Volume 1, Chapter 44: Insufficient Permissions

The fading euphoria left behind only exhaustion and an empty, hollow stillness in the workshop.

The carbon filament that had worked a miracle was carefully sealed away like a sacred relic. Yet everyone knew this was merely the first step of a long march.

"We have the filament, but the filament is just the beginning," Li Weiguo said, his raspy voice breaking the silence. He wiped his face with a greasy sleeve. "Next, we weave the cloth, prepare the prepreg, and then into the tank it goes."

The "tank" he referred to was an even more colossal monster at the other end of the workshop—the autoclave. Over three meters in diameter and ten meters long, it lay dormant like a mechanical beast of steel. Its mission was to use high temperature and high pressure to "bake" the resin-infused carbon fiber cloth into its final structural component.

"This is Shen Qingyun, Engineer Shen," Li Weiguo introduced a man of about fifty standing beside him. The man wore clean blue work clothes and gold-rimmed glasses, looking entirely out of place amidst the workshop's grease and grime. He was an expert in the field of composite materials, specifically responsible for molding processes.

Shen Qingyun pushed up his glasses and gave Du Yuze a slight nod in acknowledgement. His expression was utterly indifferent, seemingly unmoved by the heart-pounding victory that had just occurred.

"Young Du, is it? The fiber performance is decent," Shen Qingyun began, his tone carrying a textbook-like rigor. "But fibers are dead; resins are alive. Hot-press molding is a dance of chemistry and physics. Temperature, pressure, time—the slightest deviation in any single parameter spells disaster for the result."

For the next two days, the entire workshop prepared for this "dance."

Grade T300 carbon filaments were fed into the looms, woven into smooth, flat sheets of black fabric under the near-pious operations of the workers. Afterward, these fabrics were sent into the coating machine, evenly saturated with amber-colored epoxy resin, transforming them into sticky "prepregs."

The final step was layup.

Atop a massive mold, workers wearing gloves meticulously layered the prepregs sheet by sheet, following the exact angles demanded by the blueprints. What they were building was a horizontal stabilizer for an aircraft—a component with extraordinarily stringent requirements for strength and aerodynamic profile.

"Layup angles at zero degrees, ninety degrees, intersecting at plus or minus forty-five degrees. Pay attention to the overlap zones; absolutely no gaps are permitted," Shen Qingyun patrolled back and forth like a foreman, issuing continuous commands.

Everything was ready. The mold, bearing everyone's hopes, was slowly loaded into the autoclave.

"Close the door."

Propelled by hydraulic actuators, the heavy tank door swung shut with a resounding thud and locked firmly in place.

"Set the process parameters according to the curve I programmed," Shen Qingyun walked over to the console, skillfully inputting a sequence of numbers. "Heating rate of two degrees Celsius per minute, hold at one hundred and twenty degrees for two hours, then ramp up the pressure to six atmospheres. This is the most classic, most reliable curing process."

The console screen lit up, and the temperature and pressure curves began their slow ascent.

The waiting this time was far more agonizing than during the fiber-drawing process. The autoclave remained completely silent, lacking even the faint sounds of the carbonization furnace. Everyone could do nothing more than stare at those two monotonous curves on the screen, waiting hour after hour.

Du Yuze stood outside the crowd.

[Requesting access to the autoclave control system.]

[Insufficient permissions.]

[......]

Du Yuze did not try again. He merely watched those two smoothly rising curves, an unsettling sensation spreading through his chest. It was too "standard"—as standard as an example problem in a textbook. Yet reality was never a textbook problem.

The long curing cycle finally drew to a close.

The exhaust valve opened, and the high-temperature, high-pressure gas inside the tank emitted a shrill hiss. When the tank door swung open once more, a pungent, distinctive odor of cured resin filled the air.

The mold was rolled out, and everyone crowded around.

The exterior of the horizontal stabilizer component looked flawless, the black carbon fiber patterns flowing under the lights with a heavy sense of science fiction.

"Demold!" Li Weiguo ordered.

Several workers immediately stepped forward, using specialized tools to begin separating the component from the mold.

"Clack." A palm-sized fragment peeled off from the edge of the component and dropped to the ground.

Everyone's movements froze.

Li Weiguo rushed forward and picked up the fragment. It was very light, but the tactile feedback felt wrong. He rubbed it between his fingers, and the composite material—which ought to have been as hard as steel—had delaminated into several distinct layers like a flaky pastry.

Delamination!

A worker gently tapped the surface of the component with a pry bar, producing not a crisp metallic ring, but a dull, muffled thud. He struck it harder, and a dent was knocked into the surface of the component, exposing layer upon layer of dry, unbonded fibers beneath.

Large-scale delamination. From inside to out, virtually not a single spot remained intact.

This horizontal stabilizer, into which countless hours of painstaking effort had been poured, was a total, unmitigated piece of scrap.

The air in the workshop froze. The joy of success from the past two days vanished utterly, replaced by a much deeper despair.

