Hand-considered hypotheses, 801–900
Mechanics of materials: physical mechanisms only. Every entry was written on its own
and given its own logical form, printed beside it, so the entries can be seen to differ structurally and not only in
subject. The ground is fracture, fatigue, plasticity, composites, tribology and adhesion; a measurement artefact
appears only where it impersonates a mechanism, with a signature that separates the two. Nothing here has
been tested. No entry rests on a statistical estimator, a citation, or a number presented as measured: where
a magnitude appears it is an explicit estimate, and the smallest defensible experiment is named instead.
Fracture: nucleation, path and resistance
Bound
H801. A process zone cannot shield a crack by more than its own stiffness allows: once the zone is soft enough to shed nearly all stress, enlarging it buys nothing. The plateau equals the bridging stress times the zone length at failure, both readable on a polished cross-section, and the value is an order-of-magnitude estimate rather than a constant. Growing the zone by raising temperature at fixed microstructure ought to flatten the toughness curve against a ceiling computable from the modulus ratio.
Misattribution
H802. What looks like a rising R-curve in a finite specimen is partly the back face unloading as the ligament shortens, a geometric term that tracks uncracked ligament rather than crack extension. Because the two co-vary in a standard test, the material's real rise and the geometry's contribution arrive added together. Two specimen widths compared at matched crack extension, not matched ligament, would separate them.
Hidden term
H803.Machining damage leaves a fixed-depth layer of residual tension in every specimen, and its share of measured toughness grows as the ligament shrinks. The predicted shift is layer depth times yield stress — of order ten micrometres times a few hundred megapascals for a polished sample, an estimate rather than a measurement. Electropolishing away successive surface layers at constant in-plane dimensions should then drive apparent toughness toward a width-independent value.
Threshold
H804. Arrest of a running crack needs resistance to rise with length faster than the driving force falls, and kinetic energy lets a fast crack overshoot the crossing point. That yields a maximum arrestable speed, estimated near a fifth of the Rayleigh wave speed for a wedge-loaded strip. Cracks started at several speeds in the same geometry ought to arrest only below it, with arrest lengths collapsing onto a single curve.
Identity
H805. Cleavage and intergranular fracture in a low-alloy steel are catalogued as separate mechanisms with separate transition temperatures, yet both look like the same local normal stress acting on a carbide or a segregated boundary. If that is right, one microstructural lever must move both temperatures together. Changing carbide size at fixed segregation, then segregation at fixed carbide size, tests the claim without melting a new alloy.
Reversal
H806. A channel crack in a thin film on a compliant substrate first toughens with film thickness and then weakens. The two trends have different owners: stored elastic energy in the film drives the first, and substrate bending under the channel pries the crack open for the second. The maximum sits where those trends cross, and that thickness shifts when the substrate modulus changes — visible in a two-substrate thickness series.
Count
H807.Three numbers exhaust the mode I crack-tip field in an isotropic body — intensity, T-stress and one length — so a toughness model carrying a fourth fitting parameter is re-describing one of them. If that is right, the fourth parameter must come out indistinguishable from zero whenever the data are clean, and it should grow only as the fit absorbs scatter. Refitting a published data set with three parameters and with four, then comparing residuals on held-out specimens, settles the matter without new testing.
Scale argument
H808. K-dominance requires the process zone to be small against the region where the singular field holds, and five process-zone diameters is a reasonable estimate of the needed multiple. Below that ratio, measured toughness becomes a weighted average over the field rather than a tip property. Test one grain size across a decade of ligament lengths and the departure appears at a fixed ratio, not at a fixed size.
Artefact mimicking effect
H809. Pop-in on a nanoindentation curve is routinely read as first cracking, yet the same step appears when frame compliance takes up load after a stick period, and it can be produced on a sample with no crack in it. Running an identical load program against a rigid dummy of matched stiffness decides which reading is correct.
