should move the period if aliasing is the cause. A period fixed in space is a real placement defect.
Null result
H1290. If the ply interface is well bonded, transverse strength should not depend on stacking sequence at fixed ply angles, and a null result across sequences would rule out a constraint mechanism. Testing five sequences at one angle set, with the same fibre and resin, is a cheap way to find nothing. A difference appearing only where 90-degree plies are adjacent is the mechanism showing itself.
Welding and joining of thermoplastics
Misattribution
H1291. Ultrasonic weld strength is credited to interface melting at the energy director, but at low amplitude a measurable part of the bond forms by solid-state chain diffusion below the melting point, which is why welds survive when the director is machined away. Strength against amplitude should therefore have two regimes. Welds made with and without a director, at matched amplitude and hold, show whether a diffusion regime exists.
Threshold
H1292. Healing at a thermoplastic weld follows the reptation time, so strength grows as the quarter power of time at temperature until full strength, and the time to full strength is a fixed multiple of the reptation time once time-temperature superposition is applied. Hot-plate welds at three temperatures, strength against hold time, should collapse onto one master curve. A collapse that fails at short times means the interface never reached the set temperature.
Identity claim
H1293. The weld line in injection moulding and the weld interface in hot-plate welding are the same diffusive healing problem with different thermal histories, so parameters fitted to one should predict the other. Predicting hot-plate strength from moulding weld-line data, with no new fitting, is the test. A prediction that misses by a constant factor means the thermal histories differ in a way the model ignores.
Hidden term
H1294. Measured weld strength contains a term from squeeze flow, which orients chains and fibres at the interface in a direction set by the tooling rather than by diffusion. Welds made with a mechanical stop that prevents squeeze flow should differ from free-flowing welds at the same temperature and time. The difference is the orientation term, and it can be measured by sectioning.
Inversion of standard practice
H1295. Higher weld pressure is standard for thermoplastics, but in a fibre-reinforced thermoplastic it can align fibres in the weld plane and thin the interdiffusion zone, lowering strength, so a pressure series should show a maximum rather than a plateau. Weld pressure against strength, with fibre orientation at the interface measured, tests it. The optimum for a filled polymer need not be the optimum for the unfilled one.
Scale argument
H1296. Weld strength scales with the square root of interpenetration depth, and depth scales with the square root of time, so strength follows a quarter-power law in hold time; a process window quoted in seconds without that exponent looks like scatter when hold times are short. Replotting one dataset against the quarter power of time should straighten it. A straight line on a linear time axis means the mechanism is not reptation.
Artefact mimics effect
H1297. The strength of a kiss weld measured in lap shear can be the fixture's friction rather than the weld, especially when the weld is thin, because the clamps carry load through the overlap. Replacing the weld with a release film, and repeating the test, gives the fixture's contribution directly. A weld that survives the release film was never carrying load.
Count
H1298. A thermoplastic weld has at most two independent process variables that set strength: interface temperature and time at that temperature. A design of experiments over amplitude, force, and hold time is therefore turning three knobs on two variables. Measuring interface temperature directly, with a thin thermocouple or an infrared pyrometer, should collapse the three-factor response onto two.
Crossover
H1299. In laser transmission welding with an absorbing layer, raising absorber concentration increases interface temperature and strength until the interface chars, after which strength falls, so the optimum loading depends on part thickness through the absorbed energy per unit area. An absorber ladder at two thicknesses, with strength and char measured, maps the optimum and its shift.
Conservation argument
H1300. Energy delivered to an ultrasonic weld equals the energy director's mass times its enthalpy plus losses, so a measured melt volume larger than that implies extra heating from interfacial rubbing, and the weld is partly a friction weld. Weighing the collapsed director and measuring melt volume on a section closes the balance. A melt volume that grows with amplitude while director mass is fixed is friction reporting itself.
Status
One hundred entries, H1201–H1300. The logical forms are printed above each claim so that a reader can check the variety rather than take it on trust; where an argument needed a form this series had not used, the label was invented for it rather than forced into an existing one.
None has been tested. No entry reports a measurement, and no entry asserts that a published result is wrong; each states a mechanism and the comparison that would separate it from the obvious alternative. A hypothesis list is worth what its untested claims are worth, which is the cost of the experiment that would settle them.
Of the hundred, H1218 is the one worth an afternoon: if weld-line strength is governed by time above a mobility threshold rather than by temperature, then a fast fill and a slow fill at the same melt temperature should differ, and a two-speed experiment on one mould settles it without new tooling.
Incoprea Research · hand-considered hypotheses 1201–1300 · polymers and composites · 3 November 2026 · ~/Desktop/Nov3/