"How could this be?" Old Wang's lips trembled. "We wove the cloth with our own hands, we laid the material with our own hands, how could..."

"It's the resin! It has to be a problem with the resin!" a technician shouted. "The fluidity is far too poor; it didn't soak through the fibers!"

"Impossible!" Shen Qingyun immediately retorted, his face flushing crimson. "I inspected the certificate of conformity for this batch of resin; every single metric is within range. My process curve strictly followed the materials manual; it couldn't possibly be wrong!"

"Then you tell me, where is the problem?" Li Weiguo stared intently at Shen Qingyun, his eyes bloodshot.

"I..." Shen Qingyun choked for a moment, pointing at the pile of waste. "The timing of the pressurization! The timing of the pressure application must have been wrong! The pressure squeezed all the resin away, leaving the fibers without enough adhesive!"

"The timing was wrong?" Li Weiguo pressed hard. "Your process—wasn't that set by you?"

"I followed the standard! The standard!" Shen Qingyun practically roared. "Who could have known the matching characteristics between this domestic fiber and resin would be so bizarre? This is a material problem, not a process problem!"

He shifted the blame entirely off his own shoulders.

Du Yuze walked over to the scrapped horizontal stabilizer, crouched down, and picked up a fragment. His mind operated at blistering speed.

[Task assigned: Analyze the cause of the composite material curing failure.]

[Retrieving full-cycle temperature, pressure, and vacuum data of the autoclave. Retrieving resin material viscosity-temperature curve. Retrieving carbon fiber fabric structural parameters.]

[Establishing three-dimensional thermal-fluid-solid coupling model. Initiating curing process simulation.]

In an instant, countless streams of data intersected, collided, and reorganized within his mind. That failed curing process was replaying in his consciousness over and over in digital form.

"The standard process is tailored for small-sized, thin laminates. Our stabilizer is large, with a thickness exceeding thirty millimeters." Du Yuze stood up and spoke.

All the arguments halted, and dozens of gazes snapped toward him.

Shen Qingyun frowned: "What are you trying to say? The curing process for large-scale components is nothing more than extending the dwell time to ensure internal and external temperature uniformity. I accounted for that."

"Not enough," Du Yuze shook his head. "You overlooked the change in resin viscosity. At one hundred and twenty degrees, the resin's viscosity drops to an extreme low point, becoming as thin as water. When you applied the full force of six atmospheres at that exact moment, it was like using a high-pressure water gun to blast a pile of sand."

He paused, explaining in the most straightforward terms: "The resin was completely squeezed out from the gaps between the fibers. The fibers didn't even have time to be fully saturated before they were pressed together. That is why dryness and delamination occurred."

Shen Qingyun's complexion turned unsightly. "Utter nonsense! What do you know about resin rheology? How many composite parts have you ever made?"

"I haven't made any," Du Yuze admitted calmly. "But I can calculate them."

"Calculate? What are you calculating with? A pencil?" Shen Qingyun sneered.

"Director Li," Du Yuze ignored him, turning directly to Li Weiguo. "Next time, we change the method."

Li Weiguo looked at him; this young man was frighteningly calm.

"How do we change it?"

"Gradient heating, step-by-step pressurization," Du Yuze uttered eight words.

"Be specific."

"Step one: heat to eighty degrees and hold for one hour. At this temperature, the resin begins to flow, but the viscosity is still quite high—enough to saturate the fibers. At the same time, apply only two atmospheres of pressure to assist resin penetration and expel trapped air."

"Step two: heat to one hundred and twenty degrees, hold for half an hour, and simultaneously increase the pressure to four atmospheres. Allow the resin to complete its initial cross-linking."

"Finally, heat to one hundred and fifty degrees and increase the pressure to six atmospheres to complete the final cure."

The entire workshop fell silent. Everyone was baffled by this unprecedented, complex process.

"Madness!" Shen Qingyun was the first to leap to his objection. "You're just messing around blindly! Multi-stage heating will cause uneven internal stress in the resin, and step-by-step pressurization is pure nonsense! Textbooks have never written anything like this!"

"Textbooks are meant for reference, not for blind copying," Du Yuze retorted.

"You!" Shen Qingyun trembled with rage. "Director Li, you cannot listen to him! He is making a mockery of millions' worth of equipment and materials! Who will take responsibility if something goes wrong?"

Li Weiguo remained silent. He looked at the furious Shen Qingyun, then at the calm Du Yuze, and finally, his gaze fell upon the pile of scrap worth hundreds of thousands.

The standard method had failed. Dismally.

He walked up to Du Yuze.

"What is your success rate?"

"If we don't change the process, even if we do it a hundred more times, the result will be the same." Du Yuze did not answer directly. "If we use my method, there is at least a possibility of success."

Li Weiguo was silent for a full minute.

He abruptly turned around and roared at the workers in front of the control console: "Clean out the tank! Prepare the materials for the second piece!"

He swung his head back, pointed at Du Yuze, and announced to everyone:

"This time, we do everything he says."