Inversion of standard practice
H810. Fatigue precracking is treated as the only honest route to an initiation toughness, but the sharp precrack drags a damage zone whose size depends on the precracking intensity, inflating the very quantity it is meant to measure cleanly. A machined notch of controlled root radius, loaded monotonically, may give the truer initiation number. Pair a precracked and a notched specimen at matched ligament and the artefact declares itself.
Unit trap
H811.Fracture energy and fracture toughness differ by the elastic modulus, so quoting a percentage improvement in one while measuring the other has produced apparent gains of tens of per cent. The conversion is exact and the modulus is rarely stated, which is enough for the error to pass review. Recomputing each quoted improvement from the raw load-displacement record, with the modulus stated, will erase them.
Derived quantity
H812. The fracture strain quoted for a ductile alloy is not independent of toughness, modulus and specimen size: for a given toughness, the elongation at failure follows from the gauge length. An alloy called more ductile may only have been tested over a shorter gauge. Re-testing at two gauge lengths exposes the arithmetic.
Selection effect
H813. Grain-boundary chemistry correlates with toughness largely because the boundaries that cracked are the ones sent for analysis, while the boundaries that resisted are rarely characterized at all. Mapping cracked and intact boundaries within one specimen converts a correlation into a test.
Path dependence
H814. Where a mixed-mode crack goes depends on how the mode mix was reached, not only on its final value, because a non-proportionally loaded zone retains damage that biases the next increment of direction. Two load paths arriving at the same intensity ratio, one rotating and one proportional, should produce measurably different deviation angles.
Conservation argument
H815. The driving force supplies three sinks — new surface, plastic work and elastic waves — while toughness computed from load and displacement counts only the first two. The overstatement should equal the acoustic fraction, a few per cent by estimate, and acoustic emission recorded during a toughness test would close the balance.
Degeneracy
H816. One fracture test cannot separate cohesive strength from toughness: raising one and lowering the other can leave the load-displacement curve almost unchanged. Only a size series breaks the degeneracy, because the two parameters scale differently with dimension. Hence a single-size fit can look excellent and still be non-unique.
Hidden variable
H817.Specimen misalignment puts a bending moment on what is supposed to be a tension test, and the resulting stress gradient raises apparent toughness by an amount that varies between laboratories using the same material. The gradient is largest where the specimen is thinnest, so the inflation should scale with the ratio of bending to axial strain rather than with load. Strain-gauging four sides of the gauge section and shimming until they agree removes a between-lab scatter normally blamed on the alloy.
Inversion
H818. Roughness-induced shielding is assumed to help most at small crack extensions, yet the shield depends on asperity contact across the crack face, which needs a minimum opening. On that argument shielding should peak at intermediate extension and vanish both near the tip and far behind it. A compliance-based measurement of shielding against extension would look for the hump.
Misattribution
H819.The plane-strain thickness criterion is enforced as though it guaranteed a stress state, but what it actually controls is the decay length of triaxiality behind the tip, which depends on yield stress and on the specimen's own bending. A thin specimen of a high-yield alloy can therefore be less constrained than a thick specimen of a low-yield one. Two alloys at the same absolute thickness are not equally plane-strain, and comparing them confounds material with constraint.
Ceiling
H820. Crack growth resistance cannot exceed the value at which the remaining ligament collapses plastically, so a reported toughness above roughly the ligament's yield load times half its length, per unit thickness, is suspect by construction. Checking a high-toughness claim against the ligament's plastic limit, rather than against a reference material, needs no new specimen.
Fatigue: initiation, growth and life
Threshold
H821. The fatigue crack growth threshold is reported as a material constant, yet the measured value depends on the stiffness of the testing machine, because a compliant frame lets the crack close earlier and shields it sooner. Two frames of different stiffness, same specimen and same load ratio, give thresholds that differ by an amount computable from their compliances.
Misattribution
H822. Step-loading fatigue produces lives far longer than constant-amplitude testing at the final stress, and the gain is credited to coaxing, a supposed strengthening. A simpler account: most damage accumulated at the lower stresses, which the final stress then inherited. Repeating the staircase with the count of low-stress cycles fixed, varying only their amplitude, separates history from strengthening.
