Testing the iPhone Duo hinge after 32,640 folding cycles

One of the biggest concerns surrounding foldable smartphones is the crease that can develop across the display after prolonged use.

Hinge durability is another critical factor, determining whether a device can maintain a firm, consistent folding action after thousands of opening and closing cycles.

For the iPhone Duo, two questions stand out: Can its hinge remain stable over time, and can Apple's advanced engineering help minimize the visible crease in the foldable display?

Apple emphasized the importance of the hinge in the press release announcing its first foldable iPhone last month.

According to the company, the mechanism consists of more than 100 components designed to precisely control the folding motion while supporting the central portion of the display, delivering a smooth and solid feel.

However, Apple did not disclose the full extent of the durability testing conducted on the hinge of its foldable smartphone, which starts at $1,999.

To investigate, technology journalist Joanna Stern devised an unusual real-world experiment.

In a review of the iPhone Duo published on her personal YouTube channel on Wednesday, Stern teamed up with a hardware specialist to build a machine capable of repeatedly opening and closing the phone, even while she slept.

"A few weeks ago, I had an idea. What if I could test the iPhone Duo's hinge while I slept?" Stern explained.

She contacted Aron Cohen, a hardware designer and prototyping specialist, to develop a machine that could carry out the repetitive task.

Cohen's creation, named Hingey, resembles the durability-testing equipment sometimes seen in furniture stores, where chairs and other products undergo repeated mechanical movements to assess their resistance to wear.

According to Cohen, founder of Aron Studio, the limited preparation time meant he had to make use of readily available components.

Hingey was assembled using a servo motor, 3D-printed parts and a small controller positioned at the back of the machine.

Despite its relatively simple construction, the device allowed the team to adjust the folding angle, opening and closing speed, and pause intervals between cycles.

These controls enabled the testers to vary the operating conditions while putting the hinge through thousands of repeated movements.

Throughout her review of the iPhone Duo, Stern repeatedly questioned whether the hinge was becoming looser.

At times, she felt the phone was easier to open and close than before. On other occasions, she noticed no obvious difference.

Stern presented the experiment in a playful video format, interspersing the review with mock breaking-news updates on Hingey's progress.

The final measurements, however, delivered the most interesting finding.

After more than 32,000 folds, the hinge was slightly stiffer

After leaving Hingey to repeatedly open and close the iPhone Duo for four nights, Stern returned the phone to Cohen's laboratory for further testing.

Before the endurance experiment began, Cohen had used a calibrated push-pull force gauge to measure the force required to open the device.

Once Hingey had completed 32,640 folding cycles, he repeated the same measurement to compare the results.

Surprisingly, the iPhone Duo's hinge had not become looser as initially feared.

Instead, the measurements indicated that it had become slightly stiffer.

"The result was that the hinge was actually a little stiffer," Stern reported.

The finding runs counter to the common assumption that mechanical components gradually loosen with repeated use, offering an encouraging early indication of the durability of Apple's first foldable iPhone.

Stern also said the change was almost impossible to detect during normal use.

"In everyday use, I really couldn't feel a difference. So after 32,000 folds, it feels pretty much the same as it did on day one. That's a really impressive result," she observed.

Nevertheless, the experiment primarily examined the hinge's operating resistance and the physical sensation of opening and closing the phone.

It does not establish that the iPhone Duo will remain free of durability problems after years of use.

Nor does it fully address other concerns, including display creasing, dust resistance and the device's ability to withstand different environmental conditions.

The iPhone Duo still has weaknesses Apple needs to address

Beyond the hinge durability experiment, Stern discussed several strengths and shortcomings of the iPhone Duo in her video review.

She praised the phone's ability to adapt to different usage positions, its relatively good battery life and its multitasking capabilities.

The foldable design also makes the device appealing to users who frequently take selfies, thanks to the larger display and the flexibility to position the phone in different ways.

However, Stern identified several notable drawbacks.

These included an underwhelming front-facing camera for FaceTime calls, the absence of a dedicated telephoto lens and Face ID, and the tendency for the device to become warm in the hand.

Such limitations suggest Apple still has considerable room to refine its new smartphone category.

Even so, like several other reviewers assessing the device in its early days, Stern considered Apple's first attempt at a foldable iPhone a commendable achievement.

She also expressed enthusiasm for the next generation, hoping Apple will address the current shortcomings while continuing to improve the overall user experience.

Hai Phong