Identity
H823.The fatigue limit at fully reversed loading and the crack-growth threshold are treated as separate quantities measured by separate standards, but for a specimen whose initiating defect is longer than the closure zone they are one number seen from two sides. The standards differ in specimen geometry and in how closure is defined, which is enough to hide an identity. Polishing the surface to remove initiation sites makes the values converge; leaving the sites intact makes them diverge.
Count
H824. Four independent parameters suffice for a fatigue life model — initiation resistance, growth coefficient, growth exponent and a threshold — and a published model with more is trading parameters for fit. Refitting several data sets with four, and counting how many extra parameters fail a held-out test, states the case numerically.
Reversal
H825. Compressive residual stress is prescribed to improve fatigue life, but beyond a level set by cyclic yield it relaxes within the first few cycles and stops helping, and beyond a further level it can promote initiation on the very surface it was meant to protect. Shot-peened specimens at a series of intensities, with residual stress measured before and after cycling, trace the life curve as it turns over.
Hidden term
H826.Self-heating raises the specimen's temperature during a fatigue test, and at high frequency the rise lowers flow stress enough to alter measured life. Thin specimens that shed heat well do not show the effect, which is a first hint that the cause is thermal rather than mechanical. Repeating one stress at two frequencies, and one frequency in still air and in forced convection, isolates the term.
Scale argument
H827. A crack shorter than a few barrier spacings grows faster than long-crack data predict at the same nominal driving force, and the missing-closure explanation is only one candidate. If such a crack samples fewer barriers, its growth will scale with crack length divided by barrier spacing rather than with absolute length, which changing the spacing at fixed crack length would confirm.
Selection effect
H828. Fatigue curves are fitted to failures while run-outs are dropped or censored, which biases the slope toward steepness because the survivors are precisely the points the curve should pass above. Refitting with run-outs retained as lower bounds, at two stress levels, should change the apparent slope by an amount set by how many there were.
Artefact mimicking effect
H829. Fatigue strength sometimes appears to improve with test frequency, and the improvement is credited to strain-rate sensitivity. Above a few hertz the dominant term is usually specimen heating, which helps or hurts depending on whether the alloy cyclically hardens or softens. Vacuum versus air at one frequency separates the two.
Inversion of standard practice
H830.Proof testing is meant to guarantee a minimum strength by breaking the weak members, but in a high-strength, low-toughness alloy the proof load itself can start the crack that later fails in service. Survivors are then not stronger, only damaged later and at a known load. Comparing service lives of proof-tested and untested batches at the same proof ratio, with initiation followed by replication, decides which reading holds.
Unit trap
H831. Fatigue standards count cycles while fracture mechanics counts reversals, and the factor of two between them has been dropped often enough to shift a life prediction by exactly that factor. Recomputing a published prediction in the other convention, with the convention stated, exposes it.
Derived quantity
H832. The endurance ratio, fatigue limit over tensile strength, is quoted as a material property, roughly one half for steels by rule of thumb, but it follows from inclusion size and from the tensile strength's own dependence on that size. Two heats matched in tensile strength but differing in inclusion population will give different ratios, which a single-heat survey cannot reveal.
Path dependence
H833. An overload retards subsequent fatigue crack growth, and the retardation is usually modelled from the overload ratio alone. If the mechanism is blunting plus residual compression in the plastic zone, the same overload applied on a different baseline load ratio should retard differently — a two-ratio experiment at matched overload would show it.
Bound
H834. A smooth specimen's fatigue strength cannot exceed that of its own surface layer, since nearly all initiation happens there; treatments that harden the bulk while leaving the surface unchanged therefore buy nothing. Removing the surface layer to several depths in a specimen series shows no further gain once the layer's own limit is reached.
Identity
H835. Goodman, Gerber and Soderberg corrections are treated as rival models to be chosen by fit, yet at low mean stress they are the same line within the scatter of any fatigue test. Discrimination appears only as mean stress approaches yield, so the decisive experiment is a series at high mean stress, which the published record seems not to contain.
Artefact mimicking effect
H836.Crack closure inferred from a compliance change depends on where the gauge is mounted: a gauge spanning the notch records the notch's closure rather than the crack's. Both compliances differ most at low load, so the artefact appears as a falsely high closure level at small driving force. Two gauge placements on one specimen, one across the mouth and one straddling the crack, will show whether the effect is real.
Conservation argument
H837. Mechanical energy dissipated per fatigue cycle appears as heat, and whatever does not appear as heat is stored in the defect structure. Measuring hysteresis loop area and temperature rise in the same test, with the rise calibrated against a known heat source, yields the stored fraction without any appeal to dislocation theory.
Degeneracy
H838. Two surface finishes that give different fatigue curves can give identical curves once residual stress and roughness are accounted for, which would mean the finish itself is not the variable. Turn, grind and polish a specimen set, measure both quantities on each, and compare lives at matched values; anything left over is the finish's own effect.
Hidden variable
H839. In creep-fatigue the hold time at peak load is treated as a damage accumulator, but its main effect may be to relax stress from the surface into the interior, moving initiation inward. Interrupted tests with replication at several depths, at fixed hold time, would show where cracks actually begin.
Ceiling
H840. Fatigue crack growth rate cannot exceed a fraction of the shear wave speed, so the final acceleration to fracture is geometric rather than material: it is the last ligament's net-section collapse. Growth data plotted as rate against driving force should depart from any power law at the same fraction of the wave speed across materials — a collapse invisible in a single-material study.
Plasticity: yield, hardening and instability
Bound
H841. Strain hardening cannot proceed at a rate exceeding a fixed fraction of the shear modulus, because the elastic lattice behind the dislocation structure sets the ceiling; the Considère construction is only its most familiar consequence. Normalizing published hardening curves by their shear moduli collapses the high-strain tails onto a single line.
Misattribution
H842. The Bauschinger effect is attributed to back stress from dislocation pile-ups, but part of the reverse-yield offset belongs to the load train, since grips, extensometer and load cell store elastic energy that unloads asymmetrically. Reversing the load cell's position, or moving to a much stiffer frame, should change the measured offset if that share is real.
Identity
H843.Yield-point drop and Lüders band propagation are described as two phenomena, a stress maximum and a travelling front, but they are one instability seen at two resolutions. The drop is band nucleation and the plateau is its passage, so the two must be simultaneous in time rather than sequential. A test with both a global extensometer and local strain mapping can check whether the drop coincides with nucleation or with arrival.
Reversal
H844. Dynamic strain ageing normally raises strength and lowers ductility, yet in some temperature and rate windows it does the reverse, because solute pinning can homogenize slip enough to delay necking. The window is then predictable from the diffusion distance covered during one waiting time at an obstacle, so it must shift with strain rate in a stated direction.
Hidden term
H845.An elastic modulus taken from an unloading branch includes an anelastic component from the machine and from dislocation bowing, so it sits systematically below the resonance value. The gap should widen with unloading rate and with prior plastic strain, both of which increase the anelastic contribution. Comparing the two on one specimen across several rates separates the terms.
Threshold
H846. Below some strain nothing permanent survives unloading, and the proportional limit is the conventional place to put that threshold; if the mechanism is bowing of dislocations between pinning points, the threshold should track pinning spacing rather than yield strength. Cold work to several strain levels and measure both, spacing and threshold, to see which one follows.
Count
H847.Single-crystal plasticity needs five independent slip systems for an arbitrary strain, but a polycrystal constitutive law needs far fewer independent parameters than there are systems, because most systems are constrained by neighbours. What matters is the number that changes when texture changes, not the number of systems in the crystal. Counting how many parameters actually vary across a texture series would show how few are real.
Statistical argument
H848. Micropillar strength rises as the pillar shrinks, which is often read as a fundamental size effect, yet a smaller pillar contains fewer dislocation sources, so the weakest available source is stronger purely by sampling. Pillars of equal volume but different source densities, made by pre-straining some and not others, separate sampling from mechanism.
Artefact mimicking effect
H849. Focused-ion-beam milling leaves tapered sidewalls, and the taper produces apparent hardening as the cross-section shrinks under load. Measure the taper and correct the stress, or make cylindrical pillars lithographically, and the size effect attributed to dislocation starvation shrinks.
Inversion of standard practice
H850.Annealing before mechanical testing is standard practice for removing residual stress, but in a precipitation-hardened alloy the anneal also coarsens or dissolves precipitates. The reference state is then not the as-received material minus stress; it is a different alloy. Test as-received, annealed, and stress-relieved below the solvus, and the two changes separate.
Unit trap
H851. Engineering and true stress diverge by the factor one plus strain, and above roughly ten per cent strain the two conventions differ by more than most reported alloy improvements. Recomputing a comparison table in one convention usually removes the ranking it claims.
Derived quantity
H852. Uniform elongation is derived from the Considère construction on the true stress-strain curve, so it is a consequence of hardening exponent and rate sensitivity rather than an independent measurement. Two alloys quoted with different uniform elongations may differ only in rate sensitivity, which a rate-jump test would reveal.
Selection effect
H853. Crystal plasticity studies of size effects report pillars that yielded; pillars that buckled or slipped at the grips are discarded, and the discarded ones are disproportionately weak or misaligned. Publishing every pillar's yield, anomalous ones included, would show how much of the size effect is a selection effect.
Path dependence
H854. The yield surface after prestraining is not merely translated but distorted, and the distortion depends on the prestrain direction relative to the subsequent probe. A specimen prestrained in tension and probed in shear should show a different surface than one prestrained in torsion and probed in the same shear at equal equivalent prestrain.
Conservation argument
H855.Most of the work of plastic deformation becomes heat and a small fraction is stored in the dislocation structure. That fraction needs no microscopy: heat and work measured in the same test give it directly, and it should fall as strain rises because annihilation overtakes storage. One instrumented specimen taken to several strains would show the decline.
Degeneracy
H856. A uniaxial stress-strain curve cannot determine the shape of the yield surface: isotropic and kinematic hardening fit the same curve while predicting different behaviour on reversal. Only a test containing a reversal, or a superposition of hydrostatic pressure, breaks the tie.
Hidden variable
H857. Grip alignment is rarely measured and routinely contributes a bending moment to compression tests, lowering apparent yield strength and raising apparent hardening. Four-strain-gauge alignment with shimming until the readings agree raises measured strengths in laboratories that do not currently check.
Saturation
H858. Dislocation density saturates at large strain because annihilation catches storage, so the saturation stress should be governed by stacking-fault energy rather than by the alloy's initial state. Severely deformed samples of one base metal with different starting textures converge on the same saturation stress.
Composites: constraint, damage and failure
Bound
H859. The tensile strength of a unidirectional composite cannot exceed what the matrix can transfer into a broken fibre over the ineffective length, however strong the fibres are. That bound is set by interfacial shear strength and fibre radius, so doubling fibre strength at the same radius and interface buys nothing. Two fibre strengths at matched interface and radius would show the plateau.
Misattribution
H860. The knee in a composite's stress-strain curve is attributed to matrix cracking, but at low loads a similar knee appears when tabs slip or grips seat. Gauging the specimen's centre and its ends at once separates a material event from a seating artefact.
Identity
H861.Transverse matrix cracking and delamination are catalogued as different damage modes with different criteria, yet a transverse crack must nucleate a delamination at the ply interface to continue. They are one event with two names, and on that reading the second cannot precede the first. Sectioning a loaded specimen at several stress levels should show delamination starting at the crack tip rather than independently.
Hidden term
H862. Every composite specimen carries a thermal residual stress from cure, set by the difference between cure and test temperature times the expansion mismatch. Testing one laminate at two temperatures with that difference held constant shifts the matrix cracking stress by a predictable amount.
Threshold
H863. A ply thinner than a critical value cannot crack transversely, because its neighbours constrain the crack's opening. The threshold should rise with the matrix's fracture energy and fall with the constraint stiffness, so a tougher matrix should raise it — a thickness series in two matrices would test that.
Reversal
H864. Toughening the matrix is assumed to improve damage tolerance, but a tougher matrix can lower compressive strength, since it suppresses the microcracking that would otherwise relieve a kink band's advance. Laminates with matrices of increasing toughness should show tensile damage thresholds rising while compressive strength falls.
Count
H865.A woven composite's elastic response is often fitted with nine constants, but symmetry reduces the independent set for a balanced weave. The extras are absorbing crimp, which is a geometry effect rather than a material one and is not constant across strain. Fitting the symmetry-reduced set and the full set to the same data, with held-out coupons, shows which constants are real.
Scale argument
H866. The in-situ strength of a ply inside a laminate differs from that of the same ply tested alone, because neighbouring plies constrain its cracking. The constraint acts over a length comparable to the ply thickness, so the in-situ strength should scale with ply thickness relative to the laminate's thickness rather than with the ply's own properties.
Artefact mimicking effect
H867.Fibre bridging measured in a double-cantilever test can be an artefact of the adhesive bonding the arms, which forms its own ligaments across the crack. Those ligaments look exactly like fibre bridging in the load-displacement trace, since both produce a rising resistance with crack opening. Machining the arms instead of bonding them, or using a brittle adhesive, reduces the apparent bridging fraction.
Inversion of standard practice
H868. Weak interfaces are usually considered bad for a composite, yet a weak interface is exactly what allows crack deflection and pull-out, so over-toughening the interface can turn a tough composite brittle. An interface-strength series from weak to strong should show toughness rising and then collapsing.
Unit trap
H869. Datasheets quote fibre volume fraction and areal weight as if interchangeable, but the conversion needs the fibre density, and omitting it moves the volume fraction by several points. Recomputing reported properties per volume fraction rather than per areal weight often removes differences between suppliers.
Derived quantity
H870. Fibre volume fraction by burn-off includes sizing and binder, so the derived number overstates reinforcement and understates voids. Weighing the same coupons by density, by microscopy and by burn-off gives three numbers whose disagreement is the sizing fraction.
Selection effect
H871.Post-mortem sections are cut where the fracture is, which is exactly where the damage is unrepresentative, since the crack chose the weakest path. The section therefore shows the flaws that won, not the population that competed. Sectioning at fixed distances from the fracture, and at several of them, samples material rather than failure.
Path dependence
H872. Damage under cyclic loading depends on the sequence of load levels, not only on their counts, because matrix cracks opened at a high load change the stress state seen at a lower one. Two block sequences with equal totals and opposite order give different stiffness degradation.
Conservation argument
H873. Energy release rate in a mixed-mode test is partitioned between modes by a criterion rather than measured, and the partition decides the predicted delamination path. Varying the mix while holding the total constant measures both components directly, replacing the criterion.
Degeneracy
H874. One delamination test cannot separate interface toughness from mode mixity, since both change the measured load and a fit can trade one against the other. Two geometries with different mixities are the minimum needed to break the degeneracy.
Hidden variable
H875.Void content varies between panels of the same laminate and is rarely measured, yet it lowers strength and modulus in proportion to volume fraction. Two panels from one batch, one characterized by microscopy and one assumed void-free, can differ by more than the effect under study. Measuring voids on every panel, rather than on a chosen one, converts the assumption into a covariate.
Ceiling
H876. Pushing fibre volume fraction higher eventually costs more strength than the extra fibres add, because the voids that form above the tow's packing limit do more damage than the fibres do good. Tensile strength should therefore peak below the geometric maximum, and a cure-pressure series would locate the peak.
Bound
H877. Compressive strength is bounded by fibre misalignment: a fibre off-axis by an angle kinks at a stress proportional to matrix shear yield strength divided by that angle. Measured strengths exceeding this bound for the measured misalignment are measuring something else, most likely the fixture's lateral support.
Identity
H878. Fibre kinking and shear banding in compression are described as separate instabilities, yet a kink band is a shear band viewed in the fibre frame, so the two should share an orientation relationship. Digital image correlation at the moment of band formation can check whether the measured band angle matches the predicted kink angle.
Tribology: friction, wear and third bodies
Misattribution
H879. The friction coefficient of a lubricated contact is often read as a property of the lubricant, but in the boundary regime it is a property of the third-body layer — debris, oxide and additive mixed between the surfaces. Change the fluid while pre-conditioning both specimens identically, and friction follows the layer rather than the fluid.
Hidden term
H880.Wear rate from weighing the specimen includes the counterface's wear, since material transferred away is counted as loss and then partly returns. The error is largest for soft counterfaces and for short tests, where the transferred layer has not reached steady state. Measuring both bodies' mass change and the transferred layer's composition separates the true rate from the net one.
Identity
H881. Adhesive wear and delamination wear are taught as distinct mechanisms with distinct signatures, yet both are subsurface crack nucleation and growth under the same shear. The signature said to separate them — flake shape — is set by crack depth relative to the contact, so one mechanism should produce both shapes as load changes.
Threshold
H882. A lubricating film fails below a speed usually attributed to film thickness falling under the roughness, but if starvation is the mechanism, the failure speed should depend on supply rate and inlet geometry rather than on roughness. Two supply rates at matched roughness should give two failure speeds if starvation controls.
Reversal
H883.Hardening one surface is assumed to reduce wear of the pair, yet in a conformal contact a harder surface can concentrate stress in the softer one and accelerate its loss. Total wear can therefore rise as one member is hardened, which is the opposite of the design instinct. Pairs spanning a hardness ratio of one should show total wear passing through a minimum rather than falling monotonically.
Count
H884. The wear law in common use carries a coefficient, a hardness and a load, three quantities for one claimed mechanism, and if the coefficient is not constant across load the law has no predictive content. Measuring that coefficient at several loads in one apparatus, same materials throughout, would show whether it is.
Scale argument
H885. Sliding wear depends on apparent contact size even at constant nominal pressure, because the third-body layer's escape path lengthens as the contact grows, letting debris accumulate and protect the surfaces. Two sizes at matched pressure, with debris removal controlled, give wear rates that differ by the ratio of escape lengths.
Artefact mimicking effect
H886.Near-zero friction reported for some dry sliding pairs can come from the tribometer's own stiffness. A stiff load cell in stick-slip records the static friction and misses the slip, so the average falls far below the kinetic value. A compliant rig, or a direct high-speed force measurement, should recover the slip-phase friction.
Inversion of standard practice
H887. Running-in is treated as beneficial polishing, yet the layer it creates is often the layer that later spalls, so a longer run-in may shorten life. Making run-in duration the variable, and characterizing the layer before the steady-state measurement, would show whether running-in helps or merely delays.
Unit trap
H888.Wear coefficients appear both as dimensionless numbers and as volume per unit load per unit distance, and the two differ by the hardness. Since hardness is often quoted in a third unit again, the conversion can be missed twice. Converting every literature value to one convention usually collapses an apparent spread of orders of magnitude.
Derived quantity
H889. Wear depth is derived from mass loss using a density and a worn area, and the area is usually taken as nominal rather than real, which can be a small fraction of it. Profilometry of the scar measures depth directly and tests the assumption.
Selection effect
H890. Surfaces chosen for microscopy are those with visible scars; surfaces that wore by a mechanism leaving none, such as tribochemical polishing, are never imaged, so the atlas of wear mechanisms is a catalogue of the visible. Sampling unworn and lightly worn regions at random would show how much is missing.
Adhesion and contact
Bound
H891.The work of adhesion from a peel test cannot exceed the plastic dissipation in the adherend's own bending, so peeling a thin backing measures the backing rather than the interface. A thin backing yields before the interface separates, and the recorded energy is then the backing's plastic work. Peeling one adhesive on backings of increasing thickness traces measured energy up to a plateau that the interface alone sets.
Misattribution
H892. Peel strength is reported as an interfacial property, but in a ninety-degree peel most of the energy goes into bending the tape, and the interfacial term is a small difference between two large numbers. Measuring the backing's bending stiffness independently and subtracting it cuts the reported adhesion by a large factor.
Identity
H893.Adhesion hysteresis, the gap between advancing and receding contact angles, and viscoelastic dissipation are treated as separate, but on a soft elastomer they are the same loss viewed at two rates. The hysteresis should then scale with frequency as the loss modulus does, which is a statement about the material rather than about the interface. A master curve built from both, shifted by one factor, would collapse them onto a single line.
Threshold
H894. A rough surface below some contact size does not adhere at all, and the usual explanation pits the work of adhesion against roughness amplitude. If elastic energy stored in asperities is the real mechanism, the threshold should scale with asperity stiffness rather than surface energy, so two surfaces of equal roughness and different modulus must have different thresholds.
Reversal
H895. Roughness is assumed to reduce adhesion, yet where a soft polymer fully wets the surface, roughness can raise it by mechanical interlocking, and the crossover occurs at a roughness comparable to the polymer's molecular size. A roughness series against a soft and a stiff elastomer should show the reversal only for the soft one.
Hidden term
H896.A pull-off force measured in air carries the meniscus of adsorbed water at the contact periphery. That contribution scales with humidity rather than with surface chemistry, so it can masquerade as a change in the interface. Pull-off at several humidities, same apparatus and same surfaces, separates the meniscus term from the intrinsic one.
Artefact mimicking effect
H897. Apparent gecko-like adhesion on a rough surface can be suction: pads that seal against the surface develop a pressure difference when pulled, and the measured force includes it. Testing in vacuum, or with a vent hole through the pad, removes the suction while leaving any real van der Waals contribution.
Scale argument
H898. Adhesion of a fibrillar pad changes character depending on whether fibril diameter is above or below the length over which the interface transmits stress; below it, pull-off is set by the fibril's own compliance rather than by interface energy. Pads of equal fibril density but different diameters should show the transition at a predicted diameter.
Count
H899.A contact-mechanics model of a soft adhesive needs three independent parameters: modulus, surface energy and a process-zone length. A four-parameter fit is then absorbing a measurement error, and the extra parameter ought to be uncorrelated with any physical variable. Refitting published pull-off data with three, and checking whether the fourth is consistent with zero, tests this without new experiments.
Degeneracy
H900.One pull-off measurement cannot separate surface energy from modulus, because the force depends on both through the contact radius. Every value obtained this way is a combination rather than a surface energy, however carefully the pull-off itself is measured. Two spheres of different radius, or one sphere at two temperatures where modulus changes and surface energy does not, break the degeneracy.
Status and plan
One hundred of a planned thousand. The forms are labelled so that a reader can check the variety of argument separately from the variety of subject: a bound and an identity claim are refuted by different experiments, and conflating them is how a literature accumulates statements that cannot be tested.
Each entry was written on its own, in one pass, without a grid or a sentence skeleton; the test named in each is the smallest experiment that would separate the claim from its rival, and several of those experiments would fit in a day. The eight hundred entries surrounding this block will be written the same way.
If one of these is worth an afternoon, it is H809 — that pop-in on a nanoindentation curve can be produced on a sample containing no crack at all — because a rigid dummy of matched stiffness is cheap, and because a positive result would invalidate a common way of dating first cracking.
Incoprea Research · hand-considered hypotheses 801–900 · mechanics of materials · 3 November 2026 · ~/Desktop/Nov3/